We evaluated the effects of periphyton elemental composition on the rate and ratios of N and P excretions by heptageniid mayfly larvae (Ephemeroptera). We predicted that excretion N:P ratios would relate primarily to mismatches between periphyton N:P and mayfly N:P. We immersed periphyton grown in a stream above (inlet: high N) and below (outlet: low N) a lake in P-amended or control (no P) water for 12 h to increase periphyton P content and reduce periphyton N:P. We then measured release rates and ratios of N and P from Cinygmula sp. larvae that had consumed periphyton from 1 of the 4 treatments. Reducing periphyton N:P increased consumer P excretion rates (range for P-amended periphyton: 0.055 ± 0.010 to 0.076 ± 0.022 μg P g⁻¹ dry mass [DM] h⁻¹; range for control periphyton: 0.027 ± 0.008 to 0.031 ± 0.006 μg P g⁻¹ DM h⁻¹). Mayflies that consumed P-amended periphyton from the inlet excreted N at a higher rate than did mayflies that consumed P-amended periphyton from the outlet (inlet P-amended: 0.661 ± 0.244 μg N g⁻¹ DM h⁻¹; outlet P-ammended: 0.245 ± 0.020 μg N g⁻¹ DM h⁻¹). We found some evidence for N:P imbalance between consumer and resource as a predictor of excretion N:P, but other factors also appear to influence nutrient release rates. Mayflies retained significantly more P than predicted by a stoichiometric mass-balance model, a result that suggests that mayflies might be able to store P when it available in their food and use it for growth when needed. Our model also suggests that assimilation efficiencies of N and P are more important determinants of excretion N:P than elemental imbalances between mayflies and their food. We conclude that elemental imbalances between lotic macroinvertebrates and their food resources play an important role in governing nutrient release rates and ratios, but that resource characteristics (e.g., periphyton community composition) and organismal physiology (e.g., nutrient assimilation efficiency) also must be considered. The possibly substantial role of these additional factors in determining nutrient excretion bears further investigation.

The strength of biotic interactions between native and invasive species is a key component of invasive species impact, but often is not quantified explicitly. We measured biotic interaction strengths between an invasive and a native endemic snail species in 2 streams in the western United States. The invasive freshwater New Zealand mudsnail, Potamopyrgus antipodarum, was the dominant snail in a 3^rd-order stream, and a closely related endemic snail, Pyrgulopsis robusta, was the dominant snail in a 1^st-order tributary stream. We compared consumer–resource (C–R) and consumer–consumer (C–C) per biomass interaction strengths in both streams using field enclosure experiments. Consumer effects on algal resources were strong and equivalent for both snail species in both streams. Invasion success of P. antipodarum could not be attributed to an unusually high rate of resource acquisition at either site because the 2 snails exerted equivalent C–R interaction strengths. However, C–C interactions were asymmetric; the invasive snail significantly limited growth of the native snail, whereas the native snail facilitated growth of the invasive snail. These effects were stronger in the stream where P. antipodarum was dominant. Thus, per biomass interaction strengths indicated that asymmetric interactions could be contributing to patterns of dominance by invasive and endemic stream snails.

The freshwater amphipod Gammarus pulex produces cohesive, cylindrical fecal pellets that are found in large numbers in the hyporheic sediments of UK chalk streams. We investigated the rate of fecal pellet accretion (deposition in situ egestion) in chalk streams using benthic fine particulate organic matter traps. We also assessed how long pellets remain intact by observing them over time in the laboratory at 3 different temperatures (4, 10, and 20°C). Traps were sampled seasonally (winter, spring, summer, and autumn), and their vegetation cover (marginal Nasturtium, mid-channel Ranunculus beds, or no vegetation) was recorded to see if accretion rate was affected by the presence of in-stream macrophytes. Accretion rate was strongly seasonal (10 to 20× higher in autumn than in winter, spring, and summer), but was not affected by vegetation cover. Laboratory experiments showed that fecal pellets remained intact for 81 d at 4°C and 10°C, whereas they began to break apart after 40 d at 20°C. Chalk streams remain at ∼10°C most of the year. Thus, pellets transferred to hyporheic sediments during autumn remain intact over winter and into spring. In autumn, Gammarus feed on allochthonous C in the form of dead leaves and this C is transferred to hyporheic sediments where it is stored, providing a substrate for microorganisms and a food resource for detritivorous invertebrates at other times of the year.

