Influence of global change on biological assemblages in the Danube Delta

The effects of global changes on the water quality of the Danube delta (St. Gheorghe Branch) were investigated using the causal framework DPSIR, model used for describing the interactions between society and the environment adopted by the European Environment Agency (EEA): driving forces, pressures, states, impacts and responses. It is known that interactions between climate change and other drivers of change including hydro morphological modification, nutrient loading, acid deposition and contamination by hazardous substances represent sources of environmental pressures for biological assemblages. This study was done by surveying the ecological status described in EU Water Framework Directive (EU-WFD) using the biological quality elements: composition and abundance, diversity, sensitive/tolerant species, biomass (phytoplankton, macroinvertebrates) in one of the most productive socio-ecological system. The assessment of biological assemblages was based on laboratory data, results of field experiments over 3-year period (2009–2011) and aspects of hydrophysical, hydrochemical and ecological change, those being early indicators of climate change in aquatic ecosystems. Under reduced flow, combined with increasing temperature and global radiation, phytoplankton biomass increased, in contrast the food pulses have caused dilution effects on nutrients, and therefore signifcantly lower phytoplankton biomass. The foods and changes in flow regimes have also an impact on the bed and bank structures, so the benthic macroinvertebrates diversity was reduced, was observed the loss of sensitive taxa and changes in community composition. A strong reduction in non-point inputs of pollutants would be necessary to be counterbalancing the possible climate-induced effects on biological assemblages.