Spatial and seasonal associations of benthic macroinvertebrates and detritus in an Alaskan subarctic stream

Summary Seasonal and spatial patterns of benthic invertebrate abundance were examined in relation to benthic detritus in Monument Creek, an Alaskan subarctic stream. The total macroinvertebrate fauna showed a mid-summer low in abundance, increasing to seasonal highs in winter/early spring (November/May). Shredders were a small portion of the benthic fauna or leaf pack fauna in summer but increased rapidly (in biovolume) following autumnal leaf fall to dominate the fauna by early winter (October/November). Abundance was strongly correlated with quantity of detritus in the sample. Comparison of benthic macroinvertebrate densities from Alaskan streams with comparable data from temperate zone streams shows that Alaskan streams are similar to temperate zone streams in range of abundance. Each unit of benthic detritus in Monument Creek is associated with a relatively large number of small (low individual biomass) shredders compared to streams in temperate regions. Detrital resources in this subarctic stream were meager, compared to temperate streams, and appeared to strongly influence the spatial and temporal patterns of detritivores.     

Burying beetle Nicrophorus investigator reproduction on Pacific salmon carcasses

Abstract.  1. In many undisturbed watersheds along the Pacific Rim, anadromous salmon ( Oncorhynchus spp.) provide a predictable source of carrion to the riparian zone, largely due to horizontal transfer of salmon carcasses by bears ( Ursus spp.) and other vertebrates.
2. Burying beetles are important members of the north-temperate carrion fauna, and may utilise salmon carcasses and remnants for breeding. In this study, isotopic and observational data are reported that demonstrate previously unrecognised Nicrophorus investigator (Zetterstedt) reproduction on large salmon carcasses from five watersheds in coastal British Columbia.
3. Stable isotope signatures (δ¹⁵N and δ¹³C) of adult beetles collected in autumn indicate a diet of salmon origin in all but one individual from all watersheds, suggesting that this beetle–salmon association is widespread. Comparison of autumn isotope signatures to individuals collected randomly in summer suggests that isotope signatures represent the larval carrion source from the previous autumn rather than immediate adult diet.
4. In a survey of N. investigator use of salmon carcasses from two watersheds, 35 broods were observed on chum and pink salmon carcasses, including 16 natural brood complexes containing over 100 larvae, and five ranging from 250 to 750 larvae.
5. Overall, north-coastal populations of N. investigator breed on the rich and reliable salmon resource and may exhibit a system of communal breeding on these carcasses. This is most relevant when the dramatic reduction in salmon spawning biomass over the last century is considered.     

Effect of sudden flow reduction on the decomposition of alder leaves (Alnus glutinosa [L.] Gaertn.) in a temperate lowland stream: a mesocosm study

Climate change leads to summer low flow conditions and premature litter input in lowland streams in Central Europe. This may cause a sudden reduction of flow and fragmentation into isolated pools of permanently flowing streams, with a simultaneous increase in the food supply for detrivores during summer months. We performed a mesocosm study to investigate shredder and microbial mediated litter decomposition under these conditions. Leaf litter was placed in a lowland stream with a natural flow regime (reference) and in a stream mesocosm with significant flow reduction (FR) and a representative density of macroinvertebrates and detritus. Physicochemical parameters, leaf mass loss, macroinvertebrate abundance and biomass, leaf-associated respiration, fungal sporulation, and biomass were measured at regular intervals for 6 weeks. Coarse and fine-mesh bags were used to include or exclude macroinvertebrate shredders. In the coarse-mesh bags, leaf mass loss was significantly lower in the FR system than in the reference regime. In the fine-mesh bags, leaf respiration, fungal sporulation, and biomass but not leaf mass losses were substantially lower with flow reduction. Chironomid larvae (Micropsectra spp.) appeared to effectively fragment leaf litter in fine-mesh bags. In the FR system, leaf respiration was higher in the coarse-than in the fine-mesh bags. Our results suggest that, in temperate lowland streams, premature litter input during or after a sudden fragmentation into isolated pools and a reduction of stream flow reduces direct shredder-mediated litter decomposition, but shredders may indirectly influence the decomposition process. Handling editor: B. Oertli     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Spatial and temporal variability of macroinvertebrates in spawning and non-spawning habitats during a salmon run in Southeast Alaska

