Reservoirs are ubiquitous and growing in number globally. These constructed aquatic structures are differentiated from natural lakes and ponds as many are anthropogenically managed to provide varying ecosystem services, including drinking water supply, flood control, irrigation, hydropower generation, navigation, and recreation. Watershed-reservoir linkages, however, can play an integral role in driving ecological processes, nutrient and sediment cycling, and mixing regimes within the reservoir and in their receiving waters. Reservoirs tend to have large watershed area-to-reservoir area ratios (i.e., tightly coupled terrestrial-aquatic linkages) and are thus greatly influenced by changing climatic conditions, altered hydrological connectivity, and watershed disturbances. We aim to use this session to invite research contributions highlighting how physical, ecological, and biogeochemical processes respond to event/episodic and long-term changes in global stressors across different reservoir types and ecoregions. We aim to use the session to bring together the broader scientific community to improve our understanding of reservoir processes and to identify future research needs and directions. As such, we encourage contributions from scientists studying all aspects of reservoir ecosystems across the globe.
Lead Organizer: Ruchi Bhattacharya, Cleveland State University, Cleveland, Ohio, USA (ruchi.bhattacharya@gmail.com)
Co-organizers:
Lesley Knoll, Miami University, Oxford, Ohio (knolllb@miamioh.edu)
Nicole Hayes, University of Wisconsin Stout, Menomonie, WI, USA (hayesn@uwstout.edu)
Michael Vanni, Miami University, Oxford, Ohio (vannimj@miamioh.edu)
Presentations
02:00 PM
Reservoir Futures: Water quality across the land-lake continuum (8425)
Tutorial/Invited: Invited
Primary Presenter: Nandita Basu, University of Waterloo (nandita.basu@uwaterloo.ca)
River dams and reservoirs provide a suite of ecosystem services, such as irrigation, flood control, or hydropower, but are also one of the key anthropogenic disruptors of the landscape, altering the movement of water, solutes and organisms across the land ocean continuum. Hundreds of small reservoirs across the landscape not only create lags in nutrient delivery, but also harbor memories of past nutrient legacies deep in its sediments. Given their integral role in societal functioning, they also provide nodes of opportunities to actively manage our water resources, and mitigate some of the impacts of anthropogenic land use. However, reservoirs and lakes have often been studied in isolation of the watershed that drains into it, with limnologists simplifying watershed inputs in their conceptualization and models, while hillslope hydrologists often ignoring the significant role reservoirs play in altering flow and concentration dynamics. Here, we use a combination of data synthesis and modeling to explore how climate and land use in the reservoir-shed impacts reservoir functioning, and in-turn how reservoir functioning and management across a network of hundreds of reservoirs can alter the quality of downstream waters.
02:15 PM
Quantifying shifting littoral habitat in western reservoirs. (7783)
Primary Presenter: Sean Bertalot, University of Wyoming (sbertalo@uwyo.edu)
Reservoirs provide significant ecological and socioeconomic value to their surrounding landscape. In the western US, reservoirs provide important storage for drinking water, irrigation, and recreational use but are sensitive to anthropogenic stressors, including variable precipitation and land use changes, and are prone to dramatic water level fluctuations. In this study, we coupled monthly sampling with hydrologic storage and bathymetric data with the goal of understanding how two reservoirs in Wyoming change during the ice-off season and year to year. Both systems, Jackson Lake, and Boysen Reservoir, have significant differences in their watershed characteristics, elevation, bathymetry, and trophic status. Limited sampling has occurred in either reservoir, particularly Jackson Lake, making long term analyses challenging with current available data. We propose a method for separating and quantifying littoral and open-water habitat at varying water levels. Through this we explore the influence of chlorophyll-a concentrations on littoral habitat in Boysen Reservoir. We also discuss preliminary steps and challenges associated with incorporating satellite remote sensing data to increase sample frequency and better capture spatial heterogeneity across each reservoir’s surface. Understanding drivers and patterns of productivity in both systems could inform future management decisions in the face of a changing climate.
02:30 PM
FROM BROWN TO GREEN: LONG-TERM TRENDS IN PARTICULATE ORGANIC AND INORGANIC MATTER IN MISSOURI RESERVOIRS (7903)
Primary Presenter: Lorena Pinheiro-Silva, University of Maryland Center for Environmental Science / University of Missouri-Columbia (lsilva@umces.edu)
Contrasting with the trend observed in Northern lakes, visible changes in the color of Missouri reservoirs have resulted in a transition from brown to green waters; however, the root cause of this change is unknown. We analyzed two long-term water quality monitoring programs to investigate decadal trends (10-35 yrs) in the ratio between particulate organic matter (POM) and inorganic matter (PIM) to total suspended solids (TSS) in 158 reservoirs that span a broad anthropogenic gradient in land cover in the Midwest USA. We observed a statistically significant increase in the POM/TSS (i.e. greening) in 42 reservoirs with an average rate of 0.014 yr-1. Boosted Regression Tree analysis reveals that the shift toward greener waters was observed in reservoirs likely experiencing increasing transparency and total nitrogen concentrations, mediated by warming surface water temperatures, watershed to reservoir area ratio (Warea/Rarea) and precipitation anomaly (PDSI; Palmer Drought Severity Index). However, the relative importance of the drivers differed depending on the land cover type. In the northern agricultural reservoirs, surface water temperature emerged as a key factor, while in the southern forest reservoirs, the effect of total nitrogen (TN) was more pronouced. Additionally, in urban and mixed reservoirs, Warea/Rarea, TN and PDSI together had the largest relative influence. Our findings reveal that the phenomenon of shifting lake water color is not yet widespread in Midwest reservoirs but may likely represent the future of these regional aquatic ecosystems.
