Lotic dispersal of lentic macroinvertebrates

Little is known on dispersal of lentic macroinvertebrates. We quantified dispersal of lentic macroinvertebrates through pond connections in a highly connected pond system, and investigated how dispersal rates were affected by connection properties and time of the day (day, night). Furthermore, by comparing the composition of assemblages of dispersing macroinvertebrates with the macroinvertebrate assemblages of source ponds, we tested whether dispersal was neutral or a taxon-specific process. We found that many taxa dispersed through the pond connections. Taxa richness of the dispersing macroinvertebrate assemblage was proportional to taxa richness in the source ponds. The number of individuals that dispersed, however, was not related to source pond densities, possibly because of the highly patchy distribution of lentic macroinvertebrates within ponds. Elevated dispersal rates were recorded for Baetidae, Chironomidae and Physidae, indicating a taxon-specific use of pond connections as dispersal pathway. None of the physical properties of the connections affected dispersal. Macroinvertebrates dispersed more during the night than during daytime. Of seven tested families, Chaoboridae and Chironomidae showed higher dispersal during the night, probably resulting from diel vertical migration, since pond connections mainly transported near-surface water. Flying and non-flying invertebrates dispersed equally frequent through pond connections. For non-flying invertebrates that disperse infrequently over land, dispersal through pond connections may provide an important additional means of dispersal.     

Spatio-temporal nested patterns in macroinvertebrate assemblages across a pond network with a wide hydroperiod range

Nestedness has been widely used to measure the structure of biological communities and occurs when species-poor sites contain subsets of species-rich ones. Here, we examine nested patterns across the macroinvertebrate assemblages of 91 ponds in Doñana National Park, Spain, and explore temporal variation of nestedness and species richness in 19 temporary ponds over 2 years with differing rainfall. Macroinvertebrate assemblages were significantly nested; both pond spatial arrangement and environmental variation being important in driving nested patterns. Despite the nested structure observed, a number of taxa and ponds deviate from this pattern (termed idiosyncratic), by occurring more frequently than expected in species-poor sites, or having assemblages dominated by species largely absent from species-rich sites. Aquatic adults of winged insects, capable of dispersal, were more highly nested than non-dispersing taxa and life-history stages. Idiosyncratic taxa were found in ponds spanning a wide range of hydroperiods, although nestedness was higher in more permanent waterbodies. Monthly sampling demonstrated a gradual increase of species richness and nestedness from pond filling to April–May, when the most temporary ponds started to dry. Although the degree of nestedness of individual pond assemblages varied from month to month, the overall degree of nestedness in the two study years was practically identical despite marked differences in hydroperiod. Our results suggest that differential colonization and environmental variation are key processes driving the nested structure of Doñana ponds, that macroinvertebrate assemblages change in a predictable manner each year in response to cycles of pond wetting and drying, and that connectivity and environmental variability maintain biodiversity in pond networks.     

Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.     

Are distribution patterns linked to dispersal mechanism? An investigation using pond invertebrate assemblages

1. Dispersal ability influences the distribution and abundance of organisms, but empirical investigations of the relationship between dispersal ability and the composition of ecological assemblages are scarce. Here, we compare between-site variation in the species richness and community composition of actively and passively dispersing pond invertebrates.
2. Coleoptera (active dispersers) and microcrustacea (passive dispersers) were sampled over a season from 16 ponds within a 4-km radius in south-west England. Species richness and community composition were related to environmental variables using regression and Canonical Correspondence Analysis (CCA), respectively.
3. Coleopteran species richness was significantly and positively correlated with pond permanence and maximum area, whereas microcrustacean species richness was relatively equal across sites and did not correlate with environmental variables. The frequency of species' occurrence between sites was the same for both groups, which suggests that active and passive dispersers exhibited the same degree of dispersal.
4. Between-site variation in community composition was non-random for both groups, with pond permanence and area, together, explaining similar proportions of between-site variation for Coleoptera. Permanence was correlated most strongly with microcrustacean community composition and a high proportion (25%) of microcrustacean species were more numerous in smaller, more ephemeral ponds.
5. These data suggest that, at small spatial scales, Coleoptera which can undertake multiple dispersal events, are more likely to colonise large, more permanent ponds than passively dispersing microcrustacea. For microcrustacea, other traits (in this case those permitting existence in ephemeral habitats) may over-ride the influences of dispersal in driving between-site variation in species composition.     

