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

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Landscape variables influence taxonomic and trait composition of insect assemblages in Neotropical savanna streams

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Ecological integrity of upper Warri River,Niger Delta using aquatic insects as bioindicators

Aquatic insects are bioindicators of water quality. Their structure and species composition is used in assessing the ecological integrity of streams and rivers. Their composition and density of the upper Warri River, Niger Delta, Nigeria were assessed and the influence of different physical and chemical variables on their distribution was explored at three designated stations. A total of 57 taxa were recorded with station 2 accounting for the greatest Ephemeroptera–Plecoptera–Trichoptera (EPT) richness. Abundance of the aquatic insects was affected by the nature of the substrate, macrophytes and canopy cover at the various stations examined. Generally, the upper Warri River is a fairly clean water body rich in EPT organisms. Pollution tolerant insect taxa such as chironomids and culicids larvae were only sporadically present.     

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

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

Broad-scale geographical patterns in local stream insect genera richness

Comprehensive global studies of stream invertebrate assemblages are rare and have produced contradictory results. To address this shortcoming, we compiled data from 495 published estimates of local genera richness for three orders of stream‐dwelling insects (Ephemeroptera, Plecoptera, Trichoptera) from throughout the world and used these data to describe global geographic patterns in stream insect genera richness and to address two questions: 1) does local stream insect richness vary more with regional historical factors or with local ecological factors?, and 2) to what extent have streams converged in the number of taxa they support?
Maximum genera richness varied sharply across the range of latitude examined from the south to north poles for all three orders of aquatic insects. Ephemeroptera richness showed 3 peaks (～30°S, 10°N, and 40°N) with highest richness near 5–10°N and 40°N latitude. Plecoptera richness was distinctly highest at ～40°N latitude with a similar peak at 40°S latitude. Trichoptera richness showed less latitudinal variation than the other taxa but was slightly higher near the equator and at 40°N and S latitude than at other latitudes. Genera richness generally declined with increasing elevation, except for Plecoptera. Maximum genera richness increased steadily with a measure of regional terrestrial net primary production and declined sharply with a measure of hydrologic disturbance for all orders. Richness varied widely among both biogeographical realms and biomes, although ca 2 times as much variation in richness was associated with biome as biogeographic realm. Richness for each order was highest in different biogeographic realms, but all orders had highest richness in broadleaf forest biomes. These latter results imply that spatial variation in local richness of stream insects is more strongly affected by contemporary ecological factors than by historical biogeography and that maintenance of intact forested landscapes may be critical to the conservation of stream invertebrate faunas.     

Scale-dependence of the correlation between human population and the species richness of stream macro-invertebrates

Recent biogeographical studies have shown positive correlations between plant/vertebrate species richness and human population presence. The same pattern has been reported for Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) (EPT) amongst European countries. This is surprising as EPT are bio-indicators of stream pollution and most local studies report higher species richness of these macro-invertebrates where human influences on water quality are lower. Using a newly collated taxonomic dataset, we studied whether the species richness of EPT is related to human population size at finer resolutions (Italy's regions, provinces and 10×10 km² UTM cells) controlling for sampling effort, variations in area and for spatial autocorrelation. At all study grains, observed EPT species richness was strongly correlated to the number of records available for the same taxon. At the regional level, the observed number of Ephemeroptera and Plecoptera species significantly increased with increasing human population size. At the provincial level, observed species richness decreased significantly with increasing human population size for Ephemeroptera and did not vary significantly for Plecoptera and Trichoptera. At the finest grain scale, there were significant negative correlations of observed Ephemeroptera and Trichoptera species richness with human population size, although the proportion of variance explained was very low. These results were broadly confirmed when analyzing the estimated number of species using the formula of Chao2. Our analysis confirms the scale-dependence of the human population–biodiversity correlation. Over broad scales more populated regions tend to have more species than less populated ones. Restricting the study grain, the positive EPT species–people relationship disappears and turns into a negative one. Our findings suggest a challenge also for the conservation of regional EPT diversity.     

