Large North American Rivers Research Articles

Low buffering capacity and slow recovery of anthropogenic phosphorus pollution in watersheds

Excess anthropogenic phosphorus in watersheds, transported with runoff, can result in aquatic eutrophication, a serious global water quality concern. Watersheds can retain phosphorus, especially in their soils, which can serve as a buffer against the effect of excessive use of phosphorus. However, whether there is a quantifiable threshold at which a watershed exceeds its optimal phosphorus buffering capacity (beyond which riverine loads would dramatically increase) remains unknown. Here we quantified a watershed phosphorus buffering capacity threshold based on accumulation data over 110 years in 23 watersheds of a large North American river basin with globally representative agricultural soils. We found a surprisingly low threshold of just 2.1 t P km−2 (0.03–8.7 t P km−2). Beyond this, further P inputs to watersheds cause a significant acceleration of P loss in runoff. Using a simple exponential decay model, the time estimated to eliminate legacy P via runoff in our watersheds ranges from ~ 100 to over 2,000 years. The rapidity with which the watershed buffering threshold can be surpassed during accumulation, particularly given current anthropogenic phosphorus input rates, versus the long return to baseline suggests that new strategies to reconcile watershed activities and water quality are urgently needed. Watersheds have a low buffering capacity for phosphorus inputs, and their recovery from phosphorus pollution can take over 2,000 years, according to an analysis of phosphorus data from a large North American river.

Stream fish colonization but not persistence varies regionally across a large North American river basin

Many species have distributions that span distinctly different physiographic regions, and effective conservation of such taxa will require a full accounting of all factors that potentially influence populations. Ecologists recognize effects of physiographic differences in topography, geology and climate on local habitat configurations, and thus the relevance of landscape heterogeneity to species distributions and abundances. However, research is lacking that examines how physiography affects the processes underlying metapopulation dynamics. We used data describing occupancy dynamics of stream fishes to evaluate evidence that physiography influences rates at which individual taxa persist in or colonize stream reaches under different flow conditions. Using periodic survey data from a stream fish assemblage in a large river basin that encompasses multiple physiographic regions, we fit multi-species dynamic occupancy models. Our modeling results suggested that stream fish colonization but not persistence was strongly governed by physiography, with estimated colonization rates considerably higher in Coastal Plain streams than in Piedmont and Blue Ridge systems. Like colonization, persistence was positively related to an index of stream flow magnitude, but the relationship between flow and persistence did not depend on physiography. Understanding the relative importance of colonization and persistence, and how one or both processes may change across the landscape, is critical information for the conservation of broadly distributed taxa, and conservation strategies explicitly accounting for spatial variation in these processes are likely to be more successful for such taxa.

Factors Affecting Nesting Ecology ofApalone spiniferain a Northwestern Great Plains River of the United States

Abstract The nesting ecology of Apalone spinifera in large North American rivers is largely unknown despite the wide distribution of the species in these naturally dynamic ecosystems. We describe the nesting locations, timing, behavior, and habitat of A. spinifera in relation to natural and anthropogenic factors in the Missouri River. Nesting followed annual peak river stage, mostly occurred in the afternoon when air temperatures were 25°–30°C, and did not occur when human activity was nearby. Apalone spinifera nested in June in a year with average discharge (2012), but nested 20 d later in a year with a large flood event (2011). During the average discharge year, 90% of nests were found on islands, but similar proportions of nests were found on island and mainland habitats during the flood year because many islands were inundated. Nests were mostly in mixed-gravel substrates where vegetation cover was sparse or absent. Depredation occurred only after the emergence of hatchlings (∼ 60 d after nesting) and...

