Assessing the Ecological Water Level: The Case of Four Mediterranean Lakes (original) (raw)
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Water Resources Management, 2010
Lake Pamvotis, NW Greece is a shallow Mediterranean eutrophic lake that has changed drastically over the past 50 years. Strong effects, resulted mainly from anthropogenic causes, in the hydrological regime are shown for this area using long term hydrological data and a GIS system for extracting land cover/use changes. A set of aerial imagery acquired in 1945 through 2002 were used to monitor and assess the spatial and temporal changes in land cover/use, focused mainly on the lake’s surface area and its surrounding ecosystem (Natura 2000 area). The significance of the changes in land cover/use distribution within Pamvotis wetland is further discussed depicting the role of the anthropogenic influence on the fragile ecosystem that resulted in the shrinkage of lake’s habitats extent. The purpose of this analysis was to examine the long-term changes on macrophyte community composition, species occurrence and relative abundance with water quality and water level changes over the past century, using historical data, aerial photos and GIS techniques. The results showed that for the last 25 years annual water level fluctuation ranged from 70 to 159 cm. Water level starts decreasing in mid June and increasing again gradually from November until March–April. Intra annual water level fluctuation seems to be affected by land use for agricultural purpose through intensive irrigation and the summer drought as well. A dramatic decline of the submerged vegetation is apparent mainly attributed to anthropogenic pressures. Regarding the land cover/use changes, the most notable and significant alterations are concerning the urban development around the lake, the disappearance of wet meadows and the extension of reed beds. Finally it seems that water budget data as well as the response of the key eutrophication parameters are affected from both hydrological alterations and point/non-point pollution sources.
Freshwater …, 2012
1. Water-level fluctuations are typical of lakes located in the semi-arid Mediterranean region, which is characterised by warm rainy winters and hot dry summers. Ongoing climate change may exacerbate fluctuations and lead to more severe episodes of drought, so information on the effects of water level on the functioning of lake ecosystems in such regions is crucial. 2. In eutrophic Lake Eymir, Turkey, we conducted a 4-month (summer) field experiment using cylindrical 0.8-m-(low-water-level) and 1.6-m-deep (high-water-level) mesocosms (kept open to the sediment and atmosphere). Fish (tench, Tinca tinca, and bleak, Alburnus escherichii) were added to half of the mesocosms, while the rest were kept fishless. Ten shoots of Potamogeton pectinatus were transplanted to each mesocosm. 3. Sampling for physicochemical variables, chlorophyll a (chl-a), zooplankton and per cent plant volume inhabited (PVI%) by macrophytes was conducted weekly during the first 5 weeks, and subsequently biweekly. Macrophytes were harvested on the last sampling date. During the course of the experiment, the water level decreased by 0.41 ± 0.06 m. 4. Throughout the experiment, fish affected zooplankton abundance ()), nutrient concentrations (+), chl-a (+) and water clarity ()) most strongly in the low-water-level mesocosms and the zooplankton community shifted towards dominance of small-sized forms. The fishless mesocosms had a higher zooplankton ⁄ phytoplankton ratio, suggesting higher grazing. 5. Greatest macrophyte growth was observed in the low-water-level fishless mesocosms. However, despite high nutrient concentrations and low water clarity, macrophytes were also abundant in the fish mesocosms and particularly increased following a water-level decrease from midsummer onwards. Macrophyte growth was poor in the high-water-level mesocosms, even in the fishless ones with high water clarity. This was ascribed to extensive periphyton development reducing light availability for the macrophytes. 6. Our results indicate that a reduction in water level during summer may help maintain the growth of macrophytes in Mediterranean eutrophic shallow lakes, despite a strong negative effect of fish predation on water clarity. It is therefore probable that an expected negative effect of global climate change on water clarity because of eutrophication and enhanced top-down control of fish may be, at least partly, counteracted by reduced water level, provided that physical disturbance is not severe.
