The influence of glacial runoff on stream macroinvertebrate communities in the Taillon catchment, French Pyrénées

1. Benthic communities were sampled from five sites within a glacial catchment in the Cirque du Gavaranie, French Pyrénées, over two consecutive years (i) to investigate whether longitudinal patterns in zoobenthic communities exist downstream of a glacial margin and (ii) to identify the principal environmental variables influencing such patterns. 2. There was a distinct zonation of communities with increasing distance from the glacial margin. Ordination of the zoobenthic distribution indicated sites were separated by the relative contributions of taxa rather than their presence or absence. A shift in community composition and diversity separated a kryal type community dominated by Diamesa spp., Prosimulium spp., Eriopterini and Empididae at ≥2200 m a.s.l., from a more rhithral community of Orthocladiinae, Ephemeroptera, Plecoptera and Trichoptera at 1900 m a.s.l. 3. Chironomidae showed a defined gradient in distribution from Pseudokiefferiella parva and Diamesa latitarsis groups close to the glacier, through D. zernyi and D. cinerella groups, Orthocladius, Parametriocnemus and Micropsectra further downstream with Rheocricotopus, Corynoneura and Nilotanypus furthest from the glacial margin. Diamesa cinerella/zernyi group was the most euryzonal taxon. 4. Gradients in channel and hydraulic stability, groundwater input and mean water temperature were identified as the principal environmental variables associated with the downstream distribution gradient of zoobenthos. Diamesa, Empididae, Eriopterini and Nematoda were most tolerant of channel and hydraulically unstable and cold water habitats. Simuliidae (Prosimulium), Crenobia alpina, Rhyacophila, Chaetopterygini, Drusus rectus, Capnioneura, Orthocladius and Parametriocnemus were associated with intermediate conditions. Corynoneura, Tanypodinae, Perlidae, Chloroperlidae, Agapetus fuscipes and Coleoptera were least tolerant of channel and hydraulic instability and low water temperature.     

Trends of macroinvertebrate community structure in glacier-fed rivers in relation to environmental conditions: a synthesis

1. Generalized additive models (GAMs) were used to predict macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier-fed river sites from a set of 11 environmental variables. Maximum water temperature and channel stability were found to explain the most deviance in these models.
2. Using this information, and data from other recent studies of glacier-fed rivers, a modified conceptual model based on Milner & Petts (1994) is presented which predicts the occurrence of macroinvertebrate families and subfamilies as determined by maximum water temperature ( T _max) and channel stability. This deterministic model only applies to the summer meltwater period when abiotic variables drive community structure.
3. Where maximum water temperature is below 2 °C, Diamesinae chironomids are typically the sole inhabitants, but where T _max >2 °C but <4 °C Orthocladiinae are found and, where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 °C Perlodidae, Taeniopterygidae, Baetidae, Simuliidae and Empididae can be expected to be part of the glacier-fed river community, particularly in Europe.
4. At other times of the year when environmental conditions ameloriate, glacial rivers support higher macroinvertebrate abundance and diversity, with a number of taxa present that are not found during the summer melt period.
5. Dispersal constraints influence macroinvertebrate assemblages of many glacier-fed rivers located on islands and in some alpine areas.     

Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L^–1), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m^–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus .
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m^–2, although peaking as high as 9000 ind. m^–2. Average annual biomass ranged from 102 to 721 mg m^–2, and reached >2000 mg m^–2 at one site in autumn.
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.     

