Reliable quanti®cation of suspended sediment (SS) and particulate phosphorus (PP) transport, and identi®cation of the various delivery pathways at the catchment level, is an important and necessary aid to appropriate catchment management. In this study we measured storm event, seasonal and annual losses of SS and PP from a Danish arable catchment, Gelbñk Stream, using a multisampling strategy. SS losses for the study years May 1993±April 1994 and May 1994± April 1995 ranged from 71 to 88 kg ha À1 , while PP losses ranged from 0 . 32 to 0 . 36 kg P ha À1 . In both cases losses mainly occurred during infrequent storm events. In comparison with intensive storm sampling, infrequent (fortnightly) sampling underestimated annual transport during the two study years by À24 and À3317, respectively, for SS, and by À8Á6 and À1517, respectively, for PP. Reliable estimation of the transport of sediment and sediment-associated nutrients and other substances thus necessitates the use of an intensive monitoring approach. Turbidimeters proved to be a good substitute for direct measurement of SS, especially during storm events, although careful calibration is needed at the seasonal and storm event levels.Experience shows that in arti®cially drained and geologically complex catchments such as Gelbñk, simultaneous comparative monitoring of dierent sources (e.g. subsurface drainage water) is an important means of reliably discriminating between the various diuse sources of sediment and phosphorus. Subsurface drainage water was found to account for 11±15% of the annual SS export from the catchment; the corresponding ®gure for PP being 11±18%. Surface runo was only a source of SS and PP during the ®rst study year, when it accounted for 19% of SS and 7% of PP catchment export. Stream bank/bed erosion must therefore have been the major diuse source of SS and PP in both study years. The study also revealed that analysis of the trace element content (e.g. 137 Cs, 210 Pb) of the SS transported in subsurface drainage water and stream water during storm events is a useful means of discriminating between diuse losses of SS delivered from topsoil and subsoil compartments.

Abstract:Bank erosion was measured at 91 stream banks located in 15 Danish rural 1st and 2nd order streams over a 2-year period. Our aims were firstly to examine factors controlling spatial variation in bank erosion, secondly to estimate sediment and phosphorus (P) loss via bank erosion. The overall mean bank erosion rate was 11 mm year 1 . Bank erosion rate over the 2-year period was significantly related to a number of site-specific characteristics, including bank angle, bank vegetation cover, overhanging bank and estimated stream power. An empirical model for bank erosion based on these descriptive variables yielded a 55% explanation of the observed spatial variation in bank erosion rate. Bank erosion was higher at the lower 50-cm bank section (20 mm year 1 ) than at the upper bank (6 mm year 1 ). Cattle fencing in grazed areas and buffer zones with riparian woodland lowered bank erosion rates. We found that total P content of bank material was high (0Ð64 g P kg 1 ) and at the same level as found in agricultural topsoil along the streams. The overall annual catchment loss of bank-derived clay-silt sediment and total P to streams amounted to 58-72 kg sediment ha 1 and 0Ð23-0Ð28 kg P ha 1 , respectively. In comparison, the mean annual suspended sediment (SS) and total P losses from 14 similar sized Danish agricultural catchments were 122 kg SS ha 1 and 0Ð58 kg P ha 1 over the 2-year study period. Thus, bank erosion seems to be a major contributor of suspended sediment and P in this type of small channelized lowland stream.

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Movement of particles by water through the soil can be a significant pathway for P transport to surface waters in certain soil types. Our objective was to describe and quantify particulate matter (PM), particulate phosphorus (PP) and dissolved phosphorus (DP) transport tile drains during controlled plot experiments. The results were compared to corresponding studies of natural storm events in the tile‐drained catchment as a whole. Six rain simulations (irrigation 15.3–37 mm) were carried out at two 25 m2 plots on a loamy soil. Tracer chloride concentration in the drainage water peaked within 1 h of the onset of irrigation, thus indicating rapid macropore flow to the drains. PM, PP, and DP concentrations were highest in the initial drainage flow: 63 to 334 mg PM L−1, 0.177 to 0.876 mg PP L−1, and 0.042 to 0.103 mg DP L−1, respectively. Particulate matter and PP loss rates measured for the rapid drainage flow response were in the same range in the plot experiments as for nine precipitation events in the tile‐drained catchment (13.3 ha): 171 to 630 g PM ha−1 mm−1 vs. 141 to 892 g PM ha−1 mm−1, and 0.57 to 1.75 g PP ha−1 mm−1 vs. 0.71 to 5.92 g PP ha−1 mm−1, respectively. Tracer analysis using 137Cs revealed that the PM in the drainage water was derived from the topsoil.

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Abstract. Storm event and annual export of suspended sediment (SS) and particulate phosphorus (PP) was measured during three hydrological years (June 1993 to May 1996 in Gelbmk stream, a Danish lowland stream draining a 11.6 km-' arable catchment area. The contribution of subsurface drainage water, surface runoff and stream bank and bed erosion to catchment SS and PP losses was estimated using three different strategies: 1 ) Simultaneous and comparative monitoring of subsurface water. 2) A mass-balance and budget approach dividing the Gelb,"ek catchment into two subcatchments. 3) Application of the fingerprinting technique to single stonn events. Subsurface drainage water proved to be a significant SS and PP source. Subsurface drainage water from half of the catchment area accounted for 9.8-15% of the total annual SS loss from the Gelbaek catchment and 9.6-18.2% of the annual PP loss. The mass-balance and budget approach showed stream bank and bed erosion to be the major source of SS and PP in this channelized and highly managed lowland stream. These findings were consistent with the fact that the annual loss of SS and PP from an upper culverted stream sub-catchment was significantly lower than that estimated from a mass-balance for a lower sub-catchment with an open stream channel. Comparison of the tracer content (e.g. "TCs) of SS collected during four storm events with that of topsoil and subsoil using a simple mixing model revealed subsoil to be a major source of SS.

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