1a. Objectives (from AD-416)
(1) Assess the environmental impacts of land-applying different rates of municipal biosolids on the production of forage and biofuel grasses and on water quality at Austin Water Utility's Hornsby Bend Municipal Biosolid Recycling Facility. (2) Identify and quantify the composition, concentration, and distribution of nutrients (carbon, nitrogen, phosphorus), micronutrients (trace metals), and endocrine disrupting compounds (EDCs) in biosolids, soils, waters, and plants. (3) Measure the potential mobility of nutrients, micronutrients, and EDCs in surface run-off and in water infiltrating through the soil profile using rainfall simulations in the field. (4) Use empirical field data to develop and test new model components for SWAT (phosphorus, EDCs) to further validate and improve model code. (5) Provide risk assessment to the City of Austin regarding the potential watershed impacts of Austin's municipal waste recycling program.
1b. Approach (from AD-416)
We will conduct a broad survey of the Hornsby Bend site to assess the presence and concentrations of nutrients, micronutrients, and EDCs in biosolids, soils, waters, and plants. Ten-meter-wide strips of switchgrass will be established within the existing forage production system (coastal bermudagrass) receiving Class B biosolid applications. Rainfall simulations will be conducted in forage production plots and in biofuel production plots to quantify the movement of nutrients, micronutrients, and EDCs in surface run-off and in water infiltrating the soil profile. Crop productivity and soil microbial activity will also be measured across different biosolid application rates (0, 10, 20, and 30 dry tons/acre/year).
3. Progress Report
Land application is one means of managing biosolids. Biosolids contain essential plant nutrients such as nitrogen and phosphorous, as well as important trace metals, which make them a valuable fertilizer. However, biosolids also contain many anthropogenic chemicals. Land application introduces these chemicals to the environment, allowing them to interact with water quality, soil function, wildlife, and human health. The effects of biosolids application rate and history on soil potential C and N mineralization were measured over a 112-day laboratory incubation. Soils were collected from a large-scale biosolids recycling operation that surface-applies anaerobically-digested Class B biosolids for commercial forage production. Five treatments were evaluated: unamended control; 22 Mg dry biosolids/ha/y applied for 25 years; and 22, 45, and 67 Mg/ha/y applied for 8 years each. Biosolids additions enhanced total soil organic C by 32 to 92% and total N by 30 to 157% compared to unamended soils. Total N increased with application rate and was dominated by nitrate-N. Potential C mineralization (cumulative CO2 produced) was 11 to 62% greater in amended soils compared to controls and highest at 67 Mg/ha/y. Net N mineralization and immobilization were highest early in the incubation for 45 and 67 Mg/ha/y treatments. No significant differences in potential C and N mineralization between controls and soils amended at the lowest rate for 8 or 25 years suggests that biosolids applications at 22 Mg/ha/y are sustainable over the long-term. Higher potential N mineralization rates and soil nitrate concentrations under higher application rates may increase the risk of off-site nutrient transport and requires further evaluation. Soil cores, pond sediments, surface and ground waters, and aquatic and terrestrial invertebrates were subsampled for analyses of anthropogenic compounds, including hormone mimics, personal care products, and trace metals. The USGS National Water Quality Laboratory (NWQL) in Denver performed the lab analysis and quality control checks for all samples analyzed for organic contaminants and hormones. All USGS analyses were completed and data received 4/26/2011. A second set of subsamples was analyzed by the ECL (Environmental Contaminants Laboratory) in San Marcos for total metals content. All trace metals data from ECL was completed and received 4/4/2011. ECL also completed organic contaminant analyses on aquatic and terrestrial invertebrate samples, and data were received 5/24/2011. We are currently analyzing the results and preparing manuscripts. A conceptual model is being developed to simulate the fate and transport of anthropogenic compounds and will be incorporated into the SWAT watershed model. The organic pesticide submodel is being modified to simulate the transport to rivers and lakes and the impact of land management and climate on the ultimate fate of the compounds. Measured data from the Hornsby Bend facility and the Shell Creek Watershed in Nebraska will be used to calibrate and validate the model.