Recovery rates of different metrics (physiological, biological), trophic levels (phytoplankton, invertebrate consumers), and habitats (pelagic, benthic) were studied over a 16-y period in 10 boreal lakes recovering from acidification. Several of the metrics showed significant, positive trends over time that supported our expectations of biological recovery. Taxonomic diversity of phytoplankton assemblages, but not assemblage composition, showed early signs of recovery that were strongly related to increases in pH in both reference and acidified lakes. Results from benthic invertebrate assemblages were, however, equivocal. Littoral invertebrate taxon richness and diversity increased in both acidified and reference lakes, whereas sublittoral and profundal invertebrate assemblages of both lake groups showed clear negative trends. These findings indicate that sublittoral and profundal assemblages might be influenced by factors other than lake acidity, such as coincident changes in habitat quality (e.g., ambient O₂ and temperature). Our findings show that the selections of the group of organisms to monitor recovery and the habitat in which to monitor recovery must be considered carefully when designing and implementing programs to assess degradation and recovery.

In the last decades, zebra mussels (Dreissena polymorpha) have invaded many freshwater systems with severe consequences for entire communities. Most benthic macroinvertebrates, especially amphipods and chironomids, increase in abundance in the presence of zebra mussels. Increased structural complexity and an unknown biotic factor lead to this effect. Dreissena-associated factors that might influence populations of the native Gammarus roeselii and the invader Dikerogammarus villosus in Lake Constance, Central Europe, were investigated in laboratory experiments. These factors were: 1) increased structural complexity related to mussel shells, 2) Dreissena biodeposition, 3) chironomids, the presence of which is increased by biodeposited matter, and 4) Dreissena kairomones. In habitat-choice experiments, the native and omnivorous amphipod G. roeselii showed a preference for mussel shells with biodeposited material and for mussel shells with biodeposited material with chironomids, whereas the invasive and predatory amphipod D. villosus showed a preference only for mussel shells with biodeposited material with chironomids. In a kairomone y-maze experiment, both amphipods avoided zebra-mussel-conditioned lake water. These results indicate that habitat complexity and food availability, mediated directly or indirectly through biodeposited material, are the factors by which amphipod abundances are increased in the presence of Dreissena. Thus, biodeposited material can form an important new food resource, translocated from the pelagic zone to the benthos by zebra mussel filtration, and this biodeposited material might support a new detritus-based food web in the benthos.

Urban land use degrades stream ecosystems, but the nature and mechanisms of its effects on ecological processes, such as leaf breakdown, are poorly understood. Leaf litter breakdown has pivotal effects on energy and nutrient flows in stream ecosystems. Our goals were to test the effect of catchment urbanization on breakdown rates of leaves of 2 common riparian species in southeastern Australia and to identify the mechanisms responsible for changes in breakdown rates. Catchment urbanization was quantified as the percentage of catchment covered by impervious surfaces with connection to streams via stormwater sewers (effective imperviousness [EI]). Eucalyptus obliqua and Pittosporum undulatum leaf packs were placed in 6 streams that ranged from 0 to 20% EI. Packs were left for up to 69 d and, upon removal, were analyzed for mass loss, microbial activity, and abundance of associated shredding macroinvertebrates. Stream nutrient concentrations, temperature, and abrasive flow were measured as potential correlates of leaf breakdown. Pittosporum undulatum leaves broke down faster than those of E. obliqua. Breakdown rates of P. undulatum, but not E. obliqua, leaves increased as EI increased. Faster P. undulatum breakdown in streams with higher EI probably was caused by greater microbial activity (associated with higher temperatures and P concentrations) but not by differences in shredder abundance or abrasive flow. Elevated microbial activity in urban streams has a greater effect on leaf species with more-labile C than on leaf species with refractory C. In urban streams with large proportions of labile leaf litter, increased microbe-driven breakdown might decrease benthic organic matter availability and ultimately impair ecosystem function. Physical abrasion is not necessarily an important agent in faster breakdown, despite the increased hydrologic flashiness of urban streams. Effects of urbanization that accelerate leaf breakdown in streams could be mitigated through eradication of exotic riparian trees with leaves that are more labile than those of indigenous species and through management measures that reduce stream temperatures and nutrient concentrations.

