Macroinvertebrate Assemblages In Streams Research Articles

Towards a protocol for stream macroinvertebrate sampling in China

Standard protocols are critical for maximizing data comparability and aggregation in national monitoring programs, and taxa richness is a common indicator of site condition and biological diversity. There are two general approaches for sampling stream macroinvertebrate assemblages: targeted richest habitat and site wide. At seven sites, we compared three methods: Ontario Benthic Biomonitoring Network (OBBN), Environmental Monitoring and Assessment Program (EMAP), and Rapid Bioassessment Protocol (RBP). The OBBN method produced a biased sample at a site with a single small riffle, the RBP method produced the most total taxa, and the EMAP method produced the most taxa at four sites and the most individuals at six sites. The RBP method produced asymptotes for percent tolerant individuals, percent chironomid individuals, and Hilsenhoff Biotic Index score after five to ten stations. The EMAP method produced asymptotes for those metrics after 10 to 20 stations per site. The EMAP method typically required half the number of stations as the RBP method to obtain 70-90% of true taxa richness as estimated by the Jaccard coefficient. We conclude that the EMAP method is preferable because of its greater precision in taxa richness estimates.

Ecological functions of persistent Japanese cedar litter in structuring stream macroinvertebrate assemblages

Stream macroinvertebrate assemblages are expected to be affected by the abundance and constitution of litter from surrounding forests. We compared forest floor cover, overland flow, stream environment, and stream macroinvertebrate assemblages between the catchments of a Japanese cedar plantation (CP) and a primary deciduous forest (DF). Both systems experience excessive deer browsing. Understory vegetation cover was higher in the DF than in the CP in summer, although cover was low (<20 %), possibly because of excessive deer browsing. Litter cover was much higher in the CP than in the DF in summer as a result of the long abscission period, slow breakdown, and low rate of dispersal of Japanese cedar litter compared to deciduous litter. Monthly overland flow was always lower in the CP than in the DF, and substrate size was smaller in the DF stream. In the CP, cedar litter accumulated in the stream, probably because of its low breakdown rate and morphology, and abundant shredder taxa characterized the macroinvertebrate assemblage. In contrast, abundant burrower taxa characterized the macroinvertebrate assemblage in the DF stream. These results imply that Japanese cedar litter functions in structuring the macroinvertebrate assemblage by supplying persistent food resources for detritivores, and by buffering fine sedimentation via overland flow under excessive deer browsing.

Is fine sediment deposition a main driver for the composition of benthic macroinvertebrate assemblages?

Intensive agriculture causes increased fine sediment and nutrient runoff into running waters. Despite various approaches to quantify the entry of fine sediment into streams, its biological impact is not well understood. In particular, it is unclear whether the potential effects on the biota can be explained by fine sediment loads alone or in combination with other physicochemical and/or hydrological impacts. In this study, we investigated the impact of fine sediment deposition relative to other impacts on the benthic macroinvertebrates in small headwaters in Luxembourg, a region that is sparsely populated and characterised by agricultural land use on the hills and wooded stream valleys. The surficial-deposited fine sediment, content of inorganic sediment, proportions of organic matter, and carbon to nitrogen (C/N) ratio were recorded 1 year. The stream macroinvertebrate assemblages were recorded in the spring and autumn using multi-habitat sampling. A partial canonical correspondence analysis (pCCA) was applied to quantify and verify the impact of individual sediment components and other environmental variables on the community composition, whereas redundancy analysis (RDA) was used to examine the impact of environmental variables on the macroinvertebrate diversity and functional metrics. Oxygen content, C/N ratio as well as fine gravel explained best both the taxa composition and macroinvertebrate metrics, whereas large-scale variables such as land use were less important. The biological response to oxygen deficits and the C/N ratio of the deposited fine sediment indicate the potential effects of fine sediment deposition through oxygen consumption.Our results show that the chemical composition of the deposited sediment is more important than the amount of sediment, as the C/N ratio alone explained a substantial amount of variance in species composition. Thus, we suggest that future studies on the impact of fine sediment on the macroinvertebrate community should focus on small-scale factors, including the chemical composition of the deposited fine sediment in combination with the physicochemical and hydromorphological stream parameters.

