Enhancing the Chesapeake Bay report card with new indicators and new methodsBill Dennison ·
On 27 June 2013, Caroline Wicks presented the STAR seminar in anticipation of the 2012 Chesapeake Bay report card release. The seminar was entitled 'Enhancing the Chesapeake Bay report card with new indicators and new methods'.
In capturing the discussion following the seminar, I have converted the discussion into a series of Frequently Asked Questions (FAQs).
What would it take to develop 'swimability' or 'fishability' indicators?
Some of the Riverkeeper and Waterkeeper groups that we work with through the Mid-Atlantic Tributary Assessment Coalition (MTAC) do use bacteria in their regional report cards. We have developed protocols for bacteria as well as the other water quality indicators so that results are comparable. One of the things that we have observed is that different regions score quite differently. For example, the West/Rhode Rivers which are fairly well connected with the Chesapeake mainstem typically score well in terms of bacteria in spite of a fairly developed watershed. In contrast, the Nanticoke River on the Eastern Shore with very little development scores fairly low in terms of bacteria, possible due to the prevalence of naturally occurring bacteria associated with the marshes.
How does the Chesapeake Bay report card relate to the regional report cards?
The various citizen scientists and local Riverkeeper/Waterkeeper groups, like the Chester Testers, are increasingly using the MTAC protocols for tidal and nontidal indicators (e.g., Total Nitrogen, Total Phosphorus, Chlorophyll a, Water Clarity, Aquatic Grasses, and Dissolved Oxygen for tidal indicators). Some groups produce 'State of the Waterways' reports, other groups produce annual report cards. Our goal is to develop the protocols for data collection and analysis to produce a set of core indicators that can be compared between regions. The overall Chesapeake Bay report card relies on extensive data sets collected by agency scientists throughout the year, and provides a strong monitoring backbone for the different regional groups.
How does the Chesapeake Bay report card relate to the Total Maximum Daily Load?
The Total Maximum Daily Load (TMDL) is the regulatory framework for the Water Quality Implementation Plans (WIPs) which puts the Bay on a 'nutrient diet'. The TMDL is tracked by various water quality attainment indicators. The Chesapeake Bay report card addresses the overall question of "How is the Bay doing?". The Chesapeake Bay report card indicators include ones that transcend the nutrient loading, and the thresholds for the indicators are not regulatory thresholds but were chosen for ecological meaning. Thus, the Chesapeake Bay report card is not a TMDL tracking tool - rather it is an independent, rigorous and geographically explicit depiction of the status of Chesapeake Bay each year.
What is driving the Chesapeake Bay report card score?
Most of the mainstem Bay above the Potomac River could be considered the "Susquehanna Estuary" due to the predominant impact of the Susquehanna River on conditions in the Upper Bay and Mid Bay reporting regions. In addition to the overall flows and loadings from the Susquehanna River basin into the Bay, the proportionate amount of impact of a pound of nitrogen or phosphorus is much greater from the Susquehanna River than the lower Bay tributaries. Gary Shenk at the Chesapeake Bay Program indicated that the impact of a pound on nitrogen or phosphorus is approximately five times larger from the Susquehanna River than from the James, York or Rappahannock Rivers. But the tributary scores are very much about what is happening in the tributary watersheds so the pound of nitrogen and phosphorus will still have a major impact on the tributary water quality.
How do you interpret the trajectories in report card scores?
The different trajectories indicate different processes at work - we found linear trajectories and a few trajectories that had inflection points over the 27 year time course. For those trajectories with consistent linear trends, we used a linear regression model to calculate trends. For those trajectories with inflection points, we used a general additive model (GAM) to capture the curvilinear trends. It will be interesting to attempt to explain the various trajectories, both linear and with inflection points. The linear trends may actually mask several different causal forces, and the analysis of inflection point trends may be able to reveal the causal forces.
How does the report card score calculated with original six indicators compare with the new suite of seven indicators?
The overall Bay Health Index was compared between the two suites of indicators and there were no large differences in overall score or in variability between the two methods in previous years. We cannot compare 2012 scores because the Phytoplankton Index of Biotic Integrity data is not available. One of the differences in the two approaches is that the original Bay Health Index was calculated from the Water Quality Index (dissolved oxygen, chlorophyll, water clarity) and the Biotic Index (aquatic grasses, phytoplankton IBI, benthic IBI). The new methods uses all seven indicators (dissolved oxygen, chlorophyll, water clarity, total nitrogen, total phosphorus, aquatic grasses and benthic IBI) to directly calculate the Bay Health Index. The additional fisheries indicators, which are not used in calculating grades, have no previous comparisons for report cards. The change in methodology represents an adaptive monitoring approach, which like adaptive management, involves a reevaluation of the methods given a new level of understanding and available funding.
Why aren't flow adjusted values used for all regions?
The water flow gauging station network is limited in the Chesapeake watershed. Several of the tributaries are not gauged at all (e.g., Chester River) and some are only partially gauged (e.g., only 11% of the Choptank watershed is gauged). There was a suggestion that the watershed model which uses annual rainfall data could be used to provide flow estimates from ungauged areas. The trade-off of using model data in the measurement-oriented report card versus providing a more comprehensive analysis of flow adjusted scores needs to be considered.
About the author
Dr. Bill Dennison is a Professor of Marine Science and Vice President for Science Application at the University of Maryland Center for Environmental Science (UMCES). Dr. Dennison’s primary mission within UMCES is to coordinate the Integration and Application Network.