Jami E. Nettles

Hydrologic Effects of Size and Location of Fields Converted from Drained Pine Forest to Agricultural Cropland

AbstractHydrological effects of land-use change are of great concern to ecohydrologists and watershed managers, especially in the Atlantic coastal plain of the southeastern United States. The concern is attributable to rapid population growth and the resulting pressure to develop forested lands. Many researchers have studied these effects in various scales, with varying results. An extended watershed-scale forest hydrologic model, calibrated with 1996–2000 data, was used to evaluate long-term hydrologic effects of conversion to agriculture (corn–wheat–soybean cropland) of a 29.5-km2 intensively managed pine-forested watershed in Washington County in eastern North Carolina. Fifty years of weather data (1951–2000) from a nearby weather station were used for simulating hydrology to evaluate effects on outflows, evapotranspiration, and water table depth compared with the baseline scenario. Other simulation scenarios were created for each of five different percentages (10, 25, 50, 75, and 100%) of land-use con...

Impacts of fertilization on water quality of a drained pine plantation: a worst case scenario.

Intensive plantation forestry will be increasingly important in the next 50 yr to meet the high demand for domestic wood in the United States. However, forest management practices can substantially influence downstream water quality and ecology. This study analyses, the effect of fertilization on effluent water quality of a low gradient drained coastal pine plantation in Carteret County, North Carolina using a paired watershed approach. The plantation consists of three watersheds, two mature (31-yr) and one young (8-yr) (age at treatment). One of the mature watersheds was commercially thinned in 2002. The mature unthinned watershed was designated as the control. The young and mature-thinned watersheds were fertilized at different rates with Arborite (Encee Chemical Sales, Inc., Bridgeton, NC), and boron. The outflow rates and nutrient concentrations in water drained from each of the watersheds were measured. Nutrient concentrations and loadings were analyzed using general linear models (GLM). Three large storm events occurred within 47 d of fertilization, which provided a worst case scenario for nutrient export from these watersheds to the receiving surface waters. Results showed that average nutrient concentrations soon after fertilization were significantly (alpha = 0.05) higher on both treatment watersheds than during any other period during the study. This increase in nutrient export was short lived and nutrient concentrations and loadings were back to prefertilization levels as soon as 3 mo after fertilization. Additionally, the mature-thinned watershed presented higher average nutrient concentrations and loadings when compared to the young watershed, which received a reduced fertilizer rate than the mature-thinned watershed.

Status and prospects for renewable energy using wood pellets from the southeastern United States

The ongoing debate about costs and benefits of wood‐pellet based bioenergy production in the southeastern United States (SE USA) requires an understanding of the science and context influencing market decisions associated with its sustainability. Production of pellets has garnered much attention as US exports have grown from negligible amounts in the early 2000s to 4.6 million metric tonnes in 2015. Currently, 98% of these pellet exports are shipped to Europe to displace coal in power plants. We ask, ‘How is the production of wood pellets in the SE USA affecting forest systems and the ecosystem services they provide?’ To address this question, we review current forest conditions and the status of the wood products industry, how pellet production affects ecosystem services and biodiversity, and what methods are in place to monitor changes and protect vulnerable systems. Scientific studies provide evidence that wood pellets in the SE USA are a fraction of total forestry operations and can be produced while maintaining or improving forest ecosystem services. Ecosystem services are protected by the requirement to utilize loggers trained to apply scientifically based best management practices in planning and implementing harvest for the export market. Bioenergy markets supplement incomes to private rural landholders and provide an incentive for forest management practices that simultaneously benefit water quality and wildlife and reduce risk of fire and insect outbreaks. Bioenergy also increases the value of forest land to landowners, thereby decreasing likelihood of conversion to nonforest uses. Monitoring and evaluation are essential to verify that regulations and good practices are achieving goals and to enable timely responses if problems arise. Conducting rigorous research to understand how conditions change in response to management choices requires baseline data, monitoring, and appropriate reference scenarios. Long‐term monitoring data on forest conditions should be publicly accessible and utilized to inform adaptive management.

