Centre for Tropical Water and Aquatic Ecosystem Research, Catchment to Reef Research Group, James Cook University, Townsville, QLD 4811, Australia.
Centre for Tropical Water and Aquatic Ecosystem Research, Catchment to Reef Research Group, James Cook University, Townsville, QLD 4811, Australia; Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, Suffolk, UK.
J Environ Manage. 2018 May 1;213:451-466. doi: 10.1016/j.jenvman.2018.02.028.
Optically active water quality components (OAC) transported by flood plumes to nearshore marine environments affect light levels. The definition of minimum OAC concentrations that must be maintained to sustain sufficient light levels for conservation of light-dependant coastal ecosystems exposed to flood waters is necessary to guide management actions in adjacent catchments. In this study, a framework for defining OAC target concentrations using empirical light attenuation models is proposed and applied to the Wet Tropics region of the Great Barrier Reef (GBR) (Queensland, Australia). This framework comprises several steps: (i) light attenuation (Kd(PAR)) profiles and OAC measurements, including coloured dissolved organic matter (CDOM), chlorophyll-a (Chl-a) and suspended particulate matter (SPM) concentrations collected in flood waters; (ii) empirical light attenuation models used to define the contribution of CDOM, Chl-a and SPM to the light attenuation, and; (iii) translation of empirical models into manageable OAC target concentrations specific for wet season conditions. Results showed that (i) Kd(PAR) variability in the Wet Tropics flood waters is driven primarily by SPM and CDOM, with a lower contribution from Chl-a (r2 = 0.5, p < 0.01), (ii) the relative contributions of each OAC varies across the different water bodies existing along flood waters and strongest Kd(PAR) predictions were achieved when the in-situ data were clustered into water bodies with similar satellite-derived colour characteristics ('brownish flood waters', r2 = 0.8, p < 0.01, 'greenish flood waters', r2 = 0.5, p < 0.01), and (iii) that Kd(PAR) simulations are sensitive to the angular distribution of the light field in the clearest flood water bodies. Empirical models developed were used to translate regional light guidelines (established for the GBR) into manageable OAC target concentrations. Preliminary results suggested that a 90th percentile SPM concentration of 11.4 mg L should be maintained during the wet season to sustain favourable light levels for Wet Tropics coral reefs and seagrass ecosystems exposed to 'brownish' flood waters. Additional data will be collected to validate the light attenuation models and the wet season target concentration which in future will be incorporated into wider catchment modelling efforts to improve coastal water quality in the Wet Tropics and the GBR.
带有洪水羽流的光学活性水质成分 (OAC) 会影响光线水平，这些成分被输送到近岸海洋环境中。为了指导相邻集水区的管理行动，有必要确定维持暴露于洪水的光依赖沿海生态系统的足够光照水平所需的最小 OAC 浓度。在这项研究中，提出了一种使用经验光衰减模型定义 OAC 目标浓度的框架，并将其应用于大堡礁（GBR）（澳大利亚昆士兰州）的湿热带地区。该框架包括几个步骤：(i) 在洪水水中收集光衰减 (Kd(PAR)) 剖面和 OAC 测量值，包括有色溶解有机物 (CDOM)、叶绿素-a (Chl-a) 和悬浮颗粒物 (SPM) 浓度；(ii) 用于定义 CDOM、Chl-a 和 SPM 对光衰减贡献的经验光衰减模型；(iii) 将经验模型转换为针对湿季条件的可管理的 OAC 目标浓度。结果表明：(i) 湿热带洪水水中的 Kd(PAR) 变化主要由 SPM 和 CDOM 驱动，Chl-a 的贡献较低 (r2 = 0.5，p < 0.01)；(ii) 每个 OAC 的相对贡献因沿洪水存在的不同水体而异，当将原位数据聚类到具有相似卫星衍生颜色特征的水体中时，Kd(PAR) 的预测最为准确（“棕色洪水”，r2 = 0.8，p < 0.01，“绿色洪水”，r2 = 0.5，p < 0.01）；(iii) Kd(PAR) 模拟对最清澈洪水体中光场的角分布敏感。开发的经验模型用于将区域光照指南（为 GBR 制定）转换为可管理的 OAC 目标浓度。初步结果表明，在湿季应将 90 百分位数 SPM 浓度维持在 11.4mg/L 以维持暴露于“棕色”洪水的湿热带珊瑚礁和海草生态系统的有利光照水平。将收集更多数据来验证光衰减模型和湿季目标浓度，这些模型和浓度将在未来纳入更广泛的集水区建模工作中，以改善湿热带和大堡礁的沿海水质。