Spawning salmon create patches of disturbance through redd digging which can reduce macroinvertebrate abundance and biomass in spawning habitat. We asked whether displaced invertebrates use non-spawning habitats as refugia in streams. Our study explored how the spatial and temporal distribution of macroinvertebrates changed during a pink salmon (Oncorhynchus gorbuscha) spawning run and compared macroinvertebrates in spawning (riffle) and non-spawning (refugia) habitats in an Alaskan stream. Potential refugia included: pools, stream margins and the hyporheic zone, and we also sampled invertebrate drift. We predicted that macroinvertebrates would decline in riffles and increase in drift and refugia habitats during salmon spawning. We observed a reduction in the density, biomass and taxonomic richness of macroinvertebrates in riffles during spawning. There was no change in pool and margin invertebrate communities, except insect biomass declined in pools during the spawning period. Macroinvertebrate density was greater in the hyporheic zone and macroinvertebrate density and richness increased in the drift during spawning. We observed significant invertebrate declines within spawning habitat; however in non-spawning habitat, there were less pronounced changes in invertebrate density and richness. The results observed may be due to spawning-related disturbances, insect phenology, or other variables. We propose that certain in-stream habitats could be important for the persistence of macroinvertebrates during salmon spawning in a Southeast Alaskan stream.     

Zoobenthos communities and their seasonal dynamics in nonfreezing springs of Baikal region

The faunal composition, structure of the zoobenthos communities, and seasonal changes in two springs in the south of Irkutsk area are investigated. Both springs have the water temperature 4–5°C all year round. The fauna consists of widely distributed hydrobionts, crenobionts, stygobionts, and near-water organisms. Arctic relicts and elements of the Lake Baikal fauna are found. In macroinvertebrate communities, chironomid larvae dominate (by abundance and biomass), as do oligochaetes (by abundance). The lowest quantitative parameters are recorded in autumn-winter, and the highest parameters, in spring (March–April). Then they abruptly decline owing to emergence of amphibiotic insects. The structure of spring communities has regional specificity. By biomass of macrozoobenthos, the springs are comparable with mesotrophic and even eutrophic lakes.     

Long-term recovery of a mountain stream from clear-cut logging: the effects of forest succession on benthic invertebrate community structure

1. Changes in benthic invertebrate community structure following 16 years of forest succession after logging were examined by estimating benthic invertebrate abundance, biomass and secondary production in streams draining a forested reference and a recovering clear-cut catchment. Benthic invertebrate abundance was three times higher, and invertebrate biomass and production were two times higher in the disturbed stream.
2. Comparison of invertebrate community abundance 1, 5 and 16 years after clear-cutting indicated that the proportion of scrapers had decreased, whereas shredders had increased. Functional group percentage similarity indicated that the invertebrate community in the disturbed stream 16 years after clear-cutting was more similar to the reference than to that found earlier in the disturbed stream.
3. The five indices calculated from data collected over the past 16 years, as well as the abundance, biomass and production data collected during this study, proved to be of differing value in assessing recovery of the disturbed stream from logging. Percent dominant taxon and EPT (Ephemeroptera, Plecoptera and Trichoptera) taxon richness failed to show any initial differences between reference and disturbed streams, indicating that these indices may not be useful for measuring recovery from logging. The percentage Baetis and shredder–scraper indices showed significant differences only during the 1977 study and suggest recovery (no difference between reference and disturbed) by 1982. The North Carolina Biotic Index showed continued differences during 1982 in the riffle and depositional habitats and recovery by 1993. Total macroinvertebrate abundance, biomass and production, as well as EPT abundance, indicated continued differences between the reference and disturbed streams in the 1993 study.     

