In situ differences in nitrogen cycling related to presence of submerged aquatic vegetation in a Gulf of Mexico estuary

Estuaries provide a suite of ecosystem services to people but are also under heavy stress from human development including excess nutrient loading and alterations in benthic habitat that affect nutrient cycling. Here we examine the interaction of two important and common ecosystem management priorities in estuaries: limiting eutrophication and restoration of submerged aquatic vegetation (SAV). Rates of benthic nitrogen processing can vary by habitat type and there is need for more complete data on the contribution of SAV to overall nitrogen cycling in estuaries, as well as a need to examine nitrogen cycling in situ to better characterize the role of SAV areal coverage in mediating estuarine eutrophication. We compare nitrogen cycling between two common and adjacent habitat types (SAV and adjacent bare sediment [BS]) in an index coastal estuary using an in situ chamber-based approach to better capture realized habitat differences. We also examined genomic community structure of sediment bacteria and archaea to identify biological indicators of nitrogen exchange. Both mean sediment-water exchange of dissolved N-2 and microbial functional community structure differed between SAV and BS. Habitat differences were more consistent with lower variability at locations with low salinity and when sediment organic content was highest, which aligns with findings in other studies. Habitat types differed significantly in microbial composition, including functional groups and genes, like nifH, that may contribute to observed differences in nitrogen cycling. Overall, habitat type appeared most important to nitrogen cycling near the river mouth where sediment nitrogen was higher, and this information has implications for integrated management of habitat restoration/conservation and nutrient loading.

Automated summary

Estuaries play a vital role in providing ecosystem services, but they are facing increasing stress from human activities. This study focuses on the interaction between the management priorities of limiting eutrophication and restoring submerged aquatic vegetation (SAV) in estuaries. The research examines the contribution of SAV to nitrogen cycling and compares nitrogen cycling between SAV and bare sediment habitats in a coastal estuary. The findings highlight the importance of habitat type in nitrogen cycling, particularly near the river mouth where sediment nitrogen levels are higher.