Main Channel Sites Research Articles

Runoff simulation modeling method integrating spatial element dynamics and neural network for remote sensing precipitation data

Effective management of water resources amidst global climate change necessitates advancements in runoff simulation techniques. This study introduces a novel methodology that integrates a spatial element dynamic model with a neural network designed for satellite precipitation product (SPP) and remote sensing data to address the complex dynamics of precipitation-runoff processes. Implemented in the Songhua River basin of China, the methodology features a runoff estimation module that operates across both high-resolution and SPP grid scales. This module synergizes spatial attributes with fuzzy classification for refined confluence optimization, and yielding simulations through long short-term memory network. The results indicate that the proposed multi-scale production-confluence scheme achieved Nash-Sutcliffe efficiency (NSE) scores of 0.87 and 0.84 during calibration (2011–2015) and validation (2017 and 2018) periods, respectively, representing an 8.15% improvement in peak percentage error (PPE10%) over conventional hydrologic models. Additionally, the scheme demonstrated superior simulation performance at tributary sites set compared to main channel sites set, with differences of 0.08 and 0.07 in NSE and Kling-Gupta efficiency (KGE), respectively. The introduction of the surface Ⅱ operator for adjusting precipitation intensity effectively improved runoff estimation accuracy, reducing the average error by 25.48% across both site sets. This study provides a scientific foundation for applying SPP in hydrological modeling and offers decision support for managing water resources.

Post-wildfire contamination of soils and sediments by polycyclic aromatic hydrocarbons in north-central British Columbia, Canada

Background The Nechako River Basin (NRB) is a large, regulated basin in north-central British Columbia, Canada that has been impacted by numerous landscape disturbances, including a severe wildfire in 2018. Aims The aims of this study were to quantify the post-wildfire temporal and spatial extent of contamination by polycyclic aromatic hydrocarbons (PAHs) of both soils and riverine sediments, and to identify the primary sources of PAHs in the watershed. Methods Soil samples were collected at burned and unburned sites in 2018 and at the burned sites in 2020 and 2021. Sediment samples were collected at three tributaries impacted by wildfire and three Nechako River mainstem (i.e. main channel) sites from 2018 to 2021. Samples were analysed for parent PAHs. Key results PAH concentrations decreased in soil samples from 2018 to 2021 but are not below the concentrations found in unburned samples. Tributary sediment samples showed higher concentrations immediately post-fire relative to the mainstem Nechako River, but in the years since, that trend has reversed. Conclusions PAHs persist in terrestrial and aquatic environments for years following wildfire, but at concentrations below various quality guidelines. PAHs were primarily derived from the wildfires, with some mixed sources at the downstream sites. Implications Wildfires are an important source of environmental contamination of terrestrial and aquatic environments.

Do human activities affect phytoplankton biomass and composition in embayments on Lake Diefenbaker?

ABSTRACTLake Diefenbaker (LD) is an important source of water for southern Saskatchewan. LD is characterized by numerous embayments containing anthropogenic activities (e.g., housing, marinas, cattle watering). Many of these activities are increasing on this important reservoir in association with the rapidly developing economy of Saskatchewan. These activities may reduce water quality directly or indirectly by encouraging the growth of nuisance algae (i.e. cyanobacteria). Here, we examined phytoplankton biomass and composition in eight embayments exposed to anthropogenic activities, four unexposed embayments with no perceived human activities and six main channel sites adjacent to the embayments from June to October (2011 and 2012). Phytoplankton biomass and composition was not significantly different in exposed, unexposed embayments and main channel sites (p > 0.05), with the diatoms and cryptomonads constituting 87%–91% of the total phytoplankton biomass in both years. High flows from the South Saskatchewan River (SSR) in both years may have resulted in the rapid flushing of the embayments and dampened any localized impacts that could have resulted from anthropogenic activities as found in other studies. Hence, future study on LD should be conducted during years with low flow from the SSR when the rate of flushing of embayments will be reduced.

