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United States Department of Agriculture

Agricultural Research Service


Location: Southeast Watershed Research

2012 Annual Report

1a. Objectives (from AD-416):
1. Use remote sensing tools to develop rapid assessment procedures for soil and water resources in Coastal Plain agricultural systems. a. Evaluate tillage and residue management effects on soil carbon accretion, soil water content and associated changes in crop response. b. Remotely quantify variability in crop residue cover to better develop indices that may be used to rapidly assess conservation tillage adoption at the watershed scale. 2. Modify, test, and apply the Riparian Ecosystem Management Model (REMM) to evaluate and guide restoration and management of riparian buffers and wetlands. 3. Develop an improved GIS modeling framework for accurately quantifying soil moisture, evapotranspiration (ET), and infiltration in Coastal Plain watersheds. a. Evaluate techniques for assimilating estimates of soil-moisture at the soil surface into field and watershed scale hydrologic models. b. Improve methods for estimating evapotranspiration and infiltration within Coastal Plain watersheds. 4. Evaluate the effects of land use and surface water features on nutrient and dissolved oxygen levels in Coastal Plain watersheds.

1b. Approach (from AD-416):
OBJ.1: Direct measurements of soil and plant attributes will be related to crop yield and measurable changes in soil organic carbon accretion, soil water content, plant available water content, microbial community size, soil nitrogen, and nitrate leaching. Remotely sensed data will allow us to 1) integrate the combined effects of soil organic carbon accretion and nitrogen management via real-time, non-destructive assessments of crop response, 2) monitor crop response as a function of plant available water and nitrogen contents, and 3) refine crop coefficients for improved irrigation management and water use efficiency. OBJ.2: The Riparian Ecosystem Management Model will be modified to facilitate use for specific applications such as pesticide transport, P retention estimates, and watershed scale buffer scenario testing. Procedures will be tested for integrating modifications of REMM with watershed scale models. REMM integrations with watershed and channel process models will be tested using watershed data collected at ARS and cooperator watersheds in Georgia, Delaware, Mississippi, Maryland, and elsewhere. OBJ.3: A GIS based modeling system will be developed to simulate soil moisture conditions across the region. Based upon existing soil, climate, and vegetation data, the system will allow point, field, and watershed scale estimates of evapotranspiration, runoff, and soil moisture. It is anticipated that the system will be capable of estimating soil moisture across spatially variable fields for purposes of irrigation scheduling, as well as watersheds equivalent in size to the Little River Experimental Watershed for purposes of long term water resource planning. OBJ.4: Levels of dissolved oxygen will be correlated with other measured water quality parameters for 18 sites in the Suwannee River Basin to determine if relationships exist between dissolved oxygen and stream chemistry.

3. Progress Report:
This is the final report for the project that terminated on 3/07/2012. Direct measurements of soil and plant attributes were used to link crop yield and measurable changes in soil organic carbon accretion, soil water content, plant available water content, microbial community size, soil nitrogen, and nitrate leaching (Objective 1). The Riparian Ecosystem Management Model (REMM) was modified to facilitate use for specific applications such as pesticide transport, P retention estimates, and watershed scale buffer scenario testing (Objective 2). These modifications of REMM were tested on local and cooperator sites. Cooperators at North Carolina State University (NCSU) used REMM to evaluate buffers established as part of the USDA funded North Carolina Conservation Reserve Enhancement Program. A Geographic Information System (GIS) based modeling system was developed to simulate soil moisture conditions across the region (Objective 3). Factors (biological and physical) affecting dissolved oxygen in Coastal Plain streams were examined and relationships between dissolved oxygen levels and other aspects of stream chemistry and oxygen consuming processes were determined. Validation of soil moisture data collected by the European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission was conducted using data collected from the Little River Experimental Watershed along with data sets from three additional ARS research watersheds (Objective 4). As part of a National Institute of Food and Agriculture (NIFA) grant to Fort Valley State University, two sites in the southeast Coastal Plain are being used for trials of two bioenergy grasses - elephant grass(Pennisetum purpureum (L.) Schum.) and energy cane (Saccharum officinarum L.) to obtain data for Life Cycle Analysis (LCA) of the crop production enterprise. The sites are located in Tift County, Georgia (Tifton loamy sand soil) and Peach County, Georgia (Orangeburg loamy fine sand soil) on lands that were previously weed fallow. The grasses were established in a randomized complete block design (four replicates) in August, 2011. Treatments for the grasses include different winter covers (Clover, lupine, or no winter cover) and different fertilizer N rates (0, 75 kg N /ha and 150 kg N /ha). Changes in soil carbon and physical properties will be determined by comparing starting conditions to conditions at the end of the 5 year project. Biomass production for each growing season will be determined. First year harvest was done after the short growing season (from August-December). To provide specific data for the LCA, weekly sampling of greenhouse gas fluxes (CH4, N2O, and CO2) using vented chambers were started shortly after planting for the clover cover treatments receiving the three N rates. Continued research will provide data for LCA of these two bioenergy crops and provide data on the potential production of these crops under non-irrigated conditions with varying levels of N input.

