Summary

The goal of scientific research on contaminants in the Chesapeake Bay is to develop measures of ecosystem functioning that decisionmakers can use for better managing the Bay's living resources. Major tools that managers increasingly rely on are conceptual and mathematical models for predicting risk-based effects of alternative control strategies.

While such models can mimic, to some extent, basic food web relationships and predict ecological responses to various management strategies, those models - when it comes to contaminant effects on ecological processes - are limited. That is because a model's value is only as good as the data it relies on - and for the many ways in which contaminants can affect an aquatic ecosystem, the data are often ambiguous or simply not available. A major conclusion of the workhop is that research on biological effects of contaminants is especially important if science is to contribute to the kind of predictive measures that decisionmaking requires.

What We Know

In the last decade, research on contaminants - especially on the sources and transport of contaminants in the Bay - has made major strides. This research has gone a long way toward developing what we now understand as accepted fact, though scientists and managers still question how well measured values reflect various physical and chemical processes, which may affect the toxicity of chemical compounds once they enter the Bay. Despite such reservations, research and monitoring have made significant contributions to what we now know a good deal about:

• Major sources of chemical contaminants in the estuary and their general location and movement in identified contaminated areas - in the sediments of Baltimore and Norfolk harbors, for example, and in the Anacostia River
  
  
• How organic contaminants, e.g., PAHs, and metals (such as copper, cadmium and mercury), generally behave in the Chesapeake Bay and in other marine and estuarine ecosystems, though quantitative information is still limited.
  
  
• How the presence or absence of oxygen affects the behavior of heavy metals and organic compounds like PCBs and their movement between sediments and the overlying water column.
  
  
• How the uptake of specific contaminants by phytoplankton can serve as the entry of contaminants into the food web, though again quantitative information on transfers is limited.

In addition, researchers can:

• Describe the general physical transport - mediated by chemical and biological factors - of contaminants throughout the estuary, and document the effects of specific contaminants on particular organisms.
  
  
• Observe the uptake of contaminants by grazers (e.g., zooplankton) and begin to extrapolate how toxic compounds may be moving through the estuarine food web. However, because of the complexity of estuarine ecosystems, there is enormous potential for interaction among different levels of the food chain under varying environmental conditions, so our basic understanding, along with predictive tools for management, rapidly reaches its limits.
  
  
• Demonstrate numerous ways in which parts of the ecosystem are affected by chemical contaminants - whether at the surface microlayer, or in biofilms covering submerged surfaces, or in areas of dense algal blooms where trace elements become concentrated. Though these scientific findings suggest the potential for broad systemic effects, we lack adequate data, information and experiential observation to feel fully confident of the true scale of toxic impacts in the estuary.

What We Need to Know

Though research over these last five years has made fundamental discoveries about the diverse ways contaminants impact ecological functioning at different levels of organization, large gaps remain in our understanding of ecosystem effects. To date that research has helped to clarify the kinds of questions we must answer, answers that will be especially important as population in the Bay watershed increases - since population growth means development, and development inevitably brings with it increasing contaminant discharges and runoff.

As this report has made clear, we now understand, to a significant degree, the fundamental mechanisms of contaminant entry and movement through the Chesapeake Bay, though some major issues concerning contaminant sources and transport remain. For instance:

• What are the dynamics of transport for different classes of compounds from the contaminant-heavy Regions of Concern to regions which demonstrate sporadically high measures of particular contaminants?
  
  
• How well are we tracking diffuse sources of contaminants - for example household cleaners and other wastes - and their entry into the Bay - through septic tanks and groundwater seepage, for example?

As also emphasized, biological effects of low concentrations of contaminants found within the Bay remain the biggest area of uncertainty, especially in relation to species that are important both commercially and ecologically. We need to answer a number of important questions:

• How are genetic, molecular and cellular responses to representative contaminants that scientists generally measure in the laboratory related to the organism and to community structure in the estuarine environment?
  
  
• How are sublethal impacts of contaminants at different levels of biological organization transferred through trophic networks?

We also need to address the following issues:

• Since it will prove impossible to study the effects of all compounds on all organisms, we must continue to focus, systematically, on representative estuarine species and representative contaminants, such as those described in this report.
  
  
• While we understand much about the behavior of specific contaminants, we know little about combined toxic effects on organisms, let alone entire communities, under different physico-chemical factors (e.g., pH, temperature, redox potential). We do not yet understand fully the effects of the total suite of contaminants on the Bay's whole complex and integrated ecosystem.

Scientific research on contaminants in the Chesapeake Bay, while its goals are a fundamental understanding of how the Bay functions, is guided by the need to identify critical issues that will best serve resource management goals - namely protecting the integrity and health of the ecosystem itself. Towards these ends, research efforts over this last decade, including those supported by CBEEC, have been working to provide the answers that influence decision making. While science will continue to pose new questions, these questions arise from research findings that contribute the kind of knowledge that can only lead to more effective management. The linkages between science, management and policymaking are critical - and only by continuing to expand our knowledge of chemical contaminant behavior and effects in the Chesapeake will we be able to make the decisions necessary to ensure a healthier Bay for the future.

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