From Wet to Dry: Climate-Driven Water Level Oscillations Amplify Nutrient Accumulation and Chlorophyll-a Response in Shallow Lakes

Date

2025-07-22

Author

Filiz, Nur
Yıldız, Dilvin
Yalçın, Gülce
Jeppesen, Erik
Beklioğlu, Meryem

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The functioning of shallow lakes, which are extremely susceptible to variations in precipitation, evaporation, and water inflows and outflows due to their shallow form, depends heavily on hydrology. Water level changes in shallow lakes have large impacts on the physical and biological features of these ecosystems, and water chemistry; nutrient processing and nutrient retention. The Mediterranean region, characterized by warmer and dry conditions, is experiencing increased evaporation and fewer wet days due to the effects of climate change. Here, we investigated the relationships between lake nutrient and chlorophyll-a (Chl-a) concentrations in Eastern Mediterranean Lakes Mogan and Eymir in the semi-arid climate overall and in dry, mid and wet periods of long-term monitoring. We hypothesised that; (i) high alteration in water levels between dry and wet periods will be observed due to semi-arid climate in the region, (ii) external loadings will play an important role on the in-lake nutrient concentrations, (iii) hydraulic retention time (HRT) will be affected on in-lake concentrations because longer the HRT higher the water column-sediment interactions and increase the internal phosphorus loading, and (iv) increasing temperatures will increase the Chl-a concentrations especially in dry periods due to more profound effects of stratification which triggers internal phosphorus loading. We further included PCA plots to determine the relationships between Chl-a and nutrient concentrations, temperature, external loading, HRT, depth, macrophytes and fish. 28-year mass balance analysis of two shallow, semi-arid lakes yielded the following primary outcomes: (1) variability between the dry and wet periods was high showing the risk of drying out of the lakes under the less precipitation and higher evaporation future of semi-arid Mediterranean lakes, (2) even with modest external loading, the nutrient concentrations during dry periods increased with nutrient accumulation from evaporative water loss especially in Lake Mogan, (3) Chl-a concentrations were affected mainly by temperatures in Lake Eymir where cyanobacteria blooms occur during summers most likely causing by more frequent thermal stratification and increased internal loading. These results enhance the understanding of how variations in hydraulic loading, water level, and hydraulic residence time influence nutrient and chlorophyll-a concentrations in shallow, semiarid lakes under both dry and wet conditions.

URI

https://www.sefs14.com/abstract-book
https://hdl.handle.net/11511/115802

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Department of Biology, Conference / Seminar