Macroinvertebrate Production Research Articles

Dams in the last large free-flowing rivers of Patagonia, the Santa Cruz River, environmental features, and macroinvertebrate community

Three large rivers have their headwaters in the Patagonian Ice Fields (PIFs) in the Andes Mountains, the largest mid-latitude ice masses on Earth: Santa Cruz, Baker and Pascua. They are the last large free flowing rivers in Patagonia, but plans are advanced for building dams for hydroelectric power generation. The three PIF rivers, with a discharge dominated by ice melt, share a common, unique hydrograph compared to that of the other eight large rivers in the region: a distinct seasonal cycle, and an extremely stable discharge, with much lower variability than other rivers. In this study we present the first extensive survey of habitats and benthic macroinvertebrates in the least studied system, the Santa Cruz River. We assess how much of the natural capital provided and sustained by benthic invertebrates are expected to be lost by flooding and discuss how dams would affect riverine habitat and biota. In the Santa Cruz River, we conducted an intensive field survey during September 2010; a total of 52 sites located at regular 6 km intervals were sampled along the 310 river-km for macroinvertebrates and seventeen habitat variables. Although some habitat structure is apparent at the local scale, the Santa Cruz River could be described as very homogeneous. Macroinvertebrate density and the richness (38 genera) found in the Santa Cruz River resulted to be one of the lowest in comparison with 42 other Patagonian rivers. Albeit weak, the structure of the macroinvertebrates assemblages was successfully described by a reduced set of variables. The reduced flow variation and the lack of bed scouring flows have a direct and negative effect on the heterogeneity of riverbeds and banks. The high turbidity of the Santa Cruz River may also contribute to shorter food webs, by affecting autotrophic production, general trophic structure, and overall macroinvertebrate productivity and diversity. Dams will obliterate 51% of the lotic environment, including the most productive sections of the river according to our macroinvertebrate data. Since Santa Cruz River has a naturally homogeneous flow cycle, dams may provide more variable flows and more diverse habitat. Our data provide critically valuable baseline information to understand the effects of dams on the unique set of glacial driven large rivers of Patagonia.

Macroinvertebrate community structure, secondary production and trophic‐level dynamics in urban streams affected by non‐point‐source pollution

Summary1. Despite non‐point‐source (NPS) pollution being perhaps the most ubiquitous stressor affecting urban streams, there is a lack of research assessing how urban NPS pollution affects stream ecosystems. We used a natural experimental design approach to assess how stream macroinvertebrate community structure, secondary production and trophic structure are influenced by urban NPS pollution in six streams.2. Differences in macroinvertebrate community structure and secondary production among sites were highly correlated with stream‐water specific conductivity and dissolved inorganic phosphorus (DIP) concentrations. Macroinvertebrate richness, the Shannon diversity index and the Shannon evenness index were all negatively correlated with specific conductivity. These patterns were driven by differences in the richness and production of EPT and other intolerant taxa. Production of the five most productive taxa, tolerant taxa, non‐insect taxa and primary consumers were all positively correlated with stream‐water DIP.3. Despite the positive correlation between primary consumer production and DIP, there was no correlation between macroinvertebrate predator production and either total or primary consumer macroinvertebrate production. This was observed because DIP was positively correlated with the production of non‐insect macroinvertebrate taxa assumed to be relatively unavailable for macroinvertebrate predator consumption. After removing production of these taxa, we observed a strong positive correlation between macroinvertebrate predator production and production of available prey.4. Our results suggest that urban NPS pollution not only affects macroinvertebrate community structure, but also alters secondary production and trophic‐level dynamics. Differences in taxon production in our study indicate the potential for altered energy flow through stream food webs and potential effects on subsidies of aquatic insect prey to riparian food webs.

