Nitrate uptake in Central Illinois streams: a comparison along a transient storage gradient

Transient storage can be influenced by channel morphology. Anthropogenic activities can alter stream morphology by straightening channels, lining channels, or even restoration of previously altered channels. This study focused on whether relative transient storage (RTS) was related to stream type - modified lined, modified unlined, or natural. The study further sought to determine if a greater RTS is correlated to a decrease in percent nitrate-N. Eight (8) sites, encompassing three (3) different stream types - modified lines, modified unlined, and natural - were studied. Chloride and nitrate tracers were added to streams, and samples were analyzed for tracer concentrations and specific conductance. Simulated break through curves from a One Dimensional Transport with Inflow and Storage (OTIS) model were best-fit to observed data to estimate stream RTS. Solute recovery was calculated using a mass balance equation. The influence of RTS on nutrient processing was then assessed by comparing RTS to change in percent of nitrate-N. Contrary to predictions, RTS was highest in modified unlined streams (0.361) and lowest in modified lined streams (0.131). This discrepancy was attributed to elimination of sinuosity in natural streams, which further supports the importance of sinuosity in creating transient storage. Abundant vegetation in modified unlined streams and differential sampling following recharge events also contributed to these results. Change in percent nitrate-N was predicted to decrease with increasing RTS. Change in percent nitrate-N decreased with increasing RTS as predicted, supporting the importance of transient storage in nitrate uptake. However, results were not statistically significant (r2 = 0.09, p \u3c 0.05), and a larger sample size with less variation in streams could further research