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.     

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.     

Influence of a forest remnant on macroinvertebrate communities in a degraded tropical stream

Land use changes have resulted in large environmental impacts, and in agricultural landscapes sometimes only forest fragments remain. Riparian forest remnants can positively influence stream water quality, and serve as refuges for aquatic species. We evaluated whether the presence of a riparian forest remnant influenced the structure and composition of macroinvertebrate communities in a rural stream in southeastern Brazil. We sampled three reaches upstream (within abandoned sugarcane cultivation) and nine downstream the remnant edge, until 600 m inside the forested area, using leaf litter bags. The abundances of Elmidae, Chironomidae, and total macroinvertebrates increased along the forest remnant, whereas the abundance of Baetidae, proportion of Ephemeroptera, Plecoptera, and Trichoptera (EPT), rarefied taxonomic richness, and diversity decreased. Taxon richness and EPT abundance did not vary along the forest remnant. Increases in Chironomidae and total abundance within the forest remnant can be related to moderate increases in nutrient concentrations, or to the availability of high quality leaf litter patches. Forest remnants can influence macroinvertebrate communities, although variation both in temperate and tropical studies can be related to local agricultural practices and land use at the watershed scale. Forest remnants are important in maintaining stream water quality in rural landscapes, and deserve attention in watershed management projects.     

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.     

Impacts of fine sediment addition to tussock, pasture, dairy and deer farming streams in New Zealand

1. Increased fine sediment input caused by agricultural development is expected to act as a stressor for stream ecosystems. In a large‐scale field experiment, we added fine river sand to 50‐m reaches of three second‐order streams in each of four categories of catchment development (ungrazed tussock grasslands, grazed pasture, dairying and deer farming) and measured the responses of macroinvertebrates and aquatic moss. 2. Before addition, fine sediment cover differed between land uses, being lowest in tussock (7%), intermediate in pasture (30%) and dairy (47%) and highest in deer streams (88%). Sediment addition increased cover by one land‐use category (e.g. augmented sediment cover in tussock streams was similar to pre‐existing cover in pasture streams), and cover remained high in impact reaches (compared with controls) throughout the 5‐week experiment. Sediment addition did not change concentrations of phosphate, nitrate and ammonium, which were generally highest in dairy streams and lowest in tussock streams. 3. Aquatic mosses (most common in tussock, absent in dairy and deer), invertebrate density (highest in deer, lowest in tussock), taxon richness (highest in pasture, lowest in deer) and diversity (highest in pasture and tussock, lowest in dairy and deer) all differed between land uses. Sediment addition resulted in reductions of moss cover, invertebrate taxon richness and richness of Ephemeroptera, Plecoptera and Trichoptera in impact relative to control reaches. 4. The impact of sediment addition was strongest in pasture streams where pre‐existing sediment cover was moderate and richness and diversity of the invertebrate community highest. However, even in the already sediment‐rich and species‐poor deer streams, density of one common taxon was reduced significantly by sediment addition, and another two were affected in the same way in dairy streams, the second‐most intense land use. 5. Our experiment has disentangled the impact of sediment addition from other concomitant land‐use effects that could not be reliably distinguished in previous research, which has mainly consisted of correlative studies or unrealistically small‐scale experiments.     

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

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

Impact of agricultural land use on aquatic insect assemblages in the Garonne river catchment (SW France)

The impact of agricultural land use on the composition and structure of aquatic insect assemblages (i.e., taxa of Ephemeroptera, Plecoptera, Trichoptera, and Coleoptera (EPTC)) was investigated in tributary streams of the Garonne river basin, southern France. The self-organizing map (SOM) method was applied to compare both instream environmental conditions and EPTC assemblages between forest and agricultural streams. According to the SOM model, the study sites were classified into three main clusters corresponding to distinct EPTC assemblages. The SOM cluster associated with most of the agricultural sites had lower EPTC species richness and diversity. This cluster was also characterized by high levels of total dissolved solids, nitrate (NO₃), and chemical oxygen demand. Overall, our study shows that agricultural streams when compared with forest streams had lower biological integrity. In accordance with the European Water Framework Directive, our results indicate that the sites most impacted by agricultural land use should be restored and that the least-impacted forest sites could serve as reference conditions.     