Longitudinal distribution of macroinvertebrate assemblages in a glacially influenced stream system in the Italian Alps

1. The longitudinal distribution of macroinvertebrates was investigated in June, August and September 1996 and 1997 in the Conca glacial stream and its tributary (Italian Alps; 46°N, 10°E). The principal aim was to test the 22 model that predicts the succession of faunal groups downstream of the glacial snout in relation to water temperature and channel stability. The effect of a non‐glacial tributary on the taxonomic richness and density patterns occurring in the glacial stream was also considered. 2. Channel stability showed an atypical longitudinal trend in the Conca glacial stream, being high in the upper part with Pfankuch Index values between 30 and 33. Water temperature exceeded 6 °C at all stations, with average values below 2 °C occurring only within 700 m from the glacial snout. 3. Taxonomic richness and diversity increased downstream. Taxonomic richness in the glacial stream (at about 1.5 km from the glacier) was comparable with the tributary and the reach after the confluence. Abundance also increased downstream in the glacial stream, but not as greatly as the number of taxa. 4. At higher taxonomic levels, the community structure in the tributary stations appeared to be similar to the two stations in the glacial stream just upstream of the confluence. The effect of the tributary was evident mainly at the genus or species level of the Chironomidae community. Some taxa found in the non‐glacial stream (e.g. Cricotopus fuscus, Eukiefferiella coerulescens, Metriocnemus sp., Paratrichocladius rufiventris, P. skirwitensis, Rheocricotopus effusus and Smittia sp.) were found also in the Conca stream but only after the confluence. 5. The upper glacial reach (within 700 m from the glacier snout) was dominated by the chironomid Diamesa spp. Less than 400 m from the glacier other Diamesinae (Pseudokiefferiella parva) and a few Orthocladiinae, especially Orthocladius (Euorthocladius) rivicola gr., colonized the stream. Some Diamesinae maintained relatively dense populations at mean water temperature around 5 °C, while some Orthocladiinae colonized reaches with mean water temperature <3 °C. 6. Contrary to the 22 model, Dipteran families such as Empididae and Limoniidae were more abundant in the upper stations than Simuliidae; non‐insects such as Nematoda and Oligochaeta were also numerous at some sites. Leuctridae, Taeniopterygidae and Nemouridae were the first Plecoptera to appear upstream, while Chloroperlidae were restricted to the lower reaches. Among Ephemeroptera, Heptageniidae were more abundant than Baetidae in the glacial sites. 7. In this glacial system channel stability and maximum temperature did not show the expected longitudinal trend and thus a typical kryal community was confined within 700 m from the glacier snout where summer mean water temperature was below 4 °C.     

城市溪流中径流式低坝对底栖动物群落结构的影响

调查了浙江省安吉县内具径流式低坝的城市溪流(6个样点)和参照溪流(3个样点)的底栖动物群落,目的是了解城市溪流底栖动物群落结构退化规律和径流式低坝(2—3 m)对城市溪流底栖动物群落组成与结构的影响。结果表明,参照样点的底质组成以大石块(35.92%)和卵石(33.66%)为主,城市溪流以砾石为主(57.97%)。城市溪流水温和电导率显著高于参照溪流,TN和TP高于参照溪流。底栖动物总分类单元数和EPT分类单元数显著低于参照溪流。城市溪流河道内水坝上下游之间的流速(P=0.273)和宽深比(P=3.92)无显著差异。坝下游水体中的TP高于坝上游,电导率、溶解氧、pH值和水温在坝上下游之间几乎一致。除BI指数坝下游高于坝上游外,坝上下游间底栖动物总分类单元数、EPT分类单元数以及多样性指数、优势度和均匀度指数没有显著差异。但坝下游的耐污类群比例显著高于坝上游,敏感类群比例则显著低于坝上游。与坝上游相比,坝下游捕食者比例上升和集食者比例下降。NMDS结果进一步表明,城市溪流内水坝的建设导致坝上下游底栖动物群落物种组成明显改变。     

Invertebrate drift in a glacial river and its non-glacial tributary

1. Invertebrate drift was studied in a glacially fed river and a non-glacial tributary in western Norway. Samples were taken during two consecutive 24-h periods in May, July and October 1997. The 3 months are characterized by snowmelt, ice melt and rainfall runoff, respectively. The main glacial river has colder, more turbid water, especially during the period of maximum ice melt during summer.
2. Chironomidae, especially the genus Diamesa , dominated the drift in the main river in May and October, constituting 97 and 99% of total numbers, respectively. Simuliidae, Plecoptera, Ephemeroptera and Trichoptera were the other main components.
3. A comparison of drift and benthos data revealed that the tributary was of little significance for colonization of the main glacial river. Only some additional species in very low numbers were recorded downstream of the confluence.
4. During July significant differences in diel drift pattern of Chironomidae and Simuliidae existed between the glacial and non-glacial reaches. There was a mid-day peak independent of discharge in the glacial river, but this peak was not noted in the tributary. Species of the genus Diamesa appear to be adapted for daytime drift, possibly evolved through the absence of predators and competitors that are typical of rhithral systems where nocturnal drift is more usual.     