Macroinvertebrate diets reflect tributary inputs and turbidity-driven changes in food availability in the Colorado River downstream of Glen Canyon Dam

Physical changes to rivers associated with large dams (e.g., water temperature) directly alter macroinvertebrate assemblages. Large dams also may indirectly alter these assemblages by changing the food resources available to support macroinvertebrate production. We examined the diets of the 4 most common macroinvertebrate taxa in the Colorado River through Glen and Grand Canyons, seasonally, at 6 sites for 2.5 y. We compared macroinvertebrate diet composition to the composition of epilithon (rock and cliff faces) communities and suspended organic seston to evaluate the degree to which macroinvertebrate diets tracked downstream changes in resource availability. Diets contained greater proportions of algal resources in the tailwater of Glen Canyon Dam and more terrestrial-based resources at sites downstream of the 1 st major tributary. As predicted, macroinvertebrate diets tracked turbidity-driven changes in resource availability, and river turbidity partially explained variability in macroinvertebrate diets. The relative proportions of resources assimilated by macroinvertebrates ranged from dominance by algae to terrestrial- based resources, despite greater assimilation efficiencies for algal than terrestrial C. Terrestrial resources were most important during high turbidity conditions, which occurred during the late-summer monsoon season (July-October) when tributaries contributed large amounts of organic matter to the mainstem and suspended sediments reduced algal production. Macroinvertebrate diets were influenced by seasonal changes in tributary inputs and turbidity, a result suggesting macroinvertebrate diets in regulated rivers may be temporally dynamic and driven by tributary inputs.

Secondary production of sandy beach macrofauna: An evaluation of predictive models

During the last three decades, several predictive models have been developed to estimate the somatic production of macroinvertebrates. Although the models have been evaluated for their ability to assess the production of macrobenthos in different marine ecosystems, these approaches have not been applied specifically to sandy beach macrofauna and may not be directly applicable to this transitional environment. Hence, in this study, a broad literature review of sandy beach macrofauna production was conducted and estimates obtained with cohort-based and size-based methods were collected. The performance of nine models in estimating the production of individual populations from the sandy beach environment, evaluated for all taxonomic groups combined and for individual groups separately, was assessed, comparing the production predicted by the models to the estimates obtained from the literature (observed production). Most of the models overestimated population production compared to observed production estimates, whether for all populations combined or more specific taxonomic groups. However, estimates by two models developed by Cusson and Bourget provided best fits to measured production, and thus represent the best alternatives to the cohort-based and size-based methods in this habitat. The consistent performance of one of these Cusson and Bourget models, which was developed for the macrobenthos of sandy substrate habitats (C&BSS), shows that the performance of a model does not depend on whether it was developed for a specific taxonomic group. Moreover, since some widely used models (e.g., the Robertson model) show very different responses when applied to the macrofauna of different marine environments (e.g., sandy beaches and estuaries), prior evaluation of these models is essential.

Secondary production in a southern Illinois headwater stream: relationships between organic matter standing stocks and macroinvertebrate productivity

We quantified macroinvertebrate production and organic matter standing stocks in riffle/run and pool habitats for 2 y in 2 reaches of Big Creek, a 3rd-order stream in southern Illinois, USA. Habitat-weighted secondary production was 24.9 and 26.2 g ash-free dry mass (AFDM) m−2 y−1 in the upper and lower reaches, respectively, in year 1 of the study and 17.6 and 15.1 AFDM m−2 y−1 in year 2. Annual production to biomass (P/B) ratios of the macroinvertebrate assemblages ranged from 7 to 10. Collector-gatherers, which were dominated by nontanypodine Chironomidae and Oligochaeta, accounted for >60% of total habitat-weighted production in both reaches, and consumption estimates based on production efficiencies indicated they consumed high proportions of available organic matter resources ≤250 µm. Macroinvertebrate production in Big Creek was strongly correlated with organic matter standing stocks, and our subsequent analyses of production and organic matter resources across several low-order North American streams suggested standing stocks of small wood, a relatively refractory component of organic matter, are an important component of the relationship between macroinvertebrate production and organic matter. However, the apparent influence of small wood on production may be related to associated physical characteristics of these streams, such as pH and canopy cover. Secondary production estimates in our data set were a function of both adjusted total organic matter exclusive of wood and wood standing stocks. Although production–organic matter relationships may be obscured by other factors at the local level, our results indicate that patterns of macroinvertebrate production across large geographic scales may be driven largely by the availability of detrital resources.