English

This study attempts to provide an overview of the benthic macroinvertebrate assemblages of Yousmarg streams. For studying the distribution of macroinvertebrate assemblages in the two streams, that is, Doodganga and Khanshah manshah canal, a total of 4 study sites were selected. During the period of investigation, 24 species of macrozoobenthos in Yousmarg streams were recorded. Arthropoda was found to be the most dominant group, comprising of 23 species followed by Annelida with 1 species. The phylum Arthropoda was represented by class Insecta (5 orders) and Crustacea (1 orders). The diversity of benthic invertebrates was high in Doodhganga stream (21 taxa) as compared to Khanshah-manshah canal (18 taxa). An inter-site comparison revealed maximum mean population density for Doodhganga stream as compared to Khanshah-manshah canal. Besides, it was observed that boulders and cobbles provided a stable habitat for macroinvertebrates dwelling. Also, greater diversity in the summers as against winters was recorded in both the streams. On the basis of the biotic indices, the Doodhganga stream is being adjudged pristine with no organic pollution, however slight organic pollution in Khanshah&ndash;manshah canal was recorded. &nbsp; Key words:&nbsp;Kashmir Himalayas, benthic macroinvertebrates, Diversity

The influences of climatic variation and vegetation on stream biota: lessons from the Big Dry in southeastern Australia

AbstractAquatic biodiversity faces increasing threats from climate change, escalating exploitation of water and land use intensification. Loss of vegetation in catchments (= watersheds) has been identified as a substantial problem for many river basins, and there is an urgent need to better understand how climate change may interact with changes in catchment vegetation to influence the ecological condition of freshwater ecosystems. We used 20 years of biological monitoring data from Victoria, southeastern Australia, to explore the influences of catchment vegetation and climate on stream macroinvertebrate assemblages. Southeastern Australia experienced a severe drought from 1997 to 2009, with reductions of stream flows &gt;50% in some areas. The prolonged drying substantially altered macroinvertebrate assemblages, with reduced prevalence of many flow‐dependent taxa and increased prevalence of taxa that are tolerant of low‐flow conditions and poor water quality. Stream condition, as assessed by several commonly used macroinvertebrate indices, was consistently better in reaches with extensive native tree cover in upstream catchments. Prolonged drought apparently caused similar absolute declines in macroinvertebrate condition indices regardless of vegetation cover, but streams with intact catchment and riparian vegetation started in better condition and remained so throughout the drought. The largest positive effects of catchment tree cover on both water quality and macroinvertebrate assemblages occurred above a threshold of ca. 60% areal tree cover in upstream catchments and in higher rainfall areas. Riparian tree cover also had positive effects on macroinvertebrate assemblages, especially in warmer catchments. Our results suggest that the benefits of extensive tree cover via improved water quality and in‐channel habitat persist during drought and show the potential for vegetation management to reduce negative impacts of climatic extremes for aquatic ecosystems.

Environmental influences on macroinvertebrate assemblages in headwater streams of northeastern Ohio

We determined composition and trophic structure of macroinvertebrate assemblages, and also examined how environmental factors, such as riparian forest, aquatic habitat, and vertebrate predators, influenced these assemblages in relatively undisturbed headwater streams of northeastern Ohio. Using canonical correspondence analysis, we examined the relationships between macroinvertebrate assemblages, both compositional and trophic structure, and the environment. Ordination analyses showed a distinct separation of upstream and downstream macroinvertebrate faunas, while variance partitioning suggested that this may be because of the strong effects that predatory fishes and salamanders had in upstream areas. Aquatic habitat may be a strong determinant of macroinvertebrate composition and structure in these headwater streams, though this may be a reflection of site fidelity. Riparian forest habitat also explained a large portion of variation in macroinvertebrate functional feeding guild structure, emphasizing the connection between terrestrial and aquatic ecosystems in these headwater stream systems.

