Upper Mississippi River Research Articles

Juvenile Silver Carp and Bighead Carp as Forage for Predatory Fish in the LaGrange Reach of the Illinois River

AbstractIncreasing numbers of Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (commonly called “bigheaded carp”) in the Illinois River have led to concerns about the impact that their invasion has on native food web dynamics. Bigheaded Carp recruited in large numbers in the LaGrange Reach of the Illinois River during the summer of 2014. This provided an opportunity to determine whether native piscivorous fish prey upon invasive carp when they are abundant. Using electrofishing and fyke nets in the LaGrange Reach (August 1–November 8, 2014), we sampled native predatory fish (n = 1,472) for stomach content analysis. Fish community data from the Upper Mississippi River Restoration Program’s Long‐Term Resource Monitoring was used to quantify prey abundance (fish < 100 mm) in the study area and indicated that bigheaded carp represented 9% of available prey. Stomach content analysis revealed that the frequency of occurrence of juvenile bigheaded carp was greater than 15% in Shortnose Gar Lepisosteus platostomus, White Bass Morone chrysops, Black Crappie Pomoxis nigromaculatus, Channel Catfish Ictalurus punctatus, Smallmouth Bass Micropterus dolomieu, Largemouth Bass Micropterus salmoides, White Crappie Pomoxis annularis, Yellow Perch Perca flavescens, Flathead Catfish Pylodictis olivaris, Freshwater Drum Aplodinotus grunniens, and Yellow Bass Morone mississippiensis. Predators sampled in August and September foraged more heavily on juvenile bigheaded carp than those sampled in October and November. Electivity analysis suggested that juvenile bigheaded carp were selected over native forage by White Bass, Black Crappie, and Shortnose Gar, as these predators continued consuming them even as availability declined. Our results imply that native piscivores in the Illinois River consume and sometimes prefer juvenile bigheaded carp as prey. These results suggest that native predators might play a role in regulating bigheaded carp recruitment and that negative impacts to predators in areas of dense carp populations might be somewhat mitigated by the consumption of juvenile bigheaded carp.

Anthropogenic landcover impacts fluvial dissolved organic matter composition in the Upper Mississippi River Basin

Anthropogenic landcover impacts fluvial dissolved organic matter composition in the Upper Mississippi River Basin

Using Otolith Chemistry to Determine Early Life Environments and Movement of the Emerging Bigheaded Carp Population in Pools 16–19 of the Upper Mississippi River

AbstractBigheaded carp (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix) are invasive species in the USA and have spread throughout much of the Mississippi River basin. Population abundance upstream of Lock and Dam (LD) 19 (LD19) on the upper Mississippi River (UMR) has likely been limited by the high‐head dam at this location, which restricts all upstream fish passage to the lock chamber. We measured otolith (lapillus) stable isotope composition and elemental microchemistry of 146 Silver Carp (n = 77 females, 69 males) and 141 Bighead Carp (n = 76 females, 65 males) to determine early life environments (ELEs) of adult bigheaded carp captured upstream of LD19 at the invasion front, in an area of intense management (Pools 16–19). Otolith oxygen isotope ratios (δ18O) and elemental ratios (Sr:Ca and Ba:Ca) were compared to values of isotope and elemental ratios in water from putative ELEs to assign the ELE for each fish. Most Bighead Carp (68.8%) and Silver Carp (54.1%) collected upstream of LD19 had otolith core signatures consistent with ELEs downstream of LD19. Nineteen percent of Bighead Carp and 34% of Silver Carp could not be classified. The sex ratios of bigheaded carp (Pools 17–19 combined) with otolith core signatures downstream of LD19 did not differ from 1:1. Our results, when compared to those of Whitledge et al. (2019), suggest low but stable recruitment above this population pinch‐point dam in the UMR and suggest that targeting removal of bigheaded carp downstream of LD19 or inhibiting their movement upstream through the lock there might be effective as part of integrated control efforts.

