Limnology Research Papers - Academia.edu (original) (raw)

We present experimental laboratory evidence and field observations of an autocatalyzed, programmed cell death (PCD) pathway in the nitrogen-fixing cyanobacteriumTrichodesmium spp., which forms massive blooms in the subtropical and... more

We present experimental laboratory evidence and field observations of an autocatalyzed, programmed cell death (PCD) pathway in the nitrogen-fixing cyanobacteriumTrichodesmium spp., which forms massive blooms in the subtropical and tropical oceans. The PCD pathway was induced in response to phosphorus and iron starvation as well as high irradiance and oxidative stress. Transmission electron microscopy revealed morpho- logical degradation of internal

We examined the chemical composition of the water column of Lake Matano, Sulawesi Island, Indonesia, to document how the high abundances of Fe (hydr)oxides in tropical soils and minimal seasonal temperature variability affect... more

We examined the chemical composition of the water column of Lake Matano, Sulawesi Island, Indonesia, to document how the high abundances of Fe (hydr)oxides in tropical soils and minimal seasonal temperature variability affect biogeochemical cycling in lakes. Lake Matano exhibits weak thermal stratification, yet a persistent pycnocline separates an oxic epilimnion from anoxic meta-and hypolimnions. The concentration of soluble P in the epilimnetic waters is very low and can be attributed to scavenging by Fe (hydr)oxides. Chromium concentrations in the epilimnion are high (up to 180 nmol L 21 ), but below U.S. Environmental Protection Agency guidelines for aquatic ecosystems. The concentration of chromium decreases sharply across the oxic-anoxic boundary, revealing that the hypolimnion is a sink for Cr. Flux calculations using a one-dimensional transportreaction model for the water column fail to satisfy mass balance requirements and indicate that sediment transport and diagenesis play an important role in the exchange of Fe, Mn, P, and Cr between the epilimnion and hypolimnion. Exchange of water between the epilimnion and hypolimnion is slow and on a time scale similar to temperate meromictic lakes. This limits recycling of P and N to the epilimnion and removal of Cr to the hypolimnion, both of which likely restrict primary production in the epilimnion. Owing to the slow exchange, steep concentration gradients in Fe and Mn species develop in the metalimnion. These concentration gradients are 1 Present address: Large

Water managers often debate whether resuspension of sediment with high organic matter and water content accumulated during eutrophication delays improvement of water clarity after reduction of external nutrient loading. Using data from 15... more

Water managers often debate whether resuspension of sediment with high organic matter and water content accumulated during eutrophication delays improvement of water clarity after reduction of external nutrient loading. Using data from 15 shallow (mean depth Ͻ5 m) eutrophic lakes surveyed during 8-12 yr, we show that the reduction in phytoplankton biomass after external loading reductions of phosphorus or changes in the abundance of planktibenthivorous fish was accompanied by a proportional or nearly proportional reduction in detritus and inorganic suspended solids. The reduction occurred irrespective of lake size (0.1-40 km 2), extent of phytoplankton biomass reduction (up to 10-fold), and despite dominance of sediments with high water and organic content. Therefore, we conclude that recovery of shallow lakes after nutrient loading or fish stock reduction is apparently not significantly delayed by resuspension of organic or inorganic matter accumulated in the sediment during eutrophication. Worldwide , many lakes suffer from eutrophication due to high external loading from sewage, industries, and runoff from cultivated soils. Large efforts have been made during the last two decades to combat eutrophication by reducing

The conservation of endemic fauna in freshwater ecosystems is a topical issue on small oceanic islands. Because these endemics have limited distributions, they are more vulnerable to extinction. This study is the first to clarify the... more

The conservation of endemic fauna in freshwater ecosystems is a topical issue on small oceanic islands. Because these endemics have limited distributions, they are more vulnerable to extinction. This study is the first to clarify the distribution of freshwater macroinvertebrates including endemic and alien species in streams with dams and associated reservoirs on the Ogasawara Islands in the northwestern Pacific Ocean. In 2007, we conducted a field survey in streams and reservoirs of the Yatsuse River system and collected 22 taxonomic groups from 13 stations. Hierarchal cluster analysis and non-metric multi-dimensional scaling (NMDS) were performed for the presence/absence data of the macroinvertebrates, and the results indicated that (1) most of endemic species were present in inlet streams of dam reservoirs, (2) these endemic species were absent in the bottom sediments of the reservoirs because of oxygen depletion and (3) dams may be barriers to the migration of some species of amphidromous crustaceans. Because human modifications, such as dams and associated reservoirs, on a small oceanic island can rapidly result in fragmentation or loss of freshwater habitats of endemic species, the remaining habitat of these species, such as headwater streams, must be protected and preserved to avoid species extinction.

Sediment cores were collected from Upper Klamath Lake in October, 1998 and analyzed for 210 Pb, 14 C, 15 N, N, P, C, Ti, Al, diatoms, Pediastrum, and cyanobacterial akinetes. These results were used to reconstruct changes in water quality... more

Sediment cores were collected from Upper Klamath Lake in October, 1998 and analyzed for 210 Pb, 14 C, 15 N, N, P, C, Ti, Al, diatoms, Pediastrum, and cyanobacterial akinetes. These results were used to reconstruct changes in water quality in Upper Klamath Lake over the last 150 years. The results showed that there was substantial mixing of the upper 10 cm of sediment, representing the previous 20 to 30 years. However, below that, 210 Pb activity declined monotonically, allowing reasonable dating for the period from about 1850 to 1970. The sediment accumulation rates (SAR) showed a substantial increase in the 20th century. The increase in SAR corresponded with increases in erosional input from the watershed as represented by the increases in sediment concentrations of Ti and Al. The upper 20 cm of sediment, representing the last 150 years, also showed increases in C, N, P, and 15 N. The increases in nutrient concentrations may be affected to various degrees by diagenetic reactions within the sediments, although the changes in concentrations also were marked by changes in the N:P ratio and in a qualitative change in the source of N as reflected in increasing δ 15 N. The diatoms showed modest changes in the 20th century, with increases in Asterionella formosa, Stephanodiscus hantzschii, and S. parvus. Pediastrum, a green alga, was well-preserved in the sediments and exhibited a sharp decline in relative abundance in the upper sediments. Total cyanobacteria, as represented by preserved akinetes, exhibited only minor changes in the last 1000 years. However, Aphanizomenon flos-aquae, a taxon which was formerly not present in the lake 150 years ago, but that now dominates the summer phytoplankton, has shown major increases over the past 100 years. The changes in sediment composition are consistent with activities including timber harvest, drainage of wetlands, and agricultural activities associated with livestock grazing, irrigated cropland, and hydrologic modifications.

The effect of light stress on the release of volatile iodocarbons by three species of marine microalgae Abstract-We investigated the influence of high light stress on iodocarbon release by three species of marine phytoplankton from... more

The effect of light stress on the release of volatile iodocarbons by three species of marine microalgae Abstract-We investigated the influence of high light stress on iodocarbon release by three species of marine phytoplankton from different algal classes: the prymnesiophyte Emiliania huxleyi, the prasinophyte Tetraselmis sp., and the diatom Thalassiosira pseudonana. Despite a pronounced decrease in the fluorescence-based maximum quantum yield for photosystem II (F v /F m ), increased iodocarbon release relative to lower light controls was not observed in any of the experiments performed. These findings do not support the hypothesis that upper-ocean iodocarbon concentrations are influenced by light-induced algal stress.