Invertebrate drift in the regulated River Tees, and an unregulated tributary Maize Beck, below Cow Green dam

SUMMARY. The Cow Green dam was completed in the summer of 1970 and invertebrate drift was sampled below the dam and in an adjacent tributary, Maize Beck, on thirty-one occasions between July 1970 and September 1973. Drift was sampled by pumping river water through a filter. The intake was placed in Maize Beck for the first sample and in the Tees for the second, and so on alternately for the rest of the sampling period. Nets were used on ten occasions, nine of these in winter months and once when the pump broke down. A total of ninety-five taxa were recognized, of which eighty-six occurred in Maize Beck and seventy-one in the Tees. The Tees fauna was dominated numerically and in terms of biomass by a large population of micro-crustaceans originating in the reservoir. Hydra and Naididae also formed a large proportion of the Tees drift but contributed little to the biomass. Ephemeroptera were most abundant in Maize Beck samples. Diptera were abundant in drift catches in both streams with simuliid larvae most numerous in Maize Beck and chironomid larvae most numerous in the Tees. The greatest drift densities of the benthic fauna were observed between April and October; the mean number of organisms per 10 m³ were seventy-three in Maize Beck and 144 in the Tees. The mean densities in winter were very low, respectively two and seventeen per 10 m³ in the two rivers. There was no significant difference between the mean levels of the total bottom fauna (numbers and biomass) in the drift in the two rivers during the period April-October, but vrtnter biomass was significantly greater in the Tees. In July 1970 micro-crustaceans represented 29% (14 per 10 m³) of total drift numbers and 3% (0.7 mg wet-weight per 10 m³) of the biomass, whereas in 1973 they represented 99% of both the numbers (37 670 per 10 m³) and weight (2.2 g wet-weight per 10 m³). The relation between benthos and drift was examined. In the drift Plecoptera and Baetidae were more abundant in Maize Beck than in the Tees. Only Chironomidae and Nais spp. were more abundant in the Tees, In the benthos the density of Plecoptera and Baetidae was not significantly different in the two rivers, but all other groups with the exception of Simuliidae occurred at greater densities in the Tees. The proportion of baetids present in the drift was greatest in Maize Beck. No such difference was demonstrated for total fauna. Diel rhythms were observed in baetids and simuhids with densities greater in night catches. Nocturnal peaks of these organisms were less pronounced in the Tees. Chironomid larvae showed no diel changes in abundance. Significant diel changes in the mean weights of individual animals were not detected in baetid nymphs or chironomids. Micro-crustaceans showed no nocturnal peaks of abundance. Preliminary observations on the quality and quantity of seston caught in drift samples between April and October showed great differences between the rivers. In the Tees the bulk ofeach sample consisted of algal filaments derived from the river and micro-crustaceans from the reservoir. In Maize Beck algae were un-common and the sample was composed of peat and mineral particles. Data are presented on seston output at different discharges.     

Macroinvertebrate communities of non-glacial high altitude intermittent streams

1. Macroinvertebrate assemblages of five non‐glacial intermittent high altitude headwater streams (above 1400 m – Serra da Estrela, Portugal), with dry periods of different lengths (0–3 months), were investigated in nearly undisturbed conditions to (i) examine spatial differences and identify environmental variables responsible for the observed invertebrate patterns, (ii) assess the association of dry period length with invertebrate community structure and (iii) determine the influence of using different taxonomic identification levels (order, family and genus) to assess invertebrate community patterns. 2. More than 100 macroinvertebrate genera were identified. Insects clearly dominated these communities with more than 95% of total captures and around 95% of the total richness. Diptera were the most rich and abundant group with chironomid occurrences comprising over 70% of macroinvertebrate captures. 3. The highest taxon richness, diversity, EPT (Ephemeroptera + Plecoptera + Trichoptera) and OCH (Odonata + Coleoptera + Heteroptera) genus richness, the greatest number of exclusive and characteristic taxa identified by the Indicator Value (IndVal), and a distinct community structure shown by Canonical Correspondence Analyses (CCA), were found in the only stream that was never totally dry, with pools lasting over summer. Environmental gradients that spatially structured the macroinvertebrate communities were always related to flow variations. 4. Over time, the highest abundances found in these systems were also related to flow variations and maximum genus richness occurred in the connected pools or in isolated pools. Streams with longer dry periods presented a distinct recolonization phase, with higher abundance of the stonefly larvae Nemoura sp. and the presence of the chironomid larvae Krenosmittia sp., possibly arriving from the hyporheos. 5. Taxonomic level of invertebrate identification was vital for recognizing the characteristic taxa (IndVal) of streams yet was not critical for identifying streams with the highest macroinvertebrate richness/diversity or structuring environmental gradients. 6. Overall, this study emphasizes the variability of high altitude intermittent streams macroinvertebrate communities, despite spatial proximity. This variability was probably related to flow intermittency and hydrologic permanence, different vegetation covers and riverbed substrata. Consequently, the establishment of reference conditions should involve long‐term data collections and more detailed physical characterization. Also, these findings have significant implications for accurately predicting the ecological consequences of future climate change in high altitude scenarios.     

