Source of organic detritus and bivalve biomass influences nitrogen cycling and extracellular enzyme activity in estuary sediments

Author(s)
Josie Crawshaw, Theresa O'Meara, Candida Savage, Blair Thomson, Federico Baltar, Simon F. Thrush
Abstract

In aquatic ecosystems, natural processes that remove nitrogen from the biologically available pool (e.g. denitrification) have been intensively studied as an ecosystem function that reduces eutrophication. The quantity of sediment organic matter is a key driver of denitrification with percent organic content positively related to rates of nitrogen removal; however, few studies have investigated the influence of the quality of organic matter on nitrogen cycling in estuarine sediments despite shifts in primary producers with eutrophication. This laboratory study using intact benthic communities investigates the influence of various organic detritus sources, which vary in their C:N ratio, on nitrogen gas (N-2) and solute fluxes and extracellular enzyme activity in estuarine sediments. A custom-built tank with a removable front plate was used with a planar optode film to image sediment oxygenation. Mangrove leaf detritus significantly increased the net N-2 production in sediments, while the deposition of other detrital sources and control sediments produced net N-2 consumption. Sulfatase activity was significantly reduced in the mangrove leaves and seagrass treatments, suggesting alteration of heterotrophic microbial activity with reducing oxygen conditions. Leucine aminopeptidase activity, indicating nitrogen cycling, was reduced in all treatments, suggesting the organic detritus provided a nitrogen supplement or reduced the activity of extracellular enzymes producing microbes. Bivalve biomass increased net nitrogen gas fluxes in some treatments. Our results indicate different detrital sources may have varying impacts on the removal of bioavailable nitrogen through denitrification and show that feedbacks in biogeochemical cycles may occur with changes in organic detrital source pools.

Organisation(s)
Department of Limnology and Bio-Oceanography
Journal
Biogeochemistry: an international journal
No. of pages
21
ISSN
0168-2563
DOI
https://doi.org/10.1007/s10533-019-00608-y
Publication date
10-2019
Publication status
Published
Peer reviewed
Yes
Austrian Fields of Science 2012
106021 Marine biology
Keywords
Denitrification, Nitrogen fixation, Organic detritus, Extracellular enzyme activity, Bioturbation, Bivalve, Planar optode, Sediment, DISSIMILATORY NITRATE REDUCTION, AMMONIUM DNRA, ENVIRONMENTAL CONTROLS, INORGANIC NITROGEN, AQUATIC ECOSYSTEMS, SEASONAL-VARIATION, CONCEPTUAL-MODEL, BENTHIC HABITATS, OXIDE PRODUCTION, NEW-ZEALAND
Portal url
https://ucris.univie.ac.at/portal/en/publications/source-of-organic-detritus-and-bivalve-biomass-influences-nitrogen-cycling-and-extracellular-enzyme-activity-in-estuary-sediments(1ef90934-38ca-4a42-b758-012eb04921a2).html