We ask 3 questions that bear on the ability of aquatic scientists to influence public perceptions and public policy related to important environmental issues: 1) Why should scientists become better communicators? 2) What can we do to promote effective communication? 3) How can scientific societies help scientists meet this communication challenge? Shareholders in the environment include watershed groups, environmental interest groups, water-quality agencies, the general public, and the scientific community. These shareholders often are not professional scientists, but they influence the formation of natural resource policies. Individual aquatic scientists should be able to explain their science to other shareholders in a way that disabuses misconceptions of scientific principles, fosters informed dialogue concerning actions that affect aquatic ecosystems, and prevents poor decisions that can result from inaccurate information or short-sightedness. Scientific societies can effectively communicate the concerns of individual scientists by: 1) articulating the links between basic research and ecological principles to applied science, thereby building the foundation of science needed to support informed decision-making; 2) translating and disseminating results of scientific research to nonscientists to minimize inaccuracies, thereby fostering scientific literacy; and 3) taking proactive positions that promote infusion of sound science into policy debates on pressing environmental issues, especially those that bear on freshwater ecosystems.

We used an infrared video system and O₂ microelectrodes to record the behavior of 2 widespread burrowing insects, the predatory alderfly Sialis velata and the sediment-feeding mayfly Hexagenia limbata, to determine how they survive in anoxic sediment. Analysis of video recordings showed that both taxa have several common behaviors, including crawling, pushing sediment, turning around, and brushing their legs over their bodies for the purpose of cleaning. In contrast, these taxa differ in how they draw overlying oxic water into their burrows, i.e., H. limbata beats its abdominal gills, whereas S. velata undulates its abdomen. Feeding frequency also differs between the 2 taxa, i.e., the mayfly feeds frequently on sediment within its burrows, whereas S. velata feeds infrequently. Hexagenia limbata nymphs were rarely inactive (<1% of the time) and irrigated their burrows by gill-beating ¾ of the time, whereas S. velata nymphs were usually inactive (60% of the time). By vigorous irrigation of its burrow, H. limbata maintained its surroundings well oxygenated, whereas O₂ concentrations fluctuated more widely in burrows of the less-active S. velata. This behavioral difference between the species is consistent with their reported sensitivities to the low O₂ concentrations associated with eutrophication; in such situations, H. limbata is likely to be eliminated, whereas S. velata can persist. We estimate that O₂ lost from water passing through an H. limbata burrow is taken up mainly by the insect rather than diffusing into the surrounding sediment.

Creightons Creek, a rural stream in southeastern Australia, has been severely degraded by large-scale sedimentation of sand in the streambed. Our paper highlights the use of whole-stream metabolism measurements, fluorescein diacetate hydrolysis studies, and in situ enzyme mapping to examine the effect of sediment instability on benthic and hyporheic metabolism across seasonal and flow variations in Creightons Creek. Median gross primary production (GPP) and ecosystem respiration (ER₂₄) rates, determined over a 20-mo period with the whole-stream single-station diurnal O₂ change method, ranged between 0 and 0.5 g O₂ m⁻² d⁻¹ and 0.6 and 3.7 g O₂ m⁻² d⁻¹, respectively. These values gave photosynthesis/respiration (P/R) ratios between 0.00 and 0.41, indicative of a heterotrophic system. Creightons Creek was expected to support higher GPP because it has an open canopy, clear water, warm temperatures, and sufficient nutrients. However, this once-clay-bottomed stream now has an abrasive benthic layer of sand that moves continuously, even at low flows, and this layer has inhibited the growth of benthic primary producers (0–2 mg/m² of chlorophyll a). During high flows, when scour and abrasion from the bed movement were at a maximum, the highest relative enzyme activity was located in the hyporheic zone at a depth of 7 to 12 cm, where the sediment was more stable. During low flows, the highest enzyme activity occurred in the upper 4 cm of the sediment profile. Our study shows that the instability of the sediment bed is a major factor determining the rates and locations of metabolism.

