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1. We used the habitat template approach to test the hypothesis that substratum stability, freezing and nutrient supply were determinants of community structure in 19 headwater streams of arctic Alaska. Streams were selected from five categories: glacier ( n = 3), mountain (4), mountain spring (4), tundra spring (4) and tundra (4). 2. Bed movement among streams ranged from 0 to 97% during a ∼2-month summer season. Glacier and mountain streams had significantly higher bed movement than tundra and spring streams ( P < 0.001). 3. All glacier and tundra streams froze solid during winter; all mountain spring streams remained unfrozen. Freezing among mountain and tundra spring streams was variable, with a subset of streams flowing throughout winter. 4. With the exception of glacier streams, which showed high concentrations of NH and NO ( P < 0.001), differences in nutrient concentrations among stream types were not significant. 5. Algal taxon richness was greatest in tundra springs (13 taxa) and lowest in glacier streams (five taxa, P < 0.001), as was algal biovolume (7350 versus 687 mm m, P < 0.001). Macroinvertebrate taxon richness was lower in glacier streams (4.7 ± 1.7, P < 0.005) than the other stream types (20.5-25.0 taxa), and biomass was greater in mountain springs (4837 mg m) and tundra springs (3367 mg m, P < 0.001). 6. Multidimensional scaling and multiple regression analyses of macroinvertebrate (biomass) and periphyton (biovolume) indicated that a 2-dimensional habitat template with bed movement and freezing as axes provides an accurate model of major factors controlling the community structure of headwater streams in arctic Alaska. [ABSTRACT FROM AUTHOR]

1. Species-discharge relationships (SDR) are aquatic analogues of species-area relationships, and are increasingly used in both basic research and conservation planning. SDR studies are often limited, however, by two shortcomings. First, they do not determine whether reported SDRs, which normally use complete drainage basins as sampling units, are scale dependent. Second, they do not account for the effects of habitat diversity within or among samples. 2. We addressed both problems by using discrete fish zones as sampling units in a SDR analysis. To do so, we first tested for longitudinal zonation in three rivers in the southeastern U.S.A. In each river, we detected successive ‘lower’, ‘middle’, and ‘upper’ fish zones, which were characterized by distinct fish assemblages with predictable habitat requirements. Because our analyses combined fish data from multiple sources, we also used rarefaction and Monte Carlo simulation to ensure that our zonation results were robust to spurious sampling effects. 3. Next, we estimated the average discharge within each zone, and plotted these estimates against the respective species richness within each zone (log10 data). This revealed a significant, linear SDR ( r2 = 0.83; P < 0.01). Notably, this zonal SDR fit the empirical data better than a comparable SDR that did not discriminate among longitudinal zones. We therefore conclude that the southeastern fish SDR is scale dependent, and that accounting for within-basin habitat diversity is an important step in explaining the high diversity of southeastern fishes. 4. We then discuss how our zonal SDR can be used to improve conservation planning. Specifically, we show how the slope of the SDR can be used to forecast potential extinction rates, and how the zonal data can be used to identify species of greatest concern. [ABSTRACT FROM AUTHOR]

1. Studies of North American streams have shown that hydraulic parameters and stream geomorphology can explain unionid mussel abundance at both the reach and catchment scale. However, few studies have examined applicability of hydrogeomorphic variables across broader spatial scales, such as across whole catchments, or have elucidated conditions under which spates can affect mussel populations in streams. 2. We quantified freshwater mussel abundance and species richness and their physical habitat at 24 sites in eight streams in southern Appalachian catchments in 2000 and 2001. In addition, we modelled site-specific hydraulic parameters during summer baseflow and bankfull stages to estimate high- and low-discharge conditions, respectively. 3. Mussel abundance was related to stream geomorphology, whereas richness was related to stream size. Baseflow habitat parameters explained only minor variation in abundance or richness, and both measures were highly correlated with mean current velocity or stream size. Bankfull shear stress composed a relatively low proportion of overall mussel habitat variability, but it accounted for significant variation in abundance and richness. 4. Mussel abundance was highly variable at sites subject to low-shear stress during spates, whereas abundance always was low at sites subject to high-shear stress. These data suggest that habitat conditions during floods, rather than those at summer baseflow, limit the abundance of mussels in Appalachian streams. These data also suggest that mussel abundance and assemblage structure may be sensitive to any changes in channel geomorphology and hydraulic conditions that might result from land use in the catchment. [ABSTRACT FROM AUTHOR]

1. Macroinvertebrate production and macrophyte growth were studied in logged and unlogged sections of a sand-bottomed, low-gradient, blackwater stream on the Coastal Plain of Virginia, U.S.A. A section of the catchment had been clear-cut 3 years prior to sampling. No logging occurred in the upstream area of the catchment, which had experienced almost no land disturbance by humans for over 100 years. 2. A primary difference among the logged and unlogged sections of the stream was in the abundance of macrophytes. The combined biomass of Sparganium americanum and of Chara sp. was over 300-times greater in the logged than the unlogged section. 3. Annual macroinvertebrate production in the sediment was higher in the unlogged section (41 g dry mass m–2) than in the logged section (25 g m–2). 4. Annual macroinvertebrate production on Sparganium was higher in the logged section (10 g m–2 of plant surface area) than in the unlogged section (6 g m–2). Annual production associated with Chara, which occurred only in the logged section, was 196 g m–2 of stream bottom covered by this plant. 5. Whole-stream annual macroinvertebrate production, calculated by summing habitat-specific production that was weighted by habitat availability, was greater in the logged section (103 g m–2) than in the unlogged section (41 g m–2). Sediments supported 99% of the annual production in the unlogged section, whereas macrophytes supported 76% in the logged section. 6. Much of the additional macroinvertebrate production in the logged section was by collector-filterers living on macrophytes. Production by collector-gatherers was also greater in the logged section, whereas production by other functional feeding groups changed little with logging. 7. Although logging along high-gradient, rocky streams also results in increased macroinvertebrate production, that increase often is stimulated by greater periphyton growth rather than the macrophyte growth observed in this low-gradient stream. [ABSTRACT FROM AUTHOR]