Examination of Bigheaded Carp Ovaries Indicates Batch Spawning

AbstractFishes utilize several different species‐specific reproductive strategies adapted to their environment. Invasive species may display reproductive strategies that allow successful reproduction in varying environments, such as batch and protracted spawning. Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix, referred to as bigheaded carp, are invasive species that have been introduced worldwide. In some invaded ranges, they either have a protracted spawning period and/or spawn multiple times in a season, which can be advantageous in novel environments. Reproductive strategies can vary between river systems or with environmental conditions, and understanding differences in strategies can improve management of bigheaded carp. To determine reproductive strategy, we evaluated the histology of spawning capable ovaries from Silver Carp (n = 58) and Bighead Carp (n = 38) collected during May–September 2016 and June 2017 from Pools 17–20 of the upper Mississippi River (UMR). We found that 87.9% of Silver Carp (n = 51) and 86.8% of Bighead Carp (n = 33) had an ovary that contained primary growth, cortical alveolar, and vitellogenic oocytes simultaneously. Multiple stages of oocytes within an ovary indicated that individuals were capable of spawning multiple times during a single year, and the presence of postovulatory follicle complexes demonstrated that individuals had already spawned while oocytes were still present. Based on histological samples, bigheaded carp appear to be indeterminate batch spawners, with oocytes continuing to develop throughout the spawning period. Silver and Bighead carp in the UMR may exhibit protracted and batch spawning and employ flexible spawning strategies among different river systems, which can increase the probability of successful recruitment in a variable environment.

Light Trapping Reveals Multiple Bigheaded Carp Spawns Upstream of Lock and Dam 19 in the Upper Mississippi River

AbstractThe Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis are two species of invasive bigheaded carp currently invading North American rivers and watersheds. Bigheaded carp were accidentally introduced into the lower Mississippi River basin in the early 1970s and have since invaded many water bodies in the Midwestern United States. Evidence of bigheaded carp reproduction and recruitment in the upper Mississippi River upstream of Lock and Dam 19 (LD19) at Keokuk, Iowa, thought to be a critical constriction point to their upstream establishment, has been limited to a few isolated detections of eggs, larvae, and juvenile life stages since 2012. Therefore, a more comprehensive assessment of bigheaded carp reproduction in this critical management zone was needed. We used quadrafoil light traps (n = 1,387) deployed during May–September 2016–2018 in Pools 17–19 of the Mississippi River to monitor for advanced larval bigheaded carp in low‐velocity habitats. Throughout the sampling period, we captured 1,747 larval and 35 postlarval bigheaded carp (N = 1,782). Bigheaded carp were collected on 15 sampling events that spanned from May 31, 2016, to September 13, 2018, with associated hatch dates estimated to represent 10 unique reproductive events from May 2016 to September 2018. The individual captures and backdated hatch estimates revealed a protracted spawning period of up to seven events in 2016, one event in 2017, and two events in 2018. Bigheaded carp were only captured in Pool 19, possibly due to the drifting requirements for egg maturation and the low‐velocity downstream reach of Pool 19. This research provides confirmation that bigheaded carp spawned upstream of LD19 are capable of transitioning past the yolk sac stage upstream of this bottleneck to more advanced larval stages. Knowledge of reproduction and larval retention and the field‐based evidence of protracted spawning fill critical research gaps needed for the management of bigheaded carp.

Coupling terrestrial and aquatic thermal processes for improving stream temperature modeling at the watershed scale

