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21.
Improved understanding of temporal and spatial Phosphorus (P) discharge variations is needed for improved modelling and prioritisation
of abatement strategies that take into account local conditions . This study is aimed at developing modelling of agricultural
Phosphorus losses with improved spatial and temporal resolution, and to compare the accuracy of a detailed process-based model
with a rainfall-runoff coefficient-based model. The process-based SWAT model (Soil and Water Assessment Tool) was implemented
for five river basins in central Sweden, and results compared with the rainfall-runoff coefficient-based model WATSHMAN (Watershed
Management System) for one of these river basins. Parameter settings and attribute values were adapted to Scandinavian soil
conditions, crops and management practices. Model performance regarding flow dynamics was overall satisfactory. Comparable
results were achieved at several scales. The modelled P load was of high accuracy for the days when monitoring data were available
for validation, generally once a month. Modelled monthly P load did not fit as well with averaged monthly monitoring load
values, mainly since monthly monitoring often partly or entirely misses the peak flows. The comparison of SWAT and WATSHMAN
gave slightly better results for the process-based model (SWAT). Better spatial resolution for input data such as Soil-P content
and agricultural management practices will be required to reach modelling results that enable identification of measures adapted
to local conditions. 相似文献
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23.
Accelerated eutrophication of surface water is often caused by high phosphorus (P) losses from agricultural fields. Long-term measurements of P concentrations from arable fields are therefore important for understanding of processes and key factors behind losses. Unfortunately, long-time series are difficult to compare due to high variablity, non-normal distribution, precipitation variability and flow relatedness. The objective was to use locally weighted scatterplot smoothing (LOWESS) and Seasonal Kendall Test to account for discharge effects on concentrations of P forms and suspended soil material, and to identify trends for seven agricultural fields included in a Swedish water quality monitoring program. Soil P content and sorption capacity governed concentrations and losses of dissolved reactive phosphorus (DRP). Other factors, such as preferential flow may influence the importance of these factors. Suspended soil material and unreactive phosphorus (UP) concentrations in water discharge depended on soil texture, slope of the field and total soil P content. Statistically significant trends in concentrations of different P forms were found for two fields. These trends are probably a consequence of changes in P additions and soils P saturation levels. 相似文献
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Phosphorus losses from arable soils contribute to eutrophication of freshwater systems. In addition to losses through surface runoff, leaching has lately gained increased attention as an important P transport pathway. Increased P levels in arable soils have highlighted the necessity of establishing a relationship between actual P leaching and soil P levels. In this study, we measured leaching of total phosphorus (TP) and dissolved reactive phosphorus (DRP) during three years in undisturbed soil columns of five soils. The soils were collected at sites, established between 1957 and 1966, included in a long-term Swedish fertility experiment with four P fertilization levels at each site. Total P losses varied between 0.03 and 1.09 kg ha(-1) yr(-1), but no general correlation could be found between P concentrations and soil test P (Olsen P and phosphorus content in ammonium lactate extract [P-AL]) or P sorption indices (single-point phosphorus sorption index [PSI] and P sorption saturation) of the topsoil. Instead, water transport mechanism through the soil and subsoil properties seemed to be more important for P leaching than soil test P value in the topsoil. In one soil, where preferential flow was the dominant water transport pathway, water and P bypassed the high sorption capacity of the subsoil, resulting in high losses. On the other hand, P leaching from some soils was low in spite of high P applications due to high P sorption capacity in the subsoil. Therefore, site-specific factors may serve as indicators for P leaching losses, but a single, general indicator for all soil types was not found in this study. 相似文献