Land-Use Intensity Increases Benthic N2O Emissions Across Three Sub-Tropical Estuaries

Abstract

Estuaries play an important role in regulating nitrous oxide (N2O) fluxes to the atmosphere, but little is known about how catchment land-use changes influence benthic N2O cycling. We measured seasonal benthic N2O fluxes and constructed N2O budgets in three sub-tropical estuaries draining catchments with contrasting levels of land-use intensity. Benthic habitats were a net N2O sink in the minimally impacted Noosa River Estuary (−287 nmol m−2 h−1) and a net source of N2O in the highly impacted Brisbane River Estuary (126 nmol m−2 h−1). Vegetated habitats can act as an important sink of N2O with uptakes of −286 and −35 nmol m−2 h−1 in the Noosa and Maroochy River Estuaries, respectively. Benthic N2O fluxes were significantly correlated with benthic NO3− fluxes, suggesting NO3− availability was an important control on benthic N2O fluxes. Combining benthic flux data with surface water N2O emissions measurements showed that increased benthic N2O fluxes helped drive increasing water–air N2O emissions over the land-use intensity gradient. Overall, our results show that land-use driven changes to both the diversity and sediment composition of benthic habitats play an important role in regulating N2O dynamics in estuarine ecosystems. This highlights that both sediment quality and nitrogen loading need to be considered in order to reduce emissions of greenhouse gases in the coastal ecosystems.