Patterns of macroinvertebrate production, trophic structure, and energy flow along a tallgrass prairie stream continuum

We estimated benthic organic matter standing stocks, macroinvertebrate production, food‐web structure, and stream metabolism along a longitudinal continuum of Kings Creek at Konza Prairie Biological Station in Kansas. Benthic macroinvertebrates were sampled for 1 yr from three stream reaches (grass, shrub, gallery forest). Total habitat‐weighted production ranged from 9.1 g to 31.9 g ash‐free dry weight m−2 yr−1 with the grass headwaters accounting for the highest production. Functional group contributions to production were similar along the continuum, with collector–gatherers (40–56% of total) and predators (23–38%) dominating all reaches. Detrital pathways appeared to account for most energy flow in all reaches, and all reaches were net heterotrophic on all dates when metabolism was measured, except for the grass headwater reach in spring. Predators were well‐represented and consumed 65–107% of total macroinvertebrate production, whereas scrapers (11–15%), shredders (2–4%), and filterers (< 1%) consumed relatively small percentages of available resources. Dominance of predators suggested top‐down controls are important in this system. However, changes in energy flow through other groups reflected longitudinal variation in resource availability. This prairie stream continuum conforms to some predictions of conceptual stream continua models, but biotic interactions, which are often not considered, may override some predicted responses to changes in the physical template.

Direct versus indirect pathways of salmon-derived nutrient incorporation in experimental lotic food webs

The objective of our study was to examine how salmon carcass subsidization through alternative trophic pathways affected stream food web productivity. Three salmon carcass treatments (dissolved carcass nutrients only, dissolved carcass nutrients + carcass material, and a carcass-free control) were replicated five times in artificial stream channels. We quantified changes in water chemistry and the production of periphyton, macroinvertebrates, and age 0+ steelhead trout (i.e., sea-run rainbow trout, Oncorhynchus mykiss ) over 65 days. Dissolved ammonium and periphyton chlorophyll a concentrations increased for an approximate 2-week period in both carcass-augmented treatments. However, there was no commensurate effect on periphyton ash-free dry mass. Total macroinvertebrate biomass was significantly greater in the presence of nutrients + material after 65 days, but no such increase was observed in response to the addition of dissolved nutrients only. Despite modest and inconsistent effects at lower trophic levels, both the nutrients only and nutrients + material treatments increased the growth and condition of age 0+ steelhead trout, with significantly greater gains occurring in the presence of nutrients + material. These data suggest that while salmon carcasses can enhance the short-term growth of juvenile salmonids via bottom-up pathways, the availability and direct consumption of carcass biomass may promote a substantial amount of additional production.

Stream ecosystem response to chronic deposition of N and acid at the Bear Brook Watershed, Maine

The Bear Brook Watershed in Maine (BBWM) is a long-term, paired watershed experiment that addresses the effects of acid and nitrogen (N) deposition on whole watersheds. To examine stream response at BBWM, we synthesized data on organic matter dynamics, including leaf breakdown rates, organic matter inputs and standing stocks, macroinvertebrate secondary production, and nutrient uptake in treated and reference streams at the BBWM. While N concentrations in stream water and leaves have increased, the input, standing stocks, and breakdown rates of leaves, as well as macroinvertebrate production, were not responsive to acid and N deposition. Both chronic and acute increases of N availability have saturated uptake of nitrate in the streams. Recent experimental increases in phosphorus (P) availability enhanced stream capacity to take up nitrate and altered the character of N saturation. These results show how the interactive effects of multiple factors, including environmental flow regime, acidification, and P availability, may constrain stream response to chronic N deposition.

