Grinham Alistair, Costantini Tony, Deering Nathaniel, Jackson Cameron, Klein Carissa, Lovelock Catherine, Pandolfi John, Eyal Gal, Linde Michael, Dunbabin Matthew, Duncan Brendon, Hutley Nicholas, Byrne Ilha, Wilson Craig, Albert Simon
School of Civil Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia.
Urban Utilities, Brisbane, QLD 4001, Australia.
Sci Total Environ. 2024 Mar 25;918:170646. doi: 10.1016/j.scitotenv.2024.170646. Epub 2024 Feb 5.
Major floods pose a severe threat to coastal receiving environments, negatively impacting environmental health and ecosystem services through direct smothering with sediment and nutrient loading. This study examined the short and long-term impacts of the February 2022 major flood event on mud extent and sediment nitrogen flux in Moreton Bay (the Bay), a large, sub-tropical embayment in Southeast Queensland, Australia. Short-term impacts were assessed three days after the flood peak by sampling surface water at 47 sites in the direction of the predominant circulation pattern. Longer-term impacts were assessed by undertaking an intensive sediment survey of 223 sites and a nutrient flux experiment using sediment core incubations to simulate calm and resuspension conditions for the four key sediment classes. Short-term impacts revealed elevated turbidity levels extended across the Bay but were highest at the Brisbane River mouth, ammonium concentrations varied inversely with surface turbidity, whereas nitrate concentrates closely tracked surface turbidity. The sediment survey confirmed fine sediment deposition across 98 % of the Bay. Porewater within the upper 10 cm contained a standing pool of 280 t of ammonium, with concentrations more than three orders of magnitude higher than overlying surface waters. The nutrient flux experiment revealed an order of magnitude higher sediment ammonium flux rate in the sandy mud sediment class compared to the other sediment classes; and for simulated resuspension conditions compared to calm conditions for sand, muddy sand, and mud sediment classes. Scaling across the whole Bay, we estimated a mean annual sediment flux of 17,700 t/year ammonium, with a range of 13,500 to 21,900 t/year. Delivery of fine sediments by major floods over the last 50 years now impact >98 % of the benthic zone and provide a major loading pathway of available nitrogen to surface waters of Moreton Bay; representing a significant threat to ecosystem health.
重大洪水对沿海接收环境构成严重威胁，通过沉积物直接覆盖和养分负荷对环境健康和生态系统服务产生负面影响。本研究调查了2022年2月重大洪水事件对莫顿湾（该海湾）泥质范围和沉积物氮通量的短期和长期影响，莫顿湾是澳大利亚昆士兰州东南部一个大型亚热带海湾。在洪水峰值过后三天，通过沿主要环流模式方向在47个地点采集地表水样本，评估短期影响。通过对223个地点进行密集沉积物调查以及开展养分通量实验来评估长期影响，该实验利用沉积物柱培养来模拟四种关键沉积物类型的平静和再悬浮条件。短期影响显示，整个海湾的浊度水平升高，但在布里斯班河口最高，铵浓度与表面浊度呈反比，而硝酸盐浓度则与表面浊度密切相关。沉积物调查证实，海湾98%的区域有细颗粒沉积物沉积。上部10厘米内的孔隙水中含有280吨铵的存量，其浓度比上覆地表水高出三个数量级以上。养分通量实验表明，与其他沉积物类型相比，砂质泥沉积物类型中的沉积物铵通量率高出一个数量级；与砂、泥质砂和泥沉积物类型的平静条件相比，模拟再悬浮条件下的通量率更高。对整个海湾进行推算，我们估计铵的年平均沉积物通量为17700吨/年，范围为13500至21900吨/年。过去50年里，重大洪水带来的细颗粒沉积物如今影响了超过98%的底栖区域，并为莫顿湾地表水提供了主要的有效氮负荷途径；这对生态系统健康构成了重大威胁。
