As the world’s increasing human population demands greater agricultural intensity, concerns regarding environmental nutrient loading are also rising. Landowners in the Tobacco Creek Model Watershed (TCMW) in southern Manitoba, Canada, have implemented beneficial management practices to reduce nutrient loading to surface waters. Among these practices is a network of small reservoirs that have been shown to reduce nutrient concentrations downstream. It is unclear what is contributing to this ecosystem service, but bacterial denitrification is thought to be important. To understand the role of these reservoirs in excess nitrate removal and assess how this ecosystem service can be optimized, denitrification activity in reservoirs and stream pools of the watershed was measured via the chloramphenicol-amended acetylene block technique. Results indicated that denitrification activity was positively correlated with measured nitrate concentrations and sediment organic carbon (SOC), and negatively correlated with sediment particle size and pH. Regression trees typically identified nitrate as the primary node in partitioning denitrification activity. Importantly, reservoirs exhibited higher denitrification activity and were at times less likely to be nitrate-saturated than stream pools. This finding was attributed mainly to higher levels of SOC, and lower concentrations of dissolved oxygen found in reservoirs. Nitrate was added to a set of samples to test for nitrate saturation, which is an indicator of poor ecological status, as nitrate concentrations exceed the denitrification capacity of microbes. Almost half of measurements (49%) demonstrated nitrate saturation, indicative of the need for additional remediation activity in the watershed. Classification trees suggested a threshold for nitrate saturation across sites at 0.68 mg L-1 NO3 + NO2. Findings from this research reveal that reservoirs not only improve nitrate removal capacity, but could inform the proposed construction of additional reservoirs in the TCMW. Understanding nutrient retention in this system could also have implications for downstream ecosystems such as Lake Winnipeg; an intensely eutrophic lake that has become a high priority area for remediation.

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Residential on-site wastewater systems (OWS) are a potential source of phosphorus (P) which can negatively impact surface water quality in rural watersheds. The magnitude of P loading from OWS is typically not monitored, and is further complicated when agricultural land-uses are intermixed with residential dwellings. Watershed-scale computer simulations are commonly used tools for evaluating the impacts of land-use changes on P loading. Existing models simulate OWS P treatment via vertical flow transport in native soils. However, in Nova Scotia (NS) OWS designs rely pre-dominantly on lateral flow and imported sand filter media. In this thesis, a watershed-scale computer modeling framework for simulating P loads from agriculture and lateral flow OWS designs was developed and tested. The framework consists of the P on-site wastewater simulator (POWSIM), designed specifically for this study, which is used in conjunction with the Soil and Water Assessment Tool (SWAT) model. The POWSIM loading tool has three computational components: (i) OWS disposal field design type selection and treatment media mass calculation; (ii) disposal field P treatment dynamics; and (iii) soil subsurface plume P treatment dynamics. The active P treatment media mass and dynamics equations were developed from numerical modeling (HYDRUS-2D) and lateral flow sand filter (LFSF) OWS disposal field experiments. A 2-part piecewise linear model was found to best represent LFSF P treatment processes. Testing of the modeling framework in the mixed land-use Thomas Brook Watershed (TBW) in NS demonstrated improved simulation of baseflow total P (TP) loads in both a predominantly residential subcatchment and one dominated by agriculture over the SWAT model without POWSIM. Different residential and agricultural development and beneficial management practice (BMP) scenarios were evaluated in the TBW. Agricultural BMPs were most effective at reducing cumulative TP loads while OWS BMPs were best at mitigating in-stream eutrophication impacts. The 50 year simulation period for the various scenarios found peak OWS TP loading occurring between 25 and 50 years, suggesting that modeling for many decades is required for proper evaluation. This study highlights the importance in identifying specific water quality issues that need to be targeted prior to implementing a BMP strategy.

This thesis presents the results of exploratory sociological research designed to better understand how farmers select agricultural practices with the potential to effect water quality. The primary research methodology is a Rapid Rural Appraisal of thirty farms in five rural municipalities in Saskatchewan, Canada during the year 2000 growing season. The data establishes that a variety of economic, institutional, organizational, and social factors interact in dynamic ways to influence farmer resource management decisions and that the resulting agricultural practices have the potential for subtle and dramatic effects on water quality in Saskatchewan. Risk-mitigating farming methods known as Best Management Practices (BMPs) are interpreted by farmers in the field research as being both appropriate and problematic. Alternative initiatives and communication strategies are identified in the field data that offer support to production and productivity in the agriculture sector while also promoting water quality. The research suggests that measures such as providing accessible public water quality data, promoting water treatment for individual households, and educating rural women and youth about water quality issues may merit further investigation.

This thesis presents the results of exploratory sociological research designed to better understand how farmers select agricultural practices with the potential to effect water quality. The primary research methodology is a Rapid Rural Appraisal of thirty farms in five rural municipalities in Saskatchewan, Canada during the year 2000 growing season. The data establishes that a variety of economic, institutional, organizational, and social factors interact in dynamic ways to influence farmer resource management decisions and that the resulting agricultural practices have the potential for subtle and dramatic effects on water quality in Saskatchewan. Risk-mitigating farming methods known as Best Management Practices (BMPs) are interpreted by farmers in the field research as being both appropriate and problematic. Alternative initiatives and communication strategies are identified in the field data that offer support to production and productivity in the agriculture sector while also promoting water quality. The research suggests that measures such as providing accessible public water quality data, promoting water treatment for individual households, and educating rural women and youth about water quality issues may merit further investigation.