We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow (z ̅ <... more

We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow (z ̅ < 2.5 m), intermediate in depth (2.5 m < z ̅ < 4.5 m), and deep (z ̅ > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values. Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO3—N + NH4+–N) were consistently below the detection limit (0.05 μmol l-1) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l-1), total-P (0.29 μmol l-1), and total-N (33 μmol l-1), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos, GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l-1 and 0.7-3.8 μmol C l-1 day-1. Overall, however, increased z ̅ resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m-2 and 3.2-5.8 mmol C m-2 day-1. Average values of epipelic chl a ranged from 131 to 549 mg m-2 for the three depth classes, but levels were not significantly different due to high spatial variability. However, average epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m-2 day-1) than in intermediate and deep lakes (3.4 and 2.4 mmol C m-2 day-1). Total primary production (6.7-15.4 mmol C m-2 day-1) and percent contribution of the epipelon (31-66%) were inversely related to mean depth, such that values for both variables were significantly higher in shallow lakes than in intermediate or deep lakes.

Grazing experiments were performed with the zooplankters Daphnia pulex and Daphnia magna feeding on nitrogen-and phosphorus-limited cells of two green algae (Chlamydomonas reinhardtii and Selenastrum cupricornutum). To analyze the role of... more

Grazing experiments were performed with the zooplankters Daphnia pulex and Daphnia magna feeding on nitrogen-and phosphorus-limited cells of two green algae (Chlamydomonas reinhardtii and Selenastrum cupricornutum). To analyze the role of the cell wall structure in digestibility of the algae by Daphnia, the same experiments were carried out with both wild-type C. reinhardtii and a cell wall-deficient mutant.

We give an overview of the history of the ice cover studies in Lake Baikal and a detailed description of the temporal and spatial variability of Lake Baikal ice conditions based on satellite and historical data. We analyze the long-term... more

We give an overview of the history of the ice cover studies in Lake Baikal and a detailed description of the temporal and spatial variability of Lake Baikal ice conditions based on satellite and historical data. We analyze the long-term evolution of ice conditions using historical data and recent observations from satellite altimetry and radiometry for 1992-2004 for northern, middle, and southern Baikal. These data show a recent (since the 1990s) tendency for colder winters, with earlier ice formation, later ice break-up, and ice duration increase. These observations are in agreement with the long-period cycles of air temperature variability (warming between the 1970s and 1990s, with a cooling phase afterwards). We then compare air temperature data from meteorological stations to ERA-40 reanalysis and suggest that ERA-40 data can be used to assess seasonal and interannual changes of air temperature for Lake Baikal. The ERA-40 data also indicate a recent tendency for colder winters and for warmer summers. We further analyze how the ice regime is influenced by air temperature and how this influence is affected by dynamic (wind field, currents) and other (bathymetry, precipitation, etc.) factors. We estimate the relationship between air temperature parameters and the timing of ice events (ice formation and fast ice duration) and show that air temperature has the strongest effect on the ice regime. Dynamic and other factors interfere with the thermal influence, resulting in a change of ice formation dates and ice duration compared to the relationship that takes into account only the influence of air temperature.

It is commonly accepted that within-population phenotypic variation is caused by genotypic and environmental heterogeneity. Non-genotypic variation is thought to result from diversity of environmental conditions alone. This however... more

It is commonly accepted that within-population phenotypic variation is caused by genotypic and environmental heterogeneity. Non-genotypic variation is thought to result from diversity of environmental conditions alone. This however contradicts experimental data showing that even when both genetic and environmental sources of phenotypic variation are neglected, residual variation still exists. This residual phenotypic variation is caused by deviations of developmental trajectories from the target trajectory determined for particular genotype and environment, i.e. by developmental instability. This variation is well-known for morphological traits where it is measured most often by fluctuating asymmetry, i.e. random deviations from perfect symmetry, which can be easily separated from the other type of phenotypic variation. In morphological characters which do not possess symmetry or in non-morphological characters this variation cannot usually be separated from other type of non-genotypic variation, caused by environmental heterogeneity. Most researchers still believe that all non-genotypic variation, even under standardised experimental conditions, is caused by insufficient standardization of environment, rather than by other sources of phenotypic variation. When special efforts are undertaken to analyse variation caused by developmental instability, this variation contributes substantially to non-genotypic variation. To exemplify how variation caused by developmental instability can be separated from phenotypic plasticity we analysed phenotypic variation of resting egg formation in Daphnia pulicaria. The proportion of females carrying resting eggs has been shown to depend on the photoperiod of their mothers, revealing transgeneration effects . Developmental instability manifests itself in differences between clonemates within an experimental vessel in a standardized environment. Some females produce resting eggs whereas others do not. Our estimations based on results obtained in experimental conditions and extrapolation to conditions in the wild showed that phenotypic plasticity, i.e. phenotypic response to changes of day duration in maternal environment (phenotypic plasticity) explains only 1-2% of phenotypic variation whereas developmental instability explains approximately 98-99% of phenotypic variance of this trait (i.e. producing or not producing resting eggs), if other factors causing phenotypic plasticity are absent. This example demonstrates a major role of developmental instability in variation of the trait under study. The contribution of developmental instability to phenotypic variation should be considered in studying evolutionary patterns of phenotypic traits.

Total mercury (T-Hg) and organic mercury (mainly methylmercury, MeHg) concentrations in the most important compartments (water, sediment, macrophytes, zooplankton, mussels and fish) of the shallow and eutrophic Lake Candia (Turin,... more

Total mercury (T-Hg) and organic mercury (mainly methylmercury, MeHg) concentrations in the most important compartments (water, sediment, macrophytes, zooplankton, mussels and fish) of the shallow and eutrophic Lake Candia (Turin, Northern Italy) were measured. The decreasing sequence of the T-Hg concentrations is as follows: cat-fish (143 µg kg -1 d.w.), zooplankton (77 µg kg -1 d.w.), Unio pictorum mancus (37.9 µg kg -1 d.w.), macrophytes (28.9 µg kg -1 d.w.). The content of mercury in mussel tissues increased with the size of the animal, but the relationship between Hg concentration and tissue weight was negative, indicating that the rate of mercury accumulation was lower than the tissue growth rate. The amount of mercury accumulated in the mussels living in the lake sediments was estimated to be 0.54 µg m -2 . The importance of mercury biomagnification is also discussed.

Four perennial rheocrene springs located between 919 and 1252 m a.s.l. on substrata characterized by different lithologies were studied. Water samples and invertebrates were collected seasonally for one year. The crenic fauna was... more

Four perennial rheocrene springs located between 919 and 1252 m a.s.l. on substrata characterized by different lithologies were studied. Water samples and invertebrates were collected seasonally for one year. The crenic fauna was collected using three sampling techniques: moss washing, drift tubes and benthic traps. Each sampling technique was particularly efficient for collecting specific taxa typical of the different habitats (crenophilous crustaceans and crenoxenic benthic insects were dominant in benthic traps and moss; crenophilic, stygophilic and stygobiotic crustaceans in drift tubes). A total of 3,284 invertebrates belonging to 54 taxa were collected. Ostracoda, Harpacticoida, and Diptera were the most abundant taxa. Species assemblages collected at each spring, in each season, in traps and mosses, differed among springs, and, based on invertebrate assemblages, the ordination of the investigated springs did not correspond to that based on environmental parameters. Of the environmental variables only pH and temperature explained the diversity pattern. Assemblages collected from different habitats also differed: benthic traps collected mainly Chironomidae, Ostracoda, other Diptera, crenophilous Harpacticoida, and Gastropoda; in moss assemblages, the fauna was mostly represented by crenophilic Harpacticoida, Ostracoda, Plecoptera, Chironomidae. Finally, the groundwater assemblages, collected with drift tubes, were dominated by crenophilous Harpacticoida, Chironomidae and Plecoptera. Variation in number of taxa over time was observed in traps and moss samples, whereas drift tubes showed no seasonality. Meiofauna (i.e., permanent meiofauna, represented by Nematoda, Copepoda, Ostracoda, and Hydrachnidia, and temporary meiofauna, represented by early instars of insect larvae) dominated all habitats, probably because of constant flow and favourable habitats such as moss. The presence of mosses was a factor that increased the species diversity of the investigated springs; drift tubes allowed most of the stygobiotic taxa to be collected, although this technique did not necessarily increase the total number of taxa collected. In addition to the array of habitats, other factors, such as geology, might influence the structure of invertebrate communities. The diversity of the investigated springs was strictly dependent on the presence of different microhabitats and local environmental conditions.