HYDROLOGIC EFFECTS OF GLOBAL CLIMATE CHANGE ON A LARGE DRAINED PINE FOREST

A simulation study using a watershed scale forest hydrology model (DRAINWAT) was conducted to evaluate potential effects of climate change on the hydrology of a 3,000 ha managed pine forest in coastal North Carolina. The model was first validated with a five-year (1996-2000) data set from the study site and then run with 50-years (1951-00) of historic weather data from Plymouth, NC to determine the long-term hydrology. Later, separate simulations were conducted with 2001-2025 climate change data sets projected by two existing Global Circulation Models (GCM), Canadian Climate Change (CGC1) and the British model (HadCM2). The predicted average annual outflow of 308 mm for the 1996-00 study period (average annual rainfall (AAR) of 1232 mm) was 15% lower than the average of 362 mm for the 1951-00 period (AAR = 1288 mm). Simulation results using 2001-25 climate data projected by the CGC1 model yielded a significantly (p 0.5) outflow than the 50 year historic data showed. Interestingly, the distribution of runoff coefficients for the HadCM2 was almost the same as that for the historic data, indicating minor potential effect of this climate change scenario on drainage. Both the GCM climate scenarios predicted significantly (p<0.005) higher ET than the historic. Water table depth is predicted deeper by the CGC1 model due to lower precipitation input and higher ET. However, the climate changes even under a drier and hotter scenario may not have significantly reduced tree water use although drainage may have been reduced greatly. The ET predicted by the HadCM2 (1008 mm) and CGC1 (1021 mm) were similar, indicating the increase in temperature predicted by the CGC1 model has less of an effect on the soil moisture limiting the tree growth than the increased rainfall predicted by HadCM2.

Advances in forest hydrology: challenges and opportunities

Forests are an integral component of the landscape, and maintaining their functional integrity is fundamental for the sustainability of ecosystems and societies alike. Tools, innovations, and practices, analogous to those developed to improve agricultural production and quantify environmental impacts, are needed to ensure the sustainability of these forested landscapes as well as the ecosystem goods and services they produce. This article introduces ten technical articles on critical ecohydrologic processes, protection and restoration, and the effects of management practices on the hydrology and water quality of forests and forested wetlands, using both monitoring and modeling approaches. Prepared by experts in forest science, forest and agricultural hydrology, and water management, the studies reported in this special collection are concentrated in the Atlantic Coastal plain and focus on forests with shallow water tables. Experimental studies describe the effects of riparian vegetation harvest, human disturbance, and future climatic change on groundwater, the significance of emergent vegetation after harvest, and long-term hydrologic water balance of a managed pine forest. Modeling studies use the SWAT model to predict streamflow dynamics of a less disturbed, coastal forested watershed, and DRAINMOD to determine the impacts of minor silvicultural drainage on wetland hydrology and to improve wetland restoration. Finally, a study describes potential uncertainties associated with infrequent water sampling of nutrient loads from drained forested watersheds. This introductory article summarizes these studies of shallow water table forests and relates them to the broader field of forest hydrology, including its challenges and opportunities, while identifying pressing issues of land use and climate change. The results from these studies should help guide management and restoration of forest wetland ecosystems and direct future forest hydrologic research, including research in large prior converted agricultural landscapes.

Switchgrass growth and pine–switchgrass interactions in established intercropping systems

Intercropping switchgrass (Panicum virgatum L.) with loblolly pine (Pinus taeda L.) has been proposed for producing bioenergy feedstock in the southeastern United States. This study investigated switchgrass growth and pine–switchgrass interactions at two established experimental fields (7‐year‐old Lenoir site and 5‐year‐old Carteret site) located on the coastal plain of eastern United States. Position effects (edge and center of switchgrass alley in intercropping plots) and treatment effects (intercropping vs. grass‐only) on aboveground switchgrass growth were evaluated. Interspecific interactions with respect to capturing resources (light, soil water, and nitrogen) were investigated by measuring photosynthetically active radiation (PAR) above grass canopy, soil moisture, and soil mineral nitrogen contents. Switchgrass growth was significantly (P = 0.001) affected by treatments in Lenoir and by position (P < 0.0001) in both study sites. Relative to the center, PAR above grass canopy at edge in both sites was about 48% less during the growing season. Soil water content during the growing season at the edge of grass alley was significantly (P = 0.0001) lower by 23% than at the center in Lenoir, while no significant (P = 0.42) difference was observed in Carteret, in spite of more grass growth at center at both sites. Soil mineral nitrogen content at the center of intercropping plots in Lenoir (no fertilization during 2015) was significantly (P < 0.07) lower than at the edge during the peak of growing season (June, July, and August), but not during early and late parts of growing season (May, September, and November). Position effects on soil water and mineral nitrogen were less evident under conditions with higher external inputs (rainfall and fertilization) and lower plant uptake during nongrowing seasons. Results from this study contributed to a better understanding of above‐ and belowground pine–switchgrass interactions which is necessary to properly manage this new cultivation system for bioenergy production in the southeastern United States.