Detection of Lead (Pb) in Three Environmental Matrices of the Cache River Watershed, Arkansas.

Water bodies contaminated with lead (Pb) represent a considerable threat to both human and environmental health. The Cache River, located in northeastern Arkansas has been listed as impaired on the 303(d) list due to Pb contamination. However, historical data for the watershed is limited in both sampled waterways and analyses performed. This study measures concentrations of Pb in three environmental matrices of the Cache River Watershed; dissolved in the water column, total Pb (dissolved+particulate), and sediment-bound Pb. A variety of waterways were sampled including main channel and tributary sites. Frequency of detection and mean concentrations were compared to values for the entire Lower Mississippi Watershed. In general, no significant differences were found for the CRW when compared to the LMRW, with the exception of total Pb which was detected more frequently but at lower concentrations in the CRW than in the LMRW, and sediment Pb, which was detected at a significantly lower frequency in the CRW than the LMRW.

Electrofishing Effort Requirements for Estimating Species Richness in the Kootenai River, Idaho

Abstract This study was conducted on the Kootenai River, Idaho to provide insight on sampling requirements to optimize future monitoring effort associated with the response of fish assemblages to habitat rehabilitation. Our objective was to define the electrofishing effort (m) needed to have a 95% probability of sampling 50, 75, and 100% of the observed species richness and to evaluate the relative influence of depth, velocity, and instream woody cover on sample size requirements. Sidechannel habitats required more sampling effort to achieve 75 and 100% of the total species richness than main-channel habitats. The sampling effort required to have a 95% probability of sampling 100% of the species richness was 1100 m for main-channel sites and 1400 m for side-channel sites. We hypothesized that the difference in sampling requirements between main- and side-channel habitats was largely due to differences in habitat characteristics and species richness between main- and side-channel habitats. In general, main...

Ecosystem metabolism and nutrient dynamics in the main channel and backwaters of the Upper Mississippi River

Summary Photosynthesis and respiration are primary drivers of dissolved oxygen dynamics in rivers. We measured dissolved oxygen dynamics, aquatic ecosystem metabolism, algal abundance and nutrient concentrations at main channel and backwater sites on a reach of the Upper Mississippi River that borders the states of Wisconsin and Minnesota (U.S.A.). We asked (i) how ecosystem metabolism rates, dissolved oxygen dynamics and nutrient concentrations differed in the main channel and in backwaters, (ii) whether ecosystem metabolism relates to solar irradiance, nutrient concentration, algal abundance, temperature and river discharge and (iii) whether the relationships between ecosystem metabolism and these environmental factors differs between the main channel and backwaters. The rates of aquatic ecosystem metabolism in the main channel were among the highest reported for large rivers. Mean daily gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) in the main channel in the 2006 growing season were 10, 6 and 4 g O2 m2 d−1, respectively. Solar irradiance, discharge and temperature, rather than nutrients, accounted for most temporal variability in gross primary production (GPP). Discharge was negatively associated with GPP in the main channel and temperature positively associated with GPP in backwaters. Primary production consistently exceeded respiration in the main channel in summer, resulting in persistent oxygen supersaturation from late June to early August. Maximum chlorophyll concentrations (˜140 μg L−1) were observed in the main channel, rather than the backwaters. Nitrogen and phosphorus exhibited contrasting temporal patterns in backwaters probably reflecting differences in their sources and sinks; N declined during the growing season while P increased.

Survey to compare phytoplankton functional approaches: How can these approaches assess River Nile water quality in Egypt?