Phytoplankton carbon and particulate organic carbon (POC), nitrogen (PON), and phosphorus (POP) (POC : PON : POP) were analyzed in 109 temperate lakes covering a wide span in productivity and other key parameters. Seasonal means of total... more

Phytoplankton carbon and particulate organic carbon (POC), nitrogen (PON), and phosphorus (POP) (POC : PON : POP) were analyzed in 109 temperate lakes covering a wide span in productivity and other key parameters. Seasonal means of total POC (four samples) ranged from 206 to 7160 g C L Ϫ1 , with a grand mean of 960 g C L Ϫ1 , whereas estimated phytoplankton C ranged 12 to 1,770 g C L Ϫ1 , with a mean of 217 g C L Ϫ1 . Sestonic C : P ratios ranged from 59 to 553 (atom : atom), with a mean of 207. The elemental contributions from phytoplankton and other sestonic compartments (mainly detritus) were analyzed with a simple regression model, in which autochthonous and allochthonous components were separated. Model-derived estimates for N : P ratios of phytoplankton and allochthonous seston compartments were nearly equal (15.4 Ϯ 2.5 and 16.0 Ϯ 2.0) and were not significantly different from the Redfield N : P ratio (16). The estimated C : P ratio of allochthonous detritus was 2.7 times higher than that for phytoplankton (123 Ϯ 15), which again was not significantly different from the Redfield C : P ratio (106). Altogether, this indicates that sestonic components of autochthonous origin should be closer to Redfield proportions in eutrophic than in oligotrophic lakes. It also indicates that major contributions of allochthonous detrital C in oligotrophic lake seston may explain deviations from the Redfield ratio and calls for caution when interpreting elemental ratios in algae versus total seston. The regression model indicates that live phytoplankton cells rarely exceed 40% of total POC, yet it suggests that a major fraction of detritus is derived from autotrophs. This close link between live and dead cells could explain why total seston apparently carries the stoichiometric and biochemical footprints from the phytoplankton. Judged from algal biomass alone, Daphnia would face severe food limitation in a majority of lakes, while if we were to include total seston, Daphnia would be above threshold food levels in all lakes. Likewise, the effect of food quality limitation related to C : P ratios will turn out differently if total seston or only the phytoplankton fraction is considered.

Using radium (Ra) isotopes and nutrient analyses, we found that submarine groundwater discharge (SGD) is an important source of ''new'' nutrients, particularly nitrogen, to coral reefs around the world. Nitrogen input estimates associated... more

Using radium (Ra) isotopes and nutrient analyses, we found that submarine groundwater discharge (SGD) is an important source of ''new'' nutrients, particularly nitrogen, to coral reefs around the world. Nitrogen input estimates associated with SGD range from 3 to 800 mmol h Ϫ1 per meter of shoreline. The use of Ra isotopes allows us to quantify the inorganic nitrogen input from this source of nutrients. Increasing coastal population and land use practices may enhance anthropogenic nutrient loading from submarine groundwater contributing to reef degradation.

The Trentino Province (Italy) has more than 320 lakes diverse in size, geological substrate, altitude and trophic status, and representing most physico-chemical types of temperate lakes. A recent research project (SALTO) offered the... more

The Trentino Province (Italy) has more than 320 lakes diverse in size, geological substrate, altitude and trophic status, and representing most physico-chemical types of temperate lakes. A recent research project (SALTO) offered the opportunity to study the dinoflagellate flora of 27 of these water bodies representing all lake types. In this paper 34 taxa of dinoflagellates assigned to eight genera (Ceratium, Glenodiniopsis, Glochidinium, Gymnodinium, Gyrodinium, Peridinium, Peridiniopsis and Tovellia) in five families (Ceratiaceae, Glenodiniopsidaceae, Gymnodiniaceae, Peridiniaceae and Tovelliaceae) and four genera of uncertain collocation (Baldinia, Borghiella, Durinskia and Staszicella) are described. Two previously undescribed species and two new combinations are also included. Classification is based in part on , modified according to the results of recent molecular and ultrastructural analyses. Dinoflagellate taxonomy is currently undergoing extensive revision, and taxonomic decisions in the present article follow the recent orientations in dinoflagellate systematics. The taxonomical issues of the more problematic genera are discussed. Where appropriate, comments on ecological features of the species are also given.

Lake Orta (N. Italy) was severely polluted from 1927 by an effluent from a rayon factory, which discharged great amounts of ammonium nitrogen and copper into the lake. In the mid nineteen fifties, some plating factories also started... more

Lake Orta (N. Italy) was severely polluted from 1927 by an effluent from a rayon factory, which discharged great amounts of ammonium nitrogen and copper into the lake. In the mid nineteen fifties, some plating factories also started dumping chromium and aluminum. As a result of ammonium oxidation, the lake became very acid and the concentration of metals in the waters reached very high values. Phytoplankton, zooplankton and fish disappeared suddenly from the lake which was by 1930 classified as “sterile”. Later on, about the fifties, a small population of Cyclops abyssorum re-colonised the lake together with some rotifers, in particular Hexarthra fennica. In mid eighties following the introduction of anti-pollution legislation, ammonium loads were greatly reduced and Daphnia obtusa was recorded. The lake waters however were still very acid, prompting the proposal of the Istituto Italiano di Idro-biologia to lime the lake with calcium carbonate to neutralise the excess acidity and re...

Cone Pond, New Hampshire, is an acidic (pH = 4.5) clearwater lake that is currently fishless. Historical records indicate declining fish populations between 1951 and 1966, but paleolimnological work using diatoms failed to find evidence... more

Cone Pond, New Hampshire, is an acidic (pH = 4.5) clearwater lake that is currently fishless. Historical records indicate declining fish populations between 1951 and 1966, but paleolimnological work using diatoms failed to find evidence for further recent acidification of this naturally acid site. We initiated new paleolimnological studies using mallomonadacean chrysophytes to further our understanding of Cone Pond's recent past. Our stratigraphic analyses indicate recent striking changes in the chrysophyte flora of this lake, with Mallomonas hindonii, a species only common in recently acidified lakes, replacing M. crassisquama, a cosmopolitan species that dominated the flora over the preceding 8000 yr; this recent change parallels the declines in fish populations. Because chrysophytes often bloom in early spring and are known, in other lakes, to experience changes in community composition before those expressed by the diatom community, a possibility is that chrysophytes track t...

