Stable nitrogen isotope Research Papers (original) (raw)

2025, Japan Geoscience Union

Spiraling metrics are important for the better understanding of the biogeochemical processes in rivers, although it is quite demanding to measure these parameters. We explore the possibility to use the natural abundance of 15N and d18O of inorganic nitrogen (ammonium, nitrate and occasionally nitrite) as a proxy of the spiraling metrics. We measured concentrations and isotopes ratios of ammonium, nitrate and nitrite in a reach of Fuji River to figure out how concentrations and isotope ratios of these inorganic nitrogen can change according to their spiraling. We continuously collected water samples in the reach of ca. 6.5 km in the Fuji River by directly tracking a specific parcel of water following the longitudinal Lagrangian approach in June, October, November and December of 2015. We found significant inverse correlations between ammonium concentrations and d15N of ammonium in all sampling periods, implying that ammonium was removed by nitrification and assimilation. The d15N of ...

2025, Environmental Science & Technology

Deterioration of aquatic ecosystems resulting from enhanced anthropogenic N loading has become an issue of increasing concern worldwide, and methods are needed to trace sources of N in rivers. Because nitrate from sewage is enriched in 15 N relative to nitrate from natural soils, δ 15 N values of stream nitrate (δ 15 N nitrate ) should be an appropriate index of anthropogenic N loading to rivers, as should the δ 15 N values of riparian plants (δ 15 N plant ) because they are consumers of nitrate. We determined the δ 15 N values of stream nitrate and six species of riparian macrophytes in 31 rivers in the Lake Biwa Basin in Japan. We then tested the correlation between these values and various land-use parameters, including the percentage of land used for residential and agricultural purposes as well as for natural areas. These δ 15 N values were significantly positively correlated with land use (%) that had a high N load (i.e., residential or agricultural use) and significantly negatively correlated with forest (%). These findings indicate that δ 15 N values of stream nitrate and riparian plants might be good indicators of anthropogenic inputs of nitrogen.

2025

The Florida Reef Tract is the third largest barrier-bank reef in the world and has provided considerable ecological services to the local economy of the Florida Keys through commercial and sport fishing as well as tourism. Coral reefs are adapted to oligotrophic conditions and low level nutrient enrichment from anthropogenic sources can lead to eutrophication and loss of these vital resources. Long-term water quality monitoring of dissolved inorganic nitrogen, soluble reactive phosphorus, and chlorophyll a at Looe Key reef in the lower Florida Keys, established as a Marine Protected Area in 1983, has shown a doubling of these variables between 1984 and 1998. The most dramatic nutrient enrichment occurred between 1991 and 1995 when water managers increased flows of nitrogen-rich agricultural runoff from the Everglades into the Florida Bay/Florida Keys region. The long-term nutrient enrichment correlated with decreased coral cover, increased coral disease, and increased cover of algae, bioeroding sponges, soft corals, and other opportunistic biota. Comparisons among fish censuses in the early 1980s and in 2002 indicate that the relative abundances of snapper, grouper, and grunt assemblages decreased by 75 % at Looe Key, whereas the herbivorous fish assemblage doubled in relative abundance. Measurement of stable nitrogen isotopes in macroalgae provide a useful means of quantifying the relative importance of various nitrogen sources, such as natural nitrogen fixation, wastewater, fertilizers, and atmospheric deposition. These data demonstrate the sensitivity of coral reefs to nutrient enrichment and the importance of water quality management to the survival of coral reefs, associated fisheries and ecological services.

2025, Marine Biology

can alternate between long foraging trips that provide the main source of food for the adults and short foraging trips that they use to feed their young. This flexibility in foraging behaviour can lead to differences in diet composition between adults and chicks and implies that they may be vulnerable in different ways to food shortages. The trophic ecology of the Greyheaded albatross Thalassarche chrysostoma was investigated at the sub-Antarctic Prince Edward Islands during the chick-rearing period in April 2006 using a combination of approaches. Diets of adults and chicks were assessed using stable isotope ratios and fatty acid (FA) profiles of blood and/or stomach oils, in addition to stomach contents analysis. Fish from the family Macrouridae and cephalopods (particularly the onychoteuthid Kondakovia longimana) were the primary prey, whereas crustaceans (krill Euphausia superba) represented a smaller proportion of the stomach contents. Stomach oil FA profiles contained more monounsaturated FA than the profiles of plasma, which were richer in saturated FA and arachidonic acid (20:4n-6). There was also a distinct separation of adults from chicks, with higher levels of monounsaturates in chick plasma, and higher saturated FA levels (particularly 16:0) in the adult plasma. Stable carbon isotope ratios of whole blood were similar in adults and chicks, whereas stable nitrogen isotope ratios showed significant enrichment by [1% in chicks. The combined FA, stable isotopes and stomach contents analyses suggest clear differences in diet quality between adults and chicks, with chicks feeding at a higher trophic position through feeding more on highly nutritious fish and adults keeping much of the less nutritious zooplankton for themselves. Communicated by S. Garthe.

2024

Location of standardized townetting transects, Iliamna Lake and Lake Clark. 60 11 Location of standardized periphyton stations and beach seine stations, Iliamna Lake 12 Stream spawning areas of Iliamna Lake. . 62 13 Known beach spawning... more

2024

2024, Journal of Archaeological Science

This paper explores the impact of animal manure application on the δ 15 N values of a broad range of crops (cereals and pulses), under a range of manuring levels/regimes and at a series of locations extending from northwest Europe to the eastern Mediterranean. We included both agricultural field experiments and areas where 'traditional' farming is practised. Our aim is to ground-truth interpretation of δ 15 N values in archaeobotanical crop remains as evidence of past growing conditions and husbandry practices. The results confirm the potentially radical impact of manuring on δ 15 N values in cereals, depending on manuring level, but indicate only a slight effect on pulses, which can fix atmospheric nitrogen. The expected geographical trend towards greater δ 15 N with increasing climatic aridity is not apparent, probably because the growing conditions for crops are 'buffered' through crop management. Each of these observations has fundamental implications for archaeobotanical interpretation of δ 15 N values as evidence of land use practices and (together with analysis of bone collagen/tooth enamel in potential consumers) palaeodiet.

