Land use and runoff effects on tidal creek ecosystem metabolism

Tidal creeks connect coastal lands and estuaries and are important conduits of watershed runoff and pollutants. With expanding urban development in many coastal areas, increased stormwater runoff to tidal creeks has the potential to increase nutrient loading, shift salinity regimes, and change ecosystem functions. To better understand these linkages, we measured dissolved oxygen (DO), water levels, salinity, and temperature for over 1 yr at 6 tidal creeks in Alabama and western Florida, USA. We coupled these measures with watershed-model (Soil and Water Assessment Tool) estimates of nutrient (NO 3 - , NH 4 + , and mineralized P) loading, flow, and other available watershed data. We estimated gross primary productivity, ecosystem respiration (ER), and net ecosystem metabolism (NEM) and found that all creeks were heterotrophic throughout the study period and frequently experienced periods of low DO. Our results did not identify a direct relation between urban land use and metabolism measures. Stepwise regression models showed that temperature, salinity fluctuations, and nitrogen loading were associated with seasonal measures of ER and NEM, which may be related to agricultural land use in some watersheds. We also noted that severe declines in DO related to ER occurred in most creeks following rainfall events associated with tropical cyclones. While this study indicates that low- to moderate-density residential development in this region may not readily elicit a response in ecosystem metabolism, runoff factors associated with land use change and excessive precipitation were related to metabolism. Further research is needed to understand how these stressors may interact to influence tidal creeks and the larger estuary.