Abundance Of Functional Feeding Groups Research Articles

Long-term effects on water chemistry and macroinvertebrates of selective thinning along small boreal forest streams

The maintenance of narrow strips of trees (forest buffers) along the shorelines of surface water bodies during logging is a common measure to protect freshwater habitats. The functionality of forest buffers may be improved by actively managing the streamside forest early in the rotation for their eventual function as buffers, including by increasing the proportion of broadleaf trees in spruce-dominated stands. In this study, long-term effects of different selective thinning regimes along two small forest streams were investigated in south-central Sweden. In a young coniferous forest, a c. 10 m-wide band along the streams was selectively thinned in 1998 to create a band with purely broadleaf trees along one of the streams and purely conifers along the other. Forest stand characteristics, water chemistry and benthic macroinvertebrates data were collected during 1996–2003 (before and after selective thinning). The streams were re-investigated 20–22 years after thinning, together with three streams representing operational forest management. The forest adjacent to all five streams was inventoried and litterfall, stream water chemistry, and benthic macroinvertebrates composition were monitored between spring and late autumn during 2018–2020. Twenty years after thinning, the thinned bands beside the streams were still dominated by either broadleaf trees or conifers, depending on the stream. Over the longer term, the differences in water chemistry between the streams with selective thinning were mainly related to lower pH, ANC, Tot-P and Tot-N concentrations in the stream bordered by mainly broadleaf trees. Analysis of benthic macroinvertebrates was based on environmental quality indices (ASPT and EPT), diversity and abundance metrics, and relative abundances of functional feeding groups. Streams with higher broadleaf litter inputs tended to score better on the ASPT and EPT indices than those with lower broadleaf inputs, as well as supporting higher relative abundances of one or more groups of invertebrate detritivores (leaf shredders, collector-gatherers and/or passive filter feeders). This suggests that management of the density of broadleaf trees beside these streams might support higher ecological status and will support a greater proportion of detritivores in benthic food webs.

Consequences of a terrestrial insect invader on stream-riparian food webs of the central Appalachians, USA

The terrestrial invader hemlock woolly adelgid (Adelges tsugae) decimates eastern hemlock (Tsuga canadensis) stands that dominate riparian zones of Appalachian forest streams. However, the ecological consequences for linked aquatic-terrestrial ecosystems remain unknown. We measured stream-riparian trophic linkages at 21 sites of Ohio, West Virginia, and Virginia representing a chronosequence of T. canadensis decline. We measured reciprocal fluxes of basal resources (periphyton, terrestrial detritus), emerging aquatic insect flux rate and community composition, riparian orb-weaving spider density, and estimated spider trophic position and reliance on aquatically-derived energy using stable isotopes (13C, 15N, 2H) and Bayesian mixing models. Stream periphyton biomass was greater at uninvaded reference sites than at invaded sites and composition of the terrestrial-to-stream detritus flux changed with T. canadensis decline. Emergent aquatic insect community composition was partly explained by hemlock decline status, but the relative abundance of functional feeding groups was not. Riparian orb-weaving spider densities were highest at sites with severe hemlock decline (F = 4.27, p = 0.022), but were not linked to insect emergence flux rates (p > 0.10). Both trophic position ( $${\overline{x}}$$ = 2.4) and relative reliance on aquatically-derived energy ( $${\overline{x}}$$ = 83%) were comparable among spider families (Tetragnathidae, Araneidae, Pisauridae) and site decline status. Although spider δ13C signatures were unrelated to those of the most numerous emergent insect families, δ15N signatures of Araneidae and Pisauridae tracked emergent insect δ15N (r2 = 0.42 and 0.78, respectively), suggesting a trophic linkage. Overall, the ecological consequences of this invader were clearest at lower trophic levels, with more nuanced impacts on riparian spiders.