2024

In order to study recent sedimentation rates in the Eastern Gotland Basin, 52 short sediment cores collected from the deepest part (< 150 m) of the Basin in 2003 were investigated. The upper parts of all the cores were distinctly laminated and dark in colour, followed by a homogeneous, greyish lower part. The thickness of the laminated sequences varied from 17 to 300 mm. 210Pb dating analyses of selected cores revealed that the change from non-laminated to laminated sediments happened about 100 years ago, indicating a shift from predominantly oxic bottom water conditions to anoxic conditions. Used as a time marker, this shift in the sediment texture enabled sediment accumulation rates to be estimated for all sediment cores. The observed mean linear sedimentation rate for the whole basin was 0.93 ± 0.67 mm yr−1. The respective bulk sediment accumulation rates ranged from 10.5 to 527 g m−2 yr−1 with an average of 129 ± 112 g m−2 yr−1, indicating a high spatial variability of sedime...

2024

The Scheldt Estuary is a highly polluted macrotidal estuary draining one of the most densely populated areas in the world (425 inhab/km2). The present nitrogen load to the estuary is approximately of 5 0 kT N / year from which about 20% is under the form of ammonium. This ammonium is almost completely nitrified in the estuary, even in winter conditions, when low temperatures are known to limit the activity of nitrifying bacteria. This is probably linked to the fact that water residence times are very long (75 days on the average) so that even with reduced nitrification rate depletion of ammonium is still possible. The oxidation of ammonium to nitrate by nitrifying bacteria results in an enrichment of N-NH,' in its heavy isotope 15N. Indeed, the heavy isotope 15N is discriminated against the light 14N isotope during the oxidation process. Measurements of the 615N in particulate organic matter and copepods show that the heavy "N isotope of ammonium is most probably incorporated in the entire microbial food web. This indicates that, at least for some periods of the year, the microbial food web of the estuary is based on microorganisms (phyto-and bacterioplankton) finding their N requirements by assimilating NH,+ rather than any other inorganic or organic N SOU rce .

2024, Biogeochemistry

We monitored the stable nitrogen isotopic composition (d 15 N) of suspended matter and ammonium in the freshwater stretch of the Scheldt estuary (Belgium) over a full year to investigate for seasonal evolution and possible co-variation between isotopic signatures. The d 15 N value of ammonium remained rather constant during winter (average = +11.4&) but increased significantly with the spring and summer bloom, reaching values as high as +70&. This enrichment of the ammonium pool in 15 N coincided with significant ammonium depletion during summer period, suggesting a close causal relationship. Based on a semiclosed system approach we deduced an apparent fractionation factor associated with NH 4 + utilization (i.e. combining effects of uptake and nitrification) of 18.4& (SE = 2.0&), which is similar to values reported in literature. Observed variations of ammonium d 15 N could account for about 69% of d 15 N variation in suspended matter.

2024, Journal of Geophysical Research: Atmospheres

Two episodes of long‐range aerosol transport (4000 km) from southern Africa into the central tropical South Atlantic are documented. Stable nitrogen isotope analysis, multielemental analysis, and meteorological observations on local and regional scales are used to describe the observed surface aerosol chemistry during these transport episodes. The chemical, kinematic, and thermodynamic analyses suggest that for the central tropical South Atlantic, west Africa between 0° and 10°S is the primary air mass source region (over 50%) during austral spring. Over 70% of all air arriving in the lower and middle troposphere in the central tropical South Atlantic comes from a broad latitudinal band extending from 20°S to 10°N. Air coming from the east subsides and is trapped below the midlevel and trade wind inversion layers. Air from the west originates at higher levels (500 hPa) and contributes less than 30% of the air masses arriving in the central tropical South Atlantic. The source types o...

2024, Marine Pollution Bulletin

2024, Science of The Total Environment

The contribution of uptake of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from water and food to the total bioaccumulation process was studied in two experiments. In the first experiment the uptake of PCDDs and PCDFs from contaminated food was determined in guppies for 180 days in uncontaminated water. The uptake from water was studied in the second experiment, in which the fish were exposed to contaminated water and fed with uncontaminated food for 21 days. If a comparison is made between the uptake from food and the uptake from water, the former proves to be smaller than the latter, even for extremely hydrophobic PCDDs and PCDFs.

2024, Marine Ecology Progress Series

The elemental (C, N, and P) and isotope (δ 13 C, δ 15 N) content of leaves of the seagrasses Thalassia testudinum, Halodule wrightii, and Syringodium filiforme were measured across a 10 000 km 2 survey of the seagrass communities of South Florida, USA, in 1999 and 2000. Trends at local and broad spatial scales were compared to examine interspecific variation in the seagrass characteristics often used as ecological indicators. The elemental and stable isotope contents of all species were variable and demonstrated marked interspecific variation. At broad spatial scales, mean N:P ratios were lowest for T. testudinum (36.5 ± 1.1) and S. filiforme (38.9 ± 1.3), and highest for H. wrightii (44.1 ± 1.8). Stable carbon isotope ratios (δ 13 C) were highest for S. filiforme (-6.2 ± 0.2 ‰), intermediate for T. testudinum (-8.6 ± 0.2 ‰), and lowest for H. wrightii (-10.6 ± 0.3 ‰). Stable nitrogen isotopes (δ 15 N) were heaviest for T. testudinum (2.0 ± 0.1 ‰), and lightest for H. wrightii (1.0 ± 0.3 ‰) and S. filiforme (1.6 ± 0.2 ‰). Site depth was negatively correlated to δ 13 C for all species, while δ 15 N was positively correlated to depth for H. wrightii and S. filiforme. Similar trends were observed in local comparisons, suggesting that taxon-specific physiological/ecological properties strongly control interspecific variation in elemental and stable isotope content. Temporal trends in δ 13 C were measured, and revealed that interspecific variation was displayed throughout the year. This work documents interspecific variation in the nutrient dynamics of 3 common seagrasses in South Florida, indicating that interpretation of elemental and stable isotope values needs to be species specific.