Long-term assessment of ichthyoplankton in a large North American river system reveals changes in fish community dynamics

Larval fishes are sensitive to abiotic conditions and provide a direct measure of spawning success. The St. Clair – Detroit River System, a Laurentian Great Lakes connecting channel with a history of environmental degradation, has undergone improvements in habitat and water quality since the 1970s. We compared 2006–2015 ichthyoplankton community data with those collected prior to remediation efforts (1977–1978) to identify patterns in spatial and temporal variability. Both assemblages exhibited a predictable phenology, with taxa from the subfamily Coregoninae dominant in early spring followed by families Osmeridae, Percidae, and Moronidae (May–June) and Cyprinidae and Clupeidae (June–August). While higher densities of larval fish were found in the Detroit River, greater taxa richness and Shannon diversity were observed in the St. Clair River. System wide, 14 new taxa were observed in the 2000s study period. In addition, relative densities of two nonnative species, alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax), declined since the 1970s. Increased larval fish richness and decreased densities of nonnative taxa in the 2000s are consistent with improvements to environmental conditions.

Spatial variability of CO2 concentrations and biogeochemistry in the Lower Columbia River

Carbon dioxide (CO2) emissions from rivers and other inland waters are thought to be a major component of regional and global carbon cycling. In large managed rivers such as the Columbia River, contemporary ecosystem changes such as damming, nutrient enrichment, and increased water residence times may lead to reduced CO2 concentrations (and emissions) due to increased primary production, as has been shown in another large North American river (Upper Mississippi). In this work, spatial patterns of water quality, including dissolved CO2 concentrations, were assessed in the Lower Columbia River (LCR) and major tributaries using underway measurements from a small research vessel during July 2016. We observed near-equilibrium CO2 conditions and overall weak supersaturation of CO2 in the main channel (average 133.8% saturation) and tributaries. We observed only weak correlations between CO2 saturation, chlorophyll a fluorescence, and turbidity, thus not strongly supporting our hypothesis of primary productivity controls. In general, the LCR was clear (low turbidity, mean = 1.48 FNU) and had low chlorophyll fluorescence (mean = 0.177 RFU) during the sampling period. As a whole, the LCR was homogeneous with respect to biogeochemical conditions and showed low spatial variability at >100 km scales. Overall, we find that the LCR is likely a weak summertime source of CO2 to the atmosphere, in line with findings from other altered rivers such as the Upper Mississippi.

Bigheaded carps (Hypophthalmichthys spp.) at the edge of their invaded range: using hydroacoustics to assess population parameters and the efficacy of harvest as a control strategy in a large North American river

The threat posed by bigheaded carps (Hypophthalmichthys spp.) to novel ecosystems has focused efforts on preventing further range expansion; upstream progression in the Illinois River is a major concern due to its connection with the uninvaded Great Lakes. In addition to an electric barrier system, commercial harvest of silver carp (H. molitrix) and bighead carp (H. nobilis) in the upper river is intended to reduce propagule pressure and prevent range expansion. To quantify demographics and evaluate harvest efficacy, the upper river was sampled between 2012 and 2015 using mobile hydroacoustic methods. Reach-specific densities, size structures and species compositions varied interannually but the advancing population was characterized longitudinally as small-bodied, silver carp-dominated at the highest densities downstream, shifting to large-bodied, bighead carp-dominated at the low-density population front. The use of hydroacoustic sampling for harvest evaluation was validated in backwater lakes; there was a significant positive correlation between density estimates and the corresponding harvest catch-per-unit-effort of bigheaded carps. Localized densities of bigheaded carps were reduced by up to 64.4 % immediately post-harvest but generally rebounded within weeks. However, annual sampling of the entire upper river indicated that density of bigheaded carps decreased by over 40 % (between 2012 and 2013) and subsequently remained stable (between 2013 and 2014). The annual harvest of bigheaded carps increased during this period (from 45,192 to 102,453 individuals), in years of contrasting discharge conditions. At this spatiotemporal scale, harvest appears to have contributed to initial reduction, and subsequent maintenance of, bigheaded carps density levels, but discharge likely plays an important role (e.g., through immigration) in determining the extent of its impact. Mobile hydroacoustic sampling enabled robust quantification of the population over varying spatial scales and density gradients, highlighting the potential of this approach as an assessment tool for invasive fishes in riverine environments.