The approaches that researchers use to generate knowledge typically vary with the state of knowledge within a discipline: description of phenomena during early phases, documentation of patterns and explanatory proposals during intermediate stages, and tests of causal hypotheses and theory building during mature stages. Ideally, the approaches used will result in the most efficient maturation of knowledge given the current state of knowledge. However, this idea has seldom been examined for freshwater benthic science, a habitat-based discipline. We evaluated the research approaches used by recent authors of papers published in the Journal of the North American Benthological Society (J-NABS) to assess the state of freshwater benthic science as perceived by freshwater benthic scientists and members of the North American Benthological Society (NABS). To do so, we categorized articles published during 2000 to 2005 in J-NABS with respect to the general research approach (taxonomic descriptions, case studies, descriptions of empirical relationships for predictive purposes, description of patterns sometimes resulting in hypothesis generation, hypothesis testing, and synthesis), how clearly authors addressed knowledge gaps, and more specific research methods used in a study. The following types of descriptive studies were most common: case studies (20%), pattern detection (21%), and quantification of empirical relationships (25%). Tests of hypotheses (25%) or syntheses (6%) were used less often than descriptive methods. Freshwater benthic science papers published in the journal Ecology were much more likely to involve hypothesis testing (54%) than were papers published in J-NABS. The papers published in J-NABS do not seem to be indicative of the true state of knowledge in freshwater benthic science in that authors often seemed to have sufficient information to justify more rigorous research approaches designed to test meaningful hypotheses. Furthermore, only 45% of authors clearly linked predictions or hypotheses to knowledge gaps, although such gaps were clearly defined in 72% of studies. Hypothesis statements clearly were not appropriate in 24% of studies, but their use in the other 76% of studies was highly variable. Hypotheses were explicitly stated in only 24% of studies, implied but not thoroughly developed in 28% of studies, and could have been developed in an additional 24% of studies. Many patterns in freshwater benthic science are now documented, and these documented patterns should provide solid foundations for proposing causal hypotheses, testing those hypotheses, and developing theory. Periodic analyses of the type we present here provide a means by which professional societies such as NABS can assess whether their journals are contributing to the growth of scientific knowledge in a manner consistent with their goals. Such empirical assessments should foster discussion of when and how editorial policies should be adjusted to promote efficient growth of knowledge.

River health monitoring traditionally has made use of structural measurements (water quality or taxonomic composition of aquatic organisms). We argue that a more complete assessment of river health should include functional metrics, such as rates of organic matter decomposition and ecosystem metabolism. Leaf breakdown links the characteristics of riparian vegetation with the activity of both aquatic invertebrates and microbial organisms and is affected by natural and human-induced variation in a wide range of environmental factors. Measurement of leaf breakdown is relatively simple and has modest equipment requirements. River metabolism (gross primary productivity and ecosystem respiration) measures the rates of production and use of organic C in river ecosystems as a whole, providing a direct estimate of the food base that determines life-supporting capacity. Metabolism measurements require more sophisticated equipment than do measurements of leaf breakdown, but improvements in technology have made metabolism measurements relatively easy. We review the factors that influence leaf breakdown and river metabolism and pay particular attention to the effects of human-induced environmental stressors. We also describe how measurements can be standardized and suggest criteria for interpreting functional measures in terms of river ecosystem health. Last, we consider the strengths and weaknesses of both methods as functional measures and provide recommendations for their use as biomonitoring tools.

Wetlands in the central Platte River basin provide numerous ecosystem services but have been diminished and degraded by agricultural practices and development. Wetland restoration is increasingly common in this region, but the success of restorations is virtually unknown. We sampled macroinvertebrates during spring 2003 and 2004 in restored (5–16 y old) and natural slough wetlands to assess restoration success. Simple measures (e.g., total abundance, biomass, diversity) were all similar in restored and natural wetlands. Communities were similar in natural and restored wetlands, but we observed some taxonomic differences. For example, abundances of Helisoma and Pisidium and abundance and biomass of amphipods were higher in natural than in restored wetlands, and leeches were collected only in natural wetlands. These results suggest that dispersal ability is a biotic filter limiting recovery and that these noninsects are good candidates for assessing recovery. Functional structure on the basis of abundance was similar between natural and restored wetlands, but some differences in biomass-based estimates were evident. For example, relative biomass of collector-filterers was higher in natural than in restored wetlands in 2003. Multivariate analyses indicated that factors such as hydroperiod might be more important than restoration status in shaping wetland macroinvertebrate communities. Furthermore, drought conditions constrained our sampling efforts and influenced temporal patterns, thereby underscoring the need for multiyear studies, especially under extreme environmental conditions. Our results indicate that wetland macroinvertebrate communities in this region are resilient and recover rapidly after restoration, but that ongoing restoration and management efforts should focus on hydrology, which might limit recovery in restorations and is a critical factor shaping wetland macroinvertebrate communities.

