Effects of climate change on high elevation lake ecosystems, The

2019 Summer.Includes bibliographical references.High elevation lakes are an important class of the world's fresh water. Nearly 10% of all lakes globally reside above 2,100 m ASL and almost half of the world's population relies on water from high elevation regions. Also, these lakes provide important cool water habitat refugia for aquatic biota. However, high elevation areas are sensitive to changes in climate and are changing faster than other regions. Likewise, secondary effects of a changing climate like drought, forest fire, and eutrophication threaten lake habitats, exacerbating changes from air warming. Despite the importance of high elevation lakes and their increased threat from climate change, little is known about high elevation lakes and their vulnerability to these threats. The goal of my dissertation was first (Chapter 1) to determine historic changes in lake surface temperatures for a set of high elevation lakes in the Southern Rocky Mountains, USA (SRM). Then, I determined potential future changes to thermal stratification (Chapter 2) and the length of the open water season (Chapter 3) for a subset of lakes in the Rawah Wilderness Area (RWA) within the SRM. For these future predictions, I estimated alterations in lake surface and bottom temperatures from multiple stressors, as well as how these changes may affect aquatic habitat for native and nonnative fish species that reside in the region. Although historic lake temperature trend analyses are numerous, remote lakes, including many high elevation lakes, are typically underrepresented due to limited availability of long-term datasets. In Chapter 1, I developed a Bayesian modeling technique to analyze sparse data from high elevation lakes that allowed me to estimate lake surface warming across a large region (SRM). The analysis allowed for inclusion of lakes with few repeated measurements, and observations made prior to 1980 when more intensive lake monitoring began. I accumulated the largest dataset of high elevation lake surface temperatures globally analyzed to date. Data from 590 high elevation lakes in the Southern Rocky Mountains showed a 0.13°C decade-1 increase in surface temperatures and a 14% increase in seasonal degree days since 1955. Like surface temperature trends, many studies have also examined the effects of climate warming on lake thermal stratification, but few have addressed environmental changes concomitant with climate change, such as alterations in water clarity and lake inflow. Although air temperature rise is a predominant factor linked to lake thermal characteristics, climate-driven changes at watershed scales can substantially alter lake clarity and inflow, exacerbating the effects of future air warming on lake thermal conditions. In Chapter 2, I employed the mechanistic General Lake Model (GLM) to simulate future thermal conditions of typical mountain lakes of the western United States. I found that after air temperature, alterations in inflow had the largest effect on lake thermal conditions, changes in wind had the least effect, and large lakes experienced more than double the increase in lake stability than small lakes. Assuming air temperature rise alone, summer stability of mountain lakes of the western United States was predicted to increase by 15-23% at +2°C air temperatures, and by 39-62% at +5°C air temperatures. When accounting for associated changes in clarity and inflow, lake stability was predicted to increase by 208% with +2°C air warming and 318% at +5°C air warming. Finally, the open water duration at high elevations is increasing at a higher rate than at lower elevations. Earlier snowmelt, resulting in decreased ice cover duration, is having a proportionally higher effect on mountain lakes than other regions. But the effect early melt and increased air temperatures have on mountain lake thermal characteristics and implications for fish is unclear. Mountain lakes exhibit a variety of thermal conditions, altering metabolic requirements for ectotherms. In Chapter 3, I coupled GLM with a fish bioenergetics model to assess potential thermal changes and energetic consequences for native Cutthroat Trout (Oncorhynchus clarkii spp.) and nonnative but present Brook Trout (Salvelinus fontinalis) in a continuously mixed polymictic and seasonally stratified dimictic mountain lake during early and nominal snowpack melt in the SRM. I found that early snowmelt alone had a larger consumptive demand for all species than an air temperature increase of 2°C, but combined these environmental changes are most effective. Early melt coupled with 5°C air warming could more than double the food requirements for Cutthroat Trout and Brook Trout. Ultimately, food availability may dictate the future success of fish in mountain regions. My dissertation research expanded the current knowledge of high elevation lake thermal conditions, developed a novel method to utilize sparse datasets, and provided valuable holistic insight to potential future changes in lake thermal structure and habitat suitability for fish while accounting for localized and watershed scale consequences of climate change

Design Considerations for 3D Printed, Soft, Multimaterial Resistive Sensors for Soft Robotics

