Modeling climate change impacts on the thermal dynamics of polymictic Oneida Lake, New York, United States

Future projections of thermal regimes and mixing characteristics in a monomictic reservoir under climate change

Stratified structures are basic physical characteristics of lakes and reservoirs, which play important roles in vertical convection and mixing processes. Global warming is expected to alter the thermal regimes and stratified characteristics of lakes and reservoirs, leading to potential environmental risks and ecological problems. In this study, we used a two-dimensional hydrodynamic model to explore the response characteristics of the thermal regime to climate change in the Xiluodu Reservoir. The study is conducted based on four representative concentration pathways (RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5). The results show that the projected surface water temperature of the reservoir will significantly increase (0.13 °C/10a-0.34 °C/10a) from 2022 to 2099, and the warming rate of the water in the epilimnion and thermocline will be greater than that in the hypolimnion, leading to enhanced vertical stratification in the reservoir. The stratification stability index (SI) will increase by 14.4 % under RCP 8.5 compared to that under RCP 2.6. The main responses of the reservoir to climate change are earlier start date and later end date of stratification, which may increase the duration of hypoxia in the hypolimnion and promote the succession of planktonic algal communities. The withdrawal water temperature in the reservoir will significantly increase under the climate warming scenarios (0.03 °C/10a-0.22 °C/10a). Furthermore, our research results indicate that selective withdrawal is still needed to mitigate the adverse effects of cold water from the reservoir during the fish spawning period under the strongest warming scenario, and can also be an effective adaptive management strategy to regulate thermal stability in the reservoir. This study provides a scientific and theoretical reference for the sustainable management of similar deep monomictic reservoirs under climate change.

The Spatiotemporal Characteristics of Water Quality and Main Controlling Factors of Algal Blooms in Tai Lake, China

Taking Tai Lake in China as the research area, a 3D water environment mathematical model was built. Combined with the LHS and Morris uncertainty and sensitivity analysis methods, the uncertainty and sensitivity analysis of total phosphorus (TP), total nitrogen (TN), dissolved oxygen (DO), and chlorophyll a (Chl-a) were carried out. The main conclusions are: (1) The performance assessment of the 3D water environment mathematical model is good (R2 and NSE > 0.8) and is suitable for water quality research in large shallow lakes. (2) The time uncertainty study proves that the variation range of Chl-a is much larger than that of the other three water quality parameters and is more severe in summer and autumn. (3) The spatial uncertainty study proves that Chl-a is mainly present in the northwest lake area (heavily polluted area) and the other three water quality indicators are mainly present in the center. (4) The sensitivity results show that the main controlling factors of DO are ters (0.15) and kmsc (0.12); those of TN and TP are tetn (0.58) and tetp (0.24); and those of Chl-a are its own growth rate (0.14), optimal growth temperature (0.12), death rate (0.12), optimal growth light (0.11), and TP uptake rate (0.11). Thus, TP control is still the key treatment method for algal blooms that can be implemented by the Chinese government.

Effects of temperature-control curtain on algae biomass and dissolved oxygen in a large stratified reservoir: Sanbanxi Reservoir case study

A temperature-control curtain (TCC) is a new technique of selective withdrawal for controlling the outflow temperature of a reservoir. A TCC can significantly affect the reservoir hydrodynamic and thermal structure, but its effects on water quality and ecology remain unknown. In this study, we developed and calibrated a hydro-thermal-water quality model to numerically analyze how a TCC located 1 km from a dam affected algal biomass and water quality in a reservoir. According to our results, when a TCC was used, the mean annual chlorophyll a (Chl-a) concentrations in the reservoir decreased. Chl-a concentrations remained constant during the heating period until normal water levels were reached, and increased during the cooling period and decreased until year-end drawdown levels were reached. The dissolved oxygen (DO) concentrations decreased and the anoxic proportions increased throughout the year. The yearly mean Chl-a and DO concentrations in the reservoir declined continuously as the water-retaining proportion (P_r) of the TCC increased from 0 to 87.5%, while the anoxic proportion (DO < 2 mg/L) first increased and then decreased, peaking at a P_r of 62.5%. The change patterns of the anoxic proportion were consistent with those of thermal stability, demonstrating the applicability of thermal stability in predicting reservoir hypoxia. Moreover, the environmental impact of TCCs will increase under global warming, and TCCs can mitigate the increased algal biomass and further decrease DO in warmer climate conditions. Under a medium-high climate scenario, Representative Concentration Pathway 6.0, and a TCC having 75% P_r, the yearly mean Chl-a, DO concentrations, and anoxic proportions of Sanbanxi Reservoir are predicted to reach 10.7 μg/L, 4.2 mg/L, and 39.6%, respectively, by 2046-2065. Thus, changes in the water environment and ecology (particularly the likely deterioration of water quality because of selective withdrawal under global warming) should be considered as a component of water management practices.

