Variation In Macroinvertebrate Assemblages Research Articles

Benthic macroinvertebrate dynamics and responses to environmental factors in spring habitats of Kashmir Himalaya

ABSTRACT Understanding the dynamics of the macroinvertebrate community and the environmental influences is crucial for effective management and conservation of springs. This study examines diversity and spatio-temporal variation in macroinvertebrate assemblages across 12 spring habitats in the South Kashmir Himalayas. Macroinvertebrates were collected, sorted, identified, and enumerated from spring habitats on a seasonal basis from 2013 to 2015, and subjected to various statistical tests. Through statistical tests, significant distinctions are observed among springs and seasons. Permutational analysis of variance showed significant differences in macroinvertebrate assemblages across springs and seasons using both abundance and presence–absence data. Alpha diversity metrics depict variations in richness and Shannon’s H across springs. β-diversity evaluation reveals significant differences in macroinvertebrate assemblages across springs based on abundance and presence–absence data. So, the spring sites present homogeneity in group dispersion (composition varies similarly) while having significantly different compositions. Physicochemical factors like temperature, dissolved oxygen, sulphate, nitrate-nitrogen, and substrate heterogeneity strongly influence the assemblage. In addition, substrate heterogeneity, perennial flow, and spring size also played an important role in explaining the assemblage patterns. The present study provides important information on the impact of environmental factors on the ecological characteristics of macroinvertebrate assemblages vital for effective conservation and monitoring.

Interactive effects of aridity and local environmental factors on the functional trait composition and diversity of macroinvertebrate assemblages in dryland rivers

Drought and local habitat alteration are major environmental stressors shaping the aquatic biota in dryland rivers. However, the combined effects of these factors on aquatic biodiversity remain poorly understood. We collected macroinvertebrate data from Central Asian dryland rivers in Xinjiang, China, from 2012 to 2022, to investigate the individual and interactive effects of drought (as indicated by increasing values of Aridity, AI) and local habitat conditions (fine sediments, velocity and pH) on aquatic macroinvertebrate functional trait composition and diversity. We found that interactions of the selected environmental stressors exhibited more frequent additive than synergistic or antagonistic effects, leading to shifts in macroinvertebrate functional trait composition and diversity accordingly. Interaction of AI and fine sediments showed more pronounced synergistic effects (positive or negative) compared to others and had positive influences on traits like small body size, ovoviviparity, etc. Functional diversity metrics responded differently to stressor interactions, with FRic and FDis being negatively affected, whereas FEve was positively correlated to stressor interaction, suggesting the complementary roles of functional diversity metrics to diagnose impacts of stressor interactions. Overall, our study provides new insights into macroinvertebrate assemblage-stressor relationships in dryland rivers and can help better assess, predict and manage aquatic biodiversity in these rivers under ongoing environmental change.

Improving the performance of macroinvertebrate based multi-metric indices by incorporating functional traits and an index performance-driven approach

Human-driven multiple pressures impact freshwater ecosystems worldwide, reducing biodiversity, and impacting ecosystem functioning and services provided to human societies. Multi-metric indices (MMIs) are suitable tools for tracking the effects of anthropogenic pressures on freshwater ecosystems because they incorporate various biological metrics responding to multiple pressures at different levels of biological organization. However, the performance and applicability of MMIs depend on their metrics' selection and their calibration against natural environmental gradients. In this study, we aimed to unravel i) how incorporating functional trait-based metrics affects the performance of MMIs, ii) how disentangling the natural environmental gradients from anthropogenic pressures effects affects the performance of MMIs, and iii) how the performance of MMIs developed using a metric performance-driven approach compares with MMIs developed using an index performance-driven approach. We carried out a field survey measuring abiotic and biotic variables at 53 sites in the Karun River basin (Iran) in 2018. For functional trait-based metrics, we used 15 macroinvertebrate traits and calculated community-weighted mean trait values and functional diversity indices. We used random forest modeling to account for the effect of natural environmental gradients on each metric. Based on our results, incorporating functional traits increased the MMI performance significantly and facilitated ecological interpretation of MMIs. Both taxonomic and functional components of macroinvertebrate assemblages co-varied strongly with natural environmental gradients, and accounting for these covariations improved the performance of MMIs. Finally, we found that index performance-driven MMIs performed better in terms of precision, bias, sensitivity, and responsiveness than metric performance-driven MMIs.

