Benthic Macroinvertebrate Communities Research Articles

Influence of Suspended Mussel Aquaculture and an Associated Invasive Ascidian on Benthic Macroinvertebrate Communities

Many benthic macroinvertebrates are associated with cultured bivalves but are normally excluded from studies on the environmental effects of bivalve aquacultures. We evaluated the hypothesis that mussel aquaculture increases overall “benthic” macroinvertebrate productivity by considering both sediment- and mussel sock-associated macroinvertebrates. It was predicted that the presence of the invasive ascidian Styela clava would increase this effect by increasing the mussel sock’s biogenic structure. Macroinvertebrates in sediments and on mussel socks were sampled in eight bays on Prince Edward Island, Canada: three were invaded by Styela clava and there were five where it was absent. Infaunal macroinvertebrates associated with benthic sediments (sediment macroinvertebrates) within leases were less abundant relative to the control locations outside of leases and showed a trend towards decreased biomass and productivity. Abundance of mussel sock-associated macroinvertebrates was greater in bays with S. clava than in bays without it. When sediment and mussel sock macroinvertebrates were considered together as “benthic” communities within mussel leases and compared to sediment macroinvertebrate communities outside of leases, “benthic” macroinvertebrate abundance, biomass, and productivity were greater inside mussel leases than in areas outside of them. The presence of S. clava did not influence this trend. Although the ecological role of the macroinvertebrates associated with suspended mussels is likely not equivalent to those associated with benthic sediments, the presence of macroinvertebrates on suspended mussels, in some measure, offsets the impacts on the abundance, biomass, and productivity of macroinvertebrate communities at the farm-scale.

Assessing assemblage pattern, health status and environmental drivers of macrobenthic invertebrate community structure for sustainable management in a tropical tributary of River Ganga, India

Assessing assemblage pattern, health status and environmental drivers of macrobenthic invertebrate community structure for sustainable management in a tropical tributary of River Ganga, India

Development of a benthic macroinvertebrate predictive model based on the physical and chemical variables of rivers in the Republic of Korea

Predictive models for the benthic macroinvertebrate community based on environmental variables facilitate the identification of the organisms expected to inhabit an area according to the target environmental conditions when restoring rivers. In this investigation, a biotic community predictive model was developed using benthic macroinvertebrate and environmental variable data collected from 1,210 sites in the Republic of Korea from 2010 to 2020. The sites were classified into six groups according to Two Way Indicator Species Analysis (TWINSPAN) and based on their individual abundance/m2 of benthic macroinvertebrates. The TWINSPAN groups were related to 14 variables by stepwise multi-discriminant analysis. The relative importance of the environmental variables that classified each TWINSPAN group was in the order of mean diameter of particle size, catchment area, altitude, velocity, total phosphorus, latitude, pH, longitude, conductivity, water depth, suspended solids, biochemical oxygen demand, stream order, and total nitrogen. Discriminant functions 1–4 showed statistically significant and a predictive model was developed using functions 1 and 2 based on Wilks’ lambda values. The fit of the derived model was confirmed using Sørensen similarity (number of taxa) and Bray–Curtis dissimilarity (individual abundance/m2) analyses between the predicted organisms and those observed at the sites. The distributions of similarity and dissimilarity that were confirmed by stream type ranged from 0.60 to 0.72 and 0.46–0.56, respectively, based on the mean. Based on the predicted and observed values, the ratio of shredders and scrapers to collectors showed similar results overall for each stream type. The predictive model derived using nationally managed available data is expected to be applicable to stream and river restorations in the future, as it provides a statistical assessment of the biotic communities that are expected to inhabit a given environment.

