Abstract
Diffuse phosphorus loss from agricultural fields is an important contributor to the eutrophication of waterbodies. The objective of this study was to evaluate a pilot project for the implementation of mitigation measures to reduce P losses. The pilot project is situated in southwestern Norway and, covers a 14-year period (2004–2018). It included data on the implementation of mitigation measures and water quality monitoring for six small catchments. The mitigation measures consisted of no tillage in autumn, reduced P fertilizer application, grassed buffer zones, and sedimentation ponds. Extra efforts were made to reduce diffuse P losses during the period from 2008 to 2010. The project comprised economic incentives, an information campaign, and farm visits. Data from 2004 and 2010 showed that the use of P fertilizer during this period decreased by 80% and the area of no-till in autumn increased in all six catchments and covered 100% of the area in three of the six catchments in 2010. However, with decreased economic incentives after 2010, the degree to which the mitigation measures were implemented was reversed; P-fertilization increased, and no-till in autumn decreased. No significant effects of mitigation measures on total P and suspended sediment concentrations were detected. We conclude that economic incentives are necessary for the comprehensive implementation of mitigation measures and but that it is not always possible to show the effect on water quality.
Highlights
IntroductionEutrophication of waterbodies in catchments with a high share of agricultural land is common
Eutrophication of waterbodies in catchments with a high share of agricultural land is common.Both nitrogen and phosphorus contribute to this, but P has been shown to be the limiting factor for eutrophication in most freshwaters [1]
This paper summarizes the outcome of a pilot project intended to improve the water quality of a eutrophic lake, the lake Vestre Vansjø in Norway
Summary
Eutrophication of waterbodies in catchments with a high share of agricultural land is common. Both nitrogen and phosphorus contribute to this, but P has been shown to be the limiting factor for eutrophication in most freshwaters [1]. There has been focus on removing point sources such as waste water [2]. After removing the main point sources of nutrients, agricultural non-point sources are often pointed out as main contributors of P to surface waters. Agricultural mitigation measures aimed at reducing non-point sources of P include better nutrient management, improved soil and crop management, and increased retention in the landscape [3,4]
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