The objective of this thesis was to determine the potential impact on groundwater quality as a result of the release of leachate from livestock mortality burial for three species of livestock: swine, bovine and poultry. Specific objectives were to:<p> 1.Characterize the chemical composition of leachate in livestock mortality burial pits for three species: bovine, swine and poultry; and<p> 2.Evaluate the potential environmental impact of livestock burial through groundwater transport modelling.<p> A two part program was followed to achieve these objectives. The first portion involved construction of lined burial pits complete with leachate collection systems. Poultry (1300kg), swine (5900kg) and bovine (9750kg) carcasses were each placed in separate pits and the pits covered with plastic liner material and then approximately one meter of earthen cover. The pits were sampled for leachate chemical analysis at 2 weeks, 1 month, 2 months, 4 months, 8 months, 14 months and 25 months post burial. The second portion involved using the chemical analysis results from first portion and two groundwater modeling software packages (CTRAN and PHREEQC) to characterize the leachate and evaluate the potential this material could have on groundwater resources adjacent to burial pits.<p> The results indicated that livestock mortality leachate contains, on average, after two years of decomposition, concentrations of 12,600 mg/L of ammonium-N, 34,600 mg/L alkalinity (as bicarbonate), 2,600 mg/L chloride, 3,600 mg/L sulphate, 2,300 mg/L potassium, 1,800 mg/L sodium, 1,500 mg/L phosphorus along with relative lesser amounts of iron, calcium and magnesium. Maximum values for the major ions were up to 50% higher than the average in some instances. The pH of the leachate was near neutral. In comparison to earthen manure storages and landfills, the strength of the leachate was 2-4 times higher.<p> To properly characterize the leachate chemistry, speciation of the mortality leachate was performed using PHREEQC. This speciation provided evidence of phosphate compounds precipitating from solution, as well as significant amounts of phosphoric acids (0.03 mol/L). Relatively high concentrations of ammonium sulphate also formed and due to the negative charge, allow for potentially 300 mg-N/L to transport conservatively. In comparison to naturally occurring groundwater, activities of bicarbonate, sulphates, phosphates and other minerals were many orders of magnitude higher than concentrations present in groundwater.<p> Preliminary simulations were created with two software packages, Geo-Slope CTRAN and PHREEQC to simulate transport of the leachate for three different soil conditions. The Geo-Slope model models a conservative contaminant, while the PHREEQC model involves geochemical speciation and contaminant transport including ion exchange occurring along the pathway. Transport through a low permeable soil (K=1 x 10-10 m/s) was dominated by diffusion allowing unattenuated leachate to transport a distance of approximately three meters in 50 years. The moderately permeable soil situation (K=1 x 10-9 m/s) produced a transport depth of six meters with an approximate concentration of the tracer thirty to forty percent of initial concentration in 50 years. In a highly permeable soil (K=1 x 10-8 m/s), transport reached a depth of 10 meters in 10 years with approximately forty percent of initial concentration. The PHREEQC transport model demonstrated a highly concentrated calcium and magnesium plume forming in front of the ammonium plume suggesting ion exchange and attenuation of ammonium.<p> In the occurrence of a mass mortality event, regulators in Canada have decided to employ a trench burial system. Trenches could be created using on-the-farm equipment such as backhoes to obtain approximate trench dimensions of 2 m wide and 4 m deep. To assess the impact of multiple trenches and their appropriate spacing, models were created with Geo-Slope CTRAN to evaluate the effects on trench spacing. It was determined through these models that a minimum 10 m separation distance would provide a potential contaminant plume maximum soil contact and no trench-to-trench impact.<p> To further evaluate the potential impact of livestock burial leachate, mass loading into an aquifer was evaluated for a moderately permeable soil (K=1 x 10-9 m/s) for a mass mortality event in a 10,000 head feedlot. Disposal consisted of ten 200 m trenches with a 10 m separation distance. Disposal covered 2.2 hectares and provided a mass loading of ammonium to an aquifer 10 m below of 950 kg/year after 50 years and increasing from 50 years until the peak concentration of the plume reached the aquifer. At this loading rate, nitrogen concentrations exceed drinking water standards 10-15 times.