We evaluated the efficacy of different field sampling approaches for volunteers sampling macroinvertebrates in low-gradient streams. We used a series of analytical metrics to compare results using the Environmental Protection Agency (EPA) multihabitat, the Minnesota Pollution Control Agency multihabitat, and EPA single-habitat sampling protocols. We also investigated the effect of 2 scenarios in which volunteers fail to follow (and potentially bias) the widely used EPA multihabitat protocol by including either more snag and vegetated banks or more run and riffle habitat than prescribed by the protocol. We collected jab samples from cobble, snags, vegetated banks, submerged macrophytes, and sand in 4 contiguous 125-m reaches in an Anoka sand-plain stream in Minnesota. We identified up to 100 macroinvertebrates in each jab sample to family. We subjected a parent population of 40 jab samples/reach to a bootstrap analysis to sample and create metric or index scores 100 times without replacement for each of the 3 volunteer sampling methods and 2 biased scenarios. The EPA multihabitat protocol and the biased scenario in which woody debris and bank vegetation were oversampled yielded the highest diversity of organisms, whereas the biased scenario in which riffle and run habitats were oversampled yielded the lowest diversity. The EPA multihabitat protocol used correctly was more likely to indicate “good” water quality (on the basis of the EPA muddy-bottom narrative assessment tool designed for volunteers) than either biased sampling scenario. This result illustrates that poor field methods could result in underestimation of water quality.

For many years the Drunella lata complex of eastern North America consisted of 4 recognized species: 3 described from the Northeast, Drunella lata (Morgan), Drunella cornuta (Morgan), and Drunella cornutella (McDunnough), and 1, Drunella longicornis (Traver), from the southern Appalachian Mountains region. Recently, all 4 were synonymized to a single species (D. lata [Morgan], by priority) because morphological variation was perceived to be continuous and historical characterizations of species were viewed as arbitrary. We used genetic, morphometric, and life-history data to reevaluate D. lata, D. cornuta, and D. cornutella in northeastern North America, where all 3 morphotypes coexist in certain catchments and often in the same reach of stream. Pairwise genetic comparisons of coexisting morphotypes revealed fixed allelic differences at 6 to 10 of 19 allozyme loci, showing reproductive isolation among D. cornuta, D. cornutella, and D. lata even within the same reach of stream. Morphometric studies confirmed their distinction by uncovering significant differences in a suite of characters, some with nonoverlapping ranges (i.e., diagnostic). The 3 taxa also were shown to be segregated ecologically by consistent differences in seasonality, thermal requirements, and spatial distribution. We conclude that D. cornuta, D. cornutella, and D. lata are all worthy of full species status, and so reinstate D. cornuta and D. cornutella. Diagnostic descriptions are provided and existing keys emended.

Fine particulate organic matter (FPOM) plays a critical role in structuring and sustaining stream food webs by providing an essential resource for various organisms. Our goal was to elucidate FPOM dynamics by determining chemical properties, microbial respiration, and in situ decomposition rates of different FPOM fractions in relation to the parent coarse particulate organic matter (CPOM). FPOM (100–500 μm) of defined quality was produced by feeding 5 types of CPOM to shredding amphipods (Gammarus spp.): wood, filamentous green algae, and conditioned leaves of ash, alder, and oak. Feeding and defecation of Gammarus homogenized POM of the different origins in terms of proximate lignin and nutrient content. FPOM had higher lignin content (20.5–45.6%) than did parental CPOM (5.7–26.8%), whereas molar C:N decreased during the conversion of CPOM (12–109) to FPOM (10–34). Microbial respiration rates on leaf-derived FPOM were lower (0.13–0.45 mg O₂ g⁻¹ C h⁻¹) compared to rates measured for parent CPOM (0.37–0.80 mg O₂ g⁻¹ C h⁻¹). Furthermore, microbial decomposition over 2 mo in a stream was slower for leaf-derived FPOM (k < 0.0015/d) than for the parent CPOM (k = 0.0013–0.0049/d), and this pattern resulted in a positive correlation between rates of microbial respiration and decomposition. Overall, our data indicate that transformation of CPOM to FPOM has a homogenizing effect toward lower C quality, which, in turn, reduces microbial activity and decomposition rate.

