Abstract

From 1988 to 1998, silvicultural activities impacted 5,856 km of rivers and streams in the southern United States. Internal cycling of nutrients from the water column and sediment in a forest can be an important contribution to the nutrient load of aquatic ecosystems. Therefore, understanding nutrient transport in forests can aid efforts to protect aquatic resources. Two watersheds in Tate's Hell State Forest in northwest Florida were selected to conduct a study of silvicultural impacts on surface water quality. Of the two sites one had been impacted with ditching and fertilization while the other site was not. From June 2003 to May 2005 a field study determined nutrient [nitrate-nitrogen (NO3-N); ammonia-nitrogen (NH3-N) and ortho-phosphate (PO4)] concentrations in run-off water and sediment in these watersheds. Results showed NO3-N, NH3-N and ortho-phosphate concentrations in water and sediment, were higher at the impacted site verses the non-impacted site. At the impacted site NO3-N, NH3-N and ortho-phosphate concentrations in the water column were 16% to 33%, 39% to 47% and 66% higher, respectively. Nutrient concentrations in sediment from the impacted site were significantly (p< 0.05) higher than those from the un-impacted site and ranged (in mg kg−1) from 0.25 ± 0.01 to 0.44 ± 0.03 for NO3-N; 6.41 ± 0.19 to 12.77 ± 0.45 for NH3-N; and 1.01± 0.02 to 1.50 ± 0.02 for PO4. In this ecosystem sediment acted as a source of NH3-N and ortho-phosphate and as a sink for NO3-N. These results indicate that proper management of inactive silvicultural sites is necessary to mitigate nutrient transport to aquatic systems.

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