2024, Chemistry and Ecology

The decomposition of the mangrove Rhizophora mangle and the seagrass Thalassia testudinum was examined using litterbags along a natural gradient in nutrient availability. Seagrass leaves had a higher fraction of their biomass in the labile pool (57%), compared to mangrove leaves (36%) and seagrass rhizomes (29%); the overall decomposition rates of the starting material reflected the fractionation into labile and refractory components. There was no relationship between the N or P content of the starting material and the decomposition rate. Nutrient availability had no influence on decomposition rate, and mass was lost at the same rate from litterbags that were buried in the sediment and litterbags that were left on the sediment surface. The dynamics of N and P content during decomposition varied as a function of starting material and burial state. N content of decomposing mangrove leaves increased, but seagrass rhizomes decreased in N content during decomposition while there was no change in seagrass leaf N content. These same general patterns held for P content, but buried seagrass leaves increased in P content while surficial leaves decreased. d 13 C and d 15 N changed by as much as 2‰ during decomposition.

2024, Journal of the North American Benthological Society

Intraspecific and interspecific variation in the trophic position of various consumers is central to many theories of aquatic ecosystem functioning and dynamics. In recent years, such issues have been addressed using stable N isotopes (d 15 N) to estimate trophic position of consumers in aquatic ecosystems. However, one needs to correct for variation in baseline d 15 N among sites to estimate the trophic position of any aquatic consumer using d 15 N. We first discuss the steps needed to select a baseline indicator in river ecosystems, where abundant foodweb isotopic data have been published but limited attention has been paid to identification of baseline organisms. We examined within-site differences in d 15 N among primary consumers belonging to different functional and taxonomic groups and found significant differences in d 15 N. Collectors were significantly enriched compared to other primary consumers. We propose scrapers as a baseline d 15 N indicator because they showed low d 15 N values and were more widely distributed than other primary consumers throughout our study sites. Using this baseline d 15 N, we calculated continuous estimates of trophic position of consumers (invertebrates and small fish) for our 87 river food webs. Primary consumers had a significantly lower mean trophic position (2.3) than predatory invertebrates (2.9) and fish (3.5), and these results are concordant with estimates based on traditional studies. However, trophicposition estimates of consumers (both invertebrates and fish) were highly variable across sites with standard deviations spanning up to 0.67 trophic levels, which suggested potential omnivory. Comparison of these trophic-position estimates with estimates based on mean d 15 N of all primary consumers combined (no targeting of scrapers as baseline indicators) suggested that use of a constrained number of groups and corrections for isotopic differences among groups when estimating baseline d 15 N could reduce some biases induced by the use of various functional feeding groups with variable d 15 N values.

2024, Journal of Archaeological Science

We obtained stable isotope signatures (13 C, 15 N) and AMS radiocarbon dates for a small set of Dorset remains, Thule-era burials from northwest Hudson Bay and proto-historic burials from Southampton Island to assess the importance of whaling in eastern Canadian Arctic economies. Classic Thule occupation of the Eastern Arctic (ca. AD 1000-1350) coincided with the Medieval Warm Period and was thought to have been facilitated by dog traction and open-sea hunting of bowhead whale. Despite the potential economic importance of whaling, dietary reconstructions for this period are based on the relative frequency of common prey types in midden faunal assemblages and rarely include bowhead whale skeletal elements, which often comprise the superstructure of Classic Thule residential dwellings. Although our findings are constrained by the paucity of Classic Thule burials at sites under study, they provide an empirically derived estimate of reliance on whaling for the Modified Thule, those who postdate AD 1350, indicating whaling accounted for approximately 12% of dietary intake. We also examine the relationship between Thule whaling and indicators of status and identify a Dorset-aged burial and three individuals with European diets among the proto-historic collection from Southampton Island.

2024, PLOS ONE

The marbled murrelet (Brachyramphus marmoratus) is classified as a threatened species under the US Endangered Species Act in Washington, Oregon, and California USA due to population declines, loss of breeding habitat, and other factors. To date, population assessments have focused on breeding season at-sea surveys. Consequently, there is little information on this species’ distribution, abundance, and population trends during the non-breeding season, when murrelets are found exclusively in the marine environment. To address this information need, we assessed non-breeding (Sep—Mar) at-sea murrelet abundance patterns and population trends over 8 years, in a portion of its range where breeding season surveys indicate a 20-year population decline, Puget Sound, Washington, USA. This allowed us to assess whether non-breeding population trends mirrored those observed during the breeding season suggesting regional year-round conservation concerns and to also identify important over-winterin...