Small hydropower—Small ecological footprint? A multi-annual environmental impact analysis using aquatic macroinvertebrates as bioindicators. Part 2: Effects on functional diversity

Currently, across the entire European river network, there are an estimated 0.74 barriers per kilometer of river length, with hydropower production being the main cause of riverine habitat fragmentation. On the one hand, policy actions have been proposed by different institutions to limit this impact. On the other hand, the compelling need to produce energy from renewable/sustainable resources is further boosting the impoundment of rivers, since, globally, small hydropower plants are expected to contribute greatly to future energy needs. While a few studies have already analyzed the environmental impact of small hydropower plants by researching the structural communities of benthic macroinvertebrates, none have thus far assessed the potential impacts related to the functional diversity of these communities. Here, following a “Before-After-Control-Impact (BACI)” scheme, we implemented different methodologies to study the functional diversity of benthic communities sampled across 4 sites in a fish-free, glacier-fed stream of the Italian Central-Eastern Alps for 5 consecutive years. More specifically, the sampling sites were chosen in an area near the weir of a small “run-of-river” hydropower plant, which constituted the structure from which water was diverted to the turbine. Specific goals were to assess the potential variation in the functional traits of benthic macroinvertebrates in relation to the weir’s presence, investigate whether a variation in trait distribution was caused by alterations in the abundances of common and rare taxa, and quantify functional diversity in space and time through the application of specific indices. Our initial hypothesis of finding significant differences among the sampling sites after the start-up of the hydropower plant was not confirmed by our results, since the benthic communities at all sites continued to exhibit a largely similar set of traits and, consequently, functional diversity. Our results highlighted the need for a better understanding of the relationships between effect traits and ecological processes to establish thresholds from which a shift in these processes may occur. Hence, a better understanding of the assets and liabilities of already established small hydropower plants may be a guide for more conscious decisions concerning the establishment of new ones and/or changes in the management of already existing ones.

Long-term study of ecological restoration in a typical shallow urban lake

We investigated the long-term effects (6 years) of sediment improvement and submerged plant restoration of a subtropical shallow urban lake, Hangzhou West Lake China. To reveal the lake ecosystems variations, we analyzed the sediment properties, submerged macrophyte characteristics, sediment microorganisms, and benthic macroinvertebrate communities from 2015 to 2020. The ecological restoration project decreased sediment TP and OM, increased submerged macrophyte biomass and sediment microbial diversity, and improved the benthic macroinvertebrate communities in the restored area. The sediment TP decreased from 2.94 mg/g in 2015 to 1.33 mg/g in 2020. The sediment OM of the restored area decreased from 27.44 % in 2015 to 8.08 % in 2020. Principal component analysis (PCA) confirmed that the restoration improved the sediment conditions, making it suitable for the growth of submerged macrophytes, and then sped up the restoration and reconstruction of the lake ecosystem. These results have significant implications on the ecological management of shallow lakes.

Biomonitoring as a potential tool for water quality in tilapia culture: a case study of Baixa Mogiana region of São Paulo State, Brazil

The objectives of this study were to test an artificial substrate sampler method for aquaculture ponds and assess the water quality based on the benthic macroinvertebrate community living in fishpond sediment at four farms with tilapia production in the Baixa Mogiana region of São Paulo State, Brazil. Benthic macroinvertebrates were monitored every 15days for 3months. Approximately 500,000 organisms distributed in 47 taxa were collected. Chironomidae, Glossiphonidae, Hirudinidae, Libelullidae, Oligochaeta, and Polycentropodidae were present in all collected samples, with the dominance of Chironomidae in the benthic community. Polycentropodidae, a sensitive family to organic pollution, had a greater abundance in fish farms with better environmental conditions. Significant differences in dissolved oxygen and pH were observed among fishponds at different fish farms. Biomonitoring with artificial substrate is a simple and low-cost alternative to monitoring water quality of tilapia culture in fishponds. The artificial substrate sampling method was effective, but the evaluation of more critical conditions of water quality would improve the method and enhance the knowledge of taxa and ecology of macrobenthic organisms in fishponds.