Development and preliminary evaluation of an integrated field scale model for perennial bioenergy grass ecosystems in lowland areas

Computer models are useful tools for evaluating environmental and economic sustainability of proposed dedicated cellulosic grass ecosystems for biofuel production. This study developed an integrated, field scale, and process-based ecosystem model (DRAINMOD-GRASS) for simulating hydrological processes, soil carbon and nitrogen cycling, and plant growth in cropping systems for producing bioenergy grasses in lowland areas. We tested the model using measurements from three replicated switchgrass (Panicum virgatum) plots located in eastern North Carolina, USA. Results showed that the model accurately predicted 5-year (2009-2013) biomass yield. Predicted daily water table depth closely matched field measurements with Nash-Sutcliffe coefficient of 0.86. The model also accurately predicted temporal dynamics of daily soil moisture and temperature with Nash-Sutcliffe coefficients of 0.7 and 0.9, respectively. Predicted seasonal changes in net N mineralization and nitrification rates were comparable to field measurements in 2011 and 2012. Developed an integrated field scale model for perennial bioenergy grass ecosystem.DRAINMOD-GRASS was tested in a switchgrass field with 5-year measurements.The model performed well in predicting grass yield, hydrology, and N cycling.DRAINMOD-GRASS can be useful tool for bioenergy grass ecosystem in lowland areas.

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.

Calibration of paired watersheds: Utility of moving sums in presence of externalities

Historically, paired watershed studies have been used to quantify the hydrological effects of land use and management practices by concurrently monitoring two similar watersheds during calibration (pre-treatment) and post-treatment periods. This study characterizes seasonal water table and flow response to rainfall during the calibration period and tests a change detection technique of moving sums of recursive residuals (MOSUM) to select calibration periods for each control-treatment watershed pair when the regression coefficients for daily water table elevation (WTE) were most stable to minimize regression model uncertainty. The control and treatment watersheds were one watershed of 3−4 year-old intensely managed loblolly pine (Pinus taeda L.) with natural understory, one watershed of 3−4 year-old loblolly pine intercropped with switchgrass (Panicum virgatum), one watershed of 14−15 year-old thinned loblolly pine with natural understory (control), and one watershed of switchgrass only. The study period spanned from 2009 to 2012. Silvicultural operational practices during this period acted as external factors, potentially shifting hydrologic calibration relationships between control and treatment watersheds. MOSUM results indicated significant changes in regression parameters due to silvicultural operations and were used to identify stable relationships for WTE. None of the calibration relationships developed using this method were significantly different from the classical calibration relationship based on published historical data. We attribute that to the similarity of historical and 2010−2012 leaf area index (LAI) on control and treatment watersheds as moderated by the emergent vegetation. While the MOSUM approach does not eliminate the need for true calibration data or replace the classic paired watershed approach, our results show that it may be an effective alternative approach when true data is unavailable, as it minimizes the impacts of external disturbances other than the treatment of interest.

Effects of Regeneration on Hydrology and Water Quality of a Managed Pine Forest

Intensive forest management practices such as drainage, harvesting, site preparation, regeneration, and fertilization have been frequently blamed for problems related to excessive nitrogen, phosphorus, and sediment in receiving waters. Two 25 ha experimental watersheds (D1 – control; D2 – treatment) on a pine plantation in eastern North Carolina have been monitored since 1988 to study the hydrologic and water quality effects of various silvicultural and water management treatments using a paired watershed approach. Data from a two-year calibration period (1988-90) and a four-year regeneration period (2000-03) were used for the analysis. This study period recorded both the highest (2330 mm in 2003) and lowest (850 mm in 2001) rainfall of the 16-years (1988-2003) of record at this site. Nearly seven years after planting, water table elevations returned back to pre-treatment conditions. However, peak flow rates and consequently annual outflows were generally higher on the treatment watershed D2 compared to the control watershed (D1), indicating that the outflows on the treatment watershed may not have completely returned back to base line conditions. Average outflow nutrient (NO3-N, TKN, and Total-P) concentrations for the treatment (D2) watershed for the period from 2000 to 2003 were, however, similar or somewhat lower than their expected values. Although sediment concentration seems to have slightly increased compared to the calibration period, regeneration did not seem to have any effect by the third year after planting, The water quality concentrations were also much lower than the data reported for agricultural lands in the same region. These results will be evaluated and reported soon in the context of prior data after harvesting in 1995 and planting in 1997 to detect the actual effects of regeneration.