Diel Fish Habitat Selection in a Tributary Stream

This study investigated the location and diel habitat preferences (at 100 m reach scale) of fish in a small tributary stream in late spring, early summer. During the day, coho (Oncorhynchus kisutch) preferred areas with more cover (deeper, greater extent of undercut banks) vs. night when LWD was preferred (Pearson correlation and step-wise MLR). Chinook (O. tshawytscha) exhibited an opposite pattern, preferring LWD during the day vs. higher velocity at night. This suggests these two potadromous species may be partitioning resources. Pooling coho, chinook and rainbow trout (O. mykiss) indicated reaches with more LWD were selected at night (r2 = 0.86, p = 0.005) vs. deeper reaches during the day (r2 = 0.62, p = 0.04). Although not measured specifically, we believe LWD supports more macroinvertebrate production vs. the predominantly sandy substrate. Thus, a potential mechanism behind the observed patterns in reach selection may be the tradeoff between food resource abundance vs. predation risk. The majority of captured fish were juveniles supporting the premise first order tributaries can serve as important nursery habitats, especially if they exhibit stable flow and thermal regimes.

Response of secondary production by macroinvertebrates to large wood addition in three Michigan streams

Summary1. We measured responses in macroinvertebrate secondary production after large wood additions to three forested headwater streams in the Upper Peninsula of Michigan. These streams had fine‐grained sediments and low retention capacity due to low amounts of in‐channel wood from a legacy of past logging. We predicted that wood addition would increase macroinvertebrate secondary production by increasing exposed coarse substrate and retention of organic matter.2. Large wood (25 logs) was added haphazardly to a 100‐m reach in each stream, and a 100‐m upstream reach served as control; each reach was sampled monthly, 1 year before and 2 years after wood addition (i.e. BACI design). Macroinvertebrate secondary production was measured 1 year after wood addition in two habitat types: inorganic sediments of the main channel and debris accumulations of leaf litter and small wood.3. Overall macroinvertebrate production did not change significantly because each stream responded differently to wood addition. Production increased by 22% in the main‐channel of one stream, and showed insignificant changes in the other two streams compared to values before wood addition. Changes in main‐channel macroinvertebrate production were related to small changes in substrate composition, which probably affected habitat and periphyton abundance. Macroinvertebrate production was much greater in debris accumulations than in the main‐channel, indicating the potential for increased retention of leaf litter to increase overall macroinvertebrate production, especially in autumn.4. Surrounding land use, substrate composition, temperature and method of log placement are variables that interact to influence the response of stream biota to wood additions. In most studies, wood additions occur in altered catchments, are rarely monitored, and secondary production is not a common metric. Our results suggest that the time required for measurable changes in geomorphology, organic matter retention, or invertebrate production is likely to take years to achieve, so monitoring should span more than 5 years, and ecosystem metrics, such as macroinvertebrate secondary production, should be incorporated into restoration monitoring programs.

The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk stream

Abstract The effects of changes in shading (through riparian canopy removal and re‐growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in‐stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels.

Macroinvertebrate community dynamics: strong negative response to salmon redd construction and weak response to salmon-derived nutrient uptake

Densely spawning salmon (Oncorhynchus spp.) affect macroinvertebrates negatively through redd construction and positively through nutrients released during spawning and carcass decomposition. We investigated the long-term characteristics of this interaction by measuring density, biomass, and C and N sources in benthic macroinvertebrates over 1 y. Total macroinvertebrate community biomass decreased during spawning and redd construction. However, the percentage of macroinvertebrate biomass derived from salmon increased. The highest percentage (56%) and biomass (2.71 g/m2) of salmon-derived tissue in the macroinvertebrate community occurred 3 mo after spawning. Shredders accumulated the most salmon-derived biomass per individual; however, collector-filterers, scrapers, and predators accumulated the most salmon-derived biomass at the population level, a result that suggests multiple pathways of salmon nutrient acquisition. Salmon-derived macroinvertebrate biomass was never <22% of macroinvertebrate community biomass in the spawning reach, but 6 mo after spawning, no clear density or biomass differences were found between reaches with and without salmon. This pattern held true at all scales examined, from whole community to functional feeding group to individual taxa in prespawning samples from both years. These results suggest that increased macroinvertebrate production from the nutrient and energy subsidy from salmon was restricted to the recovery period following the disturbance of redd construction and might have been obscured by emergence and transfer to higher trophic levels.

