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Title: Reply to discussion of, "Adapting Existing Models to Examine Effects of Agricultural Conservation Programs on Stream Habitat Quality"

item Shields Jr, Fletcher
item Langendoen, Eddy

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2006
Publication Date: 12/1/2006
Citation: Shields Jr, F.D., Langendoen, E.J., Doyle, M.W. 2006. Reply to discussion of, "Adapting Existing Models to Examine Effects of Agricultural Conservation Programs on Stream Habitat Quality". Journal of the American Water Resources Association 42(6):1711-1713.

Interpretive Summary: Aquatic ecosystems are increasingly threatened by degradation associated with agriculture. The federal government is increasing funding for agricultural programs that provide incentives for farmers to take land out of cultivation, plant trees, establish buffers of natural vegetation along streams and watercourses, and other activities intended to protect the environment. However, the benefits of these expenditures have not been quantified. A recently initiated program seeks to estimate benefits using computer models, but these models focus primarily on water quality and have very limited capacity to simulate stream habitat quality. A preliminary assessment of the capabilities of these models was conducted, and an approach for deriving ecologically-meaningful information from the model outputs was outlined. This approach, if adopted, could assist administrators of agricultural conservation programs to achieve greater returns in ecological services for public funds invested. After publication of a paper describing this approach, journal readers suggested that the approach was flawed. They pointed out that the existing computer models do not adequately simulate small, narrow areas along streams. This reply clarifies the original proposal, which focused on the simulation of six ecologically important characteristics of stream corridors, and relied on watershed models only to provide the amount of streamflow.

Technical Abstract: Annual expenditures by the federal government in the US for agricultural conservation increased about 80% with passage of the 2002 Farm Bill. However, environmental benefits of these programs have not been quantified. A national project is underway to estimate the effect of conservation practices on environmental resources. However, watershed models selected for this project have minimal habitat assessment capability and even more limited links to ecological condition. Major impairments to aquatic ecosystems in many watersheds consist of physical habitat degradation not water quality. This paper describes approaches for adding components to these models to allow rudimentary stream habitat quality assessments. At least six types of variables could be examined for ecological impact: land use, stream flow, water temperature, stream bed material type, large woody debris, and hydraulic conditions at base flow. All of these variables are influenced by the presence, location and quality of buffers. Discussers of the paper suggest that the proposed approach is flawed because the watershed models lump land use within a subwatershed and therefore are insensitive to management measures in riparian on streamside buffer areas that do not affect the subwatershed as a whole. We reply that we do not suggest that the watershed models be used to simulate riparian processes, but simply to provide hydrologic loadings to more specialized modules.