Nitrogen and phosphorus uptake in two Idaho (USA) headwater wilderness streams

Nitrate and phosphate solutions were released into two reaches of two central Idaho streams to determine within- and between-stream variability in uptake lengths, uptake rates, and mass transfer coefficients. Physical and biotic stream characteristics and periphyton nitrate-uptake rates in recirculating chambers were measured to determine their influence on nutrient dynamics. Phosphate uptake length did not differ among the four reaches. There were no within-stream differences in nitrate uptake lengths but they did differ between the two streams. Long nitrate uptake lengths likely were due to instream concentrations above saturation but also may have been influenced by differences in active surface area and algal abundance. Nitrate and phosphate uptake lengths were longer, and uptake rates higher, than most other published values. However, mass transfer coefficients were comparable to measurements in other streams. Mass transfer coefficients may be a better parameter for temporal and spatial comparisons of instream nutrient dynamics, and for determining the underlying causes of variability in uptake length. Received: 27 May 1998 / Accepted: 11 January 1999     

Can bryophytes be used to characterize hydrologic permanence in forested headwater streams?

Recent court cases have questioned whether all headwater streams, particularly those that are not perennial, fall within the protective boundaries of the Clean Water Act. Rapid field-based indicators of hydrologic permanence are critically needed for jurisdictional determinations. The study objective was to determine whether characteristics of bryophyte assemblages in forested headwater streams can be useful indicators of hydrologic permanence. We sampled bryophytes from the channel thalweg at 113 sites across 10 forests in the U.S. which varied in hydrologic permanence. Hydrologic permanence was based on hydrologic status during spring (wet season) and late summer (dry season) visits. Perennial sites had flow (surface or visibly interstitial) during both spring and summer visits. Intermittent sites flowed during spring but were either dry or had surface water limited to isolated pools in summer. Ephemeral sites did not have flow during either visit. The species composition significantly differed between ephemeral and perennial stream reaches. The species composition of intermittent streams overlapped with both ephemeral and perennial streams. Three species and six families were identified as indicators of particular permanence classes. Liverworts occurred more frequently at perennial than at intermittent or ephemeral sites. Bryophytes with cushion and turf growth forms were common to ephemeral sites, whereas mat and weft forms were more common to perennial sites. Acrocarpous mosses were more frequent at ephemeral than at perennial sites. The frequencies of bryophyte-moisture associations (derived from the literature) across the three permanence categories were significantly different. Species associated with dry habitats were more frequently encountered at ephemeral than perennial sites, whereas species associated with wet habitats were more frequent at perennial than ephemeral sites. Species richness varied among forests and permanence classes. Ephemeral sites tended to have higher species richness than perennial sites; however, this pattern did not hold for all forests. Bryophytes should be included among the tools for jurisdictional determinations, much like vascular plants are used to help delineate wetlands. Growth forms and higher level taxonomy of bryophytes (i.e., phyla) can be particularly useful for making jurisdictional determinations because of their ability to discriminate ephemeral from intermittent and perennial reaches and they are measures that can be rapidly trained and routinely used by agencies making such determinations.     

Larval salamanders and channel geomorphology are indicators of hydrologic permanence in forested headwater streams

Regulatory agencies need rapid indicators of hydrologic permanence for jurisdictional determinations of headwater streams. The study objective was to assess the utility of larval salamanders and habitat variables for determining stream permanence across a large geographic area. We sampled four core forests (61 sites in IN, KY, and OH) in spring (April–May) and summer (August–September) over a 2-year period. Sites in each forest were selected to cover a gradient of permanence, from perennial to ephemeral. Salamanders were collected by both benthic core sampling and timed visual search on each site visit. Classification and regression tree (CART) models were used to identify indicators of seasonal permanence at core sites that were then tested using data collected from 6 satellite forests (52 sites) located nationwide. Southern two-lined salamanders, Eurycea cirrigera, were numerically dominant and were the only species included in CART models. Salamander diversity declined with distance from the Appalachians and strong longitudinal changes in assemblage composition were evident within streams. Abundance of E. cirrigera was positively correlated with watershed area, whereas dusky salamanders, Desmognathus spp., and spring salamanders, Gyrinophilus porphyriticus, comprised a greater proportion of salamander communities at intermittent sites within their range. Spring and summer CART models incorporated E. cirrigera abundance and measures of channel geomorphology to accurately classify approximately 80% of core sites as either ephemeral, intermittent or perennial. When applied to validation data from national satellite forests, correct classification rates were >85% for intermittent and ephemeral sites, but were only ～20% for perennial sites. These findings suggest that larval plethodontid salamanders and habitat variables can be valuable predictors of headwater stream hydroperiod, but indicators are largely limited to the regional scale.     

