The Impact of Trophic Status and Climate Change on the Benthic Community in Lake Sevan, Armenia

Authors : Karen Jenderedjian, Susanna Hakobyan, M. Scott Demyan

Pages : 43-62

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Publication Date : 2019-12-27

Article Type : Other

Abstract :Artificial water level drop and eutrophication radically changed the ecosystem of Lake Sevan. During 1928-2018 the Values of Primary Production of the Lake (VPPL = phytoplankton production + phytobenthos production) and varied energy equivalent of biomass (B Z ) and gross production (P Z ) of zoobenthos varied by a factor of 10 or more. Strong positive dependencies of both B Z and P Z on VPPL were found. Similar dependencies were also revealed separately for Chironomidae, Oligochaeta and detritivores. Regression equations of dependencies were then used to estimate the development of zoobenthos under different trophic conditions: oligotrophic, mesotrophic and eutrophic. Significant climate change was observed over the past 80 years. From 1935–2012, the annual mean temperature in Armenia increased by 1.03°C. The climate change projections for Lake Sevan are an increase of mean annual water temperature of 0.5 °C by 2030 , 2°C by 2070 and 4°C by 2100 against the baseline of 9.1°C. Observations showed that in Lake Sevan an order of magnitude increase of VPP L result s in an increase of the gross production of macro zoobenthos by factor of 7 . Meanwhile, a 4°C temperature increase is estimated to increase the rate of zoobenthos production (P Z /B Z ) only by a factor of 2. Therefore, the most effective measure required for the mitigation of climate change effects on the Lake Sevan ecosystem is keeping the trophic status of the lake as low as possible, and should include: - runoff prevention of of organic materials from agricultural, industrial and domestic origins into Lake Sevan; - prohibition of any activity that involves the use of organic phosphorus and organic nitrogen directly in the lake.
Keywords : trophic status, zoobenthos, climate change, temperature increase