Phytoplankton communities as indicators of environmental change and nutrient deposition in the Canadian Rockies

• Author / Creator

  Cook, Jenna

• Remote mountain water bodies integrate the impacts of regional factors (e.g. climate change, atmospheric pollutants) well because of the relative absence of confounding local perturbations (e.g. human land-use). Climatic factors can alter the abiotic environments within mountain lakes through changes in precipitation and temperature while atmospheric nutrient deposition potentially fertilizes their primary production. Therefore, changes in alpine phytoplankton communities may be among the first indicators of the cumulative impact of modern global change on mountain lake and pond ecosystems, particularly as recent rates of warming are positively correlated with elevation. I investigated the potential sensitivities of 29 alpine lake and pond ecosystems along the Eastern Front range of the Canadian Rockies to increased deposition of nitrogen (N) and phosphorus (P) were investigated based on their water chemistry (i.e. dissolved inorganic N (DIN): total P (TP) mass ratios) and phytoplankton responses to in vitro nutrient amendment bioassays previously conducted in 2008. Previous evidence of low DIN:TP mass ratios and experimental N amendments stimulating algal communities in shallower alpine sites motivated my hypothesis that nutrient limitation of phytoplankton shifts from being P- to N-driven with decreasing water depth from lakes to ponds. Although inferred and experimental lines of evidence of nutrient limitation agreed in 55% of all cases, there were some discrepancies involving co-limitation. Contrary to my hypothesis of ponds being N-limited, I found little evidence of N-limitation from bioassays of phytoplankton for sites shallower than 5 m in depth. Overall, most phytoplankton communities exhibited responses to nutrient amendments indicating that they were P- or NP- co-limited. Chromophytes and chlorophytes drove the greater responsiveness of whole phytoplankton communities to P relative to N.
  Next, I investigated the inferred sensitivity of mountain phytoplankton to climatic factors and tested whether the nature of nutrient limitation had changed in the study area over the past 10 years as a result of nutrient deposition. Water samples were collected during the ice-free season of 2017 and 2018 from a total of 82 mountain lakes within the National Parks of the Canadian Rockies, and a subset of 14 alpine lakes chosen for nutrient enrichment bioassays, following the same protocol as the 2008 bioassays. Linear regression analysis was performed to determine significant environmental predictors of net algal production and redundancy analysis was used to determine the best set of explanatory variables of taxonomic variance in phytoplankton communities across the surveyed lakes. TP was identified as both the only significant predictor of chlorophyll-inferred phytoplankton biomass across the 82 surveyed lakes, and the key nutrient stimulating phytoplankton production in the bioassays. The bioassay results also revealed a strong synergistic response to the combined NP nutrient amendments. Results also revealed local features that mediate the influence of climate change to be the most important correlates of phytoplankton community composition, namely dissolved organic carbon and light availability along with proportion of carbonate sedimentary bedrock and bare catchment. Taken together, these findings highlight the sensitivity of phytoplankton communities in the Canadian Rockies to the indirect impacts of global warming, including the increased incidence of wildfires that fuel P deposition. The synergistic response to N and P also emphasizes a need for further research into potential fertilizing effects of combined anthropogenic N emissions and P deposition on lake ecosystems at high elevations.

• Subjects / Keywords

  • mountain lakes
  • phytoplankton
  • wildfires
  • phosphorus deposition
  • DIN:TP
  • nitrogen deposition
  • environmental change

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-t41n-se18

• License

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