Sensor design for soft robots is a challenging problem because of the wide range of design parameters (e.g., geometry, material, actuation type, etc.) critical to their function. While conventional rigid sensors work effectively for soft robotics in specific situations, sensors that are directly integrated into the bodies of soft robots could help improve both their exteroceptive and interoceptive capabilities. To address this challenge, we designed sensors that can be co-fabricated with soft robot bodies using commercial 3D printers, without additional modification. We describe an approach to the design and fabrication of compliant, resistive soft sensors using a Connex3 Objet350 multimaterial printer and investigated an analytical comparison to sensors of similar geometries. The sensors consist of layers of commercial photopolymers with varying conductivities. We characterized the conductivity of TangoPlus, TangoBlackPlus, VeroClear, and Support705 materials under various conditions and demonstrate applications in which we can take advantage of these embedded sensors

A framework for ensemble modelling of climate change impacts on lakes worldwide : the ISIMIP Lake Sector

Empirical evidence demonstrates that lakes and reservoirs are warming across the globe. Consequently, there is an increased need to project future changes in lake thermal structure and resulting changes in lake biogeochemistry in order to plan for the likely impacts. Previous studies of the impacts of climate change on lakes have often relied on a single model forced with limited scenario-driven projections of future climate for a relatively small number of lakes. As a result, our understanding of the effects of climate change on lakes is fragmentary, based on scattered studies using different data sources and modelling protocols, and mainly focused on individual lakes or lake regions. This has precluded identification of the main impacts of climate change on lakes at global and regional scales and has likely contributed to the lack of lake water quality considerations in policy-relevant documents, such as the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC). Here, we describe a simulation protocol developed by the Lake Sector of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) for simulating climate change impacts on lakes using an ensemble of lake models and climate change scenarios for ISIMIP phases 2 and 3. The protocol prescribes lake simulations driven by climate forcing from gridded observations and different Earth system models under various representative greenhouse gas concentration pathways (RCPs), all consistently bias-corrected on a 0.5 degrees x 0.5 degrees global grid. In ISIMIP phase 2, 11 lake models were forced with these data to project the thermal structure of 62 well-studied lakes where data were available for calibration under historical conditions, and using uncalibrated models for 17 500 lakes defined for all global grid cells containing lakes. In ISIMIP phase 3, this approach was expanded to consider more lakes, more models, and more processes. The ISIMIP Lake Sector is the largest international effort to project future water temperature, thermal structure, and ice phenology of lakes at local and global scales and paves the way for future simulations of the impacts of climate change on water quality and biogeochemistry in lakes.Peer reviewe

Environmental DNA Marker Development with Sparse Biological Information: A Case Study on Opossum Shrimp (Mysis diluviana).

The spread of Mysis diluviana, a small glacial relict crustacean, outside its native range has led to unintended shifts in the composition of native fish communities throughout western North America. As a result, biologists seek accurate methods of determining the presence of M. diluviana, especially at low densities or during the initial stages of an invasion. Environmental DNA (eDNA) provides one solution for detecting M. diluviana, but building eDNA markers that are both sensitive and species-specific is challenging when the distribution and taxonomy of closely related non-target taxa are poorly understood, published genetic data are sparse, and tissue samples are difficult to obtain. To address these issues, we developed a pair of independent eDNA markers to increase the likelihood of a positive detection of M. diluviana when present and reduce the probability of false positive detections from closely related non-target species. Because tissue samples of closely-related and possibly sympatric, non-target taxa could not be obtained, we used synthetic DNA sequences of closely related non-target species to test the specificity of eDNA markers. Both eDNA markers yielded positive detections from five waterbodies where M. diluviana was known to be present, and no detections in five others where this species was thought to be absent. Daytime samples from varying depths in one waterbody occupied by M. diluviana demonstrated that samples near the lake bottom produced 5 to more than 300 times as many eDNA copies as samples taken at other depths, but all samples tested positive regardless of depth

The role of warm, dry summers and variation in snowpack on phytoplankton dynamics in mountain lakes

