Anthropogenic nutrient loads and season variability drive high atmospheric N2O fluxes in a fragmented mangrove system

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.

Carbon and nitrogen dynamics in a tropical mangrove along the southwestern coast of India

“…Under favourable conditions, high N load accelerates the production of the most potent greenhouse gas N 2 O (Hershey et al, 2019;Nobrega et al, 2013Nobrega et al, , 2016Suarez-Abelenda et al, 2014) with potential effects on ecosystem services, contributing to atmospheric N 2 O budget. Hershey et al (2021) reported that in the MCW, dissolved organic (DON)…”

“…Hershey et al. (2021) reported that in the MCW, dissolved organic (DON) and inorganic nitrogen (DIN) concentration was in range with other higher polluted estuaries and acted as a source of atmospheric N 2 O (Hershey et al. 2021).…”

“…(2021) reported that in the MCW, dissolved organic (DON) and inorganic nitrogen (DIN) concentration was in range with other higher polluted estuaries and acted as a source of atmospheric N 2 O (Hershey et al. 2021). However, the role of MCW in contributing to atmospheric C concentration needs to be assessed and studied further.…”

“…A recent study also suggested that the MCW is an N-rich environment and acted as a net source of N 2 O to the atmosphere (Hershey et al, 2021). Little else is known about the C, N dynamics, its source signatures in the MCW, and considering the high deforestation rates and nutrient enrichment in Indian mangrove habitats, particularly along the Kerala coast, it is vital to understand the C, N dynamics and the influences impacting these dynamics.…”

“…(2021) suggest that the organic carbon burial rate of the MCW was high (193.97 g C m −2 yr −1 ) and contributed 35.73% of primary production that was calculated from litter fall production (5.43 t C ha −1 year −1 ). A recent study also suggested that the MCW is an N‐rich environment and acted as a net source of N 2 O to the atmosphere (Hershey et al., 2021). Little else is known about the C, N dynamics, its source signatures in the MCW, and considering the high deforestation rates and nutrient enrichment in Indian mangrove habitats, particularly along the Kerala coast, it is vital to understand the C, N dynamics and the influences impacting these dynamics.…”