Water temperature is an important indicator of the health of terrestrial and aquatic ecosystems and influences numerous biological and chemical processes that affect water quality, the health and productivity of biota, and other ecosystem services. In this study, we improved the Soil and Water Assessment Tool (SWAT) model to explicitly consider the thermal processes influencing the temperature of various terrestrial water components (i.e., surface runoff, lateral flow, and base flow) and the heat balance of water in streams. The improved SWAT model with an explicit heat balance description on both terrestrial and aquatic thermal processes (SWAT-HB) was compared with previous versions of the SWAT model that employ only empirical relationships between air temperature and stream temperature (SWAT-ER) or combine empirical terrestrial water temperature estimates with the heat balance of stream water (SWAT-EH) for the Upper Mississippi River Basin (UMRB) and Greensboro Watershed (GW) in the United States. The results show that, even though the SWAT-HB better simulates terrestrial thermal processes, all three models produce comparable simulations of long-term stream temperatures, indicating that stream temperature is mainly influenced by air temperature as water travels along large rivers. Nevertheless, the SWAT-HB and SWAT-EH models achieved better performance than the SWAT-ER model in the winter and spring but exhibited mixed performance in the summer and fall. The better model performance of the SWAT-HB model than the SWAT-EH model can be attributed to the improved estimation of terrestrial water temperature components. Although, empirical methods (e.g., SWAT-ER) are suitable for providing estimation of stream temperature, the coupled terrestrial and aquatic heat balance-based methods (e.g., SWAT-HB) allow for the consideration of land and water management practices (e.g. crop irrigation, land use change, and water use for thermoelectric cooling) effects on stream temperature.

Spatial and temporal dynamics of phytoplankton assemblages in the upper Mississippi River

AbstractPhytoplankton provide large quantities of organic carbon and biomolecules that support large river ecosystems. However, when certain groups become overabundant (e.g., cyanobacteria), they can pose a risk to human health and river biota. The purpose of this study was to examine the spatial and temporal dynamics of phytoplankton community composition within the upper Mississippi River. More specifically, we analyzed samples from main channel, impounded, and backwater areas of Navigation Pools 8 and 13 to examine lateral variability within each of these pools. We analyzed samples from the main channel of Pool 26 to examine longitudinal variation among Pools 8, 13, and 26. Phytoplankton and water quality samples were collected during the summer months of 2006–2009. The main channels of Pool 8 and Pool 13 were generally dominated by diatoms, although cyanobacteria were (at times) more abundant. The backwaters were generally dominated by cyanobacteria and typified by flagellated species (e.g., cryptomonads and euglenoids). The main channel of Pool 26 was always dominated by diatoms. Discharge influenced phytoplankton community composition. In Pool 26, taxonomic richness tended to increase with increasing discharge. There were no linear correlations between cyanobacteria total or proportional biovolume and nutrient concentrations, indicating that nutrient limitation was not common. Differences in phytoplankton communities were generally associated with physical factors such as discharge, turbidity, and residence time.

Wetland restoration yields dynamic nitrate responses across the Upper Mississippi river basin

Wetland restoration is a primary management option for removing surplus nitrogen draining from agricultural landscapes. However, wetland capacity to mitigate nitrogen losses at large river-basin scales remains uncertain. This is largely due to a limited number of studies that address the cumulative and dynamic effects of restored wetlands across the landscape on downstream nutrient conditions. We analyzed wetland restoration impacts on modeled nitrate dynamics across 279 subbasins comprising the ∼0.5 million km2 Upper Mississippi River Basin (UMRB), USA, which covers eight states and houses ∼30 million people. Restoring ∼8,000 km2 of wetlands will reduce mean annual nitrate loads to the UMRB outlet by 12%, a substantial improvement over existing conditions but markedly less than widely cited estimates. Our lower wetland efficacy estimates are partly attributed to improved representation of processes not considered by preceding empirical studies − namely the potential for nitrate to bypass wetlands (i.e., via subsurface tile drainage) and be stored or transformed within the river network itself. Our novel findings reveal that wetlands mitigate surplus nitrogen basin-wide, yet they may not be as universally effective in tiled landscapes and because of river network processing.