The potential of agricultural headwater streams to retain soluble reactive phosphorus

Zooplankton may preferentially graze small, edible diatom species and therefore affect fossils relative to live assemblages by selective removal or increased sedimentation via egestion. Cladoceran zooplankton remains and diatom edibility were analyzed in sediment cores from Moon Lake and Coldwater Lake (North Dakota, USA) to assess changes in potential grazing pressure on algae and influence on diatom-inferred salinity (DIS) reconstructions. Sedimentary zooplankton in Moon Lake were dominated by littoral Cladocera, whereas Coldwater Lake assemblages were primarily small-bodied pelagic and littoral species. Relationships between cladocerans and environmental parameters over the past century varied by site and by species, with Chydorus brevilabris related most closely to drought at Moon and Bosmina sp. related to drought at Coldwater. A higher percentage of inedible diatoms occurred in the sediments of Moon Lake as compared to Coldwater Lake. DIS correlations with drought records improved in Moon Lake when only inedible diatom taxa were used to build a transfer function, but no improvement was seen for Coldwater Lake with this approach. These data suggest grazing pressure on diatoms differed between lakes and that zooplankton–phytoplankton interactions may affect the accuracy of drought reconstructions in the Great Plains.     

Microbial enzyme activity,nutrient uptake and nutrient limitation in forested streams

1. We measured NH₄⁺ and PO₄^?3 uptake length (S_w), uptake velocity (V_f), uptake rate (U), biofilm respiration and enzyme activity and channel geomorphology in streams draining forested catchments in the northwestern (Northern California Coast Range and Cascade Mountains) and southeastern (Appalachian and Ouachita mountains) regions of the United States. Our goal was to use measures of biofilm enzyme activity and nutrient uptake to assess nutrient limitation in forested streams across broad regional scales. 2. Geomorphological attributes, biofilm enzyme activity and NH₄⁺ uptake were significantly different among streams in the four study units. There was no study unit effect on PO₄^?3 uptake. The proportion of the stream channel in pools, % woody debris, % canopy closure, median substrate size (d₅₀), stream width (w), stream velocity (v), discharge (Q), dispersion coefficient (D) and transient storage (A_s/A) were correlated with biofilm enzyme activity and nutrient uptake in some study units. 3. Canonical correlation analyses across study units revealed significant correlations of NH₄‐V_f and PO₄‐V_f with geomorphological attributes (w, d₅₀, D, % woody debris, channel slope and % pools) and biofilm phosphatase activity. 4. The results did not support our expectation that carbon processing rates by biofilm microbial assemblages would be governed by stream nutrient availability or that resulting biofilm enzyme activity would be an indicator of nutrient uptake. However, the relative abundances of peptidases, phosphatase and glycosidases did yield insight into potential N‐, P‐ and C‐limitation of stream biofilm assemblages, and our use of biofilm enzyme activity represents a novel application for understanding nutrient limitations in forested streams. 5. Regressions of V_f and U against ambient NH₄⁺ and PO₄^?3 indicated that none of our study streams was either NH₄⁺ or PO₄^?3 saturated. The Appalachian, Ouachita and Coastal streams showed evidence of NH₄⁺ limitation; the Ouachita and Coastal streams were PO₄^?3 limited. As a correlate of nutrient limitation and saturation in streams, ratios of total aminopeptidase and phosphatase activities and the ratio of NH₄‐U to PO₄‐U indicate these forested streams are predominantly N‐limited, with only the streams draining Ouachita and Coastal catchments demonstrating appreciable levels of P‐limitation. 6. Our results comparing the stoichiometry of microbial enzyme activity with nutrient uptake ratios and with the molar ratios N and P in stream waters suggest that biological limitations are not strictly the result of stream chemistry and that the assessments of nutrient limitations in stream ecosystems should not be based on chemistry alone. 7. Our present study, along with previous work in streams, rivers and wetlands, suggests that microbial enzyme activities, especially the ratios of total peptidases to phosphatase, are useful indicators of nutrient limitations in aquatic ecosystems.     

