Impacts of Fertilizer Additions on Water Quality of a Drained Pine Plantation in North Carolina. A Worst Case Scenario

Intensive plantation forestry will be increasingly important in the next 50 years to meet the high demand for domestic wood in the US. However, forestry management practices can substantially influence downstream water quality and ecology. In this study, the effect of fertilization on drainage water quality of a coastal pine plantation located in Carteret County, NC was studied. The pine plantation consists of three watersheds, two mature (31-year old) and a young (8-year old) stands (age at treatment). One of the mature stands was commercially thinned in 2002. The unthinned mature stand was designated as a control and was not fertilized. The two other stands (young and thinned) were fertilized with diammonium phosphate, urea, and boron. Each treatment watershed received a different fertilizer rate. Both the flow rates and nutrient concentrations in water drained from each of the watersheds were measured. Nutrient concentrations and nutrient loadings were analyzed using a paired watershed approach and GLM statistical procedures. Three large storm events occurred soon after fertilization, a 5-year 24 hr, a 1 to 2-year, and a third event (46 mm in 46 hr) occurred six, 29 and 47 days after fertilization respectively. It was determined that peak nutrient concentrations soon after fertilization were much higher than the average concentrations, which were significantly (α = 0.05) higher on both treatment watersheds soon after fertilization than during any other period during the study. The effect of fertilization on both the nutrient concentrations and loading rates was short lived and the levels were back to pre-fertilization levels as soon as three months after fertilization. Also, the average nutrient increase on the thinned stand was higher than on the young stand as a result of a higher fertilizer rate applied on the thinned stand one.