Assessing ecological responses to catastrophic amphibian declines: Patterns of macroinvertebrate production and food web structure in upland Panamanian streams

As part of the Tropical Amphibian Declines in Streams (TADS) project, we estimated macroinvertebrate production and constructed quantitative food webs for four headwater stream reaches in the Panamanian uplands: two that had experienced massive amphibian declines and two with unaffected amphibian populations. As expected for forested headwaters, allochthonous materials were the dominant energy source. Total macroinvertebrate biomass and production ranged from 231 to 360 mg ash-free dry mass m−2 and from 3.1 to 4.4 g ash-free dry mass m−2 yr−1, respectively, and did not appear influenced by the presence or absence of amphibians. However, macroinvertebrate functional structure differed between pre- and post-decline sites, with shredder production significantly higher in pre-decline sites and scrapers significantly higher in post-decline sites. Taxonomic differences between pre- and post-decline sites were also evident. There was a shift in scrapers from smaller-bodied taxa (e.g., Psephenus) in pre-decline sites to larger-bodied groups (e.g., Petrophila) in post-decline sites. Detrital pathways were dominant in these systems, with shredders and collectors accounting for most energy flow. However, scrapers were well-represented and they were food-limited in these systems, particularly in the presence of larval amphibians at pre-decline sites. Ecological effects of catastrophic amphibian declines ranged from subtle shifts in taxonomic composition and functional structure of remaining consumers to changes in the availability and relative importance of autochthonous energy sources.

Macroinvertebrate Production in the Submerged Aquatic Vegetation of the Mobile–Tensaw Delta: Effects of an Exotic Species at the Base of an Estuarine Food Web

This study, conducted in 1997, reports the first estimates of the impacts of the proliferation of an exotic submerged aquatic vegetation (SAV) species (Myriophyllum spicatum) on macroinvertebrate production via comparisons with two co-occurring native SAV species (Heteranthera dubia and Vallisneria americana) in the tide-influenced Mobile–Tensaw Delta (located in the north-central Gulf of Mexico, 30°40′ N, 87°55′ W). Production of macroinvertebrates was greatest on M. spicatum and H. dubia and least on V. americana. The key determinant of these differences was a greater abundance of amphipods (Gammarus mucronatus) found on the leaves of M. spicatum and H. dubia. Macroinvertebrate production on M. spicatum was three times greater (>1 kg m−2 year−1) than on either of the native SAV species. No-choice palatability tests showed that these differences could not be attributed to differences in invertebrate grazing on these plants. Instead, it is probable that the high production within the structurally complex M. spicatum and H. dubia was the result of reduced predator foraging efficiency. If true, then the presence of this exotic species probably renders this elevated production inaccessible to most high-order predators.

The effect of an interstate highway on macroinvertebrate production in headwater streams

The effects of the Maine Turnpike (> 50 million vehicles y -1 ) on macroinvertebrate assemblage structure, macroinvertebrate production, and stored and suspended organic matter were examined in five 1 st and 2 nd order low-gradient streams in southern Maine. Streams were sampled upstream and downstream of roadway crossings. Differences in habitat structure, water and sediment chemistry, and biotic communities were evident among streams. However, the variability in these attributes among streams was greater than within-stream differences attributable to the presence of the roadway. Total secondary production showed little sensitivity to stresses related to the roadway, but was related to water chemistry, substrate particle size, discharge, and stored organic matter. Habitat characteristics, such as the type of stored organic matter, related to high production differed between streams with coarse versus fine substrates. Production in the study streams was comparable to estimates from other small streams on the coastal plain of the eastern United States (3.5-15.3 gAFDM m -2 y -1 ). This study demonstrates that structure and function of headwater stream ecosystems may be maintained in the presence of a major roadway.

Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat

Beach-cast wrack is a prominent feature of beaches of south-western Australia. We examined the fauna of these beaches to explore the generalisation [Polis, G.A., Hurd, S.D., 1995. Extraordinarily high spider densities on islands: flow of energy from the marine to terrestrial food webs and the absence of predation. Ecology 92, 4382–4386] that beach-cast wrack from highly productive marine ecosystems subsidises low productivity of terrestrial ecosystems, to establish whether this generalisation is relevant to oligotrophic marine systems. We sampled three beaches with high and three beaches with low volumes of beach-cast wrack to determine if: (1) the presence of wrack influences the abundance of macroinvertebrates; (2) wrack acts as a food source for beach macroinvertebrates; and (3) the influence of wrack varies between zones above the high water mark. We measured wrack volume and composition, sediment characteristics, the abundance of different epibenthic and infaunal macroinvertebrates taxa, and δ 13C and δ 15N of macrophytes and macroinvertebrates. The mean volume of wrack on high-wrack beaches was 0.27–1.07 m 3 wrack m −2 compared to 0.00–0.09 m 3 wrack m −2 on low-wrack beaches. There were no significant differences in sediment grain size, moisture content or loss on ignition between the two types of beaches or zones. Epibenthic fauna and infauna were consistently abundant on high-wrack beaches (20–291 and 0.5–3.5 individuals 0.64 m −2, respectively), but either absent or extremely rare in low-wrack beaches (0–3 and 0–0.1 individuals 0.64 m −2, respectively). Within high-wrack beaches, there were no significant differences in the abundance of epifauna or infauna among beaches or between zones. The δ 13C values of macroinvertebrates at all sites were most similar to red and brown algae, with the exception of beetles from two beaches, which were closest to seagrasses. Mixing model (Isosource) results for mesograzing amphipods and dipteran flies suggested carbon was assimilated mostly from the seagrass Posidonia spp., the dune grass Spinifex longifolia and red algae for amphipods and from brown algae, red algae and dune vegetation for dipteran flies. We conclude that the presence of marine-derived wrack plays a major role in subsidising production of macroinvertebrates on beaches of south-western Australia. We suggest that marine subsidies can play a role in supporting terrestrial production, even in oligotrophic marine environments.

Contributions of primary organic matter sources to macroinvertebrate production in an intertidal salt marsh (Scirpus triqueter) ecosystem

The trophic importance of different primary organic matter sources to macroinvertebrates was studied in the intertidal salt marsh (Scirpus triqueter) habitat of the Nakdong River estuary (Korea) using carbon and nitrogen stable isotope ratios. δ13C and δ15N values of primary producers and dominant invertebrates, along with their biomass or abundance, were monitored monthly from December 2004 to November 2005. S. triqueter flourished from spring to summer and vanished in late fall to winter. Biomass of microphytobenthos peaked in late spring to summer. Of 25 taxa of macrozoobenthos collected, 7 were found throughout the year. Despite a dramatic seasonal fluctuation in the marsh club-rush S. triqueter biomass, the expected seasonal change in the isotopic signatures of the 7 dominant macroinvertebrates was not found. A large gap (3.5 to 12.3‰) in the δ13C signature between S. triqueter (–27.9 ± 1.0‰) and the marsh-dwelling macroinvertebrates (means from –24.4 to –15.6‰) indicates little utilization of this marsh-derived organic matter by the animals. Surface grazers and deposit feeders (e.g. Hediste japonica, Heteromastus filiformis, Angustassiminea castanea, Ilyoplax pusilla and Paranthura sp.) had δ13C similar to δ15N and about 4‰ higher than those (–16.5 ± 2.1 and 8.7 ± 1.1‰, respectively) of microphytobenthos, revealing that mainly microphytobenthos-derived carbon contributed to their diets. Two suspension-feeding bivalves (e.g. Laternula marilina and Corbicula sp.) showed a similar δ13C to that of suspended particulate organic matter (POM) in the channel (–23.0 ± 0.7‰) and the Nakdong River (–24.5 ± 1.9‰). However, their δ15N values are about 4‰ higher than that of channel POM (5.7 ± 0.6‰), but lower compared to that of river POM (–11.6 ± 2.3‰), suggesting that organic matter derived from coastal phytoplankton, not river discharge, is a major nutritional source for these bivalves. Overall, our isotopic data suggest that the S. triqueter-marsh invertebrates are generally more dependent on organic matter derived from algal sources than on S. triqueter or terrestrial sources.