Feeding Patterns and Strategies of Ephemeroptera, Plecoptera and Trichoptera in Relation to Seasonality, Landscape Elements and Mesohabitats

We inspected functional feeding groups in relationship with seasonality, stream order, Land Scape Elements (LSE), and mesohabitat of Ephemeroptera, Plecoptera, and Trichoptera (EPT) based on gut content analysis and mouthparts in 27 streams of the Western Ghats and the Eastern Ghats. From the study, a total of 14,168 specimens were collected and identified. The composition of trophic categories showed a slight variation among the different seasons with the dominance of collectors. The results of the abundance of functional feeding groups of EPT across stream orders additionally showed the predominance of collectors and predators in-stream orders 1 and 2. Collectors and filter feeders dominate in-stream orders 3 and 4. By examining the LSE elements, it is found that collectors were high in the streams flowing through areca nut and low in the streams flowing through natural vegetation. The distributions of functional feeding groups within the orders were also analyzed. Mesohabitat results showed scrapers were found to be predominant in riffles whereas collectors, predators, shredders, and filter feeders overwhelm in runs. ANOVA results showed that only mesohabitat was found to be significant. The results of the present study did not broadly concur with the predictions of the River Continuum Concept (RCC) because of the lack of thickly canopied headwater stream sites and the limitation of our study to only EPT taxa.

Functional feeding groups of macroinvertebrates and their relationship with environmental parameters, case study: in Zarin-Gol River

Feeding strategies are typical traits reflecting the adaptation of species to environmental conditions. The aim of this paper was finding of proof that functional feeding groups the benthic macroinvertebrates can be unitized as surrogate for biological assessment. The composition and abundance of functional feeding groups of the benthic macroinvertebrate assemblages were surveyed along the Zarin-Gol River, Iran during winter and spring 2016. Benthic samples were collected using Surber sampler (900 cm2 area) with 3 replicates in 5 stations (agriculture, rural area, forest, fish culture and reference site). Ten environmental parameters including (temperature, Dissolved oxygen, pH, Electric conductivity, etc.) of each station were assessed. A total of abundance (901 individuals) belonging to 30 families and 9 orders were identified. In terms of relative abundance, Collector/Gatherer and Collector/ Filter were the predominant groups at most sampling stations. Shredders had low abundance in all stations and were absent in station two. Principal component analysis and cluster ordination showed that there are two distinct groups of benthic and stations. The implication of the observed pattern of variation in the abundance of functional feeding groups were discussed regarding to the ecosystem functions and water quality assessment.

Functional Assemblages of Macroinvertebrates in Pools and Ditches in Drained Forest Landscape

Artificially drained commercial forests are hydrologically novel ecosystems, where the array of aquatic habitats consists of ditches and remnant pools. In general the network of ditches has been found to have longer hydroperiod, the knowledge, however, about aquatic invertebrates in this system is scarce. We examined which environmental factors are impacting the biomass and abundance of functional feeding groups. Scrapers and shredders were aggregated to ditches and gatherers to pools. Filterers’ distribution pattern suggested that the function of filtering is carried out by different taxa in pools and ditches. Ditches were rather more suitable for feeding groups that rely on autochthonous resources. Acidity was a major driver of functional community composition, for example, one of the causes for higher scraper frequency in ditches. Predators exhibited greater quantities in extensive macrophyte cover regardless of water body type. Our results suggest that the trophic organization in ditches and pools is different because habitat factors select the feeding groups directly through food resources, but also because of the environmental filter on the other biological traits of the organisms. To support complex ecosystems with several trophic levels also in commercial forests, we suggest to avoid destroying macrophyte rich pools and ditches during silvicultural management.

