Evaluating Nutrient Loading from Agricultural Sources and the Biogeochemical Cycling Capacity of Environments Connected to Agricultural Lands in Southwestern Ontario

Savannah Knorr, University of Windsor


Southwestern Ontario is dominated by agricultural lands that are extensively tile drained throughout the region as a management practice to remove excess water from fields. While tile drainage is a common practice, the implementation of constructed preferential flow paths, along with surface runoff from agricultural lands, increases nutrient loading risks to connected and downstream environments, and receiving large lakes. Of particular concern in this region is Lake Erie which has a legacy of severely degraded water quality due to excess nutrient loading from agricultural lands within the lake’s drainage basin. While agricultural lands are a known source for nutrient loading, there is a lack of understanding on the role of microbial functional communities in environments connected to these lands, and how they respond to both nutrient inputs and agricultural management practices.

This thesis investigates how sustained agricultural management practices alter microbial nutrient cycling communities in receiving aquatic and sediment environments, and the temporal patterns in both nutrient loading and microbial nutrient cycling communities. Results indicate that fertilization practices and agricultural management practices (e.g. tillage), increase nutrient loads to receiving environments. Nitrogen fertilization in particular drives patterns in nitrogen and phosphorus limited conditions in receiving aquatic environments, and phosphorus limited conditions of both aquatic and sediment environments determines patterns in phosphorus mobilization potentials. Finally, nutrient loads and microbial nutrient cycling capacity in aquatic environments increase during precipitation events and in the non-growing season, but decline significantly with increasing distance from agricultural sources and through areas of natural filtration. In contrast sediment environments are more resilient to agricultural inputs and abiotic factors. This research provides insight into temporal patterns of nutrient loading and how nutrient cycling microbial communities respond in receiving aquatic and sediment environments in agriculturally dominated locations of the southwestern Ontario region.