Diet composition and prey preference of tench, Tinca tinca (L.), common bream, Abramis brama (L.), perch, Perca fluviatilis L. and roach, Rutilus rutilus (L.), in two contrasting gravel pit lakes: potential trophic overlap with wildfowl

The abundance of benthic macroinvertebrate taxa and the relative abundance of zooplankton taxa were compared with the diet of bream, tench. perch and roach from two gravel pit lakes during May-July 1986 and 1987. Significant food preferences were demonstrated between species and between lakes. Chironomid pupae dominated the macroinvertebrate diet of perch, roach, ate predominantly either Spirogyra sp. (St Peters Lake) or Daphniu hyalina (Main Lake).
The Main Lake, bream fed largely upon chironomid larvae and the bivalve Sphuerium but in St Peters Lake they positively selected a variety of less abundant benthic invertebrate taxa. Bream switched from benthos to zooplankton in the Main Lake in 1986. Tench ate large numbers of Aselhs and showed positive selection of various macroinvertebrate prey in St Peters but ate D. hjulim in Main Lake. Tropic overlap for chironomids and other macroinvertebrate prey was demonstrated between perch, bream and tench, and potentially with wildfowl which used the gravel pits for breeding and wintering.     

Influences of logging history and riparian forest characteristics on macroinvertebrates and brook trout (Salvelinus fontinalis) in headwater streams (New Hampshire, U.S.A.)

1. Logging can strongly affect stream macroinvertebrate communities, but the direction and magnitude of these effects and their implications for trout abundance are frequently region‐specific and difficult to predict. 2. In first‐order streams in northern New England (U.S.A.) representing a chronosequence of logging history (<2 to >80 years since logging), we measured riparian forest conditions, stream macroinvertebrate community characteristics and brook trout (Salvelinus fontinalis) abundance. Principal component analysis was used to collapse forest data into two independent variables representing variation in logging history, riparian forest structure and canopy cover. We used these data to test whether logging history and associated forest conditions were significant predictors of macroinvertebrate abundance and functional feeding group composition, and whether brook trout abundance was related to logging‐associated variation in invertebrate communities. 3. Catchments with high PC1 scores (recently logged, high‐density stands with low mean tree diameter) and low PC2 scores (low canopy cover) had significantly higher total macroinvertebrate abundance, particularly with respect to chironomid larvae (low PC2 scores) and invertebrates in the grazer functional feeding group (high PC1 scores). In contrast, proportional representation of macroinvertebrates in the shredder functional feeding group increased with time since logging and canopy cover (high PC2 scores). Brook trout density and biomass was significantly greater in young, recently logged stands (high PC1 scores) and was positively related to overall macroinvertebrate abundance. In addition, three variables – trout density, invertebrate abundance and shredder abundance – successfully discriminated between streams that were less‐impacted versus more‐impacted by forestry. 4. These results indicate that timber harvest in northern New England headwater streams may shift shredder‐dominated macroinvertebrate communities supporting low trout abundance to a grazer/chironomid‐dominated macroinvertebrate community supporting higher trout abundance. However, while local effects on brook trout abundance may be positive, these benefits may be outweighed by negative effects of brook trout on co‐occurring species, as well as impairment of habitat quality downstream. Research testing the generality of these patterns will improve understanding of how aquatic ecosystems respond to anthropogenic and natural trajectories of forest change.     

