Nutrient retention by the littoral vegetation of a large lake: Can Lake Ohrid cope with current and future loading?

Nitrogen and phosphorus budgets were compiled for the littoral (29 km2) and pelagic (329 km2) of ancient, deep, clear, and hard water Lake Ohrid (Albania and North Macedonia), to assess the importance of the littoral in nutrient retention. P originates mainly from domestic point sources (73%), for N this is karst seepage (50%). Total littoral loads are estimated at 1700 kg P and 23,200 kg N km−2 (area of littoral) yr−1; net littoral retention is 31% ± 13% for P and 40% ± 16% for N, largely in the dense charophyte belt. P retention is mainly due to detritus burial, but also due to coprecipitation; N retention is due to both detritus burial and denitrification. A Monte‐Carlo plausibility analysis balanced the budget by increasing nonconnected domestic household inputs (from 20% to 27% of external load), and decreasing pelagic sediment P burial by 27% and littoral denitrification by 25%. Scenario projections for 2100 corresponding to SRES A2 and B1 were linked to an AQUASIM lake ecosystem model. Under B1, the changes were small compared to the present. A2, however, led to a major reduction in precipitation, an increase in evapotranspiration, a reduction in river outflow (to ∼ 20%), a doubling in P‐loading, a drop in lake level of ∼ 1.5 m, and a decline in the extent of the charophyte belt. Areal loading of the littoral would increase accordingly, but water transparency would not decline much. Also, the littoral vegetation will witness a shift in species composition, and an increase in filamentous Cladophora cover.publishedVersio

Charophytes (Charales) of lake Skadar/Shkodra: Ecology and distribution

Charophytes or stoneworts (Charales, Characeae) are submerged green macroscopic algae of great importance for the environmental and economic sustainability of the aquatic ecosystem of Lake Skadar/Shkodra. In the course of many years of research of these algae in the Montenegrin and the Albanian part of Lake Skadar/Shkodra, 30 taxa of charophytes have been registered in the rank of species, forms and varieties. These taxa belong to the four genera of the Characeae family existing in the lake – namely, Chara, Nitella, Tolypella and Nitellopsis. The largest number of taxa belongs to the genus Chara, namely, 12 species, 3 forms and 2 varieties, 10 species belong to the genus Nitella, 2 species belong to the genus Tolypella and, finally, only 1 species belongs to the genus Nitellopsis. The ecological and phytocenological characteristics of each taxon, as well as the hydrological and geomorphological characteristics of their finding sites, are presented in order to emphasize the fact that Lake Skadar/Shkodra is one of the most significant charophyte diversity centres in the Balkan Peninsula. All the data presented in this study are based on our own field investigations, as well as herbarium and literature surveys