The pattern of flow or hydrological connection between a river's main channel and its floodplain can vary seasonally and spatially in frequency, duration, direction, and magnitude. Such variation is expected to promote habitat and biotic diversity. We examined this proposition in relation to zooplankton assemblage structure and environmental parameters in the Lower Mississippi River System (LMRS). Over an 18-month period, we sampled channel and off-channel floodplain lake habitats representing four categories of mean annual connection duration to the main channel (MC), or "potamal states," ranging from frequently to infrequently connected. We compared zooplankton assemblages in terms of density, richness, dominance, and turnover, and identified habitat conditions associated with variation across potamal states. Principal findings were as follows: (1) we identified 70 distinct zooplankton taxa, most not previously recorded in the LMRS; (2) assemblage structure aligned strongly with habitat conditions influenced by the MC; (3) the most pronounced differences among potamal states occurred between channel habitats and floodplain lakes collectively; (4) mean zooplankton density and richness were lowest in channel habitats, regardless of season or river stage, and highest in the least frequently connected lakes; (5) indicator taxa distinguished assemblages among potamal states; and (6) densities of large crustaceans were markedly lower than those recorded in the only previous study of LMRS zooplankton assemblages, conducted 35 years earlier. Our results highlight the critical role of variable hydrological connection in shaping habitat conditions and promoting biological diversity in large river-floodplain ecosystems.

An aquatic analysis of constructing borrow areas adjacent to the main line levees in the Lower Mississippi River was conducted as part of an Environmental Impact Statement for upgrading the levee system. A Habitat Suitability Index (HSI) regression model based on field collections was developed to predict fish species richness as a function of the morphometry and water quality of borrow areas. The HSI score was multiplied by acres of borrow areas created during construction to obtain habitat units (HUs) for each alternative indicating a substantial gain of fishery habitat in the floodplain. Environmental features identified by the model to increase fish species richness and overall habitat heterogeneity include the shape of the pit (e.g., bowl-shaped with deep water rather than long rectangular with shallower water), the availability of littoral areas for fish spawning and rearing, using best management practices such as tree screens and bank stabilization to lower turbidity, adding islands, and creating sinuous shorelines. The project results in an overall gain in aquatic habitat by creating permanent or semi-permanent water bodies on the floodplain that our research indicates may be occupied by at least 75 species of fish contributing to the overall biodiversity of the lower Mississippi River.

The effects of agriculture and flood control practices accrued over more than a century have impaired aquatic habitats and their fish communities in the Mississippi Alluvial Valley, the historic floodplain of the Lower Mississippi River prior to leveeing. As a first step to conservation planning and adaptive management, we developed and tested a conceptual model of how changes to this floodplain have affected stream environments and fish assemblages. The model is deliberately simple in structure because it needs to be understood by stakeholders ranging from engineers to farmers who must remain engaged to ensure effective conservation. Testing involved multivariate correlative analyses that included descriptors of land setting, water quality, and fish assemblages representing 376 stream samples taken over two decades and ranging in Strahler stream order from 1 to 8. The conceptual model was adequately corroborated by empirical data, but with unexplained variability that is not uncommon in field surveys where gear biases, temporal biases, and scale biases prevent accurate characterizations. Our conceptual model distinguishes three types of conservation actions relevant to large agricultural floodplains: reforestation of large parcels and riparian zone conservation, in-channel interventions and connectivity preservation, and flow augmentation. Complete restoration of the floodplain may not be an acceptable option to the agriculture community. However, in most cases the application of even the most basic measures can support the return of sensitive aquatic species. We suggest that together these types of conservation actions can bring improved water properties to impacted reaches, higher reach biodiversity, more intolerant species, and more rheophilic fishes.

Like pine trees bending in a strong wind or a river meandering over the landscape, the most energy-efficient way to deal with physical opposition may be to shift in shape or position. It is by this manner of response to physical stress, seeking the path of least resistance while still advancing, that flowing water exemplifies the concept of ecological resilience. Here, we discuss the Lower Mississippi River ecosystem (LMRS) with respect to relationships of its hydrology and floodplain to ecological resilience and ecosystem services. Following an introduction to basic features, we look backwards to when the river could still meander freely and flood expansively. Next, we discuss some impacts of 20th century engineering on contemporary system properties. We argue that despite extensive alterations, the LMRS remains resilient in provision of a multitude of valuable services. This is possible largely because the system retains a dynamic hydrograph with a more-or-less predictable pattern of strong connection to a relatively substantial floodplain mosaic of diverse natural habitats. Still, in the face of various, intense stressors, including continuing adjustments to engineered channel cut-offs, steady infilling of floodplain habitats, impacts of climate change and invasive species, there is much to learn and do to manage the system to sustain desired ends. We conclude by discussing restoration options to enhance and protect resilient services in the context of sometimes conflicting social interests.

