Eutrophication of ancient Lake Ohrid: Global warming amplifies detrimental effects of increased nutrient inputs

Abstract

Lake Ohrid in southeastern Europe is one of the few ancient, long-lived lakes of the world, and contains more than 200 endemic species. On the basis of integrated monitoring of internal and external nutrient fluxes, a progressing eutrophication was detected (,3.5-fold increase in phosphorus (P) concentration in the lake over the past century). The lake is fortunately still oligotrophic, with high concentrations of dissolved oxygen (DO) in the deep water that are requisite for the unique endemic bottom fauna. Hypolimnetic DO is not only very sensitive to changes in anthropogenic P load-via mineralization of organic material-but also to global warming via decrease of vertical mixing and less frequent complete deep convection. Moreover, these two human effects amplify each other. To keep DO from falling below currently observed minimal levels-given the predicted atmospheric warming of 0.04uC yr 21 -the P load must be decreased by 50% in coming decades. However, even with such a reduction in P load, anoxia is still expected toward the end of the century if the rate of warming follows predictions.

Spatial patterns of diatom diversity and community structure in ancient Lake Ohrid

“…Several studies showed that Lake Ohrid is under increased human pressure which poses a threat to its unique biota (Matzinger et al, 2007;Albrecht & Wilke, 2008), and our results further corroborate these findings. The significant contribution of total phosphorus and nitrogen ammonia concentrations in explaining the diatom distribution in the northern lake area should raise serious concerns about the effects of the ongoing eutrophication and pollution over the lake diversity.…”

“…The influence of TP and NH 3 -N over the diatom communities in the area of Kalishta, Struga and Sateska reflects ongoing eutrophication and wastewater pollution in the northern part of the lake. Lake Ohrid is a typical oligotrophic lake, however, increasing pollution and nutrient loads from the surrounding settlements and the river tributaries, Sateska and Koselska, were already recognized as the major source leading to eutrophication of the northern lake area (Matzinger et al, 2007;VeljanoskaSarafiloska et al, 2011;Trajanovska et al, 2014). Start of the human impact and eutrophication at * 1955 AD was inffered from the analysis of several shallow gravity cores recovered from the Kalishta spring area where changes in coastal sedimentation rate and increase in organic matter content was determined (Matter et al, 2010).…”

“…1 Location of Lake Ohrid at the Balkan Peninsula (right corner). Topographic and bathymetric map of Lake Ohrid showing the sampling locations at each transect: Kalishta, Struga, Sateska, Ohrid, Peshtani and St. Naum as result of the global warming and local anthropogenic impact (Matzinger et al, 2006(Matzinger et al, , 2007.…”

“…Moreover, global change during the 21st century and beyond is highlighted as a potential cause for increased extinction risks for a broad variety of organisms in many ecosystems, including ancient lakes (IPCC, 2014). Several studies already provide evidence for the negative effects of global change and anthropogenic pressure over the biodiversity in ancient lakes Tanganyika (Cocquyt, 2000), Ohrid (Matzinger et al, 2007) and Baikal (Moore et al, 2009). Lake Ohrid, located at the Balkan Peninsula on the border between Macedonia and Albania, is the oldest lake in Europe and well recognized for its unique biodiversity.…”

Zooplankton in Ancient and Oligotrophic Lake Ohrid (Europe) in Association with Environmental Variables

“…It has a surface area of 358.2 km 2 , a maximum depth of 288.7 m, a water volume of 58.6 km 3 and a shoreline length of 87.53 km. Detailed morphometric and limnological attributes of the lake were recorded in the study of Matzinger et al (2006Matzinger et al ( , 2007. A main characteristic of Lake Ohrid's ecosystem is the scarcity of nutrients and consequently a low level of primary production.…”