DNA barcoding is becoming widely used to provide species identifications in a variety of invertebrate taxa, but there has been little application so far to environmental monitoring. Here we make this connection using a group of aquatic macroinvertebrates, chironomids of the tribe Tanytarsini. Tanytarsini larvae commonly collected in biological surveys can be difficult to identify to species because of high intraspecific variability and because not all larvae are linked to described adult life stages. We examined whether Tanytarsini larvae could be reliably identified to species with polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) using the mitochondrial cytochrome oxidase I (COI) gene. Tanytarsini were collected from lentic environments and consisted of 3 common genera (Cladotanytarsus, Paratanytarsus, and Tanytarsus). COI PCR-RFLP profiles could discriminate larvae, including morphologically similar larvae, and could be linked to described life stages. COI sequences identified the same species from different localities. DNA identification has potential for distinguishing Tanytarsini species and facilitating their use as biological indicators.

Sediment bacteria are ubiquitous and important to the cycling of organic matter and nutrients in streams. We experimentally investigated the effect of sediment grain size on bacterial communities by using artificial substrata of different sizes incubated in a northeast Ohio (USA) stream. We examined abundances of specific bacterial taxa with fluorescent in situ hybridization. In general, taxon abundances were highest on 5.0-mm particles and lowest on 0.1-mm particles, and all taxa responded similarly to particle size. Few differences in abundance were found between substrata incubated in a pool or riffle in the stream or between substrata with or without organic matter amendment. Particle surface area and particle packing (sediment permeability) both affected bacterial abundance in our experiments. However, our results suggest that other factors, such as chemistry of interstitial spaces and susceptibility to predation, also contribute to differences in abundance among substrata of different particle sizes.

We compared the accuracy, precision, and efficiency of 2 timesaving techniques to a standard laboratory procedure for processing benthic samples used to estimate secondary production. In the coarse-sieve technique, production was quantified from invertebrate biomass collected in a 2-mm sieve and corrected for retention probabilities of individual organisms. In the sieve-fractionated technique, production per sieve was quantified from the total biomass and average body mass of organisms collected in a geometric series of 9 sieves. Production estimates for the entire assemblage (coarse-sieve: r² = 0.96, sieve-fractionated: r² = 0.99, n = 57) and for individual taxa (coarse-sieve: r² = 0.84, n = 308; sieve-fractionated: r² = 0.99, n = 544) were strongly related to production estimates derived from standard processing techniques. The analytical error introduced by coarse-sieve (entire assemblage: residual mean square [RMS] = 0.014, individual taxa: RMS = 0.001) and sieve-fractionated (entire assemblage: RMS = 0.070, individual taxa: RMS = 0.0004) techniques was insignificant relative to the variance of production estimates among replicates (entire assemblage = 0.150, individual taxa = 0.329). Coarse-sieve and sieve-fractionated techniques required, on average, only 18% and 63% of the time required for standard processing, respectively, but coefficients of variation for production means of the entire assemblage differed by <1% between standard and timesaving techniques. These timesaving techniques for processing benthic samples increase the feasibility of studies of secondary production that require multiple sampling sites and dates, and thus, should further our understanding of the mechanisms that control stream productivity.

We measured the effects of timber-harvest condition (clearcut and forested) and flow duration (perennial and intermittent) on emergent aquatic insect assemblages at 20 headwater streams in the Central Oregon Coast Range. Clearcut streams had been logged to the stream banks within 2 y prior to the start of our study. Adult aquatic insects were sampled from a 40-m reach at each study stream in 3 seasons: summer, autumn, and spring. Emergent insects were strong indicators of harvest condition and, regardless of flow duration or season, more aquatic insects emerged from streams in clearcut catchments than in forested catchments. Plecoptera had higher emergence rates from intermittent streams than from perennial streams in spring. Functional feeding group composition was not apparently affected by harvest condition or flow duration. Taxon richness was slightly higher at clearcut than at forested streams, primarily because of the occurrence of rare taxa at clearcut streams. Nonmetric multidimensional scaling (NMS) ordination of emergent aquatic insect assemblages showed community patterns that varied by season and harvest condition, but little by flow duration. Stream canopy % cover, stand age, logging debris (% slash), and substrate composition differed between clearcut and forested streams and were strongly correlated with NMS axes. Taxa that responded to conditions created by logging, such as % slash or canopy opening, contributed to differences in assemblages between headwater streams flowing through clearcut and forested catchments.

