Nutrient enrichment along the coast continues to be an environmental issue despite efforts to limit nutrient rich runoff from entering coastal ecosystems. Both nitrogen (dissolved inorganic and organic forms) and phosphorus additions have been identified as being particularly problematic. As an interface between terrestrial and near-shore ecosystems, coastal wetlands have the potential to mitigate increased nutrient loads before they enter sensitive coastal habitats. However, it is unclear if wetlands can efficiently remove dissolved organic nitrogen in the form of urea. To explore this question, we examined the urease activity of wetland sediment along a natural elevation gradient at Weeks Bay National Estuarine Research Reserve, Mobile, AL. To obtain a better spatial understanding of urease activity, the reserve was divided into three regions dominated by different vegetative communities (i.e., forest, ecotone, marsh). Urease activity was measured across both spatial and temporal scales to demonstrate the potential for differences in urease removal capacities and how changing edaphic characteristics affect these rates of activity.
Results/Conclusions
As you move inland from the coastline at Weeks Bay National Estuarine Research Reserve, clear differences in vegetation are present as a result of shifting environmental conditions. Urease activity measurements across three seasons (winter, spring, and summer) using a soil slurry method in conjunction with colorimetric analyses of ammonium were conducted at different locations along our wetland elevation gradient. Results indicated that rates of urea degradation were greatest at the lowest elevation marsh sites. Not surprisingly, ambient temperature was a factor in enzyme activity, with cooler temperatures lowering urease activities at all sites. These results suggest that wetlands have the ability to mitigate some additions of dissolved organic nitrogen before they enter coastal waters. However, the increasing worldwide use of urea as a nitrogen source in fertilizer combined with the continued loss of coastal wetlands indicate that these environments may not be sufficient for effective nutrient mitigation in the future.