The phytoplankton functional group concept (Q(r) index) was used to assess ecological status in the River Nile. Phytoplankton Functional Groups (FGs) and Morpho-Based Functional Groups (MBFGs) were described in the whole river including the main pollution sources. A total of 273 species were classified into 25 FGs and seven MBFGs. The most dominant FGs recorded (D, P, B, M, F, P, J and F) preferred nutrient rich conditions, whereas the appearance of lacustrine groups (W1, T, Y, Lo) reflected an increase of water residence time. Between MBFG groups, VI was the most dominant. The Canonical Corresponding Analysis indicated that the variance explained from environmental conditions is highest for MBFG (78.56%) than for FG (65.57%) and individual species (51.36%). Minimum Q(r) index values were synchronized to spring and the southern section of the river. The least Q(r) values were observed at the discharging point of pollutants and increase toward the highly diluted point. The highest Q(r) values were mainly observed at the upstream and main channel sites. The results suggested that the morpho-functional classification of phytoplankton and Q(r) not only reflects successfully River Nile water quality better than the individual species composition, but can also be used as a monitoring tool to assess the ecological status in the River Nile.

Decapod community structure in a subtropical mountain stream in Taiwan before and after a catastrophic typhoon

Extreme events (typhoons, floods, and mudflows) can influence the abundance and community structure of aquatic organisms. In this study, we compare freshwater decapod abundance and community structure in main channel and tributary sites in a subtropical area of Taiwan before and after the typhoon Tembin. The results indicate that the physical conditions, decapod abundance and the Shannon diversity index were significantly different between the main channel and tributary sites, but were not significantly affected by the typhoon. The decapod community structure also showed significant differences spatially, but not temporally. The results of this study suggest that decapod communities are highly resilient to the acute effects of typhoons.

Use of main channel and two backwater habitats by larval fishes in the Detroit River

Recent investigations in the Detroit River have revealed renewed spawning activity by several important fishes, but little is known about their early life history requirements. We surveyed two main channel and two backwater areas in the lower Detroit River weekly from May to July 2007 to assess habitat use by larval fishes. Backwater areas included a soft-sediment embayment (FI) and a hard-sediment area (HIW). Main channel sites were located adjacent to each backwater area. Water temperature, velocity and clarity measurements and zooplankton samples were collected weekly. A macrophyte assessment was conducted in July. Growth and diet of larval yellow perch (Perca flavescens), bluegill (Lepomis macrochirus) and round goby (Neogobius melanostomus) were used to assess habitat quality. Macrophyte diversity and percent cover were higher and velocity lower at FI than HIW. Although larval fish diversity was highest in the main channel, yellow perch and bluegill larvae only grew beyond the yolk stage at FI, where they preferentially selected copepods, while Daphnia were selected in the main channel. Round goby ate harpacticoid copepods and Daphnia and grew at similar rates in HIW and the main channel. These data indicate that FI was a valuable nursery area for yellow perch and bluegill, whereas HIW was better suited to round goby. We only assessed two backwater areas, thus a complete census of wetland areas in the Detroit River is needed to identify valuable habitats. Restoration of shallow backwater areas is essential for rehabilitating fish populations and should be a priority in the Detroit River.

Nursery sources and cohort strength of young‐of‐the‐year common carp (Cyprinus carpio) under differing flow regimes in a regulated floodplain river

AbstractOtolith chemistry and standardised catch data were used to identify key nursery sources for common carp (Cyprinus carpio) in the mid‐Murray River region, south‐east Australia, and to quantify annual young‐of‐the‐year (YOY) cohort strength under varying hydrological conditions across 4 years (2005/2006–2008/2009). Analysis of trace element concentrations (i.e., Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca) near the otolith core of post‐larval carp (< 1 month of age) resulted in moderate to very high spatial discrimination of nursery sources within years. Otolith elemental concentrations were not stable across years at all nurseries, necessitating resampling of post‐larvae each spawning season to characterise nursery sources. Annual electrofishing surveys detected a strong cohort of YOY carp (4–6 months of age) in 2006, following a period of natural and artificially augmented high flows in the Murray River main channel and tributaries and extended floodplain inundation in the Barmah‐Millewa Forest (BMF). Few YOY were captured in 2007, 2008 or 2009 – years characterised by low flow conditions in the region and no floodplain inundation in BMF. Maximum likelihood estimation of nursery origins indicated that the BMF was the primary source for YOY fish captured from main channel (Torrumbarry Weir) and tributary (lower Goulburn River) sites in 2006, with the lower Goulburn River making a smaller contribution to the YOY cohort. These results demonstrate the importance of hydrology in determining spatial and temporal patterns of carp recruitment in regulated rivers and highlight the need to consider such factors when attempting to optimise ecological outcomes from environmental flow delivery.

