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P. L. Angermeier

Publications and source records attributed to P. L. Angermeier.

At least 19 recordsLinked to original sources
USGS2011

Designing mark-recapture studies to reduce effects of distance weighting on movement distance distributions of stream fishes

Mark-recapture studies generate biased, or distance-weighted, movement data because short distances are sampled more frequently than long distances. Using models and field data, we determined how study design affects distance weighting and the movement distributions of stream fishes. We first modeled distance weighting as a function of recapture section length in an unbranching stream. The addition of an unsampled tributary to one of these models substantially increased distance weighting by decreasing the percentage of upstream distances that were sampled. Similarly, the presence of multiple tributaries in the field study resulted in severe bias. However, increasing recapture section length strongly affected distance weighting in both the model and the field study, producing a zone where the number of fish moving could be estimated with little bias. Subsampled data from the field study indicated that longer median (three of three species) and maximum distances (two of three species) can be detected by increasing the length of the recapture section. The effect was extreme for bluehead chub Nocomis leptocephalus, a highly mobile species, which exhibited a longer median distance (133 m versus 60 m), a longer maximum distance (1,144 m versus 708 m), and a distance distribution that differed in shape when the full (4,123-m recapture section) and subsampled (1,978-m recapture section) data sets were compared. Correction factors that adjust the observed number of movements to undersampled distances upwards and those to oversampled distances downwards could not mitigate the distance weighting imposed by the shorter recapture section. Future studies should identify the spatial scale over which movements can be accurately measured before data are collected. Increasing recapture section length a priori is far superior to using post hoc correction factors to reduce the influence of distance weighting on observed distributions. Implementing these strategies will be especially important in stream networks where fish can follow multiple pathways out of the recapture section.

Transactions of the American Fisheries Society↗
USGS2011

Fish community and bioassessment responses to stream network position

If organisms move beyond the boundaries of local sampling units, regional metacommunity dynamics could undermine the ability of bioassessment studies to characterize local environmental quality. We tested the prediction that fish dispersal influences local fish community structure and bioassessment metrics as a function of site position within stream networks. We evaluated fish community data from the US Environmental Protection Agency's Regional Environmental Monitoring and Assessment Program in West Virginia, USA, to compare the influences of stream network position, ecoregion, basin, and stream size on local fish community composition. We assigned sites to 1 of 3 stream network positions: 1) main channels (MC, n = 12) encompassed streams with upstream catchment areas >200 km 2 , 2) mainstem tributaries (MT, n = 43) flowed into MC-sized confluences within 15 fluvial km, 3) headwater tributaries (HT, n = 31) lacked such riverine confluences within 15 fluvial km. MT and HT sites had similar upstream catchment sizes and landuse gradients, but species richness was greater in MT sites than HT sites, whereas MT and MC sites were not different in this regard. Three bioassessment metrics were greater in MT sites than HT sites (intolerant species richness, cyprinid species richness, benthic species richness), but a multimetric index of biotic integrity did not differ among stream network positions. Ordinations revealed that fish community composition was organized primarily by zoogeographic basin (Monongahela River basin, New River basin, Ohio River basin), ecoregion (Central Appalachian Plateau, Western Appalachian Plateau, Ridge and Valley), and stream size. Riverine specialists were more abundant in MT than HT sites and were more abundant in basins connected to the Ohio River than in basins isolated from the Ohio River by a large waterfall (New River). Our results suggest that contemporary dispersal among streams influences fish community composition over small spatial scales (10 1 km), historical dispersal constrained by zoogeographic barriers influences community structure over larger areas (10 2 km), and contemporary dispersal by fishes influences certain metrics commonly used in bioassessment programs.

Journal of the North American Benthological Societ↗
USGS2010

Seasonal meso- and microhabitat selection by the northern snakehead ( Channa argus ) in the Potomac river system

The northern snakehead ( Channa argus ) is a large piscivorous fish that is invasive in eastern Europe and has recently been introduced in North America. We examined the seasonal habitat selection at meso- and microhabitat scales using radio-telemetry to increase understanding of the ecology of this species, which will help to inform management decisions. After the spawning season (postspawn season, September–November), northern snakeheads preferred offshore Eurasian water-milfoil ( Myriophyllum spicatum ) beds with shallow water (∼115 cm) and soft substrate. In the winter (November–April), these fish moved to deeper water (∼135 cm) with warmer temperatures, but habitat selection was weak at both scales. Northern snakeheads returned to shallower water (∼95 cm) in the prespawn season (April–June) and used milfoil and other cover. Habitat selection was the strongest at both meso- and microhabitat scales during the spawning season (June–September), when fish preferred macrophytes and cover in shallow water (∼88 cm). Our results help to identify habitats at the risk of invasion by northern snakeheads. We suggest that control efforts and future research focus on shallow waters, and take into consideration the seasonal habitat preferences.