The macroinvertebrate communities of two contrasting Norwegian glacial rivers in relation to environmental variables

1. Macroinvertebrate communities in two Norwegian glacial rivers, one in the western fjords (Dalelva) and one in the eastern mountains (Leirungsåi), were investigated during three time periods in 1996 and 1997.
2. Channel stability variables (substratum heterogeneity/Pfankuch index/hydraulic stress) and water temperature accounted for 54% of the total inertia in the principal components analysis (PCA) ordination of environmental variables. The importance of these variables was confirmed by cluster analysis.
3. The two rivers were well separated in the ordinations, with Leirungsåi showing much greater heterogeneity. This is explained by differences in altitudinal range, terrestrial vegetation and the importance and nature of tributary inputs.
4. Channel stability and temperature were also important in determining faunal communities in the two glacial rivers, supporting the main determining variables in the conceptual model of glacial streams ( Milner & Petts, 1994 ). However, clear temporal differences were apparent in the data, the two rivers being more similar during the summer period of high discharge dominated by glacial meltwater. During spring and especially during autumn environmental conditions and the macroinvertebrate fauna differed both within and between rivers.
5. Diamesinae dominated in the upper reaches of both rivers, with Orthocladiinae becoming more common downstream. The dominance of Diamesinae persisted further down Dalelva because of the continued influence of glacial tributaries, whereas in Leirungsåi the influence of non-glacial tributaries led to a change towards a greater proportion of Orthocladiinae. Lakes modified macroinvertebrate communities in both river systems.     

The quantification of local substrate heterogeneity in streams and its significance for macroinvertebrate assemblages

The effect of substrate heterogeneity on the structure of stream macroinvertebrate assemblages (total abundance, taxon richness, and evenness) is still not clear, but this could be due to the lack of standard methods for quantifying substrate heterogeneity. An accurate quantification of substrate heterogeneity was obtained from photographs of sampled areas (each 225 cm²), which were used to create maps that were subsequently digitized and analyzed using image analysis software. These maps allowed the calculation of multiple metrics quantifying two aspects of substrate heterogeneity: composition and spatial configuration of substrate patches. The diversity of substrate types (calculated as the Shannon diversity index), and the heterogeneity of patch compactness (calculated as the coefficient of variation of the relationship between patch dimensions) were the metrics explaining more biotic variance at the sample scale, but at higher scales there were no relationships between assemblage structure and substrate heterogeneity. Most variation in substrate heterogeneity occurred at the sample scale, while some metrics varied significantly at riffle or segment scales; these patterns of variation match those of macroinvertebrate assemblages, which had been previously studied. The importance of quantifying substrate heterogeneity and considering the spatial scales of its study are discussed.     

Salinity effects on macroinvertebrate assemblages and waterbird food webs in shallow lakes of the Wyoming High Plains

We determined the biomass and community structure of macroinvertebrates (>500 µm) associated with macrophytes, sediments, and unvegetated open water in three oligosaline (0.8 to 8.0 mS cm^–1) and three mesosaline (8.0 to 30.0 mS cm^–1) lakes in the Wyoming High Plains, USA. Total biomass of epiphytic and benthic invertebrates did not change with salinity, but biomass of macroinvertebrate zooplankton in open water was significantly higher in mesosaline lakes. Community composition of invertebrates differed between the two salinity categories: large grazer/detritivores (gastropods and amphipods) were dominant in oligosaline lakes, whereas small planktivores and their insect predators were more prevalent in mesosaline lakes. Both direct physiological effects of salinity, as well as a shift in the form of primary production from macrophytes to phytoplankton, probably explain these changes in community composition. Salinity effects on invertebrate communities appear to be less important to top avian consumers than are costs of osmoregulation.     

