Abstract
In order to assess the progress toward eutrophication management goals, it is important to understand trends in land-based nutrient use. Here we present net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) for 2000 and 2010 for the Baltic Sea watershed. Overall, across the entire Baltic, between the 5-year periods centered on 2000 and 2010, NANI and NAPI decreased modestly by −6 and −4%, respectively, but with substantial regional variation, including major increases in the Gulf of Riga drainage basin (+19 and +58%, respectively) and decreases in the Danish Straits drainage basin (−25 and −40% respectively). The changes were due primarily to changes in mineral fertilizer use. Mineral fertilizers dominated inputs, at 57% of both NANI and NAPI in 2000, increasing to 68 and 70%, respectively, by 2010. Net food and feed imports declined over that period, corresponding to increased crop production; either fewer imports of food and feedstocks were required to feed humans and livestock, or more of these commodities were exported. A strong linear relationship exists between regional net nutrient inputs and riverine nutrient fluxes for both periods. About 17% of NANI and 4.7% of NAPI were exported to the sea in 2000; these relationships did not significantly differ from those for 2010. Changes in NANI from 2000 to 2010 across basins were directly proportional rather than linearly related to changes in total N (TN) fluxes to the sea (i.e., no change in NANI suggests no change in TN flux). Similarly, for all basins except those draining to the Baltic Proper, changes in NAPI were proportional to changes in total P (TP) fluxes. The Danish Straits decreased most between 2000 and 2010, where NANI and NAPI declined by 25 and 40%, respectively, and corresponding fluxes of TN and TP declined 31 and 18%, respectively. For the Baltic Proper, NAPI was relatively unchanged between 2000 and 2010, while riverine TP fluxes decreased 25%, due possibly to lagged effects of fertilizer reduction resulting from socio-political changes in the early 1990s or improvements in sewage treatment capabilities. For most regions, further reductions in NANI and NAPI could be achieved by more efficient production and greater substitution of manure for imported mineral fertilizers.
Highlights
In the modern, developed world, nitrogen (N) and phosphorus (P) fluxes from land to coastal waters are dominated by anthropogenic sources (Howarth et al 1996, 2012; NRC 2000; Bennett et al 2001; Galloway et al 2004; Howarth 2008)
Second we examine the relationship between net anthropogenic nitrogen inputs (NANI) and net anthropogenic phosphorus inputs (NAPI) and the corresponding total N (TN) and total P (TP) fluxes in order to gain insight into primary factors controlling regional variation and temporal variation of nutrient loading to the Baltic Sea
Information compiled at the NUTS2 level from the EuroStat database together with additional regional information at the oblast level (Russia and Belarus; Belarus oblasts are referred to as voblasts) are the basis of our estimates of regional variation of NANI and NAPI across the Baltic drainage basin
Summary
In the modern, developed world, nitrogen (N) and phosphorus (P) fluxes from land to coastal waters are dominated by anthropogenic sources (Howarth et al 1996, 2012; NRC 2000; Bennett et al 2001; Galloway et al 2004; Howarth 2008). While there has been progress in reducing TN and TP loads in the past few decades (HELCOM 2015), further actions are needed on land to fulfill the commitments of existing policy measures. To assess the progress toward eutrophication management goals, it is important to understand recent trends in nutrient use on land. Such understanding is especially needed given the social, political, and economic changes that have occurred in the past decades in the former Soviet-bloc countries located in the southern and eastern regions of the Baltic Sea basin
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