Microbial activity associated with seston in headwater streams: effects of nitrogen, phosphorus and temperature

SUMMARY 1. The influences of temperature and dissolved nitrates and phosphates on microbial activity associated with suspended fine particulate organic matter (seston) were evaluated in four headwater streams in the southern Appalachian Mountains.
2. Temperature manipulations of ± 5°C always induced significant changes in [¹⁴C] glucose mineralization (ANOVA; P <0.05) and [³H]thymidine incorporation (ANOVA; P <0.05).
3. Nutrient amendments of 1.0 mg NO₃ I⁻¹ and 0.05 mg PO₄I⁻¹ induced no significant alterations in bacterial mineralization of [¹⁴C]glucose (ANOVA; P >0.05) or incorporation of [³H]thymidine (ANOVA; P >0.05) in short-term (i.e. 3 h) experiments.
4. Microorganisms attached to refractory particulate organic matter do not appear to be limited by nitrogen or phosphorus even in streams with ambient nutrient concentrations as low as 0.06 mg NO₃ I⁻¹ and <0.03 mg PO₄ I⁻¹.
5. Our results indicate that variations in water temperature resulting from diurnal and seasonal temperature fluctuations, forest clear-cutting, and catchment elevation and aspect can have marked effects upon microbial activity and production, while short-term alterations in nutrient regime appear to have no significant effect on microbial activity associated with seston.     

Effects of wood removal on stream habitat and nitrate uptake in two northeastern US headwater streams

Forested headwater streams play an important role in watershed nutrient dynamics, and wood is thought to be a key factor influencing habitat structure and nitrate-nitrogen dynamics in many forested streams. Because wood in streams can promote nitrogen uptake through denitrification, we hypothesized that nitrate uptake velocities would decrease following wood removal. We measured stream characteristics and nitrate uptake velocities before and after wood manipulation experiments conducted at Hubbard Brook Experimental Forest, NH, and the Sleepers River watershed, VT. The mean size of stream substrates and the amount of riffle habitat increased following wood removal. In contrast to our expectations, summer nitrate uptake velocities increased in the wood removal treatments relative to the reference treatments, possibly because wood removal increased the availability of stable substrates for periphyton growth, therefore increasing nitrate demand in these streams. Our results highlight that effects of wood on stream ecosystems occur through multiple pathways and suggest that the relative importance of these pathways may vary seasonally.     

Uptake of ammonium and soluble reactive phosphorus in forested streams: influence of dissolved organic matter composition

Many microbes responsible for inorganic nutrient uptake and transformation utilize dissolved organic matter (DOM) as a nutrient or energy source, but little is known about whether DOM composition is an important driver of nutrient uptake in streams. Our goal was to determine whether incorporating DOM composition metrics with other more commonly considered biological, physical, and chemical variables improved our ability to explain patterns of ammonium (\({\text{NH}}_{4}^{ + }\)–N) and soluble reactive phosphorus (SRP) uptake across 11 Lake Superior tributaries. Nutrient uptake velocities (V_f) ranged from undetectable to 14.6 mm min^?1 for \({\text{NH}}_{4}^{ + }\)–N and undetectable to 7.2 mm min^?1 for SRP. Logistic regressions suggested that DOM composition was a useful predictor of where SRP uptake occurred (4/11 sites) and \({\text{NH}}_{4}^{ + }\)–N concentration was a useful predictor of where \({\text{NH}}_{4}^{ + }\)–N uptake occurred (9/11 sites). Multiple regression analysis revealed that the best models included temperature, specific discharge, and canopy cover, and DOM composition as significant predictors of \({\text{NH}}_{4}^{ + }\)–N V_f. Partial least squares revealed fluorescence index (describing the source of aquatic fulvic acids), specific ultraviolet absorbance at 254 nm (an indicator of DOM aromaticity), temperature, and conductivity were highly influential predictors of \({\text{NH}}_{4}^{ + }\)–N V_f. Therefore, streams with higher temperatures, lower solute concentrations, more terrestrial DOM signal and greater aromaticity had greater \({\text{NH}}_{4}^{ + }\)–N V_f. Our results suggest that DOM composition may be an important, yet often overlooked, predictor of \({\text{NH}}_{4}^{ + }\)–N and SRP uptake in deciduous forest streams that should be considered along with commonly measured predictors.     

