Newport Bay water quality and eelgrass bed stability

Eelgrass (Zostera spp.) is a marine flowering plant found in coastal regions worldwide and provides critical habitat, nutrient cycling, and shoreline buffering to ecosystems. Populations are declining in many of these regions due to the negative impacts poor water quality has on light availability and photosynthesis. The Lower Newport Bay (LNB) in Southern California is a heavily developed recreational harbor and estuarine habitat supporting species from varying taxa, including eelgrass. To understand the impact water quality has on eelgrass persistence in LNB, we selected four sites with long-term stable eelgrass populations and four sites with transitional eelgrass populations to collect weekly measurements of weather conditions, light availability, and water quality parameters. Through repeated measure ANOVAs using date as a between factor, we found that stable eelgrass beds had significantly higher light availability, dissolved oxygen concentrations, and bluer water on the Forel-Ule scale. We fit a linear mixed effect model using the log of turbidity, log of chlorophyll, and log of eelgrass bed depth as fixed effects with depth nested in site as random effects, found it to be the best fit model using AIC (Akaike Information Criterion), and found that depth and turbidity are significant predictors of light availability. These results indicate that turbidity, rather than chlorophyll concentration, has a greater impact on light availability and eelgrass health in LNB. This pilot project provides a foundation for future research and recommendations for eelgrass conservation in LNB, and suggests that runoff contributing to higher turbidity may be a leading cause of unhealthy eelgrass beds.

鳗草（Zostera spp.）是一种广泛分布于全球沿海区域的海洋显花植物，可为生态系统提供关键栖息地、参与营养循环并起到岸线缓冲作用。当前全球诸多沿海区域的鳗草种群因水质不佳对光照可利用性及光合作用产生的负面影响而持续衰退。美国南加州的下纽波特湾（Lower Newport Bay, LNB）是一处开发程度较高的休闲港与河口栖息地，孕育了包括鳗草在内的多个类群的物种。为探明水质对LNB区域鳗草存续的影响，我们选取了4个拥有长期稳定鳗草种群的样地，以及4个处于过渡状态的鳗草种群样地，每周采集气象条件、光照可利用性及水质参数的相关数据。通过以采样日期为组间因子的重复测量方差分析，我们发现稳定鳗草床的光照可利用性、溶解氧浓度均显著更高，且在福尔-尤勒（Forel-Ule）色度标尺下水体颜色更偏蓝。我们构建了以浊度对数、叶绿素对数及鳗草床水深对数为固定效应，以嵌套于样地的水深为随机效应的线性混合效应模型；通过赤池信息准则（Akaike Information Criterion, AIC）筛选，该模型为最优拟合模型，且结果显示水深与浊度是光照可利用性的显著预测因子。本研究结果表明，在LNB区域，相较于叶绿素浓度，浊度对光照可利用性及鳗草健康的影响更为显著。本试点项目为后续研究奠定了基础，并为LNB区域的鳗草保护提供了建议，同时指出导致浊度升高的径流可能是鳗草床健康状况不佳的主要诱因。