2024, Marine Ecology Progress Series

Two alternative mechanisms are suggested for nitrite accumulation in the oxygenated oligotrophic water column: (1) excretion by phytoplankton or (2) microbial oxidation of ammonium (nitrification). This study assessed the role of these 2 mechanisms, based on seasonal and high-resolution diurnal depth profiles of the dissolved inorganic nitrogen (DIN) species (nitrite, ammonium, nitrate) and chlorophyll a in the Gulf of Aqaba, Red Sea. Both mechanisms operated in the water column, but in different seasons; nitrification was the prime process responsible for nitrite accumulation during the stratified summer season and phytoplankton nitrite excretion operated during winter mixing. At the onset of summer stratification two N peaks developed below the photic zone, an ammonium maximum (AM) and below it the primary nitrite maximum (PNM). Both peaks were located at a depth range where phytoplankton are thought to be inactive and not excreting nitrite. During summer stratification, the water column deep chlorophyll maximum (DCM), AM, PNM and the nitracline were ordered by a downward increase in N oxidation state similar to the temporal order of the N-species during nitrification. This similarity, together with the diurnal stability of the PNM and its coexistence with oscillating chlorophyll profiles above the DCM, is consistent with nitrification as the key process forming the PNM. We suggest that transport and reaction control the vertical order and separation of N-species in the water column. The ratios between the rate constants for ammonification, ammonium oxidation, nitrite oxidation and nitrate assimilation were estimated by a simple box model to be 1:3:1.5:0.15, respectively. These field estimates are similar to the ratios between the rate constants measured in laboratory experiments.

2024, Quaternary International

2024, Quaternary Research

This paper presents the first continuous multi-proxy record of climate and vegetation change from the central Namib Desert extending over much of the last ca. 39,000 years. Derived from rock hyrax middens, evidence from stable carbon and nitrogen isotopes, pollen, and microcharcoal reveals significant differences between glacial-age and Holocene climates and vegetation types. Although still arid to semi-arid, conditions during Marine Oxygen Isotope Stages (MIS) 2-3 were significantly more humid than in the Late Holocene. Considerable associated vegetation change is apparent, with cooler temperatures and higher/more-regular rainfall promoting the westward expansion of relatively mesic shrubby karroid vegetation during MIS 2-3. With the last glacial-interglacial transition, increasing temperatures and less/less-regular rainfall resulted in marked vegetation changes and the establishment of current xeric grasslands. The inter-plant spacing of the karroid vegetation promoted by wetter conditions does not carry fire effectively, and the microcharcoal record indicates that more extensive fires may develop only with the development of grassier vegetation under drier conditions. As with other terrestrial records from the Namib Desert and environs, no Cape flora elements were found to support previously hypothesised expansion of the Fynbos Biome during the last glacial period.

2024, Journal of Paleolimnology

Several limnological and paleolimnological investigations have linked enhanced atmospheric nitrogen (N) deposition to nutrient enrichment and potentially increased primary production. The Athabasca Oil Sands Region (AOSR) in northeast Alberta is a significant regional source of N emissions, particularly since development intensified during the 1990's, and recent paleolimnological investigations have provided some evidence of increased lake production in the AOSR. However, the AOSR has also experienced atmospheric warming and hydrological change since ca 1900 AD, and therefore the relative effects of nutrient deposition and climatic mechanisms on lake production remain unclear. To address this problem, a factorial-designed paleolimnological assessment of 16 lakes in northwest Saskatchewan was undertaken to quantify changes in abundance and species composition of scaled chrysophytes over the past 100 years. Study sites included both N-limited and P-limited lakes within control regions as well as those receiving enhanced N deposition from the AOSR. We hypothesized that a change in algal communities within N-limited AOSR-impacted lakes, without concurrent changes in the other lake groups, would suggest AOSR-derived N as a driver of enhanced primary production. Instead, recent and marked increases in concentrations of scaled chrysophytes (mainly Mallomonas crassisquama) occurred in the recent sediments in cores from all four lake groups (N v. P limited, impacted v. control), suggesting that regional climate changes rather than N deposition was the paramount process enhancing chrysophyte production. However, because chrysophyte abundances tended to be higher in deep, lower pH lakes, and chrysophyte time series were fit best by lake-specific generalized additive models (GAMs), we infer that climate effects may have additionally been meditated by catchment and/or lake-specific processes.

2024, Marine Chemistry

Using new data for the concentrations and δ 15 N of the main nitrogen species of NO 3 − , NH 4 + , PON (particulate organic nitrogen) and N 2 in the Black Sea, we studied the distributions of concentrations and δ 15 N using a coupled physical-biogeochemical model including known biogeochemical processes and nitrogen isotopic fractionation. In the deep anoxic water N 2 is supersaturated. This supersaturation results from physical exchange with the Bosporus inflow that includes entrainment of N 2 supersaturated water from above the suboxic zone and its injection into the deep water of the Black Sea. In the suboxic zone there is a N 2 maximum and a δ 15 N 2 minimum at the depth where anammox has been observed. We first used a version of the model that included both denitrification and anammox. Anammox in this case was fueled by the downward flux of NO 3 − and the upward flux of NH 4 + from the deep water. This steady state model was able to successfully simulate the concentrations of all species and δ 15 N of NO 3 − and NH 4 +. Anammox was required to be much more important than denitrification in order to have the maximum of excess N 2 be at the correct depth and to have a NO 3 − profile with the correct shape. This model can not simulate the depleted δ 15 N values of N 2 observed in the suboxic zone in 2000, 2001 and 2003, unless we assume that PON leaving the suboxic zone is 15 N enriched, as compared to observational data, or that there is a presently unaccounted process to preferably remove 15 NH 4 + from the suboxic zone. Our models support the hypothesis that 15 N depleted PON, which could be made in the euphotic zone as the result of N 2fixation, may support production of 15 N depleted N 2 in the suboxic zone. This 15 N depleted PON (with δ 15 N = −2.0‰) sinks and is remineralized to produce 15 N depleted NH 4 + , which is rapidly consumed by anammox in the suboxic zone to produce 15 N depleted N 2. The nitrogen system in the suboxic zone is variable and periods of high excess N 2 correspond to periods with depleted δ 15 N 2. We hypothesize that the system oscillates between two states. The first occurs when anammox is driven by remineralization of 15 N depleted PON produced by N 2-fixation. This results in 15 N depleted N 2. The second occurs when anammox is driven by the downward flux of NO 3 − and the upward flux of NH 4 +. This results in 15 N enriched N 2 .