Effects of episodic acidification on macroinvertebrate assemblages in Swiss Alpine streams

1. Despite long‐standing ecotoxicological evidence that episodes of acidification in streams are important biologically, there is still uncertainty about their effects on invertebrate communities. We surveyed 20 streams in an acid sensitive Alpine area (Canton Ticino, Switzerland), where episodes are driven by snowmelt in spring and by rainstorms at other times of the year. Samples of water and macroinvertebrates were collected in pre‐event conditions (winter and summer) and during periods of high flow (spring and autumn). 2. Using pH, [Ca²⁺] and [Alⁿ⁺], streams were clustered into six acid–base groups that were either well buffered (groups 4–6), soft‐water with stable pH (group 3), or poorly buffered with low pH at high flow (groups 1 and 2). 3. Severe episodes occurred during snowmelt, when the group 1 streams became acidic with pH down to 5.0 and [Alⁿ⁺] up to 140 μg L^?1. pH declined to 6.2 in streams of group 2, but remained > 6.6 in groups 3–6. 4. Detrended canonical correspondence analysis showed that the streams sensitive to episodes (groups 1 and 2) had different invertebrate assemblages from well‐buffered sites (groups 4 and 5) or soft‐water stable streams (group 3), with faunal differences largest following spring snowmelt. Empididae, Isoperla rivulorum, Rhithrogena spp. and Baetis spp. were scarce in streams sensitive to episodes (groups 1 and 2). By contrast, Amphinemura sulcicollis was scarcer in hard‐water streams (groups 4–6). Taxonomic richness was lower in the episodic streams of group 1 than in other streams. 5. Together, these results indicate clear biological differences between acid‐sensitive streams with similar low‐flow chemistry but contrasting episode chemistry. Severe episodes of acidification appear to affect macroinvertebrate assemblages in streams in the southern Swiss Alps.     

Climatic changes and 13-year trends in stream macroinvertebrate assemblages in New South Wales, Australia

Over the period from 1994 to 2007, air and water temperatures in the Australian state of New South Wales (NSW) increased while rainfall and river flows declined. Data on the occurrence of stream macroinvertebrate families in bioassessment samples collected in NSW during this period were examined to see whether a biological response to these climatic and hydrological trends could be discerned. Multiple logistic regression was used to test for long-term trends in the probability of detection of individual macroinvertebrate families within the samples, taking account of the latitude, longitude, altitude, hydraulic habitat, time of year and subsampling method associated with each sample. Of the 124 families and family groups tested, 33 had statistically significant increasing trends, 37 had significantly declining trends and 54 had no significant trend; however, many of the last group were seldom collected and their trend estimates had wide confidence limits. Significant relationships were found between the thermophily and rheophily of the families and the estimated strength and direction of their long-term trends, with families that favour colder waters and faster-flowing habitats more likely to have declined. Although many families showed trends of increasing detection within samples, such trends do not necessarily equate to increasing prevalence in the environment because the extent of wetted habitat has probably declined, especially flowing habitat. In addition, because of likely intrafamilial trait diversity, increasing or apparently increasing families may include species in decline. Many freshwater macroinvertebrate species in NSW may be threatened by anthropogenic climate change, exacerbated by water withdrawals. The thermal tolerances, rheophily and other pertinent traits of individual species need to be determined to identify those most at risk.     

