Anthropogenic Change in Estuaries

The growth and movement of human populations have resulted in a significant stressor in the form of invasive species that has altered global biodiversity patterns. For example, the introduction of invasive species worldwide has changed the community composition and physical structure of many ecosystems (Elton, 1958 Vitousek et al., 1997). Estuarine systems, like the northern San Francisco Bay, have experienced serious declines in productivity at the base of the food web over recent decades after the introduction of the 

Asian clam, Potamocorbula amurensis, in 1987 (Carlton et al., 1990). The invasive Asian Date mussel, Musculista senhousia, has invaded the west coast of the United States altering community dynamics, and has now spread to Western Australia, New Zealand, and the Mediterranean (Mistri, 2002). One of the more notable bivalve invasions, by the zebra mussel (Dreissena polymorpha), has proven to be as devastating and expansive across U.S. rivers, lakes, and estuaries as predicted in early studies (Strayer and Smith, 1993). For example, these mussels can filter a volume of water equivalent to the entire freshwater region of the Hudson River about every 2 d this has dramatically altered the total suspended load and the phytoplankton community (Roditi et al., 1996). Similarly, invasion of wetland plant species, such as Phragmites australis, has resulted in displacement of dominant marsh Spartina spp. along the eastern U.S. coast (see more in chapter 8) (Chambers et al., 2003). 

Benzo[g,h,/]perylene (BP) lndeno[1,2,3-c,d]pyrene (IP) Dibenz[a,fa]anthracene (DabA) 

In this chapter, we will discuss the basic controls on the transport of some of these contaminants mentioned above in the water column and sediments of estuaries. While there are five general classes of contaminants (petroleum hydrocarbons, halogenated hydrocarbons, heavy metals, radionuclides, and litter) considered to be critical in coastal environments (Waldichuk, 1989), the primary focus will be on the biogeochemical dynamics of a select group of contaminants as they relate to other stressors, such as nutrients, in this chapter. For a more comprehensive assessment of the actual statistics on toxicity and surveys of the distribution and loading rates of all the aforementioned contaminants in estuaries, please refer to Kennish (1997). 

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