Inverse analysis is a promising method for addressing a common problem in stream ecology: how to estimate material and energy flows through food webs when the total number of flows greatly exceeds the number of measured flows. Inverse analyses provide solutions to systems of linear difference equations, where each equation corresponds to a flow between 2 foodweb compartments. Physiological and isotopic constraints are used to reduce the number of possible solutions and to ensure that flow magnitudes are realistic. We used inverse methods to develop models of C and N flows through the food web in Kaiwiki Stream, a forested stream on the island of Hawaii. The empirical data used in the models included measurements of respiration and detritus ingestion and particulate organic matter dynamics. Constraints for the models included stable isotope ratios and assimilation and production efficiencies. Sensitivity analyses indicated that the models were robust to changes in the values of most empirical measurements. The models elucidated community- and ecosystem-level properties of Kaiwiki Stream that would have been obscured in simpler tracer or budget models. Among those properties are the flows of dissolved organic C and N through the food web, the roles of bacteria, fungi, and fruit in metazoan diets, and the differences in primary dietary sources of C and N, indicating differential assimilation of ingested food. The modeled C and N flow networks for Kaiwiki Stream had dissimilar structures, which might reflect a combination of differential C and N assimilation and dissimilar effects of physical processes on C and N flows between nonliving pools. Rates of ecosystem processes estimated by inverse analysis (e.g., gross primary productivity, community respiration) were comparable with rates measured in other tropical and temperate forested streams. Our study demonstrates the utility of inverse methods for reconstructing food webs, estimating material and energy flow rates, and generating hypotheses.

Recent court cases have questioned whether all headwater streams are jurisdictional waters under the US Clean Water Act. Rapid field-based indicators of hydrologic permanence are needed for making jurisdictional determinations. Our study objectives were to: 1) identify physical characteristics of forested headwater streams that best distinguish perennial, intermittent, and ephemeral reaches and 2) assess the applicability of existing rapid field-based tools for classifying hydrologic permanence across a wide geographic range. We surveyed reach- and drainage-scale characteristics at 113 sites across 10 study forests in the US. Streams in 4 core forests (61 core sites) were sampled over 2 consecutive years and were used in model construction. Streams in 6 satellite forests (72 satellite sites) were used to validate the models over a broader geographic range. Discriminant function models successfully differentiated hydrologic permanence categories at core sites. Drainage area, the Ohio Environmental Protection Agency Headwater Habitat Evaluation Index (HHEI), and the North Carolina Department of Water Quality Stream Classification Method (NCSC) were strongly correlated with the discriminant function that separated ephemeral from perennial and intermittent sites. Entrenchment ratio was the most consistent variable discriminating intermittent from perennial sites across the core forests. The models had mixed results when applied to the validation data set, but did classify correctly most intermittent and ephemeral sites. Classification trees were used to assess broad regional applicability of existing rapid field-based protocols and to identify important metrics. Scores from the Rapid Bioassessment Protocol Habitat Assessment, HHEI, and NCSC all clearly distinguished ephemeral from intermittent and perennial sites, but no differences were detected between intermittent and perennial sites across all sites. However, data from core sites do indicate that a suite of physical variables can be used successfully to identify hydrologic permanence at regional scales.

Predictive modeling is used increasingly often in freshwater bioassessment. These models are routinely applied across broad geographical areas, yet the influence of spatial extent on model performance has not been assessed directly. We examined the influence of changing geographical extent on the performance of River InVertebrate Prediction and Classification System (RIVPACS)–type predictive models of benthic macroinvertebrates in boreal headwater streams representative of reference conditions. Separate models were constructed for 2 hierarchical extents: within ecoregions (middle boreal and north boreal) and across ecoregions. We assessed the accuracy and precision of the models using root mean squared error (RMSE) of the observed/expected (O/E) ratio of the number of predicted taxa. We compared the RMSE of the within-ecoregion models to that of the across-ecoregions models. We tested the models using 2 thresholds for probability of species occurrence (P_t): P_t = 0 (all predicted taxa) and P_t = 0.5 (only common taxa). We also assessed the importance of catchment vs local habitat variables as predictors of macroinvertebrate fauna. Within the 2 ecoregions, region-specific models performed better than the across-ecoregions model with P_t = 0 , but the difference in performance of models with different regional extents decreased when P_t = 0.5. Catchment area and stream slope were the only consistently significant predictor variables, but overall, only minor differences were found in the relative importance of catchment vs local attributes. Models with P_t = 0.5 performed better than those with P_t = 0 ; this result suggests that models based only on common taxa might perform more consistently than models based on all taxa in the assessment of headwater streams. However, the expected number of taxa would then become very low (mean: 8.0–12.6 with P_t = 0.5), which might impede detection of human impact. Alternative approaches that do not rely solely on taxon occurrences but also incorporate aspects of assemblage composition might be needed for assessment of headwater streams.