Macroinvertebrate functional organisation along the longitudinal gradient of an austral temperate river

The Kowie River, a relatively pristine system in South Africa, was sampled on four occasions over one year to determine if relative abundances of functional feeding groups (FFGs) of invertebrates changed along the longitudinal gradient, and if these changes matched predictions of the river continuum concept (RCC). The results revealed that gatherers and filterers dominated in the Kowie River, and together represented 50–83% of the invertebrate assemblages. There was a general paucity of shredders (relative abundance was <10% at all sites and times). The changes in relative abundances of the different FFGs did not always follow the predictions of the RCC, as there were no correlations of community structure with river width or canopy cover in some seasons; however, some predictions of the RCC were supported, as a dominance of filterers (with relatively small contributions from shredders and grazers) and a consistent presence of predators were recorded. The FFG abundances were correlated with water velocity and total dissolved solids. Broadly, shifts in relative abundances of FFGs along the river continuum could not be explained by physical attributes alone, and were probably influenced by the availability of food and the chemistry of the river. Our findings highlight the need for theoretical and field studies across a broad array of African systems to refine the applicability of the RCC and FFG classifications to further develop models of ecosystem function.

Anthropogenic disturbances influencing ciliate functional feeding groups in impacted tropical streams.

Anthropogenic disturbances change the trophic structure of streams, ultimately affecting ecosystem functioning. We investigated the effects of human disturbances, mainly organic pollution, on ciliate functional feeding groups (FFG) in 10 tropical streams near agricultural and urban habitats, in the dry and rainy seasons. We hypothesised that the organic pollution would affect the ciliate composition and that the richness and abundance of ciliate FFG would be associated with different disturbances, such that an increase in the load of organic matter would result in an increase in the percentage of bacterivores ciliates, while streams with low organic matter concentration and wide canopy openness will determine a higher contribution of algivorous ciliates. Our results corroborate our hypothesis of an increased development of bacterivorous ciliates with increasing organic pollution, but only in the abundance of this FFG. Also, algivorous ciliates were found to be related to riparian vegetation clearing. Thus, ciliate FFG accurately reflected different anthropogenic disturbances, revealing a change in the trophic structure of the streams. In addition, we found that organic pollution can lead to both taxonomic and functional homogenization of the ciliate community, which implies serious consequences for ecosystem functioning.

Stream macroinvertebrate communities change with grassland afforestation in central Argentina

Lotic ecosystems are highly affected by land use changes such as afforestation of natural areas for management or commercial purposes. The aim of this study was to analyze the effect of pine plantations on benthic invertebrate communities in mountain grassland streams. Additionally, we assessed if the hydrological period modifies the effect of afforestation on stream invertebrates. Three headwater streams draining grasslands (reference streams) and three draining plantations of Pinus elliottii were selected in a mountain watershed of Córdoba province (Argentina). Hydrologic and physicochemical variables were registered and benthic invertebrate samples were collected in each stream at two different hydrological periods. Total invertebrate abundance, richness and diversity were reduced in afforested streams as well as the number of indicator taxa. In addition, invertebrate functional structure (i.e. taxonomic richness and total and relative abundance of functional feeding groups, FFG) showed differences between streams with different riparian vegetation and between hydrological periods. Total abundance of all FFGs was lower in afforested streams and scrapers’ relative abundance was higher in grassland streams at the low water period. In addition, in most FFGs richness was diminished in afforested streams. Changes in light intensity, hydrology and coarse organic matter inputs produced by afforestation alter fluvial habitats and consequently the composition and trophic structure of invertebrate communities in grassland streams of Córdoba mountains.

Beaver-Created Habitat Heterogeneity Influences Aquatic Invertebrate Assemblages in Boreal Canada

Habitat heterogeneity and wetland area play important roles in aquatic biodiversity; however, other factors are equally important in the composition and distribution of ecological communities. Over a 3-year period, including a year of drought, we demonstrate how beavers physically altered isolated shallow-water wetlands in Miquelon Lake Provincial Park, Canada, which then influenced aquatic invertebrates diversity and abundance of functional feeding groups and taxa. Digging channels by beavers extended aquatic habitats over 200 m into the upland zone and created unique aquatic habitats, which became hot-spots for predaceous aquatic invertebrates. Some taxa (e.g., Gerridae and Gyrinidae) were found exclusively in beaver ponds, while Culicidae were primarily in wetlands without beavers. Amphipoda were strongly associated with beaver ponds in drought and post-drought years. During extreme drought in 2009, species richness, diversity and abundance declined dramatically, but recovered quickly in 2010. Although species richness was associated with wetland area, increased niche availability through active maintenance of wetlands by beavers played an important role in aquatic invertebrate diversity and distribution. Understanding the role of common, but seldom surveyed within-wetland habitats in boreal wetlands expands our ability to understand aquatic biodiversity, the importance of habitat heterogeneity and the role of other taxa in species assemblages.