Do seasonal changes in habitat features influence aquatic macroinvertebrate assemblages in perennial versus temporary Mediterranean streams?

In this study we examined the importance of seasonal changes in habitat features and aquatic macroinvertebrate responses in temporary and perennial streams from two different catchments in the Western Mediterranean region in Spain. Macroinvertebrate sampling was spatially intensive to account for the relative frequency of meso- (i.e., riffles and pools) and micro-habitats (i.e., different mineral and organic-based substrata) at each site. Samples were collected at two distinctly different phases of the hydrograph: (1) during the flowing period, when pool-riffle sequences were well-established, and (2) during the dry phase, when only isolated pools were expected to occur in the temporary streams. During the dry season, both a reduction in the available total habitat and in microhabitat diversity in all sites studied was observed. As a result, taxon richness decreased in all streams, but more dramatically at temporary stream sites and particularly so in the infrequently remaining discontinuous riffles. Macroinvertebrate assemblages differed among catchments (i.e., geographical identity) and sites (perennial vs. temporary). Invertebrate differences were also strong within and among meso- and micro-habitats, particularly mineral and organic microhabitat patches, and differences were due to both loss of taxa from some habitats and some taxa exhibiting certain habitat affinities.

Relation between stream habitat conditions and macroinvertebrate assemblages in three Chinese rivers

Abstract Field investigations of macroinvertebrates in three Chinese rivers were conducted twice in 2009. Altogether 88 taxa were identified. Annelids, arthropods and mollusks were the dominant taxonomic group in the Songhua River, the Yongding River and the West River, respectively. Collector-gatherers were the most abundant group in the relatively lentic river sites, where the bottom was largely organic-rich silt. Epilithic collector-filterers and scrapers were dominant in the lotic river sites, where the bottom was mainly dominated by stone substrate. Based on statistical analyses, water physico-chemical variables (total phosphorus and conductivity) played a key role in structuring macroinvertebrate assemblages in silt substrate, while hydrological variables (median grain size of substrate and water velocity) mainly affected macroinvertebrate assemblages in stone substrate. In silt substrate, density and biomass of collector-gatherers increased with increasing total phosphorus. In stone substrate, total density peaked in the cobbles, while total biomass peaked in the bedrock.

Catchment land cover as a proxy for macroinvertebrate assemblage structure in Carpathian Mountain streams

We compared land cover, riparian vegetation, and instream habitat characteristics with stream macroinvertebrate assemblages in 25 catchments in the Carpathian Mountains in Central Europe. This study area was particularly selected because of its diverse history of forest and agricultural ecosystems linked to geopolitical dynamic, which provide a suite of unique landscape scale, land cover settings in one ecoregion. Canonical Correspondence Analysis (CCA) showed that variation in composition and structure of macroinvertebrate assemblages was primarily related to four land cover types, and not to riparian or instream habitat. These were the portions in the catchment areas of (1) broadleaved forest, (2) fine-grained agricultural landscape mosaic with scattered trees (e.g., pre-industrial cultural landscape), (3) mixed forest, and (4) natural grassland without trees. Principal Component Analysis (PCA) suggested that land cover types and stream channel substrates co-varied. The PCA also showed that chemical variables, including organic carbon, had higher values in the agricultural landscape compared to natural forests. The major source of variation among taxa in streams was higher abundance of Diptera in agricultural landscapes and of Plecoptera, Coleoptera, Trichoptera, and Amphipoda in forests. Gastropoda and Oligochaeta were more abundant in open, fine-grained agricultural landscape mosaics with scattered trees. Ephemeroptera taxa were quite indifferent to these gradients in catchment land cover, but showed a tendency of being more abundant in the pre-industrial cultural landscape. Our findings suggest that land cover can be used as a proxy of the composition and structure of macroinvertebrate assemblages. This means that land use management at the catchment scale is needed for efficient conservation and recovery of stream invertebrate communities.

