Forest Clearcutting and Site Preparation on a Saline Soil in East Texas: Impacts on Water Quality
Three 0.02 hectare plot-watersheds were installed on a saline soil in the Davy Crockett National Forest near Apple Springs, Texas. Each plot was installed with an H-flume, FW-1 automatic water level recorder, Coshocton N-1 runoff sampler, and two storage tanks. One watershed was undisturbed forested and served a control, one was clearcut without any site-preparation, and the third was clearcut, V-blade sheared, windrowed, and vegetation regrowth was prevented for the first 2 years. A total of 274 storms were recorded during the four-year study period, 1989-1992. Average annual sediment losses for the study period were 55, 197, and 1,530 kilograms per hectare per year for the control, commercial clearcut, and sheared plots, respectively. These losses are about average for most studies conducted in East Texas and the Southeast and are well below average losses for all land uses in the Southeast. Sediment losses and surface runoff were significantly greater from the sheared plot-watershed than from the control and the commercial clearcut plots. Employing Wischmeier and Smith’s (1978) long-term average Rvalue for the USLE overestimated annual sediment yield for the study period, while two shortcut models developed in the United States resulted in more accurate predictions and are good substitutes for the long-term R-value. Total losses in surface runoff of PO4, NO3, NO2, TKN, K, Ca, Mg, Na, Al, Fe, Zn, and Cu were higher on the site-prepared plot watershed than the other two. Losses of PO4, TKN, and NO2 were higher on the commercial clearcut plot than the control. Losses were not high enough to adversely affect forest productivity. Concentrations of elements were generally below established USEPA surface water quality standards and were not high enough to adversely affect plant growth.