Cyanophytes were sampled in two surveys, summer 1993 and 1995, in order to compare the algal flora of 19 small springs located in the upper part of the River Sarca catchment (Northern Italy). Measurements of the main physico-chemical... more

Cyanophytes were sampled in two surveys, summer 1993 and 1995, in order to compare the algal flora of 19 small springs located in the upper part of the River Sarca catchment (Northern Italy). Measurements of the main physico-chemical variables of the spring water were also carried out. The springs differ largely in altitude (from 1073 to 2130 m a.s.l.), lithology of the aquifer (calcareous/dolomitic mountains in the Brenta and igneous intrusive rocks in the Adamello region), discharge (from less than 1 to 137 l s-1), substrate particle size and exposure. Cyanophytes were present in all the rheocrenes and lacking in the helocrenes. Up to 41 cyanophyte species were observed. The genera Chamaesiphon, Homoeothrix and Phormidium were most frequent and rich in species, with a majority of epilithic taxa occuring mainly in oligotrophic fast flowing mountain streams. Sample grouping as obtained by numerical analysis (TWINSPAN, CANOCO) was mainly explained by lithology and conductivity (separation of siliceous from calcareous substrate). Other variables pointed out by the Canonical Correspondence Analysis were the degree of shading and altitude. Differences among springs are marked, as can be argued from the relation between the high total number of species found (41) and the low diversity (on the average six species) of the single sites. Rare species were mainly found in springs warranting low flow variability at the site of emergence.

Within the activities of the Integrated Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and of the EU Regulation 2152/2003, a Working Group on Quality Assurance/Quality Control of... more

Within the activities of the Integrated Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and of the EU Regulation 2152/2003, a Working Group on Quality Assurance/Quality Control of analyses has been created to assist the participating laboratories in the analysis of atmospheric deposition, soil and soil solution, and leaves/needles. As part of the activity of the WG, this study is a statistical analysis in the field of water analysis of chemical concentrations and relationships between ions, and between conductivity and ions for different types of samples (bulk or wet-only samples, throughfall, stemflow) considered in forest studies. About 5000 analyses from seven laboratories were used to establish relationships representative of different European geographic and climatic situations, from northern Finland to southern Italy. Statistically significant differences between the relationships obtained from different types of solutions, interacting with different types of vegetation (throughfall and stemflow samples, broad-leaved trees and conifers) and with varying influence of marine salt were tested. The ultimate aim is to establish general relationships between ions, and between conductivity and ions, with relative confidence limits, which can be used as a comparison with those established in single laboratories. The use of such techniques is strongly encouraged in the ICPF laboratories to validate single chemical analyses, to be performed when it is still possible to replicate the analysis, and as a general overview of the whole set of analyses, to obtain an indication of the laboratory performance on a long-term basis.

We examined spatial patterns of trends in ice phenology and duration for 65 waterbodies across the Great Lakes region (Minnesota, Wisconsin, Michigan, Ontario, and New York) during a recent period of rapid climate warming (1975-2004).... more

We examined spatial patterns of trends in ice phenology and duration for 65 waterbodies across the Great Lakes region (Minnesota, Wisconsin, Michigan, Ontario, and New York) during a recent period of rapid climate warming (1975-2004). Average rates of change in freeze (3.3 d decade 21) and breakup (22.1 d decade 21) dates were 5.8 and 3.3 times more rapid, respectively, than historical rates (1846-1995) for Northern Hemisphere waterbodies. Average ice duration decreased by 5.3 d decade 21. Over the same time period, average fall through spring temperatures in this region increased by 0.7uC decade 21 , while the average number of days with snow decreased by 5.0 d decade 21 , and the average snow depth on those days decreased by 1.7 cm decade 21. Breakup date and ice duration trends varied over the study area, with faster changes occurring in the southwest. Trends for each site were compared to static waterbody characteristics and meteorological variables and their trends. The trend toward later freeze date was stronger in large, low-elevation waterbodies; however, freeze date trends had no geographic patterns or relationships to meteorological variables. Variability in the strength of trends toward earlier breakup was partially explained by spatial differences in the rate of change in the number of days with snow cover, mean snow depth, air temperature (warmer locations showed stronger trends), and rate of change in air temperature. Differences in ice duration trends were explained best by a combination of elevation and the local rate of change in either temperature or the number of days with snow cover.

Pérez-Uz, B., Velasco-González, I., Murciano, A., Sanchez-Jimenez, A., García-Rodríguez, M., Centeno, J.D., Montero, E., Muñoz, C., Quintela-Alonso, P., Refoyo, P., Williams R and MercedesMartín-Cereceda (2021). Rain-fed granite rock... more

We evaluated several factors influencing the taxonomic richness of macrophytes, benthic invertebrates, snails, and fish in a series of northern Wisconsin lakes. We chose the study lakes to decouple the potential effects of ionic strength... more

We evaluated several factors influencing the taxonomic richness of macrophytes, benthic invertebrates, snails, and fish in a series of northern Wisconsin lakes. We chose the study lakes to decouple the potential effects of ionic strength of lake water and stream connection, two factors that are usually highly correlated and therefore have been confounded in previous studies. In addition, our study lakes covered a wide range in a variety of characteristics, including residential development, abundance of exotic species, nutrient concentrations, predator abundance, and lake size. Species richness within each of the four taxonomic groups was significantly positively related to ionic strength (as measured by specific conductance); we also found secondary associations with other variables, depending on the specific group of organisms. The relationship between richness and lake area was dependent on the specific conductance of the lake and the vagility of the organisms; less vagile groups of organisms showed stronger and steeper species–area relationships in low-conductivity lakes. Further, after variance owing to specific conductance was removed, the presence of stream connections was positively related to species richness for fish, snails, and macrophytes as well as familial richness in benthic invertebrates. Our results indicate that lakes with relatively more groundwater input have lower extinction rates for all four groups of taxa and that lakes with stream inlets and outlets have enhanced immigration rates for fish, snails, benthic invertebrate families, and macrophytes. These findings link processes of immigration and extinction of four groups of organisms of varying vagility to landscape-level hydrologic characteristics related to the glacial history of the region.

Multi-proxy approach was used to reconstruct the environmental conditions of remote lakes in the High Tatra Mountains (Slovakia) over the past few centuries (approximately 500-1000 years). Short sediment cores (*30 cm) taken from three... more

Multi-proxy approach was used to reconstruct the environmental conditions of remote lakes in the High Tatra Mountains (Slovakia) over the past few centuries (approximately 500-1000 years). Short sediment cores (*30 cm) taken from three morphologically similar glacial lakes distributed along altitudinal gradient (subalpine to alpine conditions) were analysed for organic matter content (LOI), diatoms and chironomids. Both descriptive and correlative approaches were used for analysing stratigraphical data. Predictive canonical correspondence analysis and co-correspondence analysis were applied to directly relate physical and biological proxies to each other. The relationship between LOI and biotic proxies was inconsistent across groups and lakes. Concordant patterns in diatom and chironomid composition were found in two non-acidified lakes. Common trends in those assemblages indicated major past environmental events such as the Little Ice Age, air pollution and lake acidification. In contrast, no relationship between the composition of diatom and chironomid assemblages was found in the formerly acidified lake, suggesting different responses of assemblages to acidification. While chironomids showed shifts that are attributable to recovery, diatoms assemblage remained relatively stable throughout the uppermost layers of the sediment record. On the other hand, climatic-driven changes in assemblages detected in the deeper layers were more pronounced in diatoms than in chironomids.