We examined the efficacy of the photosystem II inhibitor 3-(3,4-diclorophenyl)-1,1-dimethyl urea (DCMU) for inhibition of algal photosynthesis in periphyton associated with submerged decomposing litter of Typha angustifolia. We also investigated the possible nontarget effects of DCMU exposure on heterotrophic microorganisms (i.e., bacteria and fungi) and extracellular enzyme activity associated with decaying litter. Standing-dead Typha leaf litter was submerged for 34 and 73 d, returned to the laboratory, and used for controlled laboratory experiments that examined the effect of DCMU on algal ([¹⁴C]bicarbonate, pulse-amplitude modulated fluorometry), bacterial ([³H]leucine), and fungal ([¹⁴C]acetate) production. Simultaneous assays also were conducted to examine the effect of DCMU on the activities of 4 extracellular enzymes (β-glucosidase, β-xylosidase, leucine-aminopeptidase, and phosphatase). DCMU significantly inhibited algal photosynthesis in light-exposed periphyton (p always < 0.0003), with strong inhibitory effects occurring within 5 min after exposure to DCMU. In contrast, DCMU had no significant direct effect on bacterial (p > 0.5) or fungal production (p > 0.3). Extracellular enzyme activities also were not significantly affected by exposure to DCMU. Heterotrophic microbial and enzyme activity assays were conducted in darkness to avoid any indirect effects of DCMU (i.e., heterotrophic responses to the inhibition of photosynthesis, rather than to DCMU itself). The apparent lack of nontarget effects of DCMU on heterotrophic microbial processes, combined with good efficacy against algal photosynthesis, suggest that DCMU may a useful selective inhibitor for investigations of interactions among litter-inhabiting microbiota.

Aquatic foodweb models for 2 seasons (relatively high- [March] and low-flow [August] conditions) were constructed for 4 reaches on the Truckee River using δ¹³C and δ¹⁵N data from periphyton, macroinvertebrate, and fish samples collected in 2003 and 2004. The models were constructed with isotope values that included measured periphyton signatures and calculated mean isotope values for detritus and seston as basal food sources of each food web. The pseudo-optimization function in Excel's Solver module was used to minimize the sum of squared error between predicted and observed stable-isotope values while simultaneously solving for diet proportions for all foodweb consumers and estimating δ¹³C and δ¹⁵N trophic enrichment factors. This approach used an underdetermined set of simultaneous linear equations and was tested by running the pseudo-optimization procedure for 500 randomly selected sets of initial conditions. Estimated diet proportions had average standard deviations (SDs) of 0.03 to 0.04‰, and SDs of trophic enrichment factors ranged from <0.005 to 0.05‰ based on the results of the 500 runs, indicating that the modeling approach was very robust. However, sensitivity analysis of calculated detritus and seston δ¹³C and δ¹⁵N values indicated that the robustness of the approach is dependent on having accurate measures of all observed foodweb-component δ¹³C and δ¹⁵N values. Model results from the 500 runs using the mean isotope values for detritus and seston indicated that upstream food webs were the simplest, with fewer feeding groups and trophic interactions (e.g., 21 interactions for 10 feeding groups), whereas food webs for the reach downstream of the Reno–Sparks metropolitan area were the most complex (e.g., 58 interactions for 16 feeding groups). Nonnative crayfish were important omnivores in each reach and drew energy from multiple sources, but appeared to be energetic dead ends because they generally were not consumed. Predatory macroinvertebrate diets varied along the river and affected estimated trophic positions of fish that consumed them. Differences in complexity and composition of the food webs appeared to be related to season, but could also have been caused by interactions with nonnative species, especially invasive crayfish.

