Partners and International Organizations
(English)
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AT, BE, BG, CH, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IT, LT, LU, LV, NL, NO, PL, PT, RO, SE, SI, SK, UK
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Abstract
(English)
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Eutrophication of surface waters is still a big issue regarding water quality. Different studies indicate that most Phosphorus (P) losses originate from small regions of a catchment only. The localisation of such critical source areas (CSA) is expected to be critical for the design of efficient and cost-effective mitigation schemes. Within our project we aim to improve an existing model to predict and delineate critical source areas for P-losses from agricultural land. Within the first year of the project we performed a factorial field-plot experiment to investigate the role of soil-P status, band-applied manure and rainfall intensity on P losses from two Swiss grassland sites. Artificial rainfall was applied on each plot first at medium intensity using a sprinkler and then at high intensity using a watering can, simulating two different runoff conditions. Under both conditions, dissolved reactive P (DRP) in runoff increased linearly with water soluble P in the soil (WSP), but the extraction coefficients differed substantially between the two phases of runoff generation. It was 0.017 kg L?1 for runoff generated with the watering can (WCR), and 0.085 kg L?1 for runoff generated with the sprinkler (SR). Manure application increased DRP losses, but did not override the effect of soil P status. Phosphorus losses with runoff were more sensitive to soil P status for SR than for WCR. The experiments enabled us to collect data on highly P enriched soils, which was needed to establish a reliable DRP~WSP relationship within the model. The Rainfall-Runoff-Phosphorus (RRP) model, developed by P. Lazzarotto, is a parsimonious, event-based model focusing on the transport of DRP from intensively managed grassland soils in small agricultural catchments. To test the applicability of the model, which was calibrated on four catchments draining into Lake Sempach, we applied the model to the Staegbach catchment, which drains into Lake Baldegg and was not used for calibration. We tested whether (1) it is possible to simulate the discharge dynamics and P losses at the catchment outlet, whether (2) reliable predictions of CSA are possible, and (3) how the classification of soil into two classes affect model predictions. We installed several measuring devices within the catchment to collect validation data in the year 2010. Despite the low amount of input data needed for the model, the model predictions for runoff and P losses at the catchment outlet were in good agreement with the measurements. Thus, at the catchment scale the model is transferable and potentially useful for the Swiss Plateau. In contrast, the spatial predictions are more difficult to validate and more uncertain. They changed significantly depending on the soil classification. Thus, there might be a minimum of complexity necessary to generate robust spatial results. The rainfall experiments and the model results identify the P stored in the soil as major source, which needs to be reduced.
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