Benthic metabolism and nitrogen dynamics in an urbanised tidal creek: domination of DNRA over denitrificDunnation as a nitrate reduction pathway

Dunn, Ryan J.K., Robertson, David, Teasdale, Peter R., Waltham, Nathan J., and Welsh, David T. (2013) Benthic metabolism and nitrogen dynamics in an urbanised tidal creek: domination of DNRA over denitrificDunnation as a nitrate reduction pathway. Estuarine, Coastal and Shelf Science , 131. pp. 271-281.

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Abstract

Benthic oxygen and nutrient fluxes and nitrate reduction rates were determined seasonally under light and dark conditions at three sites in a micro-tidal creek within an urbanised catchment (Saltwater Creek, Australia). It was hypothesized that stormwater inputs of organic matter and inorganic nitrogen would stimulate rates of benthic metabolism and nutrient recycling and preferentially stimulate dissimilatory nitrate reduction to ammonium (DNRA) over denitrification as a pathway for nitrate reduction. Stormwaters greatly influenced water column dissolved inorganic nitrogen (DIN) and suspended solids concentrations with values following a large rainfall event being 5–20-fold greater than during the preceding dry period. Seasonally, maximum and minimum water column total dissolved nitrogen (TDN) and DIN concentrations occurred in the summer (wet) and winter (dry) seasons. Creek sediments were highly heterotrophic throughout the year, and strong sinks for oxygen, and large sources of dissolved organic and inorganic nitrogen during both light and dark incubations, although micro-phytobenthos (MPB) significantly decreased oxygen consumption and N-effluxes during light incubations due to photosynthetic oxygen production and photoassimilation of nutrients. Benthic denitrification rates ranged from 3.5 to 17.7 μmol N m² h⁻¹, denitrification efficiencies were low (<1–15%) and denitrification was a minor process compared to DNRA, which accounted for ~75% of total nitrate reduction.

Overall, due to the low denitrification efficiencies and high rates of N-regeneration, Saltwater Creek sediments would tend to increase rather than reduce dissolved nutrient loads to the downstream Gold Coast Broadwater and Moreton Bay systems. This may be especially true during wet periods when increased inputs of particulate organic nitrogen (PON) and suspended solids could respectively enhance rates of N-regeneration and decrease light availability to MPB, reducing their capacity to ameliorate N-effluxes through photoassimilation.

Item ID: 29602
Item Type: Article (Refereed Research - C1)
Keywords: benthic metabolism, stormwater impacts, nutrient fluxes, denitrification, dissimilatory nitrate reduction to ammonium, sub-tropical, Saltwater Creek
ISSN: 1096-0015
Funders: Gold Coast City Council Catchment Management Unit, Griffith Centre for Coastal Management, Griffith University
Date Deposited: 25 Mar 2014 02:19
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050206 Environmental Monitoring @ 50%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050204 Environmental Impact Assessment @ 50%
SEO Codes: 96 ENVIRONMENT > 9609 Land and Water Management > 960901 Antarctic and Sub-Antarctic Land and Water Management @ 50%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 50%
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