Zhang Qian, Fisher Thomas R, Buchanan Claire, Gustafson Anne B, Karrh Renee R, Murphy Rebecca R, Testa Jeremy M, Tian Richard, Tango Peter J
University of Maryland Center for Environmental Science / Chesapeake Bay Program, 1750 Forest Drive, Suite 130, Annapolis, MD 21401, USA.
Horn Point Laboratory, University of Maryland Center for Environmental Science, 2020 Horns Point Rd, Cambridge, MD 21613, USA.
Water Res. 2022 Nov 1;226:119099. doi: 10.1016/j.watres.2022.119099. Epub 2022 Sep 10.
Many coastal ecosystems suffer from eutrophication, algal blooms, and dead zones due to excessive anthropogenic inputs of nitrogen (N) and phosphorus (P). This has led to regional restoration efforts that focus on managing watershed loads of N and P. In Chesapeake Bay, the largest estuary in the United States, dual nutrient reductions of N and P have been pursued since the 1980s. However, it remains unclear whether nutrient limitation - an indicator of restriction of algal growth by supplies of N and P - has changed in the tributaries of Chesapeake Bay following decades of reduction efforts. Toward that end, we analyzed historical data from nutrient-addition bioassay experiments and data from the Chesapeake Bay long-term water-quality monitoring program for six stations in three tidal tributaries (i.e., Patuxent, Potomac, and Choptank Rivers). Classification and regression tree (CART) models were developed using concurrent collections of water-quality parameters for each bioassay monitoring location during 1990-2003, which satisfactorily predicted the bioassay-based measures of nutrient limitation (classification accuracy = 96%). Predictions from the CART models using water-quality monitoring data showed enhanced nutrient limitation over the period of 1985-2020 at four of the six stations, including the downstream station in each of these three tributaries. These results indicate detectable, long-term water-quality improvements in the tidal tributaries. Overall, this research provides a new analytical tool for detecting signs of ecosystem recovery following nutrient reductions. More broadly, the approach can be adapted to other waterbodies with long-term bioassays and water-quality data sets to detect ecosystem recovery.
由于氮（N）和磷（P）的人为输入过多，许多沿海生态系统受到富营养化、藻华和死区的影响。这导致了区域恢复工作，重点是管理流域的氮和磷负荷。在美国最大的河口切萨皮克湾，自20世纪80年代以来一直在努力减少氮和磷这两种营养物质。然而，经过几十年的减排努力后，尚不清楚营养限制（即氮和磷供应对藻类生长的限制指标）在切萨皮克湾的支流中是否发生了变化。为此，我们分析了营养添加生物测定实验的历史数据以及切萨皮克湾长期水质监测项目在三条潮汐支流（即帕塔克森特河、波托马克河和乔普坦克河）六个站点的数据。利用1990 - 2003年期间每个生物测定监测地点同时收集的水质参数，开发了分类和回归树（CART）模型，该模型令人满意地预测了基于生物测定的营养限制指标（分类准确率 = 96%）。使用水质监测数据的CART模型预测显示，在1985 - 2020年期间，六个站点中的四个站点，包括这三条支流中每个支流的下游站点，营养限制有所增强。这些结果表明潮汐支流的水质有可检测到的长期改善。总体而言，这项研究为检测营养物质减少后生态系统恢复的迹象提供了一种新的分析工具。更广泛地说，该方法可适用于其他有长期生物测定和水质数据集的水体，以检测生态系统恢复情况。