Elevated atmospheric CO₂ increases plant C fixation, and much of the soluble C content of deciduous leaf litter entering streams is leached as dissolved organic C (DOC). The effects of DOC from trembling aspen (Populus tremuloides Michaux) leaf litter grown under elevated (ELEV = 720 ppm) and ambient (AMB = 360 ppm) CO₂ on stream periphyton were measured during a 35-d experiment in outdoor artificial stream chambers. Crayfish feeding preferences for periphyton grown in AMB and ELEV treatments were evaluated in short-term foraging trials using a Y-maze. Periphyton was sampled through time for ash-free dry mass (AFDM), chlorophyll a, total C:N, algal biovolume and species composition, and bacterial productivity and biomass. Leaf litter from plants grown under ELEV CO₂ produced higher concentrations of refractory DOC than did leaf litter from plants grown under AMB CO₂, and chlorophyll a concentrations were lower in periphyton enriched with ELEV DOC than in periphyton enriched with AMB DOC. ELEV DOC did not significantly affect bacterial productivity and biomass or total periphyton C:N, but cyanobacterial biovolume was higher in ELEV algal assemblages than in AMB algal assemblages after 35 d. AMB algal assemblages were dominated by the diatom Epithemia adnata var. proboscidea, which contains N-fixing endosymbionts. Orconectes virilis crayfish preferred AMB periphyton stimulus when offered the choice of AMB and ELEV stimuli or AMB and control stimuli. Our results suggest that DOC from trembling aspen leaf litter produced under ELEV CO₂ alters algal accrual and species assemblages of stream periphyton, and this shift in basal resource quantity and quality could affect feeding preferences of crayfish.

The Asian clam Corbicula has become established worldwide in a wide range of freshwater ecosystems. Corbicula fluminea invaded Lake Constance (Central Europe) between 2000 and 2002 and has reached densities up to 3520 individuals >5 mm in length per square meter in sandy areas. However, the effect of this species on other benthic invertebrates remains unclear. Here, we show that ecosystem engineering via shell production by C. fluminea in Lake Constance considerably increases availability of hard surfaces in primarily soft-bottomed habitats. We studied effects of C. fluminea on littoral communities of sandy habitats using boxes containing bare sand, sand with C. fluminea shells (2000/m²), and sand with live clams (1000/m²). After 2 mo of exposure, the overall benthic community did not differ among treatments, but density of the mayfly Caenis spp. increased in boxes containing shells compared to the boxes containing sand or sand with live clams (analysis of variance [ANOVA], p < 0.0001). The density of shells greatly increased after mass mortality of C. fluminea populations. Our results indicate that shells can provide valuable hard surfaces for species that prefer structured habitats, especially in unstructured soft-bottomed habitats. In addition, density of juvenile C. fluminea was lower in boxes containing live adult clams than in boxes containing sand or sand and shells (ANOVA, p = 0.0048), possibly because of a chemical cue that might hinder settlement of juveniles in areas with high intraspecific concurrence.

Length–mass equations are valued for their efficiency and reliability because many animals, including aquatic macroinvertebrates, show predictable correlations between mass and linear body dimensions. Our paper explores overlooked aspects of length–mass applications, including relationships for adult aquatic insects, intraspecific variation, and spatiotemporal context. We analyzed the length–mass relationship in 5 species of adult dragonfly (Anisoptera: Libellulidae) during 2 collection periods (early and late summer flight) at 3 study locations in northern Mississippi, USA. Despite narrow ranges in body and wing length, and given that dragonflies gain postemergence mass without associated changes in skeletal size, both body and wing length showed potential for estimating individual dry mass (R² ≥ 0.5 in most cases). We also found strong associations between dry and wet length and consistent variation in individual dry mass as a percentage of individual wet mass (∼65% water content) in these samples. Species-level mass estimates from independently derived species-level equations were far more accurate than estimates based on previously published equations for use at higher taxonomic levels (family, order). Patterns of individual mass per unit length generally differed among study locations and, especially, collection periods. Regression models with similar slopes (i.e., similar individual differences in mass per unit length) were susceptible to length-adjusted location or time effects (i.e., elevation differences in the best-fit lines). Our study underscores the importance of intraspecific variation, taxonomic resolution, and spatiotemporal context in length-based modeling of adult dragonfly mass.