Development of a multimetric index based on benthic macroinvertebrates for the assessment of natural wetlands in Southwest Ethiopia

Biotic indices are widely applied for conservation and management of aquatic resources since they allow water resources monitoring agencies to get insight in complex biological data and yield policy relevant information. Despite the worldwide popularity of biotic indices, little information on their use and applicability in Eastern Africa is available. Here, we develop a multimetric index based on macroinvertebrates to assess the ecological condition of natural wetlands in Southwest Ethiopia. Index development was based on a dataset of 222 samples collected during two consecutive years from 63 sites located at eight different wetlands. We used physico-chemical and hydro-morphological variables (land use pattern, habitat alteration, hydrological modification and chemical water quality) to classify sites as reference or degraded. We tested a total of 58 potential metrics representing various aspects of macroinvertebrate assemblages including family richness, composition, tolerance measures and presence and abundance of functional feeding groups. Metrics were selected for the development of a final index based on their sensitivity in discriminating reference from impaired sites, strength of correlation with the anthropogenic disturbance gradient, chemical measurements, and the degree of redundancy. Metrics retained for the final index were:overall family richness, family richness of Ephemeroptera, Odonata and Trichoptera (EOT), and percentage of filterer–collectors. The final index, derived from the sum of three metric scores, was divided into five water quality classes (very bad, bad, moderate, good and very good). Our final multimetric macroinvertebrate index (MMI) distinguished well between reference and impaired wetland sites and showed a significant negative response to a gradient of disturbances (R2=0.86, p<0.05). Moreover, it classified a validation dataset accurately with a correctly classified instances of 80% and a Cohen's Kappa value of 0.6. This MMI can be considered as a robust and sensitive tool that can be applied to evaluate the ecological condition of natural wetlands in Ethiopia, where wetland resources are under high pressure as a result of agricultural activities such as grazing and urbanization.

Habitat characteristics and trophic structure of benthic macroinvertebrates in a forested headwater stream

Three channel reaches with different habitat characteristics were selected to test the variability in community structure of benthic macroinvertebrates by comparing the relative abundance of functional feeding groups among the reaches. The important factors influencing the spatial and temporal organization of community structure were explored using nonmetric multidimensional scaling (NMS). The habitat characteristics in the reaches were different in terms of habitat type, hydrological factors, and substrate composition. The first headwater reach was classified as a step-pool reach with similar relative areas of riffle and pool habitats. The second mid-reach and the third down reach had greater areas of pool habitat followed by runs and riffles whose proportions were similar between the latter two reaches. The relative abundances of functional feeding groups were different among the surveyed reaches. Gammarid shredders predominated in the upper reach, and chironomid collector–gatherers and collector–filterers were in greater abundance in the two lower reaches. The proportions of gammarids were minor in the mid and downstream reaches. NMS ordination indicated that the proportion of substrates<8mm, discharge, and water depth mainly determined the spatial and temporal distribution of samples based on the macroinvertebrate community in the study reaches. These results suggest that different habitat characteristics result in a distinct community structure in each reach.

