Conference presentation
Nitrogen reactivity gradients in estuaries under increasing anthropogenic stress
ASLO Aquatic Sciences Meeting (Honolulu, USA, 26/02/2017 - 03/03/2017)
01/03/2017
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Abstract
Increases in nitrogen (N) inputs to streams due to intensifying land-use raises concerns about the health of downstream coastal ecosystems. Information on dissolved organic N (DON) sources and sinks within transitional estuarine environments are needed to quantify terrestrial N exports, as this is both the largest and least studied portion of the aquatic N pool. Here we propose an isotope mass balance method to test the strength of connectivity between DON and more mobile inorganic N (DIN) pools. This is based on the knowledge that, in the absence of new source inputs, nutrient spiralling (N uptake and subsequent mineralisation) moves δ15N-DIN (δ15N-NO3- + δ15N-NH4+ + δ15N-N2O) closer to δ15N-DON over flow paths. This framework was used to assess changes in DON between three sub-tropical estuaries in Queensland, Australia that span a catchment land-use gradient from low (native vegetation) to moderate (low intensity agriculture) to intensive (urban and high intensity agriculture). The δ15N of particulate nitrogen (PN), DON, NO3-, NH4+, and nitrous oxide (N2O) at 18 sites over the salinity gradient from the marine mouth to the freshwater source were measured in Mar-16 (warm, wet) and Oct-16 (cool, dry). DON and DIN were relatively constant (300 – 250 µg DON l-1; 24 – 28 µg NO3--N l-1) over the salinity gradient in ‘low’, but declined steeply from source (880 µg DON l-1; 140 µg NO3--N) to mouth (180 µg DON l-1; 9.2 µg NO3--N l-1) in ‘moderate’. In contrast, DON, but not DIN, spiked up to ~1600 µg l-1 multiple times over the ‘intensive’ salinity gradient. The magnitude of these differences suggests that land-use change alters the controls on DON fluxes through estuaries.
Details
- Title
- Nitrogen reactivity gradients in estuaries under increasing anthropogenic stress
- Creators
- Naomi S Wells - Southern Cross UniversityDirk Erler - Southern Cross UniversityDamien Maher - Southern Cross UniversityBradley Eyre - Southern Cross University
- Conference
- ASLO Aquatic Sciences Meeting (Honolulu, USA, 26/02/2017 - 03/03/2017)
- Identifiers
- 991012845997302368
- Academic Unit
- Faculty of Science and Engineering; School of Environment, Science and Engineering; Science
- Resource Type
- Conference presentation