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
04:00 PM
EFFECTS OF CLIMATE AND AGRICULTURAL LAND MANAGEMENT ON LONG-TERM DEEP-WATER DISSOLVED OXYGEN DYNAMICS IN A PRODUCTIVE RESERVOIR (7915)
Primary Presenter: Lesley Knoll, Miami University (knolllb@miamioh.edu)
Many worldwide lakes show declining deep-water dissolved oxygen (DO) concentrations which may threaten ecosystem integrity by influencing biogeochemical processes, internal nutrient cycling, and suitable habitat availability. Declines in deep-water DO are largely associated with increasing air temperature or increasing nutrient inputs. Here, we use a 30 year dataset for Acton Lake, a hypereutrophic reservoir with watershed land use dominated by agriculture. Over this time period, air temperature has increased. Additionally, agricultural land management shifted toward increased conservation tillage, and concomitant decreases in sediment/nitrogen loads, early in the dataset while conservation tillage declined later in the dataset. It is within this context that we explore 1) long-term DO trends, and 2) drivers of interannual deep-water DO variability. Our results reveal that anoxia onset (i.e., day of year DO < 1 mg/L), and anoxic factor (AF) did not significantly change over time. However, anoxia onset and AF were associated with climatic factors and land management. In particular, anoxia onset occurred earlier in dry or warm springs while the AF increased with warmer summer air temperatures. Furthermore, increased conservation tillage was associated with earlier anoxia onset and greater AF suggesting that reduced sediment loads, a consequence of conservation tillage, may have elevated phytoplankton and heterotrophic respiration. Results highlight that the effects of a changing climate on lake DO may be masked by complex local factors such as shifts in farming practices.
04:15 PM
LOW WATER LEVELS AND RESERVOIR AGING INCREASE SEVERITY OF SUMMERTIME METALIMNION DISSOLVED OXYGEN MINIMA IN LAKE POWELL, DESERT SOUTHWEST USA (8306)
Primary Presenter: Bridget Deemer, USGS (bdeemer@usgs.gov)
Water level drawdowns are common in reservoirs and can affect dissolved oxygen dynamics via several pathways. In large storage reservoirs, inflow deltas are often important sites for sediment deposition, with some sediment-laden rivers forming highly dynamic delta regions as they enter the reservoir. As water levels change, deposited sediment may be remobilized and affect pelagic dissolved oxygen dynamics. Here, we interrogate a long-term set of dissolved oxygen profiles to ask how water levels have interacted with both reservoir age and spring inflow volumes to affect metalimnion low dissolved oxygen events in Lake Powell, desert Southwest, USA. The most supported model suggests that declining water levels interact with reservoir age to promote summer and fall metalimnion low dissolved oxygen events, with larger spring snowmelt inflows furthering dissolved oxygen declines. We also conducted incubations to understand how both sediment source, monsoon inputs, and water temperature affect dissolved oxygen demand and nutrient cycling. Incubations showed that oxygen demand was highly temperature dependent in the two major inflows to the reservoir (Q10 of 3.3-3.7), the highest oxygen demand was from monsoonal inputs, and there was substantial phosphorus release from two of three sediment types. Our findings underscore how reservoir aging and dynamic hydrology can combine to reduce water column dissolved oxygen availability.
04:30 PM
Differences in factors determining the taxon-based and trait-based community structures: a field test using zooplankton (8016)
Primary Presenter: Hiromichi Suzuki, Tohoku University (hiromichi.suzuki0611@gmail.com)
Ecological community structure is determined by dispersal and environmental filters. Although it has traditionally been described in terms of taxonomic units, traits have recently been recognized as alternative units for the description of community structure. However, the relative importance of dispersal and environmental filters may differ between taxon-based and trait-based communities. For example, because species distributions have geographic ranges, taxon-based community structure may be more dispersal-limited, whereas trait-based community structure may be more regulated by environmental conditions because traits are less tied to specific habitat locations. However, no study has yet quantified how the contributions of the two filters differ for taxon- and trait-based community structure. In this study, therefore, we examined zooplankton assemblages in 87 artificial reservoirs throughout the Japanese archipelago to quantify the relative importance of two filters by examining the effects of spatial configuration (reflecting dispersal filters) and biotic and abiotic variables (reflecting environmental filters) on taxon- and trait-based community structure. The variation in taxon-based community structure was explained equally well by spatial and environmental variables. However, variation in trait-based community structure was explained more by environmental variables. These results show that the relative importance of spatial and environmental filters changes with the unit describing community structure.