Determinant landscape‐scale factors on pond odonate assemblages

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Macroinvertebrate communities in Phragmites australis (Cav.) Trin. ex Steud. reed beds and open bank habitats in central victorian streams in Australia

Reed invasion is a common phenomenon of open streams with disturbed riparian vegetation in river catchments. Knowledge of the effects of such vegetation change on aquatic communities is fundamental to river management. Macroinvertebrate fauna in Phragmites australis (Cav.) Trin. ex Steud. and open bank habitats were examined in three rivers in central Victoria in order to understand the effect of such littoral habitat on macroinvertebrates. Data were analysed using Partially Nested Factorial ANOVA with season, river and habitats as main effects. Habitat structure had a significant effect (p<0.05) on macroinvertebrate species richness, however this was not seasonally consistent across the three rivers. There was a significant increase (p<0.05) in macroinvertebrate taxa richness in Phragmites habitats during winter and spring seasons. Total abundance of taxa showed no consistent significant differences in the two habitats. Results of Canonical Analysis of Principle Coordinates indicated significant differences (p<0.05) in macroinvertebrate assemblages between Phragmites and bare bank habitats in all seasons. Habitat selection by taxa could be related to the microphysical environment of the habitats. This study suggests that reed beds create important littoral habitat structures which support diverse macroinvertebrate assemblages.     

Newly created ponds complement natural waterbodies for restoration of macroinvertebrate assemblages

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Benthic macroinvertebrate biodiversity improved with irrigation ponds linked to a rice paddy field

Traditionally, many irrigation ponds supplied water to paddy fields, but most of these ponds have disappeared through improvements in irrigation systems. The aim of this study was to assess the ecological functions (especially biodiversity conservation) of irrigation ponds by using benthic macroinvertebrates that inhabit paddy fields. This study was conducted in Hwaseong‐si, Yesan‐gun, Hongseong‐gun, Uljin‐gun and Damyang‐gun, Korea. Benthic macroinvertebrates were collected using a quadrat sampler from August to September for three years (2010–2012) in paddy fields with and without an irrigation pond. In the comparisons between two paddy field types (paddy fields with and without an irrigation pond) for species richness and densities of benthic macroinvertebrates, the species richness and densities were higher in the paddy fields with a pond than in the paddy fields without a pond (P < 0.001). Biodiversity enhancement effect degree (BEED) of the irrigation pond showed positive values in all survey regions. There were no significant differences among the survey regions. BEED showed positive values in all taxonomic groups (excluding Crustacea) and were not significantly different among taxonomic groups. The BEED values for non‐insects, passive dispersers, were relatively higher than for insects, active dispersers. The results indicate that BEED is related to the dispersal abilities of each taxonomic group and an irrigation pond increases biodiversity in a paddy field in all regions. Therefore, the irrigation pond is one method that can be immediately applied in paddy fields in order to improve the biodiversity of agricultural ecosystems.     

Biological traits of European pond macroinvertebrates

Whilst biological traits of river macroinvertebrates show unimodal responses to geographic changes in habitat conditions in Europe, we still do not know whether spatial turnover of species result in distinct combinations of biological traits for pond macroinvertebrates. Here, we used data on the occurrence of 204 macroinvertebrate taxa in 120 ponds from four biogeographic regions of Europe, to compare their biological traits. The Mediterranean, Atlantic, Alpine, and Continental regions have specific climate, vegetation and geology. Only two taxa were exclusively found in the Alpine and Continental regions, while 28 and 34 taxa were exclusively recorded in the Atlantic and Mediterranean regions, respectively. Invertebrates in the Mediterranean region allocated much energy to reproduction and resistance forms. Most Mediterranean invertebrate species had narrow thermal ranges. In Continental areas, invertebrates allocated lesser energy to reproduction and dispersal, and organisms were short lived with high diversity of feeding groups. These characteristics suggest higher resilience. The main difference between ponds in the Alpine and Atlantic regions was their elevation. Alpine conditions necessitate specific adaptations related to rapid temperature fluctuations, and low nutrient concentrations. Even if our samples did not cover the full range of pond conditions across Europe, our analyses suggest that changes in community composition have important impacts on pond ecosystem functions. Consistent information on a larger set of ponds across Europe would be much needed, but their low accessibility (unpublished data and/or not disclosed by authors) remains problematic. There is still, therefore, a pressing need for the incorporation of high quality data sets into a standardized database so that they can be further analyzed in an integrated European-wide manner.     