Recovery of benthic macroinvertebrate and adult dragonfly assemblages in response to large scale removal of riparian invasive alien trees

Invasive alien organisms can impact adversely on indigenous biodiversity, while riparian invasive alien trees (IATs), through shading of the habitat, can be a key threat to stream invertebrates. We ask here whether stream fauna can recover when the key threat of riparian IATs is removed. Specifically, we address whether IAT invasion, and subsequent IAT removal, changes benthic macroinvertebrate and adult dragonfly assemblages, for the worse or for the better respectively. Natural riparian zones were controls. There were statistically significant differences between stream reaches with natural, IAT-infested and IAT-cleared riparian vegetation types, based on several metrics: immature macroinvertebrate taxon richness, average score per macroinvertebrate taxon (ASPT), a macroinvertebrate subset (Ephemeroptera, Plecoptera, Trichoptera and Odonata larvae; EPTO), and adult dragonfly species richness. Reaches with natural vegetation, or cleared of IATs, supported greater relative diversity of macroinvertebrates than reaches shaded by dense IATs. Greatest macroinvertebrate ASPT and EPTO were in reaches bordered by natural vegetation and those bordered by vegetation cleared of IATs, and the lowest where the riparian corridor was IATs. Highest number of adult dragonflies species was along streams cleared of dense IATs. Overall, results showed that removal of a highly invasive, dense canopy of alien trees enables recovery of aquatic biodiversity. As benthic macroinvertebrate scores and adult dragonfly species richness are correlated and additive, their combined use is recommended for river condition assessments.     

Longitudinal distribution of macroinvertebrates in two glacier-fed New Zealand rivers

1. Environmental variables, benthic algal biomass and macroinvertebrate fauna were examined from September 1999 to January 2000 (austral summer) along two glacier-fed rivers in South Island, New Zealand.
2. The rivers were characterized by high flow variability, high turbidity and physically disturbed beds. Water temperature ranged from <1 °C near the glacier margin to 10 °C further downstream.
3. Epilithic algal biomass was very low (<0.1 mg m^–2) in months characterized by heavy rainfall, but ranged from 1.1 to 14.4 mg m^–2 following an extended period with negligible precipitation.
4. Abundance and diversity of invertebrates in both rivers was low. Dominant taxa were Chironomidae (Orthocladiinae, Podonominae, Diamesinae), although mayfly species ( Deleatidium : Leptophlebiidae) also occurred at most sites. A species of Eukiefferiella (Orthocladiinae) was collected at all sites and was the most abundant invertebrate close to the glacier margins. No meiofauna were found in either river.
5. Faunal diversity increased at the lowermost stations where species of Plecoptera, Trichoptera, Coleoptera and non-chironomid Diptera also occurred.
6. The faunas of the two New Zealand rivers conformed to the conceptual model of Milner & Petts (1994) in that taxon richness increased downstream with water temperature. However, invertebrate abundance increased downstream in only one of the two rivers. Also in contrast to the model predictions, Leptophlebiidae and Orthocladiinae, rather than Diamesinae, dominated the fauna at the coldest sites.     

Processing of willow leaves in two Alberta Rocky Mountain streams

Nylon bags of 3.5 mm and 0.25 mm mesh were used lo investigate the processing of Salix drummondiana Barratt leaves in two second order Alberta Rocky Mountain Creeks, Twin Creek and Cabin Creek. Micro-organism processing and macroinvertebrate shredding of the leaves were significantly greater in Twin Creek where it was estimated that macroinvertebrate shredding was responsible for 45% of the weight loss. The decay coefficient (k = 0.0209) for the leaves in Twin Creek, the more typical Rocky Mountain stream, was similar to that reported for the fastest decaying leaves in warmer streams. The predominant shredder among the leaves in the mesh bags, Zapada columbiana (Classen) (Plecoptera, Nemouridae) was also the most abundant macroinvertebrate in the benthos of Twin Creek. In Cabin Creek the predominant organism in the benthos, Oreogeton sp. was poorly represented in the leaves. Low orthophosphate concentration of the water and precipitation of calcium carbonate onto the leaves may have inhibited the biotic processing of leaves in Cabin Creek.     