Surface coal mining with valley fills has impaired the aquatic life in numerous streams in the Central Appalachian Mountains. We characterized macroinvertebrate communities from riffles in 37 small West Virginia streams (10 unmined and 27 mined sites with valley fills) sampled in the spring index period (March–May) and compared the assessment results using family- and genus-level taxonomic data. Specific conductance was used to categorize levels of mining disturbance in mined watersheds as low (<500 μS/cm), medium (500–1000 μS/cm), or high (>1000 μS/cm). Four lines of evidence indicate that mining activities impair biological condition of streams: shift in species assemblages, loss of Ephemeroptera taxa, changes in individual metrics and indices, and differences in water chemistry. Results were consistent whether family- or genus-level data were used. In both family- and genus-level nonmetric multidimensional scaling (NMS) ordinations, mined sites were significantly separated from unmined sites, indicating that shifts in community structure were caused by mining. Several Ephemeroptera genera (e.g., Ephemerella, Epeorus, Drunella) and their families (Ephemerellidae, Heptageniidae) were correlated most strongly with the primary NMS axis (r > 0.59 for these genera; r > 0.78 for these families). These same Ephemeroptera were absent and, thus, eliminated from most of the mined sites. Total Ephemeroptera richness and relative abundance both declined with increasing mining disturbance. Several other metrics, such as richness, composition, tolerance, and diversity, clearly discriminated unmined vs mined sites. Most family-level metrics performed well and approximated the strength of genus-based metrics. A genus-based multimetric index (MMI) rated more mined sites as impaired than did the family-based MMI. Water-quality variables related to mining were more strongly correlated to NMS axis-1 scores, metrics, and MMIs than were sedimentation and riparian habitat scores. Generally, the correlations between the genus-level MMI and water-quality variables were stronger than the correlations between the family-level MMI and those variables. Our results show that mining activity has had subtle to severe impacts on benthic macroinvertebrate communities and that the biological condition most strongly correlates with a gradient of ionic strength.

International trade frequently moves mollusks around the globe, thereby increasing their opportunity to cause ecological and economic damage. Recent genetic studies have confirmed the identity of South American applesnails (Pomacea insularum) in the southeastern US, but limited literature exists on this species. Understanding fecundity provides direct insight into the invasive potential of mollusks. Our study documents P. insularum fecundity in Texas and offers comparisons with the closely related global invader P. canaliculata. We quantified P. insularum clutch and hatchling physical characteristics and examined field and laboratory hatching success. Clutches contained thousands of eggs (mean = 2064 eggs), and clutch size tended to increase over the reproductive season. Clutches exhibited average field and laboratory hatching efficiencies (number of hatchlings/total number of eggs) near 70 and 30%, respectively. Notably, several clutches hatched at 80% or higher in the field. Exotic P. insularum deposit more eggs/clutch than the related invader P. canaliculata, but we do not yet know how seasonal hatching efficiencies compare. However, even with a conservative estimate of 1 to 10% survival to adulthood, the average P. insularum clutch yields 14 to 144 new applesnails. The high fecundity of P. insularum translates into considerable ecological impact because adult females can contribute >1 clutch/wk over an extended growing season in the southeastern US. The need for research has increased with the emergence of P. insularum populations in the fragile Florida Everglades. We advocate life-history studies like ours to help understand the invasion potential of applesnails and other invasive mollusks.

Patterns of chironomid species richness were compared between 1 permanent and 1 temporary Mediterranean mountain stream in the same basin. From 1991 to 1995, pupal exuviae were collected at irregular intervals in the permanent stream, but the temporary stream was dry because of a long-lasting drought in the region. From March 1996 to March 2000, pupal exuviae were collected fortnightly in both streams. In contrast to other comparative studies that found more species in permanent than in temporary streams, our 2 streams harbored similar temporal γ and α diversity during the 1996 to 2000 study period. This result might be explained by the relatively long time the temporary stream was flowing. In addition, the temporary stream showed higher temporal β diversity than the permanent stream, a result that might be attributable to the greater variability in temperature and substrates in the temporary stream. Spates scarcely affected α diversity and favored colonization by new species in both streams, a result that supports the patch-dynamic concept of streams. A period of >1 y without spates also resulted in colonization by new species in the permanent stream, but led to a pool phase in the temporary stream that reduced α diversity considerably. Overall, both streams had similar chironomid species richness and species rarity and high faunal complementarity. These results support the view that temporary aquatic habitats deserve consideration in conservation plans designed to protect species and their habitats.