2024, Journal of Geophysical Research: Atmospheres

2024, Marine Ecology Progress Series

Stable isotopes were used to examine differential effects of fish farm waste on the water column and sediments. To achieve this objective, we chose 3 marine fish farms located along the coast of Sicily (Mediterranean Sea) as point-source disturbances, and a control area. The hypothesis that carbon and nitrogen isotope composition of particulate (POM) and sedimentary (SOM) organic matter varied with increasing distance (from cages to 1000 m) was tested at 3 levels of hydrodynamics: low (mean velocity of current [MVC] ~12 cm s-1), intermediate (MVC ~22 cm s-1), and high (MVC 40 cm s-1). Different isotopic signals from allochthonous (fish waste) over natural (phytoplankton, terrigenous, and sand microflora) inputs allowed identification of the 'spatial effect regime' of fish farming. The increasing water current velocities seem to proportionally enlarge the relative area of influence of the cages, particularly on sediments. At low hydrodynamics, an increasing contribution of terrigenous signals was inferred: POM and SOM showing a depleted gradient of C (ranging from-22.0 to-24.0 ‰) and N (from 5.0 to 2.0 ‰). At an intermediate hydrodynamic level, C and N showed a slight increase in waste contribution, particularly in POM (δ 15 N from 2.6 to ~4.0 ‰). At high hydrodynamics, an enriching isotopic gradient (δ 15 N POM-SOM from 1.8 to 4.6 ‰) suggested a notable contribution of fish waste. Accordingly, the dispersal of waste from the cages seemed to be related to movements at the bottom of the water column, confirming the recently identified role played by resuspension movements.

2024, Polar Biology

Diet studies of marine predators provide insights into the functioning and structure of marine ecosystems. Such studies have been greatly enhanced in recent years with technology enabling direct observation of feeding behaviour in the marine environment. We here report on observations of an interesting predation event involving Gentoo penguins (Pygoscelis papua) at sub-Antarctic Marion Island. Through the deployment of an animal-borne miniaturised video data logger, we were able to document what is to our knowledge the largest recorded prey species consumed by a Gentoo penguin. A squid (probably Greater hooked squid, Onykia ingens) with an estimated mantle length of 240 mm was consumed whole after a period of competition over the prey item with another foraging Gentoo penguin.

2024, Limnology and Oceanography

Two coral reef sponges were examined in situ off Puerto Rico for fluxes of dissolved inorganic nitrogen. Chondrilla nucula, a ubiquitous Caribbean sponge with cyanobacterial symbionts, releases large amounts of nitrate [600 nmol N g‒1 (dry wt) h‒1; 4,000 µmol N m‒2 h‒1. Since C. nucula covers a mean of 12% of the substratum, it potentially contributes between 50 and 120% of the nitrogen required to sustain reef productivity. Anthosigrnella varians, a common sponge with zooxanthellae symbionts releases lesser amounts of nitrate [19 nmol N g‒1 (dry wt) h‒1; 20 µmol N m‒2 h Although A. varians may cover between 1.2 and 11% of the reef substratum, the potential contribution is <1% of the nitrogen required for reef productivity. These release rates for C. nucula are comparable to those reported for nitrogen fixation in reef environments and in excess of rates reported for nitrate production by other reef substrata. Large populations of non‐photosynthetic symbiotic bacteria are conside...

2024, Isotopes in Environmental and Health Studies

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2023, Journal of Radioanalytical and Nuclear Chemistry

Signatures of D 14 C and d 13 C of total organic carbon in sediments as well as of total lipid extracts and phospholipid-derived fatty acid fractions isolated from the surface (0-3 cm) sediments collected in the Curonian Lagoon and in the open Baltic Sea were studied. An endmember mixing-model approach was applied to estimate relative contributions of the marine and terrestrial inputs to organic carbon in sediments, and to elucidate a possible leakage of chemical warfare agents at the Gotland Deep dumpsite. Keywords Organic carbon Á D 14 C Á d 13 C Á Chemical warfare agents & Galina Lujanien_ e

2023, Researches on population ecology

Although theoretical foodweb models predict the presence of only three to four trophic categories, estimation of "potential" vertical foodweb structure from species lists and inferred feeding interactions suggest that as many as 7 trophic categories can occur in the pelagic foodwebs of North American glaciated lakes. A compilation of data on the nitrogen isotopic composition of zooplankton from 46 Canadian Shield lakes suggested the average existence of one "realized" trophic category in addition to that of filterfeeding, herbivorous cladocerans. When phytoplankton, planktivorous invertebrates, and plantivorous and piscivorous fish are included, the vertical foodweb structure in the pelagic zones of these lakes are greater than those hypothesized from some theoretical models.

2023, Journal of Radioanalytical and Nuclear Chemistry

2023, Marine Ecology Progress Series

2023, Journal of Great Lakes Research

Lake Baikal, an ancient lake in Siberia, contains more endemic species than any other lake in the world with most of them residing in the benthic littoral zone. Explosive growth of benthic Spirogyra, a filamentous green alga, began approximately in 2011 in localized coastal areas, with the most severe examples occurring near coastal towns that lack a wastewater treatment facility or have a malfunctioning system. At other sites (small settlements, harbors), however, the cause of its excess growth is less obvious. Multiple hypotheses have been offered including lake level fluctuations, climate warming, a relaxation of grazing pressure, and coastal eutrophication. We assessed these hypotheses using data on historical lake levels, water temperature, the spatial-temporal distribution of Spirogyra along inhabited and non-inhabited shorelines, and measurements of fecal coliform bacteria and nutrients in ground water, interstitial water, and lake water. These data suggest that groundwater contamination is the primary cause of coastal eutrophication. Most houses and buildings in small settlements around Lake Baikal lack septic tanks but use unlined cesspools to collect human waste. This untreated human waste enters groundwater via passive filtration through permeable soils and flows to the coastal zone where it drives excess growth of Spirogyra. Remediationincluding installation of septic systems, modernization of existing sewage treatment plants in coastal towns, and the adoption of non-phosphate containing detergentsas well as a reconsideration of the federal monitoring system regarding the coastal zone is urgently needed to protect this extraordinary lake.

