Long‐term nutrient addition increases respiration and nitrous oxide emissions in a New England salt marsh. Issue 10 (20th April 2018)

• Record Type: Journal Article
• Authors: Martin, Rose M.; Wigand, Cathleen; Elmstrom, Elizabeth; Lloret, Javier; Valiela, Ivan
• Is Part Of: Ecology and evolution. Volume 8:Issue 10(2018)
• Page Start: 4958
• Page End: 4966
• Publication Date: 2018-04-20
• Subjects: carbon dioxide -- cavity ringdown spectroscopy -- Great Sippewissett Marsh -- methane -- nitrous oxide -- nutrient enrichment; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.3955
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Salt marshes may act either as greenhouse gas (GHG) sources or sinks depending on hydrological conditions, vegetation communities, and nutrient availability. In recent decades, eutrophication has emerged as a major driver of change in salt marsh ecosystems. An ongoing fertilization experiment at the Great Sippewissett Marsh (Cape Cod, USA) allows for observation of the results of over four decades of nutrient addition. Here, nutrient enrichment stimulated changes to vegetation communities that, over time, have resulted in increased elevation of the marsh platform. In this study, we measured fluxes of carbon dioxide (CO2 ), methane (CH4 ) and nitrous oxide (N2 O) in dominant vegetation zones along elevation gradients of chronically fertilized (1, 572 kg N ha −1 year −1 ) and unfertilized (12 kg N ha −1 year −1 ) experimental plots at Great Sippewissett Marsh. Flux measurements were performed using darkened chambers to focus on community respiration and excluded photosynthetic CO2 uptake. We hypothesized that N‐replete conditions in fertilized plots would result in larger N2 O emissions relative to control plots and that higher elevations caused by nutrient enrichment would support increased CO2 and N2 O and decreased CH4 emissions due to the potential for more oxygen diffusion into sediment. Patterns of GHG emission supported our hypotheses. Fertilized plots were substantially larger sources of N2 O and had higher community respiration rates relative to control plots, due to large emissions of these GHGs at higher elevations. While CH4 emissions displayed a negative relationship with elevation, they were generally small across elevation gradients and nutrient enrichment treatments. Our results demonstrate that at decadal scales, vegetation community shifts and associated elevation changes driven by chronic eutrophication affect GHG emission from salt marshes. Results demonstrate the necessity of long‐term fertilization experiments to understand impacts of eutrophication on ecosystem function and have implications for how chronic eutrophication may impact the role that salt marshes play in sequestering C and N. Abstract : Coastal eutrophication is a globally widespread phenomenon that has been shown to alter coastal wetland structure and function. We tested effects of over four decades of nutrient enrichment on nitrous oxide and methane emissions and respiration rates from a salt marsh in Cape Cod, Massachusetts, USA. Our findings demonstrate substantially increased nitrous oxide emissions and respiration rates, likely resulting from changes to marsh topography that nutrient enrichment stimulated over time.