Small forested streams typically are dominated by heterotrophic processes and rely on retained allochthonous material, including coarse particulate organic matter (CPOM), to support stream food webs. Within the Ottawa National Forest (ONF), Michigan, 3 small streams of similar size (discharge <130 L/s) were used to measure the retention (e.g., particle travel distance) of various allochthonous particles. Allochthonous CPOM consisted of natural (Ginkgo biloba leaves, white pine needles, and sugar maple sticks) and analog (wood dowels of 3 lengths, paper triangles, and paper rectangles) particles to test if particle type affected travel distance and if analog particles would be a good surrogate for natural particles. Travel distances of the particles were measured monthly from June to November 2003. Physical parameters, such as velocity, depth, wood density and volume, and substrate size, were measured in each reach to determine if instream characteristics affected coarse particle travel distances. Mean travel distance was >7 m for all particle types. Travel distance was not significantly different between particle analogs and natural particles or among natural particles. Significant differences in particle travel distance (p < 0.001) occurred among wood dowel lengths and between paper rectangles (mean ± standard error, 4.9 ± 0.3 m) and paper triangles (5.9 ± 0.5 m). For all particles, travel distance was positively related to current velocity, discharge, and stream depth and negatively related to instream wood volume and density (p < 0.05), but travel distances were not significantly different among months. Visual observation also indicated that particle flexibility and surface area reduced particle travel distance. Our results suggest that: 1) low-gradient streams in mixed coniferous–deciduous forests of Upper Michigan are highly retentive of a range of CPOM types and are more retentive than are other low-gradient streams; 2) the analog particles were reasonable mimics of natural particle transport, and the different lengths of wood dowels affected travel distance; and 3) instream hydraulic and physical parameters, especially large woody debris, were major factors in CPOM retention. In forested headwater streams, the ability of the channel to efficiently retain multiple types of allochthonous material might be crucial to overall stream productivity.

We compared the effects of 2 common grazers, southern redbelly dace (Phoxinus erythrogaster) and crayfish (Orconectes spp.), on ecosystem structure and function in experimental streams with pool and riffle habitats. Our goal was to identify potentially overlapping roles of these grazers in these systems. Measures of ecosystem structure included algal filament length, particulate organic matter (POM), densities of invertebrate taxa, and algal biomass. Ecosystem function was measured as gross primary productivity (GPP). Biomass-dependent effects of crayfish and dace on ecosystem properties were compared in autumn 2005 when mean water temperature was 12.9°C (range 7.6–27.9°C). Increasing crayfish biomass did not influence ecosystem properties, but increasing dace biomass negatively affected algal filament length and chironomid abundance and positively affected chydorid abundance. Effects of moderately high biomasses of dace and crayfish were compared in spring 2006 when mean water temperature was 21.4°C (range 17.5–29.9°C). Algal filament lengths were generally low relative to values obtained in autumn 2005 in both dace and crayfish treatments. In addition, algal filament length was shorter and chironomid density was lower in crayfish than in dace streams. The contrasting effects of dace and crayfish across sampling days, seasons, and habitats led us to hypothesize that physiological and behavioral traits of these species might limit the redundancy of their effects on ecosystems across broad spatial and temporal scales.

We used complementary information collected using different conceptual approaches to develop recommendations for a stream nutrient criterion based on responses of algal assemblages to anthropogenic P enrichment. Benthic algal attributes, water chemistry, physical habitat, and human activities in watersheds were measured in streams of the Mid-Atlantic Highlands region as part of the Environmental Monitoring and Assessment Program of the US Environmental Protection Agency. Diatom species composition differed greatly between low- and high-pH reference streams; therefore, analyses for criterion development were limited to a subset of 149 well-buffered streams to control for natural variability among streams caused by pH. Regression models showed that TP concentrations were ∼10 μg/L in streams with low levels of human activities in watersheds and that TP increased with % agriculture and urban land uses in watersheds. The 75^th percentile at reference sites was 12 μg TP/L. Chlorophyll a and ash-free dry mass increased and acid and alkaline phosphatase activities decreased with increasing TP concentration. The number of diatom taxa, evenness, proportion of expected native taxa, and number of high-P taxa increased with TP concentration in streams. In contrast, the number of low-P native taxa and % low-P individuals decreased with increasing TP. Lowess regression and regression tree analysis indicated nonlinear relationships for many diversity indices and attributes of taxonomic composition with respect to TP. Thresholds in these responses occurred between 10 and 20 μg/L and helped justify recommending a P criterion between 10 and 12 μg TP/L to protect high-quality biological conditions in streams of the Mid-Atlantic Highlands.