Abstract
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.
Highlights
Eutrophication of freshwater ecosystems such as natural lakes and reservoirs is a major environmental problem
The present investigation showed that Lake Trichonis seems to hold the main physicochemical features observed in the previous studies of Overbeck et al [9], Koussouris et al [10] and Tafas et al [11], conducted between 15 to 25 years before the present investigation
In comparison to the above studies, there was an increase in the maximum values of most of the physicochemical parameters recorded in the present study, their patterns of variation in the water column were similar
Summary
Eutrophication of freshwater ecosystems such as natural lakes and reservoirs is a major environmental problem. Eutrophication is the result of nutrient overenrichment of the water originated from natural processes such as decomposition of organic matter and sediment nutrient release, or to land-based activities and external nutrient loading (e.g. agricultural activities, sewage and industrial discharges, atmospheric releases from fossil fuel combustion, etc.). Dered as the major provider of nutrients in lakes, especially in the Mediterranean region, where agricultural sector comprises an important economic factor [1]. Indexes and models have been developed to assess eutrophication and water quality in aquatic ecosystems based on chemical, physical and biological parameters. Carlson’s trophic state index (TSI) is the most widely used in freshwater bodies [2]. TSI values less than 40 correspond to oligotrophic conditions, while between 40 and 50 for mesotrophic and between 50 and 70 for eutrophic. Index values greater than 70 are associated with hypertrophic conditions
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