The Effect of Short Term Inundation on Potential Nitrogen Flux in Coastal Ecosystems.

Excess nitrogen (N) loads are considered one of the greatest threats to the integrity of coastal ecosystems but a variety of influencing factors make the amount and rate of N input to the coast difficult to determine. Explored in this study is the effect of short term inundation on potential N flux from four ecosystems in St. John’s County, Florida: submerged, marsh, upland and residential. Four soil cores were collected from each of the four ecosystems. After saturation, each of the cores was inundated with a 10cm head of floodwater. Floodwater samples were then collected after 0, 3, 6, 9, 12, 18, 24, 72, 120 and 168 hours and were analyzed for TKN, NH4-N and NOx-N to determine the Total Nitrogen (TN) concentration and flux through the study period. Results found no statistical difference in the TN concentration or flux in the floodwater among the four sites after a short term 24-hour inundation. However, at the end of seven days of inundation, the residential and upland TN concentrations and flux were significantly higher than the marsh and submerged ecosystems. These results show that a short term flooding event will have similar effects on N flux regardless of ecosystem, but a longer duration of inundation of a week or more could lead to a significantly greater N flux from the residential and upland ecosystems. This could possibly pose a threat as future predictions in sea level rise leave inland communities vulnerable to increased flooding events and prolonged inundation, causing excess N concentrations in the floodwater to be transported into the coastal waters.