Persistence and stability of macroinvertebrate communities in streams of Denali National Park, Alaska: implications for biological monitoring

1. Macroinvertebrate communities were studied from 1994 to 2001/2002 (except 1997) in six streams in Denali National Park, interior Alaska. All six streams were potential reference streams with no known impairment. 2. Abundance of individual taxa varied markedly from year to year. Overall, abundance decreased over the study period, particularly with respect to mayflies. Stonefly taxa showed lower persistence and were sometimes absent from a stream in any particular year. 3. Mean community persistence for the six streams, as measured by Jaccard's similarity coefficients between years, varied from 0.48 in the year pair 1999–2000 to 0.78 in 1998–99. Tattler Creek (a small stable stream) supported the most persistent macroinvertebrate community and Highway Pass Creek (a small, unstable creek) the least. Mean community persistence showed a significant relationship with mean winter snowfall (November to March) for the six streams. 4. The highest community compositional stability was found in Tattler Creek and the lowest in Highway Pass Creek, but stability varied markedly over time for the six streams, peaking in 1994–95 and reaching a minimum in 2000–01. Compositional stability was significantly related to the Pfankuch Index of channel stability. 5. The composition metrics % Chironomidae, % dominant taxa, %EPT, % Ephemeroptera and % Plecoptera, employed as part of the Alaska Stream Condition Index, varied over almost their entire range in these pristine streams across the 9 years of the study. 6. This study demonstrates the wide range of natural variation that occurs in benthic macroinvertebrate communities in these pristine central Alaskan streams, potentially limiting the applicability of composition metrics for the biological monitoring of water quality in these systems.     

Forest proportion as indicator of ecological integrity in streams using Plecoptera as a proxy

An assessment system suitable to support implementation of the EU Water Framework Directive's local water management plans should build on quantitative knowledge about a suite of well-documented indicator and umbrella species’ requirements for different stream orders. Assuring high communication value for improving local public awareness and participation for restoring ecological integrity in impaired headwater streams is critical. Loss and fragmentation of forests are major threats to ecological integrity. The aquatic macroinvertebrate order Plecoptera is commonly used as an indicator of the ecological integrity of streams. We measured abundance and taxonomic richness of Plecoptera in relation to land cover and water chemistry in second and third order catchments’ in 25 headwater streams in Central Europe's Carpathian Mountains. Plecoptera abundance and Plecoptera taxa richness were positively correlated to each other, as well as to forest proportion in the catchments, but negatively correlated to catchment area, inorganic carbon, alkalinity and conductivity. Segmented linear regression was then used to identify thresholds associated to forest proportion as a surrogate for catchment integrity. No threshold was found for Plecoptera abundance, but for taxa richness a threshold of 54% forest cover was found, below which Plecoptera was affected in second order streams. Using Plecoptera as a proxy for ecological integrity this study indicates that forest cover is an effective bioindicator in headwater catchments for predicting the ecological status of headwater streams. The non-linear relationship between forest cover and Plecoptera can be used as a science-based norm whereby land cover monitoring can be used to assess the ecological status of streams.     

Seasonal dynamics of moss-dwelling chironomid communities

Chironomid communities of mosses in a small upland stream in central Germany were highly dynamic across the year with respect to their abundance, biomass and dominant taxa. During 1988 semi-submersed mosses near a main spring and those occurring some 700 m downstream were compared with permanently submersed mosses in immediate vicinity of the downstream site. All the chironomids sampled were conspicuously small, with nearly 98% being less than 5 mm in length. A total of 65 chironomid species from 26 genera were found, with a higher diversity occurring near the source and a change in dominant taxa along the upper stream section. The mean abundance in permanently submersed mosses (250 larvae/10 cm², n = 125) was about five times higher than in semi-submersed mosses. The maximum value of 830 larvae/10 cm² (n = 1) is the highest chironomid density ever reported, which is explained by the sampling method used. The mean standing crop was also highest in permanently submersed mosses (1.5 mg AFDW/10 cm² (n = 125)), even though the highest individual value was recorded in semi-submersed mosses near the spring (10.4 mg AFDW/10 cm²). The evidence suggested that the dominance of chironomid taxa depended mainly on the location of the moss along the stream, whereas abundance and biomass were determined mainly by constancy in the ambient discharge as well as the factors influenced by this (e.g. temperature, detritus deposition). A trend was seen towards a seasonal succession among the chironomid taxa colonizing lotic mosses.     

