The Fate of Atmospherically Deposited Mercury in Mountain Lake Food Webs, and Implications for Fisheries Management

Mountain lakes are an iconic feature of the landscape in the Mountain West. They hold significant ecological and cultural value, and are important sentinels of environmental change. Despite their pristine image, these remote waterbodies are subjected to numerous anthropogenic stressors. Mountain lakes are naturally fishless systems, but historical fish stocking has led to major changes in mountain lake food web structure, including declines of resident amphibians, large-bodied zooplankton, and emergent insect populations. Atmospherically deposited contaminants, such as mercury, can accumulate in mountain lake food webs, leading to relatively high levels in the fish relative to the water. Managing for these stressors is difficult, because although fish stocking causes ecological problems, and mercury bioaccumulation poses human health risks, the cultural value of angling remains important. The goal of this dissertation was to better understand the issues of fish stocking and mercury bioaccumulation in a socioecological context: from the importance of trophic dynamics for mercury bioaccumulation in mountain lake fish, to the implications of fish stocking and mercury bioaccumulation for mountain lake management. In Chapter 2, I identified the ecological, limnological, and landscape-level indicators of mercury bioaccumulation in mountain lake food webs in order to inform better ecosystem management. In Chapter 3, I conducted an experiment to test if fatty acid stable isotopes can partition benthic and terrestrial prey sources in fish in a simplified mountain lake food web, in hopes of providing a more informative tool for future food web studies. In Chapter 4, I used intercept surveys to determine the public perceptions of mountain lake fisheries management in two national parks, and assess the risk mercury may pose to mountain lake anglers by determining fish consumption habits. I determined that nearshore forest cover and fish diet were the best predictors of mercury concentrations in mountain lake fish, but that our understanding of the role of terrestrial prey subsidies for fish is constrained by limitations in current diet tracing methods. My experiment demonstrates that using stable isotopes of fatty acids is a promising approach to distinguishing between benthic and terrestrial diet sources, but that doing so effectively requires an in-depth understanding of physiological context specific to the ecosystem of interest. Lastly, through my surveys, I found that thousands of anglers regularly consume fish from mountain lakes, and that while most visitors have concerns about the ecological impacts of fish stocking, anglers support a conservation-based approach that balances ecological health with the cultural value of fish stocking. This dissertation provides a unique set of tools that advance our understanding of food web dynamics and mercury bioaccumulation in mountain lakes, as well as the social value of these ecosystems. My results suggest that the most effective way to protect the health of mountain lakes and their visitors will be for managing agencies to collaborate with scientists and angling groups when making fisheries management decisions, and to invest in outreach about both the ecological and toxicological implications of fish stocking and mercury bioaccumulation in mountain lakes. The use of such socioecological research approaches is becoming progressively more important, as the threats of climate change and unstable regulatory protections for mountain ecosystems increase

Public Perceptions of Mountain Lake Fisheries Management in National Parks

The legacy of fish stocking in mountain lake ecosystems has left behind a challenge for land managers around the globe. In the US and Canada, historically fishless mountain lakes have been stocked with trout for over a century. These non-native trout have cascading ecosystem effects, and can accumulate atmospherically deposited contaminants. While the negative impacts of stocking in these ecosystems have become increasingly apparent, wilderness fishing has garnered cultural value in the angling community. As a result, public lands managers are left with conflicting priorities. National park managers across the western US are actively trying to reconcile the cultural and ecological values of mountain lakes through the development of management plans for mountain lake fisheries. However, visitors\u27 social perceptions, attitudes, and values regarding mountain lake fisheries management have remained unquantified, and thus largely left out of the decision-making process. Our study evaluated the recreation habits, values, and attitudes of national park visitors towards fish stocking and management of mountain lakes of two national parks in the Pacific Northwest. We found that most visitors favor fish removal using a conservation approach, whereby sensitive lakes are restored, while fish populations are maintained in lakes that are more resilient. An important consideration for managers is that many mountain lake anglers consume fish on an annual basis, thus we emphasize the use of outreach and education regarding the accumulation of contaminants in fish tissues. Our findings help elucidate the conflicting views of stakeholders, and we provide recommendations to inform management of mountain lakes fisheries in North America and abroad

Testing the veracity of space-for-time-substitution surveys in modeling long-term zooplankton community dynamics

Climate change is rapidly altering the magnitude and phenology of ecological processes and communities. Single observation “snapshots” from multi-lake surveys over a geographic range are typically used to evaluate plankton dynamics and their responses to spatial gradients in environmental forcing (e.g. temperature). These surveys, called Space-for-Time-substitution (SFTS) surveys, make the critical assumption that environmental gradients are reliable proxies for time and are therefore useful for overcoming the tradeoff between geographic representation and detailed temporal datasets. SFTS surveys, however, have been critiqued for their assumption that spatial and temporal scales can be coupled, and the ability of large-scale snapshots to represent time-integrated patterns in zooplankton community structure and function remains untested at global scales. We compiled existing global lake time series to test whether SFTS surveys can capture zooplankton biodiversity and its relationship with lake temperature. We broadly hypothesized that single “snapshot” surveys would be unable to capture zooplankton diversity within lakes and that SFTS surveys wouldn’t be able to reproduce zooplankton diversity as a function of temperature between multiple permutations. Therefore, SFTS surveys cannot be used to infer zooplankton community dynamics over time. Results suggest that single “snapshot” surveys are unlikely to represent mean zooplankton diversity at a given moment in time, that SFTS surveys cannot reliably reproduce relationships between lake temperature and zooplankton diversity, and that the relationship between lake temperature and zooplankton diversity varies at local temporal scales