Small Hydropower—Small Ecological Footprint? A Multi-Annual Environmental Impact Analysis Using Aquatic Macroinvertebrates as Bioindicators. Part 1: Effects on Community Structure

The increasing incentives stemming from many international initiatives that target sustainable energy production have led to the global success of small hydropower plants. However, there is a growing debate about the actual environmental impact these structures have on riverine ecosystems, to the extent that some researchers argue that they could have a proportionally greater impact than large hydropower plants; nevertheless, an empirical evaluation applying a long-term true “Before-After-Control-Impact (BACI)” approach has never been conducted. In a true “BACI” experiment applying generalized linear mixed models, we assessed changes in benthic macroinvertebrate communities—taxonomic composition, spatial and temporal β-diversity, and possible indicator taxa—along 6 sites located in a glacier-fed stream in the Italian Alps before and after the installation of a small “run-of-river” hydropower plant. The “BACI” results over the 5-year study showed no significant variation in the benthic macroinvertebrate communities stemming from the activity of the hydropower plant. Moreover, spatial β-diversity showed, in relation to the “control” site, a constant dissimilarity pattern throughout all the sampling years, exhibiting a constant increase proceeding downstream. On the other hand, temporal β-diversity showed changes in the benthic macroinvertebrate communities, but these changes were largely caused by variation in densities and not by the appearance or disappearance of new taxa. In summary, we were unable to detect a significant impact of the small “run-of-river” hydropower plant on the benthic macroinvertebrate communities of the glacier-fed stream under study. Despite the need of further studies that consider the different features and operational measures of small hydropower plants, our findings illustrate that, when correctly managed, small hydropower plants and the energy they produce may represent an added resource for strategic debates on energy planning processes, especially in light of the commitments at the international level of many countries in developing strategies toward a “carbon-neutral” energy sector.

Seasonal Variation in the Macrobenthic Invertebrate Densities of Aripal and Watalara Streams of Kashmir Himalaya, India

The present study reflects the seasonal variation of macrobenthic invertebrates from Aripal and Watalara streams in Kashmir Himalaya. During the study, a significant difference (p<0.05) was observed in the density of Annelida, Mollusca, and Arthropoda on a seasonal scale. Macrobenthic invertebrates were found to be at their highest density during summer and autumn, whereas they were recorded lowest during winter and spring. The total density during summer and autumn was found to be significantly different (p<0.05) when compared to winter and spring seasons. The data also depicted the maximum density of Arthropoda followed by Mollusca and Annelida. The study reveals the seasonal stability of the stream ecosystem within the temperate region and also provides the baseline information for macrobenthic invertebrate community structure.

DETERMINANT DRIVERS FOR THE COMMUNITY STRUCTURE OF BENTHIC MACROINVERTEBRATES IN COASTAL LAGOONS AT THE RESTINGA DE JURUBATIBA NATIONAL PARK, IN THE STATE OF RIO DE JANEIRO STATE (BRAZIL)

This study aimed to characterize and evaluate factors driving the structure of the benthic macroinvertebrate community in coastal lagoons at the Restinga de Jurubatiba National Park. Sixteen lagoons were sampled in July 2010 during the dry season. At each lagoon, three samples were taken in the central region and three samples were taken near the sandbar. At each point, the limnological variables and the benthic community were collected. Richness and abundance were calculated for each sample. The correlations among the environmental parameters were tested using Pearson's correlation. A Principal Component Analysis using environmental variables was performed to visualize the similarity among samples. Simple regressions were used to assess the correlation between macroinvertebrates' metrics and environmental parameters. A redundancy test was performed to link environmental parameters to the community structure of macroinvertebrates. A total of 1,719 macroinvertebrates were identified in 25 taxa groups that were classified as exclusive marine taxa, five as brackish/marine taxa, seven as freshwater taxa, and two taxa as groups with marine and freshwater representatives. The most abundant taxa were Leonereis sp., Heleobia australis, and Kalliapseudidae. Richness and abundance were negatively related to salinity. The redundancy test indicated pH, salinity, coarse grain size, and dissolved oxygen as the environmental variables explaining the macroinvertebrate community structure variation among the lagoons. Understanding the drives and dynamics which guide the macroinvertebrates communities' turnover in coastal lagoons is a relevant tool to subsidize environmental management decisions due to the increasing threats around the park.

