Abstract
Fragmented mangroves are generally ignored in N2O flux studies. Here we report observations over the course of a year from the Mangalavanam coastal wetland in Southern India. The wetland is a fragmented mangrove stand close to a large urban centre with high anthropogenic nitrogen inputs. The study found the wetland was a net source of N2O to the atmosphere with fluxes ranging between 17.5 to 117.9 µmol m−2 day−1 which equated to high N2O saturations of between 697 and 1794%. The average dissolved inorganic nitrogen inputs (80.1 ± 18.1 µmol L−1) and N2O emissions (59.2 ± 30.0 µmol m−2 day−1) were highest during the monsoon season when the rainfall and associated river water inputs and terrestrial runoff were highest. The variation in N2O dynamics was shown to be driven by the changes in rainfall, water column depth, salinity, dissolved oxygen, carbon, and substrate nitrogen. The study suggests that fragmented/minor mangrove ecosystems subject to high human nutrient inputs may be a significant component of the global N2O budget.
Highlights
Fragmented mangroves are generally ignored in N2O flux studies
It is reported that 1% of reactive nitrogen entering estuaries are released as nitrous oxide (N2O) emissions1. N2O is a major contributor to stratospheric ozone depletion, has a lifetime of 118–131 years in the atmosphere[2] and has about 300 times greater global warming potential than carbon dioxide (CO2)3. N2O is produced as an intermediate product during the denitrification process and as a by-product during the nitrification process and it is consumed during complete denitrification of N 2O via dissimilatory reduction to N 24
In order to understand the contribution of fragmented/minor mangrove stands to atmospheric N 2O emissions, this study aimed to assess the Mangalavanam Coastal Wetland (MCW) a fragmented minor mangrove stand adjacent to the city of Kochi, India over a one year period incorporating a range of distinct seasons
Summary
Fragmented mangroves are generally ignored in N2O flux studies. Here we report observations over the course of a year from the Mangalavanam coastal wetland in Southern India. The study suggests that fragmented/minor mangrove ecosystems subject to high human nutrient inputs may be a significant component of the global N2O budget. It is estimated that the Ernakulum district in Kerala has 943 mangrove stands of which 880 (~ 93%) of them have an area less than 1 hectare The contribution of these smaller mangrove systems is often ignored and their role in global nutrient cycling has yet to be adequately determined. As most of these mangrove stands are generally observed near the vicinity of human settlements, they can be critically influenced by the N loading there. The study tested the relation between N substrates and N 2O fluxes with temperature, pH, DO, and C loading of the wetland to determine the drivers of N2O dynamics
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