Variation in macroinvertebrate assemblages and water quality as a test for different levels of ecological impairment across an Ethiopian highland river system

ABSTRACT The Ethiopian highlands is an area under high anthropogenic pressure. Despite being a hotspot for freshwater biodiversity, the ecological status of local rivers is not monitored. Physicochemical and nutrient water quality parameters and macroinvertebrate assemblages were sampled monthly from the Megech River and its tributaries from January to March 2021. Sampling locations were designated as either upstream or downstream of the Gondar City urban area. We tested for temporal (monthly) and spatial (location, river) variation in water quality and spatial (location, river) variation in macroinvertebrate assemblage structure to examine which water quality parameters were most associated with patterns in macroinvertebrate assemblages. Water quality varied significantly between locations and months but not between rivers. Water quality differences were particularly driven by higher nutrient, salinity, dissolved solids, and conductivity levels downstream, and higher pH and dissolved oxygen levels upstream. Despite the more abundant and diverse macroinvertebrate assemblages downstream, biotic index scores generally indicated slightly increased ecological impairment downstream. A clear spatial pattern emerged in macroinvertebrate assemblages between locations; we detected a significant difference between rivers, with pairwise differences between sampling locations, particularly due to high dissimilarity between the upstream and downstream locations of the Angereb, Shinta, and Qeha rivers. BIO-ENV Pearson correlations indicated that variation in macroinvertebrate assemblages were mostly explained by dissolved oxygen, salinity, and nutrient parameters including nitrate, ammonium, and sulphate. Our findings confirm the need for more rigorous monitoring of Ethiopian highland rivers and improved management of nutrient inputs.

Macroinvertebrate assemblages along a gradient of physicochemical characteristics in four riverine wetlands, Upper Blue Nile basin, Northwestern Ethiopia

This study aims to examine the physicochemical variables that influence macroinvertebrate assemblages in wetlands of the Fetam River watershed. Macroinvertebrates and water quality samples were collected from 20 sampling stations across four wetlands between February and May 2022. Principal component analysis (PCA) was used to elucidate the physicochemical gradients among datasets and canonical correspondence analysis (CCA) was applied to explore the relationship between taxon assemblages and physicochemical variables. Aquatic insects such as Dytiscidae (Coleoptera), Chironomidae (Diptera), and Coenagrionidae (Odonata) were the most abundant families, and they comprised 20-80% of the macroinvertebrate communities. As demonstrated by cluster analysis, three site groups including slightly disturbed (SD), moderately disturbed (MD), and heavily disturbed (HD) sites were identified. PCA showed a clear separation of slightly disturbed sites from moderately and highly impacted sites. Differences in physicochemical variables, taxon richness and abundance, and Margalef diversity indices were observed along the SD to HD gradient. Phosphate concentration was an important predictor that influenced richness and diversity. The extracted two CCA axes of physicochemical variables accounted for 44% of the variability in macroinvertebrate assemblages. Nutrient concentration (nitrate, phosphate, and total phosphorus), conductivity, and turbidity were the main drivers of this variation. This suggested the need for sustainable wetland management intervention at the watershed level, ultimately benefiting invertebrate biodiversity.

Seasonal variability in macroinvertebrate assemblages in paired perennial and intermittent streams in Costa Rica

Seasonal variability in macroinvertebrate assemblages in paired perennial and intermittent streams in Costa Rica

Distribution and diversity of benthic macroinvertebrates in the Mohlapitsi River, South Africa

Freshwater ecosystems are facing degradation from human activities in the form of alterations of flow regimes, changes in land-use, and intensive water abstraction, in turn generating adverse effects on biodiversity and ecological functionality. Efficient assessment of river/stream ecosystem response to such anthropogenic changes is urgently needed. Many human activities that have an effect on water quality and river health are increasing along the Mohlapitsi River, which used to be one of the rivers with good water quality in South Africa. The aim of the study was to assess spatial variation in macroinvertebrate assemblages in relation to water quality of the Mohlapitsi River. A combination of canonical correspondence analysis and univariate analyses were used to examine the macroinvertebrate assemblages at six different sites of the Mohlapitsi River. The spatial difference in macroinvertebrate abundance was mostly related to changes in water quality. The number of taxa and the diversity of macroinvertebrates remained relatively high across the river as compared to other rivers in the Olifants River System. The midstream and downstream sites were mostly dominated by macroinvertebrates tolerant to disturbance/pollution. The most abundant family was the Thiaridae (about 60%) and mainly occurred in the midstream and downstream sites of the river (more disturbed sites). The study showed a higher evenness index in the upstream than the midstream and downstream sites which is an indication of good water quality at the upstream sites of the river. The results suggest that the river is being subjected to a moderate environmental pollution, which requires continuous assessment and monitoring to determine causes and initiate remedial measures.

Main macroinvertebrate community drivers and niche properties for characteristic species in urban/rural and lotic/lentic systems

The effect of urbanization is often reflected both in lotic and lentic habitats, through changes in diversity and structural and compositional changes in macroinvertebrate communities. In this study, we focused on macroinvertebrate assemblage in lotic and lentic ecosystems of the Krąpiel River catchment area (NW Poland) with the following aims: (1) to determine the main driver in structuring lotic and lentic macroinvertebrate communities and the factors that influence them in urban versus rural landscapes; (2) to test whether the diversity of macroinvertebrate assemblages in urban lotic/lentic ecosystems is lower than that in rural landscapes; (3) to identify characteristic macroinvertebrate species for urban and rural lotic/lentic ecosystems; to (4) determine species tolerance ranges and species optimums, with special emphasis on characteristic “urban” and “rural” species. Distance from study sites to built-up areas and conductivity were the main factors contributing to the separation of urban vs. rural habitats. For lotic sites, temperature, the percentage of built-up area, insolation, and oxygen concentration were the main factors significantly associated with changes in community composition. For lentic sites, insolation, temperature, and BOD5 were recognized as the main factors which are significantly associated with changes in community composition. The results for lentic habitats were as expected: average species richness was higher in rural than in urban habitats. The characteristic species for each of the four habitat groups included Mideopsis orbicularis for Lentic rural habitats; Hygrobates longipalpis for Lotic rural habitats; Piona sp. for Lentic urban habitats; Mideopsis crassipes for Lotic urban habitats. Hygrobates longipalpis and Piona sp. were at the opposite sides with respect to the degree of urbanization. Result of this investigation has shown that the impact of urbanization and consequently the implementation of conservation measures should be viewed separately within the lentic and lotic gradient.

Temporal Variability of Macroinvertebrate Assemblages in a Mediterranean Coastal Stream: Implications for Bioassessment.

Macroinvertebrates from a small forest stream in central-south Chile were sampled monthly from September 2017 to August 2018 to assess temporal variability in the assemblage and the effects of that variability on ecological indicators. Higher precipitation and flows occurred in winter months, and water quality varied among months. We collected 59 macroinvertebrate taxa, finding higher taxa richness and abundances in summer months than in winter months. Four taxa demonstrated marked seasonality, being abundant in some months and then decreasing in following months (Limnoperla jaffueli (Navás), Nousia maculata (Demoulin), Smicridea sp. (McLachlan), Chironomidae spp.). The scores of the family Hilsenhoff Biotic Index (HBI), Hilsenhoff Species-level Biotic Index (HSBI), Multimetric Macroinvertebrate Index (MMI), and Chilean Biological Monitoring Working Party (ChBMWP) index varied throughout the year reflecting natural variability. However, only HBI and HSBI scores were significantly different among seasons, ranging across three water quality classes (excellent, very good, and good), showing the lowest water classes in spring, coinciding with higher abundances of tolerant species. The MMI and ChBMWP indicated good and very good site conditions throughout the year, respectively. Shannon-Weaver diversity ranged between 2.59 (April) and 1.78 (February); however, Pielou evenness had high values throughout the year (> 0.62), except in February. Changes in macroinvertebrates composition throughout the year were explained primarily by discharge, water temperature, and conductivity. Our findings indicate that natural monthly variability in macroinvertebrate assemblages influences the scores of biological indices throughout the year. Therefore, we recommend that natural stream variability be accounted for in biomonitoring programs. We also emphasize the need to use caution when interpreting biological index scores to avoid misinterpretations in stream quality classification.

Rapid Bioassessment Protocols Using Aquatic Macroinvertebrates in Africa–Considerations for Regional Adaptation of Existing Biotic Indices

Benthic macroinvertebrates are commonly used to assess water quality and ecological condition of aquatic ecosystems and they form the basis of several biotic indices. Many of these biotic indices are based on rapid bioassessment protocols (RBP). The first RBP based on macroinvertebrates, developed in Africa in the early 1990s, was the South Africa Scoring System (SASS). Since then SASS has been widely used in southern Africa and beyond, and has formed the basis of several other RBPs developed in Africa. This paper explores the RBPs and associated biotic indices currently used in Africa, primarily those that are rapid, field-based with low taxonomy (mostly family level) and which rely on sensitivity weightings of individual taxa to generate three metrics for interpreting water quality and ecological condition of aquatic ecosystems. Recommendations for future regional adaptation of RBPs, including calibration, validation, and modification of RBPs and biotic indices for new regions are provided. To date, five RBPs have been developed in Africa, while some existing biotic indices have been used outside their intended regional range. Key to the efficacy of any RBP and associated biotic index is the ability to detect a water quality impact, or change in river health. Important considerations when adapting an index for a new region or country include evaluating the suitability of the sampling protocol to local river conditions, evaluating the distribution of aquatic macroinvertebrate taxa in the region, assigning sensitivity weightings to new taxa in the region, evaluating the ability of the biotic index to detect impacts, evaluating within-country spatial and temporal variability in macroinvertebrate assemblages, and developing appropriate data interpretation guidelines based on metric scores and reference conditions. Often several iterations of a biotic index are needed, with improvement in efficacy with each version, following spatially and temporally comprehensive sampling. Future RBPs developed for bioassessment of rivers in Africa will promote the protection, conservation, and management of African riverine ecosystems.

Biodiversity Patterns of Macroinvertebrate Assemblages in Natural and Artificial Lentic Waters on an Oceanic Island

The Azorean islands have been historically affected by human activities, mainly due to the combined effects of habitat degradation and fragmentation, and the introduction of exotic species. We here aim to analyze the role of environmental characteristics and spatial descriptors in supporting regional biodiversity of macroinvertebrates by considering natural ponds and artificial tanks. After the monthly variation of macroinvertebrate assemblages was assessed in three temporary and two permanent ponds in the Azorean island of Terceira during a complete inundation-desiccation annual cycle, the assemblage differences of 12 ponds (three temporary and nine permanent ponds) and 8 closely-located artificial tanks were analyzed across a range of landscape disturbances. Macroinvertebrate assemblages were found to differ according to hydroperiod and sampled months. Although the former explained the highest variance, macroinvertebrate differentiation by hydroperiod was also dependent on the study month. Our results also revealed a consistent monthly pattern of species replacement. However, the contribution of nestedness to the macroinvertebrate β-diversity was notable when temporary ponds were close to desiccation, probably indicating a deterministic loss of species due to the impoverished water conditions of the ponds facing desiccation. When the macroinvertebrate assemblages were analyzed in relation to physico-chemical variations and spatial descriptors, the artificial tanks were not clearly segregated from the natural ponds, and only differentiated by pH differences. In contrast, those natural ponds exhibiting high concentrations of total phosphorous (likely signs of anthropization) also discriminated the ordination of ponds in a distance-based redundancy analysis, and showed impoverished assemblages in comparison with well-preserved ponds. The macroinvertebrate assemblages of the natural ponds showed a significant spatial pattern, but this spatial influence was not significant when tanks and ponds were considered together. Our results suggest that tanks may act as possible reservoirs of biodiversity during the desiccation period of temporary ponds, but are unable to establish successful populations. These fishless permanent tanks can complement the conservation of a biodiversity that is largely maintained by the pristine high-altitude natural ponds. The establishment of a guideline for conservation management that also considers the artificial tanks is necessary to benefit the local and regional Azorean macroinvertebrate diversity.

Spatial variability of aquatic macroinvertebrate assemblages in the Okavango Delta, Botswana: considerations for developing a rapid bioassessment tool

Spatial variability in macroinvertebrate assemblages of the Okavango Delta, Botswana, was examined to evaluate differences in assemblages at a regional and habitat scale. Sampling was undertaken six times during a one-year cycle from 2005 to 2006, with 228 macroinvertebrates samples collected from different aquatic habitats in 22 sites in four study areas. Sixty-four taxa, mainly families, and >30 000 individuals were recorded. Multivariate analysis of aquatic macroinvertebrates revealed that the distribution of macroinvertebrate fauna is relatively homogenous among study regions, with some variation in number of taxa. Differences were observed in the macroinvertebrate assemblages associated with different aquatic habitats, with fauna from deltaic habitats (floating vegetation, inundated floodplain and marginal vegetation) different from non-deltaic habitats (isolated, seasonally flooded pools and isolated, temporary, rain-filled pools). Within the deltaic habitats, there were no significant differences among the habitats in terms of number of taxa and abundance, although assemblages and frequency of occurrence of taxa differed among habitats, providing evidence of habitat preferences for certain taxa. Future development of a macroinvertebrate-based bioassessment tool should account for aquatic habitat, although the tool does not need to be region specific. Temporal variability of macroinvertebrate assemblages should be examined to evaluate potential hydrological effects on the tool.

Influence of environmental parameters on benthic macroinvertebrate assemblages in the headwaters of Bagmati river, Kathmandu valley, Nepal

The distribution of benthic macro invertebrates (BMIs) is affected by various environmental factors. Understanding their response to these factors is a key to assessing freshwater quality. The aim of this research is to understand the influence of different environmental parameters on BMIs assemblages in the headwaters of Bagmati River. The BMIs were sampled following a multi-habitat sampling protocol and the – hydrological and physico-chemical parameters were measured using standard methods. The relationship between environmental parameters and macro invertebrate assemblages was analyzed through Multivariate analysis - Redundancy Analysis and Variation Partitioning. Stream discharge, pH and Dissolved Oxygen were selected for multivariate analysis through backward elimination method. pH and Dissolved Oxygen were important contributing factors explaining the variation in BMIs community. Physico-chemical parameters were found to be the most important group of variables explaining the variation in macro invertebrate assemblages. Only about twenty-five per cent of the variation in the BMIs community was explained by the model so the parameters studied here do not have a high degree of explanatory power.

Macroinvetebrate Assemblages as Indicators of Water Quality of the West Seti River, Bajhang, Nepal

Water quality of the West Seti River, a tributary of the Karnali in West Nepal was assessed using macroinvertebrates as bioindicators. The main objective of the study was to assess the ecological water quality of the West Seti River and to generate a baseline data on macroinvertebrate assemblages. The sampling was conducted during December 2015 and a total of 11 sampling sites were selected from the West Seti River and its tributaries. Qualitative samples of macroinvertebrates were collected from different habitats. Selected physico-chemical parameters such as pH and temperature were estimated on-site. Dissolved oxygen (DO) was estimated by Winkler’s method. The macroinvertebrate samples were enumerated and identified up to Family level following standard literature. Chi-square test was performed to see whether macroinvertebrate taxa varied significantly along the altitudinal gradient and between the West Seti River and its tributaries. An ecological assessment tool Nepalese Biotic Score/ Average Score Per Taxon (NEPBIOS/ASPT) was applied to assess the water quality of the sampling sites. The pH value ranged from 7.9 to 8.7 indicating the alkaline nature of the river. A total of 1666 individuals belonging to 34 Families and 7 Orders of macro-invertebrates were observed. The highest diversity of the macroinvertebrate taxa was observed at site T5 with nineteen Families whereas the lowest taxa diversity was observed at R3 with only five Families. The variation in macroinvertebrate assemblages between the sub-tropical and temperate zones; and the West Seti River and its tributaries were not significant. NEPBIOS/ASPT revealed a score of Water Quality Class of III-IV at Site R3 indicating that the site was polluted. This site was characterized by the abundance of red Chironomids which are considered as the indicators of organic pollution.International Journal of EnvironmentVolume-6, Issue-3, Jun-Aug 2017, page: 25-45

Effects of local land-use on riparian vegetation, water quality, and the functional organization of macroinvertebrate assemblages

Land-use change is a principal factor affecting riparian vegetation and river biodiversity. In Chile, land-use change has drastically intensified over the last decade, with native forests converted to exotic forest plantations and agricultural land. However, the effects thereof on aquatic ecosystems are not well understood. Closing this knowledge gap first requires understanding how human perturbations affect riparian and stream biota. Identified biological indicators could then be applied to determine the health of fluvial ecosystems. Therefore, this study investigated the effects of land-use change on the health of riparian and aquatic ecosystems by assessing riparian vegetation, water quality, benthic macroinvertebrate assemblages, and functional feeding groups. Twenty-one sites in catchment areas with different land-uses (i.e. pristine forests, native forests, exotic forest plantations, and agricultural land) were selected and sampled during the 2010 to 2012 dry seasons. Riparian vegetation quality was highest in pristine forests. Per the modified Macroinvertebrate Family Biotic Index for Chilean species, the best conditions existed in native forests and the worst in agricultural catchments. Water quality and macroinvertebrate assemblages significantly varied across land-use areas, with forest plantations and agricultural land having high nutrient concentrations, conductivity, suspended solids, and apparent color. Macroinvertebrate assemblage diversity was lowest for agricultural and exotic forest plantation catchments, with notable non-insect representation. Collector-gatherers were the most abundant functional feeding group, suggesting importance independent of land-use. Land-use areas showed no significant differences in functional feeding groups. In conclusion, anthropogenic land-use changes were detectable through riparian quality, water quality, and macroinvertebrate assemblages, but not through functional feeding groups. These data, particularly the riparian vegetation and macroinvertebrate assemblage parameters, could be applied towards the conservation and management of riparian ecosystems through land-use change studies.

Spatial organization of macroinvertebrate assemblages in the Lower Mekong Basin

In this study, we investigated patterns of spatial variation in macroinvertebrate assemblages in the Lower Mekong Basin (LMB) and examined their relationship with environmental factors. Cluster analysis was used to group macroinvertebrate samples and Linear Discriminant Analysis was performed to discriminate the major factors associated with the macroinvertebrate assemblages. Four clusters could be distinguished based on the dissimilarity between macroinvertebrate assemblages. The assemblages related to the tributaries and the upstream parts (cluster II) were characterized by a lower richness, abundance, diversity and a lower number of indicator taxa compared to the assemblage found downstream in the Mekong delta (cluster I). Aquatic insects and their indicator taxa (e.g. Caenodes sp., Dipseudopsis sp. and Gomphidae sp.), preferring a high-altitude environment with a high dissolved oxygen concentration and a high density of wood/shrub and evergreen forests, were the most predominant group in the assemblages occupying the tributaries and the upstream parts (cluster IIa). The assemblage found in the delta, consisting largely of molluscs and a moderate richness and abundance of worms, crustaceans and dipteran insects, was mainly represented by Corbicula leviuscula and C. moreletiana (molluscs), Namalycastis longicirris and Chaetogaster langi (worms), Corophium minutum and Grandidierella lignorum (crustaceans), and Cricotopus sp. and Clinotanypus sp. (dipteran insects). This assemblage was associated with a large watershed surface area, deep and wide rivers and a high water temperature. The intermediate assemblage (cluster IIb1) in-between could be discriminated based on land cover types including inundated, wetland and agricultural land, and was represented most by molluscs. Strikingly, the assemblage occupying the upstream parts (cluster IIa), which is related to intensified agriculture and a moderate conductivity, was characterized by a higher macroinvertebrate diversity compared to the mountainous and less impacted tributaries. This could mean that the natural stress is high in these systems for some taxa, leading to a lower overall taxonomic richness and abundance. Nevertheless, the number of taxa and the diversity of macroinvertebrates remained relatively high across the basin, especially in the delta assemblage. Therefore, the LMB deserves a particular attention for conservation.

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.

Longitudinal and seasonal patterns of macroinvertebrate communities in a large undammed river system in Southwest China

Abstract Identifying naturally-regulated spatial and temporal variations of benthic macroinvertebrates is critical to effective assessment and conservation of aquatic ecosystems, but little is known about these variations in large rivers in East Asian monsoon region. Here, we address this issue by measuring within-one-year longitudinal and seasonal variability in macroinvertebrate assemblages in such a broadly natural river across its whole watershed. Along longitudinal gradients, taxon richness, Shannon–Wiener diversity and mayflies and caddisflies significantly decreased downstream but chironomids and oligochaeta increased. Taxon richness, diversity indices, and abundance of most taxa all had lowest value in summer. Assemblage structure showed both significant but larger longitudinal than seasonal variations, with a clear separation of upstream and most midstream sites from downstream ones in ordination plot. Different environmental and spatial variables were significant for distinguishing macroinvertebrate assemblages among four seasons, although substrate and PCNM1 emerged as important in all seasons. Variance partitioning analyses indicated stronger environmental control than spatial structuring of community composition in all seasons, with pure environmental factors explaining most community variation. These observed patterns contribute to understanding of sources of uncertainty in bioassessment and thus have implications for ecological monitoring and assessment using macroinvertebrates in rivers in monsoon regions.

Temporal Patterns and Environmental Correlates of Macroinvertebrate Communities in Temporary Streams.

Temporary streams are characterised by short periods of seasonal or annual stream flow after which streams contract into waterholes or pools of varying hydrological connectivity and permanence. Although these streams are widespread globally, temporal variability of their ecology is understudied, and understanding the processes that structure community composition in these systems is vital for predicting and managing the consequences of anthropogenic impacts. We used multivariate and univariate approaches to investigate temporal variability in macroinvertebrate compositional data from 13 years of sampling across multiple sites from autumn and spring, in South Australia, the driest state in the driest inhabited continent in the world. We examined the potential of land-use, geographic and environmental variables to predict the temporal variability in macroinvertebrate assemblages, and also identified indicator taxa, that is, those highly correlated with the most significantly associated physical variables. Temporal trajectories of macroinvertebrate communities varied within site in both seasons and across years. A combination of land-use, geographic and environmental variables accounted for 24% of the variation in community structure in autumn and 27% in spring. In autumn, community composition among sites were more closely clustered together relative to spring suggesting that communities were more similar in autumn than in spring. In both seasons, community structure was most strongly correlated with conductivity and latitude, and community structure was more associated with cover by agriculture than urban land-use. Maintaining temporary streams will require improved catchment management aimed at sustaining seasonal flows and critical refuge habitats, while also limiting the damaging effects from increased agriculture and urban developments.

Home advantage? Decomposition across the freshwater-estuarine transition zone varies with litter origin and local salinity

Expected increases in the frequency and intensity of storm surges and river flooding may greatly affect the relative salinity of estuarine environments over the coming decades. In this experiment we used detritus from three contrasting environments (marine Fucus vesiculosus; estuarine Spartina anglica; terrestrial Quercus robur) to test the prediction that the decomposition of the different types of litter would be highest in the environment with which they are associated. Patterns of decomposition broadly fitted our prediction: Quercus detritus decomposed more rapidly in freshwater compared with saline conditions while Fucus showed the opposite trend; Spartina showed an intermediate response. Variation in macro-invertebrate assemblages was detected along the salinity gradient but with different patterns between estuaries, suggesting that breakdown rates may be linked in part to local invertebrate assemblages. Nonetheless, our results suggest that perturbation of salinity gradients through climate change could affect the process of litter decomposition and thus alter nutrient cycling in estuarine transition zones. Understanding the vulnerability of estuaries to changes in local abiotic conditions is important given the need to better integrate coastal proceses into a wider management framework at a time when coastlines are increasingly threatened by human activities.