Structural and functional aspects of treated mine water and aquaculture effluent streams

Multiple effluent streams may flow into a single receiving stream making it difficult to understand the effects of a single effluent source or the interactions between effluents. In this study, we examined benthic community structure and function in an effluent stream formed by the release of treated mine water, in treated mine water that had been used as a water source for flow-through aquaculture and below the confluence of the two. This study demonstrated that macroinvertebrate communities, while taxonomically simple, developed in treated mine water. The addition of aquaculture effluent to the treated mine water allowed colonization by additional taxa, increased leaf decomposition rates and may have conferred resistance to a turbidity event. Ecosystem responses were mediated by the surrounding terrestrial environment. In shaded conditions macroinvertebrate densities could be as much as 10× higher and the taxa were dominated by simuliids and chironomids, while in open conditions filamentous algae flourished and the taxa were dominated by hydroptilids and chironomids. Consequently, consideration of stream processes that promote preferred ecological processes, such as macroinvertebrate production and organic matter processing, when siting effluent streams may reduce impacts on receiving streams.

Role of habitat in determining macroinvertebrate production in an intermittent‐stream system

Summary1. The effect of channel drying on macroinvertebrate production was studied at the habitat and reach scale in a catchment drained by intermittent streams in Maine, U.S.A. The catchment includes two first‐order streams and their second‐order confluence. Six reaches were selected for study based on differences in channel slope and habitat cover (bedrock, riffle/run, debris dam and pool). Stream water in each reach was acidic and oligotrophic.2. The study reaches had different degrees of channel drying. In the first‐order reaches, surface flow ceased earlier in the season and for longer periods than second‐order reaches. Regardless of reach, pool and debris dam habitats retained water longer than riffle/runs and bedrock. Unlike other habitats, debris dams retained moisture for relatively long periods following cessation of surface flow.3. Reach‐specific macroinvertebrate production ranged from approximately 1.7 to 2.9 g AFDM m−2 year−1 which are among the lowest values ever reported. Habitat‐specific production ranged from approximately 0.5 to 5.0 g AFDM m−2 year−1 (bedrock and debris dams, respectively).4. At the reach scale, quantities of stored benthic organic matter (range approximately 200–600 g AFDM−2) decreased in a downstream direction.5. A combination of differences in the timing and duration of channel drying, habitat structure and detritus standing stocks appeared to influence levels of invertebrate production among the study reaches.6. Our interpretation of a canonical correspondence analysis indicates that drying is more important than habitat in affecting macroinvertebrate production in this intermittent stream system.

The response of macroinvertebrate production to a pollution gradient in a headwater stream

Summary1. This study quantified patterns of macroinvertebrate secondary production and stored benthic organic matter along a gradient of pollution and habitat channelisation over a 3‐km reach of Goosefare Brook, a first‐order stream in southern Maine (U.S.A.).2. Whole‐community invertebrate production decreased from 26.4 g ash‐free dry mass (AFDM) m−2 year−1 at the reference station to 1.1 g AFDM m−2 year−1 at stations with the greatest levels of pollution. Production decreased along the pollution gradient for most taxa, although decreases were partly offset by production increases in tolerant taxa. Biomass turnover rates (P/B) were less affected by the stresses than was production.3. Differences in functional characteristics of the community were evident at stations with channelised habitat, but overall production declined in a linear pattern that mirrored the pollution gradient. Stored organic matter showed a decline along the gradient, but was also lower at channelised stations. Populations of taxa with documented pollution tolerance were more likely to maintain or increase production and P/B.4. Decreasing biomass because of decreasing stored organic matter and lethal effects of pollutants resulted in shifts in the pathways of energy flow observed at stations exposed to moderate physical or chemical stress, to the loss of most taxa and an extreme (96%) decrease in production at the stations receiving the highest levels of metal pollution.5. The shifting prominence of different taxa along a continuum of stress in Goosefare Brook shows that describing the nature of an impairment in a functional context requires consideration of chemical stressors, habitat alterations and food resources.