Maryland, Virginia↗
USGS2008

Microsatellite markers for the endangered Roanoke logperch, Percina rex (Percidae) and their potential utility for other darter species

The Roanoke logperch (Percina rex Jordan and Evermann), an endangered fish, occurs in only six watersheds in the Roanoke and Chowan river drainages of Virginia, USA. The species' population genetic structure is poorly known. We developed 16 microsatellite markers that were reliably scorable and polymorphic P. rex. Markers were also screened in seven other darter species of the genus Percina. Most markers exhibited successful amplification and polymorphism in several species. These markers may therefore prove useful for population genetic studies in other darters, a diverse but highly imperiled group. ?? 2008 The Authors.

Molecular Ecology Resources↗
USGS2008

Evidence for fish dispersal from spatial analysis of stream network topology

Developing spatially explicit conservation strategies for stream fishes requires an understanding of the spatial structure of dispersal within stream networks. We explored spatial patterns of stream fish dispersal by evaluating how the size and proximity of connected streams (i.e., stream network topology) explained variation in fish assemblage structure and how this relationship varied with local stream size. We used data from the US Environmental Protection Agency's Environmental Monitoring and Assessment Program in wadeable streams of the Mid-Atlantic Highlands region (n = 308 sites). We quantified stream network topology with a continuous analysis based on the rate of downstream flow accumulation from sites and with a discrete analysis based on the presence of mainstem river confluences (i.e., basin area >250 km2) within 20 fluvial km (fkm) from sites. Continuous variation in stream network topology was related to local species richness within a distance of ???10 fkm, suggesting an influence of fish dispersal within this spatial grain. This effect was explained largely by catostomid species, cyprinid species, and riverine species, but was not explained by zoogeographic regions, ecoregions, sampling period, or spatial autocorrelation. Sites near mainstem river confluences supported greater species richness and abundance of catostomid, cyprinid, and ictalurid fishes than did sites >20 fkm from such confluences. Assemblages at sites on the smallest streams were not related to stream network topology, consistent with the hypothesis that local stream size regulates the influence of regional dispersal. These results demonstrate that the size and proximity of connected streams influence the spatial distribution of fish and suggest that these influences can be incorporated into the designs of stream bioassessments and reserves to enhance management efficacy. ?? 2008 by The North American Benthological Society.

Journal of the North American Benthological Societ↗
USGS2006

Spatiotemporal variability of stream habitat and movement of three species of fish

Relationships between environmental variability and movement are poorly understood, due to both their complexity and the limited ecological scope of most movement studies. We studied movements of fantail (Etheostoma flabellare), riverweed (E. podostemone), and Roanoke darters (Percina roanoka) through two stream systems during two summers. We then related movement to variability in measured habitat attributes using logistic regression and exploratory data plots. We indexed habitat conditions at both microhabitat (i.e., patches of uniform depth, velocity, and substrate) and mesohabitat (i.e., riffle and pool channel units) spatial scales, and determined how local habitat conditions were affected by landscape spatial (i.e., longitudinal position, land use) and temporal contexts. Most spatial variability in habitat conditions and fish movement was unexplained by a site's location on the landscape. Exceptions were microhabitat diversity, which was greater in the less-disturbed watershed, and riffle isolation and predator density in pools, which were greater at more-downstream sites. Habitat conditions and movement also exhibited only minor temporal variability, but the relative influences of habitat attributes on movement were quite variable over time. During the first year, movements of fantail and riverweed darters were triggered predominantly by loss of shallow microhabitats; whereas, during the second year, microhabitat diversity was more strongly related (though in opposite directions) to movement of these two species. Roanoke darters did not move in response to microhabitat-scale variables, presumably because of the species' preference for deeper microhabitats that changed little over time. Conversely, movement of all species appeared to be constrained by riffle isolation and predator density in pools, two mesohabitat-scale attributes. Relationships between environmental variability and movement depended on both the spatiotemporal scale of consideration and the ecology of the species. Future studies that integrate across scales, taxa, and life-histories are likely to provide greater insight into movement ecology than will traditional, single-season, single-species approaches. ?? 2006 Springer-Verlag.