State of the art in the functioning of shallow Mediterranean lakes: workshop conclusions
Hydrobiologia, 2007
Studies on shallow lakes from the north temperate zone show that they alternate between clear and turbid water states in response to control factors. However, the ecology of semiarid to arid shallow Mediterranean lakes is less explored. Hydrological effects (e.g. water level fluctuations, water residence time) on major ions and nutrient dynamics and processes, and ecology of submerged macrophytes appear to have a crucial role for food webs in shallow Mediterranean lakes. Nutrient control may be of greater priority in eutrophicated warm shallow lakes than in similar lakes at higher latitudes. This will be relevant for the implementation of the European Water Framework Directive, and conservation and management of these ecosystems. Strong trophic cascading effects of fish resulting from dominance of omnivorous and benthivorous fish species, whose diversity is usually high, together with frequent spawning and absence of efficient piscivores, seem to be the reason for the lack of large-bodied grazers that could control phytoplankton. However, such effects may vary within the region depending on fish distribution and community. These factors need elaboration in order to allow shallow lake ecologists and managers to develop better restoration strategies for eutrophicated shallow Mediterranean lakes. Consequently, modifications for the implementation of the European Water Framework Directive for determining ecological status in shallow Mediterranean lakes appear to be necessary. Furthermore, the implications of climate warming may be even more challenging than in high latitude lakes since shallow lakes in the Mediterranean region are among the most sensitive to extreme climate changes. There is an urgent need for data on the ecology of shallow lakes in the region.
Fish communities of five shallow Spanish Mediterranean lakes were studied and stomach content analysed to determine the foraging pattern of each species and the influence on the lake food web. Lakes ranged from 0.5 to 2300 ha with less than 3 m mean depth, while the trophic state varied from mesotrophy to hypertrophy. We fished during summer 2000 and 2001, and for one lake also during spring 2002. Almost no piscivores species were recorded and in general omnivorous species dominated independently of lake trophic state. Fish dietary differences were found among lakes and prey availabilities. Maximum fish biomass and diversity were found in the Albufera lake, where mugilids (Mugil cephalus and Liza aurata) and Cyprinus carpio dominated. The other lakes had young populations of Atherina boyeri and Liza ramada, endemic species (Barbus guiraonis, Aphanius iberus) or introduced species (Lepomis gibbosus, Micropterus salmoides, Gambusia holbrooki). Fish were mainly detritivorous and shifted to zooplanktivorous depending on abundance of large zooplankton. Fish demographic changes and facultative preys influenced food webs of the lakes by both direct predation and indirect nutrient recycling from the sediment. Omnivorous structure of fish communities in these Mediterranean warmer lakes resembles that described in some food webs of tropical lakes. Bottom-up mechanisms seem to be more relevant in warmer lakes and submerged plants were special key factors to maintain clear waters in the study lakes.
Effects of a dry period on the limnological characteristics of a Mediterranean high mountain lake
Limnetica, 2011
Effects of a dry period on the limnological characteristics of a Mediterranean high mountain lake This investigation assesses the effects of a drought period on the physical and chemical properties and on the plankton community of a Mediterranean high mountain lake (Río Seco, Sierra Nevada, Spain). The study was performed over two consecutive years, 2005 and 2006. Both years were characterised by strong differences associated with rainfall patterns. The first year was extremely dry and had rainfall values far below the mean annual average of 813 mm that has been observed over the previous twenty years. The results of the study confirm that the dissolved inorganic nitrogen:soluble reactive phosphorus ratio (DIN:SRP) showed notable differences throughout both study years, with a greater nitrogen limitation during 2005. The ratio of total biovolume of autotrophic to heterotrophic organisms (A:H) also presented interannual differences. The A:H ratio was generally below 1 during 2005, whereas it was above this value in 2006. Therefore, the main plankton component was mesozooplankton in 2005 and phytoplankton in 2006. Ciliates and bacteria showed a mean biovolume significantly higher in 2005, whereas the biovolume of heterotrophic nanoflagellates was similar during both years. These results indicate a prevalent "top-down" control by zooplankton during the dry year and, on the contrary, a predominant "bottom-up" control during the wetter year as a consequence of the nutrient limitation of primary production.