The objective of this thesis was to determine the potential impact on groundwater quality as a result of the release of leachate from livestock mortality burial for three species of livestock: swine, bovine and poultry. Specific objectives were to:<p> 1.Characterize the chemical composition of leachate in livestock mortality burial pits for three species: bovine, swine and poultry; and<p> 2.Evaluate the potential environmental impact of livestock burial through groundwater transport modelling.<p> A two part program was followed to achieve these objectives. The first portion involved construction of lined burial pits complete with leachate collection systems. Poultry (1300kg), swine (5900kg) and bovine (9750kg) carcasses were each placed in separate pits and the pits covered with plastic liner material and then approximately one meter of earthen cover. The pits were sampled for leachate chemical analysis at 2 weeks, 1 month, 2 months, 4 months, 8 months, 14 months and 25 months post burial. The second portion involved using the chemical analysis results from first portion and two groundwater modeling software packages (CTRAN and PHREEQC) to characterize the leachate and evaluate the potential this material could have on groundwater resources adjacent to burial pits.<p> The results indicated that livestock mortality leachate contains, on average, after two years of decomposition, concentrations of 12,600 mg/L of ammonium-N, 34,600 mg/L alkalinity (as bicarbonate), 2,600 mg/L chloride, 3,600 mg/L sulphate, 2,300 mg/L potassium, 1,800 mg/L sodium, 1,500 mg/L phosphorus along with relative lesser amounts of iron, calcium and magnesium. Maximum values for the major ions were up to 50% higher than the average in some instances. The pH of the leachate was near neutral. In comparison to earthen manure storages and landfills, the strength of the leachate was 2-4 times higher.<p> To properly characterize the leachate chemistry, speciation of the mortality leachate was performed using PHREEQC. This speciation provided evidence of phosphate compounds precipitating from solution, as well as significant amounts of phosphoric acids (0.03 mol/L). Relatively high concentrations of ammonium sulphate also formed and due to the negative charge, allow for potentially 300 mg-N/L to transport conservatively. In comparison to naturally occurring groundwater, activities of bicarbonate, sulphates, phosphates and other minerals were many orders of magnitude higher than concentrations present in groundwater.<p> Preliminary simulations were created with two software packages, Geo-Slope CTRAN and PHREEQC to simulate transport of the leachate for three different soil conditions. The Geo-Slope model models a conservative contaminant, while the PHREEQC model involves geochemical speciation and contaminant transport including ion exchange occurring along the pathway. Transport through a low permeable soil (K=1 x 10-10 m/s) was dominated by diffusion allowing unattenuated leachate to transport a distance of approximately three meters in 50 years. The moderately permeable soil situation (K=1 x 10-9 m/s) produced a transport depth of six meters with an approximate concentration of the tracer thirty to forty percent of initial concentration in 50 years. In a highly permeable soil (K=1 x 10-8 m/s), transport reached a depth of 10 meters in 10 years with approximately forty percent of initial concentration. The PHREEQC transport model demonstrated a highly concentrated calcium and magnesium plume forming in front of the ammonium plume suggesting ion exchange and attenuation of ammonium.<p> In the occurrence of a mass mortality event, regulators in Canada have decided to employ a trench burial system. Trenches could be created using on-the-farm equipment such as backhoes to obtain approximate trench dimensions of 2 m wide and 4 m deep. To assess the impact of multiple trenches and their appropriate spacing, models were created with Geo-Slope CTRAN to evaluate the effects on trench spacing. It was determined through these models that a minimum 10 m separation distance would provide a potential contaminant plume maximum soil contact and no trench-to-trench impact.<p> To further evaluate the potential impact of livestock burial leachate, mass loading into an aquifer was evaluated for a moderately permeable soil (K=1 x 10-9 m/s) for a mass mortality event in a 10,000 head feedlot. Disposal consisted of ten 200 m trenches with a 10 m separation distance. Disposal covered 2.2 hectares and provided a mass loading of ammonium to an aquifer 10 m below of 950 kg/year after 50 years and increasing from 50 years until the peak concentration of the plume reached the aquifer. At this loading rate, nitrogen concentrations exceed drinking water standards 10-15 times.

Soil carbon is the largest sink and source of the global carbon cycle and is disturbed by several natural, anthropogenic, and environmental factors. The global increase of atmospheric CO2 affects soil carbon cycling through varied biogeochemical processes. The first chapter is a compilation of current information on potential factors triggering soil acidification and weathering mechanisms under elevated CO2 and their consequences on soil inorganic carbon (SIC) pool and quality. Soil water content and precipitation were critical factors influencing elevated CO2 effects on the SIC pool. The second chapter examines a detailed column experiment in which six soils from the state of Mississippi, USA, representing acidic, neutral, and alkaline pH, were exposed to different CO2 enrichments (100%, 10%, and 1%) for 30 days. The leachates’ pH tended to attain an equilibrium state (neutral) with time under CO2 saturation. SIC increased under CO2 saturation, whereas cation exchange capacity (CEC) showed a decreasing pattern in all soils. In the third chapter, an eXplainable artificial intelligence (XAI) was performed to visualize the different forms of soil carbon variability across the Mississippi River Basin area. This model explains key insights and local discrepancies, suggesting a solution to the “Black-Box” issue. The best performing model, stack ensemble, showed improved RMSE (3 to 8%) and spatial variability for soil carbons than other ML models, especially after adding the residuals from regression analyses. Land cover type > soil pH > total nitrogen, > NDVI were identified as the top four crucial factors for predicting SOC when bulk density > precipitation, soil pH > mean annual temperature described SIC. The proposed automatic machine learning (AutoML) model with model agnostic interpolations might be a hallmark to mitigate the C loss under adverse climate change conditions and allow diverse knowledge groups to adopt a new interpretable ML algorithm more confidently. Findings from this study help predict the impact of elevated atmospheric CO2 on soil pH, acidification, and nutrient availability and develop strategies for sustainable land management practices under a changing climate.