Parking-lot pavement sealants recently have been recognized as a major source of polycyclic aromatic hydrocarbons (PAHs) in urban stream sediments in Austin, Texas. Laboratory and field studies have shown that PAHs in sediments can be toxic to aquatic organisms and can degrade aquatic communities. After identifying increases in concentrations of PAHs in sediments below seal-coated parking lots, we investigated whether the increases had significant effects on stream biota in 5 Austin streams. We sampled sediment chemistry and biological communities above and below the point at which stormwater runoff from the parking lots discharged into the streams, thus providing 5 upstream reference sites and 5 downstream treatment sites. Differences between upstream and downstream concentrations of total PAH ranged from 3.9 to 32 mg/kg. Analysis of the species occurrence data from pool and riffle habitats indicated a significant decrease in community health at the downstream sites, including decreases in richness, intolerant taxa, Diptera taxa, and density. In pool sediments, Chironomidae density was negatively correlated with PAH concentrations, whereas Oligochaeta density responded positively to PAH concentrations. In general, pool taxa responded more strongly than riffle taxa to PAHs, but riffle taxa responded more broadly than pool taxa. Increases in PAH sediment-toxicity units between upstream and downstream sites explained decreases in taxon richness and density in pools between upstream and downstream sites.

We compared the within- and among-lake variability of benthic communities in small, near-pristine lakes vs lakes affected by nonpoint-source pollution in southern Finland. We used 2 sampling methods, profundal grab sampling and the chironomid pupal exuvial technique (CPET), and compared the signal-to-noise ratios (S/N) of the 2 data sets. We also assessed lake condition using the benthic quality index, identified macroinvertebrate taxa indicative of different trophic conditions, and evaluated the concordance of species ordinations obtained using the 2 collection methods. Both data sets discriminated effectively among the lake groups, and the 2 community ordinations were significantly concordant. The number of chironomid species in the CPET samples was higher than the total number of macroinvertebrate taxa found in the profundal grab samples, and the CPET method appeared more efficient than profundal grab sampling at detecting profundal taxa. Despite the slightly stronger signal strength of the profundal grab samples, randomization tests showed that only the CPET data had S/N significantly higher than expected by chance. CPET data also better reflected the trophic status of the lakes. Indicator species analysis showed that 7 chironomid taxa and Pisidium spp. (Sphaeridae) indicated good water quality, whereas 5 chironomid species and the phantom midge Chaoborus flavicans indicated impacted conditions in these lakes. Our results suggest that CPET might be more efficient than profundal grab sampling for describing the chironomid fauna and the ecological status of small mesohumic lakes, and it should be considered as an alternative or supplementary assessment tool to more traditional methods.

