River Salaca

1982 – up to now.

Gunta Spriņģe.

Three river sites in the the North Vidzeme Biosphere Reserve: outflow of the river at Vecate (latitude 57° N 47.722, longitude 25° E 08.948), below town Mazsalaca (latitude 57° N 52.446, longitude 25° E 00.057) and 4 km above river inflow in the Gulf of Riga at Vecsalaca (latitude 57° N 45.119, longitude 24° E 24.406).

In the Salaca drainage basin natural territories are dominating: forests (56,17%), bogs (3,77%) and waterbodies (1,88%). Arable lands are 37,5%, and urban territories 1,88% from the drainage area.

Investigation of long-term ecological processes in river communities and ecosystems on the background of climate warming and changing riverine load.

Water chemistry (COD, BOD, nutrients, ionic composition), bacteriology (aerobic saprophytic and oligocarbophylic bacteria), phytoplankton and periphyton, macrophytes, benthic macroinvertebrates.

Methods: For water chemistry and biology „Standard Methods for the Examination of Water and Wastewater” (American Public Health Association/American Water Works Association/ Water Environment Federation, USA) were used. Indices of saprobity and biodiversity were calculated.

• An increase in mean annual temperature, increase in precipitation, decrease in ice-covered days, increase in winter discharge, increase in number of extremely wet days and days with intensive precipitation are typical for river basin. Trends of long-term assessment of the River Salaca reveal increase in water discharge in winter season, and simultaneous decrease in water discharge in summer season. There are changes in water chemical composition, e.g., COD and water colour have increasing trends, oxygen – decreasing trend.
• Changes in structure and distribution of freshwater communities have been observed (e.g. increases proportion of emergent macrophytes, ratio of Cyanobacteria in total phytoplankton biomass, amount of green algae in benthic communities). These changes will have prolonged effects on freshwater biodiversity in future. Changes in Shannon’s index of freshwater communitiesw at the Salaca outflow confirm that they are quite diverse.