Effects of stream size on taxa richness and other commonly used benthic bioassessment metrics

Benthic macroinvertebrate samples were collected from natural substrates in disturbed and undisturbed South Carolina upper coastal plain streams to determine if taxa richness and other bioassessment metrics were significantly related to stream size as predicted by the River Continuum Concept (RCC). Linear, quadratic, and lognormal regression models indicated that stream width was positively related to total number of taxa; number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa; and total number of organisms. Linear regression showed that the expected number of taxa at undisturbed sites ranged from 35 in 2.0 m wide streams to 64 in 16.0 m streams. Comparable values were 8–20 for EPT and 109–261 for number of organisms. Stream width was inversely related to biotic index values indicating a decrease in average organism tolerance with increasing stream size. ANCOVA showed that the effects of stream size were similar for disturbed and undisturbed sites. Rank correlations and multidimensional scaling (MDS) showed that Lepidoptera and Trichoptera were more abundant in larger streams and Annelida in smaller streams. Stream size related changes in benthic macroinvertebrate community composition are often ignored in bioassessment protocols; however, failure to adjust metrics for stream size can lead to erroneous conclusions. Adjustments are possible by analyzing regression residuals stripped of stream size related variance, dividing the area beneath the maximum taxa richness line into equal size units for metric scoring, or scaling metrics based on predicted reference values. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Relationships between the Seasonal Variations of Macroinvertebrates,and Land Uses for Biomonitoring in the Xitiaoxi River Watershed,China

The impacts of differences in watershed land uses, and differences in seasonality on benthic macroinvertebrate communities, were evaluated in 12 stream sites within the Xitiaoxi River watershed, China, from April 2009 to January 2010. The composition of macroinvertebrate community differed significantly among three land use types. Forested sites were characterized by high taxa richness, diversity and the benthic‐index of biotic integrity (B‐IBI), while farmland and urban disturbed stream sites presented contrary patterns. The percentage of urban land use, conductivity, dissolved oxygen, ammonia nitrogen and total phosphorus were the major drivers for the variations. The land use related water quality stress gradients of the four sampling seasons were determined by means of four independent Principal Component Analyses. The responses of macroinvertebrate community metrics, to anthropogenic stressors, were explored using Spearman Rank Correlation analyses. All the selected metrics, including total numbers of taxa, numbers of Ephemeroptera, Plecoptera and Trichoptera taxa, percentage of non‐insect abundance, percentage of scrapers abundance, Pielou’s evenness index, Simpson diversity index, and the Benthic Index of Biotic Integrity were correlated significantly with environmental gradients (PC1) in autumn. In other seasons such correlations were less pronounced. Our results imply that autumn is the optimal time to sample macroinvertebrate communities, and to conduct water quality biomonitoring in this subtropical watershed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Response of benthic macroinvertebrate communities to highway construction in an Appalachian watershed

Highway construction in mountainous areas can result in sedimentation of streams, negatively impacting stream habitat, water quality, and biotic communities. We assessed the impacts of construction of a segment of Corridor H, a four-lane highway, in the Lost River watershed, West Virginia, by monitoring benthic macroinvertebrate communities and water quality, before, during, and after highway construction and prior to highway use at upstream and downstream sites from 1997 through 2007. Data analysis of temporal impacts of highway construction followed a Before-After-Control-Impact (BACI) study design. Highway construction impacts included an increase in stream sedimentation during the construction phase. This was indicated by an increase in turbidity and total suspended solids. Benthic macroinvertebrate metrics indicated a community more tolerant during and after construction than in the period before construction. The percent of Chironomidae and the Hilsenhoff Biotic Index (HBI) increased, while percent of Ephemeroptera, Plecoptera, and Trichoptera (EPT) decreased. Our 10-year study addressed short-term impacts of highway construction and found that impacts were relatively minimal. A recovery of the number of EPT taxa collected after construction indicated that the benthic macroinvertebrate community may be recovering from impacts of highway construction. However, this study only addressed a period of 3 years before, 3 years during, and 4 years post construction. Inferences cannot be made concerning the long-term impacts of the highway, highway traffic, runoff, and other factors associated with highway use. Continual monitoring of the watershed is necessary to determine if the highway has a continual impact on stream habitat, water quality, and biotic integrity.     