Oecologia↗
USGS2006

Impacts of new highways and subsequent landscape urbanization on stream habitat and biota

New highways are pervasive, pernicious threats to stream ecosystems because of their short- and long-term physical, chemical, and biological impacts. Unfortunately, standard environmental impact statements (EISs) and environmental assessments (EAs) focus narrowly on the initial direct impacts of construction and ignore other long-term indirect impacts. More thorough consideration of highway impacts, and, ultimately, better land use decisions may be facilitated by conceptualizing highway development in three stages: initial highway construction, highway presence, and eventual landscape urbanization. Highway construction is characterized by localized physical disturbances, which generally subside through time. In contrast, highway presence and landscape urbanization are characterized by physical and chemical impacts that are temporally persistent. Although the impacts of highway presence and landscape urbanization are of similar natures, the impacts are of a greater magnitude and more widespread in the urbanization phase. Our review reveals that the landscape urbanization stage is clearly the greatest threat to stream habitat and biota, as stream ecosystems are sensitive to even low levels (<10%) of watershed urban development. Although highway construction is ongoing, pervasive, and has severe biological consequences, we found few published investigations of its impacts on streams. Researchers know little about the occurrence, loading rates, and biotic responses to specific contaminants in highway runoff. Also needed is a detailed understanding of how highway crossings, especially culverts, affect fish populations via constraints on movement and how highway networks alter natural regimes (e.g., streamflow, temperature). Urbanization research topics that may yield especially useful results include a) the relative importance and biological effects of specific components of urban development - e.g., commercial or residential; b) the scenarios under which impacts are reversible; and c) the efficacy of mitigation measures - e.g., stormwater retention or treatment and forested buffers. Copyright ?? Taylor & Francis Inc.

Reviews in Fisheries Science↗
USGS2004

Geographic variation in patterns of nestedness among local stream fish assemblages in Virginia

Nestedness of faunal assemblages is a multiscale phenomenon, potentially influenced by a variety of factors. Prior small-scale studies have found freshwater fish species assemblages to be nested along stream courses as a result of either selective colonization or extinction. However, within-stream gradients in temperature and other factors are correlated with the distributions of many fish species and may also contribute to nestedness. At a regional level, strongly nested patterns would require a consistent set of structuring mechanisms across streams, and correlation among species' tolerances of the environmental factors that influence distribution. Thus, nestedness should be negatively associated with the spatial extent of the region analyzed and positively associated with elevational gradients (a correlate of temperature and other environmental factors). We examined these relationships for the freshwater fishes of Virginia. Regions were defined within a spatial hierarchy and included whole river drainages, portions of drainages within physiographic provinces, and smaller subdrainages. In most cases, nestedness was significantly stronger in regions of smaller spatial extent and in regions characterized by greater topographic relief. Analysis of hydrologic variability and patterns of faunal turnover provided no evidence that interannual colonization/extinction dynamics contributed to elevational differences in nestedness. These results suggest that, at regional scales, nestedness is influenced by interactions between biotic and abiotic factors, and that the strongest nestedness is likely to occur where a small number of organizational processes predominate, i.e., over small spatial extents and regions exhibiting strong environmental gradients. ?? Springer-Verlag 2004.

Oecologia↗
USGS2004

Using fish communities to assess streams in Romania: Initial development of an index of biotic integrity

Multimetric biotic indices increasingly are used to complement physicochemical data in assessments of stream quality. We initiated development of multimetric indices, based on fish communities, to assess biotic integrity of streams in two physiographic regions of central Romania. Unlike previous efforts to develop such indices for European streams, our metrics and scoring criteria were selected largely on the basis of empirical relations in the regions of interest. We categorised 54 fish species with respect to ten natural-history attributes, then used this information to compute 32 candidate metrics of five types (taxonomic, tolerance, abundance, reproductive, and feeding) for each of 35 sites. We assessed the utility of candidate metrics for detecting anthropogenic impact based on three criteria: (a) range of values taken, (b) relation to a site-quality index (SQI), which incorporated information on hydrologic alteration, channel alteration, land-use intensity, and water chemistry, and (c) metric redundancy. We chose seven metrics from each region to include in preliminary multimetric indices (PMIs). Both PMIs included taxonomic, tolerance, and feeding metrics, but only two metrics were common to both PMIs. Although we could not validate our PMIs, their strong association with the SQI in each region suggests that such indices would be valuable tools for assessing stream quality and could provide more comprehensive assessments than the traditional approaches based solely on water chemistry.

