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The influence of forest operations on forest soil and water continues to be an issue of concern in forest management. Research has focused on evaluating forest operation effects on numerous soil and water qualify indicators. However, poorly drained forested watersheds with organic soil surface horizons have not been extensively investigated. A study was initiated in the Tidewater region of North Carolina to gain a better understanding of the impact of harvesting operations on poorly drained organic soils. Soils on the study site, having >80% organic matter (OM) content to a depth of 60 cm below the soil surface, were classified as shallow organic soils. Soil physical properties were examined by collecting soil cores from control and treatment watersheds in a nested design. Compaction caused by the harvest operation increased bulk density (Db) from 0.22 to 0.27 g cm-3, decreased saturated hydraulic conductivity (ksat) from 397 to 82 cm h-1, and decreased the drained volume for a given water table depth. However, Db following the harvest remained low at 0.27 g cm-3. The drained volume at equilibrium following the lowering of the water table from the soil surface to a depth of 200 cm was reduced by 10% from that of control watershed as a result of harvesting. [ABSTRACT FROM AUTHOR]

Sedimentation basins are built at construction sites to reduce the load of suspended solids in runoff water discharged into surface waters. However, these basins are not effective in reducing turbidity caused by fine suspended particles such as clay and silt. The objective of his field study was to evaluate the efficiency of moulding plaster (CaSO4-0.5 H2O) as a chemical flocculant for reducing the turbidity of water discharged from sedimentation basins equipped with a floating skimmer device. Following each of 14 rainfall events, sedimentation basins at two urban construction sites were either treated with moulding plaster or left untreated, and the turbidity and chemical properties of the impounded water and discharge water were monitored as the basins drained during a 50- to 70-h time period. Each sedimentation basin was equipped with a floating skimmer device that discharged water at a controlled rate from 5-cm below the surface of the imPounded water. The turbidity of discharge water from untreated basins ranged from 100 to 1650 NTU (nephelometric turbidity units), while a surface-applied moulding plaster treatment of 450 to 520 m decreased the turbidity to g L- 1 <50 NTU. The time required for the discharge water from treated basins to reach either 100 NTU (2--20 h) or 50 NTU (5--52 h) was inversely proportional to theconcentration of dissolved moulding plaster. Chemical flocculation using plaster reduced the turbidity of discharge water to<50 NTU whileproducing dissolved SO4 concentrations of <250 mg L-1. [ABSTRACT FROM AUTHOR]

A high-suspended solids load in surface waters is one of the biggestwater quality problems in the Piedmont region of the southeastern USA. Sedimentation basins at construction sites are designed to redace suspended solids in discharged water, but they are not effective in reducing turbidity. A survey of sedimentation basin water at two urbanconstruction sites showed that turbidity levels during a 9- to 12-moperiod were always greater than the 50-NTU (nephelometric turbidity units) standard adopted in North Carolina for surface waters. Furthermore, water chemistry varied over time, with pH ranging from 5.8 to 8.9 and electrical conductivity (EC) ranging from 3.0 to 23.0 mS m-'. Laboratory experiments demonstrated that temporal variations in the water chemistry were likely caused by contact with concrete and crushed stone. Laboratory flocculation experiments were completed to evaluate the efficiency of calcium sulfate compounds (hemihydrate, agricultural gypsum, and phosphogypsum) as chemical tlocculants for reducing the turbidity of sedimentation basin water from two field sites and for different pH conditions. Moulding plaster (hemihydrate) was a moreefficient flocculant than agricultural gypsum and has fewer environmental restrictions on its use than phosphogypsum. Moulding plaster application rates of 350 to 700 mg L -1 were needed to reduce the turbidity of unstirred sedimentation basin water to 50 NTU within 3 h after addition of the flocculant. To achieve a given turbiditylevel, less flocculant was required for longer flocculation and settling times, or when sedimentation basin water had a lower pH. [ABSTRACT FROM AUTHOR]