title: Impact of alternating wet and dry periods on long-term seasonal phosphorus and nitrogen budgets of two shallow Mediterranean lakes.
abstract: The water balance, with large seasonal and annual water level fluctuations, has a critical influence on the nitrogen and phosphorus dynamics of shallow lakes in the semi-arid climate zone. We constructed seasonal water and nutrient budgets for two connected shallow lakes, Lakes Mogan and Eymir, located in Central Anatolia, Turkey. The study period covered 20years with alternations between dry and wet years as well as restoration efforts including sewage effluent diversion and biomanipulations in Lake Eymir. Both lakes experienced a 1-2m water level drop during a drought period and a subsequent increase during the wet period, with seasonal water level fluctuations of 0.60 to 0.70m. During wet years with high water levels, small seasonal differences were observed with a nutrient peak in spring caused by external loading and nutrient loss via retention during summer. During years with low water levels, nutrient concentrations increased due to internal and external loading, exacerbated by evaporative water loss. In Lake Eymir, a shift to eutrophic conditions with turbid water occurred under low water level conditions and consequent internal loading of P from the sediment, causing high nutrient concentrations in summer. Our results indicate a threat of lakes drying out in the semi-arid climate zone if evaporation increases and precipitation decreases as anticipated from the global climate change predictions. In addition, our results show the influence of the water balance on the eutrophication of shallow lakes in the Mediterranean climate zone and highlight the ultimate consequences for lake management.
authors.affiliation: Middle East Technical University, Limnology Laboratory, Department of Biology, Universiteler Mahallesi, Dumlupinar Bulvarı, No. 1, 06800 Ankara, Turkey. Electronic address: jan.coppens@metu.edu.tr.
authors.forename: Jan
authors.initials: J
authors.lastname: Coppens
authors.affiliation: Çankırı Karatekin Üniversitesi, Department of Forest Engineering, Yeni Mah. Bademlik Cd., Çankırı, Turkey.
authors.forename: Arda
authors.initials: A
authors.lastname: Özen
authors.affiliation: Middle East Technical University, Limnology Laboratory, Department of Biology, Universiteler Mahallesi, Dumlupinar Bulvarı, No. 1, 06800 Ankara, Turkey.
authors.forename: Ü Nihan
authors.initials: ÜN
authors.lastname: Tavşanoğlu
authors.affiliation: Middle East Technical University, Limnology Laboratory, Department of Biology, Universiteler Mahallesi, Dumlupinar Bulvarı, No. 1, 06800 Ankara, Turkey; Department of Biology, Faculty of Science and Art, Bozok University, 66900 Yozgat, Turkey.
authors.forename: Şeyda
authors.initials: Ş
authors.lastname: Erdoğan
authors.affiliation: Middle East Technical University, Limnology Laboratory, Department of Biology, Universiteler Mahallesi, Dumlupinar Bulvarı, No. 1, 06800 Ankara, Turkey.
authors.forename: Eti E
authors.initials: EE
authors.lastname: Levi
authors.affiliation: Middle East Technical University, Department of Statistics, Universiteler Mahallesi, Dumlupinar Bulvarı, No. 1, 06800 Ankara, Turkey.
authors.forename: Ceylan
authors.initials: C
authors.lastname: Yozgatlıgil
authors.affiliation: Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark; Sino-Danish Centre for Education and Research, Chinese Academy of Sciences, Beijing, China.
authors.forename: Erik
authors.initials: E
authors.lastname: Jeppesen
authors.affiliation: Middle East Technical University, Limnology Laboratory, Department of Biology, Universiteler Mahallesi, Dumlupinar Bulvarı, No. 1, 06800 Ankara, Turkey; Kemal Kurdaş¸ Ecological Research and Training Stations, Lake Eymir, Middle East Technical University, Ankara, Turkey. Electronic address: meryem@metu.edu.tr.
authors.forename: Meryem
authors.initials: M
authors.lastname: Beklioğlu
mesh_terms: D002980:Climate; D060106:Lakes / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D058458:Nitrogen Cycle; D010758:Phosphorus / Q000032:analysis*; D012621:Seasons; D014421:Turkey
chemical_list: D010758:Phosphorus; D009584:Nitrogen
keywords: Arid region; Climate change; Eutrophication; Seasonality; Water level fluctuation