Original Research ARTICLE
Chesapeake Bay Dissolved Oxygen Criterion Attainment Deficit: Three Decades of Temporal and Spatial Patterns
- 1University of Maryland Center for Environmental Science (UMCES), United States
- 2Chesapeake Bay Program, United States
- 3MD-DE-DC Water Science Center, U.S. Geological Survey, United States
- 4Chesapeake Biological Laboratory, United States
- 5Environmental Protection Agency (EPA), United States
Low dissolved oxygen (DO) conditions are a recurring issue in waters of Chesapeake Bay, with detrimental effects on aquatic living resources. The Chesapeake Bay Program partnership has developed criteria guidance supporting the definition of state water quality standards and associated assessment procedures for DO and other parameters, which provides a binary classification of attainment or impairment. Evaluating time series of these two outcomes alone, however, provides limited information on water quality change over time or space. Here we introduce an extension of the existing Chesapeake Bay water quality criterion assessment framework to quantify the amount of impairment shown by space-time exceedance of DO criterion (“attainment deficit”) for a specific tidal management unit (i.e., segment). We demonstrate the usefulness of this extended framework by applying it to Bay segments for each three-year assessment period between 1985 and 2016. In general, the attainment deficit for the most recent period assessed (i.e., 2014-2016) is considerably worse for deep channel (DC; n = 10) segments than open water (OW; n = 92) and deep water (DW; n = 18) segments. Most subgroups -- classified by designated uses, salinity zones, or tributary systems -- show better (or similar) attainment status in 2014-2016 than their initial status (1985-1987). Some significant temporal trends (p < 0.1) were detected, presenting evidence on the recovery for portions of Chesapeake Bay with respect to DO criterion attainment. Significant, improving trends were observed in seven OW segments, four DW segments, and one DC segment over the 30 three-year assessment periods (1985-2016). Likewise, significant, improving trends were observed in 15 OW, five DW, and four DC segments over the recent 15 assessment periods (2000-2016). Subgroups showed mixed trends, with the Patuxent, Nanticoke, and Choptank Rivers experiencing significant, improving short-term (2000-2016) trends while Elizabeth experiencing a significant, degrading short-term trend. The general lack of significantly improving trends across the Bay suggests that further actions will be necessary to achieve full attainment of water quality standards. Insights revealed in this work are critical for understanding the dynamics of the Bay ecosystem and for further assessing the effectiveness of management initiatives aimed toward Bay restoration.
Keywords: dissolved oxygen, criteria attainment, Monitoring and assessment, Chesapeake Bay, ecosystem management, spatial aggregation, Water quality standards, Mann-Kendall test
Received: 30 Jul 2018;
Accepted: 23 Oct 2018.
Edited by:Jacob Carstensen, Aarhus University, Denmark
Copyright: © 2018 Zhang, Tango, Murphy, Forsyth, Tian, Keisman and Trentacoste. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Qian Zhang, University of Maryland Center for Environmental Science (UMCES), Cambridge, Maryland, United States, firstname.lastname@example.org