Evidence of a threshold level of fine sediment accumulation for altering benthic macroinvertebrate communities

When land use practices alter natural hydrologic and sediment delivery regimes, the effects usually are negative to macroinvertebrates. We hypothesized a threshold level of fine sediment accumulation in the substrate may exist where benthic macroinvertebrate abundance and diversity will be significantly reduced. We surveyed seven Appalachian streams with different levels of substrate fine sediment twice yearly from fall 1998 to spring 2000. Three riffles (with 2 replicates each) were sampled with a 0.25 mm Surber sampler in each season and stream. Simple linear regression was used to test relationships between substrate size classes and metrics, and nested ANOVA was used to test macroinvertebrate differences among streams. Consistent negative relationships with the finest substrate particles (<0.25 mm) were observed with EPT (Ephemeroptera, Plecoptera, and Trichoptera) taxa richness. In seasons of normal hydrology, EPT taxa richness significantly decreased (p<0.05) in streams where fine substrate particles (<0.25 mm) exceeded 0.8–0.9% of riffle substrate composition. In drought seasons, fine sediment (<0.25 mm) exceeded 0.8–0.9% in most surveyed streams, lowering macroinvertebrate diversity in all streams. In these streams, a threshold for EPT diversity appears to be in excess of 0.8–0.9% fine sediment (<0.25 mm) substrate accumulation. We suggest similar threshold levels exist in other streams where macroinvertebrate taxa are altered with potential effects on trophic webs and nutrient processing.     

Development of a macroinvertebrate multimetric index for the assessment of low-land streams in the neotropics

The water and habitat quality in Panamanian streams and rivers are being degraded by agriculture, urbanization, industrial activities, mining, and other forms of development. Thus, the need for standards, especially those examining the biological attributes of lotic systems, are urgently required. We describe the development of a multimetric index based on macroinvertebrates collected in low-land streams in the Panama Canal Watershed (PCW), which differed in their levels of human impacts. The index was developed using 12 streams and validated using a further three, all of which were sampled on four occasions, in the dry and wet seasons of 2007 and 2008. We examined 42 metrics related to macroinvertebrate community structure, composition, and function. Based on their ability to distinguish reference from moderately or severely impacted streams, and on their independence, we selected seven metrics (Margalef's index (taxa), Shannon's evenness index (taxa), number of EPT (taxa), % of Trichoptera, ratio of Chironomidae/Diptera individuals, % of scrapers, and % of shredders). These metrics were then standardized and developed into the Neotropical Low-land Stream Multimetric Index (NLSMI). Overall, the NLSMI distinguished well among the different levels of impairment (Reference, Moderate impact, and Severe impact) and showed a strong, significant correlation with principal component analysis (PCA) axis one values, with the PCA based on a set of physico-chemical variables indicative of stream quality. The wet season generally resulted in lower NLSMI values, leading us to suggest that sampling for biomonitoring be carried out in the dry season. Overall, this preliminary macroinvertebrate NLSMI shows promise for developing a biomonitoring programme to assess the ecological integrity of streams, to aid with management, restoration, and conservation, and to serve as a basis to develop a more geographically extensive multimetric index.     

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

1. 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.     

