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Geoinformatics-8-2008
article figure 3 port and substance exchange processes based on quantitative field measurements and modeling. while point sources are easy to detect, diffuse sources are difficult to estimate. nowadays, however, non-point source emissions in particular have substantial effects on the ecological statuses of surface waters. hence, state-of-the-art integrated modeling approaches are used to link up different input and output datasets. these combinations are realized through the modelbuilder framework in arcgis 9.2 and allow for the transparent deduction of phosphorus emission calculations. mathematical modeling is applied to different spatially explicit processes, controlling flows and fluxes of water and substances in the landscape. in particular, dissolved phosphorus transport as well as particle bound discharge of phosphorus are of importance when considering the nutrient status of lakes. this article proposes a geo-processing procedure to enhance spatially lumped and semi-lumped models by including weighted variables to consider the spatial variation of emissions. this procedure is evaluated for the mondsee catchment in austria comprising 96 sub-catchments where water samples have been taken for calibration. the characterization of the nutrient balance has been established by means of the following pathways of distribution: surface runoff, water-driven soil erosion, land drainage retention, interflow and groundwater as well as direct discharge through the atmosphere (figure 3). the case study area the pre-alpine lake district in the wider region around the austrian city of salzburg, capital of the federal state of salzburg, is endowed with about a dozen medium-sized lakes (plus a large number of small ones). the study area is embedded in a landscape of hills in the north and west, and alpine mountains in the south. although the lake district can be regarded as one natural entity created by glaciers, the lakes are situated in different administrative regions: some in the federal state of salzburg, some in what is known as the "salzkammergut" area which belongs mainly to the federal state of upper austria, and some in the german federal state of bavaria. this has implications for environmental planning and public action, which require collaboration across state and national borders. accordingly, different parts of the lake district are subject to different legislative conditions regarding, for instance, the regulations governing construction, the use of lakeshore areas, (waste) water management, environmental protection, and the preservation of nature (figure 4). discharge constituent processes since water is the driving factor for phosphorus transport, a precise reflection of discharge processes is an indispensable requirement. the total volume of rainwater which is not lost by evaporation contributes to discharge. this net precipitation is then split into two pathways: surface runoff and infiltration. water infiltrated into the soil can either be transported laterally through interflow processes or vertically, percolating and contributing to groundwater recharge. furthermore, water infiltrating to the soil can be collected within land drainage facilities (retention). depending on the kind of distribution channel the water follows, water concentration time speeds up or slows down. when there is longer contact time (retention period) of the nutrients dissolved in the water, the self-purification potential of soils and streams lowers the nutrient contribution to the lakes. this buffer capacity or regulation potential is dependent on the efficiency of nutrient degradation through organisms, immobilization or precipitation based on certain soil properties or elements (e.g. fe, ca, and al), the overall retention period, and the filtration rate through the soil. main objectives the main objective of the interreg iiia project "seenlandwirtschaft" was to secure and enhance socio-economic and ecological functionality in the bavarian and austrian pre-alpine "lake district" with particular focus on the description of diffuse emissions pathways of phosphorus considering transport-related processes based on topographic and climate influences. since water pollution control noted an increase of phosphorus loads to the mondsee and irrsee in the years 2002 and 2003, the quality of those water bodies (see fugure 6) has seemed to decrease due to the eutrophication of lakes causing toxic algal blooms. if the process of eutrophication and respective oxygen consumption continues, a change from aerobic to anaerobic conditions might result in the death of plants and fish. however, we assumed a change in the system cycle causing increasing substance flows and hence increased loads of phosphorus to surface waters. therefore, an investigation program encompassing a measuring program with 96 measuring sites and the development of a dispersion model describing the behavior of phosphorus in a defined hydrological system was implemented. latest news? visit www.geoinformatics.com phosphorus concentration rates the amount of phosphorus discharge is based on its concentration within organic and inorganic matter of the topsoil. however, inorganic phosphorus compounds are not easily soluble. in part they are present in mineral form, especially in al, fe and ca bounds. organic phosphorus connections december 2008 33
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