The Lonar crater situated in Buldana District, Maharashtra is natural hyper saline lake formed by hypervelocity meteoritic impact in basaltic rock. An attempt has been made to evaluate physicochemical qualities of Lonar Lake water.Water... more

The Lonar crater situated in Buldana District, Maharashtra is natural hyper saline lake formed by hypervelocity meteoritic impact in basaltic rock. An attempt has been made to evaluate physicochemical qualities of Lonar Lake water.Water samples were analyzed from 2012 to 2013 for seasonal variation in physicochemical qualities of Lonar lake water and revealed that, the water is alkaline (pH 10.5) and characterized by high concentration of Salts (9060mg/L), Alkalinity (5786 mg/L), Salinity (6391 mg/L), Total hardness (480 mg/L) and Dissolved Oxygen (0.034 mg/L). The data indicated that the alkalinity is increased in monsoon and post-monsoon season while decrease in pre-monsoon season. Likewise the chloride and salinity is increased in pre monsoon season while decreased in monsoon and post-monsoon season. As the Lonar Lake is unique in the world for its alkalinity and salinity of the water but its alkalinity, pH and salinity goes on decrease day by day. Hence this World heritage should be preserved for its alkalinity and salinity.

An overview of the literature is presented on the biology of the rivers entering the Humber, eastern England, together with some of their tributaries. Particular emphasis is given to dynamic aspects, including transport and movement... more

An overview of the literature is presented on the biology of the rivers entering the Humber, eastern England, together with some of their tributaries. Particular emphasis is given to dynamic aspects, including transport and movement within rivers, movement between rivers, processes within rivers and long-term changes. 0 1997 Elsevier Science B.V.

The seasonal and inter-annual dynamics of phytoplankton in two Italian sand-pit lakes have been analysed over three years (2004)(2005)(2006). The studied lakes, Ca' Morta (CM) and Ca' Stanga (CS), have a common origin and are contiguous,... more

The seasonal and inter-annual dynamics of phytoplankton in two Italian sand-pit lakes have been analysed over three years (2004)(2005)(2006). The studied lakes, Ca' Morta (CM) and Ca' Stanga (CS), have a common origin and are contiguous, but are of different ages and have been managed in different ways. CM was created in 2002 and was still being dredged during the study period, while sand quarrying in CS began in 1998 and ended at the beginning of the study period. These conditions were thought to be of particular interest in assessing the influence of dredging activities on algal assemblages. Physical and chemical water parameters were also analysed to characterise the two lakes and investigate the effects of hydro-chemical features on phytoplankton. CS was stratified from April to October each year during the study period, while CM showed weaker thermal stratification. Conductivity, dissolved nitrate and dissolved reactive silica concentrations were greater in CM than in CS. The mixing depth/euphotic depth ratio was also higher in CM, probably because of water column mixing induced by hydraulic dredging. Overall, 185 phytoplankton taxa were found, of which ca 50% were present in both lakes. No significant differences in species richness were observed between lakes, but the decreasing trend of Simpson index values measured in CS showed a reduction in biodiversity after the excavation phase. Phytoplankton biomass was higher in CS than in CM, the latter being oligo-mesotrophic and the former mesotrophic. Diatoms and dinoflagellates were the dominant taxa in both lakes. The main differences in phytoplankton assemblages were related to the persistence of chryptophytes and chlorophytes in CM. Multivariate analyses support the hypothesis that different thermal patterns induced by dredging activities, along with certain physico-chemical parameters of the water, were the major factors shaping phytoplankton communities.

Variation of abundance, dominance and diversity of tardigrades were studied over a period of 54 months in a carpet of the moss Rhytidiadelphus squarrosus that covered a lawn in the Black Forest (Germany). Altogether 19,909 individuals... more

Variation of abundance, dominance and diversity of tardigrades were studied over a period of 54 months in a carpet of the moss Rhytidiadelphus squarrosus that covered a lawn in the Black Forest (Germany). Altogether 19,909 individuals belonging to 24 species were extracted from the moss. Macrobiotus hufelandi (56%), Macrobiotus richtersi (18%) and Diphascon pingue (12%) were the most abundant and dominant species. Dominances of the other species varied between 0.01 to 2.15%. Generally, species diversity (Shannon-Index and evenness) was highest during the winter. A temporal variation in numbers with a decline in winter and an increase in spring until fall was seen in M. hufelandi, D. pingue and less clear in M. richtersi. Three species (Diphascon rugosum, Hypsibius dujardini, Hypsibius cfr. convergens) showed a cyclic variation with clear peaks in wintertime. The moist season favoured species that were considered as hygrophilous in the literature, whereas the relatively dry sunny seasons promoted the relative increase of euryhygric species. The composition of the tardigrade community was strikingly robust over the years. Fourteen species were always present during the entire period of investigation. However, changes in the species composition over the years, and cyclical temporal presence of certain species stress the significance of long-term studies to estimate species richness in a given habitat. Application of the Spearman rank correlation test to the data set of the whole study period showed different correlations between the mean number of tardigrades as well as the mean number of individuals of selected species (dominance >1) and rainfall, humidity and temperature. Correlations confirmed some of the ecological dependences of tardigrade species known from literature. Conflicting classifications suggest dependence from other variables or perhaps presence of ecotypes.

We describe the population biology and life-history traits of two Eurasian ruffe [Gymnocephalus cernuus (L.), Pisces: Percidae] populations which have recently colonised two small lakes in the lake Maggiore catchment of Northern Italy,... more

We describe the population biology and life-history traits of two Eurasian ruffe [Gymnocephalus cernuus (L.), Pisces: Percidae] populations which have recently colonised two small lakes in the lake Maggiore catchment of Northern Italy, the eutrophic lake (l.) Ghirla (ruffe first recorded in the early 1990s) and the oligotrophic l. Mergozzo (ruffe first recorded during the present sampling in 2010). Survey gill net catches revealed that ruffe has become one of the most abundant fish species in both lakes. Relative weight and weight-length relationships indicated better growth of ruffe in l. Mergozzo. Thus, gonad weight, adjusted for body size, was higher in l. Mergozzo, indicating a stronger individual reproductive potential in the more recently colonised lake. The stomach contents of ruffe were dominated by chironomid larvae and other benthic organisms, while pelagic microcrustaceans only occurred in small amounts. The ratio of benthic vs pelagic prey in the diet increased with ruffe size. Ruffe intraspecific food niche overlap (based on prey numbers) between age classes was slightly higher in oligotrophic l. Mergozzo than in eutrophic l. Ghirla and decreased with age in both lakes.

An attempt has been made to study the phytoplankton diversity of a freshwater, seasonal oxbow lake, Baishar Beel of Nadia district of West Bengal. This particular beel is located within Chakdaha block of Nadia district and shows a... more

An attempt has been made to study the phytoplankton diversity of a freshwater, seasonal oxbow lake, Baishar Beel of Nadia district of West Bengal. This particular beel is located within Chakdaha block of Nadia district and shows a connection between rural and urban areas. A total of 30 phytoplankton species were recorded from the wetland during the study period of March-November, 2012. Phytoplankton composition of the Baishar Beel was fluctuated by seasonal changes and four algal classes namely Chlorophyceae, Cyanophyceae, Bacillariophyceae and Euglenophyceae form the phytoplankton spectrum within the study period. Among this, Chlorophyceae dominates in monsoon and post-monsoon and Cyanophyceae dominates in pre-monsoon season. Various diversity indices (Shannon Wiener diversity index, Margalef species richness index, Pielou evenness index, and Simpson dominance index) were calculated to illustrate the seasonal changes of phytoplankton. The Shannon Wiener diversity index values (2.52, 2.33 and 2.66 for pre-monsoon, monsoon and postmonsoon season respectively) were recorded. Which pinpoint a moderate pollution status of this beel?