In order to solve problems related to water resources protection, each country has to develop methods for the assessment of the ecological status of water bodies. Such evaluation schemes have to comply with the requirements of the EU WATER FRAMEWORK DIRECTIVE (2000) in all member states. This study presents a method for macrophyte-based assessment of the ecological status of lakes, developed and implemented for the purpose of environmental protection in Poland, and the results of the conducted evaluation. In Poland - field investigations were carried out based on data on the entire lake vegetation (hydrophytes + helophytes). Vegetation samples were also collected along transects, as recommended in CEN 230 (2003). Assessment was based on the values of the Ecological State Macrophyte Index (ESMI) - according to the macrophytoindication method developed in Poland (MPhI - Rejewski 1981). A total of 13 abiotic types of lakes were determined in view of the environmental (including climati...
Trophic State Evaluation of a Large Mediterranean Lake Utilizing Abiotic and Biotic Elements
The trophic state of a freshwater ecosystem reflects its environmental quality. This is why several trophic indicators have been developed for such water bodies based on chemical, physical and biological parameters. Apart from that, there are several biotic elements which can be used in accessing the environmental condition of a freshwater ecosystem. Zooplankton organisms are important elements of the structure and function of lakes and are considered useful indicators of alterations in their trophic dynamics and ecological state related to changes in nutrient loading and climate. In accordance to the above, the present study is an attempt to assess the trophic condition of the largest lake in Greece (Lake Trichonis) through the investigation of the physicochemical elements, along with the biotic indications provided by a three-year study of the lake's zooplankton. The present results, compared with previous studies conducted between 15 and 25 years before, showed that there was an increase in the maximum values of the concentrations of chlorophyll-α and nutrients, while there was a decrease in water transparency. The implementation of Carslon's trophic state index (TSI) revealed that Lake Trichonis still remains an oligo-to mesotrophic ecosystem as it was in the past. However, although the zooplankton investigation showed several features that are common in oligotrophic lakes, there are certain eutrophic characteristics of the zooplankton community (e.g. abundance variation pattern, indicator species, seasonal succession of cladocerans) pointing out a different state of the ecosystem in comparison to the past. In conclusion, the use of a biotic element like zooplankton revealed that Lake Trichonis is experiencing a transitional condition towards the eutrophic state and points out the necessity for constant inspection and monitoring of this ecosystem.
A new multimetric macroinvertebrate index for the ecological assessment of Mediterranean lakes
Ecological Indicators, 2018
This study outlines the development and application of a new multimetric index (Greek Lake Benthic macroinvertebrate Index-GLBiI) for the assessment of the ecological quality of Greek lakes, based on the ecological quality ratio (EQR), under the requirements of the Water Framework Directive. Profundal and sublittoral benthic macroinvertebrates from 18 lakes were biannually sampled across Greece. Additionally, 21 environmental parameters and 5 human pressures were assessed for each lake. The hindcasting approach was used for the establishment of reference conditions after minimizing human pressures. A pool of 84 candidate metrics, representing diversity/richness, sensitivity, functional traits, and taxonomical composition, were tested for the development of the multimetric index. Spearman's rank correlation extracted seven environmental parameters (lake area, mean depth, altitude, alkalinity, dissolved oxygen at bottom and conductivity at bottom) and three human pressures (total phosphorus, population density and non-natural land cover) that were further stepwise linear regressed against each biological metric for pressure-response relationships. Finally, three metrics, the number of taxa and the Simpson's diversity index in the profundal and sublittoral zones, and the relative contribution of Chironomidae (%) family in the profundal zone, were selected as the most appropriate, responding to eutrophication (expressed as total phosphorus and non-natural land cover). The multimetric index GLBiI was expressed as the mean of the EQRs of its metrics following a five class ecological status system. This assessment method may be used in other Mediterranean lakes with similar characteristics.