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[Submission]: Chesapeake Bay Water Quality Standards Attainment #44

Open BBeltz1 opened 7 months ago

BBeltz1 commented 7 months ago

Primary Contact

qzhang@chesapeakebay.net

Secondary Contact

No response

Data Name (This will be the displayed title in Catalog)

Chesapeake Bay Water Quality Standards Attainment

Indicator Name (as exists in ecodata)

ches_bay_wq

Family (Which group is this indicator associated with?)

Data Description

Chesapeake Bay Water Quality Attainment Indicator

Introduction to Indicator (Please explain your indicator)

To protect the aquatic living resources of Chesapeake Bay, the Chesapeake Bay Program (CBP) partnership has developed a guidance framework of ambient water quality criteria with designated uses and assessment procedures for dissolved oxygen, chlorophyll-a, and water clarity/submerged aquatic vegetation (SAV) ([@us_epa_ambient_2003]). To achieve consistent assessment over time and between jurisdictions, a multimetric indicator was proposed by the CBP partnership to provide a means for tracking the progress in all 92 management segments of Chesapeake Bay ([@hernandez_cordero_development_2020]; [@us_epa_ambient_2017]). This indicator has been computed for each three-year assessment period since 1985-1987, providing an integrated measure of Chesapeake Bay’s water quality condition over the last three decades.

The multimetric indicator required monitoring data on dissolved oxygen (DO) concentrations, chlorophyll-a concentrations, water clarity, SAV acreage, water temperature, and salinity. SAV acreage has been measured by the Virginia Institute of Marine Science in collaboration with the CBP, which is available via http://web.vims.edu/bio/sav/StateSegmentAreaTable.htm. Data for all other parameters were obtained from the CBP Water Quality Database (http://www.chesapeakebay.net/data/downloads/cbp_water_quality_database_1984_present). These data have been routinely reported to the CBP by the Maryland Department of Natural Resources, Virginia Department of Environmental Quality, Old Dominion University, Virginia Institute of Marine Science, and citizen/volunteer monitoring initiatives.

Monitoring data of DO, chlorophyll-a, and water clarity/SAV were processed and compared with water quality criteria thresholds according to different designated uses (DUs). These DUs are migratory spawning and nursery (MSN), open water (OW), deep water (DW), deep channel (DC), and shallow water (SW), which reflect the seasonal nature of water column structure and the life history needs of living resources. Station-level DO and chlorophyll-a data were spatially interpolated in three dimensions. Salinity and water temperature data were used to compute the vertical density structure of the water column, which was translated into layers of different DUs. Criteria attainment was determined by comparing violation rates over a 3-year period to a reference cumulative frequency distribution that represents the extent of allowable violation. This approach was implemented using FORTRAN codes, which are provided as a zipped folder. For water clarity/SAV, the single best year in the 3-year assessment period was compared with the segment-specific acreage goal, the water clarity goal, or a combination of both. For more details, refer to the Methods section of Zhang [@zhang_chesapeake_2018].

The multimetric indicator quantifies the fraction of segment-DU-criterion combinations that meet all applicable season-specific thresholds for each 3-year assessment period from 1985-1987 to 2019-2021. For each 3-year assessment period, all applicable segment-DU-criterion combinations were evaluated in a binomial fashion and scored 1 for “in attainment” and 0 for “nonattainment”. The classified status of each segment-DU-criterion combination was weighted via segments’ surface area and summed to obtain the multimetric index score. This weighting scheme was adopted for two reasons: (1) segments vary in size over four orders of magnitude, and (2) surface area of each segment does not change with time or DUs, unlike seasonally variable habitat volume or bottom water area ([@us_epa_ambient_2017]). For more details, refer to the Methods section of Zhang [@zhang_chesapeake_2018].

Key Results and Visualization

The indicator provides an integrated measure of Chesapeake Bay’s water quality condition (Figure 1). In 2019-2021, 28.1% of all tidal water segment-DU-criterion combinations are estimated to have met or exceeded applicable water quality criteria thresholds. Overall, the indicator has a positive and statistically significant trend between 1985-1987 and 2019-2021, which shows that Chesapeake Bay is on a positive trajectory toward recovery. This pattern has been statistically linked to total nitrogen reduction, indicating responsiveness of attainment status to management actions implemented to reduce nutrients ([@zhang_chesapeake_2018]).

Implications

Patterns of attainment of individual designated uses are variable (Figure 1). There have been periods of significant long-term decline and periods of significant long-term improvement in dissolved oxygen criterion attainment. However, variation in recent years has shown that there is no clear trend in these patterns of attainment in Chesapeake Bay.

Spatial Scale

Chesapeake Bay

Temporal Scale

3-year assessment period between 1985-1987 and 2019-2021.

Synthesis Theme

Define Variables

Period: Assessment period Year 1: Starting year of the assessment period Year 2: Ending year of the assessment period Total: The overall attainment indicator MSN-DO: Estimated attainment of the dissolved oxygen criterion for the migratory spawning and nursery designated use OW-DO: Estimated attainment of the dissolved oxygen criterion for the open water designated use DW-DO: Estimated attainment of the dissolved oxygen criterion for the deep water designated use DC-DO: Estimated attainment of the dissolved oxygen criterion for the deep channel designated use OW-CHLA: Estimated attainment of the chlorophyll-a criterion SW-Clarity/SAV: Estimated attainment of the bay grasses / water clarity criterion for the shallow water designated use

Indicator Category

If other, please specify indicator category

No response

Data Contributors

Qian Zhang, Richard Tian, and Peter Tango

Point(s) of Contact

Qian Zhang, qzhang@chesapeakebay.net

Affiliation

?

Public Availability

Source data are publicly available.

Accessibility and Constraints

No response

andybeet commented 4 months ago

checked box indicates entry listed in zotero