Comparison of watershed disturbance predictive models for stream benthic macroinvertebrates for three distinct ecoregions in western US

The successful use of macroinvertebrates as indicators of stream condition in bioassessments has led to heightened interest throughout the scientific community in the prediction of stream condition. For example, predictive models are increasingly being developed that use measures of watershed disturbance, including urban and agricultural land-use, as explanatory variables to predict various metrics of biological condition such as richness, tolerance, percent predators, index of biotic integrity, functional species traits, or even ordination axes scores. Our primary intent was to determine if effective models could be developed using watershed characteristics of disturbance to predict macroinvertebrate metrics among disparate and widely separated ecoregions. We aggregated macroinvertebrate data from universities and state and federal agencies in order to assemble stream data sets of high enough density appropriate for modeling in three distinct ecoregions in Oregon and California. Extensive review and quality assurance of macroinvertebrate sampling protocols, laboratory subsample counts and taxonomic resolution was completed to assure data comparability. We used widely available digital coverages of land-use and land-cover data summarized at the watershed and riparian scale as explanatory variables to predict macroinvertebrate metrics commonly used by state resource managers to assess stream condition. The “best” multiple linear regression models from each region required only two or three explanatory variables to model macroinvertebrate metrics and explained 41–74% of the variation. In each region the best model contained some measure of urban and/or agricultural land-use, yet often the model was improved by including a natural explanatory variable such as mean annual precipitation or mean watershed slope. Two macroinvertebrate metrics were common among all three regions, the metric that summarizes the richness of tolerant macroinvertebrates (RICHTOL) and some form of EPT (Ephemeroptera, Plecoptera, and Trichoptera) richness. Best models were developed for the same two invertebrate metrics even though the geographic regions reflect distinct differences in precipitation, geology, elevation, slope, population density, and land-use. With further development, models like these can be used to elicit better causal linkages to stream biological attributes or condition and can be used by researchers or managers to predict biological indicators of stream condition at unsampled sites.     

Lake macroinvertebrate assemblages and relationship with natural environment and tourism stress in Jiuzhaigou Natural Reserve,China

With increasing human population and urbanization, tourism in natural reserves and other protected lands is growing. It is critical to monitor and assess the impacts of tourism on ecosystem health. However, there is a general lack of information on biological communities in natural reserves of developing countries and of tools for assessing human impacts. In the present study, we investigated macroinvertebrate assemblages in nine lakes in Jiuzhaigou Natural Reserve of China. Both benthic (20 dips of D-net) and light-trap samples (2 h) were collected at each lake and all benthic specimens and adults of Ephemeroptera, Plecoptera, and Trichoptera (EPT) were identified and counted. Water temperature and water quality variables were measured on site or in the Lab. Seventy taxa were recorded and dominated by dipterans and caddisflies. Light traps contributed 47% of taxa richness and 66% of EPT richness at the lakes. Detrended Correspondence Analysis showed that water temperature and tourism index were strongly associated with the changes of assemblage composition. Taxa richness and EPT richness calculated for the composite samples (benthic + light trap) were well fit with Poisson generalized linear model (adjusted R² = 0.83 and 0.85, respectively), generally decreasing with increasing elevation, tourism index, and total-N. Tourism index was ranked as the top predictor for EPT richness based on multiple model weights, and elevation for taxa richness. In comparison, when based on benthic samples, neither of the metrics could be fitted with the seven environmental variables selected. These findings highlight the benefit of combined use of the sampling methods for lake monitoring and offered an analytical guide to developing biological indicators of lake ecosystem health in protected areas.     

Biotelemetry of crustacean decapods: sampling design,statistical analysis,and interpretation of data