Climate change is altering biogeochemical, metabolic, and ecological functions in lakes across the globe. Historically, mountain lakes in temperate regions have been unproductive because of brief ice-free seasons, a snowmelt-driven hydrograph, cold temperatures, and steep topography with low vegetation and soil cover. We tested the relative importance of winter and summer weather, watershed characteristics, and water chemistry as drivers of phytoplankton dynamics. Using boosted regression tree models for 28 mountain lakes in Colorado, we examined regional, intraseasonal, and interannual drivers of variability in chlorophyll a as a proxy for lake phytoplankton. Phytoplankton biomass was inversely related to the maximum snow water equivalent (SWE) of the previous winter, as others have found. However, even in years with average SWE, summer precipitation extremes and warming enhanced phytoplankton biomass. Peak seasonal phytoplankton biomass coincided with the warmest water temperatures and lowest nitrogen-to-phosphorus ratios. Although links between snowpack, lake temperature, nutrients, and organic-matter dynamics are increasingly recognized as critical drivers of change in high-elevation lakes, our results highlight the additional influence of summer conditions on lake productivity in response to ongoing changes in climate. Continued changes in the timing, type, and magnitude of precipitation in combination with other globalchange drivers (e.g., nutrient deposition) will affect production in mountain lakes, potentially shifting these historically oligotrophic lakes toward new ecosystem states. Ultimately, a deeper understanding of these drivers and pattern at multiple scales will allow us to anticipate ecological consequences of global change better

Correction: Environmental DNA Marker Development with Sparse Biological Information: A Case Study on Opossum Shrimp (Mysis diluviana).

[This corrects the article DOI: 10.1371/journal.pone.0161664.]

Mountain Lakes: Eyes on Global Environmental Change

Mountain lakes are often situated in protected natural areas, a feature that leads to their role as sentinels of global environmental change. Despite variations in latitude, mountain lakes share many features, including their location in catchments with steep topographic gradients, cold temperatures, high incident solar and ultraviolet radiation (UVR), and prolonged ice and snow cover. These characteristics, in turn, affect mountain lake ecosystem structure, diversity, and productivity. The lakes themselves are mostly small and shallow, and up until recently, have been characterized as oligotrophic. This paper provides a review and update of the growing body of research that shows that sediments in remote mountain lakes archive regional and global environmental changes, including those linked to climate change, altered biogeochemical cycles, and changes in dust composition and deposition, atmospheric fertilization, and biological manipulations. These archives provide an important record of global environmental change that pre-dates typical monitoring windows. Paleolimnological research at strategically selected lakes has increased our knowledge of interactions among multiple stressors and their synergistic effects on lake systems. Lakes from transects across steep climate (i.e., temperature and effective moisture) gradients in mountain regions show how environmental change alters lakes in close proximity, but at differing climate starting points. Such research in particular highlights the impacts of melting glaciers on mountain lakes. The addition of new proxies, including DNAbased techniques and novel stable isotopic analyses, provides a gateway to addressing novel research questions about global environmental change. Recent advances in remote sensing and continuous, high-frequency, limnological measurements will improve spatial and temporal resolution and help to add records to spatial gaps including tropical and southern latitudes

The Role of Warm, Dry Summers and Variation in Snowpack on Phytoplankton Dynamics in Mountain Lakes

Climate change is altering biogeochemical, metabolic, and ecological functions in lakes across the globe. Historically, mountain lakes in temperate regions have been unproductive because of brief ice-free seasons, a snowmelt-driven hydrograph, cold temperatures, and steep topography with low vegetation and soil cover. We tested the relative importance of winter and summer weather, watershed characteristics, and water chemistry as drivers of phytoplankton dynamics. Using boosted regression tree models for 28 mountain lakes in Colorado, we examined regional, intraseasonal, and interannual drivers of variability in chlorophyll a as a proxy for lake phytoplankton. Phytoplankton biomass was inversely related to the maximum snow water equivalent (SWE) of the previous winter, as others have found. However, even in years with average SWE, summer precipitation extremes and warming enhanced phytoplankton biomass. Peak seasonal phytoplankton biomass coincided with the warmest water temperatures and lowest nitrogen-to-phosphorus ratios. Although links between snowpack, lake temperature, nutrients, and organic-matter dynamics are increasingly recognized as critical drivers of change in high-elevation lakes, our results highlight the additional influence of summer conditions on lake productivity in response to ongoing changes in climate. Continued changes in the timing, type, and magnitude of precipitation in combination with other globalchange drivers (e.g., nutrient deposition) will affect production in mountain lakes, potentially shifting these historically oligotrophic lakes toward new ecosystem states. Ultimately, a deeper understanding of these drivers and pattern at multiple scales will allow us to anticipate ecological consequences of global change better