WATER QUALITY FROM UNDISTURBED, FORESTED, INTER-STREAM WETLANDS: AN EMPIRICAL APPROACH FOR LAND

Abstract

Non-point source pollution accompanies land disturbance activities. More frequent and intense disturbance creates higher levels of non-point source pollution. Land disturbance for silviculture may be less frequent and intense than land disturbance activities from some other uses (agriculture or housing development), but increased sediment and nutrient concentrations have been observed in affected outflow waters. Areas that experience no land disturbance due to human use, however, produce some baseline levels of sediment and nutrient export. From the perspective of a land manager, it would be helpful to have some knowledge of the natural variation in water quality originating on undisturbed lands. Given a long period of observation, baseline values of surface water concentrations of nutrients and sediment from undisturbed watersheds can be established and used by the manager to compare with surface water concentrations draining lands undergoing disturbance due to management activities. Routine water quality monitoring of major outfalls on Hofmann Forest has been going on for more than 10 years. As part of that effort, two water quality sampling locations on nearby undisturbed Croatan National Forest lands have also been sampled during the past decade to provide a reference water quality condition. Chescheir et al., (2003), recently documented water quality concentrations and loadings from a variety of forested inter-stream wetlands in coastal North Carolina. Combining these data yields a dataset from which baseline values can be calculated for sediment and nutrient concentrations in surface waters draining undisturbed forested inter-stream wetlands. Baseline surface water concentrations in milligrams per liter (mg/L) are calculated as the 90th percentile value of observed distributions for nitrate [NO3 = 0.14 mg/L ], ammonium [NH4 = 0.20 mg/L ], dissolved inorganic nitrogen [DIN = 0.40 mg/L ], organic nitrogen [OrgN = 1.4 mg/L ], total nitrogen [TN = 1.8 mg/L ], phosphate [PO4 = 0.01 mg/L ], total phosphorus [TP = 0.10 mg/L], total suspended solids [TSS = 33 mg/L ] and total organic carbon [TOC = 65.0 mg/L]. The predominant soil type of the undisturbed forested inter-stream wetland drainage area and seasonal variations are also considered. These values are compared with similarly measured concentration values from surface waters draining watersheds utilized for agricultural and silvicultural purposes.