山地河流浅滩深潭生境大型底栖动物群落比较研究——以重庆开县东河为例

浅滩和深潭是山地河流中常见的河流生境结构。2011年7月,在重庆开县东河上游双河口-杉木桥河段,选择21个浅滩和深潭,调查大型底栖动物,研究影响不同生境中底栖动物组成、分布和多样性的生态机理。结果表明:调查河段浅滩和深潭中大型底栖动物分别为31种和24种,密度分别为450.62 个/m²和86.24 个/m²,生物量分别为2.88 g/m²和0.55 g/m²。浅滩有指示种11种,即纹石蛾(<em>Hydropsyche </em>sp.)、假蜉(<em>Iron </em>sp.)、假二翅蜉(<em>Pseudocloeon </em>sp.)、舌石蛾(<em>Glossosoma </em>sp.)、高翔蜉(<em>Epeorus </em>sp.1)、背刺蜉(<em>Notacanthurus</em> sp.)、<em>Heterocloeon</em> sp、锯形蜉(<em>Serratella</em> sp.)、朝大蚊(<em>Antocha </em>sp.)、等蜉(<em>Isonychia</em> sp.)、溪颏蜉(<em>Rhithrogena </em>sp.)。深潭指示种仅蜉蝣(<em>Ephemera </em>sp.)和黑大蚊(<em>Hexatoma </em>sp.)两种。刮食者为两类生境的优势功能摄食类群。浅滩中滤食者和刮食者比例显著高于深潭,而收集者和捕食者显著低于深潭。两类生境中大型底栖动物群落结构差异显著。浅滩中大型底栖动物的密度、生物量、丰富度指数、Shannon-Wiener 指数、改进的Shannon-Wiener指数均明显高于深潭。受地貌形态、水力特征和冲淤变化规律影响的生境稳定性和异质性差异是导致大型底栖动物群落差异的主要原因。;Riffle and pool, which exhibit very different physical characteristics (such as depth, velocity, substrate), are basic and common habitat units in mountain rivers. The benthic macroinvertebrate is an important connector among the different trophic levels of stream ecosystem and its community could be easily affected by variation of physical characteristics of microhabitat. However, previous researches did not always demonstrate a clear difference of community structure and diversity between riffle and pool macroinvertebrate. Dong River is a typical mountain stream which is located in a karst area of southwestern China, namely Kaixian County of Chongqing. In order to study variations in structure, composition and diversity between riffle and pool macroinvertebrate assemblage, we chose twenty one pairs of riffles and pools to investigate benthic macroinvertebrate species in upstream of Dong River in July 2011. Our results indicated that the difference of water quality was not significant between the two habitats. However, the riffle habitat not only had a wider water surface and faster flow velocity, but also contained bigger substrate than those of the pool habitat. The number of species was thirty one in riffles and twenty four in pools. Density and wet biomass of macroinvertebrate assemblage in riffles were 450.62 ind/m²and 2.88 g/m², respectively, comparing to 86.24 ind/m²and 0.55 g/m²in pools. Mayfly was the group with the highest density, abundance and species richness in both habitats. Virtually all species were more abundant in riffles than those in pools, except chironomids, <em>Ephemera </em>sp and <em>Hexatoma </em>sp which were more abundant in pools. Indicator Species Analysis indicated that a greater number of taxa, including <em>Hydropsyche </em>sp, <em>Iron </em>sp, <em>Pseudocloeon </em>sp, <em>Glossosoma </em>sp, <em>Epeorus </em>sp2, <em>Notacanthurus</em> sp, <em>Heterocloeon</em> sp,<em> Serratella</em> sp,<em> Antocha </em>sp,<em> Isonychia</em> sp and <em>Rhithrogena </em>sp, were restricted to riffles, while only two species, <em>Ephemera </em>sp and <em>Hexatoma </em>sp, were indicator species of pools. Kruskal-Wallis Test indicated that relative abundance of each functional feeding group was significantly different between the two habitats. Scraper was the dominant functional feeding group in both habitats, while shredder had the lowest relative abundance. Relative abundance of functional feeding groups between riffle and pool were significantly different except that of shredder. Riffles exhibited significantly higher percentage of collector-filterer and scraper, while percentage of collector-gatherer and predator in pools were significantly higher than that of riffles. Detrended Correspondence Analysis indicated that the difference of macroinvertebrate community structure was obvious between the two habitats. Density, wet biomass, species richness, Shannon-Wiener index and Improved Shannon-Wiener index of riffles were significantly higher than those of pools, which was similar with former researches conducted in mountain stream with stony substrate. Pool characterized by small and loose substrate is unstable and vulnerable habitat for benthic macroinvertebrate to resist fast flow during the flooding period. However, bigger substrate of riffle as a result of erosion creates a much more diverse and stable for macroinvertebrate to escape predators and disturbance of scouring. Therefore, habitat stability and heterogeneity affected by habitat morphology, hydraulic characteristics and erosion/deposition pattern may be the major explanation.