An assessment of structural attributes and ecosystem function in restored Virginia coalfield streams

As human populations continue to grow, expanding energy needs enhance freshwater resource conservation challenges. Mining for coal has significantly altered the landscape in the United States’ Appalachian region, with significant negative effects on downstream water quality and ecosystem function. With recent policy changes concerning the impacts of coal mining on aquatic ecosystems, many coal companies choose to restore sections of stream located on older coal mining areas as mandated compensatory mitigation for mining-related stream disturbances. We assessed such mitigation using measures of both structure and function in restored and unrestored streams affected by surface mining operations. Macroinvertebrate assemblages in streams affected by older mining and recent restoration practices were rated as “stressed” and “severely stressed,” with streams varying from fair to optimal in terms of habitat. All streams were net heterotrophic with varying levels of ammonium uptake. No site differences were found for any measured physicochemical or functional variables, while invertebrate community metric scores were higher in unrestored streams. There were also no significant relationships found between structural and functional measurements in these streams. Principal components analysis implicated the importance of measuring physicochemical, structural, and functional variables in further analyses of restoration success. This study was unable to document pre-disturbance conditions, and as a result, we were unable to find evidence that restoration is currently having a significant effect on ecosystem processes within these systems. Further research is needed to understand the changes in ecosystem structure and function that come with time.

The effect of streamflow reductions on aquatic habitat availability and fish and macroinvertebrate assemblages in coastal plain streams

ABSTRACTThe purpose of this study was to estimate changes to aquatic habitat availability and fish and aquatic macroinvertebrate assemblages in coastal plain streams that may result from groundwater withdrawals. Hypothetical streamflow reductions of 5, 10, 20, and 30% of average annual streamflow and the 7‐day low flow were calculated for 14 study sites. Using study‐site streamflow and channel morphology data, relationships were developed to estimate five physical habitat metrics including average stream width, stream depth, stream cross‐sectional area, stream‐reach volume, and stream velocity. A second set of relationships was then developed to estimate the percentage reduction to each habitat metric under the hypothetical streamflow reduction scenarios. The average percentage decrease and variability of each habitat metric increased with successive streamflow reductions. Average percentage decreases in stream width, stream depth, stream cross‐sectional area, and stream‐reach volume were more pronounced for the reductions of average flow, whereas the average percentage decreases in stream velocity were more pronounced for the reductions of low flow. Models derived from a separate fish and macroinvertebrate study were used to estimate assemblage structure responses based on hypothetical reductions in average annual streamflow. The results of this study can be used to estimate the potential impact of groundwater withdrawals and subsequent streamflow reductions on available aquatic habitat and changes to fish and macroinvertebrate assemblages in coastal plain streams. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Experimental effects of sediment deposition on the structure and function of macroinvertebrate assemblages in temperate streams

AbstractFine sediment in streams and rivers is one of the most globally widespread of all freshwater pollutants. However, the ecological implications are still poorly quantified, and field experiments to assess likely functional and structural effects are scarce.We assessed the response of stream invertebrates to fine sediment (i.e. inert sand) added to trays (n = 65) containing otherwise natural substrata over a three‐week period in three replicate streams in the Usk catchment, Wales.Sediment addition to 0.6–18 kg m−2 affected both the structure and functional composition of invertebrate assemblages while also reducing overall abundance and in some common species (Baetis rhodani, Ecdyonurus sp. and Leuctra geniculata).Sediment also reduced richness and overall trait diversity (TD), while different life‐history traits were either favoured (polivoltinism, tegumental respiration and burrowing behaviour) or disfavoured (swimmers, attached taxa, gill respiration). Moreover, sediments appeared to promote a nested subset pattern in species composition, with generalists favoured at the expense of specialists either through exclusion or impaired colonization. Effects were due largely to the loss of five taxa that contributed to the significant nestedness across the sand gradient: B. rhodani, Ecdyonurus sp., Leuctra geniculata, Simuliidae and Ephemerella ignita.This short‐term experiment supports recent surveys in indicating how sedimentation can change the structural and functional composition of stream invertebrate assemblages even at low to moderate rates of deposition. In revealing direct effects on trait adversity, trait representation and nestedness, the data are also consistent with survey data in indicating that sediments have potentially important ramifications for conservation by removing organisms systematically according to life‐history features. Copyright © 2010 John Wiley &amp; Sons, Ltd.

