Condition and trends of estuarine water quality in Colonial National Historical Park: Northeast Coastal and Barrier Network, 2008-2022

Nagel, Jessica; Paisted, Holly; Peck, Christopher; Duffy, Paul

doi:10.36967/2310814

This report summarizes conditions and trends in routine long-term water quality monitoring data collected at Colonial National Historical Park in Virginia from 2008 through 2022 as part of the NPS NCBN Vital Signs Estuarine Nutrient Enrichment monitoring program. This comprehensive program incorporates spatial surveys, repeated monitoring at trend stations, and continuous monitoring at a fixed logging station in an effort to establish overall condition of the estuary as well as to identify potential trends or changes in condition over time. All monitoring was conducted biennially during a four-week summer index period within two subunits (strata) in the park. Monitored variables included dissolved oxygen concentration, chlorophyll-a concentration, attenuation of downwelling photosynthetically available radiation (PAR), salinity, temperature, turbidity, and pH. Condition and trends were generally consistent between the spatial station surveys, the trend stations, and continuous logging station. Despite a significant decline in turbidity, the entirety of the estuary was classified as having poor water clarity, as measured by PAR attenuation (> 1.61 m-1), with no significant change or improvement observed over time. Although there were several years when the majority of the estuary was classified as being in fair condition with respect to chlorophyll-a concentrations, more than 50% of the estuary was typically classified as being in poor condition, and the area-weighted mean consistently indicated poor condition overall (> 20 µg/L). Bottom dissolved oxygen concentrations increased significantly over time with greater than 90% of the estuary consistently classified as being in good condition. Salinity within the estuary was highly variable and declined significantly after 2010. While there was no statistical evidence of significantly increasing water temperature over time, temperatures in the majority of the estuary exceeded 28°C for most years, which may be detrimental to some species of local estuarine flora and fauna. The identification of status and trends may help managers to make better informed decisions, develop effective mitigation measures, reduce management costs, and provide a means of measuring progress towards goals.

Condition and trends of estuarine water quality in Colonial National Historical Park: Northeast Coastal and Barrier Network, 2008-2022

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