T. W. Appelboom

MANAGEMENT PRACTICES FOR SEDIMENT REDUCTION FROM FOREST ROADS IN THE COASTAL PLAINS

Sediment has been identified as one of the most important non-point source pollutants of surface waters. In forested areas, the predominant source of sediment is from the construction and maintenance of access roads, which contribute as much as 90% of the total eroded sediments. Seven different road management practices were studied to determine their effectiveness in reducing sediment production from forest roads on nearly flat lands in the lower coastal plains of North Carolina. One practice utilized a continuous berm along the roadside, while the other six practices had a non-continuous berm with different combinations of road surface gravel and roadside vegetative strips. Runoff samples collected during eleven different rainfall events of varying intensity and duration were analyzed for sediment content. The rainfall amount, intensity, infiltration, and antecedent rainfall conditions were combined into a single energy rating to assist in the overall analysis. The results of the study showed that a continuous berm maintained along the edge of a forest road can reduce total sediment loss by an average of 99% compared to the same type road without the presence of a continuous berm. When a continuous berm is not present, graveling the road surface can reduce the total loss of sediment from roads by an average of 61% compared to a non-graveled road surface. A 90 cm wide grass strip on the edge of the driving surface can reduce total sediment loss by an average of 56% compared to a road without a grass strip.

Estimating Nitrogen, Phosphorus, and Carbon Fluxes in Forested and Mixed-Use Watersheds of the Lower Coastal Plain of North Carolina: Uncertainties Associated with Infrequent Sampling

Assessing the impact of a land use change or the water quality improvement provided by a treatment system almost always involves computation of the difference in nutrient loads before and after implementation, or upstream and downstream of the system studied. Reporting meaningful values on mass balance or differences in nutrient loads implies that the uncertainty in the computed loads is several times smaller than the difference itself. This may imply very small uncertainties for the nutrient load measurements. The level of uncertainty induced by infrequent sampling on annual loads was investigated for a suite of nutrients in runoff from a forested watershed and a mixed land use watershed in the lower coastal plain of North Carolina. Reference data were used to simulate discrete sampling and to calculate new annual load estimators, which were then compared to the reference loads to calculate the level of uncertainty. Uncertainties depended on the watershed and the nutrients and other constituents, but their level was generally found to be high, around ±20% and ±40% or more for weekly and monthly sampling for most nutrients. This was generally attributed to the short periods of active flow in these watersheds and the flashiness of flow associated with subsurface drainage. The results suggest that to obtain uncertainties of ±2% or ±5% for nitrogen forms, 100 or more than 200 samples over six months of the year might be necessary in the forested and mixed-use watersheds of the lower coastal plain.

Effects of Site Preparation for Pine Forest/Switchgrass Intercropping on Water Quality

A study was initiated to investigate the sustainability effects of intercropping switchgrass ( L.) in a loblolly pine ( L.) plantation. This forest-based biofuel system could possibly provide biomass from the perennial energy grass while maintaining the economics and environmental benefits of a forest managed for sawtimber. Operations necessary for successful switchgrass establishment and growth, such as site preparation, planting, fertilizing, mowing and baling, may affect hydrology and nutrient runoff. The objectives of this study were (i) to characterize the temporal effects of management on nutrient concentrations and loadings and (ii) to use pretreatment data to predict those treatment effects. The study watersheds (∼25 ha each) in the North Carolina Atlantic Coastal Plain were a pine/switchgrass intercropped site (D1), a midrotation thinned pine site with natural understory (D2), and a switchgrass-only site (D3). Rainfall, drainage, water table elevation, nitrogen (total Kjedahl N, NH-N, and NO-N), and phosphate were monitored for the 2007-2008 pretreatment and the 2009-2012 treatment periods. From 2010 to 2011 in site D1, the average NO-N concentration effects decreased from 0.18 to -0.09 mg L, and loads effects decreased from 0.86 to 0.49 kg ha. During the same period in site D3, the average NO-N concentration effects increased from 0.03 to 0.09 mg L, and loads effects increased from -0.26 to 1.24 kg ha. This study shows the importance of considering water quality effects associated with intensive management operations required for switchgrass establishment or other novel forest-based biofuel systems.

Nitrogen Balance for a Plantation Forest Drainage Canal on the North Carolina Coastal Plain

Human alteration of the nitrogen cycle has led to increased riverine nitrogen loads, contributing to the eutrophication of lakes, streams, estuaries, and near-coastal oceans. These riverine nitrogen loads are usually less than the total nitrogen inputs to the system, indicating nitrogen removal during transport through the drainage network. A two-year monitoring study quantified the ammonium, nitrate, and organic-N inputs, outputs, and inferred in-stream processes responsible for nitrogen transformations and removal in a 1900 m reach of a drainage canal located in a managed pine plantation. Total nitrogen inputs to the canal section were 527.8 kg in 2001 and 1422.7 kg in 2002. Total nitrogen discharge at the outlet was 502 kg in 2001 and 1458 kg in 2002. The mass balance of nitrogen inputs and outputs indicated a loss of 25.8 kg (5.1%) of total nitrogen from the system in 2001, and a gain of 35.3 kg (2.4%) of total nitrogen to the system in 2002. Variability in the input and output estimates was high, especially for groundwater exchange. Different hydrologic and nitrogen inputs and outputs were identified and quantified, but measurement variability obscured any potential nitrogen removal from the system.

Effects of forest-based bioenergy feedstock production on shallow groundwater quality of a drained forest soil

Managed forests in southern U.S. are a potential source of lignocellulosic biomass for biofuel production. Changes in management practices to optimize biomass production may impact the quality of waters draining to nutrient-sensitive waters in coastal plain regions. We investigated shallow groundwater quality effects of intercropping switchgrass (Panicum virgatum L.) with managed loblolly pine (Pinus taeda L.) to produce bioenergy feedstock and quality sawtimber in a poorly drained soil of eastern North Carolina, U.S.A. Treatments included PINE (traditional pine production), PSWITCH (pine-switchgrass intercropped), SWITCH (switchgrass monoculture) and REF (mature loblolly pine stand). Each treatment was replicated three times on 0.8ha plots drained by parallel-open ditches, 1.0-1.2m deep and 100m apart. Water samples were collected monthly or more frequently after fertilizer application. Water samples were analyzed for organic nitrogen (ON), ammonium N (NH4+- N), and nitrite+nitrate N (NO3-+ NO2-- N), ortohophosphate phosphorus (OP), and total organic carbon (TOC). Overall, PSWITCH did not significantly affect shallow groundwater quality relative to PINE and SWITCH. ON, NO3-+ NO2-- N, and TOC concentrations in PSWITCH, PINE and SWITCH were substantially elevated during the two years after tree harvest and site establishment. The elevated nutrient concentrations at the beginning of the study were likely caused by a combination of rapid organic matter decomposition of the abundant supply of post-harvest residues, warming of exposed soil surfaces and reduction of plant nutrient uptake that can occur after harvesting, and pre-plant fertilization. Nutrient concentrations returned to background levels observed in REF during the third year after harvest.