Reconnecting Fragmented Sturgeon Populations in North American Rivers

The majority of large North American rivers are fragmented by dams that interrupt migrations of wide‐ranging fishes like sturgeons. Reconnecting habitat is viewed as an important means of protecting sturgeon species in U.S. rivers because these species have lost between 5% and 60% of their historical ranges. Unfortunately, facilities designed to pass other fishes have rarely worked well for sturgeons. The most successful passage facilities were sized appropriately for sturgeons and accommodated bottom‐oriented species. For upstream passage, facilities with large entrances, full‐depth guidance systems, large lifts, or wide fishways without obstructions or tight turns worked well. However, facilitating upstream migration is only half the battle. Broader recovery for linked sturgeon populations requires safe “round‐trip” passage involving multiple dams. The most successful downstream passage facilities included nature‐like fishways, large canal bypasses, and bottom‐draw sluice gates. We outline an adaptive approach to implementing passage that begins with temporary programs and structures and monitors success both at the scale of individual fish at individual dams and the scale of metapopulations in a river basin. The challenge will be to learn from past efforts and reconnect North American sturgeon populations in a way that promotes range expansion and facilitates population recovery.

Controls on dissolved organic carbon quantity and chemical character in temperate rivers of North America

Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershed‐scale controls on bulk DOC flux and concentration among small basins but fewer studies have explored controls among large basins or simultaneously considered the chemical composition of DOC. Because the chemical character of DOC drives riverine biogeochemical processes such as metabolism and photodegradation, accounting for chemical character in watershed‐scale studies will improve the way bulk DOC variability in rivers is interpreted. We analyzed DOC quantity and chemical character near the mouths of 17 large North American rivers, primarily between 2008 and 2010, and identified watershed characteristics that controlled variability. We quantified DOC chemical character using both specific ultraviolet absorbance at 254 nm (SUVA254) and XAD‐resin fractionation. Mean DOC concentration ranged from 2.1 to 47 mg C L−1 and mean SUVA254 ranged from 1.3 to 4.7 L mg C−1 m−1. We found a significant positive correlation between basin wetland cover and both bulk DOC concentration (R2 = 0.78; p < 0.0001) and SUVA254 (R2 = 0.91; p < 0.0001), while other land use characteristics were not correlated. The strong wetland relationship with bulk DOC concentration is similar to that found by others in small headwater catchments. However, two watersheds with extremely long surface water residence times, the Colorado and St. Lawrence, diverged from this wetland relationship. These results suggest that the role of riverine processes in altering the terrestrial DOC signal at the annual scale was minimal except in river systems with long surface water residence times. However, synoptic DOC sampling of both quantity and character throughout river networks will be needed to more rigorously test this finding. The inclusion of DOC chemical character will be vital to achieving a more complete understanding of bulk DOC dynamics in large river systems.

Factors Influencing Radio Wave Transmission and Reception: Use of Radiotelemetry in Large River Systems

AbstractMany technical and environmental variables affect radio wave transmission and reception in aquatic environments. We used a controlled experimental design in three large North American rivers (Illinois and Mississippi rivers, Illinois, and Skeena River, British Columbia) to examine the effects of water conductivity, transmitter depth, electromagnetic noise, antenna height, and transmitter type on detection distance. Detection distance was significantly affected by water conductivity, transmitter depth, and electromagnetic noise from a boat motor. Detection distance and maximum depth of signal reception increased with decreasing conductivity except at conductivities from 60 to 90 μS/cm (Skeena River). In contrast to terrestrial radiotelemetry, antenna height did not significantly affect detection distance. We also determined that a transmitter with a 3.5‐V battery had an approximately 2.5 times greater detection distance than a transmitter with a 1.5‐V battery. We provide quantitative results for several variables influencing radio wave transmission and reception, and we present two regression equations that can be used by researchers to obtain estimated detection distances in rivers of similar conductivity and depth. Furthermore, we compared our detection distances with those calculated from theoretical equations and found that our field results yielded higher detection distances. We strongly believe that there are gaps between results reported in technical papers and those obtained in field method studies; we argue for more collaborative research between aquatic telemetry users and engineers to reduce the current need for trial and error in telemetry study design.