4. Accomplishments
1. Estimation of soil moisture from remotely collected satellite data. Soil moisture products from satellite sensors have the potential to dramatically improve the accuracy and timeliness of weather, climate, and agricultural assessments and forecasts used by USDA, National Oceanic and Atmospheric Administration (NOAA), and other agencies. ARS researchers at Tifton, Georgia, Beltsville, Maryland, Tucson, Arizona, El Reno, Oklahoma, and Boise, Idaho worked cooperatively on the testing. Comparisons between estimates of soil moisture from satellite data and field data collected at the ARS Little River Experimental Watershed in Tifton, Georgia, indicate that the satellite based estimates of soil moisture track soil moisture trends fairly well. Additional research is being conducted to improve the methods used to relate basic satellite measurements to actual soil moisture conditions on the ground.

2. Estimation of biofuels feedstock production potentials from non-forested riparian zones and grass waterways. USDA's Regional Roadmap to Meeting the Biofuels Goals of the Renewable Fuels Standard by 2022 targets the southeastern U.S. for delivery of 49.8% of the feedstock contributions needed to meet the advanced biofuels goal of 79.5 billion liters per year. Using corporate estimates that 14,160 ha must be dedicated to feedstock production within 40 km of a 136 million liter per year biofuel conversion facility converting perennial grass feedstocks via cellulosic ethanol production, we used field trial data to estimate that from 6% to 38% of the needed acreage could be gained from riparian buffers and grassed waterways. The remaining acreage, if taken from agricultural land in the 40 km radius would be from 3% to 18% of current agricultural lands. The analysis suggests a potential to produce> 1.98 billion liters of ethanol per year (at 270 liters per Mg dry matter and 33 Mg ha-1 yr-1 dry matter) from riparian zones alone around 11 case study cities in the coastal plain of south Georgia. Another 814 million liters per year could come from nonprime agricultural lands (at 22 Mg ha-1 yr-1 dry matter).

3. Natural stream features rather than anthropogenic pollution causes low dissolved oxygen in Coastal Plain blackwater streams. Blackwater streams are found throughout the Coastal Plain of the southeastern United States and are characterized by low gradients, high summertime temperatures, and extensive inundation of surrounding floodplains during high flows. Typically lasting from winter to early spring, the long inundated floodplain swamps play a vital role in overall water quality. Over 90% of the blackwater streams listed as impaired on the Coastal Plain of Georgia are listed as being in violation of the state’s dissolved oxygen (DO) standard. A key influence on the DO levels within these floodplain swamps is sediment oxygen demand (SOD), a critical and dominant sink for oxygen in many river systems that is often poorly investigated or roughly estimated in oxygen budgets. SOD rates in Little River were up to 18 times higher than values reported for other southeastern sandy-bottomed streams and suggest that in-stream swamps are repositories of large amounts of organic matter and are thus areas of intense oxygen demand and a major factor in determining the oxygen balance of the stream as a whole. These areas of intense oxygen demand in relatively unimpacted areas indicate that low DO concentrations may be a natural phenomenon. SOD rates were significantly correlated with a number of sediment parameters with total organic carbon being the best predictors of SOD rate. The estimated SOD was adequate to reduce DO levels from saturation levels to below the water quality standard during flow through a swamp on the Little River.

4. A small unmanned aerial vehicle, equipped with a thermal infrared camera can be used to evaluate crop response to irrigation and winter cover crop management. Thermal infrared (TIR) emittance has been well-correlated with canopy temperature and is often used as a measure of a plant’s ability to dissipate excess energy. However, until recently field-scale estimates of TIR emittance have been compromised by expense and lack of temporal resolution. Recent advancements in TIR cameras mounted in small unmanned aerial systems have allowed researchers to assess crop response to irrigation and winter cover crop management at the field scale. Findings from recent studies indicate that TIR data acquired in this way are more sensitive to crop response to micro-climate conditions compared to traditional, and more time intensive, methods of assessment. Practical implications of this tool include in-season mitigation of crop stress, improved irrigation strategies, and an assessment of landscape level effects on crop productivity.