Spatial patterns in macroinvertebrate assemblages in surface-flowing waters of a glacially-influenced floodplain

We examined the spatial structure of macroinvertebrate assemblages in surface-flowing waters of a glacially-influenced floodplain. The floodplain main-channel responded longitudinally to changes in hydrology with evident coarse-scale zones of upwelling and downwelling; the lower floodplain main channel fell dry in late winter. Physico-chemical attributes differed among tributaries and the main channel. The main channel had lower values of conductivity, alkalinity and nitrate–N than tributaries, with right-side (east-facing) tributaries having the highest values. Left-side (west-facing) tributaries flowing over an exposed rock-face had warmer water temperatures than the main channel and right-side tributaries. The biomass of benthic organic matter and periphyton was highest in right-side tributaries, followed by main channel sites then left-side tributaries. Similarly, macroinvertebrate density and richness were higher in right-side tributaries, intermediate in main channel sites, and lowest in left-side tributaries. Macroinvertebrate assemblages clearly differed between main channel sites, right-side tributaries, and left side tributaries based on an NMDS analysis. Minor differences were observed among main channel sites, although most upstream sites showed some structural differences from downstream sites. Ephemeropterans and plecopterans were most common in main channel sites and right-side tributaries, whereas chironomids and trichopterans also were common in right-side tributaries. Although the main channel changed longitudinally in physico-chemical characteristics, no real patterns of zonation were evident in macroinvertebrate assemblages. Coarse spatial patterns in macroinvertebrate assemblages in the floodplain were reflected in the physico-chemical differences between the main channel and tributaries, and between left-side and right-side tributaries. We conclude that coarse-scale floodplain properties enhance the overall diversity of lotic macroinvertebrates. Consequently, floodplain alterations that reduce surface water heterogeneity/connectivity limits the potential macroinvertebrate diversity of floodplains.

Larval and early juvenile fish dynamics in main channel and backwater lake habitats of the Illinois River ecosystem

AbstractThe spatial and temporal complexity of large river ecosystems likely promotes biological diversity within riverine larval fish assemblages. However, the focus of most previous riverine studies of larval fish distribution has tended to concentrate mainly on backwater habitats. There has been less focus on the value of the main channel for larval fishes. We sampled two habitats types (three main channel sites and three backwater lakes) along 20 km of the Illinois River ecosystem during 2 years to compare the larval fish distribution along both spatial and environmental gradients between these habitats. Across the 2 years of this study, we found similar trends in the spatial and temporal distribution of larval fish, although there were some differences in densities between years. The relative abundance and size of many of the different fish taxa varied among habitats. Centrarchids, clupeids, poeciliids, cyprinids (excluding common carp) and atherinids were more abundant within backwater lake habitat. In contrast, common carp (Cyprinus carpio), sciaenids, moronids and catostomids were more abundant in main channel habitats. Furthermore, sciaenid and clupeid larvae captured in the backwater lake habitat were larger as the season progressed than those captured in the main channel. Our study suggests that larval fish show habitat specialisation, similar to adults, indicating that both the backwater lakes and the main channel are both important for larval fish and preserving the diversity of the fish assemblages in large floodplain rivers.