Warmer Winters Increase the Biomass of Phytoplankton in a Large Floodplain River

AbstractWinters are changing rapidly across the globe but the implications for aquatic productivity and food webs are not well understood. In addition, the degree to which winter dynamics in aquatic systems respond to large‐scale climate versus ecosystem‐level factors is unclear but important for understanding and managing potential changes. We used a unique winter data set from the Upper Mississippi River System to explore spatial and temporal patterns in phytoplankton biomass (chlorophyll a, CHL) and associated environmental covariates across 25 years and ∼1,500 river km. To assess the role of regional climate versus site‐specific drivers of winter CHL, we evaluated whether there were coherent long‐term CHL dynamics from north to south and across lotic‐lentic areas. We then estimated the degree to which these patterns were associated with climate variability (i.e., the Multivariate El Nino‐Southern Oscillation Index), winter severity (freezing degree days), river discharge, or site‐specific environmental variables (ice depth, snow depth, and nutrient concentrations). We found that winter CHL was typically highest in ice‐free reaches and backwater lakes, occasionally exceeding summer values. We did not find highly synchronous CHL dynamics across the basin, but instead show that temporal trends were independent among river reaches and lotic‐lentic areas of the river. Moreover, after accounting for these spatial dynamics, we found that CHL was most responsive to winter air temperature, being consistently higher in years with warmer winters across the basin. These results indicate that although productivity dynamics are highly dynamic within large river ecosystems, changes in the duration and severity of winter may uniformly increase wintertime productivity.

Evaluating the Life-History Responses of Adult Invasive (Bithynia tentaculata) and Native (Physa gyrina) Snails Exposed to a Cu-Based Pesticide (EarthTec® QZ)

The faucet snail, Bithynia tentaculata, is an invasive snail that facilitates outbreaks of waterfowl disease in the Upper Mississippi River of the United States. In response, there is interest in identifying strategies that mitigate its population and spread. In this study we assessed the effects of a copper (Cu) molluscicide, EarthTec® QZ, at three concentrations (0, 0.1 and 0.6mg/L Cu) on adult B. tentaculata and a coexisting native species, Physa gyrina. We found that in the 0.6mg/L Cu treatment, ~ 68% of B. tentaculata snails remained alive after a 4-day exposure whereas all P. gyrina snails died. In contrast, a majority of both snail species remained alive and active after 4 days in the control and 0.1mg/L Cu treatments. Although B. tentaculata demonstrated higher survivorship, it bioaccumulated more Cu than P. gyrina. Additionally, examination of B. tentaculata individuals revealed that females tended to exhibit higher mortality than males.

Timing and hydrological conditions associated with bigheaded carp movement past navigation dams on the upper Mississippi river

Timing and hydrological conditions associated with bigheaded carp movement past navigation dams on the upper Mississippi river

A Quick Method for Estimating Batch Fecundity in Bigheaded Carp

AbstractFecundity is a necessary metric to assess reproductive potential (e.g., spawning potential ratio and recruitment overfishing) in invasive fishes, yet the direct measurement of fecundity is often difficult, impractical, and time consuming. Therefore, the ability to estimate fecundity from field measurements (i.e., TL, relative weight [Wr], or ovary weight) can be a valuable tool for fisheries managers to estimate reproductive potential. The goal of this study was to relate the batch fecundity of invasive Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis to metrics that can be quickly measured to eliminate the need for direct enumeration. Silver and Bighead carp were collected from the upper Mississippi River (UMR) in the summer of 2016 and 2017. Subsamples of mature (spawning capable) ovaries were preserved, enumerated, and then related to ovary weight, TL, weight, and Wr. An equation for estimating Silver Carp batch fecundity from ovary weight in the UMR, corrected for ovary membrane weight, was developed: {ovary weight – [0.222 × (ovary weight0.7589)]} × 794 (SE = 11). Batch fecundity for Silver Carp from Pools 17–20 of the UMR averaged 1,230,930 ± 68,983 eggs (mean ± SE). Ovary weight was the strongest predictor of fecundity, but TL, weight, and Wr also showed significant relationships with fecundity for Silver Carp. Batch fecundity for Bighead Carp averaged 1,043,953 ± 82,360 eggs, but the number of eggs per gram showed significant spatial variation; therefore, no fecundity equation was developed for this species. Future work should evaluate the frequency of Silver Carp spawns within a season and how batch fecundity varies among multiple spawning events. Fecundity estimates can be used to determine spawning potential ratios, which can help in evaluating management strategies.

Pronounced Increases in Future Soil Erosion and Sediment Deposition as Influenced by Freeze-Thaw Cycles in the Upper Mississippi River Basin.