The Bonnet Carre’ Spillway diverts water from the Mississippi River through a floodway into Lake Pontchartrain to reduce river stages at New Orleans and prevent flood damages. Pallid Sturgeon, a federally listed species under the Endangered Species Act, and Shovelnose Sturgeon, listed under the Similarity of Appearance rule, are entrained through the Spillway structure and become trapped in the Spillway canals and other waterbodies. Five openings and corresponding rescue operations occurred between 2008 and 2019 after each Spillway closure. Operational parameters spanned a range of water temperatures and seasons with magnitude and duration of discharge varying across all openings. A total of 70 days with crew number ranging from 6 to 12 were expended to rescue 57 Pallid Sturgeon and 362 Shovelnose Sturgeon after the five openings that spanned 240 total days. More sturgeon were entrained at higher water temperatures, with greater numbers of bays opened, and for longer periods of time. Recovery of sturgeon is initially high but over time declines as sturgeon are depleted from the floodway, stranded in isolated waterbodies in the floodway, and/or displaced further downstream into Lake Pontchartrain during longer openings. Sturgeon that cannot find their way back to the floodway are unlikely to be rescued. Recent population studies indicate that less than 1% of the total population size in the Lower Mississippi River are entrained. However, this does not take into account those individuals entrained but not captured and the potential impacts of more frequent openings of the structure. Conservation recommendations are provided to increase catch efficiency and recovery of the endangered sturgeon.

In large rivers, secondary channels occur where the main channel is divided by an instream island, forming one or multiple smaller channels outside the main channel. Secondary channels are highly variable in morphometry, flow characteristics, and degree of connectivity to the main channel. Engineered closing structures at the upstream end of most secondary channels restrict inflow from the main channel, resulting in gradients of flow connectivity among secondary channels that vary with river stage. We investigated the relationship of flow connectivity to benthic macroinvertebrate assemblage richness and structure among a series of secondary channels of the Lower Mississippi River. Samples were collected over 2 years at times of high and low river stages. We discovered (1) macroinvertebrate assemblage structure and taxonomic richness varied along the flow connectivity gradient, and (2) there was a legacy effect of prior connection on assemblage structure that lasted up to a year. We contend that for management and restoration planning aimed at conservation of large river biological diversity, an important consideration are the life history requirements of animals utilizing secondary channel habitats.

Mortality of fish early life stages was measured in a pressure vessel to simulate vertical displacement within the water column. Mortality was measured for three pressure regimes for four fish species: larval bigmouth buffalo Ictiobus cyprinellus, larval blue catfish Ictalurus furcatus, juvenile bluegill Lepomis macrochirus, and juvenile largemouth bass Micropterus salmoides. The maximum pressure-change tested, 344.8 kPa, equivalent to a 35.2 m displacement of fish within the water column, did not cause significant mortality of larvae or juveniles. Since 32.5 m exceeds depths in most inland navigation channels and possibly the depth to which rapid propeller induced water mixing occurs, the range of pressure changes that could be experienced by early life stages during towboat mixing of the water column will not result in significant mortality.

Hypophthalmichthys molitrix (Silver Carp) are invasive and abundant in the Mississippi River system, where they consume phytoplankton. There is concern that Silver Carp may influence phytoplankton community structure with cascading effects on other trophic levels. Information is needed regarding Silver Carp phytoplankton-consumption rates and prey selection to assess their potential impact on the food-web in the river. We investigated Silver Carp diets in a backwater lake of the Lower Mississippi River in order to quantify phytoplankton prey selectivity. We made measurements on 4 dates over a 2-y period, which spanned a range of hydrologic connectivity between the lake and the river and a variety of fish sizes. We quantified selection by comparing phytoplankton community composition in the lake to prey in foreguts of captured Silver Carp using Vanderploeg and Scavia's (1979) relativized selection index. With a possible exception of diatoms on 1 date, there was no relationship of sample date or fish size on prey selection. However, there was a consistent pattern in prey selection: euglenoid algae were positively selected, selection of colonial algae and diatoms was variable, and flagellates and filamentous cyanobacteria were negatively selected. Results are discussed in the context of a conceptual model for Silver Carp phytoplanktivory that incorporates the roles of habitat selection, prey availability, prey capture and processing, and digestive physiology.

Fish communities of southern forested wetlands were first characterized by William Bartram in 1791. The Mississippi Basin, the Appalachians, and near-shore waters of the continental shelf are important conduits of fish dispersal and adaptive radiation, so the fish fauna of the Southeast is extremely rich. Fish species richness is high in bottomland hardwood systems and some mangrove forests. Fish communities in wetlands exhibit log-normal patterns of species abundance. Two or three species are numerically dominant, several species are extremely rare, and the majority of species are intermediate in abundance. Most wetland fish are moderately tolerant of degraded water quality. Collectively, wetland fish spawn throughout most of the year, principally during spring and summer. Most wetland fish are littoral spawners, and lateral movement of the "aquatic-terrestrial transition zone" during flooding provides expanded habitat for reproduction.

