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Explainable machine learning improves interpretability in the predictive modeling of biological stream conditions in the Chesapeake Bay Watershed, USA

Authors: Kelly O. Maloney, Claire Buchanan, Rikke D. Jepsen, Kevin P. Krause, Matthew J. Cashman, Benjamin P. Gressler, John A. Young, Matthias Schmid Published in November 2022

Anthropogenic alterations have resulted in widespread degradation of stream conditions. To aid in stream restoration and management, baseline estimates of conditions and improved explanation of factors driving their degradation are needed. We used random forests to model biological conditions using a benthic macroinvertebrate index of biotic integrity for small, non-tidal streams (upstream area ≤200 km2) in the Chesapeake Bay watershed (CBW) of the mid-Atlantic coast of North America. We utilized several global and local model interpretation tools to improve average and site-specific model inferences, respectively. The model was used to predict condition for 95,867 individual catchments for eight periods (2001, 2004, 2006, 2008, 2011, 2013, 2016, 2019). Predicted conditions were classified as Poor, FairGood, or Uncertain to align with management needs and individual reach lengths and catchment areas were summed by condition class for the CBW for each period. Global permutation and local Shapley importance values indicated percent of forest, development, and agriculture in upstream catchments had strong impacts on predictions. Development and agriculture negatively influenced stream condition for model average (partial dependence [PD] and accumulated local effect [ALE] plots) and local (individual condition expectation and Shapley value plots) levels. Friedman’s H-statistic indicated large overall interactions for these three land covers, and bivariate global plots (PD and ALE) supported interactions among agriculture and development. Total stream length and catchment area predicted in FairGood conditions decreased then increased over the 19-years (length/area: 66.6/65.4% in 2001, 66.3/65.2% in 2011, and 66.6/65.4% in 2019). Examination of individual catchment predictions between 2001 and 2019 showed those predicted to have the largest decreases in condition had large increases in development; whereas catchments predicted to exhibit the largest increases in condition showed moderate increases in forest cover. Use of global and local interpretative methods together with watershed-wide and individual catchment predictions support conservation practitioners that need to identify widespread and localized patterns, especially acknowledging that management actions typically take place at individual-reach scales.

Find more information on the ScienceDirect page.

Nutrient limitation of phytoplankton in three tributaries of Chesapeake Bay: Detecting responses following nutrient reductions

Authors: , , , , Published in September 2022

ABSTRACT: Many coastal ecosystems suffer from eutrophication, algal blooms, and dead zones due to excessive anthropogenic inputs of nitrogen (N) and phosphorus (P). This has led to regional restoration efforts that focus on managing watershed loads of N and P. In Chesapeake Bay, the largest estuary in the United States, dual nutrient reductions of N and P have been pursued since the 1980s. However, it remains unclear whether nutrient limitation – an indicator of restriction of algal growth by supplies of N and P – has changed in the tributaries of Chesapeake Bay following decades of reduction efforts. Toward that end, we analyzed historical data from nutrient-addition bioassay experiments and data from the Chesapeake Bay Long-term Water Quality Monitoring Program for six stations in three tidal tributaries (i.e., Patuxent, Potomac, and Choptank Rivers). Classification and regression tree (CART) models were developed using concurrent collections of water-quality parameters for each bioassay monitoring location during 1990-2003, which satisfactorily predicted the bioassay-based measures of nutrient limitation (classification accuracy = 96%). Predictions from the CART models using water-quality monitoring data showed enhanced nutrient limitation over the period of 1985-2020 at four of the six stations, including the downstream station in each of these three tidal tributaries. These results indicate detectable, long-term water-quality improvements in the tidal tributaries. Overall, this research provides a new analytical tool for detecting signs of ecosystem recovery following nutrient reductions. More broadly, the approach can be adapted to other waterbodies with long-term bioassays and water-quality data sets to detect ecosystem recovery.

See more on the ScienceDirect page.

Considerations for Monitoring Microplastics in the Non-Tidal Potomac River

Authors: Christina C. Davis Published in September 2022

The Interstate Commission on the Potomac River Basin’s 2022 Clean Water Act Section 106 Potomac Basin Water Quality Improvement grant included an activity to “assist water suppliers in VA, MD, and DC in developing microplastic sampling and analysis methodologies and conduct field sample collection.” This white paper, which explores the feasibility of a microplastic monitoring program in the nontidal Potomac basin, represents the output for this activity. Section 2 describes considerations for collecting and processing samples for microplastics analysis. Section 3 provides a brief explanation of analytical methods and quality control recommendations for the detection, quantification, and identification of microplastics.

An Inventory of Potomac Basin Entities with a Role in Sustainable Water Resources Management

Authors: Interstate Commission on the Potomac River Basin Published in May 2022

This pamphlet is used in concert with a spreadsheet inventory to identify entities in the Potomac basin that either directly or indirectly affect the realization of the Potomac Basin Comprehensive Water Resource Plan’s vision for the basin. It also summarizes the roles, responsibilities, and areas of authority of those entities to inform and integrate future comprehensive planning and implementation activities.

Edited to add: Click here for an updated version of this pamphlet was published in March, 2025.

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

Authors: Gordon Michael Selckmann, Charles O’Brien, Claire Buchanan, and Rikke Jepsen | Pub: # ICP22-3 | Published in July 2022

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.

Little Pipe Creek Watershed Assessment: Lower Little Pipe Creek Sub-Watershed

Authors: Christina C. Davis, Rikke Jepsen, Heidi L.N. Moltz, Andrea Nagel, Stephanie Nummer, Gordon Mike Selckmann, Carlington Wallace | Pub: # ICP22-6a | Published in July 2022

This watershed assessment was conducted as part of the National Water Quality Initiative (NWQI) of the Natural Resources Conservation Service (NRCS) to serve as Planning (or Readiness) Phase effort in the Little Pipe Creek watershed of Frederick and Carroll counties, Maryland. The purpose of the assessment is to assist Maryland with reducing downstream Enterococci levels, improving macroinvertebrate scores, and reducing nutrient (i.e., nitrogen and phosphorus) levels through implementation of agricultural practices. The ultimate goal is to de-list the Little Pipe Creek watershed from the impaired waters list for its phosphorus, sediment, and bacterial impairments.

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

Authors: Rikke Jepsen, Claire Buchanan, Andrea Nagel, Deb Caraco, Lisa Fraley-McNeal | Pub: # ICP 22-1 | Published in May 2022

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 Basin Unreported Water Use

Authors: Heidi Moltz, Andrea Nagel, Erfaneh Sharifi, Carlington Wallace Published in May 2021

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

Authors: Qian Zhang, Thomas R. Fisher, Emily M. Trentacoste, Claire Buchanan, Anne B. Gustafson, Renee Karrh, Rebecca R. Murphy, Jennifer Keisman, Cuiyin Wu, Richard Tian, Jeremy M. Testa, Peter J. Tango. Published in January 2021

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:
https://doi.org/10.1016/j.watres.2020.116407

Potomac River Water Quality at Great Falls: 1940 – 2019

Authors: DeeDee Hunter, Rikke D. Jepsen, Christina C. Davis, and Claire Buchanan | Pub: # ICP 21-5 | Published in November 2021

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: