Macroinvertebrate Assemblages In Streams Research Articles

Incorporating functional traits to enhance multimetric index performance and assess land use gradients.

Taxonomic-based multimetric indices (MMIs) have been widely employed for assessing ecosystem status, particularly through the use of stream macroinvertebrate assemblages. However, the functional diversity and composition of assemblages is also important for maintaining stream ecosystem condition. Nonetheless, aquatic insect functional diversity and composition have not commonly been included in MMIs. Our goal was to advance our understanding of the performance and ecological interpretation of an MMI that potentially combined functional and taxonomic metrics. We sampled aquatic insects and natural and land-use variables at 74 temperate Chinese streams. We selected a candidate set of 36 functional and 20 taxonomic metrics that were screened by range tests, natural variation, responsiveness to anthropogenic disturbance, and redundancy for subsequent inclusion in MMIs. We determined if natural variation adjustments improved the performance of a functional-taxonomic MMI. Finally, we evaluated the degree to which the functional-taxonomic MMI served as an early-warning indicator of land use intensity. Natural variation explained between 19.62% and 71.02% of metric variability, indicating that functional metrics changed systematically along natural gradients. The final functional-taxonomic MMI adjusted for natural variation incorporated multiple aspects of assemblage characteristics: functional richness, Rao's quadratic entropy, abundance-weighted frequency of soft bodies, abundance-weighted frequency of predators, and number of Diptera taxa. In contrast to the natural variation unadjusted MMI, the functional-taxonomic adjusted MMI clearly distinguished least-disturbed sites from most-disturbed sites, exhibited high precision and low bias, and showed a significant negative response to land uses. The slope of a linear regression relative to 0-10% urban and 0-20% agriculture was significantly steeper for the functional-taxonomic adjusted MMI than that of the taxonomic adjusted MMI. We conclude that functional-taxonomic adjusted MMIs are more effective indicators of ecological condition and risks to biota from human pressures than are purely taxonomic unadjusted MMIs because functional-taxonomic MMIs are more sensitive to subtle anthropogenic pressures.

Two tropical biodiversity hotspots, two different pathways for energy

Abstract Local factors, such as riparian vegetation and stream type, affect the structure and composition of benthic macroinvertebrate assemblages in streams. To better understand the effects of biomes on lotic ecosystems, we evaluated whether Atlantic Forest (AF) and Neotropical Savanna (NS) biomes showed distinct patterns in (i) benthic macroinvertebrate assemblage structure and (ii) the shredder functional feeding group. We predicted that (i) richness, density, biomass, instant secondary production, eco-exergy, and specific eco-exergy would be higher for benthic macroinvertebrate assemblages in AF stream sites than in NS sites. We also predicted that (ii) length, density, biomass, instant secondary production, eco-exergy, and specific eco-exergy would be higher for shredders in AF stream sites. We found that benthic macroinvertebrate assemblage composition and taxa richness were significantly different between stream sites in the two biomes, with the AF biome being the richest. But we found no differences in density, biomass, instant secondary production, eco-exergy, or specific eco-exergy between AF and NS stream sites. For AF shredders, the mean length, density, biomass, secondary production and eco-exergy were significantly higher than for NS stream sites. These differences were attributed to the quality of leaf litter, which was generally higher in AF than in NS stream sites. This indicates that the intrinsic characteristics of the AF and NS biomes act as structuring factors for benthic macroinvertebrate assemblages, influencing the structure and functioning of tropical lotic ecosystems.

Forest canopy affects stream macroinvertebrate assemblage structure but not trophic stability

AbstractUnderstanding the determinates of community structure and function is a central theme in community ecology. The form in which energy is supplied to food webs can strongly influence communit...

Weighting effective number of species measures by abundance weakens detection of diversity responses

Abstract The effective number of species (ENS) has been proposed as a robust measure of species diversity that overcomes several limitations in terms of both diversity indices and species richness (SR). However, it is not yet clear if ENS improves interpretation and comparison of biodiversity monitoring data, and ultimately resource management decisions. We used simulations of five stream macroinvertebrate assemblages and spatially extensive field data of stream fishes and mussels to show (a) how different ENS formulations respond to stress and (b) how diversity–environment relationships change with values of q, which weight ENS measures by species abundances. Values of ENS derived from whole simulated assemblages with all species weighted equally (true SR) steadily decreased as stress increased, and ENS‐stress relationships became weaker and more different among assemblages with increased weighting. The amount of variation in ENS across the fish and mussel assemblages that was associated with environmental gradients decreased with increasing q. Synthesis and applications. Species diversity is valued by many human societies, which often have policies designed to protect and restore it. Natural resources managers and policy makers may use species richness and diversity indices to describe the status of ecological communities. However, these traditional diversity measures are known subject to limitations that hinder their interpretation and comparability. The effective number of species (ENS) was proposed to overcome the limitations. Unfortunately, our analyses show that ENS does not improve interpretability of how species diversity responds to either stress or natural environmental gradients. Moreover, incorporating the relative abundance of individuals in different species (evenness) into diversity measures as implemented in ENS can actually weaken detection of diversity responses. Natural resources managers and policy makers therefore need to be cautious when interpreting diversity measures, including ENS, whose values are jointly influenced by richness and evenness. We suggest that both researchers and practitioners measure and report three aspects of diversity (species richness, evenness, and composition) separately when assessing and monitoring the diversity of ecological communities.

River health assessment of the Yellow River source region, Qinghai-Tibetan Plateau, China, based on tolerance values of macroinvertebrates

For decades, the river health of the Yellow River source region (YRSR) on the Qinghai-Tibetan Plateau has been a focal issue owing to its unique geographic location and ecological functions. This study investigated the ecological status of the headwater streams, the main stem, and the tributaries of the Yellow River in the YRSR using the tolerance values of macroinvertebrates and those related to biotic indices. The macroinvertebrate assemblages of the headwater streams were characterized by lower biodiversity than the tributaries downstream, based on comparisons of taxonomical composition, functional feeding group composition, and the pollution-tolerant capacity of taxa. The headwater streams had a lower ratio (16%) of pollution-sensitive macroinvertebrate taxa than that of the tributaries downstream (30%). The biotic indices (family- and genus-level biotic indices) indicated that the ecological health of the headwater streams was comparably poorer than that of the downstream tributaries. The combined effect of vulnerable natural conditions and increasing human disturbance is likely the main cause of eco-environmental degradation in the Yellow River headwater streams.

Sub-basin and temporal variability of macroinvertebrate assemblages in Alpine streams: when and where to sample?

The seasonal dynamics and spatial variability of macroinvertebrate assemblages in Alpine streams are becoming better understood. However, the implications of this knowledge for indices used in monitoring programs have yet to be fully considered. Establishing the ecological status of such streams using macroinvertebrates may then be difficult if what is expected to be found, and where, varies across small distances between streams at a given altitude, or between years in response to different climatic characteristics. In this paper, we evaluated the degree of spatial variability in macroinvertebrate abundance and diversity for 14 tributaries at similar altitude that feed a 6-km reach of an Alpine stream, and how this spatial variability differs within and between years. Environmental variables and macroinvertebrates were sampled on 10 dates for assessment. The data showed that differences in environmental characteristics over relatively short distances lead to between tributary differences in the “windows of opportunity” and hence when a tributary should be sampled for monitoring purposes. Superimposed on this spatial variability was inter-annual variability linked to climate differences that shifted this “window of opportunity” in time, and thus altered when monitoring was optimal for any one tributary in any one year. If biological indices are not rendered sensitivity to these variations, the results obtained may reflect more natural variability than possible human impacts.

Concordance in biological condition and biodiversity between diatom and macroinvertebrate assemblages in Chinese arid-zone streams

Understanding the concordance between aquatic assemblages in ecological assessments and their responses to human-induced disturbances are fundamental steps toward achieving sustainable stream and catchment management. Using diatom, macroinvertebrate, and environmental data collected from northwest Chinese arid-land streams, we tested the concordance between the two assemblages in (1) the assessment results using multimetric indices (MMIs), (2) the stressors affecting the MMIs and beta-diversity, and (3) the response trajectories of MMI and beta-diversity to disturbances. Random Forest analyses revealed that diatom and macroinvertebrate metrics responded most sensitively to climatic and geomorphic variables, respectively. Diatom MMI scores had greater precision and responsiveness than macroinvertebrate MMI scores. Diatom MMI scores were negatively related to gradients in observed–expected conductivity, chemical oxygen demand, and vegetated riparian zone width. Macroinvertebrate MMI scores responded strongly to observed–expected mean substrate composition, conductivity, and phosphate. Diatom beta-diversity decreased, as nitrate, channel alternation, and phosphate increased beyond expected natural background levels. Macroinvertebrate beta-diversity was the lowest when both nitrite and % cobble neared their natural background expectations. Our results indicate that protecting aquatic systems from anthropogenic pressures depends not only on revealing causes of impairment, but also on anticipating and understanding the responses to various stressors of multiple stream biotic assemblages.

Riparian buffers mitigate impacts of oil palm plantations on aquatic macroinvertebrate community structure in tropical streams of Borneo

Southeast Asia is undergoing extensive conversion to oil palm (Elaeis guineensis) monocultures with fast growth expected in West Africa and South America. Despite rapid conversion rates, few tropical studies evaluate land-use change impacts on stream communities, with even fewer studies examining oil palm plantations (OP). In this pioneer study we compare macroinvertebrate community assemblages and their relationships with physico-chemical properties in OP streams bordered by different riparian buffer types to streams in a lowland dipterocarp forest in Sabah, Malaysian Borneo. Our study sites were in increasing levels of riparian disturbance (reduced vegetation density, diversity and structural complexity): (i) Native reference forested sites (NF); (ii) OP streams buffered with patches of natural forest (OPF); (iii) OP streams buffered with untreated oil palm (no chemical application at buffer sites; OPOP); and (iv) OP streams without buffer (OPNB). Macroinvertebrates were collected from leaf litter bags deployed with leaves of varying quality - native Macaranga tanarius and exotic oil palm, and retrieved after 14 days. We found that although invertebrates are typically influenced by resource quality, no differences were detected in their assemblages between the leaf species. All litter bags were dominated by collector-gatherers, with few shredding invertebrates, indicating that they were using the leaves as a habitat rather than a food source. We found no significant differences in macroinvertebrate abundance, richness and sensitive taxa richness (EPT) regardless of the rate of riparian disturbance. However, PERMANOVA showed significant differences between the macroinvertebrate community composition of heavily disturbed OPNB and pristine NF streams. Retaining high quality riparian buffers in OPF streams and lower quality understory in OPOP streams posed intermediate effects on macroinvertebrate community composition. The differences between sites were explained by the increase in nutrients, particularly potassium and phosphorus, stream water temperatures and erosion levels that negatively correlated with macroinvertebrate assemblages in oil palm streams. These findings support the use of riparian buffers in oil palm plantations to mitigate land conversion impacts on macroinvertebrate communities in tropical streams.

Exploring multiple presence-absence data structures in ecology

Ecological studies may produce presence-absence data sets for different taxonomic groups, with varying spatial resolution and temporal coverage. Comparisons of these data are needed to extract meaningful information on the background ecological factors explaining community patterns, to improve our understanding of how beta diversity and its components vary among communities and biogeographical regions, and to reveal their possible implications for biodiversity conservation. A methodological difficulty is that the number of sampling units may be unequal: no method has been designed as yet to compare data matrices in such cases. The problem is solved by converting presence-absence data matrices to simplex plots based on the decomposition of Jaccard dissimilarity into species replacement and richness difference fractions used together with the complementary similarity function. Pairs of simplex plots representing different data matrices are then compared by quantifying, for each of them, the relative frequency of points in small, pre-defined subregions of the simplex, and then calculating a divergence function between the two frequency distributions. Given more than two data matrices, classification and ordination techniques may be used to obtain a synthetic and informative picture of metacommunity structure. We demonstrate the potential of our data analytical model by applying it to different case studies spanning different spatial scales and taxonomic levels (Mediterranean Island faunas; Finnish stream macroinvertebrate assemblages; Hungarian forest assemblages), and to a study of temporal changes in small islands (insect fauna in Florida). We conclude that, by accounting for various structural aspects simultaneously, the method permits a thorough ecological interpretation of presence-absence data. Furthermore, the examples illustrate succinctly how similarity, beta diversity and two of its additive components, species replacement and richness difference influence presence-absence patterns under different conditions.

Assessing the extent and relative risk of aquatic stressors on stream macroinvertebrate assemblages in the neotropical savanna

Freshwater ecosystems are among the most threatened by human activities, influencing losses of biodiversity. To efficiently address management practices to conserve and restore those ecosystems it is important to correctly identify and quantify the severity and magnitude of anthropogenic stressors degrading freshwater biota. In this study we assessed seven stressors describing poor water quality, physical habitat alteration, and land use by means of the relative risk (RR) and relative extent (RE) approach. The RR measures the co-occurrence probability of high stressor condition and poor biological condition. The RE measures the proportion of stream length in the region in high stressor condition. To obtain accurate estimations of RR and RE we used a probabilistic survey design to select a representative sample of perennial, wadeable and accessible streams within four hydrologic units in the neotropical savanna. Results were evaluated at two spatial scales: local – within each of the four hydrologic units, and regional – all four units combined. From 143 randomly selected sites we inferred our results to a target population of 9466 km of streams. Regionally, we found turbidity, % fine sediments and % agriculture as key stressors associated with poor biological condition. At the local scale, we also found that % pasture and total nitrogen were key stressors of biological condition, but their extent was relatively small. By evaluating both RR and RE we conclude that reducing excess sedimentation on streambeds should be the most effective means of improving biological condition over the region. That finding should guide decision makers and land managers to better focus their efforts and resources on improving biological condition of savanna streams.

Large-scale climatic phenomena drive fluctuations in macroinvertebrate assemblages in lowland tropical streams, Costa Rica: The importance of ENSO events in determining long-term (15y) patterns.

Understanding how environmental variables influence the distribution and density of organisms over relatively long temporal scales is a central question in ecology given increased climatic variability (e.g., precipitation, ENSO events). The primary goal of our study was to evaluate long-term (15y time span) patterns of climate, as well as environmental parameters in two Neotropical streams in lowland Costa Rica, to assess potential effects on aquatic macroinvertebrates. We also examined the relative effects of an 8y whole-stream P-enrichment experiment on macroinvertebrate assemblages against the backdrop of this long-term study. Climate, environmental variables and macroinvertebrate samples were measured monthly for 7y and then quarterly for an additional 8y in each stream. Temporal patterns in climatic and environmental variables showed high variability over time, without clear inter-annual or intra-annual patterns. Macroinvertebrate richness and abundance decreased with increasing discharge and was positively related to the number of days since the last high discharge event. Findings show that fluctuations in stream physicochemistry and macroinvertebrate assemblage structure are ultimately the result of large-scale climatic phenomena, such as ENSO events, while the 8y P-enrichment did not appear to affect macroinvertebrates. Our study demonstrates that Neotropical lowland streams are highly dynamic and not as stable as is commonly presumed, with high intra- and inter-annual variability in environmental parameters that change the structure and composition of freshwater macroinvertebrate assemblages.

Impacts of rapid urbanization on the water quality and macroinvertebrate communities of streams: A case study in Liangjiang New Area, China

Rapid urbanization in China has dramatically deteriorated the water quality of streams and threatening aquatic ecosystem health. This study aims to 1) assess the impacts of urbanization on water quality and macroinvertebrate composition and 2) address the question of how urbanization affects macroinvertebrate distribution patterns. Environmental variables over multispatial scales and macroinvertebrate community data were collected on April (dry season) and September (wet season) of 2014 and 2015 at 19 sampling sites, of which nine had a high urbanization level (HUL), six had moderate urbanization level (MUL) and four had low urbanization level (LUL), in the Liangjiang New Area. The results of this study showed that macroinvertebrate assemblages significantly varied across the three urbanization levels. The sensitive species (e.g., EPT taxa) were mainly centralized at LUL sites, whereas tolerant species, such as Tubificidae (17.3%), Chironomidae (12.1%), and Physidae (4.61%), reached highest relative abundance at LUL sites. The values of family biotic index (FBI) and biological monitoring working party (BMWP) indicated the deterioration of water quality along urbanization gradient. Seasonal and inter – annual changes in macroinvertebrate communities were not observed. The results of variation partitioning analyses (CCAs) showed that habitat scale variables explained the major variation in macroinvertebrate community composition. Specifically, the increased nutrient concentrations favored tolerant species, whereas high water flow and substrate coarseness benefitted community taxa richness, diversity and EPT richness. Considering the interactions between scale-related processes, the results of this study suggested that urbanization resulted in less diverse and more tolerant stream macroinvertebrate assemblages mainly via increased nutrient concentrations and reduced substrate coarseness.

Hierarchical dynamics influence the distribution of immature black flies (Diptera: Simuliidae)

Adult black flies (Simuliidae) are medically important insects and they are the sole vector of Onchocerca volvulus. Immature black flies are major components of aquatic macroinvertebrate assemblages in streams and play a vital role in nutrient dynamics. In this study, we examined effect of hierarchical dynamics (spatio-temporal pattern) on the distribution of immature black flies in South Indian streams. The sampling was done in streams of Western Ghats, South India. A total of 16 species belong to two subgenera: Simulium (10 species) and Gowmphostilbia (6 species) of Simulium were observed. Alpha diversity indices were analyzed, which indicate the abundance and species richness between sampling sites. Non-parametric analysis recognized the key environmental variables including latitude and stream order. Subsequently, the monsoon influences the larval assemblages and its association was high in leaf litter as revealed through statistical analyses. Although the members of the immature black fly assemblage with different environmental factors, they are very closely related to spatial and temporal organization and secondarily with other factors prevailing in streams.

Compliance of secondary production and eco-exergy as indicators of benthic macroinvertebrates assemblages' response to canopy cover conditions in Neotropical headwater streams

Riparian vegetation cover influences benthic assemblages structure and functioning in headwater streams, as it regulates light availability and autochthonous primary production in these ecosystems.Secondary production, diversity, and exergy-based indicators were applied in capturing how riparian cover influences the structure and functioning of benthic macroinvertebrate assemblages in tropical headwater streams. Four hypotheses were tested: (1) open canopy will determine the occurrence of higher diversity in benthic macroinvertebrate assemblages; (2) streams with open canopy will exhibit more complex benthic macroinvertebrate communities (in terms of information embedded in the organisms' biomass); (3) in streams with open canopy benthic macroinvertebrate assemblages will be more efficient in using the available resources to build structure, which will be reflected by higher eco-exergy values; (4) benthic assemblages in streams with open canopy will exhibit more secondary productivity. We selected eight non-impacted headwater streams, four shaded and four with open canopy, all located in the Neotropical savannah (Cerrado) of southeastern Brazil. Open canopy streams consistently exhibited significantly higher eco-exergy and instant secondary production values, exemplifying that these streams may support more complex and productive benthic macroinvertebrate assemblages. Nevertheless, diversity indices and specific eco-exergy were not significantly different in shaded and open canopy streams. Since all the studied streams were selected for being considered as non-impacted, this suggests that the potential represented by more available food resources was not used to build a more complex dissipative structure. These results illustrate the role and importance of the canopy cover characteristics on the structure and functioning of benthic macroinvertebrate assemblages in tropical headwater streams, while autochthonous production appears to play a crucial role as food source for benthic macroinvertebrates. This study also highlights the possible application of thermodynamic based indicators as tools to guide environmental managers in developing and implementing policies in the neotropical savannah.

Linking riparian forest harvest to benthic macroinvertebrate communities in Andean headwater streams in southern Chile

Headwater streams are fully linked to surrounding riparian vegetation through coarse and fine organic matter inputs. However, forestry operations in or close to riparian corridors, particularly in mountainous forested microcatchments, can alter both the organic matter dynamics and the composition, structure and function of stream macroinvertebrate assemblages. Although it is an issue of great concern elsewhere, in Andean headwater streams scarce information exist about this respect. By using a paired-catchment approach (thinned vs. unthinned) in two sets of selected evergreen and deciduous small streams in southern Chile (39°S), we evaluated the effects of forest harvest on seasonal and annual litterfall dynamics and the structural and functional attributes of macroinvertebrates between January 2008 and January 2009. Metrics used to assess changes included riparian litterfall input, invertebrate colonization and leaf decomposition of dominant plant species (evergreen: Laureliopsis philippiana, Myrceugenia planipes; deciduous: Nothofagus alpina), taxa richness, functional feeding group (FFG) composition, and their densities and biomasses for each stream. In both experimental trials, microcatchments registered significant differences in the seasonal litterfall input. The total organic matter input was as follows: Unthinned evergreen (UE)=3699, thinned evergreen (TE)=3249, unthinned deciduous (UD)=3151, and thinned deciduous (TD)=2981kgha−1y−1. Leaf dry mass losses were significantly higher during summer and spring for L. philippiana and during summer and autumn for N. alpina. These results were concomitant to decomposition rates and macroinvertebrate abundance during colonization of the leaf bags. Macroinvertebrate density and biomass were also contrasted; shredders were the dominant FFG and showed significant seasonal differences between microcatchments in both in-stream and leaf bag studies. There were generally no major changes in FFG composition or taxa richness, but differences were detected comparatively in the abundance or density of collectors and shredders. Our results suggest that forestry activities carried out on riparian vegetation of Andean headwater streams can affect the structural and functional role of plants and benthic invertebrates and nutrient fluxes downstream.

Decreased habitat specialization in macroinvertebrate assemblages in anthropogenically disturbed streams

Habitat specialists are considered to be more sensitive to anthropogenic disturbance than habitat generalists. However, a number of studies have shown that habitat specialists can be tolerant to or even benefit from environmental degradation, suggesting that the effect of disturbance on distributions and abundances of habitat generalists and specialists can be unpredictable. In this study, we assessed the effects of anthropogenic disturbance on the degree of specialization of stream macroinvertebrates in boreal streams. We first measured the niche width for each macroinvertebrate species using the Outlying Mean Index (OMI) analysis and then, using independent data sets of near-pristine and anthropogenically altered streams, we examined the effects of human disturbances on stream macroinvertebrates with different tolerances to environmental conditions. As expected, human disturbance significantly decreased the level of the specialization in stream macroinvertebrate assemblages, and taxa with narrow environmental tolerances were more sensitive to disturbance than taxa with wide tolerances. Despite being more sensitive to disturbance, taxa with narrow environmental tolerances were locally more abundant than tolerant taxa in near-pristine streams, indicating their better performance in their optimal environments. However, many tolerant taxa decreased in their occurrence in disturbed streams, suggesting that habitat generalists also tend to negatively respond to disturbance. Species-rich assemblages harboured more taxa with narrow tolerances compared with species poor assemblages, suggesting a high conservation value of streams with diverse macroinvertebrate assemblages. Consistent with findings for many biological groups, our results indicate that macroinvertebrate species specialised in certain habitats are more sensitive to environmental degradation than habitat generalists. However, contrary to many previous studies, our results suggest that only a few species are likely to benefit from anthropogenic disturbance and, therefore, environmental degradation does not necessary result in macroinvertebrate assemblages composed of a few tolerant taxa.

Stream macroinvertebrate assemblage uniformity and drivers in a tropical bioregion

Summary Understanding spatial and environmental drivers of undisturbed stream assemblages is important for separating natural and human‐induced changes, but has rarely been attempted for an entire tropical bioregion. We sampled riffle macroinvertebrate assemblages and measured associated biophysical variables in post‐wet and dry seasons from 68 streams of orders 1–5 across the Australian Wet Tropics, a small bioregion (18 497 km2) defined by its warm moist climate and closed‐forest vegetation. As climate and landscape were relatively uniform across the bioregion, we predicted that assemblages would be similar, with turnover (beta diversity) unrelated to distance, and with composition determined mainly by habitat. We identified 93 higher taxa. Density and richness of macroinvertebrates were greatest in the dry season because of habitat contraction and minimal flow disturbance. Richness was greatest in higher order streams. Relative abundance and richness of functional groups showed minor effects of catchment, lithology and stream order, and a positive relationship with altitude for richness of collectors, predators and shredders, and for abundance of shredders. Distance‐based linear modelling showed that among‐assemblage differences were explained by landscape‐scale variables (9.5% of the variation), stream size (13.0%), riparian characteristics (9.6%), water quality (4.6%), substratum (21.1%) and organic resources (22.4%); for models of individual taxa and functional groups, habitat and organic‐resource variables also predominated. Similarities among site assemblages differed little among catchments and there was no relationship between pairwise similarities of catchments and their geographical distances. Nestedness analysis confirmed that samples and catchment groupings were nested subsets of the total set of samples. Across the Australian Wet Tropics, uniformity of assemblages (identified to family or above) conformed to the bioregional classification, probably as a result of the great age of the region. The habitat variables that most influenced macroinvertebrate assemblages support the idea that a suite of biophysical influences is common to stream macroinvertebrate assemblages globally.

Agricultural land use and macroinvertebrate assemblages in lowland temporary streams of the Willamette Valley, Oregon, USA

Streams that dry during part of the year are common throughout the world, yet studies of the macroinvertebrate assemblages in these types of streams are rare compared to those in permanent streams; and studies that assess the effects of agriculture on temporary stream invertebrates are even rarer. We studied macroinvertebrate assemblages in lowland temporary streams of a region with high agricultural land use, the southern Willamette Valley, Oregon, USA. Overall assemblages were dominated by non-insects, and invertebrates tolerant of organic pollution. Nonetheless, these invertebrates displayed adaptations to life in temporary habitats, and as such they may be unique to temporary streams and seasonal wetlands, providing an important addition to regional biodiversity. Stream invertebrates are also important as a prey base for native fish and amphibians using these channels. Benthic invertebrate densities were higher at sites with slower water and more in-stream vegetation; to a lesser degree greater agricultural land use was associated with lower densities. Taxon richness was also negatively affected by agriculture, but this was most evident when least disturbed and highly agricultural sites were compared. Sites in watersheds with a lower proportion of their area under agriculture (mostly west of the Willamette River) had a variety of taxa in disturbance-sensitive insect orders Ephemeroptera, Plecoptera, and Trichoptera (EPT), plus flies in the family Simuliidae present. In addition, they had greater relative abundances of 2 types of flies in the family Chironomidae. In contrast, sites in watersheds with high agricultural land use (mainly east of the Willamette River) had greater relative abundances of non-insects, including ostracods, nematodes, and oligochaete worms. In highly agricultural watersheds, when stream-bottom vegetation was abundant, it was associated with greater benthic invertebrate density, but not with higher taxon richness. Our results suggest that increasing stream-bottom vegetation could be useful when food is limiting for native vertebrates. On the other hand, reduced agricultural land use allows for the development of more diverse benthic invertebrate assemblages.

Does environmental disturbance also influence within-stream beta diversity of macroinvertebrate assemblages in tropical streams?

ABSTRACTRiparian deforestation is a major threat to the ecological integrity of streams and aquatic biodiversity, influencing microhabitat availability and susceptibility to disturbances. Here we tested if riparian deforestation of tropical streams influenced beta diversity of macroinvertebrate assemblages, by comparing indices that weighted differentially rare and dominant taxa, and testing if nestedness in community composition increased in deforested streams. Within-stream beta diversity was higher in deforested than forested streams, mainly due to taxon loss and higher dominance. In disturbed streams, higher sedimentation in pool mesohabitats resulted in larger differences in community composition, whereas mesohabitats in forested streams were more stable.

Interactive effects of urban stormwater drainage, land clearance, and flow regime on stream macroinvertebrate assemblages across a large metropolitan region

AbstractUrban impacts on streams are mediated by alteration of land cover and subsurface drainage. Understanding interactions of these 2 effects is critical for urban land and water management. We used boosted regression trees to analyze relationships between environmental predictors, including land-cover measures that indicate urban impacts, and Stream Invertebrate Grade Number Average Level (SIGNAL) or the occurrence of 60 macroinvertebrate families across the Melbourne (Australia) region. SIGNAL and 51 families were negatively correlated with attenuated imperviousness (AI). Twenty-four families exhibited a steep decline in probability of occurrence between 0 and ≤3% AI, consistent across the range of natural discharge (Q). Responses to attenuated forest cover (AF) were more variable among families (39 positive, 15 negative). AF had a less positive influence on SIGNAL at high than at low AI because the many (high SIGNAL-grade) families that were strongly negatively correlated with AI were likely to be a...