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Considerations for Benthic Harmful Algal Bloom Detection and Monitoring in Virginia Free-flowing Freshwater Rivers (Version 1)

The Commonwealth of Virginia currently does not have an active Harmful Algal Bloom (HAB) surveillance program for benthic algae. Rather, it has a response-based program triggered by reports of suspected benthic HABs from the public and/or field observations made by state agency staff. The Virginia Department of Health (VDH) coordinates the Commonwealth’s responses to suspected benthic HAB events. Virginia Department of Environmental Quality (DEQ) normally conducts the initial response to any potential HAB, which may include visits to the HAB site for visual observations and collection of water column samples above or near the benthic algal mats. DEQ does not collect algal material from solid mats, benthic or floating, and has limited resources to commit beyond the initial response investigation of reported potential HABs. VDH is charged with the responsibility to weigh the available evidence and determine whether there is sufficient information to issue an advisory or alert notifying the public of possible risk due to the presence of harmful algae.

Advisories may be issued based on confirmed, quantitative data such as an exceedance of a toxin threshold measured in the water column. Alerts may be based, partially or fully, on qualitative information such as the widespread presence, or suspected presence, and extent of solid floating/benthic mats or scums. The subsequent benthic HAB response monitoring program must therefore consider protocols to be implemented in both circumstances, i.e., an advisory based on confirmed, quantitative measurements versus a qualitative “abundance of caution” alert informing the public of a possible health risk.

This project report describes systematic protocols that could be implemented if an advisory or alert is issued by VDH for a benthic HAB event. The report identifies the information needed to issue an advisory or alert, the recommended actions, an effective schedule of activities, and the resources needed to characterize the nature and extent of the HAB and implement the protocols. The suggested monitoring program considers the conditions and information that led to the HAB advisory or alert. The report describes how decision-makers are informed of the health risks associated with recreational swimming, fishing, and other water contact activities.

An Analysis of Pooled Monitoring Data in Maryland to Evaluate the Effects of Restoration on Stream Quality in Urbanized Watersheds. Final report

The project examined whether stormwater management practices implemented under MS4 permits can lead to measurable differences in stream conditions compared to similar watersheds with few or no stormwater practices and to highly forested reference watersheds.

Copies of Appendix A and Appendix B are available online.

Potomac Environmental Flows Workshop 2022

In 2021, Commissioners of the Interstate Commission on the Potomac River Basin (ICPRB) passed a Resolution on Enhancing Water Supply Resilience for the Washington Metropolitan Area. This resolution is the first step in updating the two foundational agreements of the Washington metropolitan area cooperative water supply system: the Low Flow Allocation Agreement (LFAA) of 1978 and the Water Supply Coordination Agreement (WSCA) of 1982. To facilitate such an update the resolution called for the following action items:

  • Develop a Task Force on the WSCA to reinitiate dialogue on revisions that would accurately reflect changing conditions. This includes the need for strengthening water security against spills, cybersecurity attack, and water scarcity and the ability to include additional suppliers;
  • Convene a Work Group to discuss the ten sets of options identified in the 2018 review of the LFAA; and
  • Convene scientific workshops on state-of-the-art approaches to environmental flows for large river systems.

To address the third action item, a virtual workshop was held over one-and-a-half days in May 2022, with the explicit purpose of answering the following questions with respect to the Potomac River, which supplies most of the Washington, D. C., metropolitan area drinking water:

  • Are there other approaches now for determining environmental flows in large, relatively unregulated rivers like the Potomac?
  • If there are, what data, analysis tools, and assessments are needed to make a scientifically defensible change?

The information presented and discussed during the workshop provides input to the LFAA workgroup in the event the group recommends revisiting the current environmental flow-by target used during low flow periods. The question of whether or not to study the flow-by was informally discussed during the workshop but the intent of the workshop was to gather the relevant information, not recommend a course of action.

Potomac Basin Unreported Water Use

This flyer documents high-level results of one technical recommendation of the Potomac Basin Comprehensive Water Resources Plan’s water use and supplies challenge area: specifically, to “conduct additional studies on water uses that fall below state water reporting thresholds.”

Click here for the Supplemental Table of data used for the Potomac Basin Unreported Water Use report.

