How much runoff do riparian wetlands affect

Abstract Nitrate runoff from pastoral fanning is of concern because it contributes to lake eutrophication. Surface flow in wetlands is a measure of the runoff likely to experience nitrate attenuation. This study assessed the potential of small headwater wetlands to reduce catchment nitrate loads by quantifying the proportion of total runoff that occurred as surface flow at the outlet of wetlands. Surface flow can be measured from wetlands in side valleys (valley wetlands) with well defined flow channels, but not in those parallel to the stream (riparian wetlands) with distributed flow. This study, from November 2004 to June 2008: (1) measured the mean specific flow yield (mm yr−1) at the outlet of 6 wetlands; (2) classified wetlands into 3 types based on hydrology; (3) mapped and classified all wetlands in the catchment; and (4) calculated the area‐weighted mean specific yield of wetlands for the whole catchment. The 6.6 km2 study catchment at Taupo, North Island, New Zealand, was predominantly pasture on...