Lake ecosystems are sentinels of change in a landscape, integrating upstream terrestrial and aquatic effects of climate and land use drivers. Climate and land use change is mediated by socio-cultural and economic processes, resulting in complex responses in lake ecosystems as a part of coupled natural human (CNH) systems. I used multiple approaches within a CNH framework to better understand the effects of climate and land use on freshwater-human interactions. I first conducted a literature synthesis and found that slow processes (e.g., cultural change) are underrepresented in CNH-freshwater models relative to fast processes (e.g., daily decision-making), though both fast and slow processes are key to assessing decadal trajectories of change. I then examined the interaction of fast and slow variables in lakes through two ecosystem modeling assessments. I used a process-based model to assess drivers of annual chlorophyll-a concentration, a metric of phytoplankton biomass, over three decades in a low-nutrient lake and found that increases in summer median versus maximum chlorophyll-a are related to rising air temperatures and external phosphorus load, respectively. I also conducted a single-year study in the same lake to examine variability in site-specific gross primary production (GPP) and respiration (R), two fast-changing variables that serve as robust indicators of slowly-changing trophic state. I found that higher rates of near-shore GPP and R were partially due to stream-related variables, providing insight into how inflowing streams connect to in-lake processes. These two ecosystem assessment studies indicate fast-changing response variables can be indicative of specific slow-changing variables: annual maximum versus median chlorophyll-a can be used to assess differing impacts from climate and land use change, and estimation of GPP and R near inflow streams integrate sub-catchment drivers. Finally, I evaluated the effectiveness of an online model visualization relating current land use decisions, a fast process, to future water quality outcomes, a slow process, and found that the visualization was effective in altering property owner beliefs and intended behavior related to applying lawn fertilizer and installing waterfront buffers. Collectively, this work advances our understanding of how fast and slow variables interact to improve assessments of changes in CNH-lake systems. / Doctor of Philosophy / People depend on freshwater lakes for many reasons. However, lake water quality is threatened by climate change and increased land development. Here, I examined the complex interactions between people and freshwater lakes, using different types of computer simulation models to represent lake ecosystems. First, I found that the interaction of long-term and short-term processes are key in understanding trajectories of water quality change. For example, shorter term processes, such as people's decision-making about fertilizer use, may result in significant water quality changes over the long-term. Second, I used a lake ecosystem model to identify how long-term increases in air temperature due to climate change will cause average summer water quality to worsen. However, climate impacts may be offset if current land use change is properly managed to reduce runoff, thereby maintaining high water quality into the future. Third, I found that streams flowing into the lake directly influence short-term variations in water quality. Finally, I evaluated the effectiveness of an interactive online visualization in educating lakefront property owners about the importance of current human behavior for long-term water quality in the lake. After using the visualization, property owners were more likely to avoid applying lawn fertilizer and install waterfront buffers, in line with the educational goal. Management that incorporates models of short- and long-term processes in society and lakes will provide a better understanding of future trajectories of ecosystem change. Collectively, this work highlights connections between society and lake ecosystems that can be used to help manage water quality for generations to come.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/112643 |
| Date | 24 May 2021 |
| Creators | Ward, Nicole Kristine |
| Contributors | Biological Sciences, Carey, Cayelan C., Brown, Bryan Lyle, Hanson, Paul C., Sorice, Michael G., Weathers, Kathleen C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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