Effective management of eutrophication in tidal ecosystems requires a thorough understanding of the dynamics of their responses to decreases in nutrient loading. We analyze a 34-year dataset on a shallow embayment of the tidal freshwater Potomac River, Gunston Cove, for long-term responses of ambient nutrient levels, light transparency measures, phytoplankton biomass, and coverage of submersed aquatic vegetation (SAV) to decreased nutrient loading. Point source loading of phosphorus, the nutrient most limiting primary production in this system, was greatly curtailed coincident with the study onset (1983/84) exhibiting a sharp decrease of 95% from peak loading levels. However, water column total phosphorus decreased much more slowly and gradually. Phytoplankton chlorophyll a did not show a distinctive decrease until 2000 and SAV responded strongly beginning in 2004. The habitat suitability model for SAV developed by Chesapeake Bay researchers was able to explain the recovery of SAV coverage based on data on light transparency and basin morphometry collected in this study. The study results were consistent with the alternative stable state theory with a sharp transition from a phytoplankton-dominated “turbid water” state to an SAV-dominated “clear water” state in a 2-year period from 2003 to 2005. The system eventually responded to nutrient load reductions, but the nonlinear and incomplete nature of this recovery and the two-decade delay illustrate the complexities of managing these systems.

中文翻译：

---

从富营养化中回收潮汐淡水河道：一项多年代研究

在潮汐生态系统中对富营养化进行有效管理，需要全面了解其对养分含量降低的反应动力学。我们对潮汐淡水波托马克河（Gunston Cove）的浅层堤坝进行了为期34年的数据集分析，以分析环境养分水平，透光性措施，浮游植物生物量以及淹没水生植被（SAV）对养分减少的长期响应加载中。磷的点源负荷是该系统中最主要的营养物质，在该研究开始时（1983/84），磷的峰值源水平急剧下降了95％，磷的源头负荷大大减少了。但是，水柱中的总磷下降的速度要缓慢得多。浮游植物叶绿素a直到2000年SAV才出现明显的下降，SAV在2004年开始反应强烈。切萨皮克湾研究人员开发的SAV栖息地适应性模型能够根据本研究收集的透光率和盆地形态数据解释SAV覆盖率的恢复。该研究结果与替代稳态理论相吻合，在2003年至2005年的2年中从浮游植物为主的“浑水”状态急剧转变为SAV为主的“净水”状态。系统最终做出了响应减少养分负荷，但是这种恢复的非线性和不完全性质以及两个十年的延迟说明了管理这些系统的复杂性。