PS 51-186 - Relating agricultural land use to ecosystem metabolism and nutrient ratios in streams within Southwestern Ontario

Background/Question/Methods

Eutrophication is an ongoing problem in Lake Erie and its major tributaries. It can result in impaired water quality, harmful algal blooms, disrupted food webs and hypoxic conditions, which can decrease biodiversity and ecosystem services. Recent research has suggested that long hypothesized links between phosphorus loading and eutrophication of surface waters are oversimplified, and that the role of organic carbon should be considered via nutrient resource ratios (C:N, C:P and N:P). Here, we examined the effects of agricultural land use on the structure and functioning of streams along the north shore of the Lake Erie watershed. A broad view of the nutrient status of streams in this area was quantified and a stoichiometric approach, rather than a single nutrient approach, was used to quantify relationships between land use and stream nutrients within this area. Additionally, a subset of streams was surveyed to determine relationships between land use, nutrient ratios (structure) and ecosystem metabolism (functioning).

Results/Conclusions

Results indicate a decoupling of phosphorus from nitrogen and carbon cycles at the landscape scale. Further, streams in less agriculturally dominated catchments show less variability in metabolism compared to conventional agricultural sites. This suggests intricate relationships between nutrient ratios and metabolism in streams that must be considered for future land use and management practices to mitigate agricultural effects on aquatic ecosystem structure and function. This study provides a link between the structure and functioning of the streams on agricultural landscapes, which researchers have suggested is necessary to obtain a holistic view of ecosystems and how they are impacted by disturbances.