Investigating the Potential for Nitrate-N Removal in Rhode Island Transient Headwater Streams

Robert L. Carothers Library and Learning Commons

Excess nitrogen (N) can have detrimental effects on the environment, particularly in coastal waters where inputs from septic systems and agricultural runoff can lead to algal blooms and hypoxic zones. However, transient headwater streams, which comprise a significant portion of streams in watersheds, may have the potential to remove N given their low flow rates, high surface to volume ratios, long retention times, and hydric soils. We investigated the physical characteristics and N removal capacity of transient headwater streams. Four bromide (Br) and nitrate-N slug tests were conducted in four streams in southern RI. Streams were sampled repeatedly as the plume traveled 30 m. Nitrogen removal was determined by changes in the Br:N ratio from start to end. Three out of the four slug tests demonstrated substantial N removal – 25-65% N removal. Removal occurred towards the end of the slug tests due to hyporheic interactions. Streams with longer retention times demonstrated greater N removal. Transient headwater streams may be important N sinks and future research should focus on determining the in-stream processes that facilitate N removal.