Fatty Acid Stable Isotopes Add Clarity, but Also Complexity, to Tracing Energy Pathways in Aquatic Food Webs

Tracing the flow of dietary energy sources, especially in systems with a high degree of omnivory, is an ongoing challenge in ecology. In aquatic systems, one of the persistent challenges is in differentiating between autochthonous and allochthonous energy sources to top consumers. Bulk carbon stable isotope values of aquatic and terrestrial prey often overlap, making it difficult to delineate dietary energy pathways in food webs with high allochthonous prey subsidies, such as in many northern temperate waterbodies. We conducted a feeding experiment to explore how fatty acid stable isotopes may overcome the challenge of partitioning autochthonous and allochthonous energy pathways in aquatic consumers. We fed hatchery‐reared Arctic Char (Salvelinus alpinus) diets of either benthic invertebrates, terrestrial earthworms, or a mixture of both. We then compared how the stable carbon isotopes of fatty acids (δ13CFA) distinguished between diet items and respective treatments in S. alpinus liver and muscle tissues, relative to bulk stable isotopes and fatty acid profiles. Although a high degree of variability of fatty acid stable carbon isotope values was present in all three measures, our results suggest that the ability of this method to overcome the challenges of bulk stable isotopes may be overstated. Finally, our study highlights the importance of further experimental investigation, and consideration of physiological and biochemical processes when employing this emerging method

Toxic Chemical Governance Failure in the United States: Key Lessons and Paths Forward

Over 40 years of regulations in the United States have failed to protect human and environmental health. We contend that these failures result from the flawed governance over the continued production, use, and disposal of toxic chemicals. To address this failure, we need to identify the broader social, political, and technological processes producing, knowing, and regulating toxic chemicals, collectively referred to as toxic chemical governance. To do so, we create a conceptual framework covering five key domains of governance: knowledge production, policy design, monitoring and enforcement, evaluation, and adjudication. Within each domain, social actors of varying power negotiate what constitutes acceptable risk, creating longer-term path dependencies in how they are addressed (or not). Using existing literature and five case studies, we discuss four paths for improving governance: evolving paradigms of harm, addressing bias in the knowledge base, making governance more equitable, and overcoming path dependency

Trade-Offs by Whom for Whom? A Response to Calow

We welcome Calow\u27s (2019) critique of our recent manuscript (Chiapella et al. 2019) and the opportunity to elaborate a few key points. Calow\u27s argument that governance must come to terms with trade-offs between health risks and “benefits from industrial and agrichemicals and pharmaceuticals in terms of lifestyle, food supply, and health,” has already been the key logic underpinning the current regime of toxic chemical governance. This framing has resulted in extreme inequities in exposure to chemical risk and in the distribution of their benefits. Focusing on the need for improved CBA, while welcome, does not address our more substantive claim: that toxic chemical governance failure has resulted from..

Can space-for-time-substitution surveys represent zooplankton biodiversity patterns and their relationship to environmental drivers?

Space-for-Time-Substitution surveys (SFTS) are commonly used to describe zooplankton community dynamics and to determine lake ecosystem health. SFTS surveys typically combine single point observations from many lakes to evaluate the response of zooplankton community structure and dynamics (e.g., species abundance and biomass, diversity, demographics and modeled rate processes) to spatial gradients in hypothesized environmental drivers (e.g., temperature, nutrients, predation), in lieu of tracking such responses over long time scales. However, the reliability and reproducibility of SFTS zooplankton surveys have not yet been comprehensively tested against empirically-based community dynamics from longterm monitoring efforts distributed worldwide. We use a recently compiled global data set of more than 100 lake zooplankton time series to test whether SFTS surveys can accurately capture zooplankton diversity, and the hypothesized relationship with temperature, using simulated SFTS surveys of the time series data. Specifically, we asked: (1) to what degree can SFTS surveys capture observed biodiversity dynamics; (2) how does timing and duration of sampling affect detected biodiversity patterns; (3) does biodiversity ubiquitously increase with temperature across lakes, or vary by climate zone or lake type; and (4) do results from SFTS surveys produce comparable biodiversity-temperature relationship(s) to empirical data within and among lakes? Testing biodiversity-ecosystem function (BEF) relationships, and the drivers of such relationships, requires a solid data basis. Our work provides a global perspective on the design and usefulness of (long-term) zooplankton monitoring programs and how much confidence we can place in the zooplankton biodiversity patterns observed from SFTS surveys.info:eu-repo/semantics/publishedVersio