Environmental factors accounting for benthic macroinvertebrate assemblage structure at the sample scale in streams subjected to a gradient of cattle grazing

Macroinvertebrate assemblages were related to environmental factors that were quantified at the sample scale in streams subjected to a gradient of cattle grazing. Environmental factors and macroinvertebrates were concurrently collected so assemblage structure could be directly related to environmental factors and the relative importance of stressors associated with cattle grazing in structuring assemblages could be assessed. Based on multivariate and inferential statistics, measures of physical habitat (% fines and substrate homogeneity) had the strongest relationships with macroinvertebrate assemblage structure. Detrital food variables (coarse benthic and fine benthic organic matter) were also associated with assemblage structure, but the relationships were never as strong as those with physical habitat measures, while autochthonous food variables (chlorophyll a and epilithic biomass) appeared to have no association with assemblage structure. The amount of variation explained in taxa composition and macroinvertebrate metrics is within values reported from studies that have examined macroinvertebrate metric–sediment relationships. The % Coleoptera and % crawlers had consistent relationships with % fines during this study, which suggests they may be useful metrics when sediment is a suspected stressor to macroinvertebrate assemblages in Blue Ridge streams. Findings from this study also demonstrate the importance of quantitative sampling through time when research goals are to identify relationships between macroinvertebrates and environmental factors.     

Strong spatial influence on colonization rates in a pioneer zooplankton metacommunity

The magnitude of community-wide dispersal is central to metacommunity models, yet dispersal is notoriously difficult to quantify in passive and cryptic dispersers such as many freshwater invertebrates. By overcoming the problem of quantifying dispersal rates, colonization rates into new habitats can provide a useful estimate of the magnitude of effective dispersal. Here we study the influence of spatial and local processes on colonization rates into new ponds that indicate differential dispersal limitation of major zooplankton taxa, with important implications for metacommunity dynamics. We identify regional and local factors that affect zooplankton colonization rates and spatial patterns in a large-scale experimental system. Our study differs from others in the unique setup of the experimental pond area by which we were able to test spatial and environmental variables at a large spatial scale. We quantified colonization rates separately for the Copepoda, Cladocera and Rotifera from samples collected over a period of 21 months in 48 newly constructed temporary ponds of 0.18–2.95 ha distributed in a restored wetland area of 2,700 ha in Doñana National Park, Southern Spain. Species richness upon initial sampling of new ponds was about one third of that in reference ponds, although the rate of detection of new species from thereon were not significantly different, probably owing to high turnover in the dynamic, temporary reference ponds. Environmental heterogeneity had no detectable effect on colonization rates in new ponds. In contrast, connectivity, space (based on latitude and longitude) and surface area were key determinants of colonization rates for copepods and cladocerans. This suggests dispersal limitation in cladocerans and copepods, but not in rotifers, possibly due to differences in propagule size and abundance.     