The challenge of monitoring impacts of water abstraction on macroinvertebrate assemblages in unregulated streams

AbstractMonitoring of the ecological impacts of water abstraction from unregulated streams in the state of New South Wales (NSW), Australia, is challenging because water is abstracted by thousands of geographically dispersed users who pump intermittently according to temporally varying needs and the limitations imposed by licences and access rules. Detailed, quantitative monitoring methods are too costly for widespread routine application because of the size of the state (801 000 km2) and the large number of streams affected by abstraction. We therefore tested the possibility of detecting abstraction impacts on aquatic macroinvertebrates with rapid biological assessment (RBA) methods similar to those that are routinely used for biological monitoring of Australian rivers. We sampled 85 sites on unregulated streams in north‐eastern NSW during a period of prolonged and recurring drought, 54 of which were designated as reference sites with respect to water abstraction because upstream entitlement for abstraction was less than 1% of their mean annual flow (MAF). The remaining, non‐reference sites had an average of 4% of MAF licensed for upstream abstraction (range 1–20%). Sweep and kick samples were collected at each site in two seasons, and invertebrates were picked for 30 min per sample and analysed at genus level. We found a small but statistically significant overall difference in macroinvertebrate assemblages between the reference and non‐reference sites, but the amount of upstream entitlement did not affect the degree to which assemblages at individual sites deviated from site‐specific reference conditions. We attribute the absence of evident impact mainly to the low proportions of streamflow abstracted, but limitations of RBA methods may also be a factor. We recommend a risk‐based approach to future monitoring whereby effort is focussed on those streams where a high proportion of flow is abstracted. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Comparison of stream macroinvertebrate assemblages in canyon ecosystems of the Blue Mountains (Australia) with and without recreational traffic: a pilot study in impossible terrain

In Australia, the adventure sport of canyoning occurs predominantly in the protected areas of the Greater Blue Mountains World Heritage Area, 50 km west of Sydney. It involves travelling through narrow, deep gorges using a combination of walking, abseiling, wading, rock scrambling and/ or swimming through the canyon streams. The sport’s popularity is reported to have increased substantially over time, causing concern for the sustainability of these fragile ecosystems. To investigate visitor impacts, benthic macroinvertebrate assemblages and water quality were compared among four canyons subject to high visitation (average 20 – 100 visits per week) with those in four unvisited/low visitation canyons (0 - 5 visits per week). Comparison was also made between impacted and nonimpacted areas within two of the high visitation canyons. Sampling was undertaken over two canyoning seasons (early spring to late autumn). No significant relationship between macroinvertebrate assemblage composition or water quality was observed due to visitation level within and among canyons, although there were inherent differences among canyons. Water quality was consistent with pristine conditions in all locations. Macroinvertebrate assemblages included a range of pollution sensitive taxa (e.g., Ephemeroptera represented by 42.3% of all animals). Although family richness was concentrated within a few orders (84.2% of families were represented by 50% of orders), most families were represented by 2 Recognisable Taxonomic Units, 47.4% of these were represented by a single taxon. We concluded that, at current visitation levels, there is no measurable impact on the predominant animal component of these ecosystems. This finding was contrary to the expectations of the land managers of this area.