02:45 PM
Annual Residence Time Drives Sediment Nitrogen Concentrations in Reservoirs Using Paleolimnological Techniques (8276)
Primary Presenter: Benjamin Webster, Auburn University (benjcwebster@gmail.com)
Reservoirs are hotspots for sediment and nutrient deposition. However, less is known of how reservoir nitrogen (N) deposition is altered at the watershed scale. In this study, we compared average annual hydrologic residence time (RT) along with other physical parameters to the sediment N concentrations for eight reservoirs in the SE USA. RT is determined by water storage in a reservoir and dam release rate and can be linked to dynamic processes like trap efficiency. The eight reservoirs varied regarding RT, surface area, water volume, land use, catchment area, primary usage (hydropower and storage), and other parameters. Using long-term reservoir flow data, federal long-term drought indices, GIS tools, and paleolimnological techniques, average annual RT was found to have the strongest relationship with sediment N concentrations (R2 = 0.79) when compared to all other reservoir parameters. RT drives N deposition by allowing longer periods of algal growth followed by deposition of N in particulate organic form. Photosynthetic pigments supported this inference and identified cyanobacteria being the primary producer group most related to RT (R2 = 0.73) followed by diatoms (R2 = 0.56). In periods of drought, basin managers are forced to abide by critical yields and base flow regulations to maintain reservoir water storage thus increasing water retention times. Following our sediment and RT based model, during these extreme long-term drought periods, RT increased by 45 – 60% increasing N delivery to the sediments by roughly 2.5 – 4%.
03:00 PM
A GLOBAL ASSESSMENT OF SOURCE, COMPOSITION, AND DRIVERS OF DISSOLVED ORGANIC MATTER IN RESERVOIR ECOSYSTEMS (7967)
Primary Presenter: Ruchi Bhattacharya, Cleveland State University (ruchi.bhattacharya@gmail.com)
Reservoirs are ubiquitous, critical part of aquatic continuum, and known hotspots of Carbon (C) cycling. Yet, in comparison to the riverine and natural lake ecosystems, studies focusing on sources and composition of dissolved organic matter and bound C in these managed systems are limited. The existing studies often are at a local (single reservoir) to small regional scale, and thus the evolving patterns and drivers of reservoir C dynamics in response to global scale stressors remain limited. To address this research gap, a global dataset of reservoir DOM quantity, source, and composition is developed. The study reservoirs span geographical gradients of hydro-climate, productivity, and landscape characteristics (e.g., mean depth, watershed area, watershed: reservoir area, and human disturbance). The key regional to global scale drivers of the underlying biogeochemical processes governing reservoir DOM dynamics are explored. Finally, the current needs and future study directions to improve the understanding of C dynamics in reservoirs are proposed.
03:15 PM
DEGREE OF CONNECTIVITY CAN DRIVE NUTRIENT DYNAMICS IN SMALL AND SHALLOW RESERVOIRS (8044)
Primary Presenter: Uchechukwu Ogbenna, University of Nebraska-Lincoln (ogbennauchechukwu@gmail.com)
Aquatic ecosystems, particularly reservoirs, play vital roles in global nutrient cycling and retention along the river continuum. Small, shallow reservoirs (<1000 hectares and <10m deep) are typically constructed on small and intermittent streams. These flow patterns affect the degree of connectivity between reservoirs and their catchments, as well as the structure of reservoirs over time. This affects nutrient cycling and retention within reservoirs. Our study analysed existing data from the United States Army Corps of Engineers (USACE ) and water quality portal to understand how connectivity changes over time. We evaluated its impact on the absolute and relative concentration of nitrate (NO3) and phosphate (PO4) in nine small, shallow reservoirs in southeast Nebraska. Our findings revealed interannual variation in the surface area of reservoirs (proxy of connectivity) with the annual changes ranging from -0.057 to 3.31 hectares per year. Both absolute NO3 and PO4 concentrations varied significantly over time in all reservoirs and were strongly influenced by the degree of connectivity. The relative (N:P) concentration varied across reservoirs and over time in most reservoirs. This study enhanced our understanding of how connectivity shapes nutrient dynamics in small reservoirs. Furthermore, it underscores the importance of investigating how the degree of connectivity influences hydrodynamic functions like mixing dynamics and residence time, which in turn impacts biogeochemical processes in small and shallow reservoirs.
SS23A - Dynamics of Reservoir Ecosystems in the Anthropocene: Ecology, Biogeochemistry, and Physics
Description
Time: 2:00 PM
Date: 5/6/2024
Room: Meeting Room MN