Relating macroinvertebrate community structure to environmental characteristics and sediment contamination at the scale of the St. Lawrence River

There is still no assessment of the impact of sediment chemicals and environmental conditions on macroinvertebrates at the scale of the St. Lawrence River. In order to assess these impacts in the fluvial section of the St. Lawrence River including the Montreal harbour, the community structure of macroinvertebrates using different taxonomic aggregations (genus and family) and taxa attributes (abundance, presence–absence, indicator taxa) was assessed. The goal of the study was to determine the indicator taxa of macroinvertebrates along the fluvial continuum and relate changes in macroinvertebrate community to sediment chemical conditions and environmental characteristics of habitats using variance partitioning. This study also evaluated which taxonomic level and taxa attributes of macroinvertebrates were the most suitable for bioassessment of quality of sediments and habitat environment in the St. Lawrence River. Four different macroinvertebrate assemblages were found distributed along the fluvial continuum using either abundance or presence–absence data and genus or family levels. Indicator taxa characteristic of the different macroinvertebrate communities were associated with the sediment contamination gradient. However, habitat environmental characteristics (water masses, sulphur and DOC in sediments) had more influence on macroinvertebrate assemblages than sediment contamination. Our study confirms that family level analysis can give information comparable to the genus level analysis using presence–absence or abundance of macroinvertebrates, yet a higher number of indicator taxa were detected at the genus level.     

Local and landscape scale determinants of macroinvertebrate assemblages and their conservation value in ponds across an urban land-use gradient

Urbanisation represents a growing threat to natural communities across the globe. Small aquatic habitats such as ponds are especially vulnerable and are often poorly protected by legislation. Many ponds are threatened by development and pollution from the surrounding landscape, yet their biodiversity and conservation value remain poorly described. Here we report the results of a survey of 30 ponds along an urban land-use gradient in the West Midlands, UK. We outline the environmental conditions of these urban ponds to identify which local and landscape scale environmental variables determine the biodiversity and conservation value of the macroinvertebrate assemblages in the ponds. Cluster analysis identified four groups of ponds with contrasting macroinvertebrate assemblages reflecting differences in macrophyte cover, nutrient status, riparian shading, the nature of the pond edge, surrounding land-use and the availability of other wetland habitats. Pond conservation status varied markedly across the sites. The richest macroinvertebrate assemblages with high conservation value were found in ponds with complex macrophyte stands and floating vegetation with low nutrient concentrations and little surrounding urban land. The most impoverished assemblages were found in highly urban ponds with hard-engineered edges, heavy shading and nutrient rich waters. A random forest classification model revealed that local factors usually had primacy over landscape scale factors in determining pond conservation value, and constitute a priority focus for management.     

流溪河大型底栖动物群落的时空分布及其影响因子

流溪河位于我国热带与亚热带过渡区,其底栖动物种类丰富,群落的物种组成结构具有明显的区域性,掌握该地区的物种组成特征及与环境要素的关系是建立生态监测与评估方法的基础。于2018年的枯水期（3月、12月）和丰水期（6月、9月）,自流溪河上游至下游共计20个段面对底栖动物进行了定量采样,同时测定了相应的环境因子,采用多元统计方法对流溪河水环境与群落结构及其相关关系进行了分析。共检出底栖动物76个分类单元,隶属于7纲20目50科,其中水生昆虫相对丰度最高,占69.39%。在4个优势分类单元中,摇蚊族（Chironomini）相对丰度为20.19%,河蚬（Corbicula fluminea）、短沟蜷属的一种（Semisulcospira sp.1）、双突细蜉（Caenis bicornis）,相对丰度在7%-9%之间。底栖动物丰度和种类多样性均与浊度呈显著负相关;枯水期底栖动物丰度与总磷呈显著负相关,丰水期则呈显著正相关。在丰水期,不同河流级别上底栖动物群落具有明显的差异,表现较强的分布格局,而在枯水期这种分布格局不明显。典范对应分析（CCA）表明,在丰水期,影响或解释流溪河底栖动物群落变化的主要因子为pH、溶解氧、水温、电导率和硅酸盐,而在枯水期则为pH和硝态氮。受电站与采沙的影响,部分河段发生非自然断流和底质的显著改变,导致底质与水深等数据的异常变化,反映了人类活动对该河流生境与环境的重要影响。     

Inter- and intra-annual variations of macroinvertebrate assemblages are related to the hydroperiod in Mediterranean temporary ponds