Numerical modelling of spatio-temporal thermal heterogeneity in a complex river system

Accurate quantification and effective modelling of water temperature regimes is fundamental to underpin projections of future Arctic river temperature under scenarios of climate and hydrological change. We present results from a deterministic two-dimensional hydrodynamic model coupled with a heat transfer model that includes horizontal advection and vertical water surface energy fluxes. Firstly, we model longitudinal, lateral and temporal thermal heterogeneity of a braided reach of an Arctic river; Karsajokk, Sweden. Model performance was assessed against water temperature data collected at 11 monitoring sites for two independent 1-week time periods. Overall, model performance was strongest (r values >0.9, RMSEs~. 0.6°C and ME< 0.4 °C) for main channel sites with relatively deep fast-flows where water temperature was comparatively low and stable. However, model performance was poorer for sites characterised by shallow and/or temporarily-stagnant streams at the lateral margins of the braidplain, where a lag of 60-90. min persisted between the modelled and measured water temperatures. Secondly, we present novel automated statistical analyses and quantify channel thermal connectivity and complexity. Our results lead us to suggest that with further development our modelling approach offers new opportunities for scenario-based predictions of response to environmental change and to assess anthropogenic impacts on water temperature.

Examining 20th century water quality and ecological changes in the Lake of the Woods, Ontario, Canada: A paleolimnological investigation

Comparisons between diatom assemblages preserved in modern and pre-industrial sediments were made to provide a lake-wide paleolimnological assessment of environmental change in 17 sites located throughout the Ontario portion of the Lake of the Woods (LoW). Diatom changes were consistent across all sites, although the magnitude of these changes varied along a trophic gradient (i.e., main channel sites versus isolated bays). The most notable taxonomic shift was towards a higher relative abundance of small, centric Cyclotella taxa and other planktonic, pennate diatoms (e.g., Asterionella formosa, Fragilaria crotonensis) in the modern sediments, with corresponding lower relative abundances of heavily silicified Aulacoseira taxa and small benthic Fragilaria taxa. To aid in determining whether changes in nutrients can explain the diatom trends, weighted-averaging partial-least-squares (WA-PLS) techniques were used to develop a diatom-based inference model to reconstruct changes in total phosphorus (TP) concentrations. Diatom-inferrred TP (DI-TP) reconstructions revealed that 88% of the sites showed either no change or a slight, but not significant decline in DI-TP since pre-industrial times. Diatom-based inferences suggest that TP concentrations at many sites in the Ontario portion of the LoW were moderately elevated in nutrients prior to any major human disturbances (i.e., pre-1850). Results suggest that substantial increases in temperature over the last few decades, and the associated changes to ice cover and water column properties, have likely exacerbated the effects of existing stressors on the system and were key factors influencing a lake-wide restructuring of the diatom communities over the past ca. 150 years.

Fishes of the King Edward River in the Kimberley region, Western Australia

The King Edward River, in the far north of the Kimberley region of Western Australia drains approximately 10,000 km2 and discharges into the Timor Sea near the town of Kalumburu. This study represents an ichthyological survey of the river’s freshwaters and revealed that the number of freshwater fishes of the King Edward River is higher than has previously been recorded for a Western Australian river. Twenty-six strictly freshwater fish species were recorded, which is three species higher than the much larger Fitzroy River in the southern Kimberley. The study also identified a number of range extensions, including Butler’s Grunter and Shovel-nosed Catfish to the west, and the Slender Gudgeon to the north and east. A possibly undescribed species of glassfish, that differs morphologically from described species in arrangement of head spines, fin rays, as well as relative body measurements, is reported. A considerable proportion of Jenkins’ Grunter, which is widespread throughout the system but essentially restricted to main channel sites, had ‘blubber-lips’. There were significant differences in the prevailing fish fauna of the different reaches of the King Edward River system. Thus fish associations in the upper King Edward River main channel were significantly different to those in the tributaries and the main channel of the Carson River. Similarly, the fauna of the Carson River, which was much more diverse than the King Edward River main channel and tributary sites, was characterised by many species that were not found in other parts of the river. The presence of natural barriers, such as waterfalls or rock bars do not permit upstream migrations of fishes and are considered to be the main factor in limiting the distribution of some species. For example, many species are restricted to the lower sections of the Carson River, and include Bony Bream, Lesser Salmon Catfish, Shovel-nosed Catfish, Black Catfish, False-spined Catfish, Freshwater Longtom, Prince Regent Hardyhead, Mouth Almighty, Barred Grunter and Butler’s Grunter. It is hypothesised that these natural barriers were in place long before many of these latter species colonised the King Edward River. Some species tend to only be found within tributary sites, e.g. Kimberley Mogurnda, while others are most abundant in tributaries rather than main channel sites, e.g. Western Rainbowfish and Spangled Perch. Waterfalls are also seen as limiting the number of migratory marine/estuarine species that enter freshwaters. For example, only three species that require the marine/estuarine environment to complete their life-cycle were captured in the freshwaters of the King Edward River system. This compares to 14 species that utilise the freshwaters of the Fitzroy River.

