Effects of large-scale changes in emissions on nutrient concentrations in Estonian rivers in the Lake Peipsi drainage basin

The fall of the Iron Curtain resulted in dramatic changes in Eastern Europe, including substantial reductions in the use of fertilisers and livestock production, as well as a marked decrease in water consumption by both the general population and industries. This situation has created a unique opportunity to study the way that rivers have responded to these changes. Here, the impact of these reductions on concentrations of nutrients (N and P) at 22 sampling sites on Estonian rivers are examined. There were statistically significant downward trends (one-sided test at the 5% level) in total nitrogen (TN) concentrations at 20 of the 22 sites. These decreases in TN relate to: (i) substantial reductions in the use of organic and inorganic fertilisers, (ii) reduction of cultivated and ploughed areas and increased proportions of grassland and abandoned land and (iii) improvements in farm management practices. For total phosphorus (TP), significant downward trends were detected at only two sites, and there were also two upward trends. The TP trends can be mainly explained by changes in phosphorus discharges from municipal sewage treatment plants. Fifteen downward trends and one statistically significant upward trend were found for the TN:TP ratio. The general decline in this ratio has likely been conducive to blue-green algae blooms in the recipient, Lake Peipsi.