Soil erosion and sediment deposition are relevant to multiple important ecosystem services essential for natural and human systems. The present study aims to project future soil erosion and sediment deposition in the Upper Mississippi River Basin (UMRB) using climate projections by five Global Circulation Models (GCMs) under the Representative Concentrations Pathway (RCP) 8.5 scenario. To understand the importance of freeze-thaw cycles (FTCs) for soil erosion and sediment deposition estimation with climate change, this study compared two Soil and Water Assessment Tool (SWAT) models with different representations of the FTCs, with the standard SWAT using a simple regression method and SWAT-FT employing a physically based method. Modeling results show that future climate change can pronouncedly intensify soil erosion and increase sediment deposition, and the impacts are sensitive to how FTCs are represented in the model. The standard SWAT projected an increase in soil erosion by nearly 40% by the end of the 21st century, which is much lower than the projected over 65% increase in soil erosion by SWAT-FT. For sediment deposition, the projected percent changes by the standard SWAT and SWAT-FT also deviate from each other (i.e., about 70% by the standard SWAT vs about 120% by SWAT-FT). Overall, these results demonstrate the important roles of FTCs in projecting future soil erosion and sediment deposition and underline the need to consider the effects of conservation practices on FTCs to realistically assess the effectiveness of those measures.

Identifying mineralogical variation in Baraboo pipestone quarry sources and its implications for Mississippian-era exchange in the midcontinent

Pipestones of the midcontinental U.S. have a long history of use by native peoples to craft high status and religious objects, especially pipes, that were often widely exchanged. In this research we describe native use of west central Wisconsin Baraboo Range pipestone as well as identify chemical and mineralogical variation within that formation. The pipestone variants are Baraboo A (dominated by kaolinite, muscovite, and pyrophyllite) and Baraboo B (dominated by pyrophyllite with minor quartz). The recognition of Baraboo pipestone variation allows us to identify previously unsourced pipestone objects. This sourcing project modifies assumptions of Cahokia-centric patterns of earspool manufacture and exchange during the Mississippian period (CE 1000-1400). It demonstrates that Baraboo pipestone Mississippian earspools were quarried, produced, and circulated among a small group of contemporaneous Mississippian societies located in the northern Upper Mississippi River valley — quite outside the Cahokia exchange network. This work establishes that employing rigorous, scientifically sound, and reproducible methodologies to identify the geological source of objects is essential to the interpretation of native interactions.

Floodplain forest structure and the recent decline of Carya illinoinensis (Wangenh.) K. Koch (northern pecan) at its northern latitudinal range margin, Upper Mississippi River System, USA

Floodplain hardwood forests that exist on islands and immediately adjacent to channels along the Upper Mississippi River System (UMRS) are ecologically important due to high floral and faunal biodiversity. The recent decline and regeneration failure of hard mast species—e.g. Quercus spp. and Carya spp.—along the UMRS has been well documented, but causes of these trends have not been widely examined and are thus poorly understood. To investigate the mechanisms of this decline, we installed three 0.20-ha plots within the floodplain forests of the UMRS amongst communities known to contain the northernmost documented individuals of Carya illinoinensis (Wangenh.) K. Koch, a regionally imperiled, yet ecologically, economically, and culturally important hard mast species. Tree density (>5 cm dbh) averaged 355 stems ha−1 (n = 239, 12 representative species across 9 genera) and mean basal area was 77 m2 ha−1 across the three sites. Acer saccharinum L. was the most dominant species (49.0 m2 ha−1). The diameter distribution of trees demonstrated a negative exponential pattern, generally indicative of uneven-aged, regenerating forests. Over the past ca. 120 years, decadal-scale pulses of tree establishment across species show linkages with riparian engineering installments and flood and drought events. C. illinoinensis demonstrated a consistent establishment pattern since at least the 1860s through the 1950s, but experienced regeneration failure over the past ca. 50 years. Widespread ecological growth releases in C. illinoinensis are linked with known large-scale flood events along the UMRS (1965, 1993, 2001, 2011 CE). Correlation analysis revealed relationships between C. illinoinensis growth rings and drought, precipitation, maximum temperature, and river flow to be temporally unstable with an inflection point at the beginning of the lock and dam era (ca. 1930s–1940s). The coincidental decoupling of climate and flow variability with tree growth in the post-lock and dam era suggests that peripheral, disjunct populations of C. illinoinensis are sensitive to impacts from anthropogenic land and hydrologic modifications. Forest structure, disturbance history, and climate analyses demonstrate that without management intervention, C. illinoinensis will no longer have a significant presence within floodplain forests of the UMRS in the near future, contributing to loss in diversity. Direct forest restoration techniques, such as planting and creation of canopy gaps via regeneration-focused harvesting, are needed if C. illinoinensis is to return to historical abundance and distribution.