Effects of environmental factors and predation on benthic communities in headwater streams

Structure and composition of benthic macroinvertebrate assemblages were investigated during three consecutive years in six headwater streams that exhibit a high variation in environmental conditions, habitat structure and predatory pressure. We examined whether the abundance of functional feeding groups could be best predicted by the abundance of predators and some habitat and chemical variables. Mean density and biomass of macroinvertebrate functional feeding groups varied significantly throughout the study area. Stepwise multiple regression analyses revealed that both density and biomass of functional feeding groups was influenced primarily by chemical features of water. Shredder biomass and scraper density were also influenced by habitat features, the abundance of scrapers increasing in deeper localities at lower altitudes and with abundant macrophytes. The abundance of predatory invertebrates was related to the density and biomass of benthic prey. An influence of fish predation on invertebrate communities was not observed in the study streams. The finding that benthic communities in undisturbed headwater streams are mainly affected by water chemistry variables irrespective of fish predation and habitat features clearly highlight the sensitivity of functional feeding groups to changes in chemical features and their role as indicators for bioassessment.

Resistance and resilience of macroinvertebrates to irrigation water withdrawals

Summary1. Water withdrawal for irrigated agriculture is one of the leading uses of freshwater resources in the world; however, effects of low flow disturbances on lotic ecosystems are poorly understood. We studied an intensively managed agricultural catchment to determine: (i) how macroinvertebrate assemblages and environmental variables respond to water withdrawals of varying magnitude and duration; (ii) what environmental variables are associated with macroinvertebrate responses and (iii) the resiliency of macroinvertebrate communities to irrigation water withdrawals.2. We sampled above and below four irrigation diversions that create a gradient of increasing water withdrawal from upstream to downstream (i.e. 0%, 22%, 87%, 90% and 97% water withdrawn) along a 36 km river section. Three reaches were sampled above and below each point of diversion from June to September 2004 and 2005, which represented average and drought water conditions respectively.3. Irrigation water withdrawals were associated with both direct and indirect changes to the physicochemical environment. Direct effects (e.g. decreased velocity, depth and wetted habitat) were approximately proportional to the amount of water withdrawn, while indirect effects (e.g. increased conductivity and temperature) occurred when water withdrawals exceeded 85% of ambient levels.4. Changes in macroinvertebrate communities were more strongly related to indirect than direct effects of irrigation water withdrawals. In an average water year, community changes were associated with interacting thresholds of reduced discharge and increased conductivity. During a drought year, community changes were related to the interacting thresholds of reduced discharge and increased temperature.5. Between years, macroinvertebrate responses differed with the magnitude and duration of low flow conditions. In 2004, high‐intensity, relatively short‐duration water withdrawals (&lt;2 months) and alterations to the physicochemical environment changed the relative abundance of macroinvertebrate communities, while macroinvertebrate indices and proportional abundances of functional feeding groups remained unchanged. In contrast, discharge reductions exceeding 90% of ambient levels and temperatures above 30 °C from July to September 2005 were associated with shifts in community composition from a dominance of collector‐gatherer and filterer Ephemeroptera, Plecoptera and Trichoptera taxa to predatory insects, non‐insect taxa and scraping elmid beetles.6. On an annual basis macroinvertebrate communities appeared resilient to the impacts of water withdrawals following winter high flows. In contrast, recovery was not observed after discharge and physicochemical variables returned to predisturbance conditions for only one month.7. Irrigation water withdrawals appear to impact macroinvertebrates through indirect effects that intensify with the magnitude and duration of water withdrawals and annual water availability. Preserving environmental conditions within natural ranges of variability, especially during low water years, appears critical to mitigating adverse biological responses to water withdrawals.