2023, Marine Ecology Progress Series

Investigating the foraging ecology of seabirds is especially challenging given their wide-ranging movements and the practical difficulties of obtaining unbiased information on their feeding behavior. Despite the development of animal-borne tracking devices, several limitations preclude investigations at the scale of a whole community in a given season or year, and, until recently, during the non-breeding period. Here we analyzed δ 13 C and δ 15 N in feathers of chicks and adults to investigate inter-and intra-specific variation in the foraging habitat and trophic position of 9 large procellariiform seabirds from 6 southern breeding localities during the breeding and non-breeding periods. Isotopic ratios of each species were generally consistent among different breeding populations, despite the large geographical scale and potential variation in oceanography in surrounding waters. Both spatial and trophic segregation apparently allowed the coexistence of sympatric species in most breeding localities, except at South Georgia, where both δ 13 C and δ 15 N in chicks showed high overlap among species, probably resulting from the superabundance of alternative food resources during the summer. Low variance in stable isotope ratios among adults in several species indicated high overlap between individuals in feeding habits and trophic levels (i.e. isotopic specialist populations) during the non-breeding period. By contrast, large isotopic variances and the high within-and between-individual components of the trophic niche width suggested that grey-headed and light-mantled sooty albatrosses are generalists. Based on δ 13 C, the species that breed in the Southern Ocean can be categorized as residents or subtropical migrants, with the latter including oceanic and neritic subtropical migrants. Albatrosses meet the high energetic challenge of feather synthesis by foraging in different habitats, depending on the length of the non-breeding period. Annual breeders renew their plumage in productive neritic waters in ~4 mo, whereas biennially breeding species moult in less productive oceanic waters over much longer periods (~12 to 16 mo).

2023, The Paleontological Society Special Publications

Stable carbon and nitrogen isotopes in fossil ostrich eggshell (OES) proteins have the potential to provide paleodietary information on ostriches through the Late Pleistocene in arid and semiarid regions of the Old World. Carbon isotopes may be used as a monitor for floral composition (C3 vs. C4 plant abundance), for example. The stable isotope composition of the organic matter in modern OES and Middle Holocene fossil OES samples from Bir Tarfawi (an archaeological site in southern Egypt) are presented, as well as the nature of modern proteins in OES and the degree to which they are preserved in the fossil samples.The organic fraction was extracted from OES samples and subsequently desalted by (1) decalcification in 0.5 N EDTA, followed by dialysis against water in >6-8,000 molecular weight cut off (MWCO) tubing, or (2) hydrolysis in 6N HCl for 20 minutes at 153°, followed by the addition of concentrated HF to facilitate the precipitation of CaF2. There is good agreement between ...

2023, Environmental Research

Mercury pollution is a global environmental problem that threatens ecosystems, and negatively impacts human health and well-being. Mercury accumulation in fish within freshwater lakes is a complex process that appears to be driven by factors such as individual fish biology and water chemistry at the lake-scale, whereas, climate, and land-use/land-cover conditions within lake catchments can be influential at relatively larger scales. Nevertheless, unravelling the intricate network of pathways that govern how lake-scale and large-scale factors interact to affect mercury levels in fish remains an important scientific challenge. Using structural equation models (SEMs) and multiple long-term databases we identified direct and indirect effects of lake-scale and larger-scale factors on mercury levels in Walleye and Northern Pike-two species that are valued in inland fisheries. At the lake-level, the most parsimonious path models contained direct effects of fish weight, DOC, and pH, as well as an indirect effect of DOC on fish mercury levels via fish weight. Interestingly, lakeshed-, climate-, and full-path models that combine the effects of both lakeshed and climate revealed indirect effects of surrounding landscape conditions and latitude via DOC, pH, and fish weight but no direct effects on fish mercury levels. These results are generally consistent across species and lakes, except for some differences between stratified and non-stratified lakes. Our findings imply that understanding climate and land-use driven alterations of water chemistry and fish biology will be critical to predicting and mitigating fish mercury bioaccumulation in the future.

2023, Environmental Science & Technology

Unlike large dams which favor methylation of Hg in flooded soils over long periods, run-of-river dams are designed to flood a limited area of soils and are therefore not expected to significantly affect mercury (Hg) cycling or carbon processing. We studied the Hg and carbon cycles within food webs from several sectors along the Saint-Maurice River, Quebec, Canada, that differ in how they are influenced by two run-of-river dams and other watershed disturbances. We observed peak Hg concentrations in fish five-year post-impoundment, but these levels were reduced three years after this peak. Methylmercury concentrations in low trophic level fish and invertebrates were related to their carbon source (δ 13 C) rather than their trophic positions (δ 15 N). Biomagnification, measured by trophic magnification slopes, was driven mainly by methylmercury concentrations in low trophic level organisms and environmental factors related to organic matter degradation and Hg methylation. River sectors, δ 13 C, and δ 15 N predicted up to 80% of the variability in food web methylmercury concentrations. The installation of run-of-river dams and the related pondages, in association with other watershed disturbances, altered carbon processing, promoted Hg methylation and its accumulation at the base of the food web, and led to a temporary increase in Hg levels in fish.