Nutrient limitation of phytoplankton in Chesapeake Bay: Development of an empirical approach for water-quality management

Understanding the temporal and spatial roles of nutrient limitation on phytoplankton growth is necessary for developing successful management strategies. Chesapeake Bay has well-documented seasonal and spatial variations in nutrient limitation, but it remains unknown whether these patterns of nutrient limitation have changed in response to nutrient management efforts. We analyzed historical data from nutrient bioassay experiments (1992–2002) and data from long-term, fixed-site water-quality monitoring program (1990–2017) to develop empirical approaches for predicting nutrient limitation in the surface waters of the mainstem Bay. Results from classification and regression trees (CART) matched the seasonal and spatial patterns of bioassay-based nutrient limitation in the 1992–2002 period much better than two simpler, non-statistical approaches. An ensemble approach of three selected CART models satisfactorily reproduced the bioassay-based results (classification rate = 99%). This empirical approach can be used to characterize nutrient limitation from long-term water-quality monitoring data on much broader geographic and temporal scales than would be feasible using bioassays, providing a new tool for informing water-quality management. Results from our application of the approach to 21 tidal monitoring stations for the period of 2007–2017 showed modest changes in nutrient limitation patterns, with expanded areas of nitrogen-limitation and contracted areas of nutrient saturation (i.e., not limited by nitrogen or phosphorus). These changes imply that long-term reductions in nitrogen load have led to expanded areas with nutrient-limited phytoplankton growth in the Bay, reflecting long-term water-quality improvements in the context of nutrient enrichment. However, nutrient limitation patterns remain unchanged in the majority of the mainstem, suggesting that nutrient loads should be further reduced to achieve a less nutrient-saturated ecosystem.

Published in the Journal of Water Research, Volume 188, January 2021:

Potomac River Water Quality at Great Falls: 1940 – 2019

The U.S. Army Corps of Engineers operates Washington Aqueduct and provides drinking water to the Washington, D.C. area. Washington Aqueduct routinely samples its source of water, the Potomac River. Each year, it reports the monthly averages for basic water parameters and several pollutants and metals. Reports since 2001 are available online. Reports from 1905 to 2000, however, had limited distribution and their legibility has faded over time.

Dr. Norbert A. Jaworski recognized the historical value of these reports. To prevent their loss, he digitized the monthly values for several parameters. The Interstate Commission on the Potomac River Basin (ICPRB) later updated his dataset through 2019 and checked the entered data for accuracy. This report focuses on changes in temperature, hardness, pH, total solids, chloride, nitrate, and sulfate over the 80 years since ICPRB was formed in 1940. Visual representations (“heatmaps”) and trend analysis show significant increasing trends in all these parameters except nitrate. The report is intended to introduce the historical Washington Aqueduct water quality data to a broader audience and highlight their potential value to Potomac studies.

The Supplemental Materials document contains additional graphical representations of the data.

See the video summary of the report:

2020 Washington Metropolitan Area Drought Exercise

This report describes activities conducted during the 2020 drought exercise. The exercise was virtual, and took place on Monday, Tuesday, and Wednesday, November 16-18, from 7:30 AM to 4:00 PM.
Communications during the exercise were via telephone, email, and Microsoft Teams Meeting, and all
operations were “simulated.” Twice daily email reports were sent out to stakeholders reporting on current flow and demand conditions and on simulated operations. The exercise included two special events:

  • An actual test release from Little Seneca Reservoir, which was conducted over an approximately
    12-hour period, beginning at 10:00 AM on Tuesday, November 17.
  • A webinar by Hazen & Sawyer on the use of the Potomac OASIS model to provide probabilistic
    information on future streamflows and reservoir storage levels. A PDF of the webinar on forecast informed reservoir operations is available.

Learn more about previous drought exercises and the ICPRB’s Section for Cooperative Water Supply Operations on the Potomac on the Drought Monitoring and Operations page.

Linking Altered Flow Regimes to Biological Condition: an Example Using Benthic Macroinvertebrates in Small Streams of the Chesapeake Bay Watershed

