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Geoinformatics-8-2008
article estimating the number of grassland cuts the number of grassland cuts per growing season (during the year 2005 in this case) was taken as the measure for grassland intensity. the assumption is that a higher percentage of intensively-used plots (more than two cuts per year) will result in a higher amount of nutrients been offloaded. the nutrient dynamics imply that material is removed in the form of harvested grass, but also an increase in disseminating manure for balancing out the removal, whereby the timing of the manure offload is critical with respect to precipitation. an increased contribution of nutrients transported into the surface drainage seems most likely. several pathways are possible: surface runoff, drainage channels, interflow, the groundwater system and erosion. monitoring annual land use changes to locate areas of different intensities was carried out by the monthly acquisition of satellite imagery from the aster (advanced spaceborne thermal emission and reflection radiometer) sensor. two aster scenes following in sequence are combined for spectral temporal change classification (stcc). this results in a spatially explicit representation of grassland intensity documented by the number of cuts during the 2005 growing season (figure 5). figure 4 occur in adsorbed form in orthophosphate ions and hence are also nearly insoluble. based on the high phosphorus adsorption potential of mineral soils, the phosphor content of the soil solution is very low. phosphorus is highly immobile within the soil. considerable phosphorus loss is therefore assumed by soil erosion processes. hence, the phosphorus content of topsoil is a crucial parameter in modeling phosphorus emissions. but in a grassland-dominated area like the mondsee catchment, soil erosion is assumed to be low. however, it is not only soil erosion that causes phosphorus emissions. surface runoff and infiltration through macro pores also carry soluble nutrients; this is especially the case under sandy layers, soils with a high groundwater level and after fertilization with slurry shortly before heavy rain events. therefore, we consider grassland intensity an important parameter explaining phosphorus emissions. the number of cuts is related to the frequency with which fertilizers are brought out. the reason is that the amount of nutrients brought to the field equilibrates the nutrients taken off of the field. additionally, the datasets from the integrative administration control system (iacs) which provides data on farm and parcel relations as well as livestock numbers help to capture the annual nutrient farm balance and an estimate of the amount of nutrients brought to the farm parcels. surface runoff surface runoff reflects the portion of water which flows above ground before reaching surface water bodies. hence, it is dependent on runoff and drainage capacity. while the first mainly depends on average ground slope and vegetation cover (percentage of cover and vegetation type), the latter is influenced by rainfall (amount, intensity, storms, duration, frequency), time distribution of precipitation, soil moisture, soil water reduction time based on pore size distribution and pore volume. particle bound phosphorus emissions soil erosion caused by surface water runoff can be estimated using the universal soil loss equation (usle). predicting soil erosion by means of usle has already been implemented as a standard by the german institute for standardization (din 19798). the predicted erosion represents the potential long-term average annual soil loss in tons per hectare and year, and this amount of loss is compared to the "tolerable soil loss" limits. the soil erosion equation consists of a number of parameters which can be processed within a gis: the rainfall and runoff factor by geographic location (r), the soil erodibility factor (k), the slope length-gradient factor (ls) to be derived from dem data, the crop/vegetation and management factor (c) to be derived from satellite imagery and/or correspondence with farmers, and finally the support practice factor reflecting the effects of practices that reduce the amount and rate of the water runoff (p). interflow and groundwater discharge the process of water percolating into the soil is called infiltration. this subsurface drainage is based on pores filled up with air and water. the amount of water able to infiltrate is dependent upon soil texture, pore volume, pore size distridecember 2008 figure 5 34
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