Hydrobiologia↗
USGS2004

Ecological correlates of fish movement in a network of Virginia streams

Identifying factors that influence fish movement is a key step in predicting how populations respond to environmental change. Using mark-recapture (four species) and trap capture (eight species) data, we examined relationships between three attributes of movement and 15 ecological variables. The probability of emigrating from a reach was positively related to intermittency (one species) and body size (one species) and negatively related to distance from the mainstem creek (two species) and habitat complexity (one species). The number of fish moving upstream through traps was positively related to increases in flow (five species), day length (three species), and water temperature (two species); the number moving through downstream traps was positively associated with increases in flow (three species). Distance moved was greater for fish moving through unsuitable reaches (one species). Floods have a pervasive effect on fish movement, and human activities that affect flows will have widespread implications. The importance of other factors varies interspecifically, which may translate into variation in persistence and colonization rates. For example, species that exhibit reach fidelity in complex habitats may increase movement if habitats are homogenized. These species may suffer population declines because of the cost of increased movement and may ultimately be replaced by ecological generalists.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2003

Development of a multimetric index for assessing the biological condition of the Ohio River

The use of fish communities to assess environmental quality is common for streams, but a standard methodology for large rivers is as yet largely undeveloped. We developed an index to assess the condition of fish assemblages along 1,580 km of the Ohio River. Representative samples of fish assemblages were collected from 709 Ohio River reaches, including 318 "least-impacted" sites, from 1991 to 2001 by means of standardized nighttime boat-electrofishing techniques. We evaluated 55 candidate metrics based on attributes of fish assemblage structure and function to derive a multimetric index of river health. We examined the spatial (by river kilometer) and temporal variability of these metrics and assessed their responsiveness to anthropogenic disturbances, namely, effluents, turbidity, and highly embedded substrates. The resulting Ohio River Fish Index (ORFIn) comprises 13 metrics selected because they responded predictably to measures of human disturbance or reflected desirable features of the Ohio River. We retained two metrics (the number of intolerant species and the number of sucker species [family Catostomidae]) from Karr's original index of biotic integrity. Six metrics were modified from indices developed for the upper Ohio River (the number of native species; number of great-river species; number of centrarchid species; the number of deformities, eroded fins and barbels, lesions, and tumors; percent individuals as simple lithophils; and percent individuals as tolerant species). We also incorporated three trophic metrics (the percent of individuals as detritivores, invertivores, and piscivores), one metric based on catch per unit effort, and one metric based on the percent of individuals as nonindigenous fish species. The ORFIn declined significantly where anthropogenic effects on substrate and water quality were prevalent and was significantly lower in the first 500 m below point source discharges than at least-impacted sites nearby. Although additional research on the temporal stability of the metrics and index will likely enhance the reliability of the ORFIn, its incorporation into Ohio River assessments still represents an improvement over current physicochemical protocols.

Transactions of the American Fisheries Society↗
USGS2002

Intercontinental convergence of stream fish community traits along geomorphic and hydraulic gradients

Community convergence across biogeographically distinct regions suggests the existence of key, repeated, evolutionary mechanisms relating community characteristics to the environment. However, convergence studies at the community level often involve only qualitative comparisons of the environment and may fail to identify which environmental variables drive community structure. We tested the hypothesis that the biological traits of fish communities on two continents (Europe and North America) are similarly related to environmental conditions. Specifically, from observations of individual fish made at the microhabitat scale (a few square meters) within French streams, we generated habitat preference models linking traits of fish species to local scale hydraulic conditions (Froude number), Using this information, we then predicted how hydraulics and geomorphology at the larger scale of stream reaches (several pool-riffle sequences) should quantitatively influence the trait composition of fish communities. Trait composition for fishes in stream reaches with low Froude number at low flow or high proportion of pools was predicted as nonbenthic, large, fecund, long-lived, nonstreamlined, and weak swimmers. We tested our predictions in contrasting stream reaches in France (n = 11) and Virginia, USA (n = 76), using analyses of covariance to quantify the relative influence of continent vs. physical habitat variables on fish traits. The reach-scale convergence analysis indicated that trait proportions in the communities differed between continents (up to 55% of the variance in each trait was explained by "continent"), partly due to distinct evolutionary histories. However, within continents, trait proportions were comparably related to the hydraulic and geomorphic variables (up to 54% of the variance within continents explained). In particular, a synthetic measure of fish traits in reaches was well explained (50% of its variance) by the Froude number independently of the continent. The effect of physical variables did not differ across continents for most traits, confirming our predictions qualitatively and quantitatively. Therefore, despite phylogenetic and historical differences between continents, fish communities of France and Virginia exhibit convergence in biological traits related to hydraulics and geomorphology. This convergence reflects morphological and behavioral adaptations to physical stress in streams. This study supports the existence of a habitat template for ecological strategies. Some key quantitative variables that define this habitat template can be identified by characterizing how individual organisms use their physical environment, and by using dimensionless physical variables that reveal common energetic properties in different systems. Overall, quantitative tests of community convergence are efficient tools to demonstrate that some community traits are predictable from environmental features.