Macroinvertebrate functional organization and water quality in a large arid river from Patagonia (Argentina)

The composition and abundance of functional feeding groups of the macroinvertebrate communities were investigated along the Chubut River in the Patagonian Precordillera and Plateau, Argentina. Chubut River (>1000 km) is the largest river in the area and the hydrological regime is modified in the lower section by an artificial reservoir (Florentino Ameghino Dam). Quantitative benthic samples were collected at 13 sites in the upper, middle and lower sections of the river basin. Sites were visited four times during 2004 and physicochemical parameters, chlorophyll a and particulate organic matter (POM) were assessed. In terms of relative abundance, collector-gatherers and scrapers/grazers were the predominant groups at most sites. Shredders were not abundant in the upper sites and were practically absent at middle and lower basin sites. Collector filterers that comprised more than 25 % of abundance at the pre-regulated site were practically absent right below the dam. POM biomass decreased significantly with distance from the source and chlorophyll a showed a marked increase below the reservoir. We conclude that although there was a distinct headwaters fauna in the Chubut River, and sequential downstream changes in species composition, most functional feeding groups (apart from shredders) were represented down the whole length of the river. Finally, the usefulness of biotic indices and metrics in relation with main environmental features of the Chubut River basin is discussed.

Seasonal Succession in the Aquatic Insect Community of an Ozark Stream

ABSTRACT We studied the temporal pattern of the aquatic insect assemblage of an Ozark stream by sampling riffle areas every two weeks from early February through late July, 2002. Total richness of the assemblage, for the entire study, was 138 taxa, including 57 from the dipteran family Chironomidae. Richness levels, per sampling period, ranged from the low 40s to the high 50s and were highest in late March through mid-April. Assemblage composition shifted from one dominated by chironomids in the winter and spring to one dominated by mayflies in the late spring and early summer and by caddisflies in summer. EPT richness levels, diversity, biotic index values, and relative abundances of functional feeding groups varied substantially during the study, occasionally even between two-week sampling periods. The data suggested that, for this type of stream, winter and summer are the times of year that the insect assemblage is least dynamic. These periods, despite lower overall community richness, may therefore be more appropriate to compare samples from different locations or years.

Impacts of irrigation on fisheries in rain‐fed rice‐farming landscapes

Summary Expanding irrigation development threatens the productive and diverse fisheries of rain‐fed rice‐farming landscapes. Environmental management of irrigation can minimize negative impacts on fisheries, but its effectiveness is constrained by a lack of reliable information on the nature and magnitude of impacts. To quantify the impacts of small‐ to medium‐scale irrigation schemes on aquatic habitat availability, fish catches, species richness and ecological composition of fish assemblages in these landscapes, we conducted a field study in Laos. The observational study was replicated at irrigation scheme level, covering 10 weir and 10 dam irrigation schemes paired with non‐impacted control sites. Weir schemes had no significant impact on aquatic habitat, but caused a significant decline (−36%) in fish catches that was only partly explained by a reduction in fishing effort. Weirs had no effect on species richness, but were associated with a significant increase (+17%) in the relative abundance of omnivores. Dam irrigation schemes significantly reduced riverine habitat area, and increased lacustrine and dry‐season rice‐field areas. Dams led to a marked redistribution of catch and fishing effort from non‐reservoir habitats into reservoirs, but no overall change in catch or effort occurred. The redistribution reflected a response to fishing opportunities in the reservoir, rather than a loss of productivity in non‐reservoir habitats. No significant impacts were detected on fish species richness or the relative abundance of functional feeding groups. Overall impacts of irrigation on fisheries were related mostly to changes in fishing effort, rather than ecological effects on the resources. The unexpectedly moderate level of ecological impacts may reflect compensatory effects at the landscape level and the fact that rice fields, which dominated the wet‐season habitat, continued to be managed as rain‐fed deep‐water systems even where dry‐season irrigation had been developed. Synthesis and applications. Small‐ to medium‐scale irrigation schemes in rain‐fed rice‐farming landscapes have only moderate impacts on fisheries, which remain productive and diverse. Changes in agricultural practices in the wet season are likely to have greater effects on fisheries than dry‐season irrigation.