Lotic systems in many regions of the country have experienced habitat degradation and biodiversity loss due to agricultural activity and urbanization. Southeastern Michigan is no exception, as agriculture in the River Raisin watershed and increased urbanization in the Huron River watershed threatens both systems. To further understand the ecological impact of land use on trophic interactions in Midwestern streams and assess the use of a selected set of weighted, quantitative food web metrics as a tool for investigating the influence of anthropogenic disturbance on these systems we compared summer food webs for nine second-order streams. All streams were categorized as developed, undeveloped, or agricultural based on land cover data. Developed and undeveloped streams were located in the Huron River watershed and agricultural streams were located in the River Raisin watershed. Reach-level habitat quality was also assessed at each study site using the EPA’s Rapid Habitat Assessment. Fish diets (n = 410) were analyzed to create summer food webs for each site. Comparisons of food webs were made using a suite of weighted, quantitative metrics to identify differences in fish–macroinvertebrate interactions across streams with differing land cover at the sub-basin scale and habitat quality at the local scale. Although undeveloped streams had higher species richness and less habitat degradation, no significant patterns were observed in the quantitative metrics across the three stream categories or based on reach-level habitat conditions. Decapoda, terrestrial Hymenoptera, and Chironomidae were the primary prey taxa in all stream categories. Decapods accounted for the majority of biomass consumed and the pattern of this consumption strongly influenced metric scores. The suite of quantitative metrics tested in this study did not detect significant differences in fish–macroinvertebrate food webs across land use categories, likely in part due to the dominance of a large, tolerant prey taxa in fish diets, regardless of land use and local habitat quality.     

Development of a regional macroinvertebrate index for large river bioassessment

Large river bioassessment protocols lag far behind those of wadeable streams and often rely on fish assemblages of individual rivers. We developed a regional macroinvertebrate index and assessed relative condition of six large river tributaries to the upper Mississippi and Ohio rivers, Midwest USA. In 2004 and 2005, benthic macroinvertebrates, water chemistry, and habitat data were collected from randomly selected sites on each of the St. Croix, Wisconsin, Minnesota, Scioto, Wabash, and Illinois rivers. We first identified the human disturbance gradient using principal components analysis (PCA) of abiotic data. From the PCA, least disturbed sites showed strong separation from stressed sites along a gradient contrasting high water clarity, canopy cover, habitat scores, and plant-based substrates at one end and higher conductivity and nutrient concentrations at the other. Evaluation of 97 benthic metrics identified those with good range, responsiveness, and relative scope of impairment, as well as redundancies with other metrics. The final index was composed of Diptera taxa richness, EPT taxa richness, Coleoptera taxa richness, percent oligochaete and leech taxa, percent collector-filterer individuals, predator taxa richness, percent burrower taxa, tolerant taxa richness, and percent facultative individuals. Each of the selected metrics was scored using upper and lower thresholds based on all sites, and averaging across the nine metric scores, we obtained the Non-wadeable Macroinvertebrate Assemblage Condition Index (NMACI). The NMACI showed a strong response to disturbance using a validation data set and was highly correlated with non-metric multidimensional scaling (NMDS) ordination axes of benthic taxa. The cumulative distribution function of index scores for each river showed qualitative differences in condition among rivers. NMACI scores were highest for the federally protected St. Croix River and lowest for the Illinois River. Other rivers were intermediate and generally reflected the mixture of land use types within individual basins. Use of regional reference sites, though setting a high level of expectation, provides a valuable frame of reference for the potential of large river benthic communities that will aid management and restoration efforts.     

Ecological response differentials: an alternative benchmark to inform stream and river bioassessment

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Louisiana waterthrushes (Seiurus motacilla) and habitat assessments as cost-effective indicators of instream biotic integrity

1. Benthic stream animals, in particular macroinvertebrates, are good indicators of water quality, but sampling can be laborious to obtain accurate indices of biotic integrity. Thus, tools for bioassessment that include measurements other than macroinvertebrates would be valuable additions to volunteer monitoring protocols. 2. We evaluated the usefulness of a stream‐dependent songbird, the Louisiana waterthrush (waterthrush, Seiurus motacilla) and the Environmental Protection Agency Visual Habitat Assessment (EPA VHA) as indicators of the macrobenthos community in headwater streams of the Georgia Piedmont, U.S.A. We sampled macrobenthos, surveyed waterthrushes and measured habitat characteristics along 39 headwater reaches across 17 catchments ranging from forested to heavily urbanised or grazed by cattle. 3. Of the indicators considered, waterthrush occupancy was best for predicting relative abundances of macrobenthic taxa, while the EPA VHA was best for predicting Ephemeroptera–Plecoptera–Trichoptera (EPT) richness. Individual components of EPA VHA scores were much less useful as indicators of EPT richness and % EPT when compared with the total score. Waterthrushes were found along streams with higher % EPT, a lower Family Biotic Index (FBI) values and greater macrobenthos biomass. 4. While macroinvertebrates remain one of the most direct indicators of stream water quality, stream bird surveys and reach‐scale habitat assessments can serve as cost‐effective indicators of benthic macroinvertebrate communities. Using stream‐dependent birds as an early warning signal for degradation of stream biotic integrity could improve the efficacy of catchment monitoring programmes in detecting and identifying perturbations within the catchment.     

