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TECHNICAL REPORTS

Surface Water Quality

Water Quality Effects of Clearcut Harvesting and Forest Fertilization with Best Management Practices

^a Arthur Temple College of Forestry and Agriculture, Stephen F. Austin State Univ., Box 6109 SFA Station, Nacogdoches, TX 75962
^b National Council for Air and Stream Improvement, PO Box 458, Corvallis, OR 97339

^* Corresponding author (mcbroommatth{at}sfasu.edu).

Received for publication December 20, 2006. Nine small (2.5 ha) and four large (70–135 ha) watersheds were instrumented in 1999 to evaluate the effects of silvicultural practices with application of best management practices (BMPs) on stream water quality in East Texas, USA. Two management regimes were implemented in 2002: (i) conventional, with clearcutting, herbicide site preparation, and BMPs and (ii) intensive, which added subsoiling, aerial broadcast fertilization, and an additional herbicide application. Watershed effects were compared with results from a study on the same small watersheds in 1981, in which two combinations of harvesting and mechanical site preparation without BMPs or fertilization were evaluated. Clearcutting with conventional site preparation resulted in increased nitrogen losses on the small watersheds by about 1 additional kg ha^–1 each of total Kjeldahl nitrogen (TKN) and nitrate-nitrogen (NO₃–N) in 2003. First-year losses were not significantly increased on the large watershed with a conventional site preparation with BMPs. Fertilization resulted in increased runoff losses in 2003 on the intensive small watersheds by an additional 0.77, 2.33, and 0.36 kg ha^–1 for NO₃–N, TKN, and total phosphorus, respectively. Total loss rates of ammonia nitrogen (NH₄–N) and NO₃–N were low overall and accounted for only 7% of the applied N. Mean loss rates from treated watersheds were much lower than rainfall inputs of about 5 kg ha^–1 TKN and NO₃–N in 2003. Aerial fertilization of the 5-yr-old stand on another large watershed did not increase nutrient losses. Intensive silvicultural practices with BMPs did not significantly impair surface water quality with N and P.

Abbreviations: BMPs, best management practices • DAP, diammonium phosphate • LW, large watershed • SMZ, streamside management zone • SW, small watershed • TKN, total Kjeldahl nitrogen • TN, total nitrogen • TP, total phosphorus