梯级水坝运行对漫湾库区底栖动物群落结构及分布格局的影响

底栖动物是对水生态系统退化和生境条件改变最为敏感的生物类群之一,同时也是开展梯级水坝水生态系统变化和演替研究的指示生物.本研究以国际生物多样性保护及水电梯级开发生态影响研究的热点地区澜沧江中下游为例,以澜沧江干流兴建的第一座水坝漫湾库区为研究区域,分别于2011和2016年开展底栖动物定点采样,并结合其蓄水前(自然河段,1996年)和单级水坝蓄水初期(1997年)的历史调研数据,全面分析了梯级水坝运行前后漫湾库区底栖动物群落的结构、分布格局及演变趋势.结果表明: 漫湾库区底栖动物群落的优势种组成逐渐由寡毛纲和昆虫纲种类演变为软体动物门类占绝对优势;沿库区生境的纵向梯度变化,底栖动物密度和生物量均表现为升高的趋势,而静水区增加更为显著;对底栖动物功能摄食群的分析表明,静水区由掠食者和收集者占优势演变为滤食者类占绝对优势;梯级水坝运行后,采用生物指数评价结果表明,2016年库区综合水质指标明显优于2011年.漫湾库区底栖动物群落的演变与上游梯级小湾水坝的调度运行及库区的水文状况和泥沙淤积情况密切相关,并随着梯级水坝的运行处于动态变化之中.     

Longitudinal patterns of invertebrates in the hyporheic zone of a glacial river

1. Longitudinal changes in physicochemical factors and the composition of the invertebrate community were examined in the hyporheic zone of a glacial river (Val Roseg, Switzerland) over a distance of 11 km from the glacier terminus. Multivariate analysis was used to determine the habitat preferences of taxa along an upstream‐downstream gradient of increasing temperature and groundwater contribution to river flow. 2. The hyporheos conformed to the longitudinal distribution model described for zoobenthic communities of glacial rivers in that taxonomic richness increased with distance from the glacier terminus. Spatial variation in taxonomic richness was best explained by temperature, the influence of groundwater, and the amount of organic matter. The overriding importance of these variables on the distribution of taxa was confirmed by the multivariate analysis. 3. The hyporheic zone contributed significantly to the overall biodiversity of the Roseg River. Whereas insect larvae were predominant in the benthos, hyporheic invertebrates were dominated by taxa belonging to the true groundwater fauna and the permanent hyporheos. Several permanently aquatic taxa (e.g. Nematoda, Ostracoda, Cyclopoida, Harpacticoida, Oligochaeta) appeared exclusively in the hyporheic zone or they extended farther upstream in the hyporheic layer than in the benthic layer. Leuctridae, Nemouridae, and Heptageniidae colonised hyporheic sediments where maximum water temperature was only 4 °C. 4. Despite strong seasonal changes in river discharge and physicochemistry in hyporheic water, the density and distribution of the hyporheos varied little over time. 5. Taxonomic richness increased markedly in the downstream part of a floodplain reach with an extensive upwelling zone. Upwelling groundwater not only maintained a permanent flow of water but also created several species‐rich habitats that added many species to the community of the main channel.     

Longitudinal patterns of dissolved organic carbon concentration and suspended bacterial density along a blackwater river

Dissolved organic carbon (DOC) is the dominant form of carbon in transport in blackwater rivers, and bacteria are the major biological agents of its utilization. This study describes longitudinal patterns in DOC concentration and relates them to suspended bacterial populations in the channel. Concentrations of total DOC, three molecular weight fractions, and bacterial numbers were determined at 12 sites along the Ogeechee River in 1985–1986 and 1989 during periods of low and high discharge. Suspended bacterial populations were compared with DOC concentrations to determine if differences in bacterial abundance were related to longitudinal patterns of DOC concentration. Three distinct longitudinal patterns were observed: (1) The longitudinal pattern followed by both total and intermediate molecular weight DOC concentrations was a linear function of the geographic distance along the river. (2) During low flow conditions, there was a high degree of correspondence between patterns of bacterial numbers and low MW DOC (< 1000 apparent MW). (3) During periods of high discharge, the proportion of high (> 10,000) and intermediate (1000–10,000) MW fractions increased, and there was no longer a clear relationship between bacterial cells and low MW DOC.     