Community structure of benthic invertebrates in interior Alaskan (USA) streams and rivers

Taxonomic composition of benthic invertebrates in interior Alaskan streams and rivers is summarized from published and unpublished data. Diptera dominate the Alaskan stream fauna and constitute a larger proportion of the benthos in Alaskan streams than in streams of temperate North America. Plecoptera and Ephemeroptera are the next most abundant in Alaskan streams with Trichoptera generally very scarce. Several orders that occur regularly in streams of temperate North America are absent (or in very low abundance) in interior Alaskan streams: Hemiptera, Odonata, Megaloptera, Coleoptera. Net-spinning caddisflies, burrowing mayflies, and several families of stoneflies (Pteronarcyidae, Peltoperlidae and Perlidae) are conspicuous by their absence or extreme scarcity. Taxonomic composition varies significantly among hydrologic regions (major watersheds) and among stream types (springs, headwater streams, small rivers, and large rivers). Only two taxa (Chironomidae and Nemouridae) significantly increase in proportional contribution from south to north while many taxa decrease.     

Temporal dynamics of benthic macroinvertebrate communities and their response to elevated specific conductance in Appalachian coalfield headwater streams

Coal mining in central Appalachia USA causes increased specific conductance in receiving streams. Researchers have examined benthic macroinvertebrate community structure in such streams using temporally discrete measurements of SC and benthic macroinvertebrates; however, both SC and benthic macroinvertebrate communities exhibit intra-annual variation. Twelve central Appalachian headwater streams with reference quality physical habitat and physicochemical conditions (except for elevated SC in eight streams) were sampled ≤fourteen times each between June 2011 and November 2012 to evaluate benthic macroinvertebrate community structure. Specific conductance was recorded at each sampling event and by in situ data loggers. Streams were classified by mean SC Level (Reference, 17–142 μS/cm; Medium, 262–648 μS/cm; and High, 756–1535 μS/cm). Benthic macroinvertebrate community structure was quantified using fifteen metrics selected to characterize community composition and presence of taxa from orders Ephemeroptera, Plecoptera, and Trichoptera. Metrics were analyzed for differences among SC Levels and months of sampling. Reference streams differed significantly from Medium-SC and High-SC streams for 11 metrics. Medium-SC streams had the most metrics exhibiting significant differences among months. Relative abundances of Plecoptera and Trichoptera were not sensitive to SC, as the families Leuctridae and Hydropsychidae exhibited increased relative abundance (vs. reference) in streams with elevated SC. In contrast, Ephemeroptera richness and relative abundance were lower, relative to reference, in elevated-SC streams despite increased relative abundance of Baetidae. Temporal variability was evident in several metrics due to influence by taxa with seasonal life cycles. These results demonstrate that benthic macroinvertebrate communities in elevated-SC streams are altered from reference condition, and that metrics differ in SC sensitivity. The time of year when samples are taken influenced measured levels and differences from reference condition for most metrics.     

Methane-derived carbon flows through methane-oxidizing bacteria to higher trophic levels in aquatic systems

Recent investigations have shown that biogenic methane can be a carbon source for macro invertebrates in freshwater food webs. Stable carbon isotopic signatures, used to infer an organism's food source, indicated that methane can play a major role in the nutrition of chironomid larvae. However, the pathway of methane-derived carbon into invertebrate biomass is still not confirmed. It has been proposed that chironomid larvae ingest methane-oxidizing bacteria (MOB), but this has not been experimentally demonstrated to date. Using ¹³C-labelled methane we could show for the first time that chironomid larvae assimilate methane-derived carbon through MOB. Chironomid larval biomass was significantly ¹³C-enriched after dwelling for 10 days in lake sediment enriched with labelled methane. Moreover, phospholipid fatty acids diagnostic for MOB were detected in larval tissue and were significantly ¹³C-enriched, which encompasses the ¹³C-uptake predicted for a methane-based nutrition. Additionally, chironomid larvae fed on sediment and water-column derived MOB biomass.