The utility of hydropsychid (Trichoptera:Hydropsychidae) caddisfly larvae for freshwater biomonitoring has been demonstrated, but the major impediment to its implementation has been the lack of species-level larval descriptions and illustrations. A rapid and reliable molecular protocol that also uses morphology is proposed because conventional approaches to associating undescribed larvae with adults have been slow and problematic. Male adults were identified before DNA sequence analyses were used. These identifications established morphospecies boundaries that were mapped on phylograms constructed from 2 independent gene fragments: mitochondrial cytochrome c oxidase subunit I (COI) and large subunit (28S) nuclear ribosomal DNA expansion fragment D2 (D2). Species boundaries were confirmed if they were monophyletic on both molecular phylograms. Larval associations were made with reference to the phylogenetic analyses under 2 criteria: sequence identity across both genes or nested placement within a reference species boundary. A total of 133 individuals belonging to Chinese Hydropsyche sensu lato group (including Hydropsyche [Hydropsyche], Hydropsyche [Occutanspsyche], Ceratopsyche, Mexipsyche, Hydatomanicus, and Herbertorossia) were included in our study to test the new protocol. D2 sequences (all individuals) and COI sequences (101 individuals) were obtained, and 2 independent phylograms were constructed using neighbor joining. Both fragments provided enough nucleotide changes to differentiate independently most Hydropsyche sensu lato species, with ambiguity in only a few species that eventually could be resolved with additional sequences and specimens. COI diverges significantly within some species, suggesting a need for caution when applying typical genetic divergence thresholds in species diagnoses. The study enabled us to establish a procedure for delimiting species boundaries and associating larvae and adults using DNA sequences and morphological evidence. Ideal sampling strategies for larval–adult association are suggested. Associating larvae and adults of hydropsychids using DNA sequences appears to be promising in terms of both reliability and speed.

Fine particulate organic matter (FPOM) is an important source of C and energy in aquatic systems, but the decomposition of FPOM has rarely been studied. Litterbags were used to study the decomposition of particles in 2 size fractions of FPOM in surface sediments of a cypress swamp in southeastern Louisiana for slightly over 1 y. Particles in both size fractions followed linear decay models, but fine particles (0.25–1 mm) derived from the remains of coarser material decomposed more slowly than very fine particles (0.063–0.25 mm) that probably were derived from a number of sources. The activities of 6 microbial extracellular enzymes involved in the degradation of lignocellulose also were analyzed, and enzymatic decomposition models were developed to relate the decomposition of particles in each size fraction of FPOM to microbial activity. Very fine particles decomposed more rapidly than fine particles, although enzyme activities were lower, suggesting that this material was more efficiently degraded than fine particles. Enzymatic activity also was measured on particles in 2 size fractions of unconfined FPOM in sediment, and the enzymatic decomposition models were used to predict instantaneous mass-loss rates. Unconfined fine particles decomposed 1.5× faster than fine particles confined in litterbags, whereas unconfined very fine particles decomposed 2 to 4× faster than very fine particles confined in litterbags. Confining FPOM within litterbags clearly led to underestimation of decomposition rates, which might be more effectively determined using enzymatic decomposition models. The differences in microbial activity and decomposition rates between particles in different size fractions show that the concept of FPOM as uniform particles <1 mm in diameter is simplistic, and that a more accurate concept would recognize the distinction between different sizes of particles that might be derived from different sources.

Water abstraction can alter invertebrate community composition by changing the availability or suitability of habitat for invertebrates. The consequences of water abstraction for the physical habitat and invertebrate communities of small permanent streams are not clear. Therefore, we used whole-channel flow manipulations to imitate real water abstractions. We used weirs and diversions to reduce discharge by >85% in 3 small New Zealand streams (mean discharges: 11–84 L/s), ranging in water quality from pristine to moderately polluted. We sampled benthic invertebrates and periphyton at control and impact sites on each stream before and during 2 mo of artificially reduced discharge during summer 2005, and then we left the diversions in operation throughout the following year and sampled invertebrates again after 9 and 12 mo of flow reduction. During the experiment, wetted width decreased by 24 to 34% at impact sites. Water velocity and depth also decreased at impact sites, but only small changes to conductivity, pH, dissolved O₂, and temperature were observed. At the pristine site, density of invertebrates and percentage of Ephemeroptera, Plecoptera, Trichoptera (EPT) individuals decreased in response to reduced flows. Only taxonomic richness decreased at the mildly polluted stream, and reduced discharge had no effect on the invertebrate community at the stream with the poorest water quality. Overall community structure also changed in response to flow reduction at all but the poorest-water-quality stream. Alterations to community composition involved changes in the density of common taxa and collection of fewer rare taxa per sample. Our results indicate that the impacts of water abstraction on invertebrate communities differ between streams that vary in water quality, probably because of the relative sensitivities of invertebrate communities to changes in the physical habitat of these streams.

