Constraining nitrogen sources to a seagrass-dominated coastal embayment by using an isotope mass balance approach
Russell, D.G.; Kessler, A.J.; Wong, W.W.; van Oevelen, D.; Cook, P.L.M. (2022). Constraining nitrogen sources to a seagrass-dominated coastal embayment by using an isotope mass balance approach. Mar. Freshw. Res. 73(5): 703-709. https://dx.doi.org/10.1071/mf21320 In: Marine and Freshwater Research. CSIRO: East Melbourne. ISSN 1323-1650; e-ISSN 1448-6059, more |   |
| Keywords | | | Author keywords | 15N; denitrification; isotope; nitrogen; nitrogen budget; nitrogen fixation; seagrass; tidal flat |
| Authors | | Top | - Russell, D.G.
- Kessler, A.J.
- Wong, W.W.
| - van Oevelen, D., more
- Cook, P.L.M.
| |
| Abstract | Nitrogen (N) is often the key nutrient limiting primary production in coastal waters. Quantifying sources and sinks of N is therefore critical to understanding the factors that underpin the productivity of coastal ecosystems. Constraining nitrogen inputs can be difficult for some terms such as N fixation and marine exchange as a consequence of uncertainties associated with scaling and stochasticity. To help overcome these issues, we undertook a N budget incorporating an isotope and mass balance to constrain N sources in a large oligotrophic coastal embayment (Western Port, Australia). The total N input to Western Port was calculated to be 1400 Mg N year−1, which is remarkably consistent with previous estimates of sedimentation rates within the system. Catchment inputs, N fixation, marine sources and atmospheric deposition comprised 44, 28, 28 and 13% of N inputs respectively. Retention of marine-derived N equated to ~3 and ~10% of total N and NOx flushed through the system from the marine end-member. The relatively high contribution of N fixation compared with previous studies was most likely to be due to the high proportion of nutrient-limited intertidal sediments where N is mediated by seagrasses and sediment cyanobacteria. |
|