Efficacy of Bacteroides Measurements for Reducing the Statistical Uncertainty Associated with Hydrologic Flow and Fecal Loads in a Mixed Use Watershed

This paper presents an analysis of the occurrence and uncertainty of source-specific Bacteroides and Escherichia coli in a stream in a mixed land-use watershed with human, cattle, and wildlife fecal inputs located in a karstic geologic region during baseflow conditions. The objectives of the study were to evaluate the occurrence, hydrologic significance, and source of fecal mass in the stream using assays for total Bacteroides (AllBac) and bovine-specific Bacteroides (BoBac), and then to compare these measurements with E. coli densities and loads. Samples were collected during baseflow conditions over several months at seven different main channel sites in the Stock Creek watershed, a 49.3 km2 basin located in Knoxville, TN (USA). We determined instantaneous loads for total fecal loads, bovine fecal loads, and E. coli from measured flow rates and the representative Bacteroides fecal masses and/or E. coli densities. The study indicated a strong correlation between total fecal load (kg d(-1)), bovine fecal load (kg d(-1)), E. coli load rate (CFU d(-1)), 7-d antecedent precipitation, and turbidity. The various datasets were used to establish parameter correlations and spatial dependencies throughout the watershed. The data analysis demonstrated two prevalent patterns throughout the watershed: (i) a runoff-dominated transport and occurrence; and (ii) potential groundwater-dominated transport and occurrence.

Iron isotopes in the Amazon River system: Weathering and transport signatures

Trace metal clean plankton tows, river samples, aerosol leachates, and porewater samples from the Amazon River system were measured for their iron isotopic composition. The overall isotopic range observed was 1.5‰ with Fe isotopic variability observed between different types of tributaries. Dissolved Fe and suspended load Fe from two main channel sites were isotopically similar (≈ − 0.1 to − 0.3‰). In contrast, the dissolved Fe and suspended load Fe from an organic rich tributary, the Negro River, were isotopically distinct with the dissolved slightly isotopically heavy (+ 0.3‰) and the suspended load isotopically light (− 0.9‰). The isotopically lightest sample from the Amazon region was shelf porewater (− 1.3‰). In river water–seawater mixing experiments, the Fe isotopic signal of dissolved Fe of river water was modified by flocculation of isotopically heavy Fe. The variability of the Fe isotopic composition of natural samples including biological and aqueous samples demonstrates that significant fractionation is associated with Fe biogeochemistry in the environment.

Hydrological seasonality and benthic algal biomass in a Neotropical floodplain river