Effects of Adult Biomass and Environmental Conditions on Bigheaded Carp Reproductive Output

AbstractBighead Carp Hypothalmichthys nobilis and Silver Carp Hypothalmichthys moltrix (hereafter collectively referred to as Bigheaded Carp) have spread throughout the majority of the Mississippi River since the 1970s. The current northern invasion edge of Bigheaded Carp in the Upper Mississippi River (UMR) spans between Pools 14 and 20 because of limited passage at Lock and Dam (LD) 19. Mechanisms limiting adult Bigheaded Carp abundance above LD19 are unknown but may be due in part to lack of reproductive success influenced by adult abundance and environmental factors. Our objective was to investigate how relative adult biomass and river temperature and discharge affect maximum annual Bigheaded Carp larval production in the UMR using a Ricker stock-recruitment model. Adult Bigheaded Carp relative biomass (kg/h) was estimated annually with boat electrofishing and larvae were collected every 10 d between May and August 2014–2017 in Pools 14–20 in the UMR. Adult relative biomass ranged from 0.0 to 880.9 kg/h, whereas maximum annual larval densities ranged from 0.0 to 2,869.4 larvae/m3. After accounting for variability among pools and years, the most supported linear Ricker stock-recruitment model indicated the number of recruits per spawner decreased with increasing adult relative biomass and increased with mean discharge. Our results highlight the importance of adult biomass and river discharge conditions for reproduction of Bigheaded Carp along leading edges of invasion. Management strategies that aim to maintain low adult abundance where reproduction is not yet occurring could help limit population increases via reproduction, whereas reducing high adult biomass (e.g., commercial harvest, barriers) may result in greater Bigheaded Carp reproductive output in the UMR.

Prioritizing native migratory fish passage restoration while limiting the spread of invasive species: A case study in the Upper Mississippi River

Despite increasing efforts globally to remove dams and construct fish passage structures, broad-scale analyses balancing tradeoffs between cost and habitat gains from these mitigations infrequently consider invasive species. We present an optimization-based approach for prioritizing dam mitigations to restore habitat connectivity for native fish species, while limiting invasive species spread. Our methodology is tested with a case study involving 240 dams in the Upper Mississippi River, USA. We integrate six native migratory fish species distribution models, distributions of two invasive fishes, and estimated costs for dam removal and construction of fish passes. Varying budgets and post-mitigation fish passage rates are analyzed for two scenarios: ‘no invasives’ where non-selective mitigations (e.g., dam removal) are used irrespective of potential invasive species habitat gains and ‘invasives’ where a mixture of selective (e.g., lift-and-sort fish passage) and non-selective mitigations are deployed to limit invasive species range expansion. To achieve the same overall habitat connectivity gains, we find that prioritizations accounting for invasive species are 3 to 6 times more costly than those that do not. Habitat gains among native fish species were highly variable based on potential habitat overlap with invasive species and post-mitigation passabilities, ranging from 0.4–58.9% (‘invasives’) and 7.9–95.6% (‘no invasives’) for a $50M USD budget. Despite challenges associated with ongoing nonnative fish invasions, opportunities still exist to restore connectivity for native species as indicated by individual dams being frequently selected in both scenarios across varying passabilities and budgets, however increased restoration costs associated with invasive species control indicates the importance of limiting their further spread within the basin. Given tradeoffs in managing for native vs. invasive species in river systems worldwide, our approach demonstrates strategies for identifying a portfolio of candidate barriers that can be investigated further for their potential to enhance native fish habitat connectivity while concurrently limiting invasive species dispersal.

