Comparing ecological structure of Turkish shallow lakes between the seasons, and wet & dry years

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2015
Çağan, Ali Serhan
Due to global climate change, lakes in Mediterranean climate face the problem of reduced precipitation and enhanced evaporation along with increased water abstraction for irrigation that are largely causing changes in water level, salinity and nutrient dynamics. In this study 22 Turkish shallow lakes were investigated in the Mediterranean climate zone. All lakes were sampled with a well-established snapshot sampling protocol. There are 19 lakes, which were sampled once during both spring and summer seasons within the same year and 9 lakes that were sampled once during both drought and wet years. Also, data of 1997 - 2012 period from Lake Eymir and Mogan were used to investigate the effects of drought in a longer term period. Environmental data were tested for normality and variables that do not follow normal distribution were transformed. Principal Component Analysis (PCA) was applied to the environmental data, including surface water temperature, salinity, pH, mean air temperature, Secchi depth, alkalinity, total phosphorus, total nitrogen, net evaporation, net precipitation and chlorophyll a (spring – summer) and without total nitrogen (Lake Eymir - Mogan) and additionally number of fish and total zooplankton biomass (for wet – dry years). Lakes sampled during spring seasons were associated with high Secchi and maximum depth, dissolved oxygen and precipitation. So, in spring seasons lakes can be characterized as in a clear water state, whereas lakes sampled in summer seasons were identified with high chlorophyll a, total nitrogen and total phosphorous concentration and salinity. Thus, lakes sampled during summer seasons could be considered as eutrophic. Furthermore, lakes sampled in drought years show increased salinity and nutrient concentrations. According to Procrustes analyses of lakes sampled in drought and wet years, the southern lakes displayed small environmental variable differences except Lake Gölcük Ödemiş, and Lake Saka, Poyrazlar and Hamam which were all northern lakes in our dataset of lakes sampled in wet and dry years. Also, Lake Gölcük Ödemiş displayed a low degree of similarity. In northern lakes, Secchi depth and precipitation decrease higher than in southern lakes and total phosphorus and number per unit effort of fish increase due to the effect of eutrophication. On the other hand, in Lake Eymir and Mogan, the internal loading of nutrients and salinity change were explained by high evaporation and increase of water residence time in drought years. Since climate change enhances the drought events and frequency in the Mediterranean climate zone, our results suggest that shallow lakes will turn to eutrophic condition in the future like in drought periods.

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Citation Formats
A. S. Çağan, “Comparing ecological structure of Turkish shallow lakes between the seasons, and wet & dry years,” M.S. - Master of Science, Middle East Technical University, 2015.