Förändring av nitratläckage och växtproduktion från låglänt jordbruksmark vid en ny reglering av vattennivån i Mälaren

Abstract: The water level of Lake Mälaren has been regulated since the 1940’s. A recentinvestigation suggests that the current regulation needs to be adjusted in order toprevent a decline in water level, salt water from infiltrating from Lake Saltsjön,and risk of floodings. In addition to these preventions, the new regulation couldpotentially effect the natural environment and agriculture practices in the lowlands that surround the lake. The new regulation proposal calls for an increase invariations in Mälaren’s water level during seasons, while the annual mean waterlevel will remain the same. The Swedish Agriculture Industry has been given a lotof restrictions by the Swedish government in order to decrease it’s nitrogen leakageto ground and surface water. Nitrogen is very much affected by the water contentin the soil through microbial activity as well as for transportation in the soil.The aim of this thesis was to investigate how the water flow in the soil in lowlandareas around lake Mälaren would change with the proposed regulation. Based onresults from the modelling program Drainmod. A comparison was made betweenthe old regulation and the new regulation proposal. Based on the Drainmod results,the differences in nitrate-nitrogen flow to ground water and fictitious spring cropproduction are likely to be minimal between the two regulation proposals. In thenew regulation there is a possibility for delayed spring agricultural tilling due to ahigher water level during the spring season. Over the whole period of 30 years, theold regulation has a slightly bigger runoff volume which indicates a possiblegreater loss of nitrogen. There are differences between the input data and the actualsimulated data for the precipitation in the model which gives reason to questionthe results in this study.