La Lupa Colección Fueguina de divulgación científica. Comité Editorial: Franch Bach, Anna Marina, Tomás. Ignacio. Lasa, Adriana. Bartoli, Valeria Roulier, Catherine. Kaminsky, Julieta. Balza, Ulises. Granitto, María. Pal, Nélida. García,... more

La Lupa Colección Fueguina de divulgación científica.
Comité Editorial:
Franch Bach, Anna
Marina, Tomás. Ignacio.
Lasa, Adriana.
Bartoli, Valeria
Roulier, Catherine.
Kaminsky, Julieta.
Balza, Ulises.
Granitto, María.
Pal, Nélida.
García, Victoria. Julieta.

We used the instantaneous growth rate method to determine the effects of food, temperature, krill length, sex, and maturity stage on in situ summer growth of krill across the southwest Atlantic sector of the Southern Ocean. The main aims... more

We used the instantaneous growth rate method to determine the effects of food, temperature, krill length, sex, and maturity stage on in situ summer growth of krill across the southwest Atlantic sector of the Southern Ocean. The main aims were to examine the separate effects of each variable and to generate a predictive model of growth based on satellite-derivable environmental data. Both growth increments in length on moulting (GIs) and daily growth rates (DGRs, mm d Ϫ1 ) ranged greatly among the 59 swarms, from 0.58-15% and 0.013-0.32 mm d Ϫ1 . However, all swarms maintained positive mean growth, even those in the low chlorophyll a (Chl a) zone of the central Scotia Sea. Among a suite of indices of food quantity and quality, large-scale monthly Chl a values from SeaWiFS predicted krill growth the best. Across our study area, the great contrast between bloom and nonbloom regions was a major factor driving variation in growth rates, obscuring more subtle effects of food quality. GIs and DGRs decreased with increasing krill length and decreased above a temperature optimum of 0.5ЊC. This probably reflects the onset of thermal stress at the northern limit of krill's range. Thus, growth rates were fastest in the ice edge blooms of the southern Scotia Sea and not at South Georgia as previously suggested. This reflects both the smaller size of the krill and the colder water in the south being optimum for growth. Males tended to have higher GIs than females but longer intermoult periods, leading to similar DGRs between sexes. DGRs of equivalent-size krill tended to decrease with maturity stage, suggesting the progressive allocation of energy toward reproduction rather than somatic growth. Our maximum DGRs are higher than most literature values, equating to a 5.7% increase in mass per day. This value fits within a realistic energy budget, suggesting a maximum carbon ration of ϳ20% d Ϫ1 . Over the whole Scotia Sea/South Georgia area, the gross turnover of krill biomass was ϳ1% d Ϫ1 .

A prototype in-water laser line-scanning multispectral fluorescence imaging system was evaluated for its ability to provide data that could be used to determine the quantitative distribution and abundance of various functional groups on... more

A prototype in-water laser line-scanning multispectral fluorescence imaging system was evaluated for its ability to provide data that could be used to determine the quantitative distribution and abundance of various functional groups on coral reefs. The system collected fluorescence imagery in three spectral bands with 1 cm 2 resolution at sites in Florida and the Bahamas. Fluorescence excitation was at 488 nm, and imagery was collected in emission bands centered at 520, 580, and 685 nm. Ground truth data on bottom cover was collected by divers using conventional line transect and photographic quadrat methods. A set of classification rules based on the relative signal levels in the three fluorescence channels was developed to assign the image pixels to functional groups. Once the image was classified, percent cover data for the groups were computed for the full image and for subsets of the image chosen to simulate line transect, grid survey, and photographic quadrat surveys. The statistics of percent cover of various bottom types derived from the fluorescence image compared favorably with those determined by diver survey techniques. The results demonstrate that fluorescence imaging has the long-term potential to provide coverage of large spatial areas of coral reefs at high resolution, with automated classification and quantification of functional groups in the image.

In the framework of the Mountain Lake Research (MOLAR) project, the water chemistry of 23 lakes covering Europe from the Svalbard Islands to the South of Spain were studied. The lakes are located above or beyond the timber line in the... more

In the framework of the Mountain Lake Research (MOLAR) project, the water chemistry of 23 lakes covering Europe from the Svalbard Islands to the South of Spain were studied. The lakes are located above or beyond the timber line in the most important mountain areas in Europe. Atmospheric deposition was sampled at 11 sites, representative of different lake districts. 24 institutions took part in the activity. The comparability of the analytical results performed in 18 laboratories was assured by strict sampling and analysis protocols and by a detailed programme of Analytical Quality Assessment/Control. The paper summarises the main morphometric and hydrological characteristics of the lakes and their watersheds and discusses the results of the atmospheric deposition and lake water chemistry. An overview on the main processes controlling the composition and ionic ratio of deposition and lake chemistry is given.
Key words: remote lakes, water chemistry, deposition chemistry

Dissolved organic carbon (DOC) is a key parameter in lakes that can affect numerous features, including microbial metabolism, light climate, acidity, and primary production. In an attempt to understand the factors that regulate DOC in... more

Dissolved organic carbon (DOC) is a key parameter in lakes that can affect numerous features, including microbial metabolism, light climate, acidity, and primary production. In an attempt to understand the factors that regulate DOC in lakes, we assembled a large database (7,514 lakes from 6 continents) of DOC concentrations and other parameters that characterize the conditions in the lakes, the catchment, the soil, and the climate. DOC concentrations were in the range 0.1-332 mg L 21 , and the median was 5.71 mg L 21. A partial least squares regression explained 48% of the variability in lake DOC and showed that altitude, mean annual runoff, and precipitation were negatively correlated with lake DOC, while conductivity, soil carbon density, and soil C : N ratio were positively related with lake DOC. A multiple linear regression using altitude, mean annual runoff, and soil carbon density as predictors explained 40% of the variability in lake DOC. While lake area and drainage ratio (catchment : lake area) were not correlated to lake DOC in the global data set, these two factors explained significant variation of the residuals of the multiple linear regression model in several regional subsets of data. These results suggest a hierarchical regulation of DOC in lakes, where climatic and topographic characteristics set the possible range of DOC concentrations of a certain region, and catchment and lake properties then regulate the DOC concentration in each individual lake.

A synthesis is made of biological data collected in the last three decades on five volcanic lakes in Central Italy with the aim of evaluating their environmental status by means of biological parameters related to zooplankton, littoral... more

A synthesis is made of biological data collected in the last three decades on five volcanic lakes in Central Italy with the aim of evaluating their environmental status by means of biological parameters related to zooplankton, littoral and profundal zoobenthos frequently used to detect water quality changes in lakes. A number of bioindicators and bioindices were selected for this purpose, as far as possible following an integrated approach using information drawn from physical and chemical variables. Our results allowed the lakes to be classified according to their biological quality level, which proved to be in good agreement with physical and chemical diagnoses. Lake Bracciano exhibited the best environmental quality, due to the presence of a ring waste water collecting system, to its large size and depth, and to its strong hydrodynamism. Lake Martignano followed, with some symptoms of stress in the hypolimnion due to a marked summer deoxygenation. Oxygen depletion in the profundal characterized also Lake Vico, which showed a mesotrophic condition in the sixties, and 20 years later now shows clear signs of increased trophy (meso-eutrophy). Lake Albano seemed meso-eutrophic with total absence of fauna below a depth of 120 m due to a meromictic status. Finally Lake Nemi, exposed to domestic wastes in the 70s, suffered a heavy eutrophication with dramatic algal blooms and fish kills. Following the diversion of discharges that occurred in the early 90s, today this lake is characterized by the partial improvement of many ecological features. The need for integration between physical and chemical analyses and biological data in order to obtain a reliable evaluation of lake environmental quality is stressed, especially as far as routine implementation in managing and recovery procedures is concerned.

