The response of mountain lakes to environmental change
Loading...
Authors
Culpepper, Joshua Abel
Issue Date
2022
Type
Dissertation
Language
Keywords
dissolved oxygen , dust deposition , ice phenology , lake ice , mountain lakes
Alternative Title
Abstract
Lakes act as sentinels of environmental change by incorporating forcing across scales: climate scales, catchment scales, and within-lake scales. To fully understand the changes that lake ecosystems undergo, we must explore past changes and present trends, both on a fine scale �" in individual lake systems �" and on a macroscale �"across broad geographic regions. Mountain lakes are useful as study systems because they are often remote and generally free of direct human influence. However, external impacts still affect mountain lake ecosystems, both through input of exogenous material and air temperature warming that influences the formation and breakup of lake ice. In this work, we use a combination of sediment records, intensive sampling, and remote sensing to understand the effects of climate change on mountain lake ecosystems. We refine our understanding of winter mountain lake hydrology through three studies that address: 1. Whether aeolian dust records in mountain lake cores capture deposition rate changes of exogenous dust input 2. Whether North American mountain lake ice cover period is changing 3. How mountain lake ecohydrology responds to shifts in ice cover timing (i.e., ice phenology) We found heterogeneity in mountain lake responses across scales in each of our studies. In the case of exogenous dust deposition to lakes, sediment cores revealed that dust can be an important source of nutrients to lakes; however, sediment records do not reveal changing rates of deposition between the distant and recent past. Apparent changes are rather an artifact of timescale dependence. When taking a continental-scale view of ice phenology, using a remote sensing dataset of 1,629 lakes, we find that ice phenology patterns do not readily cohere with ice phenology patterns from single lakes or lakes within a similar geographic region. Instead, lake ice phenology shows heterogeneous responses in different geographic regions (e.g., between the Sierra Nevada and the Rocky Mountains), hinting at potential resiliency to climate forcing in different regions of North America. Lastly, using high-frequency time series of dissolved oxygen concentration across morphologically distinct lakes, I found that lakes experiencing similar winter conditions showed heterogeneous oxygen dynamics along a depth gradient. Shallow lakes respond to winter ice cover conditions by depleting oxygen more quickly than deep lakes. I additionally explore the effects of sediment organic matter and winter meteorological dynamics. I anticipate that these results will be useful for understanding linkages between broader climate forcing. As air temperatures increase, heterogeneous landscape factors may confound the anticipated physical, chemical, and ecological lake responses, leading to questions about how lakes may show variations in timing or resiliency in response to climate change in the future.