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

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

Impacts of acidification on macroinvertebrate communities in streams of the western Adirondack Mountains,New York,USA

Limited stream chemistry and macroinvertebrate data indicate that acidic deposition has adversely affected benthic macroinvertebrate assemblages in numerous headwater streams of the western Adirondack Mountains of New York. No studies, however, have quantified the effects that acidic deposition and acidification may have had on resident fish and macroinvertebrate communities in streams of the region. As part of the Western Adirondack Stream Survey, water chemistry from 200 streams was sampled five times and macroinvertebrate communities were surveyed once from a subset of 36 streams in the Oswegatchie and Black River Basins during 2003–2005 and evaluated to: (a) document the effects that chronic and episodic acidification have on macroinvertebrate communities across the region, (b) define the relations between acidification and the health of affected species assemblages, and (c) assess indicators and thresholds of biological effects. Concentrations of inorganic Al in 66% of the 200 streams periodically reached concentrations toxic to acid-tolerant biota. A new acid biological assessment profile (acidBAP) index for macroinvertebrates, derived from percent mayfly richness and percent acid-tolerant taxa, was strongly correlated (R² values range from 0.58 to 0.76) with concentrations of inorganic Al, pH, ANC, and base cation surplus (BCS). The BCS and acidBAP index helped remove confounding influences of natural organic acidity and to redefine acidification-effect thresholds and biological-impact categories. AcidBAP scores indicated that macroinvertebrate communities were moderately or severely impacted by acidification in 44–56% of 36 study streams, however, additional data from randomly selected streams is needed to accurately estimate the true percentage of streams in which macroinvertebrate communities are adversely affected in this, or other, regions. As biologically relevant measures of impacts caused by acidification, both BCS and acidBAP may be useful indicators of ecosystem effects and potential recovery at the local and regional scale.     

Macroinvertebrate assemblage patterns as indicators of water quality in the Xindian watershed,Taiwan

In the present study, we assessed the water quality along a stretch of the watershed with considerable economic importance at the Xindian in Taiwan, using macroinvertebrate assemblages, along with environmental variables. The research was carried out at the seven sampling sites (abbreviated as XD1–XD7) where human impacts varied in intensity from upstream tributaries to the downstream of the Xindian watershed from December 2010 to December 2011. All variables except for the hardness, pH, dissolved oxygen, conductivity, turbidity, phosphate, ammonia, and alkalinity were significantly different (P < 0.05) between the sampling sites. A total of seventy seven taxa belonging to forty five families within eight insect orders, along with three non-insect invertebrate taxa were recorded, with most representative orders being Ephemeroptera and Diptera. Mean values of the density, abundance of macroinvertebrates, Shannon index, Simpson index, and Pielou's evenness were much higher in the reference sites, XD2, XD3, and XD4 compared with impacted sites, XD5, XD6, and XD7. Most of the benthic metrics were greatest in the reference site compared to the impacted site. Only the composition measures, percentages of Chironomidae and Oligochaeta which are more tolerant to pollution were dominant in the impacted site, XD7. As the results of assessment by different benthic metrics, water quality of Xindian watershed became gradually worse from upstream to downstream. Generally, our results suggest that macroinvertebrate assemblages can be used for assessment of water quality.     

