Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.


Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18103)
Authors:   A.M.S. McFarland and A. Bekele
Keywords:   water quality, trends, TMDL, nutrients, phosphorus, animal wastes

Excess nutrients have been a concern for the North Bosque River (NBR) watershed with regard to excessive growth of algae since 1990. In response to this concern, a total maximum daily load (TMDL) directing about a 50% reduction in soluble reactive phosphorus (SRP) was approved in December 2001. Within the implementation plan, a number of programs are outlined to help reduce SRP loading to the NBR. These programs include comprehensive nutrient management planning and a manure-composting program to haul manure out of the watershed. Intensive monitoring of nutrients along the NBR was initiated in the early to mid 1990s. To evaluate changes in water quality, trend analysis was performed on flow adjusted and unadjusted monthly data from routine grab and/or estimated loading concentrations using the nonparametric Kendall's tau test. Nutrient constituents for N and P, total suspended solids and chlorophyll-a were evaluated. Statistically significant but small downward trends were indicated for CHLA and SRP at several sites along the NBR. A complicating factor in interpreting these downward trends was the fact that the reference site monitored also showed decreasing trends for CHLA and SRP. In some smaller tributary watersheds of the NBR, decreases in SRP were indicated that could be associated with the dairy manure-composting program. While it appears that implementation practices are having some impact on in stream water quality, other factors may also be influencing observed decreasing trends. More time should allow a fuller indication of the impact of land use practices on changes in water quality.

(Download PDF)    (Export to EndNotes)