Nutrient limitation of periphyton in agricultural streams: Implications for watershed management

  • Author / Creator
    Huculak, Sydney R
  • Freshwater streams are ecologically important as sources of habitat, unique biodiversity, and valued ecosystem services. Yet, stream health can be threatened by intensified nutrient loading derived from adjacent anthropogenic land-uses such as agricultural and municipal developments. Since algal growth can be limited by nitrogen (N), phosphorus (P), or co-limited by both (N+P), increases in the supply of these nutrients can stimulate primary production, leading to eutrophication. Eutrophication is a primary stressor of freshwater streams as it can deplete dissolved oxygen, promote blooms of toxic algae, and cause the loss of critical biodiversity within affected ecosystems. Despite the well-known ecological implications of eutrophication, nutrient limitation is poorly understood in low-order streams found throughout the agricultural region of Alberta. Determining the limiting nutrients for algae associated with microbial biofilms, termed periphyton, is critical for the management of nutrient loading and the health of stream ecosystems. Past nutrient management efforts in Alberta have relied solely on correlations between within-stream nutrient concentrations and the standing stock of algae, primarily targeting P endpoints. However, empirical evidence that P input is always the key cause of eutrophication of streams in Alberta is lacking. Thus, experimentally identifying which nutrients are limiting will improve the efficacy of management practices designed to improve stream health within Alberta. Here, we performed in-situ nutrient diffusing substrate (NDS) bioassays, using a crossed factorial design (N x P), to experimentally identify the drivers of nutrient limitation (i.e., N, P, or N+P) and nutrient-driven shifts in algal community composition in freshwater streams across Alberta’s agricultural region. NDSs were deployed in each of 30 streams, which were chosen to span three ecoregions, a gradient of land-use intensity, and ambient stream nutrient concentrations. Nitrogen, rather than phosphorus, was identified as the limiting nutrient driving algal biomass within the streams studied. Yet, nutrient-driven shifts in algal community composition were detected as P differentially affected bacillariophytes and chlorophytes. N-limitation was driven primarily by the response of bacillariophytes, while co-limitation was driven primarily by chlorophyte response to P, not N. However, stimulation of algal growth via N additions was still universal across both algal groups. The magnitude of nutrient limitation was not found to vary across ecoregions, despite distinct differences in predominant vegetation and soil type. Unexpectedly, underlying abiotic stream characteristics did not significantly influence the magnitude of algal nutrient limitation. Overall, these results suggest that nutrient management efforts focused on limiting inputs of nitrogen will be the most effective at averting eutrophication of low-order streams in Alberta’s agricultural region.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.