Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—Wood is an important component of small to medium-sized streams in forested regions, but has been poorly studied in agricultural areas. Our goals were to (1) characterize the abundance, size, and distribution of wood in low-gradient streams in two agricultural regions, (2) quantify the influence of reach- and landscape-scale factors on the abundance and distribution of wood in these streams, and (3) compare trends across two study areas. Wood abundance was quantified in stream reaches in two diverse agricultural regions of the Midwestern United States: central Michigan and southeastern Minnesota. Wood abundance was quantified in 71 stream reaches, and an array of channel, riparian zone, and landscape features were characterized. Multiple regressions were conducted to predict abundance from those explanatory variables. We found that large wood was relatively scarce in these low-gradient streams compared to low-gradient streams in forested regions. Mean log size was greater, but total abundance was lower in Minnesota than Michigan. In Minnesota, greatest wood abundance and greatest extent of accumulations were predicted in wide, shallow stream channels with high substrate heterogeneity and woody riparian vegetation overhanging the channel. Models were dominated by reach-scale variables. In Michigan, largest densities of wood and accumulations were associated with catchments in hilly regions containing urban centers, with low soil water capacity, wide, shallow stream channels, low coarse particular organic matter standing stocks, and woody riparian zones. Models contained both reach- and landscape-scale variables. Difference in the extent of agricultural and forest land use/cover between Michigan and Minnesota may explain the differences in the models predicting wood variables. Patterns in wood abundance and distribution in these Midwestern streams differ from those observed in high gradient regions, and in low-gradient streams within forested regions. This has important implications for ecosystem processes and management of headwater streams in agricultural regions.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—We describe a geographic information systems (GIS) framework for conducting research related to the functional linkages between rivers and multiscale landscape descriptors. Our purpose in presenting this framework is to provide a template for those wishing to conduct their own research and to encourage the adoption of standardized GIS methodologies when conducting stream ecological research. A standardized framework will strengthen the abilities of stream ecologists to communicate and reach broad conclusions regarding the relationships between rivers and conditions in the surrounding landscape and ultimately will improve conservation and management efforts. The GIS framework consists of three spatial units: stream reaches, riparian buffers, and catchments. The basic spatial unit is a stream reach, which is defined primarily as interconfluence stretches of water. A riparian buffer is that portion of the landscape within a bounded distance (e.g., 60 m) of a reach, while a catchment is the total land area draining to a reach. We distinguish between two forms of riparian buffers and catchments, reach and network, which helps with variable attribution and provides a method for differentiating between local and accumulative upstream conditions. Each of these spatial units can be delineated from the national hydrography and elevation data sets using ArcInfo GIS functions. Variables that are attributed to the spatial units either occur in preexisting GIS data sets (e.g., land use) or else are calculated (e.g., reach sinuosity) or statistically modeled (e.g., river temperature) using attributes available in preexisting GIS data sets. Several potential applications (landscape-based statistical modeling of reach-scale characteristics, identification of conservation gaps, and environmental impairment assessment and management) of this GIS framework are described to illustrate the benefits and flexibility of this approach in addressing common river conservation and management objectives.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—At broad scales, the types and intensities of human disturbances to ecosystems vary along natural gradients. Biological assemblages also vary with natural and human disturbance gradients. We defined least-disturbed conditions for a set of water chemistry, catchment, and site-scale indicators of disturbance, for 835 Environmental Monitoring and Assessment Program sites in the Mountains, Xeric, and Plains regions of 12 conterminous western United States. For each disturbance indicator, the definition of least-disturbed was adjusted by the sites’ locations on the primary natural gradients. For example, the least-disturbed condition for phosphorus in eastern Plains streams allowed up to 100 µg/L total phosphorus, while in western Plains streams, less than 30 µg/L total phosphorus was required. Sites were scored by the number of times they met the least-disturbed condition for all disturbance indicators. We also applied this process to score for most-disturbed condition. The importance of disturbance types varied regionally and along natural gradients. For example, catchment-scale disturbance measures did not distinguish between least- and most-disturbed sites for small streams at higher elevations, but were important for larger streams and at lower elevations. We examined regional-scale patterns in aquatic vertebrate species and assemblage metrics, and macrobenthos assemblage metrics at least- and most-disturbed sites. Most-disturbed sites in the Mountains and Xeric regions had higher proportions of nonnative and tolerant vertebrates and noninsect macrobenthos, and lower proportions of Ephemeroptera, Plecoptera, and Trichoptera individuals and taxa than did the least-disturbed sites. The Plains region has been extensively used by humans and showed less contrast between disturbance classes for most of these measures.