5. Quantifying crop residue cover at spring planting using remotely sensed data. Conservation tillage can reduce erosion, increase infiltration and help build soil organic carbon but monitoring adoption of conservation tillage within a watershed using a line-transect or windshield survey approach is time-consuming, subject to bias, and can misrepresent within field variability in crop residue coverage. A ground-based remotely sensed index using blue (445 nm) and middle infrared (1650 nm) regions of the light spectrum has been used to differentiate between conventional and conservation tillage treatments. Indices were tested over a period of weeks, and exhibit a strong linear relationship with increasing amounts of crop residue coverage in Coastal Plain systems. These data provided the foundation of a satellite-based mapping algorithm developed in Project 6602-13000-020-00D, depicting conservation tillage adoption in the Little River Experimental Watershed.

6. Nutrient levels in coastal plain agricultural streams have not caused excess algal production. Low dissolved oxygen (DO) levels in coastal plain streams are a major reason that these streams do not meet water quality standards set by state and federal regulatory agencies. The low DO may be due to excess nutrients from agricultural non point source pollution that stimulates algae growth in streams. Most streams we studied had levels of nutrients below those needed for maximum algae growth, indicating that the growth is not currently affected by excess nonpoint source nutrients. If coastal plain streams have intact riparian forest buffers that provide shade for the stream channel, it is unlikely that nutrient additions will increase algae growth. These findings have contributed to removal of these streams from lists of impaired waters in Georgia.

7. Remote sensing as a method for estimating soil moisture. Soil moisture content is a critical soil property which can affect many geophysical processes in the environment including flooding, drought, climate, and plant/soil interactions. Knowledge of the amount of water existing in the soil is critical to understanding many fundamental environmental processes. Soil moisture measurements interpreted from satellite collected data as well as estimates from a large-scale computer simulation model were compared to data collected from a ground-based network in South-central Georgia. The comparison indicated the simulation model provided estimates of ground-based soil moisture within reasonable error ranges and accurately predicted the extremes of the observed soil moisture. This study indicates that the satellite estimates and the computer simulation model may be useful tools for estimating soil moisture in regions where ground-based data are not available.

8. Evaluation of riparian forest buffers in North Carolina using the Riparian Ecosystem Management Model (REMM). REMM was calibrated and validated for three buffer sites in the Coastal Plain of North Carolina that are being used as test sites for the Conservation Reserve Enhancement Program (CREP) in that state. The model was successfully calibrated and validated and then used to look at long term performance of the buffers and to look at varying widths of the buffers. The modeling results showed that the buffers can be expected to remove nitrate for at least the next 30 years of use. The modeling results also showed that the optimum buffer width for long term nitrate attenuation was about 35 m which is narrower than the buffers that were studied (actual buffers range from 43m to 60m). These results will be used to guide future implementation of the CREP program in North Carolina and other states.

9. Effects of climate change on dissolved organic carbon transport can be estimated from long-term watershed data. Rivers play important roles in global carbon cycling through carbon mineralization and transport to coastal areas. Climate-change-induced alterations to river discharge may have large implications for riverine carbon cycling. Under a specific cooperative agreement (sibling project 6602-13000-026-10S 421 report,) with University of Georgia and Agricultural Research Service (ARS), the scientists at Tifton, Georgia collaborated and assessed impacts of drought on carbon transport and mineralization by coupling long-term datasets with laboratory experimentation for the Little River Experimental Watershed (LREW). The LREW has experienced lengthening droughts since monitoring began in 1972. The composition of dissolved organic carbon (DOC) appeared to be stable despite hydrologic differences between two years. However, annual DOC transport decreased by eight metric tons for each one-day increase in drought length. After years with short hydroperiods, resulting in less DOC exported, the concentration of DOC was significantly higher. Also, the concentration of DOC increased at high temperature and low discharge. Chamber incubations indicated that bacteria consume more DOC and release more CO2 when the concentration of DOC is high. Our findings suggest river carbon cycling will be significantly altered as droughts intensify, temperatures rise, and discharge decreases, resulting in reduced DOC transport to coastal areas.

Review Publications
Finn, M.P., Lewis, D., Bosch, D.D., Giraldo, M., Yamamoto, K., Sullivan, D.G., Luna, R., Kincaid, R., Allam, G.K., Kvien, C., Williams, M.S. 2011. Remote sensing of soil moisture using airborne hyperspectral data. GIScience and Remote Sensing. 48:(4)522-540.

Last Modified: 2/23/2016
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