Abstract:
Climate change is anticipated to significantly increase temperatures and alter
current rainfall patterns, which will have important ramifications for aquatic habitats and
their biological communities. Current observations indicate that climate effects will vary
depending on region and lake type, and some lacustrine areas, such as the Great Plains,
are particularly sensitive to these effects. Variations in local climate and lake
morphometry create different habitats, which each have unique environmental controls.
The anticipated impacts of climate change on aquatic biota can be difficult to evaluate
because of potentially contrasting effects of temperature and hydrology on lake
ecosystems, particularly in closed-basin lakes within semi-arid regions.
To address these challenges, I quantified decade-scale changes in chemical and
biological properties of 20 endorheic lakes in central North America in response to a
pronounced transition from a drought to a pluvial period during the early 21st century.
Lakes exhibited marked changes in chemical characteristics and formed two discrete
clusters corresponding to periods of substantially differing effective moisture (as per
Palmer Drought Severity Index, PDSI). Discriminant function analysis (DFA) explained
90% of variability in fish assemblage composition and showed that fish communities
were predicted best by environmental conditions during the arid interval (PDSI < -2).
DFA also predicted that lakes could support more fish species during pluvial periods, but
their realized occurrences may be limited by periodic stress due to recurrent droughts and
physical barriers to colonization. Zooplankton taxonomic compositions in fishless lakes
were resilient to short-term changes in meteorological conditions, and did not vary
between drought and deluge periods. Conversely, zooplankton taxa that were exposed to fish decreased substantially in biomass during the wet interval, likely due to increased
zooplanktivory by fish.
Based on my results, climate change is expected to alter fish species distributions,
but it is less clear to what extent non-lethal environmental effects will influence physical
health of populations in fish-habitable lakes. To address this question, I investigated the
environmental controls of body condition and parasite load in walleye (Sander vitreus),
northern pike (Esox lucius) and yellow perch (Perca flavescens) in seven lakes from the
prior study. Over a two-year observation period (2009 vs. 2010), I observed large
differences in the number of days within the favorable temperature range for ambient fish
species. Surprisingly, environmental variables such as lake morphometry and nutrient
levels had little relevance, despite their importance in previous studies conducted in
boreal lakes. Instead, temperature and salinity were important correlates of fish health.
In regard to species-specific effects, walleye was most sensitive to interannual
temperature differences, as well as salinity, while yellow perch and northern pike
exhibited temperature sensitivity to a lesser degree. Apparently, temperature increases
are of particular concern in prairie lakes, as their polymictic nature deprives fishes of a
hypolimnetic thermal refuge.
Together these findings suggest that semi-arid lakes provide a useful model
system for anticipating the effects of global climate change on aquatic communities in
closed-basin lakes of semi-arid regions. The particular importance of temperature and
salinity indicates that the interaction of global climate change and local hydrology may
have particularly detrimental effects not only on the health but also the survival of
established fish populations of the Great Plains.
Description:
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Biology, University of Regina. xi, 75 l.