Salmonella and the changing environment: systematic review using New York State as a model

Salmonella is a public health concern, for which a complex interplay between host, agent, and environment exists. An improved understanding of causal processes can be used to better gauge the causes and trajectory of Salmonella in a changing environment. This would be useful in determining the impact of climate change on the New York State (NYS) environment, the effect of climate change on Salmonella in NYS, factors contributing to Salmonella vulnerability in humans, and aspects of climate change and Salmonella which necessitate further research. A systematic review was conducted to study associations between Salmonella and the environment. Using the search criteria, a total of 91 relevant articles were identified from four electronic databases. Key information was abstracted, organized, and synthesized to identify causal processes and linkages between climate change, the environment of NYS, and Salmonella-related outcomes, as well as risk factors to characterize Salmonella vulnerabilities. Three inter-related domains were identified for consideration and application to epidemiological research to confirm and extrapolate disease patterns using climate change scenarios: improved quantification of causal relationships, inclusion of factors linked to sectors not immediately associated with the exposure and outcome, and increased capacity to validate models in diverse settings.

Impact of intra-annual runoff uniformity and global warming on the thermal regime of a large reservoir

Thermal stratification is common in reservoirs and greatly influences the aquatic environment. Changes in the uniformity of intra-annual runoff have been detected in several basins, but few studies have focused on the impacts that these changes have on thermal regimes. Using runoff data for Sanbanxi Reservoir, China, during 1950-2015, the long-term trends of intra-annual runoff uniformity were statistically analyzed and extrapolated for the 2050s and 2090s, and the relationship between these trends and the thermal regime of the reservoir were investigated. Moreover, the thermal regime was evaluated for future climate scenarios accounting for global warming. This study shows the following: 1) for South China, the concentration degree (C_d) for the distribution of intra-annual runoff in natural basins such as Sanbanxi Reservoir tended to be higher, but for rivers significantly impacted by human activities, C_d tended to be lower. 2) a higher C_d was associated with an increased reservoir temperature and released water temperature, and decreased thermal stability. For Sanbanxi Reservoir, a 10% increase in C_d corresponded to a change in annual average temperature, thermal stability, and released water temperature of 0.036 °C, -48.4 J m^-2, and 0.153 °C, respectively. These changes were larger in summer than in other seasons; 3) global warming is predicted to increase reservoir temperature, released water temperature, and thermal stability, having a more significant influence on these parameters than intra-annual runoff uniformity; 4) future changes in thermal regimes will intensify oxygen stratification and hypolimnetic anoxia, promoting algal blooms, and delaying fish spawning. Effects of two methods aimed at controlling the thermal regime were also analyzed, including changing the operation level and intake elevation of the reservoir. This study investigated the response of the thermal regime of Sanbanxi Reservoir to climate change, and provides theoretical support for the management of water temperature and the reservoir's aquatic environment.

Drivers and Management Implications of Long-Term Cisco Oxythermal Habitat Decline in Lake Mendota, WI

Cisco (Coregonus artedi) are an important indicator species for cold-water lake habitats in the Great Lakes region, and many populations have been extirpated at their southern range limit over the last century. Understanding the roles of climate and water quality in these extirpations should inform protection of cold-water fishes. Using the water temperature at the depth where dissolved oxygen falls to 3 mg L^-1 (TDO3) as a metric, we investigated the roles of climate and water quality as drivers of habitat availability for cisco in Lake Mendota, WI, USA from 1976 to 2013. We find that summer (Jun-Aug) air temperatures, spring (Mar-May) phosphorus load, and spring inflow influence summer TDO3. Warm air temperatures lead to the greatest increases in TDO3, whereas reduced phosphorus loads can reduce TDO3, thus alleviating oxythermal stress. Under air temperatures expected under the A1B climate change scenario, a 25% reduction in phosphorus load would stabilize TDO3 at current levels, while a 75% reduction in phosphorus loading would be required to expand oxythermal habitat. Costs of these reductions are estimated to range from US$16.9 million (-25%) to US$155-167 million (-75%) over a 20-year period but may be feasible by expanding upon current watershed phosphorus reduction initiatives if sustained funding were available. Identifying targeted reductions will become increasingly important throughout the region as warmer temperatures and longer stratification reduces cool- and cold-water fish habitat in many Midwestern lakes under the expected future climate.