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—We analyzed data from 38 sites on 31 large rivers in Wisconsin to characterize the influence of environmental variables at the basin, reach, and site scales on fish assemblages. Electrofishing and site habitat data were collected for a distance of 1.6 km per site. Environmental variables included conductivity, substrate, and fish cover at the site scale; distance to impoundments, dams, and length of riverine habitat at the reach scale; and land cover, climate, and geology at the basin scale. Of the 77 fish species found, 39 occurred in more than 10% of the sites and were retained for analyses of fish abundance and biomass. Redundancy analysis (RDA) was used to relate species abundance, biomass, and 16 assemblage metrics to environmental variables at the three spatial scales. The site and basin scales defined fishes along a gradient from high conductivity, fine substrate, and agricultural land cover to low conductivity, rocky substrate, and forested land cover. For abundance and biomass, the strongest assemblage pattern contrasted northern hog sucker <em>Hypentelium nigricans</em>, blackside darter <em>Percina maculata</em>, and logperch <em>P. caprodes </em>with common carp <em>Cyprinus carpio</em>, channel catfish <em>Ictalurus punctatus</em>, and sauger <em>Sander canadensis</em>. The <em>H. nigricans </em>group, along with high values of index of biotic integrity and some assemblage metrics (percent lithophilic spawners, percent round-bodied suckers), corresponded with the forested end of the ecological gradient, whereas the <em>C. carpio </em>group and percent anomalies corresponded with the agricultural end. Natural environmental conditions, including bedrock geology type, bedrock depth, surficial geology texture, basin area, and precipitation, also influenced the fish assemblage. Partial RDA procedures partitioned the explained variation among spatial scales and their interactions. We found that widespread land cover alterations at the basin scale were most strongly related to fish assemblages across our study area. Understanding the influence of environmental variables among multiple spatial scales on fish assemblages can improve our ability to assess the ecological condition of large river systems and subsequently target the appropriate scale for management or restoration efforts.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—Ecologists recognize that surrounding land use can influence the structure and function of aquatic ecosystems, but few studies have explicitly examined the relative effects of different types of land use on stream ecosystems. We quantified the relationships between different land uses (forested, urban, agricultural with or without riparian buffers) and stream physicochemical variables and resident fish assemblages in 21 southwestern Michigan streams. These streams were located within a single basin (Kalamazoo River) and ecoregion to minimize differences in natural landscape conditions. Streams responded to a gradient of land use, with forested streams having the least degraded water quality, physical habitat, and fish assemblages, and agricultural streams lacking buffers being the most degraded. Urban and agricultural streams with buffers displayed characteristics intermediate to forested and agricultural streams lacking buffers. In general, habitat complexity and water quality declined across this land-use gradient from forested to agricultural streams, whereas fish density, richness, and dominance by tolerant species increased along the land-use gradient. Although urban streams had lower percentages of altered land use (i.e., <40% urban) in their catchments compared to agricultural streams (i.e., >50% agriculture), both land uses appeared to have similar detrimental effects on streams suggesting higher per unit area impacts of urbanization on streams. The presence of forested riparian buffers along agricultural streams increased the complexity of instream habitat, but resulted in few benefits to fish assemblages, suggesting that stream water quality in altered landscapes may be constraining fish assemblages more than physical habitat.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—We describe a methodology for developing species–habitat models using available fish and stream habitat data from New York State, focusing on the Genesee basin. Electrofishing data from the New York Department of Environmental Conservation were standardized and used for model development and testing. Four types of predictive models (multiple linear regression, stepwise multiple linear regression, linear discriminant analysis, and neural network) were developed and compared for 11 fish species. Predictive models used as many as 25 habitat variables and explained 35–91% of observed species abundance variability. Omission rates were generally low, but commission rates varied widely. Neural network models performed best for all species, except for rainbow trout <em>Oncorhynchus mykiss</em>, gizzard shad <em>Dorosoma cepedianum</em>, and brown trout <em>Salmo trutta</em>. Linear discriminant functions generally performed poorly. The species–environment models we constructed performed well and have potential applications to management issues.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—–Describing the unique spatial context of any river unit requires integrating catchment and local valley characters. We believe that adding hydrologic regime and key fish species to standard geomorphic variables improves the delineation and characterization of river valley segments as ecological units. Valley segments constrain habitat units, and several segments together can encompass home ranges of mobile fishes. Segments can be accurately defined and characterized using maps and then analyzed across large geographic areas, making them practical for statewide planning and management. By incorporating prior knowledge from modeling landscape–river relationships, we interpreted multiple landscape maps to delineate and assign initial attributes to river valley segments. The resulting classification system provides a new, ecologically informed view of Michigan’s rivers that has helped managers better perceive and consider environmental patterns that constrain habitat and biological variation within and among individual rivers. It is being used throughout Michigan and regionally as a framework for fisheries and water management, conservation planning, and education.