Urbanisation gradients, riparian-loss and contaminant effects on macroinvertebrate distribution within a tropical river (Nigeria)

ABSTRACT Riparian vegetation and built-up density along the urbanised section of the Calabar river were estimated using NDVI (Normalised Differential Vegetation Index) and NDBI (normalised differential built-up index), respectively. Four sampling stations representing riparian density and built-up gradients i.e. Station 1 (sparse riparian + high-density built-up), 2 (sparse riparian + high to intermediate-density built-up), 3 (moderate riparian + intermediate to low-density built-up) and station 4 (moderate riparian + low-density built-up) were selected. Station-specific variations of metal (Pb, Cd, Cr, Fe and Cu) in surface water and benthic macro-invertebrate communities were examined between January and December 2013 and correlated using redundancy analysis (RDA). Buffer analysis revealed that stations having low NDBI with over 120 m dense riparian areas showed a marked abundance of muddy/coarse substrate while sparse riparian areas showed siltier and sandier substrate. Redundancy analysis revealed a marked delineation of macroinvertebrate occurrence with the riparian density of stations. High diversity macroinvertebrate assemblages showed a strong positive association with alkaline pH, the density of riparian vegetation and substrate type. This first report highlights the critical relationship between riparian density, water quality and benthic macroinvertebrates in a tropical river.

Benthic Macroinvertebrates of Five Small Lakes in Ciliwung Watershed and Estuary, Indonesia

Small lakes are biodiversity hotspots of freshwater ecosystems, home for fauna including benthic macroinvertebrates fauna which play vital roles as it supports food sources for higher-level organisms such as fishes. This research aims to investigate the composition of benthic macroinvertebrates community in some small lakes located in the Ciliwung watershed that surrounds Bogor, Depok, and Jakarta. Samples were undertaken on April and June 2021 from four small lakes located at the Ciliwung watershed. They are Telaga Warna, Situ Cikaret, Cincin urban lake, and Sunter urban lake. Also includes an estuary urban lake ecosystem, Angke lake. A total of 22 taxa were found, which consist of Mollusks (55.44%), Insects (6.27%), and Annelids (38.29%). Mollusk was composed of six families of Gastropods and one family of Bivalves. Meanwhile, the family of Diptera was the only Insect group. The abundance ranges between 101-4471 Ind/m2. The pattern shows that Gastropods were the predominant group in the downstream area meanwhile Annelids were the most abundant groups in the upstream, middle, and estuary areas.

Contribution of sediment contamination to multi-stress in lowland waters

Water bodies in densely populated lowland areas are often impacted by multiple stressors. At these multi-stressed sites, it remains challenging to quantify the contribution of contaminated sediments. This study, therefore, aimed to elucidate the contribution of sediment contamination in 16 multi-stressed drainage ditches throughout the Netherlands. To this end an adjusted TRIAD framework was applied, where 1) contaminants and other variables in the sediment and the overlying water were measured, 2) whole-sediment laboratory bioassays were performed using larvae of the non-biting midge Chironomus riparius, and 3) the in situ benthic macroinvertebrate community composition was determined. It was hypothesized that the benthic macroinvertebrate community composition would respond to all jointly present stressors in both water and sediment, whereas the whole-sediment bioassays would only respond to the stressors present in the sediment. The benthic macroinvertebrate community composition was indeed related to multiple stressors in both water and sediment. Taxa richness was positively correlated with the presence of PO4-P in the water, macrophyte cover and some pesticides. Evenness, the number of Trichoptera families and the SPEARpesticides were positively correlated to the C:P ratios in the sediment, whilst negative correlations were observed with various contaminants in both the water and sediment. The whole-sediment bioassays with C. riparius positively related to the nutrient content of the sediment, whereas no negative relations to the sediment-associated contaminants were observed, even though the lowered SPEARpesticides index indicated contaminant effects in the field. Therefore, it was concluded that sediment contamination was identified as one of the various stressors that potentially drove the benthic macroinvertebrate community composition in the multi-stressed drainage ditches, but that nutrients may have masked the adverse effects caused by low and diverse sediment contaminants on C. riparius in the bioassays.

Diversity and distribution of benthic invertebrates dwelling rivers of the Kruger National Park, South Africa

Meiobenthos (or meiofauna) are microscopic invertebrates that inhabit biofilms and interstitial spaces in rivers. They are diverse and extremely abundant, and they perform essential ecological functions by linking microbial production to higher trophic levels (e.g. macrobenthic invertebrates and fishes). However, meiobenthic communities remain poorly studied in Africa. Here, we sampled meio- and macrobenthic invertebrate communities associated with biofilms and sediments across an upstream–downstream gradient along the Olifants, Sabie and Crocodile rivers flowing through the Kruger National Park (KNP). We expected to link differences in community structure to environmental gradients as those rivers show different degrees of anthropogenic stress as they enter the park. Both meio- and macrobenthic communities differed across rivers and also structured along an upstream–downstream gradient. The upstream sites, which were the closest to the park borders, consistently showed a lower diversity in all three rivers. There, the invasive snail Tarebia granifera strongly dominated (making up 73% – 87% of the macrobenthos), crowding hard substrates, while concomitantly the abundances of biofilm-dwelling meiobenthos like nematodes and rotifers were substantially reduced. Nevertheless, the diversity and evenness of communities then tended to increase as water flowed downstream through the park, suggesting a beneficial effect of protected river reaches on benthic invertebrate diversity. However, for the Crocodile River, which makes up the southern border of the park, this trend was less conspicuous, suggesting that this river may experience the greatest threats. More generally, benthic invertebrate communities were driven by the concentrations of phosphates, sulphates, ammonium and organic matter and by substrate characteristics.Conservation implications: Meiobenthic organisms are very abundant in KNP rivers and react to environmental gradients; thus, they should be more considered for bio-monitoring or conservation of comprehensive assemblages of animals. Interestingly, protected reaches tended to show a reduced dominance of the invasive T. granifera and a higher diversity of benthic invertebrates.

Evaluating the biological validity of European river typology systems with least disturbed benthic macroinvertebrate communities

Humans have severely altered freshwater ecosystems globally, causing a loss of biodiversity. Regulatory frameworks, like the Water Framework Directive, have been developed to support actions that halt and reverse this loss. These frameworks use typology systems that summarize freshwater ecosystems into environmentally delineated types. Within types, ecosystems that are minimally impacted by human activities, i.e., in reference conditions, are expected to be similar concerning physical, chemical, and biological characteristics. This assumption is critical when water quality assessments rely on comparisons to type-specific reference conditions. Lyche Solheim et al. (2019) developed a pan-European river typology system, the Broad River Types, that unifies the national Water Framework Directive typology systems and is gaining traction within the research community. However, it is unknown how similar biological communities are within these individual Broad River Types. We used analysis of similarities and classification strength analysis to examine if the Broad River Types delineate distinct macroinvertebrate communities across Europe and whether they outperform two ecoregional approaches: the European Biogeographical Regions and Illies' Freshwater Ecoregions. We determined indicator and typical taxa for the types of all three typology systems and evaluated their distinctiveness. All three typology systems captured more variation in macroinvertebrate communities than random combinations of sites. The results were similar among typology systems, but the Broad River Types always performed worse than either the Biogeographic Regions or Illies' Freshwater Ecoregions. Despite reaching statistical significance, the statistics of analysis of similarity and classification strength were low in all tests indicating substantial overlap among the macroinvertebrate communities of different types. We conclude that the Broad River Types do not represent an improvement upon existing freshwater typologies when used to delineate macroinvertebrate communities and we propose future avenues for advancement: regionally constrained types, better recognition of intermittent rivers, and consideration of biotic communities.

Effects on macroinvertebrate communities a year after the rehabilitation of an urban river (Tinto River, Portugal)

The Tinto River is a small urban watercourse in the Douro River basin (Portugal) that has been subject to various types of environmental disturbances over the years, which has led to severe degradation of its ecological status. Between 2013 and 2017, several studies were carried out to characterize and monitor some environmental parameters and to identify sources of environmental disturbances. From these studies, a set of actions and projects were undertaken in 2017–2019 to mitigate some of the environmental problems and to rehabilitate the river and its riverside areas. Here, we compare some parameters related to the river’s ecological state (naturalness of the channel and banks, physicochemical conditions and benthic macroinvertebrate community) before the interventions and one year after the interventions at Tinto River. Conductivity, oxygen concentration and biotic indices improved after one year, especially during the adverse hydrological conditions brought on by a very dry summer and autumn with some flood episodes.

