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Use of spatially explicit physicochemical data to measure downstream impacts of headwater stream disturbance
Citation:
JOHNSON, B. R., A. Haas, AND K. M. FRITZ. Use of spatially explicit physicochemical data to measure downstream impacts of headwater stream disturbance. WATER RESOURCES RESEARCH. American Geophysical Union, Washington, DC, 46:W09526, (2010).
Impact/Purpose:
Use of semivariograms or predictive confluence models can help regulatory agents identify downstream influence of headwater streams and presence of a "significant nexus" with downstream waters.
Description:
Regulatory agencies need methods to quantify the influence of headwater streams on downstream water quality as a result of litigation surrounding jurisdictional criteria and the influence of mountaintop removal coal mining activities. We collected comprehensive, spatially-referenced physicochemical data from the partially mined Buckhorn Creek KY watershed in summer 2005 and spring 2006. We found conductivity was >10 times higher in mined streams than in forested streams. Semivariograms, which quantify the degree of spatial dependence in chemistry values, indicated summer temperatures in both mined and unmined portions of the watershed had similar lag distances. Data for other parameters and seasons, however, violated model assumptions because of strong confluence effects in headwaters. We therefore developed a post-hoc predictive model for water physicochemistry downstream of confluences using watershed areas as weighting factors. This weighted-average model accurately predicted downstream conductivity and temperature for confluences in Buckhorn Creek and two additional watersheds with headwater disturbance in West Virginia and Ohio.