The efficiency of wetlands in reducing nutrient and sediment
concentrations in runoff from agricultural areas can be used as an argument
for not tackling nutrient and sediment losses at source within the basin.
However, evidence from the Slapton basin shows that this efficiency varies
seasonally and is much less marked in the winter than in the summer,
pointing to the need for basin management during winter flows. In addition,
while wetlands may reduce nutrient and sediment concentrations, thus
improving downstream water quality, the accumulation of nutrients and
sediments in the wetland can lead to progressive eutrophication and, in
addition, terrestrialization of valued wetland habitats, further reinforcing the
need for basin source control.