Condition and trends of estuarine water quality and seagrass in Assateague Island National Seashore: Northeast Coastal and Barrier Network, 2005-2022

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

doi:10.36967/2310561

This report summarizes conditions and trends in routine long-term water quality monitoring and seagrass data collected at Assateague Island National Seashore in Maryland and Virginia from 2005 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 water quality condition of the estuary as well as to identify potential trends or changes in condition over time. All monitoring was conducted during a four-week summer index period, biennially Monitored variables included dissolved oxygen concentration, chlorophyll-a concentration, attenuation of downwelling photosynthetically available radiation (PAR), salinity, temperature, turbidity, and pH. In addition, long-term monitoring of seagrass condition was conducted at permanently established transects. Water quality condition and trends were generally consistent between the spatial station surveys, the trend stations, and continuous logging station. Despite declines in turbidity over time, water clarity, as measured by PAR attenuation, was typically poor throughout the majority of the monitored area in most years sampled. Although there were several years when approximately 50% of the estuary was classified as being in poor condition with respect to chlorophyll-a concentrations, the majority of the estuary was typically classified as being in fair condition in most years. Bottom dissolved oxygen concentrations were consistently classified as being in good condition throughout the majority of the estuary. While there was no statistical evidence of significantly increasing water temperature over time, summertime temperatures at the logging station, most trend stations, and in a large percentage of the estuary exceeded 28°C in several years. Trends in seagrass condition varied by species with eelgrass experiencing significant declines and widgeon grass increasing significantly over the monitoring timeframe. 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 and seagrass in Assateague Island National Seashore: Northeast Coastal and Barrier Network, 2005-2022

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