Exploring how vessel activity influences the soundscape at a navigation lock on the Mississippi River

Vessel sound is now globally recognized as a significant and pervasive pollutant to aquatic life. However, compared to marine environments, there is a paucity of data on sound emitted by vessel activity in freshwater habitats. The Upper Mississippi River (UMR) is home to a diverse array of aquatic life as well as being a key route for barge transportation with 29 locks and dams. In this study, passive acoustic monitoring was conducted at Lock and Dam 19 near Keokuk, Iowa, on the UMR between 20 June – August 28, 2019 to coincide with peak navigation use. There was a significant increase in median sound pressure level (SPL; 50–12,000 Hz) recorded during vessel passages (123 dB re. 1μPa for recreational vessels and 137 dB re. 1μPa for commercial vessels) compared to median background levels (111 dB re. 1μPa). Results provide information on the ambient soundscape at a navigation lock, providing a baseline essential for future studies gauging the effect of anthropogenic sound on aquatic life. Lock 19 has also been identified as a potential site for acoustic deterrent deployment to prevent invasive fish movements. The results of this study can help determine the sound level or frequency deterrents would need to emit, to avoid those currently produced during vessel passage.

Understanding Constraints on Submersed Vegetation Distribution in a Large, Floodplain River: the Role of Water Level Fluctuations, Water Clarity and River Geomorphology

Aquatic vegetation is a key component of large floodplain river ecosystems. In the Upper Mississippi River System (UMRS), there is a long-standing interest in restoring aquatic vegetation in areas where it has declined or disappeared. To better understand what constrains vegetation distribution in large river ecosystems and inform ongoing efforts to restore submersed aquatic vegetation (SAV), we delineated areas in ~1200 river km of the UMRS where the combined effects of water clarity, water level fluctuation, and bathymetry appeared suitable for establishment and persistence of SAV based on a 22-year dataset for total suspended solids (TSS), water surface elevation, and aquatic vegetation distribution. We found a large increase in suitable area downstream from a large natural riverine lake near the northern end of the UMRS (river km 1230) that functions as a sink for suspended material. Downstream from river km 895, there was much less suitable area due to decreased water clarity from tributary input of suspended material, changes in river geomorphology, and increased water level fluctuation. A hypothetical scenario of 75% reduction in TSS resulted in only minor increases in suitable area in the southern portion of the UMRS, indicating limitations by water level fluctuation and/or bathymetry (i.e., limited shallow area). These results improve our understanding of the structure and function of large river systems by illustrating how water clarity, fluctuations in water level, and river geomorphology interact to create complex spatial patterns in habitat suitability for aquatic species and may help to identify locations most and least likely to benefit from management and restoration efforts.

Timing, provenance, and implications of two MIS 3 advances of the Laurentide Ice Sheet into the Upper Mississippi River Basin, USA

Evidence for a glacial advance into the Upper Mississippi River Basin between Marine Isotope Stage (MIS) 2 and MIS 6 has been debated for over a century. New sedimentological and chronological data provide evidence for two advances of the Laurentide Ice Sheet (LIS) into Iowa during MIS 3 to the east and west of the local glacial maximum margin. The lithology of the MIS 3 till is similar to the MIS 2 Des Moines Lobe till, which suggests both tills were sourced from the Keewatin Dome. A synthesis of new and previously collected radiocarbon ages indicate the two advances reached their terminus near 42⁰ N around 42 ka and 30 ka. A comparison of this record with published loess chronology and provenance studies suggests that these advances were likely a glacial source for the Mississippi Valley Roxana Silt and the Pisgah Formation loess in the Missouri River Valley. The apparent discrepancy between the basal ages of the Roxana and Pisgah loesses may be due to the timing of Des Moines Lobe entering the Mississippi River watershed before the Missouri River watershed. The results of this study demonstrate that the LIS advanced much farther south during MIS 3 than previously recognized, which has significant implications for ice sheet and paleoclimate modeling.