Influences of catchment and corridor imperviousness on urban stream macroinvertebrate communities at multiple spatial scales

Resolving land cover hierarchy relationships in urban settings is important for defining the scale and type of management required to enhance stream health. We investigated associations between macroinvertebrate assemblages in urban streams of Hamilton, New Zealand, and environmental variables measured at multiple spatial scales comprising (i) local-scale physicochemical conditions, (ii) impervious area in multiple stream corridor widths (30, 50 and 100 m) along segments (sections of stream between tributary nodes) and for entire upstream networks, and (iii) total impervious area in stream segment sub-catchments and upstream catchments. Imperviousness was higher for stream segment sub-catchments than for entire catchments because of the agricultural headwaters of some urban streams. Imperviousness declined as corridor width declined at both segment and catchment scales reflecting the vegetated cover along most urban stream gullies. Upstream catchment imperviousness was strongly and inversely correlated with dissolved organic carbon concentration, whereas segment and upstream corridor scales were correlated with water temperature and pH. Corridor imperviousness appeared to be a stronger predictor than catchment imperviousness of Ephemeroptera, Plecoptera and Trichoptera taxa richness and the Quantitative Urban Community Index specifically developed to assess impacts of urbanisation. In contrast, imperviousness at all measured scales added only marginal improvement in assemblage-based models over that provided by the local-scale physicochemical variables of reach width, habitat quality, macrophyte cover, pH and dissolved oxygen concentration. These findings infer variable scales of influence affecting macroinvertebrate communities in urban streams and suggest that it may be important to consider local and corridor factors when determining mechanisms of urbanisation impacts and potential management options.

Response of stream macroinvertebrate assemblages to erosion control structures in a wastewater dominated urban stream in the southwestern U.S.

Effects of stream erosion control struc- tures on aquatic macroinvertebrates were studied (2000-2009) in a wastewater dominated drainage (Wash) in Las Vegas, Nevada. Mainstem sites with and without structures, wastewater treatment plant outfalls, a reference site above treatment plant inputs, and tributary sites were sampled. Ordination sug- gested hydrology and channel characteristics (current velocity, stream depth, and width), and water quality (conductivity) were primary factors in organizing macroinvertebrate communities, with some variables altered at structures. Treatment plant inputs changed hydrology (increased flows), water chemistry (con- ductivity decreased below treatment plants), and temperature. Assemblages differed between site types, with midges and damselflies important at tributary sites and Fallceon mayflies and Smicridea caddisflies common at erosion control structures. Locally unique communities developed at structures which also may have facilitated exotic species invasions. Analyses showed that taxa richness increased over time at these sites and differed significantly from richness at sites without structures. Structures appeared important in retaining organic matter and, among mainstem sites, coarse particulate organic matter was highest, but variable, at structures and at wetlands above the structures. Erosion control structures, coupled with warm effluent, high base- flows, and altered water quality resulted in develop- ment of a macroinvertebrate community that did not trend towards reference or tributary sites. In this case, ecological communities at structures used for river restoration were not on a continuum between dis- turbed and reference sites. Goal setting of community responses at these structures would have required insight beyond the simple use of reference site attributes.

Stream invertebrate responses to a catastrophic decline in consumer diversity

AbstractTadpoles are often abundant and diverse consumers in headwater streams in the Neotropics. However, their populations are declining catastrophically in many regions, in part because of a chytrid fungal pathogen. These declines are occurring along a moving disease front in Central America and offer the rare opportunity to quantify the consequences of a sudden, dramatic decline in consumer diversity in a natural system. As part of the Tropical Amphibian Declines in Streams (TADS) project, we examined stream macroinvertebrate assemblage structure and production for 2 y in 4 stream reaches at 2 sites in Panama. One site initially had healthy amphibians but declined during our study (El Cope), and 1 site already had experienced a decline in 1996 (Fortuna). During the 1st y, total macroinvertebrate abundance, biomass, and production were generally similar among sites and showed no consistent patterns between pre- and post-decline streams. However, during the 2nd y, tadpole densities declined precipitousl...

Quantifying the responses of macroinvertebrate assemblages to simulated stress: are more accurate similarity indices less useful?