Macroinvertebrate diversity in headwater streams: a review

1. Headwater streams are ubiquitous in the landscape and are important sources of water, sediments and biota for downstream reaches. They are critical sites for organic matter processing and nutrient cycling, and may be vital for maintaining the 'health' of whole river networks.
2. Macroinvertebrates are an important component of biodiversity in stream ecosystems and studies of macroinvertebrate diversity in headwater streams have mostly viewed stream systems as linear reaches rather than as networks, although the latter may be more appropriate to the study of diversity patterns in headwater systems.
3. Studies of macroinvertebrate diversity in headwater streams from around the world illustrated that taxonomic richness is highly variable among continents and regions, and studies addressing longitudinal changes in taxonomic richness of macroinvertebrates generally found highest richness in mid-order streams.
4. When stream systems are viewed as networks at the landscape-scale, α-diversity may be low in individual headwater streams but high β-diversity among headwater streams within catchments and among catchments may generate high γ-diversity.
5. Differing ability and opportunity for dispersal of macroinvertebrates, great physical habitat heterogeneity in headwater streams, and a wide range in local environmental conditions may all contribute to high β-diversity among headwater streams both within and among catchments.
6. Moving beyond linear conceptual models of stream ecosystems to consider the role that spatial structure of river networks might play in determining diversity patterns at the landscape scale is a promising avenue for future research.     

Amphibians as metrics of critical biological thresholds in forested headwater streams of the Pacific Northwest, U.S.A.

1. Amphibians are recognized both for their sensitivity to environmental perturbations and for their usefulness as cost-effective biometrics of ecosystem integrity (=system health).
2. Twenty-three years of research in headwater streams in the Klamath-Siskiyou and North Coast Bioregions of the Pacific Northwest, U.S.A., showed distinct patterns in the distribution of amphibians to variations in water temperature, % fine sediments and the amount of large woody debris (LWD).
3. Here, we review seven studies that demonstrate connections between species presence and abundance and these three in-stream variables. These data were then used to calculate realized niches for three species, the southern torrent salamander, the larval coastal tailed frog and the larval coastal giant salamander, relative to two of these environmental stressors (water temperature and % fine sediments). Moreover, multivariate generalized additive models were used to predict the presence of these three amphibians when these three stressors act in concert.
4. Stream-dwelling amphibians are shown to be extremely sensitive to changes in water temperature, amounts of fine sediment and LWD, and specific thresholds and ranges for a spectrum of animal responses can be used to manage for headwater tributary ecosystem integrity.
5. Consequently, amphibians can provide a direct metric of stream ecosystem integrity acting as surrogates for the ability of a stream network to support other stream-associated biota, such as salmonids, and their related ecological services.     

Structural and functional responses of benthic macroinvertebrates to acid precipitation in two forested headwater streams (Vosges Mountains, northeastern France)

From December 1996 to August 1997, beech litter breakdown and stream benthic macroinvertebrate communities were investigated to assess the effects of acidic precipitation on community structure and function in two second-order headwater streams of the Vosges Mountains (NE France). Because of microscale changes in bedrock mineral composition, one of the streams was acidified (mean pH=4.53, mean total Al=421 g.l^-1) and the other circum-neutral (mean pH=7.23, mean total Al=36 g.l^-1). Results showed that both litter breakdown rate and macroinvertebrate community structure were drastically affected under acidic conditions. The rate of leaf litter breakdown decreased by nine times in the acidic stream. Benthic sampling showed that scrapers were totally eradicated and both gathering and filtering collectors were drastically reduced. Such drastic effects appear to be the consequences of the toxicity of acid water including both proton and aluminum toxicity. A decrease in shredder abundance and a shift from the efficient acid-sensitive Amphipoda Gammarus fossarum to acid-tolerant Nemouroidea (mainly Leuctra sp.) was observed in the acidic stream. Our results indicate that freshwater acidification significantly alters the action of shredders processing leaf litter in the acidic stream. Consequently, interactions between structural and functional responses to acidification probably have profound consequences on the efficiency of acidified stream ecosystems, which in return may alter downstream functioning.     

Context dependency and metacommunity structuring in boreal headwater streams

We studied the relative importance of spatial and environmental factors as determinants of algal, bryophyte, and macroinvertebrate metacommunities in two boreal drainage basins differing in spatial extent. We used eigenfunction spatial analysis to model the spatial relationships among sites and distance‐based redundancy analysis to partition the variability in biotic communities between the spatial filters generated through spatial eigenfunction analysis and the environmental factors measured in the field. In the smaller study area, each metacommunity was structured mostly by environmental factors. This was evidenced by the fact that either the pure environmental effect was significant or environmental factors were strongly spatially structured. In the larger study area, only pure environmental effects were significant. These findings suggest that the environmental control prevails in boreal headwater streams. However, our findings also suggest that the specific details of the community‐environment and community–space relationships are dependent on the focal organism group and drainage basin.     