Macroinvertebrate assemblages of 22 temporary ponds with different hydroperiod were sampled monthly during a dry year (2005–2006) and a wet year (2006–2007). Coleopteran and Heteropteran adults were most abundant at the end of the hydroperiod, while Coleopteran larvae, mainly Dytiscidae, were mostly recorded in spring. Macroinvertebrate assemblages differed between study years. The shorter hydroperiod of ponds in the dry year constrained the length of the aquatic period for macroinvertebrates, and three distinct wet phases of community composition could be distinguished: filling phase, aquatic phase and drying phase. In the wet year, with a longer pond hydroperiod, five phases could be identified, with the aquatic phase differentiated into winter, early spring and late spring phases. Dispersers such as Anisops sardeus, Berosus guttalis or Anacaena lutescens were typical during the filling phase and Corixa affinis or Enochrus fuscipennis during the drying phase. The ponds with intermediate hydroperiod showed a similar composition (mainly dispersers) at the beginning and end of their wet period; this is not being seen in early drying or long hydroperiod ponds. A general pattern was detected, with similar variation between both years, which may be associated with the life histories of the macroinvertebrate taxa recorded. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Inter-annual patterns in macroinvertebrate communities of wilderness streams in Idaho, U.S.A.

This study examined the inter-annual variation in macroinvertebrate assemblages in six wilderness streams in central Idaho over a 6-year period (1990–1995). Benthic macroinvertebrates and associated environmental correlates were sampled during baseflow each summer. Little environmental change, as assessed using coefficients of variation (CVs) for substrate size and embeddedness, width, depth and periphyton standing crops, occurred in the streams over the period of study. There was also little temporal change in macroinvertebrate assemblages based on the relative abundance of the 10 most abundant taxa, all shredder taxa and all plecopteran taxa. CVs for individual taxa were substantially greater than those of most community measures, with rare taxa contributing 30–50% of the variation for any one stream. Frequency distributions for taxa CVs excluding rare taxa were more normally distributed. Differences in assemblage structure among streams were attributed to stream size (shift in shredder assemblages) and temperature (shift in plecopteran taxa). These data indicate a long-term (multi-year) persistence in the macroinvertebrate composition of these pristine streams, thus supporting the premise that such streams are excellent references for use in long-term biomonitoring programs.     

Macroinvertebrate communities of mediterranean ponds (North Iberian Plateau): importance of natural and human-induced variability

1. The effects of natural and human‐induced variability on the composition of macroinvertebrate communities of 28 ponds located in the North Iberian Plateau (Spain) were studied to determine the best predictors of community structure. 2. Constrained ordination was used to identify the main factors explaining the among‐pond variance in abundance (as catch per unit effort) of total macroinvertebrate and Chironomidae assemblages and trophic structure (functional feeding groups). 3. Variance partitioning showed that human disturbance (represented by a pond condition index, total phosphorus concentration and pesticides) was the best predictor of macroinvertebrate community structure, whereas factors, such as habitat and biotic variables were of secondary importance. Factors controlling the chironomid community were broadly similar to those acting on the whole community of macroinvertebrates. In contrast, trophic structure was mainly determined by habitat and biotic variables. 4. Our results show that macroinvertebrates may be used as effective indicators of the ecological status of Mediterranean ponds. The Chironomidae deserve special attention because they were the dominant group in the study ponds and the strongest explanatory variable for their distribution was degradation.     

Freshwater diatom and macroinvertebrate diversity of coastal permanent ponds along a gradient of human impact in a Mediterranean eco-region