We conducted field surveys and experiments to determine whether observed distributions of crayfish among habitats were influenced by differential resource availability, foraging profitability, and predation rates and whether these factors differed with crayfish size and habitat depth. We sampled available food resources (detritus and invertebrates) and shelter as rock substrate in deep (>50 cm) and shallow (<30 cm) habitats. We used an enclosure–exclosure experiment to examine the effects of water depth and crayfish size on crayfish biomass and survival, and to determine whether these factors affected silt accrual, algal abundance (chlorophyll a [chl a]), and detritus and invertebrate biomass (g ash-free dry mass) differently from enclosures without crayfish. We conducted tethering experiments to assess predation on small (13–17 mm carapace length [CL]) and large (23–30 mm CL) Orconectes marchandi and to determine whether predation rates differed with water depth. Invertebrate biomass was significantly greater in shallow water than in deep water, whereas detritus biomass did not differ significantly between depths. Cobble was significantly more abundant in shallow than in deep water. Depth and crayfish size had a significant interactive effect on change in size of enclosed crayfish when CL was used as a measure of size but not when biomass was used as a measure of size. CL of small crayfish increased significantly more in enclosures in shallow than in deep water, but CL of large crayfish changed very little at either depth. Silt, chl a, and detritus biomass were significantly lower on tiles in large- than in small- and no-crayfish enclosures, and invertebrate biomass was significantly lower in large- than in no-crayfish enclosures. Significantly more crayfish were consumed in deep than in shallow water regardless of crayfish size. Our results suggest that predation and resource availability might influence the depth distribution of small and large crayfish. Small crayfish grew faster in shallow habitats where they might have had a fitness advantage caused by high prey availability and reduced predation risk. Size-dependent reduction of silt by crayfish might influence benthic habitats where large crayfish are abundant.

Large river floodplains potentially include the full range of freshwater ecosystems from permanently flowing channels to temporary pools and springs. Attempts to restore such complex systems require tools adapted to assess restoration success. In an analysis of invertebrate assemblages in the Rhône River floodplain (France), taxonomic-based indices (rarefied richness and assemblage composition) were compared with functional metrics using trait-based ratios as surrogates of ecosystem processes. Their ability to respond to a gradient of hydrological connectivity was assessed in 7 cut-off channels. The sampling design included 2 sites/channel (upstream and downstream), 4 randomly chosen sampling points (0.5 × 0.5-m quadrats)/site, and 2 sampling seasons (spring and summer). Water physicochemical and habitat variables were recorded when invertebrates were sampled. Environmental variables, including water conductance, [NH₃-N], submerged vegetation cover, diversity of sediment grain size, and organic matter content of the sediment, were used to construct a synthetic variable describing the hydrological connectivity of each site with the main river channel. A quadratic regression of rarefied taxonomic richness and the connectivity gradient was not quite significant, but assemblage composition was strongly related to the gradient. Four of 8 trait-based metrics were correlated with the connectivity gradient. Values of metrics that are surrogates for top-down control of assemblage structure and habitat stability (based on functional feeding groups) declined along the gradient from disconnected sites to more connected sites. Values of metrics that are surrogates for voltinism and food supply for water-column-feeding fish increased with connectivity. Top-down control and voltinism surrogates suggested a decline in predator–prey relationships and lower habitat stability, respectively, in the more connected sites. Assemblage composition and some of the trait-based metrics were sensitive to a flood that occurred before one of the sampling dates. Some of the trait-based metrics showed potential for explaining floodplain invertebrate assemblages and for monitoring postrestoration conditions in floodplain water bodies. However, the metrics were developed initially for studies of lotic systems and their use in heterogeneous floodplain water bodies will require further investigation, e.g., delineation of reference conditions for trait-based metrics.

The North American Benthological Society and the Editors of J-NABS gratefully acknowledge the contributions of the following during the past year.¹