Nutrient limitation of phytoplankton in three tributaries of Chesapeake Bay: Detecting responses following nutrient reductions. (1st November 2022)

• Record Type: Journal Article
• Authors: Zhang, Qian; Fisher, Thomas R.; Buchanan, Claire; Gustafson, Anne B.; Karrh, Renee R.; Murphy, Rebecca R.; Testa, Jeremy M.; Tian, Richard; Tango, Peter J.
• Is Part Of: Water research. Volume 226(2022)
• Publication Date: 2022-11-01
• Subjects: Nutrient limitation -- Phytoplankton -- Water quality -- Long-term monitoring -- Nutrient management -- Ecosystem recovery; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.119099
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Nutrient limitation in three tributaries of Chesapeake Bay was categorized using bioassay observations. CART models were developed to predict bioassay results for each tributary station using concurrent water quality data. CART models satisfactorily reproduced bioassay-based nutrient limitation in 1990–2003. CART predictions show enhanced nutrient limitation at most stations from 1985–1994 to 2011–2020. These results show detectable ecosystem recovery following nutrient load reductions. Abstract: 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. Graphical abstract: Image, graphical abstract