Water Studies, School of Chemistry, Monash University, Clayton, Australia.
School of Earth, Atmopsheric and Environment, Monash University, Clayton, Australia.
Sci Total Environ. 2022 Feb 1;806(Pt 1):150408. doi: 10.1016/j.scitotenv.2021.150408. Epub 2021 Sep 20.
The identification of nitrogen sources and cycling processes is critical to the management of nitrogen pollution. Here, we used both stable (δN-NO, δO-NO, δN-NH) and radiogenic (Rn) isotopes together with nitrogen concentrations to evaluate the relative importance of point (i.e. sewage) and diffuse sources (i.e. agricultural-derived NO from groundwater, drains and creeks) in driving nitrogen dynamic in a shallow coastal embayment, Port Phillip Bay (PPB) in Victoria, Australia. This study is an exemplar of nitrogen-limited coastal systems around the world where nitrogen contamination is prevalent and where constraining it may be challenging. In addition to surrounding land use, we found that the distributions of NO and NH in the bay were closely linked to the presence of drift algae. Highest NO and NH concentrations were 315 μmol L and 2140 μmol L, respectively. Based on the isotopic signatures of NO (δN: 0.17 to 21‰; δO: 3 to 26‰) and NH (δN: 30 to 39‰) in PPB, the high nitrogen concentrations were attributed to three major sources which varied between winter and summer; (1) nitrified sewage effluent and drift algae derived NH mainly during winter, (2) NO mixture from atmospheric deposition, drains and creeks predominantly observed during summer and (3) groundwater and sewage derived NO during both surveys. The isotopic composition of NO also suggested the removal of agriculture-derived NO through denitrification was prevalent during transport. This study highlights the role of terrestrial-coastal interactions on nitrogen dynamics and illustrates the importance of submarine groundwater discharge as a prominent pathway of diffuse NO inputs. Quantifying the relative contributions of multiple NO input pathways, however, require more extensive efforts and is an important avenue for future research.
氮源的识别和循环过程对氮污染的管理至关重要。在这里，我们使用稳定同位素（δN-NO、δO-NO、δN-NH）和放射性同位素（Rn）以及氮浓度来评估点源（即污水）和弥散源（即地下水、排水渠和小溪中农业来源的 NO）在驱动澳大利亚维多利亚州菲利普港（PPB）浅海岸湾氮动态方面的相对重要性。本研究是一个具有代表性的氮限制沿海系统，在全球范围内，氮污染普遍存在，限制氮污染可能具有挑战性。除了周围的土地利用情况外，我们发现海湾中 NO 和 NH 的分布与漂移藻类的存在密切相关。最高的 NO 和 NH 浓度分别为 315 μmol L 和 2140 μmol L。根据 PPB 中 NO（δN：0.17 至 21‰；δO：3 至 26‰）和 NH（δN：30 至 39‰）的同位素特征，高氮浓度归因于三个主要来源，这些来源在冬季和夏季之间有所不同；（1）硝化污水和漂移藻类衍生的 NH，主要在冬季产生，（2）夏季主要来自大气沉降、排水渠和小溪的 NO 混合物，（3）冬季和夏季均来自地下水和污水的 NO。NO 的同位素组成还表明，农业来源的 NO 通过反硝化去除在运输过程中很普遍。本研究强调了陆地-海岸相互作用对氮动态的作用，并说明了海底地下水排放作为弥散 NO 输入的主要途径的重要性。然而，量化多种 NO 输入途径的相对贡献需要更多的努力，这是未来研究的一个重要方向。