Biodiversity and Litter Breakdown in a Karstic Freshwater System (Doberdò Lake, Northeast Italy) in Relation to Water Level Fluctuations and Environmental Features

The present study reports seasonal data about chemico-physical trends, macrobenthic invertebrates, and Phragmites australis decomposition rates within a karstic freshwater system in the western classic Karst. Results presented herein were compared with those obtained from the same system five years ago. Chemico-physical data showed higher temperatures and lower levels of pH and conductivity than in the past. The macrobenthic invertebrate community varied through the seasons and through the years, though they are dominated by few taxa, such as Asellus and Gammarus. These shredders were the most abundant functional feeding guild, playing a pivotal role in the decomposition of the vegetal organic matter. Decomposition rates k ranged between 0.009 and 0.016 days−1 and varied seasonally. k values were different from those previously reported for the investigated system. Differences are mainly due to changes in water supply, depending on decreasing rainfall regimes and hydrometric levels of the Soča River, which showed lower levels than in the previous study. Changes in water supply altered the fluctuating pulse that is typical of ephemeral karstic lakes, changing the system dynamics. Potential effects of climate change on local scale are also discussed.

The Relationship between Benthic Macroinvertebrate Assemblages and Water Quality Parameters in the Sanyati Basin, Lake Kariba, Zimbabwe.

Biological monitoring of reservoirs is important in assessing aquatic health. This study aimed at assessing the structure of benthic macroinvertebrate communities in relation to physicochemical parameters along Sanyati basin shoreline in Lake Kariba, Zimbabwe. Six sites (S1 to S6) characterized by various human disturbances were sampled for physicochemical parameters and benthic macroinvertebrates from January to March 2018. We computed macroinvertebrate metrics and classified them into functional feeding groups (FFGs). A canonical correspondence analysis (CCA) triplot was constructed to assess species-physicochemical relations. Significant differences across the sampling sites were observed for pH, electrical conductivity, turbidity, nitrate-nitrogen (NO3-N), ammonium nitrogen (NH4-N), total nitrogen (TN), phosphate-phosphorus (PO4-P), total phosphates (TP), and dissolved oxygen (DO). The results from CCA highlighted that S1 was generally associated with high pH, NH4-N, and TN, and Oligochaeta, Syrphidae, and Hydrophilidae families. The highest percentage of EPT taxa (39.83%) was recorded at S6, while the lowest was recorded at S1. The taxa were made up of 50% predators, 26% collector-gatherers, 6% scrappers, 6% shredders, and 3% collector-filters with 3 taxa (Chironomidae, Hydropsychidae, and Leptoceridae) having more than two FFGs. Site S1 had a significantly higher mean abundance of collector-gatherers than the other sites. A high correlation between water parameters and SASS and ASPT scores was observed indicating their ability to detect environmental changes. These findings suggest that macroinvertebrate communities are good candidates for delineating the effects of industrial pollution on water quality.

Community Structure of Benthic Macrofauna and the Ecological Quality of Mangrove Wetlands in Hainan, China

Few studies have systematically assessed the ecological status of mangrove wetlands following the stress of anthropogenic activities in China. This study investigated the spatial and seasonal distribution of benthic macroinvertebrate communities and assessed the ecological quality of mangrove habitats on an island scale in Hainan, China (containing the third largest mangrove area of China and the highest mangrove species richness). For the benthic macrofauna community structure, a total of 102 macrobenthic taxa belonging to 50 families were identified, with Crustaceans, Molluscs, Polychaetes, and Oligochaeta having relative abundances of 52.3%, 36.1%, 10.8%, and 0.8%, respectively. Decapoda and Gastropoda dominated the benthic community abundance. Non-metric multidimensional scaling and an analysis of similarities revealed significantly different macroinvertebrate assemblages among the regions during the two seasons. The South mangroves had the lowest macrofauna species numbers, biodiversity, richness, and abundance. The macrofaunal species richness, Shannon index, Margalef index, abundance, and biomass markedly affected by region and season. As indicated by the biotic indices AMBI (AZTI’s Marine Biotic Index) and M-AMBI, more than half of the mangrove habitats on Hainan Island were slightly to heavily disturbed and had poor to moderate ecological quality. Our results recommend long-term monitoring for evaluating the quality status of mangrove wetlands and avoiding extensive land-use conversion of mangroves. Holistic approaches considering ecological characteristics and combining information on both floral and faunal functionality would contribute to the effective management and conservation of mangroves in disturbed areas.