2023, Progress in Oceanography

The structure and variability of pelagic food webs along the north and northwestern shelf of the Iberian Peninsula were analysed using natural abundance of nitrogen stable isotopes of plankton and pelagic consumers. Plankton composition was mainly studied in sizefractionated samples, but also the isotopic signatures of three copepod species, as representative of primary consumers, were considered. Several fish species were included as planktivorous consumers, with special attention to sardine (Sardina pilchardus). Finally, top pelagic consumers were represented by the common dolphin (Delphinus delphis). The relationship between trophic position and body size implies large variability in the ratio of predator to prey sizes, likely because widespread omnivory and plankton consumption by relatively large predators. Planktivorous species share a common trophic position, suggesting potential competition for food, and low nitrogen isotope enrichment between prey and consumers suggest nutrient limitation and recycling at the base of the food web. Both experimental and field evidences indicate that the muscle of sardine integrates fish diet over seasonal periods and reflects the composition of plankton from large shelf areas. The low mobility of sardines during periods of low population size is consistent with differential isotopic signatures found in shelf zones characterised by upwelling nutrient inputs.

2023, Arctic, Antarctic, and Alpine Research

Northern lakes provide many ecosystem services, including the provision of traditional foods and clean water. These systems are vulnerable to climate-driven changes in hydrology and contaminant accumulation, but the direction and magnitude of projected changes are poorly constrained. One contaminant of concern is mercury; currently, we cannot accurately predict how mercury accumulation in lakes will respond to climate-induced changes, especially in lakes with glacial inflows and complex hydrology. Sediment cores collected from two regions of a glacially fed lake (Lhù'ààn Mân'; Kluane Lake, Yukon, Canada) were analyzed to investigate controls on sediment mercury accumulation in the context of previously described hydrological changes. Differences in catchment contributions drove differences in sediment mercury accumulation between lake regions during the Duke River hydrological period (ca. 750-1650). During the more recent Slims River hydrological period (ca. 1650-2015), mercury accumulation did not differ between regions, and mercury was delivered to the lake primarily via catchment organic matter and carbonate-rich sediments from the largest, glacially derived inflow (Slims River). Recent climate-induced geomorphic change caused loss of the main lake inflow (Slims River) in 2016, making Kluane Lake an ideal system for future investigations of how loss of glacial inflow will affect mercury accumulation in northern lakes.

2023, Journal of Earth Science & Climatic Change

D ecomposition of soil organic matter (SOM) plays an important role in the global carbon cycle because the CO 2 emitted from soil respiration is an important source of atmospheric CO 2. Carbon isotopic fractionation occurs during SOM decomposition, which leads to 12C to enrich in the released CO 2 while 13C to enrich in the residual SOM. Understanding the isotope fractionation has been demonstrated to be helpful for studying the global carbon cycle. Soil and litter samples were collected from soil profiles at 27 different sites located along a vertical transect from 1200 to 4500 m above sea level (a.s.l.) in the southeastern side of the Tibetan Plateau. Their carbon isotope ratios, C and N concentrations were measured. In addition, fiber and lignin in litter samples were also analyzed. Carbon isotope fractionation factor (α) during SOM decomposition was estimated indirectly as the slope of the relationship between carbon isotope ratios of SOM and soil C concentrations. This study shows that litter quality and soil water play a significant role in isotope fractionation during SOM decomposition, and the carbon isotope fractionation factor, α, increases with litter quality and soil water content. However, we found that temperature had no significant impact on the α variance.

2023, Hydrobiologia

Thermal stratification of reservoirs can lead to anaerobic conditions that facilitate the microbial conversion of mercury (Hg) to neurotoxic and bioaccumulative methylmercury (MeHg). But MeHg production is just the first step in a complex set of processes that affect MeHg in fish. Of particular relevance is uptake into suspended particulate matter (SPM) and zooplankton at the base of the pelagic food web. We assessed plankton dynamics and Hg uptake into the pelagic food web of four Hg-impaired California water reservoirs. Combining water chemistry, plankton taxonomy, and stable carbon (C) and nitrogen (N) isotope values of SPM and zooplankton samples, we investigated differences among the reservoirs that may contribute to differing patterns in MeHg bioaccumulation. Methylmercury accumulated in SPM during the spring and summer seasons. Percent MeHg (MeHg/Hg*100%) in SPM was negatively associated with δ15N values, suggesting that “fresh” algal biomass could support the production and ...

2023, Marine Ecology Progress Series

The foraging ecology of small seabirds remains poorly understood because of the difficulty of studying them at sea. Here, the extent to which 3 sympatric seabirds (blue petrel, thinbilled prion and common diving petrel) alter their foraging ecology across the annual cycle was investigated using stable isotopes. δ 13 C and δ 15 N values were used as proxies of the birds' foraging habitat and diet, respectively, and were measured in 3 tissues (plasma, blood cells and feathers) that record trophic information at different time scales. Long-term temporal changes were investigated by measuring feather isotopic values from museum specimens. The study was conducted at the subantarctic Kerguelen Islands and emphasizes 4 main features. (1) The 3 species highlight a strong connection between subantarctic and Antarctic pelagic ecosystems, because they all foraged in Antarctic waters at some stages of the annual cycle. (2) Foraging niches are stagedependent, with petrels shifting their feeding grounds during reproduction either from oceanic to productive coastal waters (common diving petrel) or from subantarctic to high-Antarctic waters where they fed primarily on crustaceans (blue petrel and thin-billed prion). (3) The common diving petrel segregated from the surface-feeders blue petrel and thin-billed prion by a coastal habitat and lower trophic level prey, while the blue petrel segregated from the thin-billed prion by foraging further south and including more fish in its diet. (4) Feather δ 13 C and δ 15 N values from historical and recent specimens of thin-billed prion depicted a pronounced temporal shift to higher latitudes in its main moulting ground, where it feeds on higher trophic level prey. The study contributes to growing evidence that seabirds exhibit considerable foraging plasticity and sheds new light on their flexibility at different time scales (from intra-seasonal to decadal).