Relationship between Riparian Vegetation and Stream Benthic Communities at Three Spatial Scales

We examined the influence of riparian vegetation on macroinvertebrate community structure in streams of the Upper Thames River watershed in southwestern Ontario. Thirty-three μ-basins (129–1458 ha) were used to identify land cover variables that influenced stream macroinvertebrates. Micro-basins represented the entire drainage area of study streams and were similar in stream order (first, second) and land cover (agricultural or forest; no urban). We described the structure and composition of riparian vegetation and benthic macroinvertebrate communities at the outflow reach. The nature of the land cover was quantified for the stream network buffer (30 m) and the whole μ-basin. The objective of this study was to measure the magnitude and nature of the relationship between the riparian vegetation and benthic macroinvertebrate community at the outflow reach, stream network buffer, and whole μ-basin scales. Taxon richness (including total number of Ephemeroptera, Plecoptera, and Trichoptera taxa) and Simpson’s diversity of the macroinvertebrate community all increased with increased tree cover in the riparian zone at the outflow reach scale. Simpson’s equitability was lower with greater agricultural land cover in the stream network buffer. No relationship between the macroinvertebrate community and land cover was found at the whole μ-basin scale. Analysis of the influence of land cover on stream communities within a spatial hierarchy is important for understanding the interactions of stream ecosystems with their adjacent landscapes.     

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.     

A comparison of benthic macroinvertebrate assemblages among different types of alpine streams

1. Benthic macroinvertebrate assemblages were compared among a diverse array of first‐order alpine tundra streams of the Swiss Alps. 2. A principal components analysis separated sites into three main groups: rhithral streams, rhithral lake outlets, and kryal sites including outlets and streams. Rhithral streams contained the most diverse and taxon rich assemblages, being colonised by both non‐insect taxa and Ephemeroptera, Plecoptera, Trichoptera and Diptera. 3. Rhithral lake outlets supported high densities of non‐insect taxa such as Oligochaeta, Nemathelminthes and crustaceans. Despite low taxon richness, kryal sites had high Ephemeroptera and Plecoptera abundances. Chironomidae were most common at all sites. 4. Collector‐gatherers were dominant at all sites, whereas filter‐feeders were rare. Scrapers and shredders were more common in streams than lake outlets. 5. Water temperature and algal standing crops were higher at rhithral lake outlets than rhithral streams, perhaps providing more favourable habitat for non‐insect taxa. Glacial runoff was the dominant factor influencing macroinvertebrate assemblages of kryal streams and kryal lake outlets. Alpine lakes influenced the environmental conditions of their outlets and, consequently, their macroinvertebrate assemblages unless being constrained by a glacial influence.     

Macroinvertebrate community response to natural and forest harvest gradients in western Oregon headwater streams

1. To examine the effects of forest harvest practices on headwater stream macroinvertebrates, we compiled a 167 site database with macroinvertebrate, fish, physical habitat and catchment land cover data from the three forested ecoregions in western Oregon. For our analysis, headwater streams were defined by catchment areas <10 km² and perennial water during summer low flows. Almost all sites in the database were selected using a randomised survey design, constituting a representative sample of headwater streams in these ecoregions. 2. Macroinvertebrate taxonomic and functional feeding group composition were very similar among the three ecoregions in the study area (Coast Range, Cascades and Klamath Mountains). On average, 55% of the individuals at each site were in the orders Ephemeroptera, Plecoptera or Trichoptera. Dipteran taxa (mostly chironomids) accounted for another 34%. At almost all sites, non‐insects made up <10% of the macroinvertebrate assemblage. Almost half (49%) of the assemblages were collectors; remaining individuals were about evenly divided among scrapers, shredders and predators. 3. There were 189 different macroinvertebrate taxa at the 167 sites with richness at individual sites ranging from 7 to 71 taxa. Ordination by non‐metric multidimensional scaling revealed a strong association between % Ephemeroptera, especially Baetis, and site scores along the first axis. This axis was also strongly related to % coarse substratum and fast water habitat. The second axis was strongly related to % intolerant individuals, site slope and altitude. No strong relationships were evident between any ordination axis and either logging activity, presence/absence of fish, catchment size or ecoregion. 4. Based on macroinvertebrate index of biotic integrity (IBI) scores, 62% of the sites had no impairment, 31% of the sites had slight impairment and only 6% of the sites had moderate or severe impairment. IBI scores were not strongly related to forest harvest history. All four severely impaired sites and five of the seven sites with moderate impairment were lower altitude, shallower slope stream reaches located in the Coast Range with evidence of agricultural activity in their catchment or riparian zone. % sand + fine substratum was the environmental variable most strongly related to macroinvertebrate IBI.     