Mediterranean coastal areas are characterised by heavily transformed landscapes and an ever-increasing number of ponds are subjected to strong alterations. Although benthic diatoms and macroinvertebrates are widely used as indicators in freshwater ecosystems, little is still known about the diatom communities of lowland freshwater ponds in the Mediterranean region, and, furthermore, there are few macroinvertebrate-based methods to assess their ecological quality, especially in Italy. This article undertakes an analysis of benthic diatom and macroinvertebrate communities of permanent freshwater ponds, selected along a gradient of anthropogenic pressures, to identify community indicators (taxa and/or metrics) useful to evaluate the effect of human impacts. A series of 21 ponds were sampled along Tyrrhenian coast in central Italy. Five of these ponds, in a good conservations status and surrounded by woodland were selected as ‘reference sites’ for macroinvertebrates and epipelic diatoms. The remaining sixteen ponds were located in an agricultural landscape subject to different levels of human impact. The total number of macroinvertebrate taxa found in each pond was significantly higher in reference sites than in both the intermediate and heavily degraded ones, whereas the diatom species richness did not result in a good community variable to evaluate the pond ecological quality. The analysis revealed a substantial difference among the compositions of diatom communities between reference ponds and degraded ponds. The former were characterised by the presence of several species belonging to genera, such as Pinnularia sp., Eunotia sp., Stauroneis sp., Neidium sp., all of which were mostly absent from degraded ponds. Furthermore, the taxonomic richnesses of some macroinvetebrate groups (Odonata, Ephemeroptera, Trichoptera, Coleoptera), and taxa composition attributes of macroinvertebrate communities (total abundance, percentages of top three dominant taxa, percentages of Pleidae, Ancylidae, Hirudinea, Hydracarina) significantly correlated with variables linked with anthropogenic pressures. The results of the investigation suggested that diatoms tended more to reflect water chemistry through changes in community structure, whereas invertebrates responded to physical habitat changes primarily through changes in taxonomic richness. The methodologies developed for the analysis of freshwater benthic diatom and macroinvertebrate communities may have a considerable potential as a tool for assessing the ecological status of this type of water body, complying with the European Union Water Framework Directive 2000/60/EC. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Distribution of selected macroinvertebrates in a mosaic of temporary and permanent freshwater ponds as explained by autologistic models

We investigated the aquatic macroinvertebrate fauna of 76 ponds and small pools in an urban fringe landscape, and related the presence of ten species to measures of water permanence, pond area and environmental conditions using logistic models. The incidence of all the species was strongly associated with variation in hydroperiod, but patterns were more variable with the other explanatory variables. To determine whether the presence of a species at neighbouring ponds increased its probability of occurance at a pond we constructed a series of autologistic models, that differed from the aspatial logistic model in that they included a spatial autocovariate in the predictor terms. The improvement of model fit on inclusion of this autocovariate, measured as the decline in deviance compared to the aspatial models, was determined across a range of lag distances. In seven of the ten species, the autologistic models explained the incidence of the species amongst the ponds better than the aspatial models. Spatial effects were typically over short distances (<200 m) before declining, but in two species appeared to reach an asymptote, and we propose that variation in dispersal ability is the most likely factor producing these spatial effects. We conclude that it is essential that some measure of spatial autocorrelation is considered when evaluating the distribution of aquatic macroinvertebrates at small or medium scales.     

Seasonal shifts in the assembly dynamics of benthic macroinvertebrate and diatom communities in a subtropical river

Identifying seasonal shifts in community assembly for multiple biological groups is important to help enhance our understanding of their ecological dynamics. However, such knowledge on lotic assemblages is still limited. In this study, we used biological traits and functional diversity indices in association with null model analyses to detect seasonal shifts in the community assembly mechanisms of lotic macroinvertebrates and diatoms in an unregulated subtropical river in China. We found that functional composition and functional diversity (FRic, FEve, FDis, MNN, and SDNN) showed seasonal variation for macroinvertebrate and diatom assemblages. Null models suggested that environmental filtering, competitive exclusion, and neutral process were all important community assembly mechanisms for both biological groups. However, environmental filtering had a stronger effect on spring macroinvertebrate assemblages than autumn assemblages, but the effect on diatom assemblages was the same in both seasons. Moreover, macroinvertebrate and diatom assemblages were shaped by different environmental factors. Macroinvertebrates were filtered mainly by substrate types, velocity, and COD_Mn, while diatoms were mainly shaped by altitude, substrate types, and water quality. Therefore, our study showed (a) that different biological assemblages in a river system presented similarities and differences in community assembly mechanisms, (b) that multiple processes play important roles in maintaining benthic community structure, and (c) that these patterns and underlying mechanisms are seasonally variable. Thus, we highlight the importance of exploring the community assembly mechanisms of multiple biological groups, especially in different seasons, as this is crucial to improve the understanding of river community changes and their responses to environmental degradation.