Summary 1. Similarity indices are commonly used for multivariate analyses, estimations of β-diversity and assessments of ecological impacts of disturbances. Both statistical and ecological criteria have guided index selections. The former criteria includes accuracy (i.e. how close an estimate is to the true value) and precision (i.e. how repeatable different estimates are) while the latter is focused on detection of known assemblage changes or environmental gradients. 2. These two types of criteria, however, often lead to conflicting recommendations of similarity indices. We hypothesized that a key statistical criterion, accuracy, is either irrelevant or incompatible with the ecological criteria. 3. To test this hypothesis, we compared eight commonly used similarity indices for quantifying the responses of stream macroinvertebrate assemblages to a simulated stress gradient based on both types of criteria. 4. Chao’s abundance-based Jaccard and Sorenson coefficients, and Morisita index were most accurate but strongly nonlinear in response to linear community changes and the least or less capable of discriminating stress levels. By comparison, the Bray–Curtis index, CY similarity index and Canberra Metric were less or least accurate, but outperformed the first three indices in all ecological criteria used. Multiple linear regressions confirmed that accuracy is irrelevant to or incompatible with the ecological criteria. 5. Synthesis and applications. By examining the relationships between the statistical and ecological performances of similarity indices, our study provides a critical synthesis of index evaluations and clarified much existing confusion about index selection.

Reliable sample sizes for estimating similarity among macroinvertebrate assemblages in tropical streams

Studies in tropical streams are relatively few, and one of the still-unresolved methodological is- sues is sample size. Adequate sample size for temperate streams cannot be extrapolated for tropical sites, be- cause of the differences in species richness and the proportions of rare species. We evaluated reliable sample size for estimation of resemblance among samples of macroinvertebrate assemblages inhabiting riffles of tropi- cal streams, using the autosimilarity approach. Sample sizes were much larger than those currently employed in tropical studies. Sampling units consisted of individuals associated with single stones (15-20 cm). Evaluations employed the Bray-Curtis index for abundance data and the equivalent Sorensen index for pre- sence-absence data. Autosimilarity curves were constructed using both sampling units and individuals. The estimation of resemblance among samples was strongly dependent upon sample size at reduced sampling ef- fort, particularly for the Bray-Curtis index. For the same sampling effort, fixed counts of individuals obtained randomly from sampling units gave better estimations of resemblance, and their similarity curves tended to stabilize earlier than those using sampling units. A minimum of 9-15 sampling units (stones) or 150-850 in- dividuals is necessary for adequate estimations of resemblance using presence-absence data, and 13-18 sam- pling units or 750-1550 individuals are required for relative abundance data in tropical streams.

Determining hydrologic factors that influence stream macroinvertebrate assemblages in the northeastern US

AbstractThe effects of changes in the landscape and alteration of natural flow process on aquatic macroinvertebrate assemblages were investigated in 67 small‐to‐medium sized (15–526 km2) upland streams in the northeastern United States. Environmental characteristics that were found to be important in determining macroinvertebrate‐assemblage composition include urbanization and concomitant changes in natural streamflow patterns. In particular, hydrologic attributes accounted for a significant proportion of the variability and were important in driving modifications to assemblage structure after natural environmental variability was extracted. For example, mean April flow accounted for the greatest amount of assemblage variability in any single multiple linear regression (MLR) model (65%) and duration of high flows accounted for a significant portion of the assemblage variability in the five, four and one‐variable models (25, 26, and 23%, respectively). Seasonal predictability of low flow consistently accounted for a significant proportion of the assemblage variability in all but the two‐variable (MLR) model. Significant (p &lt; 0·05) bivariate flow–ecology response relations were established, especially for hydrologic measures that account for the frequency, duration, and magnitude of flow events, and these relations generally followed increasing or decreasing trends that would be expected given changes in stream hydrology. This study demonstrates that there are likely specific negative consequences to stream biotic integrity in northeastern streams as the result of hydrologic alteration associated with basin urbanization. Understanding the relations between hydrologic modification and aquatic assemblages will help efforts to set sustainable flow standards for protection of aquatic assemblages while providing water for human needs. Published in 2009 by John Wiley &amp; Sons, Ltd.