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—Iowa leads the nation in percentage of land area converted to cropland, with a resulting negative impact on streams. We examined physical habitat, land use, and fish assemblage data from 37 second- to sixth-order stream sites, representing 7 of the 10 ecoregions within Iowa. Physical habitat conditions varied widely among sites, with sand dominating substrate composition. A nonmetric multidimensional scaling ordination of physical habitat variables suggested a pattern of among-site similarities defined by a stream size axis, an axis contrasting sites dominated by either woody or rocky fish cover, and an axis characterizing degree of riparian canopy coverage. Bluntnose minnow <em>Pimephales notatus </em>and sand shiner <em>Notropis stramineus </em>were the most abundant fish species, followed by green sunfish <em>Lepomis cyanellus </em>and common carp <em>Cyprinus carpio</em>. These four species were collected in more than 80% of the sites. Fish species richness at sites averaged 22, ranging from 6 to 38, and fish index of biotic integrity (IBI) at sites averaged 47 (fair), ranging from 21 (poor) to 96 (excellent). Species richness and IBI were highest at sites characterized by rocky fish cover and relatively coarse substrates. Values for several physical habitat and land use variables were significantly different between sites with IBI ≤ 30 (fair) and sites with IBI ≥ 50 (good). We found a general pattern of IBI, species richness, total fish abundance, and width-to-depth ratio decreasing from the northeast to the southwest ecoregions, and percentage of unvegetated banks and bank slope increasing from northeast to southwest. Stable and vegetated banks, wide stream channels with coarse substrates, and rocky fish cover were associated with high biotic condition; while unvegetated and eroding banks, and deep channels with predominantly fine substrates were associated with lower biotic condition. Land use was calculated at three spatial scales: catchment, network riparian buffer, and local riparian buffer. We found few relationships of fish assemblages with land use, potentially due to sampling design and the pervasiveness of agriculture across Iowa. There is substantial variation among physical habitat, land use, and fish assemblage conditions across Iowa, due to a combination of geology, climate, zoogeography, and human alteration.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—Longitudinal analysis of the distribution and abundance of river fishes provides a context-specific characterization of species responses to riverscape heterogeneity. We examined spatially continuous longitudinal profiles (35–70 km) of fish distribution and aquatic habitat (channel gradient, depth, temperature, and water velocity) for three northeastern Oregon rivers. We evaluated spatial patterns of river fishes and habitat using multivariate analysis to compare gradients in fish assemblage structure among rivers and at multiple spatial scales. Spatial structuring of fish assemblages exhibited a generalized pattern of cold- and coolwater fish assemblage zones but was variable within thermal zones, particularly in the warmest river. Landscape context (geographic setting and thermal condition) influenced the observed relationship between species distribution and channel gradient. To evaluate the effect of spatial extent and geographical context on observed assemblage patterns and fish–habitat relationships, we performed multiple ordinations on subsets of our data from varying lengths of each river and compared gradients in assemblage structure within and among rivers. The relative associations of water temperature increased and channel morphology decreased as the spatial scale of analysis increased. The crossover point where both variables explained equal amounts of variation was useful for identifying transitions between cool- and coldwater fish assemblages. Spatially continuous analysis of river fishes and their habitats revealed unexpected ecological patterns and provided a unique perspective on fish distribution that emphasized the importance of habitat heterogeneity and spatial variability in fish–habitat relationships.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—The Topeka shiner <em>Notropis topeka </em>is a small cyprinid listed as endangered in 1999 due to an 80% reduction in its former range across six Great Plains states. Conservation and recovery plans require information on structural indices of existing populations, distribution, and habitat relations at several spatial scales. We examined physical habitat associations of Topeka shiners at the valley segment and reach scales, and associations with fish species using stepwise logistic regression. Fish and habitat data were collected at 52 sites. Habitat features at the valley segment scale were acquired using data from a geographic information system. At the valley segment scale, Topeka shiners were associated with stream condition variables (stream size, groundwater potential, channel slope, streamflow, network position) and land-cover variables (% pasture, % trees). At the reach scale, Topeka shiners were associated with low grazing and small trees in riparian zones, low bank height, less submerged vegetation, and coarse substrates. Topeka shiners were associated with five fishes that inhabit small, intermittent, warmwater streams. Evidence of greater abundance of Topeka shiner populations in our region compared to other regions may be a result of the natural character of the streams and associated wetlands, which can influence the habitat variables associated with Topeka shiners at both scales. We identified management strategies that would be effective at conserving habitat of Topeka shiners at large and local scales.