Spatial variation in rates of benthic denitrification and environmental controls in four New Zealand estuaries

Abstract

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 556:59-77 (2016) - DOI: https://doi.org/10.3354/meps11865 Spatial variation in rates of benthic denitrification and environmental controls in four New Zealand estuaries Catherine Gongol1, Candida Savage1,2,* 1Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand 2Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa *Corresponding author: candida.savage@otago.ac.nz ABSTRACT: Denitrification plays a key role in global biogeochemical cycles as the main nitrogen (N) loss process that limits availability of N to primary producers. This study presents the first measurements of sediment denitrification rates for New Zealand estuaries. Spatially explicit rates of direct denitrification (Dw) and coupled nitrification-denitrification (Dn) were quantified using the isotope pairing method in 4 oligotrophic to moderately nutrient-enriched estuaries on the South Island, New Zealand (Avon-Heathcote, Waikouaiti, Tokomairiro, Tautuku). Coupled nitrification-denitrification dominated (>86%), with most sites having low dissolved inorganic nitrogen (DIN) concentrations (<30 µmol l-1). Rates of total denitrification (Dtot) and Dn were negatively correlated with percent sand and positively related to oxygen penetration depth (OPD). Surface sediment chlorophyll a concentrations and percent carbon (%C) were also identified as significant predictors of Dtot and Dn in the single-factor models. By contrast, Dw was the main nitrogen removal process at moderately nutrient-enriched sites and was positively related to DIN concentrations in the water column and negatively correlated with percent sand. OPD and %C were also identified as significant predictors of Dw. While Dw was positively related to DIN concentrations, overall rates of denitrification were not, demonstrating that predictive relationships between N loading and removal are not always possible in oligotrophic estuaries. Our findings demonstrate the importance of grain size as a driver of denitrification rates in estuaries and imply that an increase in fine-grained sediments from land-use intensification may alter rates of N removal in estuaries through complex direct and indirect processes. KEY WORDS: Denitrification · Estuaries · New Zealand · Nitrogen · Benthic · Sediment grain size · Isotope pairing method · Oxygen flux Full text in pdf format PreviousNextCite this article as: Gongol C, Savage C, (2016) Spatial variation in rates of benthic denitrification and environmental controls in four New Zealand estuaries. Mar Ecol Prog Ser 556:59-77. https://doi.org/10.3354/meps11865 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 556. Online publication date: September 08, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.