School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, 2052, Australia.
School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, 2052, Australia; Fisheries Research, New South Wales Department of Primary Industries, Huskisson, NSW, 2540, Australia.
Water Res. 2018 Nov 15;145:757-768. doi: 10.1016/j.watres.2018.08.071. Epub 2018 Sep 1.
Desalination is an increasingly common method of meeting potable water demands, but the associated ecological risks are not well understood. Seawater desalination plants discharge large volumes of hypersaline brine directly into the ocean, raising concerns about potential impacts to marine life. In order to reduce impacts of brine, newer desalination outfalls are often fitted with high-pressure diffusers that discharge brine at high velocity into the water column, increasing the mixing and dilution of brine with ocean water. However, there are few published studies of marine impacts of desalination brine, and no well replicated before-after designs. Here we report a six-year study testing for impacts and subsequent recovery of sessile marine invertebrate recruitment near a desalination outfall with high-pressure diffusers. We used a Multiple Before-After-Control-Impact (MBACI) design to test for impacts and recovery at two distances (30 m and 100 m) from a 250 ML/day plant outfall, as well as a gradient design to test the strength of impacts relative to distance from the outfall. The diffusers achieved the target of less than 1 psμ salinity difference to surrounding ambient waters within 100 m of the discharge outfall, but sessile invertebrates were nonetheless impacted. Polychaetes, bryozoans and sponges reduced in cover as far as 100 m from the outfall, while barnacles showed the opposite pattern and were more abundant near the discharging outfall. Ecological impacts were disproportionate to the relatively minor change in salinity (∼1 psμ), suggesting a mechanism other than salinity. We propose that impacts were primarily driven by changes in hydrodynamics caused by the diffusers, such as higher near-bed flow away from the outfall. This is consistent with flow preferences of various taxonomic groups, which differ due to differences in settlement and feeding abilities. High-pressure diffusers designed to reduce impacts of hypersalinity may inadvertently cause impacts through hydrodynamics, leading to a trade-off in minimizing combined salinity and hydrodynamic stress. This study provides the first before-after test of ecological impacts of desalination brine on sessile marine communities, and rare insight into mechanisms behind impacts of a growing form of human disturbance.
海水淡化是满足饮用水需求的一种越来越常见的方法，但相关的生态风险还没有得到很好的理解。海水淡化厂将大量高盐度卤水直接排入海洋，这引发了对海洋生物潜在影响的担忧。为了减少卤水的影响，新型海水淡化排放口通常配备高压扩散器，以高速将卤水排入水柱中，增加卤水与海水的混合和稀释。然而，关于海水淡化卤水对海洋的影响，发表的研究很少，也没有经过很好的复制前后设计。在这里，我们报告了一项为期六年的研究，该研究测试了高压扩散器海水淡化排放口附近附着海洋无脊椎动物的繁殖的影响及其随后的恢复情况。我们使用多前-后-对照-影响（MBACI）设计来测试距离 250 ML/天工厂排放口 30 米和 100 米处的影响和恢复情况，以及梯度设计来测试距离排放口的距离与影响强度的关系。扩散器在距离排放口 100 米范围内实现了将盐度差控制在小于 1 psμ 的目标，但附着无脊椎动物仍然受到影响。多毛类、苔藓动物和海绵的覆盖率在距离排放口 100 米处减少，而藤壶则呈现相反的模式，在排放口附近更为丰富。生态影响与盐度的相对较小变化（约 1 psμ）不成比例，这表明存在除盐度以外的其他机制。我们提出，影响主要是由扩散器引起的水动力变化造成的，例如远离排放口的近床流速增加。这与各种分类群的流动偏好一致，这些偏好因定居和摄食能力的不同而不同。旨在减少高盐度影响的高压扩散器可能会通过水动力造成影响，从而在最小化盐度和水动力应激的综合影响方面产生权衡。本研究首次对海水淡化卤水对附着海洋生物群落的生态影响进行了前后测试，并罕见地了解了人类日益增长的干扰形式影响背后的机制。
