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Land-use intensity increases benthic N₂O emissions across three sub-tropical estuaries

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Date
2022-08
Type
Journal Article
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.
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