Extreme Flooding and Nitrogen Dynamics of a Blackwater River

Extreme floods, including those expected to become more frequent in a warming world, may impact nutrient metabolism streams. However, flood impacts on spatial and temporal variability of dynamics large rivers (e.g., fourth order higher) have been understudied. In 2016, Hurricane Matthew provided unique opportunity evaluate nitrate retention processing the Lumbee River, blackwater stream southeastern North Carolina. The 3,000+ km2 watershed received as much 400 mm rain 48 hr storm moved across Atlantic Coastal Plain. Resulting floods were largest record, based than 80 years continuous streamflow measurements at outlet. We used modified Lagrangian sampling method collect water samples supporting quality data multiple points along three reaches River for several months before after Matthew. Samples analyzed nitrate-nitrogen estimate areal uptake rates subsections within each reach. Although concentrations did not change significantly flood, we found that within-reach increased substantially following evidenced by changes interquartile ranges. returned pre-flood levels approximately eight Matthew, but remained elevated end our field study. These results highlight potential extreme flooding biogeochemical processes long waters subside.