Association of macroinvertebrate assemblages with dissolved oxygen concentration and wood surface area in selected subtropical streams of the southeastern USA

Woody debris (CWD) is an important habitat component in northern Gulf of Mexico coastal plain streams, where low gradients and low flows allow accumulation of CWD and promote low dissolved oxygen (DO) concentrations. We tested the influences of CWD and DO on stream macroinvertebrates experimentally by placing two surface area CWD treatments each in three concentrations of ambient DO in two streams in Louisiana, USA, with macroinvertebrates collected from ambient woody debris used as a control. We also sampled macroinvertebrates in benthic and woody debris habitats in three streams twice yearly over 2 years to examine the applicability of the experimental results. Total abundance, richness (generic), and Shannon–Wiener diversity were all higher in lower DO conditions during the experiment, and total abundance was higher in the larger CWD treatment. Stream sampling corroborated the relationship between higher diversity and low DO in both benthic and woody debris habitats, but the relationship between richness and low DO only was supported in benthic habitats. Few taxa correlated with DO or CWD in the experiment (5 of 21 taxa) or stream survey (2 of 54 taxa). Whereas most taxa were uncorrelated with experimentally manipulated and in-stream measured variables, we suggest these taxa respond as generalists to stream habitat and physicochemistry. Based on this experiment and stream sampling, we believe the majority of macroinvertebrates in these streams are tolerant of seasonally low DO conditions.     

Effects of livestock exclusion on in‐stream habitat and benthic invertebrate assemblages in montane streams

1. Stream and riparian ecosystems in arid montane areas, like the interior western United States, are often just narrow mesic strands, but support diverse and productive habitats. Meadows along many such streams have long been used for rangeland grazing, and, while impacts to riparian areas are relatively well known, the effect of livestock grazing on aquatic life in streams has received less attention. 2. Attempts to link grazing impacts to disturbance have been hindered by the lack of spatial and temporal replication. In this study, we compared channel features and benthic macroinvertebrate communities (i) between 16 stream reaches on two grazed allotments and between 22 reaches on two allotments where livestock had been completely removed for 4 years, (ii) before and after the 4‐year grazing respite at a subset of eight sites and (iii) inside and outside of small‐scale fenced grazing exclosures (eight pairings; 10+ year exclosures) in the meadows of the Golden Trout Wilderness, California (U.S.A.). 3. We evaluated grazing disturbance at the reach scale in terms of the effects of livestock trampling on per cent bank erosion and found that macroinvertebrate richness metrics were negatively correlated with bank erosion, while the percentage of tolerant taxa increased. 4. All macroinvertebrate richness metrics were significantly lower in grazed areas. Bank angle, temperature, fine sediment cover and erosion were higher in grazed areas, while riparian cover was lower. Regression models identified riparian cover, in‐stream substratum, bank conditions and bankfull width‐to‐depth ratios as the most important for explaining variability in macroinvertebrate richness metrics. 5. Small‐scale grazing exclosures showed no improvements for in‐stream communities and only moderate positive effects on riparian vegetation. In contrast, metrics of macroinvertebrate richness increased significantly after a 4‐year period of no grazing. 6. The success of grazing removal reported here suggests that short‐term removal of livestock at the larger, allotment meadow spatial scale is more effective than long‐term, but small‐scale, local riparian area fencing, and yields promising results in achieving stream channel, riparian and aquatic biological recovery.     