Regionally scaled assessments of hydrologic alteration for small streams and its effects on freshwater taxa are often inhibited by a low number of stream gages. To overcome this limitation, we paired modeled estimates of hydrologic alteration to a benthic macroinvertebrate index of biotic integrity data for 4522 stream reaches across the Chesapeake Bay watershed. Using separate random-forest models, we predicted flow status (inflated, diminished, or indeterminant) for 12 published hydrologic metrics (HMs) that characterize the main components of flow regimes. We used these models to predict each HM status for each stream reach in the watershed, and linked predictions to macroinvertebrate condition samples collected from streams with drainage areas less than 200 km2. Flow alteration was calculated as the number of HMs with inflated or diminished status and ranged from 0 (no HM inflated or diminished) to 12 (all 12 HMs inflated or diminished). When focused solely on the stream condition and flow-alteration relationship, degraded macroinvertebrate condition was, depending on the number of HMs used, 3.8–4.7 times more likely in a flow-altered site; this likelihood was over twofold higher in the urban-focused dataset (8.7–10.8), and was never significant in the agriculture-focused dataset. Logistic regression analysis using the entire dataset showed for every unit increase in flow-alteration intensity, the odds of a degraded condition increased 3.7%. Our results provide an indication of whether altered streamflow is a possible driver of degraded biological conditions, information that could help managers prioritize management actions and lead to more effective restoration efforts.

The report has been published in Environmental Management.

Rapid Response Survey of Cyanobacteria Toxin Levels Downstream of North Fork Shenandoah River Algal Bloom After Tropical Storm Ida, 2021

The Virginia Department of Health issued a Harmful Algae Bloom (HAB) Advisory for a 53-mile stretch of the North Fork of the Shenandoah River on August 10, 2021 (Figure 1, left). Samples from multi-species algal mats on the river bottom contained harmful levels of toxins produced by cyanobacteria. Three weeks later, Tropical Storm Ida passed over the North Fork, dumping torrential rain on the watershed. Sharply rising streamflows were expected to scour the benthic algal mats, potentially lysing their cells and releasing toxins as they washed downstream. The ICPRB’s Emergency River Spill Model (ERSM) indicated the scoured material’s leading edge would reach the Potomac River mainstem by September 2nd – 4th and Great Falls near Washington, D. C. by September 3rd – 6th.

Virginia Department of Environmental Quality staff confirmed the algal mats were scoured off the river bottom. Water samples collected by ICPRB at the Shenandoah River mouth indicate the storm’s high flows diluted the algal cells and their associated toxins to below-detection levels before they reached the Potomac River. If flows had been less intense, we hypothesize the scoured material and toxins could potentially have reached the Potomac River mainstem. More advanced flow modeling and additional sampling during algal blooms could better characterize the potential transport of scoured or senescing algal blooms in the Shenandoah River under different river conditions.

Scientist sends testing equipment attached to a rope over the side of a bridge. Shenandoah river is below the bridge.

Rt. 340 bridge over Shenandoah River near Harpers Ferry, WV

Assessing the effectiveness of riparian buffers for reducing organic nitrogen loads in the Coastal Plain of the Chesapeake Bay watershed using a watershed model

Riparian buffers are an important conservation practice to mitigate water quality degradation in the Coastal Plain of the Chesapeake Bay watershed (CBW). Although forested and grassed riparian buffers have been implemented in this region through government programs, the impacts of riparian buffers on water quality have been rarely examined. The objective of this study was to assess the long-term effects of riparian buffers to improve water quality in the Coastal Plain of the CBW. A watershed model, Soil and Water Assessment Tool (SWAT), was employed for this study. Considering impacts of model uncertainty (i.e., equifinality) on the effectiveness of riparian buffers, we adopted all parameter sets that produced acceptable simulation results. Multiple riparian buffer implementation scenarios were developed to generate the baseline condition on total organic nitrogen (TON) loads without riparian buffers and examine variation of TON loads with areal coverage of riparian buffers. Through the calibration processes, a total of 235 acceptable parameter sets were identified and used to simulate TON loads. The simulation results indicated that riparian buffers significantly reduce TON loads. Without riparian buffers, annual TON loads from the 220 km2 study watershed were 18 to 34 metric tons, but declined to 8 to 21 metric tons with riparian buffers. The effectiveness of riparian buffers on reducing annual TON loads increased from 17% to 45% with an increase in the extent of riparian buffer implementation. The effectiveness of riparian buffers tended to be higher during early spring than other seasons as high soil water conditions promote occurrence of surface water flow and thus TON loads. Riparian buffers were more efficient on croplands than other land use types due to high soil nutrient levels caused by fertilizer applications. The effectiveness of riparian buffers differed considerably by parameter set. Thus, efforts to consider model uncertainty are important to provide better insight into the impacts of conservation practices. This study supports ongoing riparian buffer programs for the Mid-Atlantic Coastal Plain by demonstrating the effectiveness of riparian buffers and informing implementation guidelines.

Published in the Journal of Hydrology, Volume 585, June 2020: