Seasonal Precipitation is a Hydrologic Driver of Salt Marsh Nitrogen Removal
Abstract
Salt marshes provide the important ecosystem service of nitrogen (N) removal, mitigating nutrient loads to coastal environments. The dynamic redox conditions and accumulation of organic carbon (OC) in salt marsh sediments result in conditions favorable for permanent N removal through denitrification, a microbial process by which reactive nitrogen (as nitrate, NO3-) is reduced to gaseous forms (nitrous oxide and dinitrogen gas, N2). Although edaphic and biotic drivers of denitrification such as sulfide accumulation and plant productivity in these tidal systems are well understood, less is known about non-tidal hydrologic drivers, particularly seasonal changes in freshwater inputs. The objective of this study is to investigate how changes in freshwater delivery to marshes associated with seasonal changes in precipitation affects N removal by denitrification. We measured N2 flux rates on intact sediment cores collected from a salt marsh located in the Elkhorn Slough National Estuarine Reserve. The regional precipitation patterns at Elkhorn Slough result in wet and dry seasons that can affect the amount of fresh water delivered to the marsh. Cores were collected from an elevation gradient spanning low, mid, and high marsh positions every 4-6 weeks starting at the beginning of the rainy season (November 2020) and concluding during the dry season (July 2021). Denitrification (i.e., N2 production) decreased over the course of the rainy season at all marsh elevations. In general, denitrification rates were higher at the mid and upper marsh elevations compared to the low marsh. Nutrient flux calculations support observed N2 fluxes, suggesting hydrologically driven changes in dominant N cycling process across the wet winter to dry summer seasonal transition. Investigating the hydrologic drivers of N removal marshes provides insight into patterns of nutrient processing within marshes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.B45B1621T