Multivariate approaches to assess the drivers of benthic macroinvertebrate communities and biotic indices in a highly urbanized fluvial-estuarine system

Urban estuaries are amongst the most severely altered systems worldwide and undergo a wide range of ecological crises such as habitat destruction, nutrient enrichment and hydrodynamic alterations, resulting in an irreversible loss of biodiversity as well as a further environmental deterioration. Differentiating the main driving forces of multiple stressors is of utmost importance to provide beneficial insights for environmental restoration and management. In the present study, comprehensive investigations and multivariate approaches were performed to reveal the spatio-temporal variations of benthic macroinvertebrate communities and biotic indices and to examine their responses to environmental alterations within a highly urbanized fluvial-estuarine system. The nutrient levels gradually dwindled from urban fluvial sections to estuarine sections, meanwhile, macroinvertebrate community composition and dominant species considerably varied along the estuarine gradient. Overall, environmental parameters, macroinvertebrate communities and biotic indices varied significantly among sections and seasons. Salinity, dissolved oxygen, ammonia, total nitrogen, chemical oxygen demand and total organic carbon significantly explained the spatio-temporal variations of macroinvertebrate communities and biotic indices. Despite some inconsistencies in assessment outcomes, all indices revealed that urban fluvial sections of the Pearl River Estuary were disturbed, more or less severe depending upon the index. Among the tested indices, AMBI, BENTIX and average taxonomic distinctness (Δ+) presented better performance in assessing the ecological quality status and showed high responses to environmental stresses. More importantly, the relative contribution of water parameters vastly overrode sediment parameters in shaping variations of macroinvertebrate communities and biotic indices, demonstrating that anthropogenic activities (e.g., discharge of municipal and industrial sewage) directly altered the benthic community composition and diversity.

Taxon and trait-based sampling curves can be used as a tool for assessing impairment in salinized headwater streams

Many ecosystems are losing biodiversity, raising concern for the services they provide. However, the extent of loss is uncertain, especially for diverse insects, because of incomplete sampling. Modeling techniques for estimating upper bounds on diversity are needed to assess benthic freshwater insect abundances, taxa richness, and diversity because some species are declining at alarming rates while others are increasing. In central Appalachian streams of the U.S.A., aquatic insect communities have lost diversity following salinization caused by mining activities. However, the number of taxa observed are dependent upon sampling effort. Incomplete sampling could misrepresent biodiversity and functional losses. Our goal was to use taxon sampling curves to estimate sampling effort required to maximize the probability of accurate benthic macroinvertebrate characterization in dominant riffle habitats of headwater streams. We collected 5 to 10 quantitative benthic macroinvertebrate samples in each of six, first-order streams in the central Appalachian region. For our single-habitat, mesoscale approach, we predicted: (1) macroinvertebrate taxa richness would be the most robust indicator of salinization response compared to diversity, evenness, and density, (2) less sampling effort would be needed to capture taxonomic richness in salinized streams compared to reference streams, and (3) response diversity would also be lower in salinized streams because select trait states would be represented by fewer taxa. Results suggested nominally lower taxa richness, evenness, and diversity in some salinized streams but not in all despite greater or more variable within-stream densities. Nonetheless, sampling effort required to characterize macroinvertebrate communities did not differ between reference and salinized streams, though uneven within-stream taxa distributions corresponded with greater sampling effort requirements for complete characterization. Benthic macroinvertebrate community characteristics were different where higher densities and richness of small-bodied and fast-developing taxa were more common in salinized streams. Response diversity depended on trait states. For example, only about five shredder taxa were represented in salinized streams compared to eight taxa in reference streams. Despite some indication of lower response diversity across some functional feeding groups, more than five samples were needed for robust comparisons. Taxon and trait-based sampling curves suggest that greater overall sampling effort is needed and equal samples per stream was critical for complete diversity assessments regardless of the level of mining-induced salinization. Model-based sampling curves can serve as a tool to assess upper bounds on diversity metrics and sample-effort rigor.