Publikasjoner
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1999
Forfattere
Johannes DeelstraSammendrag
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Sammendrag
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Forfattere
Nicholas ClarkeSammendrag
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Forfattere
Jan Mulder J.F. Gallardo E. Matzner Edward Tipping Charlotte Bryant Nicholas Clarke S. Lofts B. Michalzik M.A. VicenteSammendrag
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Sammendrag
DOC concentrations in soil water in podzols decreased from median values of 37 and 39 mg/l in the F and H layers, respectively, to about 6 mg/l in the B horizon. The decrease was most pronounced in the mineral soil. An increase in concentrations was found in the surface soils in late summer and autumn, apparently due in large part to increased production, which took place in both the canopy and the forest floor, although evaporative concentration of soil water could also have been partially responsible. In the B horizon, increased concentrations of DOC could be observed in the autumn, although these increases were much lower than for the surface horizons. A correlation was found between the surface soil DOC concentrations and the mean surface soil temperature 1 to 2 months previously, which could be due to the buffering effect of sorption processes. However, the increase in the net amount leached could not be clearly attributed to increased temperature. In the autumn, concentrations did not decline immediately when temperature decreased, which may be due to leaching of previously adsorbed organic matter. During the autumn, concentrations of DOC in streams increased in periods of high discharge due to increased input of high-DOC surface soil water. At the same time, DOC concentrations in surface soil water largely decreased, presumably as DOC was washed out. An increase in DOC was not seen in periods of high discharge in the early spring. The highest concentrations of TOC (both with and without flux-weighting) at the weir were also found in the autumn). Correlation of TOC in streamwater with temperature was poor but, for the winter months, often significant. A positive correlation in the winter was probably associated with higher fluxes due to temperature-induced snowmelt. DON, which is the dominant form of dissolved nitrogen at all depths in the podzols at Birkenes, also decreased sharply in concentration in the mineral soil. However, there was an increase in the concentration of DON relative to DOC. The C/N ratio thus decreased downwards in the soil, indicating a possible preferential adsorption of N-poor DOC. Much of the DON in throughfall appeared to be of low molecular weight. This was not the case for DON in soil water.
Sammendrag
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Sammendrag
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Sammendrag
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Sammendrag
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Sammendrag
One of the major objects of the Agricultural Environmental Monitoring Program in Norway is to document the effect of different agricultural production systems and site-specific characteristics on erosion losses and losses of nutrients to surface waters. The program registers and reports on the extent of erosion and nutrient losses from 10 different agricultural dominated catchments (65 to 8 700 ha) under various agro-climatological conditions. One of the most striking results from the monitoring so far are the enormous variability between the catchments. Erosion varies from around 100 kg ha-1year-1 in three of the catchments to nearly 3 000 kg ha-1 arable land in one catchment. Highest erosion are measured in catchments with large autumn-ploughed area. Losses of phosphorus are highly connected to SS. It varies from around 0,4 kg ha-1 in catchments with low erosion to around 4 kg ha-1 in catchments with high erosion and high livestock density. In catchments with high livestock density manure is mainly (60-100 %) spread in spring. The losses of nitrogen also show large variability between catchments and are highly correlated to water discharge. Nitrogen losses vary from 20 kg ha-1 to nearly 90 kg ha-1, highest in an intensive horticultural catchment. Lowest losses of nitrogen are measured in two areas of cereal production, where silty soils are dominating and in two areas with pasture and low temperatures in summer. Nitrogen losses are generally high in catchments with high livestock density. Monitoring on catchment scale gives the effect of many different agricultural practices and site-specific characteristics in one point. Variations in erosion and nutrient losses are a sum of positive and negative effects within the catchment area. Nevertheless the results suggest that erosion and nutrient losses be related to a set of agricultural practices and site specific characteristics.