2023

Abstract: The difference in arsenic concentration and speciation between benthic (Pteromylaeus bovinus, Myliobatis aquila) and pelagic rays (Pteroplatytrygon violacea) from the northern Adriatic Sea (Gulf of Trieste) in relation to their size (age) was investigated. High arsenic concentrations were found in both groups with tendency of more efficient arsenic accumulation in benthic species, particularly in muscle (32.4 to 362 µg·g−1 of total arsenic). This was attributed to species differences in arsenic access, uptake and retention. In liver most arsenic was present in a form of arsenobetaine, dimethylarsinic acid and arsenoipids, whereas in muscle mainly arsenobetaine was found. The good correlations between total arsenic/arsenobetaine and size reflect the importance of accumulation of arsenobetaine with age. Arsenobetaine is an analogue of glycine betaine, a known osmoregulator in marine animals and both are very abundant in mussels, representing an important source of food for b...

2023, Limnology and Oceanography

Two coral reef sponges were examined in situ off Puerto Rico for fluxes of dissolved inorganic nitrogen. Chondrilla nucula, a ubiquitous Caribbean sponge with cyanobacterial symbionts, releases large amounts of nitrate [600 nmol N g I (dry wt) h-l; 4,000 Mmol N me2 h-l]. Since C. nucula covers a mean of 12% of the substratum, it potentially contributes between 50 and 120% of the nitrogen required to sustain reef productivity. Anthosigrnella varians, a common sponge with zooxanthellae symbionts releases lesser amounts of nitrate [ 19 nmol N g-' (dry wt) h-l; 20 pmol N m-2 h-I]. Alth ough A. varians may cover between 1.2 and 11% of the reef substratum, the potential contribution is < 1% of the nitrogen requiredi For reef productivity. These release rates for C. nucula are comparable to those reported for nitrogen fixation in reef environments and in excess of rates reported for nitrate production by other reef substrata. Large populations of nonphotosynthetic symbiotic bacteria are considered to nitrify amino nitrogen to nitrate and the differences are attributed to the size of bacterial populations and the nature of photosynthetic symbionts.

2023, Analytica Chimica Acta

A diffusion method for extracting ammonium from marine, estuarine and fresh waters for 15 N/ 14 N isotopic ratio determinations at enriched level was developed and validated. The method is based on the conversion of NH 4 + to NH 3 gas under alkaline conditions, diffusion of NH 3 out of the solution to the headspace, NH 3 trapping on an acidified GF/D glass fiber filter, and subsequent 15 N/ 14 N isotope ratio determination with mass spectrometry. The diffusion period necessary to extract sufficient N in order to accurately measure the atom% 15 N was reduced to less than 15 h by bubbling the sample with a carrier gas (Air) at room temperature. The technique uses 250 mL sample volume and enables accurate atom% 15 N measurements in NH 4 + pools as small as 1.25 M. A standard operating procedure for ammonium extraction is given involving method performance criteria, such as accuracy, precision, detection limit, quantification limit and robustness. The efficiency of the NH 4 + extraction ranged from 40 to 100%. The quantification limit of the method was estimated at around 0.26 mol% N, for an initial 15 N abundance of ∼1%. The within-laboratory reproducibility amounted to 0.03 atom% 15 N. It was shown that the recovery rate obtained after extraction of the certified reference material (CRM: IAEA-311) solution falls within the 95% confidence interval of the certified values. By applying the developed method to fortified natural water samples of different conductivities, the atom% 15 N determinations were precise and accurate for α = 1-5%.

2023, Aquatic Botany

Measurements of chlordecone, an organochlorine insecticide with high persistence in natural environments, have been carried out on several species and genus of macroalgae in Guadeloupe and Martinique. These data were statistically compared to determine the ability of the genus Dictyota to accumulate chlordecone, compared to other collected macroalgae. The comparisons were conducted between phylogenetic groups (Rhodophyta, Phaeophyta and Chlorophyta), and between sites (Guadeloupe vs Martinique). Concentrations of chlordecone measured in Dictyota spp. samples were significantly higher than the other groups regardless to the site. Phaeophytes are generally characterized by a higher capacity for biosorption of contaminants. In this study, however, only the Dictyota spp. samples followed this pattern. Therefore, this genus is of interest in cases of phycoremediation of the chlordecone.

2023, Hydrobiologia

2023, Tellus B

In an effort to investigate the influence of different atmospheric flow patterns on the composition of precipitation on the island of Bermuda, a cluster analysis of atmospheric trajectories was performed to identify periods of similar transport. The cluster analysis technique represents a relatively objective alternative to the more subjective method of classifying trajectories according to compass sector. Data were stratified into two broad seasons, defined as a warm (April-September) and a cool (October-March) season. Relative to the cool season, significantly higher per event concentrations of non-seasalt sulfate and nitrate occurred in the warm season on Bermuda. There was no significant difference in the per event precipitation amount between seasons; however, there was significantly higher per event deposition of warm season non-seasalt sulfate, and nitrate. Significant differences in precipitation composition were also identified between flow patterns. It was found that the source regions which contributed the largest fraction of hydrogen ion deposition and nonseasalt sulfate deposition on Bermuda differed by season. During the cool months, 40% of the deposition occurred with transport from the west, off the East Coast of the US, implicating anthropogenic sources. In the warm season, an equally large fraction of deposition was associated with flow from the Bahamas region, suggesting an oceanic source of biogenic sulfur as the precursor. * Average per event equivalents ratios. Cool season Warm season Total Dnss-SOT 2.35 @eq/m2) 3.61 &q/m2) 741.5 @eq/m2) DNO, 0.79 @eq/mZ) 1.01 @eq/m2) 226.7 @eq/mZ) DH+ 2.30 @eq/m2) 3.22 @eq/m2) 691.0 @eq/m2) DNHZ 0.48 @eq/m2) 0.64 @eq/m2) 140.7 @eq/m2) Tellus 408 (1988), 5