www.epa.gov/research
                            science   in   ACTION
                            INNOVATIVE RESEARCH  FOR A SUSTAINABLE FUTURE
CONNECTIVITY OF STREAMS
AND WETLANDS TO
DOWNSTREAM WATERS:
A REVIEW AND SYNTHESIS
OF THE SCIENTIFIC
EVIDENCE

General Information
The Environmental Protection Agency's
(EPA) Office of Research and
Development (ORD) has finalized the
science report, Connectivity of Streams
and Wetlands to Downstream Waters: A
Review and Synthesis of the Scientific
Evidence.

The purpose of this report is to
summarize the current scientific
understanding about the connectivity
and mechanisms by which streams and
wetlands, singly or in aggregate, affect
the physical, chemical, and biological
integrity of downstream waters. EPA has
conducted a thorough review of the
literature regarding the effects that
streams, nontidal wetlands, and open
waters have on larger downstream
waters such as rivers, lakes, estuaries,
and oceans. The report addresses three
main questions related to connectivity:
(1)  What are the physical, chemical,
    and biological connections to, and
    effects of, ephemeral, intermittent,
    and perennial stream on
    downstream waters?
(2)  What are the physical, chemical,
    and biological connections to, and
    effects of, riparian orfloodplain
    wetlands and open waters on
    downstream waters?
(3)  What are the physical, chemical,
    and biological connections to, and
    effects of, wetlands and open
    waters in non-floodplain settings on
    downstream waters?

Summary of Findings and Conclusions
Based on a review of more than  1,200
publications from the peer-reviewed
scientific literature, this final report
reviews and summarizes the scientific
evidence regarding the effects that
streams, nontidal wetlands and open
waters have on larger downstream
waters such as rivers, lakes, estuaries,
and oceans. The final report contains 5
major conclusions:

•   The scientific literature
    unequivocally demonstrates that
    streams, regardless of their size or
    frequency of flow, are connected to
    downstream waters and strongly
    influence their function.

•   The scientific literature clearly
    shows that wetlands and open
    waters in riparian areas (transitional
    areas between terrestrial and
    aquatic ecosystems) andfloodplains
    are physically, chemically, and
    biologically integrated with rivers
    via  functions that improve
    downstream water quality. These
    systems act as effective buffers to
    protect downstream waters from
    pollution  and are essential
    components of river food webs.

•   There is ample evidence that many
    wetlands and open waters located
    outside of riparian areas and
    floodplains, even when lacking
    surface water connections, provide
    physical, chemical, and biological
    functions that could affect the
    integrity of downstream waters.
    Some potential benefits of these
    wetlands are due to their isolation
    rather than their connectivity.
    Evaluations of the connectivity and
    effects of individual wetlands or
    groups of wetlands are possible
    through case-by-case analysis.

•   Variations in the degree of
    connectivity are determined by the
    physical, chemical and biological
    environment, and by human
    activities. These variations support a
    range of stream and wetland
    functions that affect the integrity
    and sustainability of downstream
    waters.

•   The literature strongly supports the
    conclusion that the incremental
    contributions of individual streams
    and wetlands are cumulative across
    entire watersheds, and their effects
    on downstream waters should be
    evaluated within the context of
    other streams and wetlands in that
    watershed.
Next Steps
Now final, this scientific report can be
used to inform future policy and
regulatory decisions, including the
proposed Clean Water Rule being
developed by EPA's Office of Water and
the U.S. Army Corps of Engineers.
Contact
Laurie Alexander, Ph.D.
Ecologist
Web site: http://epa.gov/ncea
       U.S. Environmental Protection Agency
       Office of Research and Development

-------