Eutrophication remains a challenge for water quality, and leaching of phosphorus (P) from agriculture remains usually the determining factor as point source emissions of sewage are mainly under control. The Morsa watershed, southeast of Oslo, is a case in point. In spite of abatement actions during the past 20 years, the total concentration of P in the lake has decreased less than expected, causing growing frustration and scepticism among farmers. Hydro-biochemical interactions between phosphate (PO4) and calcium, aluminium and iron in soil and water have produced unexpected results. Decline in acid rain deposition over Norway has reduced the leaching of aluminium into water. This has caused a loss of an important fixation and removal of P by sorption to precipitating aluminium oxy-hydroxides. The combination of more precipitation and higher winter temperatures causes more flushing of P from surface soil horizons. Furthermore, water-logged soil loses much of its ability to hold PO4 in that iron is reduced, thereby allowing more P to escape. Farmers proved to have good agronomical knowledge and are taking part in an active network for spreading of agricultural practices. Reducing the amount of P in fertilizers was accepted fairly easily, whereas minimal autumn tillage has been a much harder task to implement. Therefore, just applying economic incentives will not do; developing basic environmental literacy with an ability to understand feedback loops and rebound effects is necessary. Following this, interaction between science and stakeholders is required, calling for trans-disciplinary research and trans-disciplinary processes.
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