Phosphorus Load to Surface Water from Bank Erosion in a Danish Lowland River Basin

Phosphorus loss from bank erosion was studied in the catchment of River Odense, a lowland Danish river basin, with the aim of testing the hypothesis of whether stream banks act as major diff use phosphorus (P) sources at catchment scale. Furthermore, the study aimed at analyzing the impact of diff erent factors infl uencing bank erosion and P loss such as stream order, anthropogenic disturbances, width of uncultivated buff er strips, and the vegetation of buff er strips. A random stratifi ed procedure in geographical information system (GIS) was used to select two replicate stream reaches covering diff erent stream orders, channelized vs. naturally meandering channels, width of uncultivated buff er strips (<= 2 m and >= 10 m), and buff er strips with diff erent vegetation types. Th irty-six 100-m stream reaches with 180 bank plots and a total of 3000 erosion pins were established in autumn 2006, and readings were conducted during a 3-yr period (2006-2009). Th e results show that neither stream size nor stream disturbance measured as channelization of channel or the width of uncultivated buff er strip had any signifi cant (p < 0.05) infl uence on bank erosion and P losses during each of the 3 yr studied. In buff er strips with natural trees bank erosion was signifi cantly (p < 0.05) lower than in buff er strips dominated by grass and herbs. Gross and net P input from bank erosion amounted to 13.8 to 16.5 and 2.4 to 6.3 t P, respectively, in the River Odense catchment during the three study years. Th e net P input from bank erosion equaled 17 to 29% of the annual total P export and 21 to 62% of the annual export of P from diff use sources from the River Odense catchment. Most of the exported total P was found to be bioavailable (71.7%) based on a P speciation of monthly suspended sediment samples collected at the outlet of the river basin. Th e results found in this study have a great importance for managers working with P mitigation and modeling at catchment scale.