Abundance estimates are essential for assessing the viability of populations and the risks posed by alternative management actions. An effort to estimate abundance via a repeated mark‐recapture experiment may fail to recapture marked individuals. We devised a method for obtaining lower bounds on abundance in the absence of recaptures for both panmictic and spatially structured populations. The method assumes few enough recaptures were expected to be missed by random chance. The upper Bayesian credible limit on expected recaptures allows probabilistic statements about the minimum number of individuals present in the population. We applied this method to data from a 12‐year survey of pallid sturgeon ( Scaphirhynchus albus ) in the lower and middle Mississippi River (U.S.A.). None of the 241 individuals marked was recaptured in the survey. After accounting for survival and movement, our model‐averaged estimate of the total abundance of pallid sturgeon ≥3 years old in the study area had a 1%, 5%, or 25% chance of being <4,600, 7,000, or 15,000, respectively. When we assumed fish were distributed in proportion to survey catch per unit effort, the farthest downstream reach in the survey hosted at least 4.5–15 fish per river kilometer (rkm), whereas the remainder of the reaches in the lower and middle Mississippi River hosted at least 2.6–8.5 fish/rkm for all model variations examined. The lower Mississippi River had an average density of pallid sturgeon ≥3 years old of at least 3.0–9.8 fish/rkm. The choice of Bayesian prior was the largest source of uncertainty we considered but did not alter the order of magnitude of lower bounds. Nil‐recapture estimates of abundance are highly uncertain and require careful communication but can deliver insights from experiments that might otherwise be considered a failure.

Pursuant to Section 729 of the Water Resources Development Act of 1986 (as amended), a watershed study was conducted on the Duck River watershed located in the Interior Plateau, Tennessee. The objectives of the watershed study were to establish current (baseline) conditions and identify water resource problems, needs and opportunities. A knowledge base was developed by compiling biological and geomorphological data across HUC12 watersheds from existing fish databases. Additional stream data were collected from low altitude, high resolution video resulting in a final subset of eleven of 18 stream geospatial test variables compiled on 213 stream segments and subjected to statistical analysis. An ecological model, stream condition index (SCI), was formulated based on the degree of statistical correlation (dependency) between the variables. Stream segments were averaged within 63 HUC12 watersheds in the Duck Watershed. Based on the results of the model, the final HUC12 watersheds were scored followed by normalization on a scale from 0 to 1.0. Thirty-eight watersheds were considered major to severely disturbed, 18 watersheds were minimally disturbed, and seven watersheds were minor disturbed. In addition to the analysis of geospatial data, fish Index of Biotic Integrity (IBI) scores were evaluated based on twelve metrics which addressed species richness and composition, trophic structure, fish abundance, and fish condition. Scores for the twelve metrics were summed to produce the IBI value for the site. By comparing the SCI to IBI scores, aquatic biota impairment was predominantly due to loss of streamside canopy, reduction of in-stream cover, and impacts to channel stability, all of which were considered to be limiting factors in regards to sustaining a healthy aquatic ecosystem in the Duck River watershed. The findings of this study can be utilized to prioritize watersheds for restoration, enhancement and conservation, plan and conduct site-specific, intensive ecosystem studies, and assess ecosystem outcomes (i.e., ecological lift) applicable to future with and without restoration actions including alternative, feasibility, and cost/benefit analyses and adaptive management.

The St. John's Bayou water control structure near New Madrid, MO, connects the main Mississippi River to two large backwater areas called the New Madrid Floodway and St. John's Bayou. While this area has been altered, the New Madrid Floodway and St. John's Bayou account for the only substantial portion of the historic Mississippi River floodplain that remains and provides the only critical connection between backwater/floodplain habitat and the river. Fish passage was evaluated during April-December 2010 using ultrasonic telemetry. Stationary receivers were placed strategically at five locations above and below the structure in St. John's Bayou, in the floodway and the outlet to the Mississippi River. A total of 100 individuals representing 14 species were tagged. Total number of detections during an 8-month period was 1264717. Fifteen individuals representing five species moved into the Mississippi and Ohio rivers; seven individuals returned to St. John's Bayou. Thirteen of the 14 species moved upstream through the structure. Of the 85 individuals that stayed in the bayou, 29 fish passed through the structure for a total of 92 passage events. The downstream:upstream passage was roughly 50:50. Passage was correlated with river rise, with frequency of passage being higher in spring, but passage occurred each month during the study. Copyright (c) 2015 John Wiley & Sons, Ltd.

