Estimating interactions between a stream channel and a diversion wetland

Background/Question/Methods

Straightened channels and altered and drained adjacent riparian wetlands have adversely impacted streams and rivers throughout the US Midwest. This research investigated the biological connection and water quality of a 0.07 ha diversion wetland and adjacent stream at the Olentangy River Wetland Research Park in central Ohio.    Results/Conclusions

Before the flowthrough conditions were established, we demonstrated with mark and recapture techniques that the wetland already was a biorefuge for fish under extreme conditions; two species (Centrarchidae) captured in the stream before a total drawdown of the stream were found in the wetland a year later. In addition, water at the bottom remained at around 4 °C over the winter likely due to groundwater input, which possibly provided a warmer shelter for fish. Stream water quality of the lower section, downstream of the wetland outlet, generally improved with hydrologic pulsing after flow-through reconnection due to the trapping of nutrients in the wetland. Mean removal per flood pulse for nitrate-nitrite, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP) were 1.81 g-N m^-2 per pulse, 1.02 g-N m^-2 per pulse, 0.014 g-P m^-2 per pulse, and 0.004 g-P m^-2 per pulse respectively.  The wetland exported 2.8 g-C m^-2 per pulse of organic carbon. A greater attenuation of NO₃^- and TP occurred in the marshy outlet channel section of the wetland than the open water section. The diversion wetland successfully removed nitrate and phosphorus during storm pulses. Similar designs should be applied to other locations to examine their function under different climatic and hydrological conditions.