城市溪流中径流式低坝对底栖动物群落结构的影响

调查了浙江省安吉县内具径流式低坝的城市溪流(6个样点)和参照溪流(3个样点)的底栖动物群落,目的是了解城市溪流底栖动物群落结构退化规律和径流式低坝(2—3 m)对城市溪流底栖动物群落组成与结构的影响。结果表明,参照样点的底质组成以大石块(35.92%)和卵石(33.66%)为主,城市溪流以砾石为主(57.97%)。城市溪流水温和电导率显著高于参照溪流,TN和TP高于参照溪流。底栖动物总分类单元数和EPT分类单元数显著低于参照溪流。城市溪流河道内水坝上下游之间的流速(P=0.273)和宽深比(P=3.92)无显著差异。坝下游水体中的TP高于坝上游,电导率、溶解氧、pH值和水温在坝上下游之间几乎一致。除BI指数坝下游高于坝上游外,坝上下游间底栖动物总分类单元数、EPT分类单元数以及多样性指数、优势度和均匀度指数没有显著差异。但坝下游的耐污类群比例显著高于坝上游,敏感类群比例则显著低于坝上游。与坝上游相比,坝下游捕食者比例上升和集食者比例下降。NMDS结果进一步表明,城市溪流内水坝的建设导致坝上下游底栖动物群落物种组成明显改变。     

In‐stream habitat and macroinvertebrate responses to riparian corridor length in rangeland streams

Conservation and restoration of riparian vegetation in agricultural landscapes has had mixed success at protecting in‐stream habitat, potentially due to the mismatch between watershed‐scale impacts and reach‐scale restoration. Prioritizing contiguous placement of small‐scale restoration interventions may effectively create larger‐scale restoration projects and improve ecological outcomes. We performed a multi‐site field study to evaluate whether greater linear length of narrow riparian tree corridors resulted in measurable benefits to in‐stream condition. We collected data at 41 sites with varying upstream tree cover nested within 13 groups in rangeland streams in coastal northern California, United States. We evaluated the effect of riparian tree corridor length on benthic macroinvertebrate communities, as well as food resources, water temperature, and substrate size. Sites with longer riparian corridors had higher percentages of invertebrates sensitive to disturbance (including clingers and EPT taxa) as well as lower water temperatures and less fine sediment, two of the most important aquatic stressors. Despite marked improvement, we found no evidence that macroinvertebrate communities fully recovered, suggesting that land use continued to constrain conditions. The restoration of long riparian corridors may be an economically viable and rapidly implementable technique to improve habitat, control sediment, and counter increasing water temperatures expected with climate change within the context of ongoing land use.     

Effects of urbanization on stream benthic invertebrate communities in Central Amazon

Urbanization and its physical and chemical effects on aquatic environments influence invertebrate communities negatively. Yet, it is not clear how urbanization affects inter-annual variation of invertebrate assemblages in streams. We 1) evaluated urbanization effects on the ecological conditions (biotic and abiotic) of streams in Manaus and 2) analyzed invertebrate community variation over time (between 2003 and 2010). Data on abiotic variables and invertebrates from 2003 were obtained from a previous study. In 2010 we sampled abiotic variables and invertebrate communities in the same low-order urban streams sampled in 2003 (n = 40). We recorded high values of total nitrogen, total phosphorous, deforestation, total impervious area (TIA), water temperature, pH, and electrical conductivity in the most urbanized streams, as compared to the least-impacted ones. In contrast, the least-impacted streams had high dissolved oxygen concentrations. Water quality was poorer in 2010 than in 2003: oxygen concentration was lower and total nitrogen, total phosphorous, deforestation, and TIA significantly higher in 2010. We recorded higher inter-annual variation of abiotic variables in the most-impacted streams as compared to the least-impacted streams. EPT (%, Ephemeroptera, Plecoptera, and Trichoptera) and richness metrics decreased with urbanization. On the other hand, % OP (percent of Oligochaeta and Psychodidae) increased with urbanization. Observed and EPT richness and% OP increased between 2003 and 2010. On the other hand, rarefied richness decreased between years. Increases of observed and EPT richness between 2003 and 2010 were related to low inter-annual variability in streams conditions; however, differences of% OP and rarefied richness were not related to inter-annual variability in environmental conditions. The degree of urbanization did not explain the magnitude of the within-stream difference of invertebrate communities between 2003 and 2010. The increased effects of urbanization represented by the abiotic variables sampled and the reduction of invertebrate richness and increased dominance of tolerant taxa indicate that public policy is not enough to protect or mitigate human impacts on the urban water systems under study.