In the central United States, recovery efforts for populations of the federally endangered Pallid Sturgeon Scaphirhynchus albus have been ongoing since its listing in 1990. Its congener, the Shovelnose Sturgeon S. platorynchus, has also recently been listed as threatened where it overlaps with Pallid Sturgeon. The status of both species in the Mississippi River is unknown and so are habitat enhancement priorities that would benefit their recovery. Using field data collected from 2002 through 2005, we (1) estimated the adult population size of both species using mark-recapture methods and (2) quantified habitat use of these sturgeons with multiple gears to elucidate habitat enhancement priorities in the middle Mississippi River-an important fluvial corridor that connects the upper Mississippi River and Missouri River basins with the lower Mississippi River basin. Population size was estimated to be 1,516 (95% CI = 710-3,463) Pallid Sturgeon (five individuals per river kilometer [rkm]) and 82,336 (95% CI = 59,438-114,585) Shovelnose Sturgeon (266 individuals/rkm). Our population estimate showed a low relative abundance of Pallid Sturgeon in this corridor. However, the population estimate suggests Pallid Sturgeon abundance has increased since its listing in 1990. Shovelnose Sturgeon were more abundant than Pallid Sturgeon, but whether the Shovelnose Sturgeon population is increasing, decreasing, or stable remains unknown. Among 10 habitat types, both species were most frequent at the downstream ends of alluvial islands. Pallid and Shovelnose sturgeons were restricted to flow rates < 1.0 m/s, and their abundance was greatest in depths ranging from 4.5 to 14 m. We suggest alluvial island enhancement may facilitate sturgeon recovery in the middle Mississippi River.

Ecosystem restoration of the Mississippi River main stem has been ongoing since the early 1970s. After the passage of environmental laws in the late 1960s to the early 1970s, private citizens and state and federal natural resource agency managers began to seek programs and funding for restoration and conservation that eventually resulted in mitigation measures of adverse impacts. Environmental-type actions that include the Great River Environmental Action Team, the Avoid and Minimize program, the middle Mississippi River biological opinion, and the lower Mississippi River conservation plan and biological opinion originated from laws or legal action. The Upper Mississippi River Restoration, Navigation and Ecosystem Sustainability Program, Restoring America's Greatest River, and Operation and Maintenance activities, which support system ecological restoration measures, are, to a large extent, done in a cooperative setting to improve the river for multiple benefits. This coalition of agencies and professions has resulted in the application of hundreds of different types of measures to restore form and function to the third largest river in the world. Over the years, dredging and disposal practices have improved in an effort to minimize the impacts from these activities. Lost floodplain islands have been replaced, backwater lakes and channel depths have been recovered, active river flow has been reintroduced to backwaters, and microhabitats for special concern species have been restored, all to recreate broad functional floodplain habitat. Wing-dike and side-channel closure structures have been shortened, notched, or removed to recover flow along the main-channel border and side channels, increasing hydraulic residence time and recovering valuable habitat along with restoring nutrient and sediment assimilation processes the floodplain provides. Field monitoring has shown positive responses from endangered and threatened species, migratory and resident aquatic and wildlife species, abiotic conditions like water quality, and increased use by humans enjoying the benefit of a restored river system. Collectively, this work is some of the most extensive large river restoration in the world, but it only represents a small contribution to what is necessary to maintain a diverse and resilient Mississippi River. The information provided in this chapter provides a basis for continuing restoration efforts that should become a routine part of Mississippi River management.

: The Chicago Ship and Sanitary Canal (CSSC) is a navigable channel that connects Lake Michigan to the Mississippi River Basin. Electric barrier systems have been constructed to create waterborne electric fields within the CSSC to prevent Asian carp from swimming from the Mississippi River basin through the canal into the Great Lakes. A laboratory study was conducted to determine which characteristics of the waterborne electric fields of pulsed direct current (pulsed DC) are effective at immobilizing (preventing passage of) small Asian carp that enter the electrified zone. This experiment was the first step in a comprehensive study to determine optimum operating parameters for electric barrier systems in operation to prevent dispersal of aquatic nuisance species -- including Asian carp -- through the CSSC and other aquatic systems.

Suckermouth catfi shes, native to Central and South America, have been established in US and Mexican waters since the 1950s (Fuller et al. 1999, Hill 2002) and have become problematic since the late 1990s (Hoover et al. 2004, Mendoza-Alfaro et al. 2009). Nuisance populations of these fi shes in three states (Hawaii, Texas, and Florida) have been implicated in a broad range of ecological problems, including erosion of streambanks and imperilment of threatened species, but documented accounts of their impacts are often equivocal and sometimes contradictory. This bulletin presents a conceptual model based on reports by the press and fi ndings by researchers working throughout the non-native range of these animals. The model is intended as a tool for identifying potential impacts of introduced suckermouth catfi shes on local fauna.