Macrozoobenthos in 2 shallow, mesotrophic Chinese lakes with contrasting sources of primary production

Comparative studies on macrozoobenthos were done in 2 shallow mesotrophic lakes in the middle basins of the Yangtze River, China: Lake Biandantang where macrophytes were abundant, and Lake Houhu where macrophytes were scarce. Samples were taken monthly at 4 stations in each lake from April 1997 to March 1999, and a total of 67 and 31 taxa of macrozoobenthos were recorded in Lake Biandantang and Lake Houhu, respectively. Both annual mean density and biomass of macrozoobenthos were higher in Lake Biandantang than in Lake Houhu: 780 vs 532 indivials/m2 and 37.1 vs 25.9 g wet mass/m2, respectively. Abundance of functional feeding groups followed the order: scraper > collector > predator > shredder in Lake Biandantang, and collector > predator > scraper > shredder in Lake Houhu. Only 1 density peak occurred from winter to early spring in Lake Houhu; however, in Lake Biandantang, there were 2 peaks, the winter peak and spring peak. K-dominance curves and Shannon–Wiener, Simpson, and Margelef indices indicated that macrozoobenthos were more diverse in Lake Biandantang than in Lake Houhu. Our study suggests that, in shallow lakes, submerged macrophytes are essential for the maintenance of biodiversity of macrozoobenthos mainly because the macrophytes increase habit heterogeneity and availability of suitable food, and may also decrease predation by fish on the macrozoobenthos.

Role of Predatory Fish in Community Dynamics of an Ephemeral Stream

In enclosed runs in a third-order ephemeral stream in west-central Kentucky, the effects of predatory sunfish (Lepomis) on benthic macroinvertebrates, benthic algae, and detritivory were compared (1) before stream intermittence, (2) after stream intermittence when transport was restricted, and (3) between substrata offering differential cover from fish predation. Ambient fish densities had little effect on total macrobenthic densities and processes on lower trophic levels before intermittence. Fish modestly affected macroinvertebrate densities after intermittence, when surface exchange of prey was interrupted by sections of dry stream. Among substrata, fish influenced macroinvertebrates on bedrock, but not on stony, coarse substrata. Densities of two taxa were significantly affected by fish, and this significantly altered the relative abundance of functional feeding groups in enclosures on bedrock by increasing the proportion of invertebrate predators in fish treatments. Macroinvertebrate densities in microhabitats on both substrata were not affected by fish presence. Dense growths of the stalked diatom Cymbella generally covered microhabitats and added structural complexity, particularly to bedrock surfaces. Unobstructed, natural migration of prey in the large (40 m2) fencelike enclosures (versus containers), ample refuge space, and low natural densities of fish were important in minimizing fish effects in enclosures.

BENTHIC INVERTEBRATE RESPONSE TO POLLUTION ABATEMENT: STRUCTURAL CHANGES AND FUNCTIONAL IMPLICATIONS1

ABSTRACTWe examined changes in certain structural and functional aspects of the benthic invertebrate community in the Penobscot River, Maine, between 1974 and 1981. During this period, two pulp and paper manufacturers and three municipalities spent an estimated $33 million to reduce point source effluents harmful to aquatic life. We developed a biotic index based on objectively derived pollution tolerance values for resident taxa. Analysis of the benthic invertebrate community indicated that substantial improvement in water quality had resulted from pollution abatement. We established a four‐group water quality classification scheme based on biotic index ranges, and showed that every site that was not in the best water quality classification in 1974 improved its classification to a better water quality group in 1981, and that the sites in the best group did not change. Relative abundances of functional feeding groups also changed, as were predicted by the river continuum theory. The effluents had acted as a “reset mechanism” that shifted polluted areas from autotrophic to more heterotrophic conditions. The direction of the shift was reversed in response to abatement efforts. Functional analyses of energy dynamics could lead to a more ecologically sound classification of water quality.