Abstract
Abstract. In this paper, we estimate the surface water retention of nitrogen (N) in all the 117 drainage basins to the Baltic Sea with the use of a statistical model (MESAW) for source apportionment of riverine loads of pollutants. Our results show that the MESAW model was able to estimate the N load at the river mouth of 88 Baltic Sea rivers, for which we had observed data, with a sufficient degree of precision and accuracy. The estimated retention parameters were also statistically significant. Our results show that around 380 000 t of N are annually retained in surface waters draining to the Baltic Sea. The total annual riverine load from the 117 basins to the Baltic Sea was estimated at 570 000 t of N, giving a total surface water N retention of around 40%. In terms of absolute retention values, three major river basins account for 50% of the total retention in the 117 basins; i.e. around 104 000 t of N are retained in Neva, 55 000 t in Vistula and 32 000 t in Oder. The largest retention was found in river basins with a high percentage of lakes as indicated by a strong relationship between N retention (%) and share of lake area in the river drainage areas. For example in Göta älv, we estimated a total N retention of 72%, whereof 67% of the retention occurred in the lakes of that drainage area (Lake Vänern primarily). The obtained results will hopefully enable the Helsinki Commission (HELCOM) to refine the nutrient load targets in the Baltic Sea Action Plan (BSAP), as well as to better identify cost-efficient measures to reduce nutrient loadings to the Baltic Sea.
Highlights
Expanding human activities have had a great impact on nutrient dynamics and nutrient export from watersheds (Hill and Bolgrien, 2011; Mayorga et al, 2010)
Our results show that around 380 000 t of N are annually retained in surface waters draining to the Baltic Sea
The total annual riverine load from the 117 basins to the Baltic Sea was estimated at 570 000 t of N, giving a total surface water N retention of around 40 %
Summary
Expanding human activities have had a great impact on nutrient dynamics and nutrient export from watersheds (Hill and Bolgrien, 2011; Mayorga et al, 2010). Increased nutrient export from coastal watersheds has had severe impacts on the ecological functions and community composition of estuaries, with algal blooms, increased water turbidity, oxygen depletion, and severe fish deaths as the most prominent consequences (Kellogg et al, 2010; Mayorga et al, 2010; Hoffmann et al, 2009). For nitrogen (N), the term retention is widely used to describe the processes leading to a temporary immobilisation of reactive (non-N2) N by incorporation into biomass or sedimentation, or the permanent loss of reactive N by conversion into the non-reactive atmospheric form (N2) by denitrification (Billen et al, 2009). Nitrogen is primarily removed (or retained) from surface water by denitrification (i.e. the microbial production of N2 from fixed N), followed by processes such as sorption to sediment or organic matter, and biological uptake (Hejzlar et al, 2009). Results from mass-balance studies across a wide range of geographic scales indicate that
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