Remotely sensed chlorophyll a (Chl a) concentrations are determined by the ratio of upwelled radiances within the Soret band of Chl a (443 nm) and at 550 nm. Absorption at wavelengths outside this band (Ͼ460 nm) is dominated by accessory... more

Remotely sensed chlorophyll a (Chl a) concentrations are determined by the ratio of upwelled radiances within the Soret band of Chl a (443 nm) and at 550 nm. Absorption at wavelengths outside this band (Ͼ460 nm) is dominated by accessory pigments and for the successful measurement of Chl a (e.g., 490 : 550 nm and 520 : 550 nm ratios) early Coastal Zone Color Scanner investigators speculated that these accessory pigments must covary with Chl a, although routine methods to measure these pigments had not yet been developed. Nearly 7,000 (high performance liquid chromatography) pigment samples, collected within the euphotic zone, were measured to test the consistency of the relationship between accessory pigments and Chl a. Despite the various sampling periods (1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998) and numerous geographic locations, consistent patterns have emerged in the ratios of the log accessory pigments to log total Chl a (TCHLA ϭ Chl a, Chl a allomer, Chl a epimer, and chlorophyllide a). There were strong log-linear relationships within cruises for these ratios with an average r 2 of 0.889. An even more impressive relationship was observed on a global scale when all the data were combined. Individual relationships were also calculated for case I and case II waters, as well as for the first optical depth (K Ϫ1 ), termed the remote sensing depth. There were some statistical differences between these relationships, yet on a practical sense many could be combined. Despite a wide range of environments sampled, the overall slope of the log accessory pigments : log TCHLA was found to be 0.934 with a relative-difference root-mean-square error of 28% in log accessory pigment concentrations. This global log-linearity largely explains the success in remotely sensed Chl a algorithms, even though phytoplankton populations can vary in their composition and suite of pigments.

Lignin, elemental, and stable carbon isotope compositions are reported for local plants and for coarse (>63 pm) and fine (~63 pm) suspended particulate materials collected along a 1,950-km reach of the lower Amazon River during four... more

Lignin, elemental, and stable carbon isotope compositions are reported for local plants and for coarse (>63 pm) and fine (~63 pm) suspended particulate materials collected along a 1,950-km reach of the lower Amazon River during four contrasting stages of the 1982-1983 hydrograph. Fluxes of chemically recognizable lignin in the two size classes generally parallel each other along the mainstem with the fine fraction usually predominating. Particulate organic matter transported in the coarse size fraction of the mainstem and its major tributaries is composed of recently formed and well preserved tree leaf debris along with some wood. Organic matter in the fine size fraction is comparatively old, degraded, and rich in immobilized nitrogen and derives primarily from soils. C-4 grasses, which are abundant in the mainstem floodplain (varzea), are not major components of either the coarse or fine particulate material in the river.

Currently, loss of habitat is the greatest threat to biodiversity, yet little is known about its effect on microscopic animal taxa, such as Tardigrada. One of the causes of habitat destruction is forest fire, both natural and... more

Currently, loss of habitat is the greatest threat to biodiversity, yet little is known about its effect on microscopic animal taxa, such as Tardigrada. One of the causes of habitat destruction is forest fire, both natural and anthropogenic. The latter is commonly used in agriculture to kill insect pests, as a soil preparation, or conservation to create habitat mosaics. In Portugal, 42% of fire frequency is anthropogenic. There is no consensus on the impact of fires on biodiversity, with studies pointing towards different conclusions. Different methods and target taxonomic study groups may partly explain this paradigm. This study is the first into possible effects of habitat destruction on tardigrade populations, in which we analysed the taxonomic and genetic variations of tardigrades from a fire affected location in a Portuguese natural park. Sampling was performed over a 10-year period, from 2000 to 2010. The location was affected by a small fire in 1998 and a big fire in 2003. A total of 11 species from nine separate genera was recorded, from which 19 cox1 haplotypes were identified. Our data suggest a negative effect of a forest fire on tardigrade populations. Taxonomic and genetic richness, as well as abundance show lower levels in the years after a fire, compared with the preceding years. Additionally, the population recovered visibly faster after the small fire than after the bigger one. This is consistent with larger fires destroying larger forest areas, leaving fewer animals at a farther distance available for re-colonisation. Most species found before the main fire are also found after it, indicating these tardigrades have a high recolonisation capability. However, only three of all recorded haplotypes were found both pre and post the main fire, which indicates genetic diversity loss as a direct consequence of fire. Therefore, we conclude that habitat destruction by means of forest fire has a detrimental effect on tardigrade biodiversity, and may have similar effects on other small animals.

We determined the chemical speciation of lead and copper in remote mountain and high-latitude lakes at different times of the year, providing background data for regions in Europe least affected by anthropogenic effects. The lakes are... more

We determined the chemical speciation of lead and copper in remote mountain and high-latitude lakes at different times of the year, providing background data for regions in Europe least affected by anthropogenic effects. The lakes are characterized by low ionic strength, clear waters, and oligotrophic conditions; are fed predominantly by atmospheric precipitation; and are ice-covered during a large part of the year. Lead-and copper-complexing ligands were determined by cathodic stripping voltammetry with ligand competition using Calcein blue and salicylaldoxime, respectively. Water column averages of the dissolved lead concentrations ranged from 0.2 to 0.9 nmol L Ϫ1 , with generally lowest levels during the prolonged winter ice cover, whereas dissolved copper concentrations, varying from 1 to 1.7 (Ϯ0.1) nmol L Ϫ1 , showed no significant seasonal variations. The lead speciation was controlled by complexation with ligands at concentrations mostly below 2 nmol L Ϫ1 , with values for the stability constant (log K ) of 12.5-13.7; calculated ionic lead concentrations Ј PbL (Ϫlog[Pb 2ϩ ] values) were 11.9-14.5. Copper complexation was controlled by ligands at concentrations of 12-21 nmol L Ϫ1 , with values for log K of 13.5-14.0 and Ϫlog[Cu 2ϩ ] values of 14.4-15.1. The concentration of Ј CuL the copper-binding ligands, but not those for lead, varied seasonally, with about 50% higher concentrations during open water conditions compared to periods of ice cover. The data were consistent with the presence of only one class of ligands for copper and lead. The stability constant of the ligands is similar to that of fulvic acid; however, evidence regarding the actual nature of the ligands is still lacking. The lake data show that (1) competition between calcium and lead causes a reduction in the stability constant of approximately one log-unit for each order of magnitude of Ca 2ϩ , and (2) lead scavenging in the lakes is moderated by complexation.