Impacts of urbanization on stream habitats and macroinvertebrate communities in the tributaries of Qiangtang River,China

The impacts of watershed urbanization on streams have been studied worldwide, but are rare in China. We examined relationships among watershed land uses and stream physicochemical and biological attributes, impacts of urbanization on overall stream conditions, and the response pattern of macroinvertebrate assemblage metrics to the percent of impervious area (PIA) of watersheds in the middle section of the Qiantang River, Zhejiang Province, China. Environmental variables and benthic macroinvertebrates of 60 stream sites with varied levels of watershed urban land use were sampled in April, 2010. Spearman correlation analysis showed watershed urbanization levels significantly correlated with increased stream depth, width, and values of conductivity, total nitrogen, ammonia, phosphate, calcium, magnesium, and chemical oxygen demand for the study streams. There was significant difference in total taxa richness, Empheroptera, Plecoptera, and Trichoptera (EPT) taxa richness, and Diptera taxa richness, percentages of individual abundances of EPT, Chironomidae, shredders, filterers, and scrapers, and Shannon–Wiener diversity index between reference streams and urban impacted streams. In contrast, percentages of individual abundances for collectors, oligochaeta, and tolerant taxa, and biotic index were significantly higher in urban impacted than reference streams. All the above metrics were significantly correlated with PIA. The response patterns of total taxa richness, EPT taxa richness, and Shannon–Wiener diversity index followed a drastic decrease at thresholds of 3.6, 3.7, and 5.5% of PIA, respectively. Our findings indicate that stream benthic macroinvertebrate metrics are effective indicators of impacts of watershed urban development, and the PIA-imperviousness thresholds we identified could potentially be used for setting benchmarks for watershed development planning and for prioritizing high valued stream systems for protection and rehabilitation.     

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.     

Aligning indicators of community composition and biogeochemical function in stream monitoring and ecological assessments

Reliable and inexpensive indicators of ecosystem function are essential for accurately monitoring and describing ecosystem integrity. Currently, most state and federal assessments of aquatic ecological integrity rely on structural indicators and assume tight coupling of structure and function. We used fluorescent composition of dissolved organic matter as a metric for certain ecosystem functions and compared the resulting index of autochthonous microbial dissolved organic matter (DOM) to macroinvertebrate indicators and classifications of water quality attainment reported by the Maine Department of Environmental Protection (Maine DEP) at 142 stream sites. We observed that metrics of sensitive insect orders such as relative Plecoptera generic richness, relative Ephemeroptera abundance, and generic richness of EPT (Ephemeroptera, Plecoptera, and Trichoptera) were negatively correlated with higher values of metrics based on autochthonous microbial DOM sources. At the same time we observed an increase in the Hilsenhoff Biotic Index with increasing microbial DOM. We compared the abundance of this microbial DOM component to Maine DEP measured attainment classes and found that microbial DOM generally separated sites with high biological integrity from sites where the biotic community was highly degraded. This highlights that measures of biogeochemical ecosystem function complement measures of structure in biological assessments.