An observation‐based formulation of snow cover fraction and its evaluation over large North American river basins

Snow cover strongly interacts with climate through snow albedo feedbacks. However, global climate models still are not adequate in representing snow cover fraction (SCF), i.e., the fraction of a model grid cell covered by snow. Through an analysis of the advanced very high resolution radiometer (AVHRR) derived SCF and the Canadian Meteorological Centre (CMC) gridded snow depth and snow water equivalent (SWE), we found that the SCF–snow depth relationship varies with seasons, which may be approximated by variations in snow density. We then added snow density to an existing SCF formulation to reflect the variations in the SCF–snow depth relationship with seasons. The reconstructed SCF with the gridded snow depth and SWE by employing this snow density–dependent SCF formulation agrees better with the AVHRR‐derived SCF than other formulations. The default SCF formulation in the National Center for Atmospheric Research community land model (CLM), driven by observed near‐surface meteorological forcings, simulates a smaller SCF and a shallower snow depth than observations. Implementation of the new SCF formulation into the NCAR CLM greatly improves the simulations of SCF, snow depth, and SWE in most North American (NA) river basins. The new SCF formulation increases SCF by 20–40%, decreases net solar radiation by up to 20 W m−2, and decreases surface temperature by up to 4 K in most midlatitude regions in winter and at high latitudes in spring. The new scheme reproduces the observed SCF, snow depth, and SWE in terms of interannual variability and interbasin variability in most NA river basins except for the mountainous Columbia and Colorado River basins. It produces SCF trends similar to that of AVHRR. However, it produces greater decreasing trends in ablation seasons and smaller increasing trends in accumulation seasons than those of the CMC snow depth and SWE.

Adaptive management of environmental flows: lessons for the Murray-Darling Basin from three large North American Rivers

Throughout the Murray-Darling Basin it is recognised that rivers are being degraded by changes to flow caused by development of water resources. Proposals to reverse this degradation include the provision of environmental flows, that is, water specifically managed to meet environmental needs. So far, implementation of environmental flows has proved difficult because of competition for water and uncertainties in environmental water requirements. Economic losses from allocating water to the environment are easy to quantify but the benefits can only be vaguely specified, which makes changes difficult to justify.A possible way forward is to use an adaptive management approach to the implementation of environmental flows. The promise of adaptive management is that it facilitates public policy in the face of uncertainty through a structured dialogue between scientists and managers and allows meaningful participation of stakeholders. Adaptive management has been used to address natural resources management issues in large river systems in the United States and three case studies are considered here: the Columbia, Colorado and Mississippi River projects. The case studies show that adaptive management can promote rapid learning and address complex environmental management issues but the process can be also be derailed. Barriers to adaptive management include: jurisdictional and institutional complexity, lack of credible science, and difficulties with developing system models. Adaptive management is more likely to be successful where there are few, well defined points of intervention, early successes for experimental management, shared goals and strong political support. Where experimental policies are seen as too risky or costly, the promise of adaptive management has not been realised. There is the potential to use adaptive management to address implementation of environmental flows in the Murray-Darling Basin but it will be necessary to select a project wisely.

Patterns in abundance of fishes in main channels of the upper Mississippi River system

Abundance of fishes of the main channels of the upper Mississippi River system and of other large North American rivers is largely unknown because historic sampling methods have been inadequate. We used a bottom trawl to estimate spatial and temporal patterns in abundance in the navigation channels of Pool 26 of the Mississippi River and the lower Illinois River. Total biomass density averaged 21 and 29 kg·ha–1in the navigation channels of Pool 26 and the lower Illinois River, respectively. We identified spatial and temporal patterns in catches of key species using a generalized linear model based on the negative binomial distribution. Some species, including shovelnose sturgeon (Scaphirhynchus platorynchus), are persistent residents of the main channel. Multiple-season residents, including freshwater drum (Aplodinotus grunniens), rely heavily on the main channel during most of the year but leave it briefly, for example to seek thermal refugia in backwaters during winters. We suggest revision of the prevailing notion that main channels of large temperate rivers serve mainly as corridors for movement among other habitat types.

Assemblage Organization of Stream Fishes: The Effect of Rivers on Adventitious Streams

Assemblage Organization of Stream Fishes: The Effect of Rivers on Adventitious Streams