Ecosystem services of tidal wetlands in Barnegat Bay: nitrogen removal
Creators: name: Velinsky, David
name: Quirk, Tracy
name: Piehler, Michael
name: Smyth, Ashley
Publisher: name: No Publisher Supplied
Year: 2013

description: There is a debate going on about Barnegat Bay in New Jersey, namely whether nutrienteutrophication, specifically nitrogen, is causing phytoplanktom blooms and increased macroalgae, and possibly secondary impacts (e.g., anoxia, loss of seagrass, increase in jelly fish, decreases in fish and crab populations, etc). The debate revolves around the fact that Barnegat Bay is poorly flushed, and that current eutrophication effects are only part of the natural conditions exacerbated by nitrogen loading along with some negative effects resulting from other stressors such as boat traffic, loss of connected wetlands, loss of freshwater flows and the withdrawal of cooling waters for the Oyster Creek Nuclear Generating Station.Salt marshes play a large role in removing pollutants and nutrients from water. The main mechanisms of removal are burial in the soil and microbial denitrification. Based on nutrient and radiometric data collected from soil cores, burial in the 26,000 acres of salt marshes in Barnegat Bay removes over 90% of the estimated 7.0 x 105 kg/yr N load. Our goal was to quantify N removal via denitrification in salt marshes of Barnegat Bay to contribute to our quanification of the Barnegat Bay N budget. A total of 18 soil cores were collected in 3 locations of the Bay in May, July and October 2012. While we know that the N load is relatively high, the concentration of dissolved N in the tidal creeks is relatively low. Nitrate + nitrite-N concentration ranged from not detectable to 2.0 μM and ammonium-N concentration ranged from 0.3 to 5.6 μM. Denitrification rates were similar among sites despite differences in creek water nutrients and salinity. Denitrification ranged from an average of 40 to 130 μmol/m2/hr, depending on season. Denitrificaiton rates were generally highest in the mid-summer (July) with similar rates at each site during each season. During mid-summer and fall there was a significant relationship between ammonium and SOD fluxes in the marshes.Salt marshes of Barnegat Bay are currently subject to a mosquito management technique, Open Marsh Water Management (OMWM), where interior vegetated marsh is converted to shallow ponds. Over 10,000 acres of salt marsh has been physically altered with OMWM in Barnegat Bay, thus making it important to measure the effect of OMWM ponds on denitrification. In July 2012, we collected five core in OMWM ponds, five cores in adjacent vegetated marsh, and five cores from vegetated marsh areas that have not been subject to OMWM. OMWM pond sediments had lower and less variable denitrification rates than vegetated soils. Overall, salt marsh denitrification has the potential to remove approximately 13 to 33% of the incoming estimated N load entering the Bay (7.0 x 105 kg/yr). Both sediment burial and denitrification can sequester or remove between 91 and 111% of the incoming load. Tidal marshes within the Barnegat system are an important component of the ecosystem and help to remove a substantial amount of N entering the bay.This study determined that tidal marshes in the Bay can remove a substantial amount of N entering the system. On a seasonal time scale (over the course of the study) upwards of a third of the N is converted to nitrogen gas. Burial works on longer time scales, years to decades, and may then bias the total removal to higher than expected values. In this regard, shorter term burial estimates need to be accomplished to make the two removal mechanisms more comparable. Studies using sediment deposition plates and 7Be analysis would aid in this comparison.Importantly, OMWM appears to lower the overall rate of denitrification during peak warm months. An areal survey of the extent of OMWM and rates within these sub-systems needs to be undertaken to better determine the impact on the overall budget of N to the Bay. Denitrification and burial in the sub-tidal waters of the Bay need to be assessed in order to make a complete determination of the removal processes in the Bay and the services they provide.