AQUATIC VEGETATION OF SHALLOW HYPERTROPHIC LAKE IN DIFFERENT HYDROLOGICAL CONDITIONS

Comparison of the distribution of aquatic vegetation in shallow hypertrophic Lake Nero (Yaroslavl oblast, Russia) in different hydrological conditions – during low water phase in 2002–2004 and water level rise in 2017 is presented. The total area covered by aquatic vegetation increased from 14.8 km2 in 2000–2004 to 15.8 km 2 in 2017. Correspondingly, the lake area covered by macrophytes showed its increase from 27% to 29%. The observed increase in the total plant coverage was mainly driven by helophytes which increased in the coverage area from 8.4 km2 to 11.2 km2. The coverage area of submerged vegetation during this period decreased from 5.4 km2 to 3.6 km2. Potamogeton perfoliatus showed the highest reduction in the coverage area by factor of 2.6 in the central part of the lake. In contrast, the coverage area of Ceratophyllum demersum and Myriophyllum verticillatum did not change mostly in the shallow, southern part of the lake. The analysis of literature and our data revealed that increase in water level due to building a dam on the River Veksa in the 1980s and impact of climatic factors had a negative influence on submerged vegetation. Thus, the high water level is one of the mechanisms stabilising the ecosystem of the Lake Nero in the turbid, phytoplankton-dominated state.

Grazing affects periphytic algal biomass in the periphyton-macrophyte relationship independently of the substrate type and nutrient status

The macrophyte–algae relationship has primary importance in affecting the functioning of shallow lake ecosystems. However, how substratum type, grazing, and nutrient status affect the relationship, is still largely unknown. Here, we studied algal assemblages covering either the submerged macrophyte, Ceratophyllum demersum, or artificial plastic plants with similar morphological complexity to answer these questions. Nutrient status was assessed as eu- and hypertrophic conditions in two separate lakes. In contrast to previous studies, the algal community on artificial substrates resembled to those observed on C. demersum. Independently of nutrient status (lakes), algae colonised artificial substrates intensively, but the highest algal biomass was observed in the hypertrophic lake. The community of periphytic algae was represented by diatoms, chlorophytes, and cyanobacteria. In the eutrophic lake, rather diatoms were present with high relative abundance, whereas, in the hypertrophic lake, rather cyanobacteria prevailed. Grazing pressure was high in both lakes and in the case of both substrate types, affecting the biomass of periphytic algae significantly. Our results indicate that macroinvertebrate grazing plays a crucial role in affecting periphytic algal biomass, independently of nutrient status and substratum type in shallow lakes.