Top-down and bottom-up processes in grassland and forested streams

The influence of predatory fish on the structure of stream food webs may be altered by the presence of forest canopy cover, and consequent differences in allochthonous inputs and primary production. Eight sites containing introduced brown trout (Salmo trutta) and eight sites that did not were sampled in the Cass region, South Island, New Zealand. For each predator category, half the sites were located in southern beech (Nothofagus) forest patches (range of canopy cover, 65–90%) and the other half were in tussock grassland. Food resources used by two dominant herbivores-detritivores were assessed using stable isotopes. ¹³C/¹²C ratios were obtained for coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), algal dominated biofilm from rocks, and larvae of Deleatidium (Ephemeroptera) and Olinga (Trichoptera). Total abundance and biomass of macroinvertebrates did not differ between streams with and without trout, but were significantly higher at grassland sites than forested sites. However, taxon richness and species composition differed substantially between trout and no-trout sites, irrespective of whether streams were located in forest or not. Trout streams typically contained more taxa, had low biomass of predatory invertebrates and large shredders, but a high proportion of consumers with cases or shells. The standing stock of CPOM was higher at forested sites, but there was less FPOM and more algae at sites with trout, regardless of the presence or absence of forest cover. The stable carbon isotope range for biofilm on rocks was broad and encompassed the narrow CPOM and FPOM ranges. At trout sites, carbon isotope ratios of Deleatidium, the most abundant invertebrate primary consumer, were closely related to biofilm values, but no relationship was found at no-trout sites where algal biomass was much lower. These results support a role for both bottom-up and top-down processes in controlling the structure of the stream communities studied, but indicate that predatory fish and forest cover had largely independent effects.     

Fish size and habitat depth relationships in headwater streams

Summary Surveys of 262 pools in 3 small streams in eastern Tennessee demonstrated a strong positive relationship between pool depth and the size of the largest fish within a pool (P<0.001). Similarly, the largest colonizers of newly-created deep pools were larger than the colonizers of shallow pools. We explored the role of predation risk in contributing to the bigger fish — deeper habitat pattern, which has been noted by others, by conducting five manipulative field experiments in two streams. Three experiments used stoneroller minnows (Campostoma anomalum); one used creek chubs (Semotilus atromaculatus); and one used striped shiners (Notropis chrysocephalus). The stoneroller experiments showed that survival of fish approximately 100 mm in total length (TL) was much lower in shallow pools (10 cm deep) than in deep (40 cm maximum) pools (19% versus 80% survival over 12 d in one experiment) and added cover markedly increased stoneroller survival in shallow pools (from 49% to 96% in an 11-d experiment). The creek chub experiment showed that, as for stonerollers, pool depth markedly influenced survival: the chubs survived an average of 4.9 d in shallow pools and >10.8 d in deep pools. In the striped shiner experiment in shallow artificial streamside troughs, no individuals 75–100 mm TL survived as long as 13 d, where-as smaller (20–25 mm) fish had 100% survival over 13 d. The results of the experiments show that predation risk from wading/diving animals (e.g., herons and raccoons) is much higher for larger fishes in shallow water than for these fishes in deeper water or for smaller fish in shallow water. We discuss the role of predation risk from two sources (piscivorous fish, which are more effective in deeper habitats, and diving/wading predators, which are more effective in shallow habitats) in contributing to the bigger fish — deeper habitat pattern in streams.     

Litter retention in Tasmanian headwater streams after clear-fell logging

Clear-fell logging around small headwater streams in Tasmanian wet eucalypt forests was predicted to affect both the retention of leaf litter and the composition and size of leaf packs. Retention structures were surveyed in six natural streams and six streams in forest regenerated 3–5 years after clear-fell and burn logging. Logged streams had more wood, but retained less leaves than natural streams, and consequently had fewer and smaller leaf packs. Leaf packs from natural streams contained 200% more leaves, bark and twigs than packs from logged streams. The effect of buoyancy on leaf retention was assessed with release and recapture of marked Eucalyptus obliqua and Nothofagus cunninghamii leaves. Eucalypt leaves were more likely to be trapped by retention structures on the bed of the stream, while smaller, more buoyant N. cunninghamii leaves were mainly trapped by leaf packs. Leaf packs in natural streams were formed on a matrix of small twigs and long strips of bark, shed from the upper branches of mature stringybark eucalypts, while leaf retention was reduced in logged streams because there are no mature trees to provide effective retention structures. Changes to the channel form increase both discharge and sedimentation. These factors have strong implications for downstream nutrient processing and riverine food webs.     

