Author(s): Agnija Skuja
Email (s): email@example.com
Institution or organization of origin: University of Latvia, Institute of Biology
The increasing world population and the growing demand for electricity has led to damming of the majority of the large rivers worldwide. Besides changes in hydrology and morphology, the construction of dams can change the structure and quality of aquatic ecosystems. Riga HPP reservoir on a large lowland river Daugava was built in 1974 and long-term ecological monitoring in the reservoir has been carried out since 1976. The data show re-structurisation of benthic communities from lotic to lentic ones and stabilisation thereafter. Until 1977, lithophilous active filter-feeders represented mostly by non-native species Dreissena polymorpha were the dominant functional group in the profundal zone. In littoral, their dominance was less pronounced. After 1977, pelophilous gatherers/collectors were dominating in both littoral and profundal zones. Long-term data did not show any significant change in the dominant functional groups over the period 1977-2020, however year-to-year variations were found in relation to water level fluctuations. One of the unresolved problems in water management is how to determine the ecological conditions of reservoirs. A recent European Guide proposes a common methodological framework for defining and assessing the good ecological condition of heavily modified water bodies, which includes two approaches: the reference approach and the mitigation measure approach. Both approaches critically depend on good knowledge available on the links and interactions between biology, hydromorphology and mitigation measures. In this study, we test both approaches using functional groups of benthic macroinvertebrates and evaluate their applicability and suitability to assess reservoirs` ecological conditions and to propose relevant management measures.