With the objective of assessing the condition of the San Francisco Estuary, the authors provided a framework to help develop San Francisco.
Estuary indicators. They proposed appropriate assessment questions and set of indicators, indices, and metrics for the San Francisco Estuary Project. The framework identified a number of important ecosystem attributes that should be tracked based on environmental regulations and goals and a general understanding of estuarine science. From those attributes, the authors posed assessment questions that could be answered using specific indicators and metrics. They proposed using 12 primary indicators to describe the condition of the Estuary, including the state of major habitat and biological components as well as the impacts of public behavior and government management. Each primary indicator consists of several indices or metrics, with a total of 47 metrics that measure a variety of environmental or management variables. Each set of metrics should be aggregated into an expression of condition before it can be used as a primary indicator, which had not been determined at the time the report was written.
In this document, the authors defined indicator the following way:
An ecological indicator may be a measurement of an environmental variable or state, an index composed of several environmental metrics, or a model that characterizes an ecosystem or ecosystem component (USEPA 2000c). Indicators are usually expressed in meaningful or useful terms, and are not necessarily quantitative. An index is a numerical aggregation of several different types of related information that expresses condition or status. A metric is a measurement of a single environmental variable, such as number of acres of tidal marsh, number of shorebirds, or number of water quality exceedances. Ecological assessments commonly include multimetric indices. For example, an Index of Biotic Integrity (IBI) for fish, may consider the number of fish taxa, and the abundances of several fish species, as part of a single indicator that describes the condition of fish (Karr and Chu 1999; Weisberg et al. 1997). All of these terms are often simply referred to as “indicators”, and may be used interchangeably; an index may be an indicator, and an index may be composed of several different indices.
The authors used four principles to guide indicator development:
- Assessment should be relevant to existing legal and regulatory mandates; and adopted goals and objectives in public planning documents;
- Assessment should be meaningful to the general public;
- Assessment must retain scientific credibility; and
- Assessment must rely on data from existing monitoring and research programs whenever possible.
The 12 primary indicators are grouped into three major categories—habitats, biological resources, and human use and governance (see Table 1 in the document for a full list of associated metrics):
Estuary Habitats
- Freshwater inflow
- Water and sediment quality and contaminants
- Habitat quality—by tidal and subtidal
Biological Resources
- Invertebrates, including shellfish—metrics include the following:
- Average annual abundance and young-of-the-year biomass of representative invertebrates and shellfish
- Average diversity and dominance of benthos and zooplankton in selected communities
- Abundance or trends in abundance of threatened and endangered species
- Percent of total community, trends in total abundance, or numbers of introduced invertebrate species
- Fish—metrics include the following:
- Average abundance of all native fish in selected habitats
- Average annual abundance and young-of-the-year biomass of representative fish from selected communities
- Average diversity and dominance of fish in selected communities
- Abundance or trends of threatened and endangered fish taxa
- Percent or trends in introduced fish
- Aquatic birds—metrics include the following:
- Average annual abundance and young-of-the-year biomass of important and representative birds from selected habitats
- Average diversity and dominance of birds in selected communities
- Abundance or trends of threatened and endangered birds
- Percent or trends in introduced birds
- Marine mammal
- Annual harbor seal census
- Estuary food web
- Annual chlorophyll a biomass and intertidal plants
- Annual zooplankton, benthos, and fish biomass
Human Use and Governance
- Land use
- Dredging
- Fishable, swimmable, drinkable
- Stewardship
References:
Karr, J. R., and E. W. Chu. 1999. Restoring Life in Running Waters: Better Biological Monitoring. Washington, DC: Island Press.
Thompson, B. and A. Gunther. 2004. Development of Environmental Indicators of the Condition of San Francisco Estuary. SFEI Contribution 113. Prepared for the San Francisco Estuary Project. San Francisco Estuary Institute. Oakland, CA. Accessed October 2016. http://www.sfei.org/sites/default/files/biblio_files/Indicatorreport_final.pdf Exit.
USEPA. 2000c. Evaluation Guidelines for Ecological Indicators. EPA/620/R-99/005. Office of Research and Development. Washington, DC. Accessed October 2016. https://archive.epa.gov/emap/archive-emap/web/pdf/ecol_ind.pdf.
Weisberg, S.B., J.A. Ranasinghe, D.M. Dauer, L.C. Schafner, R.J. Diaz, and J.B. Frithsen. 1997. An estuarine benthic index of biotic integrity (B-IBI) for Chesapeake Bay. Estuaries 20:149–158.