Nitrogen and phosphorus from agricultural and human sewage is transported by rivers to the Baltic Sea. Nutrient loads to the Baltic Sea have increased dramatically during the last century due to growing populations and modernization of agriculture. These nutrient loads result in eutrophication, a condition causing harmful algal blooms and dead zones with low oxygen. In the past few decades, nutrient loads have declined due to improvements in sewage treatment and agricultural nutrient management. Because of increased demand for meat, there has been an increase in large-scale livestock operations. Historically, manure was a valuable resource that was recycled in crop production. Today, manure is produced in such large quantities in some areas that excess nutrients can leak into the environment and become pollutants.

Mapping the nutrients

An important first step is to understand the role of manure in eutrophication is quantifying the magnitude of current and historical agricultural nutrient flows in the Baltic Sea region. How much is imported into the region as livestock feed and how much is exported as meat or other products? What portion of fertilizer and manure nutrients do crops use? What portion of nutrients is lost in manure handling?

Researchers at the Baltic Sea Centre at Stockholm University, in collaboration with researchers at Cornell University (USA) are estimating the flows of nitrogen and phosphorus in fertilizer, crops, animal feed, and manure. Products of this collaboration will include a ”tool box” that collects data from Eurostat and estimates nutrient flows and maps for the entire catchment that show regions with ”excess” nutrients.

The challenge of diffuse nutrient sources

Direct (or point) sources of nutrients from wastewater treatment plants and industries are relatively easy to estimate compared to nutrients from diffuse sources such as agriculture. Recent studies have found that about 15% of the nitrogen and 3% of the phosphorus inputs to the region will end up in the sea. Large portions of these nutrients come from agricultural activities.

Countries around the Baltic Sea are well aware of the problem of excess nutrients and have made progress reducing nutrient loads under the Helsinki Commission and EU environmental directives. During the workshop, participants presented different examples of manure management from the region. There are challenges to using manure in an optimal way, because it is unevenly distributed and the costs of processing and transporting manure can be greater than the costs of chemical fertilizer. In other words, it can be cheaper for farmers to buy chemical fertilizer than to use manure. Also, the structure of farms differs between countries. In Poland for example, the majority of farms are small (< 2 hectares). In contrast, farms in Denmark are much larger. There are also differences in policies between the countries. For example, Denmark has strict rules for manure handling and fertilizer use while Finland provides subsidies to farmers for using certain management practices.

How effective are different measures?

Baltic Compass, a large, EU-financed research project, evaluated how different countries implemented best practices for nutrient management. Another project, Baltic Manure, focused on how manure can be used optimally within agriculture to decrease nutrient leakage. Even after measures are taken on land, it may take decades for the ecological condition of the Sea to improve. As a result, it is very difficult to predict the environmental effect of different manure management practices, but modeling tools, like those used by the Baltic Nest Institute at Stockholm University, can help.

Building a network of researchers

The workshop brought together about 20 invited participants from 6 countries and 10 institutions in the Baltic Sea region and was an important first step to build a network of researchers who share common interests in sustainable manure management as a way to reduce eutrophication. The workshop produced a number of profitable discussions and an agreement for further knowledge sharing and collaboration.

Author: Kristina Viklund