Selective foraging on terrestrial invertebrates by rainbow trout in a forested headwater stream in northern Japan

The important contribution of terrestrial invertebrates to the energy budget of drift-foraging fishes has been well documented in many forested headwater streams. However, relatively little attention has been focused on the behavioral mechanisms behind such intensive exploitation. We tested for the hypothesis that active prey selection by fishes would be an important determinant of terrestrial invertebrates contribution to fish diets in a forested headwater stream in northern Japan. Rainbow trout, Oncorhynchus mykiss, were estimated to consume 57.12 mg m^–2 day^–1 (dry mass) terrestrial invertebrates, 77% of their total input (73.89 mg m^–2 day^–1), there being high selectivity for the former from stream drift. Both the falling input and drift of terrestrial invertebrates peaked at around dusk, decreasing dramatically toward midnight. In contrast, both aquatic insect adults and benthic invertebrates showed pronounced nocturnal drift. Because the prey consumption rates of rainbow trout were high at dawn and dusk, decreasing around midnight, the greater contribution of terrestrial invertebrates to trout diet was regarded as being partly influenced by the difference in diel periodicity of availability among prey categories. In addition, selectivity also depended upon differences in individual prey size among aquatic insect adults, and benthic and terrestrial invertebrates, the last category being largest in both the stream drift and the trout diets. We concluded that differences in both the timing of supplies and prey size among the three prey categories were the primary factors behind the selective foraging on terrestrial invertebrates by rainbow trout.     

Collection strategies for quantifying protist assemblages in temperate headwater streams

We aimed at indicating some regularities of a constructed wetland treating agricultural runoff in China. The regularities, including the nitrogen removal capacity all year round, the nitrogen distribution pathways, and the nitrogen species removal kinetics, of a free water surface constructed wetland (2,800 m²) in the Dianchi Valley, which has been in operation for 27 months, were studied. The planted Phragmites australis and Zizania caduciflora were harvested biannually. The average inflow rate was recorded by an ultrasonic flow instrument, and then the hydraulic loading rate (HLR) and hydraulic retention time (HRT) were calculated. The average inflow and outflow concentrations of total nitrogen (TN), ammonia, and nitrate were measured, while the corresponding removal rates were calculated, showing better results than other constructed wetlands. Then the distribution pathways of nitrogen were analyzed, which indicated that plant harvesting was more important in wetland-treated agricultural runoff than in domestic wastewater. The reason for a good nitrogen removal capability and the obvious function of plants in the present wetland is the sound climate and intermittent inflow in the wetland. Results showed that inflow load had significant correction with both TN and ammonia removal efficiency. HLR, inflow rate, inflow nitrogen concentration, and temperature had significant and positive correction with both TN and ammonia removal. However, HRT had negative correction with both TN and ammonia removal, and the nitrate removal efficiency and parameters mentioned earlier were not significantly correlated. The rate constant values for nitrate and ammonia in summer were obviously larger than in winter. It is possible that bacterial and microbial activities were more active in summer than winter, and more conducive to bacterial and vegetative growth in summer than winter. Since this study was a pioneer for the implementation of constructed wetlands in China treating agricultural runoff, it has proved that this eco-technology could be used effectively for water quality enhancement in China and other areas with a similar climate.     

Habitat characteristics and trophic structure of benthic macroinvertebrates in a forested headwater stream

Three channel reaches with different habitat characteristics were selected to test the variability in community structure of benthic macroinvertebrates by comparing the relative abundance of functional feeding groups among the reaches. The important factors influencing the spatial and temporal organization of community structure were explored using nonmetric multidimensional scaling (NMS). The habitat characteristics in the reaches were different in terms of habitat type, hydrological factors, and substrate composition. The first headwater reach was classified as a step-pool reach with similar relative areas of riffle and pool habitats. The second mid-reach and the third down reach had greater areas of pool habitat followed by runs and riffles whose proportions were similar between the latter two reaches. The relative abundances of functional feeding groups were different among the surveyed reaches. Gammarid shredders predominated in the upper reach, and chironomid collector–gatherers and collector–filterers were in greater abundance in the two lower reaches. The proportions of gammarids were minor in the mid and downstream reaches. NMS ordination indicated that the proportion of substrates < 8 mm, discharge, and water depth mainly determined the spatial and temporal distribution of samples based on the macroinvertebrate community in the study reaches. These results suggest that different habitat characteristics result in a distinct community structure in each reach.