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Phosphorus Losses from Agricultural Areas in River Basins

Effects and Uncertainties of Targeted Mitigation Measures

^a National Environmental Research Institute, Department of Freshwater Ecology, Vejlsøvej 25, 8600, Silkeborg, Denmark
^b Jordforsk, Frederik A. Dahls Vei 20, N-1432 Ås, Norway
^c Norwegian University of Life Sciences, Department of Plant and Environmental Sciences, Box 5003, N-1432 Ås, Norway
^d Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany
^e Danish Institute of Agricultural Sciences, Department of Agroecology, Blichers Allé, Postbox 50, 8830 Tjele, Denmark
^f Alterra, Wageningen UR, PO Box 47, 6700 AA Wageningen, the Netherlands

View larger version (16K): [in a new window]   Fig. 1. A concept for river basin managers to use for their analyses under the EU Water Framework Directive, looking into ecological impacts, environmental state, pressures, and how to respond to implementing mitigation measures to achieve a good ecological quality.

View larger version (40K): [in a new window]   Fig. 2. Schematic diagram of important P pathways and targeted mitigation options taking place along the border of agricultural fields and riparian areas. (A) Downstream part of the river continuum where under natural conditions the river often inundates the floodplain. (B) Middle part of the river continuum where tile drainage pipes often penetrate the riparian areas with water and substances from upland agricultural fields, thus short-cutting the biogeochemical processes in riparian areas. Cutting tile drains and inundating riparian areas can help re-start these retention processes. (C) Most upstream in the river continuum agricultural fields bordering the streams are often steep, resulting in both soil erosion and surface runoff and tillage erosion transport soil and P toward low-lying areas or across the stream edge so that over time low-lying soils bordering streams are enriched in P content.

View larger version (28K): [in a new window]   Fig. 3. Soil and total phosphorus losses (A) and surface runoff (B) at five sites with Universal Soil Loss Equation (USLE) plots of different soil erodibility. The USLE plots were either plowed in autumn or not (only spring tillage) during the period 1992–1999.

View larger version (28K): [in a new window]   Fig. 4. Schematic diagram (A) of the iron treatment of soils in different depths along stream channels or ditches, and (B) the modeled reduction in phosphorus loss to surface waters following mixing of iron material in different concentrations into various depths of the soil column near ditches.

View larger version (17K): [in a new window]   Fig. 5. Removal efficiency (%) for suspended solids (SS) and total phosphorus (TP) in surface runoff during summer and winter. Experiments were conducted with 5- and 10-m-wide buffer zones at the Grorud site during 1992–1999 and 5-m-wide zones at the Mørdre site during 1999–2003.

View larger version (12K): [in a new window]   Fig. 6. The probability of sediment material to escape through a buffer zone of different widths under natural conditions when larger rills (>100 cm2 cross-sectional dimension) are formed on the adjoining fields.

View larger version (58K): [in a new window]   Fig. 7. Maps of phosphorus application with fertilizer and animal manure and soil erosion risk classes in the Danish River Odense catchment for agricultural blocks of an average size of 9 ha.

View larger version (28K): [in a new window]   Fig. 8. Relationship between (A) one year of measured daily mean concentrations of total phosphorus and daily mean discharge in the Gelbæk stream, Denmark, and (B) the enrichment ratio between total phosphorus concentration (µg P L–1) and the concentration of suspended solids (mg L–1) applying autumn plowing and spring harrowing in two experimental Universal Soil Loss Equation (USLE) plots at Askim, Norway.