Our study evaluated spatiotemporal variation of physicochemical parameters and benthic and sestonic algal biomass in littoral areas of the main channel and floodplain lakes of the Cinaruco River, a lowland tributary of the Orinoco River in Venezuela. The Cinaruco is characterized by a highly predictable annual flood pulse, high transparency, and extremely low conductivity and suspended sediment load. During 2002 and 2003, 10 sites in the main channel and floodplain lagoons were sampled on 12 occasions. Correspondence analysis based on water physicochemical variables and algal biomass showed that ˜80% of the variation in the multivariate space among sites and sampling dates was explained by 2 axes. During the high-water periods, river and lagoon sites showed high similarity in water variables and algal biomass. Conductivity, SiO3, and chlorophyll a concentrations (both benthic and sestonic) were low during the high-water phase. On the other hand, water variables and algal biomass differed between river and lagoon sites during the low-water period. The absence of flow in lagoons and consistently low algal biomass (sestonic and benthic) in river sites were the most important features of the spatial variability between main channel and lagoon sites during low-water phases. Benthic chlorophyll a was highly uniform at small spatial scales and significantly heterogeneous at large spatial scales. The annual flood regime of the Cinaruco, which drives the concentrations of dissolved materials and affects material interchanges between aquatic and terrestrial systems, also appears to be responsible for creating strong patterns of seasonal and spatial variation in benthic algal crops.

Fish assemblages and biotic integrity of a highly modified floodplain river, the Upper Mississippi, and a large, relatively unimpacted tributary, the Lower Wisconsin

The Upper Mississippi River is a dynamic floodplain river that has been largely transformed by navigational levees and dams since the 1930s. The pools upstream of each dam are lake-like and only about the upper third of each reach retains a riverine character. In contrast, the Wisconsin River is not managed for commercial navigation and today its lower 149 km represent one of the least-degraded large river reaches in central North America. Riverine reaches in both the Mississippi and Wisconsin rivers have similar macro-habitats including numerous islands, large side channels, and connected backwaters and floodplain lakes. In this study, shoreline electrofishing samples were collected during summer 2002 and 2003 to characterize resident fish assemblages. We compared fish species abundance, biomass, and biotic integrity along main and side channel borders between the Upper Mississippi River and the Lower Wisconsin River. We expected that, in the absence of environmental degradation, fish composition and structure would be similar between the Mississippi and Wisconsin rivers, and between channel types within each river. Nonmetric multidimensional scaling and redundancy analysis revealed that fish species in the Mississippi River, unlike in the Wisconsin River, were characteristic of non-riverine habitats. We consider non-riverine fish assemblages indicative of environmental impairment. The main and side channel sites in the Mississippi River had more variable fish assemblages than the Wisconsin River. Analyses of fish index of biotic integrity scores showed that environmental condition was excellent for both channel types in the Wisconsin River, whereas in the Mississippi River the side channel was rated good and the main channel only fair. We conclude that differences between the two rivers and between channel types of the Mississippi River are consistent with direct and indirect effects of navigation. This study demonstrates the utility of a fish index of biotic integrity, an inexpensive and rapid bioassessment tool, for detecting change in ecological health on one of the world's largest rivers. Copyright © 2006 John Wiley & Sons, Ltd.

Biodiversity and resource use of larval chironomids in relation to environmental factors in a large river

1. Larval chironomids were examined at four sites on a cross‐section of the River Danube in Austria between September 1995 and August 1996. The sites differed in hydraulics, sediment composition and habitat stability.2. Species–accumulation curves, showing the increase in number of species with increasing sampling effort, from three main channel sites were best described by a logarithmic model, suggesting that most of the species occurring at these sites were found. Data from a site connected to a backwater fitted best to a power model, indicating a random assemblage with additional species immigrating from the backwater area.3. Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 32–91), H′ diversity (1.5–2.3), evenness (0.23–0.28), spatial resource width (0.01–0.06), spatial resource overlap (0.13–0.20), spatial species aggregation (0.60–0.77), temporal community persistence (Kendal's correlation coefficient: 0.47–0.60) and beta‐diversity (6.2–9.7).4. Redundancy analysis (RDA) was used to relate the community properties and species abundance to environmental factors. Habitat stability was the major factor associated with community structure. Higher sediment turnover led to higher spatial aggregation and, consequently, a decrease in spatial resource width and overlap, and to a decline in larval density and species richness.5. Species‐abundance patterns agreed well with the log‐normal model. Moderate community persistence and stability of the streambed sediments suggest that the log‐normal model may be a good descriptor for communities of intermediately disturbed habitats, like large rivers, rather than stable habitats.