Macroinvertebrate community structure in relation to environmental variables in a Swiss glacial stream

1. Benthic macroinvertebrate distribution was examined in relation to channel characteristics (including stability), substratum, hydraulic variables, primary production (chlorophyll a ) and coarse particular organic matter (CPOM) in an alpine glacial stream, the Mutt (Upper Rhône valley, Switzerland). Co-inertia analysis and canonical correspondence analysis were used to identify the major environmental gradients influencing community variations.
2. The Mutt (length: 3.6 km, altitudinal range: 1800–3099 m a.s.l.) exhibited typical characteristics of a kryal stream. Average summer temperature remained below 2 °C immediately downstream from the snout but was on average 5 °C higher 1700 m downstream. Seasonal variations in water sources were evidenced by the high late-summer (September) contribution of groundwater with increased conductivity.
3. Sixty-six taxa were recorded from the five reaches sampled at three periods (snowmelt, ice melt and low water in late summer) in 1996 and 1997, of which 29 were Chironomidae. Three taxa of Diamesinae were the first colonizers of the stream below the glacier, but 16 taxa, including Ephemeroptera, Plecoptera and Trichoptera, were already recorded 200 m downstream. Water depth, channel slope and Pfankuch's Index of channel stability were strongly correlated with the longitudinal faunal gradient. Maximum temperature, current velocity and water conductivity were also correlated, but to a lesser extent.
4. The rapid incorporation of non-chironomid taxa into the stream community represented a departure from Milner & Petts's (1994) conceptual model of invertebrate succession downstream of glacial margins. The results confirmed that glacial stream communities are primarily driven by physical determinants.     

Thermal patterns in the surface waters of a glacial river corridor (Val Roseg, Switzerland)

SUMMARY 1. We examined the thermal patterns of the surface waters in the catchment of the Roseg River, which is fed by the meltwaters of two valley glaciers. One of the glaciers has a lake at its terminus. The river corridor comprised a proglacial stream reach below one glacier, the glacier lake outlet stream, a 2.5‐km long complex floodplain and a constrained reach extending to the end of the catchment. 2. Temperatures were continuously measured with temperature loggers at 27 sites between 1997 and 1998. Moreover, from 1997 to 1999, spot measurements were taken at 33–165 floodplain sites (depending on water level) at monthly intervals. 3. The temperature regime of glacial streams, including the glacier lake outlet, was characterised by rapidly increasing temperatures in April and May, a moderate decline from June to September (period of glacial melt) and a subsequent fast decline in autumn. During summer, the lake increased temperatures in the outlet stream by 2–4 °C, compared with the adjacent proglacial stream reach. 4. In the main channel (thalweg) of the Roseg River, annual degree‐days (DD) ranged from 176 DD in the upper proglacial reach to 1227 DD at the end of the catchment. 5. Thermal variation among different channels within the floodplain was higher than the variation along the entire main channel. Floodplain channels lacking surface connection to the main channel accumulated up to 1661 annual DDs. 6. Thermal heterogeneity within the floodplain was linked to the glacial flow pulse. With the onset of ice melt, temperatures in the main channel and in channels surface‐connected to the main channel began to decline, whereas in surface‐disconnected channels temperatures continued to increase; as a consequence, thermal heterogeneity at the floodplain scale rose slightly until September. 7. High thermal heterogeneity was not anticipated in the harsh environment of a largely glacierised alpine catchment. The relatively wide range of thermal environments may contribute to the highly diverse zoobenthic community.     

Comparative study on macroinvertebrate communities along a reservoir cascade in Xiangxi River Basin

