Freshwater - Drivers and pressures (Belgium)
The excess of nitrogen in the agricultural soils of Belgium is decreasing.
Figure 3: Gross nutrient balance for nitrogen
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High nutrient balances exert pressures on the environment in terms of an increased risk of leaching of nitrates to ground- and surface waters. The gross nitrogen balance was calculated to be 126 kg N/ha in 2006, which is 48 % lower than the balance in 1990 (241 kg N/ha). In 1990 the Belgian nitrogen balance was characterised by a huge difference between the northern (Flemish Region) and the southern (Walloon Region) part of the country. The balance surplus was nearly three times higher in Flanders than in the Wallonia, mainly due to high livestock densities in the north and north-west of the Flemish Region. Between 1990 and 2006, not only the surpluses were reduced in both regions but the range became much smaller. The nitrogen balance of Flanders was decreased to 147 kg N/ha in 2006 (-61 % compared to 1990). This reduction is mainly caused by a decrease in livestock nutrient production (-15 %), inorganic fertiliser use (-43 %) and atmospheric nitrogen deposition (-25 %). In the Walloon Region the nitrogen balance was reduced to 111 kg N/ha in 2006 (-20 % compared to 2000). This is mainly due to a decrease in livestock production (-9 %), inorganic fertiliser use (-24 %) and atmospheric N-deposition (-8 %) between 1990 and 2006.
Fluctuating and slightly decreasing trend of nutrients discharge in the North Sea.
Nutrients to the North Sea
The Belgian part of the North Sea covers approximately 3 454 km², which is barely half a percent of the total surface of the North Sea. The North Sea is a sensitive ecosystem that is under a great deal of pressures from intense human activities such as fishing, sand and gravel extraction, shipping, oil and gas extraction, tourism and industry. According to the last Quality Status Report of the OSPAR Commission, the consequences of fishing, the inflow of harmful substances and the excessive quantities of nutrients in the sea (eutrophication) cause the main problems in the North Sea.
In the Belgian coastal zone (BCZ), the Scheldt watershed is the main source of nutrients, contributing to 69 % of the total emission of N and 73 % of the total emissions of P. The Coast watershed is responsible for some 20 % of N and P discharge while the Ijzer contribute to only 10 % of N and 7 % of P total emissions (Brion et al., 2006).
Long-term trends (1966-2005) of nutrient loads (N, P) from the Scheldt1 show marked variations during this period. Nutrients originating mainly from point source, such as NH4+ and PO43-, show a marked decreasing long-term trend in their loads. This improvement mainly comes from the progressive ban of phosphates from detergents, the increased wastewater treatment capacity and the intensification of estuarine nitrification resulting from the net improvement of the oxygenation of the Scheldt river system following the implementation of secondary wastewater treatment. However nutrients of diffuse origin (agriculture) are mainly modulated by fluctuations of the Scheldt runoff. Despite the fluctuations related to hydrological conditions, NO3- + NO2- loads show a global increase since the mid-seventies, reflecting not only the evolution of diffuse sources of nitrate through leaching of agricultural soils but also the improvement of the oxygen status of the river, which reduced denitrification but increased the nitrification of the ammonium load. As a result of NH4+ and NO3- + NO2- load fluctuations, total nitrogen loads show a slight decreasing trend from the early eighties up to 2008 (Brion et al., 20062).
From 1990 to 1996, the data comprise riverine as well as direct discharges in the sense of the OSPAR convention. Since 1997, there have been no direct discharges as a result of generalised water treatment in the coastal river and polder basins. From 1990 to 1996, these direct N and P discharges were only a minor fraction of the total N and P loads.
1 This trends integrate changes in both nutrient emissions in the Scheldt watershed and their biogeochemical transformations along the aquatic continuum
2 See Figure 2.8 : http://www.belspo.be/belspo/home/publ/pub_ostc/OA/OA14_en.pdf