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Ocean acidification modifies the impact of warming on sediment nitrogen recycling and assimilation by enhancing the benthic microbial loop
Journal article   Peer reviewed

Ocean acidification modifies the impact of warming on sediment nitrogen recycling and assimilation by enhancing the benthic microbial loop

Michelle N. Simone, Joanne M. Oakes, Kai G. Schulz and Bradley D. Eyre
Marine ecology. Progress series (Halstenbek), Vol.681, pp.53-69
06/01/2022
DOI: https://doi.org/10.3354/meps13913

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Abstract

Ecology Environmental Sciences & Ecology Life Sciences & Biomedicine Marine & Freshwater Biology Oceanography Physical Sciences Science & Technology Ocean acidification Marine sediments Climate change Microphytobenthos Estuaries Nitrogen cycling
Nitrogen that has been recycled in the benthos supports high rates of primary and secondary production in estuaries. However, little is known about the effect of future climate on benthic nitrogen recycling and assimilation. An ex situ core incubation was used to assess the impact of combinations of warming (8 degrees C range) and ocean acidification (OA) (i.e. increased pCO(2) and decreased pH) on ammonium (NH4+) and nitrate/nitrite (NOx) fluxes and N-15-nitrate assimilation in shallow unvegetated estuarine sediments. Dissolved inorganic nitrogen (DIN = NH4+ + NOx) fluxes were significantly affected by the interaction of warming and OA, highlighting the importance of considering combined stressor treatments when investigating ecosystem responses to future climates. Warming alone increased DIN efflux from the sediments. At current mean ambient temperatures (23 degrees C) and below (Delta-3 degrees C), OA significantly increased DIN effluxes, but there was little to no effect of OA on DIN fluxes at warmer temperatures (Delta+3 degrees C and Delta+5 degrees C). OA reduced the N-15 assimilation/retention of the sediments across all temperatures, suggesting that nitrogen retention in bacterial biomass was reduced, despite OA also increasing primary productivity. As such, under the projected future climate of similar to 3 degrees C warming and doubling of pCO(2) (similar to 1000 mu atm), unvegetated estuarine sediments are likely to have a more rapid turnover of DIN driven by greater microphytobenthos production and recycling.

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