Three cascade reservoirs (Gudongkou Reservoir 1 (GR1), Gudongkou Reservoir 2 (GR2), and Xiangxi Bay of Three-Gorge Reservoir in Xiangxi River Basin, China were selected to investigate macroinvertebrate ecology in a cascade reservoir system. Principal Components Analysis (PCA) implied that water quality was degrading along the reservoir cascade. Non-metric Multidimensional Scaling (NMS) showed that sampling stations located in the lacustrine zone of a reservoir are representatives in comparing macroinvertebrate assemblages along the reservoir cascade. Oligochaetes were numerically dominant in both GR1 and Xiangxi Bay, and chironomids were dominant in GR2. A similar pattern was also exhibited in taxon composition. Benthic assemblages of the 3 reservoirs were all dominated by pollution-tolerant taxa in spite of their differences in water quality. Canonical Correspondence Analysis (CCA) disclosed that turbidity influenced the benthic assemblages significantly. Total organic carbon (TOC)/Turbidity was applied to determine the influence of organic matter on turbidity. The ratio in GR2 was the lowest among the 3 reservoirs, which implicated that the influence of organic matter on turbidity was smaller in GR2 than in the other 2 reservoirs, suggesting that inorganic matter contributed substantially to the turbidity of GR2.     

Comparative study on macroinvertebrate communities along a reservoir cascade in Xiangxi River Basin

Three cascade reservoirs (Gudongkou Reservoir 1 (GR1), Gudongkou Reservoir 2 (GR2), and Xiangxi Bay of Three-Gorge Reservoir in Xiangxi River Basin, China were selected to investigate macroinvertebrate ecology in a cascade reservoir system. Principal Components Analysis (PCA) implied that water quality was degrading along the reservoir cascade. Non-metric Multidimensional Scaling (NMS) showed that sampling stations located in the lacustrine zone of a reservoir are representatives in comparing macroinvertebrate assemblages along the reservoir cascade. Oligochaetes were numerically dominant in both GR1 and Xiangxi Bay, and chironomids were dominant in GR2. A similar pattern was also exhibited in taxon composition. Benthic assemblages of the 3 reservoirs were all dominated by pollution-tolerant taxa in spite of their differences in water quality. Canonical Correspondence Analysis (CCA) disclosed that turbidity influenced the benthic assemblages significantly. Total organic carbon (TOC)/Turbidity was applied to determine the influence of organic matter on turbidity. The ratio in GR2 was the lowest among the 3 reservoirs, which implicated that the influence of organic matter on turbidity was smaller in GR2 than in the other 2 reservoirs, suggesting that inorganic matter contributed substantially to the turbidity of GR2.     

Changes in tropical fish assemblages associated with small-scale fisheries: a case study in the Pacific off central Mexico

Information from artisanal marine fisheries inColima, Mexico is analyzed to find evidence ofchange in the composition of fish assemblagesresulting from fishing pressure. Catchcomposition from up to 20 boats per day, during2 to 6 days a month, were recorded from 1983 to1998. Stability of the species composition wasanalyzed using rank correlation methods, andmeasures of diversity (specific richness,Shannon-Wiener index, evenness) were estimatedfrom data. The resulting time-series wereanalyzed to detect trends. No significantdifferences were found in the number of speciescaught by month nor were significant trends indiversity detected. The composition of the fishassemblages is dynamic. The presence ofpersistent and resilient species that definedthe values obtained of diversity and evennesswas detected, but did not determine thestructure of the community, which is apparentlydefined by other factors. The changes incomposition of the catch probably are aconsequence of environmental fluctuations andrandom events, and not a direct consequence offishing pressures on the fish community.     

基于大型底栖无脊椎动物确定河流营养盐浓度阈值——以西苕溪上游流域为例

水体富营养化是一个全球性的问题,中国也面临严重威胁.目前,中国的水体富营养化研究主要集中在湖泊和水库,对河流的研究极少.根据大型底栖无脊椎动物的群落结构对营养盐胁迫的响应,运用非参数转变点分析方法计算西苕溪上游营养盐浓度突变点.结果表明:总氮和总磷的突变点分别为1.409mg·mL-1和0.033～0.035mg·mL-1.参照点的总氮和总磷浓度基本都低于阈值,城市干扰点则全部高于阈值,而当总氮和总磷超过各自阈值时会导致大型底栖无脊椎动物群落结构的严重退化.通过建立与水生生物群落结构有关的水体营养盐标准,可充分发挥生物监测在水环境管理中的作用,为计算水体中总氮和总磷的最大日负荷总量提供科学数据.