Virginia↗
USGS2002

Meeting ecological and societal needs for freshwater

Human society has used freshwater from rivers, lakes, groundwater, and wetlands for many different urban, agricultural, and industrial activities, but in doing so has overlooked its value in supporting ecosystems. Freshwater is vital to human life and societal well-being, and thus its utilization for consumption, irrigation, and transport has long taken precedence over other commodities and services provided by freshwater ecosystems. However, there is growing recognition that functionally intact and biologically complex aquatic ecosystems provide many economically valuable services and long-term benefits to society. The short-term benefits include ecosystem goods and services, such as food supply, flood control, purification of human and industrial wastes, and habitat for plant and animal life—and these are costly, if not impossible, to replace. Long-term benefits include the sustained provision of those goods and services, as well as the adaptive capacity of aquatic ecosystems to respond to future environmental alterations, such as climate change. Thus, maintenance of the processes and properties that support freshwater ecosystem integrity should be included in debates over sustainable water resource allocation. The purpose of this report is to explain how the integrity of freshwater ecosystems depends upon adequate quantity, quality, timing, and temporal variability of water flow. Defining these requirements in a comprehensive but general manner provides a better foundation for their inclusion in current and future debates about allocation of water resources. In this way the needs of freshwater ecosystems can be legitimately recognized and addressed. We also recommend ways in which freshwater ecosystems can be protected, maintained, and restored. Freshwater ecosystem structure and function are tightly linked to the watershed or catchment of which they are a part. Because riverine networks, lakes, wetlands, and their connecting groundwaters, are literally the “sinks” into which landscapes drain, they are greatly influenced by terrestrial processes, including many human uses or modifications of land and water. Freshwater ecosystems, whether lakes, wetlands, or rivers, have specific requirements in terms of quantity, quality, and seasonality of their water supplies. Sustainability normally requires these systems to fluctuate within a natural range of variation. Flow regime, sediment and organic matter inputs, thermal and light characteristics, chemical and nutrient characteristics, and biotic assemblages are fundamental defining attributes of freshwater ecosystems. These attributes impart relatively unique characteristics of productivity and biodiversity to each ecosystem. The natural range of variation in each of these attributes is critical to maintaining the integrity and dynamic potential of aquatic ecosystems; therefore, management should allow for dynamic change. Piecemeal approaches cannot solve the problems confronting freshwater ecosystems. Scientific definitions of the requirements to protect and maintain aquatic ecosystems are necessary but insufficient for establishing the appropriate distribution between societal and ecosystem water needs. For scientific knowledge to be implemented science must be connected to a political agenda for sustainable development. We offer these recommendations as a beginning to redress how water is viewed and managed in the United States: (1) Frame national and regional water management policies to explicitly incorporate freshwater ecosystem needs, particularly those related to naturally variable flow regimes and to the linking of water quality with water quantity; (2) Define water resources to include watersheds, so that freshwaters are viewed within a landscape, or systems context; (3) Increase communication and education across disciplines, especially among engineers, hydrologists, economists, and ecologists to facilitate an integrated view of freshwater resources; (4) Increase restoration efforts, using well-grounded ecological principles as guidelines; (5) Maintain and protect the remaining freshwater ecosystems that have high integrity; and (6) Recognize the dependence of human society on naturally functioning ecosystems.