1. Shallow lakes are often cited as classic examples of systems that exhibit trophic cascades but, whilst they provide good model systems with which to test general ecological theory and to assess long-term community change, their food... more

1. Shallow lakes are often cited as classic examples of systems that exhibit trophic cascades but, whilst they provide good model systems with which to test general ecological theory and to assess long-term community change, their food web linkages have rarely been resolved, so changes associated with the structure and dynamics of the ecological network as a whole are still poorly understood.
2. We sought to redress this, and to demonstrate the potential benefits of integrating palaeolimnological and contemporary data, by constructing highly resolved food webs and stable isotope derived measures of trophic interactions and niche space, for the extant communities of two shallow U.K. lakes from different positions along a gradient of eutrophication. The contemporary surface sediment cladoceran and submerged macrophyte assemblages in the less enriched site, Selbrigg Pond, matched the palaeolimnological assemblages of the more enriched site, Felbrigg Hall Lake, in its more pristine state during the 1920s. Thus, Selbrigg was a temporal analogue for
Felbrigg, from which the consequences of long-term eutrophication on food web structure could be inferred. These data represent the first steps towards reconstructing not only past assemblages (i.e. nodes within a food web), but also past interactions (i.e. links within a food web): a significant departure from much of the previous research in palaeolimnology.
3. The more eutrophic food web had far fewer nodes and links, and thus a less reticulate network, than was the case for the more pristine system. In isotopic terms, there was vertical compression in d15N range (NR) and subsequent increased overlap in isotopic niche space, indicating increased trophic redundancy within Felbrigg. This structural change, which was associated with a greater channelling of energy through a smaller
number of nodes as alternative feeding pathways disappear, could lead to reduced dynamic stability, pushing the network towards further simplification. These changes reflected a general shift from a benthic-dominated towards a more pelagic system, as the plant-associated subweb eroded.
4. Although these data are among the first of their kind, the palaeo-analogue approach used here demonstrates the huge potential for applying food web theory to understand how and why these ecological networks change during eutrophication. Furthermore because of the rich biological record preserved in their sediments, shallow lakes represent potentially important models for examining long-term intergenerational dynamics, thereby providing a means by which models and data can be integrated on meaningful timescales – a goal that has long proved elusive in food web ecology.

High-elevation lakes are sensitive to acidification from atmospheric deposition owing to their generally small catchment areas, thin soils and low bedrock weathering rates. The Georgia Basin, southwest British Columbia, Canada, receives... more

High-elevation lakes are sensitive to acidification from atmospheric deposition owing to their generally small catchment areas, thin soils and low bedrock weathering rates. The Georgia Basin, southwest British Columbia, Canada, receives atmospheric inputs from emissions originating in Vancouver, Victoria, and from marine traffic in the Strait of Georgia. There is growing concern on the influence of this air pollution on high-elevation systems in the region. Water chemistry and catchment characteristics were used to assess the sensitivity of 72 lakes in the Georgia Basin to acidic deposition. Twenty percent of the study lakes had pH levels less than 6, and acid neutralising capacity (ANC) concentrations below 20 µeq L-1 , which are key thresholds for biological sustainability. Base cation and trace metal concentrations were low, typical of the dilute nature of high-elevation lakes (median conductivity = 7.0 µS cm-1). Nonetheless, concentrations of trace metals (such as lead) decreased with distance from major cities. The primary factors influencing the pH and ANC of surface waters were investigated using multiple linear regression; both ANC and pH were related to longitude and the proportion of the catchment dominated by ice and glaciers. Increasing sulphur deposition resulted in decreasing pH. The median critical load of acidity (sulphur) for the study lakes was approximately 70 meq m-2 y-1 ; 18% of the lakes received sulphur deposition (range: 6-81 meq m-2 y-1 for the period 2005-2006) in excess of their critical load.

Abiotic fragmentation of large, rapidly sinking aggregates into smaller, suspended particles by fluid shear has been suggested as an important process governing the particle size spectrum in the ocean and as one explanation for the... more

Abiotic fragmentation of large, rapidly sinking aggregates into smaller, suspended particles by fluid shear has been suggested as an important process governing the particle size spectrum in the ocean and as one explanation for the exponential decrease of particulate flux with depth below the euphotic zone. We investigated this process by quantifying the small-scale energy dissipation rates required to disaggregate marine snow settling through a gradient of turbulent kinetic energy in a laboratory tank. Aggregates of detrital debris, gelatinous houses of larvacean tunicates, and aggregates of living bacteria did not break apart even at energy dissipation rates > 1 cm2 ss3. The rate of energy dissipation required to disaggregate fragile diatom floes up to 25 mm long ranged from 10m3 to > 1 cm2 se3 and increased exponentially with decreasing maximum aggregate diameter. Aged diatom aggregates were significantly stronger than otherwise identical but unaged particles. These results indicate that only the highest shears associated with storm events or flows in tidal channels would be able to fragment even the most fragile organic aggregates in the upper ocean. Biological processes of disaggregation, such as animal grazing, appear far more likely to mediate the size spectrum of aggregated particulate matter in the ocean than abiotic fragmentation due to fluid motion.

Evaporation was determined by the energy-budget method for Mirror Lake during the open water periods of [1982][1983][1984][1985][1986][1987]. For all years, evaporation rates were low in spring and fall and highest during the summer.... more

Evaporation was determined by the energy-budget method for Mirror Lake during the open water periods of [1982][1983][1984][1985][1986][1987]. For all years, evaporation rates were low in spring and fall and highest during the summer. However, the times of highest evaporation rates varied during the 6 yr. Evaporation reached maximum rates in July for three of the years, in June for two of the years, and in August for one of the years. The highest evaporation rate during the 6-yr study was 0.46 cm d Ϫ1 during 27 May-4 June 1986 and 15-21 July 1987. Solar radiation and atmospheric radiation input to the lake and long-wave radiation emitted from the lake were by far the largest energy fluxes to and from the lake and had the greatest effect on evaporation rates. Energy advected to and from the lake by precipitation, surface water, and ground water had little effect on evaporation rates. In the energy-budget method, average evaporation rates are determined for energy-budget periods, which are bounded by the dates of thermal surveys of the lake. Our study compared evaporation rates calculated for short periods, usually ϳ1 week, with evaporation rates calculated for longer periods, usually ϳ2 weeks. The results indicated that the shorter periods showed more variability in evaporation rates, but seasonal patterns, with few exceptions, were similar.

Aquatic ecosystems are particularly vulnerable to environmental change and many are currently under pressure from direct human impacts such as hydraulic modifications, channelization, water abstraction, eutrophication and climate change.... more

Aquatic ecosystems are particularly vulnerable to environmental change and many are currently under pressure from direct human impacts such as hydraulic modifications, channelization, water abstraction, eutrophication and climate change. A recent national assessment revealed that almost a quarter of lakes and reservoirs across the lower 48 states are in poor biological condition. This study also shows that poor habitat conditions along the lakeshore and high levels of plant nutrients (nitrogen and phosphorus) are the most significant stressors of lakes and reservoirs in the US. About 20% of all lakes/reservoirs evaluated in the study contain high levels of nutrients, mostly resulting from anthropogenic pressure. This human-induced eutrophication affects the water quality and the ecosystem structure and function of these freshwater habitats. It can also have a significant economic impact due to losses in recreational water usage, waterfront real estate, spending on recovery of threatened and endangered species, and drinking water. Recent estimates have suggested that the economic losses due to eutrophication of US freshwaters are over $2 billion annually. Therefore, assessing the physical and anthropogenic controls on the water quality of lakes/reservoir is a critical challenge for both environmental scientists and water resource managers. Here we present the preliminary results of an ongoing study to determine the trophic state of nine lakes and reservoirs in north-central Ohio, as well as the physical and anthropogenic factors controlling the spatial and seasonal changes on the nutrient dynamic in these systems. We evaluate the influence of land and water use, geology, vegetation, snowmelt, precipitation and atmospheric deposition on the water quality in these lakes, and what are the sources and sinks of nutrients and the magnitude of these material fluxes. The surface area of the studied lakes/reservoirs varies from 28 to 1350 acres. They are nested in mixed-use catchments, with some being surrounded by parks, state forests, and wilderness areas, and others by cropland and developed landscapes. Since this is the first time these ecosystems are being assessed, we also evaluated the geochemistry of major ions (Mg2+, Ca2+, Na+, K+, Cl-, SO42-) and trace elements concentration on all nine lakes/reservoirs.