Chesapeake Bay Monitoring
2. understanding the bay's
An understanding of the problems that confront today's Chesapeake Bay is central to a strategy to restore and protect this valuable resource. Without an understanding of how this complex system responds to pollutants, it will be difficult to target effective management actions. Likewise, an understanding of the physical, chemical and biological processes in Chesapeake Bay played a central role in the formulation of the water quality monitoring program. Since the program is directed at specific management issues, there is a logical basis for including particular elements in the design. While it is necessary to monitor the obvious problem, for example low dissolved oxygen, it is also necessary to monitor the principal causes such as nutrient enrichment, phytoplankton growth and deposition, and water stratification which prevents oxygen from mixing into the bottom waters. Usually, the underlying causes, such as nutrient enrichment in the example just presented, are more directly under our control than are the impacts that develop as the Bay responds to pollutants. There are also natural processes, such as water stratification, which must be examined to place an evaluation of pollutant impacts in the proper perspective.
In this chapter, some of the major problems confronting Chesapeake Bay will be examined within the ecological context of natural physical, chemical and biological processes. This information is intended to assist in an understanding of why the monitoring program is designed as it is and to provide background information that may be helpful in the comprehension of subsequent chapters.
PROBLEMS CONFRONTING THE BAY
Most of the problems currently perceived as causing decliners in the Bay's health have a common denominator - man. Man has acted directly by adding "wastes" to the Bay and its tributaries and by withdrawing its resources. Man has acted indirectly by changing the character of the land and air that surround and interact with the Bay.
The most profound Bay-wide impacts have resulted from large inputs of nutrients and other chemicals from sewage treatment plants or industrial operations, referred to as point sources, and from stormwater running off urban or rural land, referred to as nonpoint sources. These inputs are primarily composed of natural elements which are entering the Bay in excessive quantities. These are elements that normally recycle in the environment between plant and animal or between land, water and air. Problems have been created because of major perturbations in the balance of these recycling processes due largely to high populations along the shores of Chesapeake Bay. This imbalance results in an abnormal shift of recycled products, such as nutrients, so that they now enter and accumulate in Bay waters. When the shift in the balance of recycling is considerable, as it is in some regions of Chesapeake Bay, these natural products can cause severe problems. The nature of these impacts will be discussed later.
Another type of problem confronting the Bay comes from toxic compounds, unnatural products created by man or naturally-occurring chemicals that are concentrated to levels far exceeding the trace quantities normally found in the environment. These compounds are usually discharged during the manufacture, application or disposal of various products. These toxicant problems tend to be most severe in regions of the Bay where manufacturing industries or waste disposal sites are concentrated. The problems caused by toxic compounds are difficult to predict or understand because of their extremely complex chemical properties. It is known, however, that serious human and environmental health impacts may result when these compounds enter the Bay.
THE BAY ECOSYSTEM
Chesapeake Bay - the mainstem and tidal tributaries - constitutes an ecosystem. An ecosystem is a unit within which there is close linkage of many physical, chemical and biological processes such as water circulation, nutrient recycling and food chains. Ecosystems interact with adjacent ecosystems, making their boundaries sometimes difficult to distinguish. Chesapeake Bay is an estuarine ecosystem.
As an estuarine system, Chesapeake Bay is one of the most complete, ecosystems. Within its boundaries exist a range of aquatic environments, from fresh to nearly full-strength seawater, allowing a broad spectrum of organisms to flourish and chemical reactions to proceed. It has complex physical circulation patterns that vary with season, tide and weather. Outside of its boundaries, adjacent or sometimes remote ecosystems influence Chesapeake Bay, thereby contributing additional complexity (Figure 1). Many of these external effects are mediated through the atmosphere such as rainfall which affects freshwater, nutrient and sediment inputs to the Bay and wind patterns which exert strong influences on water circulation within the Bay. Acidic precipitation, originating from distances of hundreds of miles surrounding the Bay, is also transported by the atmosphere. Other external effects arise because several key living resources such as blue crabs and striped bass migrate to spend part of their lives outside of the Bay. Unfavorable currents in coastal waters off the mouth of the Bay and successful fishermen off the New England coast can have appreciable impacts on the abundance within the Bay of blue crabs and striped bass, respectively.
POLLUTANT IMPACTS IN THE CONTEXT OF NATURAL PROCESSES
Chemistry plays a large role in both the natural processes and
anthropogenic disturbances of an estuary. All life is dependent upon
numerous chemical reactions which are ultimately driven by the energy of
sunlight. This energy is captured by plants during a process known as
photosynthesis. This captured energy is stored in chemical bonds between
elements such as carbon, oxygen, hydrogen, nitrogen and phosphorus which
serve as building blocks for the complex molecules synthesized by the
photosynthetic chemical reactions within plants. In turn, animals and
bacteria, as they digest their food, break down the complex molecules to
capture energy stored in their chemical bonds. In this breakdown process,
the building block elements are released back into the water. This
continuing process of synthesis and degradation is known as recycling. As
noted earlier, it is often the imbalance of these normal recycling
processes that have impacted the Bay's health.
The preceding discussion has emphasized the need to understand physical, chemical and biological factors and their interactions when confronted with the task of protecting and restoring the Bay. One of the most profound conditions affecting the Bay -eutrophication- is a typical example of how physical, chemical and biological processes interact in response to anthropogenic inputs to produce a significant impact on the Bay (Figure 4). It also points out the need for a monitoring program that is comprehensive in its approach so it can yield the information necessary to guide management actions.
Eutrophication is a term used to describe the over enrichment of
aquatic systems by excessive inputs of phytoplankton nutrients, typically
phosphorus and/or nitrogen. In unimpacted systems, nutrients are present in
such low quantities that algal growth is controlled. In systems with an
oversupply of these nutrients, the growth of phytoplankton is stimulated,
initiating a chain of events that leads to the symptoms of eutrophication.
Usually, a major fraction of the enhanced phytoplankton growth cannot be
assimilated through the normal food web. This situation occurs because
there simply is too much phytoplankton being produced or because certain
phytoplankton species, which are unpalatable and thus not eaten by the
important small animal consumers, start to flourish under these conditions.
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