04:45 PM
DISTINCT PATTERNS OF CHANGE IN ZOOPLANKTON COMMUNITIES OVER MULTIPLE SUMMERS IN A EUTROPHIC RESERVOIR (8059)
Primary Presenter: Heather Wander, Virginia Tech (hwander@vt.edu)
Much research on plankton dynamics has focused on glacially-formed, north temperate lakes, leaving a gap in our understanding of the variability and community succession of zooplankton in reservoirs. Zooplankton play a central role in freshwater food webs, and thus changes in their communities can have cascading effects on other freshwater organisms. While it is widely expected in glacially-formed lakes that zooplankton communities follow predictable patterns of succession within a year, reservoirs may exhibit less predictable patterns, especially as climate change exacerbates variability. To identify the predictability of zooplankton succession, we collected monthly zooplankton samples from May-September over six years in a eutrophic reservoir. We used multivariate approaches to compare the trajectory of zooplankton succession among cladoceran, copepod, and rotifers each year. Our goals were to: 1) determine whether zooplankton followed similar patterns of succession and 2) identify environmental drivers of zooplankton succession. We found that zooplankton communities followed predictable patterns of succession in some years, but observed high variability in zooplankton density and community composition from year-to-year. Additionally, dissolved oxygen and nutrient concentrations were associated with variability between months and years. Ultimately, our data suggest that zooplankton succession in reservoirs inconsistently follows expected patterns from glacially-formed lakes, and this seasonal variability may further increase in the future due to climate change.
05:00 PM
MICROBIAL COMMUNITY STUDY LINKED TO BIOGEOCHEMISTRY: INSIGHTS INTO MANGANESE CYCLING IN A DRINKING WATER RESERVOIR (7890)
Primary Presenter: Lea Hahn, University of Koblenz (leahahn@uni-koblenz.de)
Reservoir water quality, especially with respect to Mn and Fe concentrations, is closely tied to redox conditions like oxygen availability, which in turn is influenced by thermal stratification. Warmer surface temperatures and elongated stratification periods have been demonstrated for bodies of standing waters, including the Wahnbach Reservoir (Germany). Increasing levels of dissolved Mn trouble raw water treatment. Sediment may function as a sink or source for Mn. As microorganisms play a crucial role here, we investigated sediment for Mn compounds as well as Mn oxidizers and Mn reducers. Mn-reducing activities were more pronounced and selective cultures enriched phylogenetically highly diverse microorganisms including members of the genera Azospira, Rhodoferax, Bacillus, Aeromonas, Anaeromyxobacter, Geothrix, and Methanosarcina. Extensive long-term monitoring unveils biogeochemical processes in the water column. To link these processes to key microorganisms and their metabolisms, the water column and surface sediments were sampled at three sites in the reservoir monthly for one year (2022/2023). 16S rRNA amplicon sequencing was performed. Data analysis will primarily focus on Mn dynamics and putative Mn metabolizing microorganisms in relation to the availability of O2, organic carbon, N and P nutrients. In addition, the interplay with other anaerobic respiration processes such as Fe(III) reduction, sulfate reduction, and methanogenesis will be investigated. Gained knowledge can offer valuable insights to guide future water quality management strategies.
05:15 PM
IMPACTS OF INCREASED PUMPED-STORAGE HYDROPOWER OPERATIONS ON TWO NORWEGIAN RESERVOIRS (8176)
Primary Presenter: Francesca Hinegk, University of Trento (hinegk.francesca@unitn.it)
The transition to a renewable energy system requires an increased energy storage capacity to balance the intermittent and not fully predictable production. Pumped-storage (PS) hydropower (HP) offers a flexible and carbon-neutral storage option through increased bidirectional water volume exchanges between reservoirs, whose impact is not yet fully understood. We investigated the effects on two case study reservoirs in Norway, planned for conversion from traditional to PS plants, using an interdisciplinary approach and focusing on three core processes. First, we explored the response of the thermal stratification to PS operations with a 2D hydro-thermodynamic model and in-situ monitoring. Second, we analyzed how the water level variations influence the extent of the littoral zone affected by periodic wetting and drying, by integrating hydro-morphological modeling, future climate scenarios and environmental indexes. The water level data for both these analyses were generated with a medium-term optimal price-based scheduling model. Finally, we studied the response of the ice cover to the water level fluctuations by combining a simple mechanical model and the analysis of in-situ and satellite data. Our preliminary results reveal a complex framework, where the modulation of the HP operations determines the nature and the magnitude of the impacts. This highlights the need to include environmental indices besides economic efficiency in the optimization process of HP operations.
SS23B - Dynamics of Reservoir Ecosystems in the Anthropocene: Ecology, Biogeochemistry, and Physics
Description
Time: 4:00 PM
Date: 5/6/2024
Room: Meeting Room MN