Ecological Applications↗
USGS2002

Sampling effort affects multivariate comparisons of stream assemblages

Multivariate analyses are used widely for determining patterns of assemblage structure, inferring species–environment relationships and assessing human impacts on ecosystems. The estimation of ecological patterns often depends on sampling effort, so the degree to which sampling effort affects the outcome of multivariate analyses is a concern. We examined the effect of sampling effort on site and group separation, which was measured using a mean similarity method. Two similarity measures, the Jaccard Coefficient and Bray–Curtis Index were investigated with 1 benthic macroinvertebrate and 2 fish data sets. Site separation was significantly improved with increased sampling effort because the similarity between replicate samples of a site increased more rapidly than between sites. Similarly, the faster increase in similarity between sites of the same group than between sites of different groups caused clearer separation between groups. The strength of site and group separation completely stabilized only when the mean similarity between replicates reached 1. These results are applicable to commonly used multivariate techniques such as cluster analysis and ordination because these multivariate techniques start with a similarity matrix. Completely stable outcomes of multivariate analyses are not feasible. Instead, we suggest 2 criteria for estimating the stability of multivariate analyses of assemblage data: 1) mean within-site similarity across all sites compared, indicating sample representativeness, and 2) the SD of within-site similarity across sites, measuring sample comparability.

Journal of the North American Benthological Societ↗
USGS2000

Hydrologic influences on soil properties along ephemeral rivers in the Namib Desert

Soils were examined along three ephemeral rivers in the Namib Desert to assess the influence of their hydrologic characteristics on soil properties. Soils consisted of layers of fluvially deposited, organic-rich silts, interstratified with fluvial and aeolian sands. The most significant influence of the ephemeral hydrologic regime upon soils was related to the downstream alluviation associated with hydrologic decay. This alluviation increased the silt proportion of soils in the lower reaches of the rivers. Organic carbon, nitrogen and phosphorous were correlated with silt content, and silt deposition patterns influenced patterns of moisture availability and plant rooting, creating and maintaining micro-habitats for various organisms. Localized salinization occurred in association with wetland sites and soluble salt content tended to increase downstream. Because of the covariance between silt and macronutrients, and the influence of silt upon moisture availability and habitat suitability, alluviation patterns associated with the hydrologic regime strongly influence the structure, productivity, and spatial distribution of biotic communities in ephemeral river ecosystems. (C) 2000 Academic Press.

Journal of Arid Environments↗
USGS1999

Transport, retention, and ecological significance of woody debris within a large ephemeral river

The spatiotemporal patterns and ecological significance of the retention of coarse particulate organic matter and large woody debris have been intensively studied in perennial rivers and streams but are virtually unknown in ephemeral systems. We examined the influence of 2 features characteristic of ephemeral systems, downstream hydrologic decay and in-channel tree growth, on the distribution, transport, and retention of woody debris following a flood having a ∼2.6-y recurrence interval in the ephemeral Kuiseb River in southwestern Africa. A total of 2105 pieces of wood were painted at 8 sites along the river channel to measure retention patterns. The flood had a peak discharge of 159 m<sup>3</sup>/s at the upper end of the study area, decaying to <1 m<sup>3</sup>/s by 200 km downstream. Downstream export of wood from marking sites totaled 59.5% (n = 1253). Transport distances ranged from 1 to 124 km, and 34.8% (n = 436) of the exported wood was recovered. Marked wood retained within marking sites was significantly longer than exported wood (p < 0.001, t-test). Once in transport, there was little correlation between wood length and distance traveled (r = 0.11, correlation analysis, n = 369). Length influenced the site of retention; material retained on debris piles was significantly longer than that stranded on channel sediments (p < 0.001, t-test). In-channel growth of Faidherbia trees significantly influenced wood retention; 83.7% of marked wood not moved by the flood was associated with debris piles on Faidherbia trees. Similarly, 65% of the exported wood retained within downstream debris piles was associated with Faidherbia trees. In contrast to many perennial systems, we observed a general increase in wood retention downstream, peaking in the river's lower reaches in response to hydrologic decay. Debris piles induced sediment deposition and the formation of in-channel islands. Following flood recession, debris piles and their associated sediments provided moist, organic-rich microhabitats, which were focal points for decomposition and secondary production, mimicking patterns reported from the channels of perennial streams and rivers. The ecological significance of retentive obstacles and associated organic debris is a feature common to all fluvial ecosystems, irrespective of their hydrologic regime.

Journal of the North American Benthological Societ↗