Maja Brandt

Watershed modelling of nonpoint nitrogen losses from arable land to the Swedish coast in 1985 and 1994

Abstract Eutrophication problems in the Baltic Sea have drawn attention to the contribution of nutrients from surrounding countries. By using the HBV-N model in southern Sweden (145 000 km2) daily nitrogen leaching, reduction in rivers and lakes, net transport to the sea and source apportionment have been calculated in 3725 subbasins for the period 1985–1994, with calibration at 722 sites against measured time series. On average, 48% of the nonpoint losses from agriculture were reduced during the transport towards the sea, which left about 33 500 tonnes in annual mean net transport. This represents 45% of the total land-based load. Land cover and emissions for the years of 1985 and 1994 were used in two separate simulations of the 10-year period. The normalized gross leakage from arable land in 1985 was estimated to 29 kg N ha−1 year−1, which corresponds to 15 kg N ha−1 year−1 in net leakage to the sea. In 1994 these transports were reduced by 20 and 15%, and thereby the total load on the sea was decreased by 7%. This is still far from the Swedish goal of 50% reduction. The article presents the spatial variation of nitrogen leakage and retention within the southern half of Sweden, and emphasizes the importance of allocating measures where down-stream retention is low in order to achieve efficiency with respect to the sea. It is shown that the model approach may be used in the decision making process for best management practices in watersheds.

Simulation of runoff and nitrogen leaching from two fields in southern Sweden

ABSTRACT A conceptual model for the simultaneous computation of runoff and inorganic nitrogen leaching is described. The model is semi-empirical with coefficients that are calibrated against observed data. Two applications of the model, using well-controlled data from small fields of arable land in southern Sweden, are demonstrated. These show that a major part of the variations of concentrations of inorganic nitrogen in runoff water can be explained by this model approach. Finally, the sensitivity and limitations of this type of model are discussed.

Measurement of areal water equivalent of snow by natural gamma radiation—experiences from northern Sweden

ABSTRACT The Kultsjon basin in northern Sweden has been the subject of detailed studies of the potential of airborne γ-ray spectrometry for snow mapping and hydrological forecasting since the spring of 1980. A brief introduction to the theory behind this technique is given. Results from five melt seasons are presented, and problems and uncertainties are discussed. A verification against ground “truth” based on snow courses, runoff measurements, and hydrological models is given. Finally it is shown how the data can be used for updating and improving more conventional forecasting models.