Assessing the role of constructed floodplains on the biogeochemistry of agricultural streams

Streams in the midwestern United States are managed to rapidly convey runoff downstream, carrying with it nutrients and sediment. My thesis quantifies the effect of the two-stage ditch, which constructs 'mini-floodplains' adjacent to channelized streams to 1) retain nutrients and sediment, and 2) enhance ecosystem function. The two-stage ditch increased water clarity during floodplain inundation; however, total suspended solids were not reduced in any of the study streams. Nutrients that are 'sticky' (total phosphorus, soluble phosphorus, and ammonium) were decreased in 2 of the 4 two-stage reaches, whereas nitrate, a 'leaky' nutrient, was not reduced in any of the streams. Floodplains increased gross primary production during warm seasons at baseflow, and consistently increased ecosystem respiration at all stages in all seasons. Constructed floodplains can improve water quality in agricultural streams, but is most likely to be successful when 'stacked' with other best management practices within a watershed.