Sediment microbial enzyme activity as an indicator of nutrient limitation in the great rivers of the Upper Mississippi River basin

We compared extracellular enzyme activity (EEA) of microbial assemblages in river sediments at 447 sites along the Upper Mississippi, Missouri, and Ohio Rivers with sediment and water chemistry, atmospheric deposition of nitrogen and sulfate, and catchment land uses. The sites represented five unique river reaches—impounded and unimpounded reaches of the Upper Mississippi River, the upper and lower reaches of the Missouri River, and the entire Ohio River. Land use and river chemistry varied significantly between rivers and reaches. There was more agriculture in the two Upper Mississippi River reaches, and this was reflected in higher nutrient concentrations at sites in these reaches. EEA was highest in the two Upper Mississippi River reaches, followed by the lower Missouri River reach. EEA was generally lowest in the upper Missouri River reach. Canonical correlation analysis revealed a strong correlation between EEA and the suite of water and sediment chemistry variables, and the percent of the catchment in anthropogenically dominated land uses, including agriculture and urban development. Nutrient ratios of the waters and sediments suggested carbon (C), nitrogen (N), or phosphorus (P) limitation at a large number of sites in each reach. C-limitation was most pronounced in the unimpounded Mississippi River and lower Missouri River reaches; N-limitation was prevalent in the two Missouri River reaches; and P-limitation dominated the Ohio River. Linking microbial enzyme activities to regional-scale anthropogenic stressors in these large river ecosystems suggests that microbial enzyme regulation of carbon and nutrient dynamics may be sensitive indicators of anthropogenic nutrient and carbon loading.     

Changes in biota along a dry-land river in northwestern Zimbabwe: declines and improvements in river health related to land use

Macroinvertebrates were sampled from 15 sites along a dry-land river in northwestern Zimbabwe to assess biotic responses to land use changes along the course of the river. The headwater sites were protected by a riparian corridor of native forest, but this was replaced by intensive subsistence agriculture in the mid-reaches while the lower reaches were located within a protected wildlife area with diverse and wide riparian forests. Canonical correspondence analysis indicated that intensive agricultural activities within the mid-reaches caused severe degradation of the stream physical habitat through increased fine sediment deposition. This coincided with a significant decline in macroinvertebrate richness, diversity, and abundance at the agriculturally impacted mid-reach sites. The presence of wide riparian zones at the lower river sites resulted in significant improvements in stream physical habitat quality, and this was paralleled by significant recovery or reappearance of taxa that had disappeared from the mid-reaches. We suggest that restoration of the riparian vegetation within the mid-reaches of the Nyaodza River would lead to improved physical habitat and biotic health of this dry-land river.     

Spatial and seasonal changes in species diversity of epilithic fungi along environmental gradients of a river

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Combined influence of river discharge and wind on littoral nematode communities of a river mouth area of Lake Constance

The littoral nematode community adjacent to a river mouth (River Schussen) on Lake Constance (Germany) was studied from February 1999 to January 2000 in order to determine the influence of stress resulting from fluctuations in river discharge on local nematode assemblages. Additionally, the influence of wind as a second important stress factor was considered. Six sample sites were chosen, reflecting a gradient of river influence within the broader river mouth area. Nematode communities, varying in a mean range from 121 to 165 ind/10 cm², were found to differ significantly in terms of abundance, feeding type composition and species diversity. Deposit feeders were most abundant at all sites followed by chewers. Deposit feeders were affected mainly by wind events, while species diversity and the occurrence of chewers were influenced mainly by river discharge. The impact of both these stress factors was modified by a third variable, water level. Moderate and high levels of combined habitat stress led to significant changes in community structure. Under conditions of calm weather and low discharge, reduced species diversity and an increased predominance of deposit feeders were observed. In most cases, species diversity was found to be higher under moderate stress conditions, an observation that offers support for Connel’s Intermediate Disturbance Hypothesis.     

Impact of agricultural land use on aquatic insect assemblages in the Garonne river catchment (SW France)

The impact of agricultural land use on the composition and structure of aquatic insect assemblages (i.e., taxa of Ephemeroptera, Plecoptera, Trichoptera, and Coleoptera (EPTC)) was investigated in tributary streams of the Garonne river basin, southern France. The self-organizing map (SOM) method was applied to compare both instream environmental conditions and EPTC assemblages between forest and agricultural streams. According to the SOM model, the study sites were classified into three main clusters corresponding to distinct EPTC assemblages. The SOM cluster associated with most of the agricultural sites had lower EPTC species richness and diversity. This cluster was also characterized by high levels of total dissolved solids, nitrate (NO₃), and chemical oxygen demand. Overall, our study shows that agricultural streams when compared with forest streams had lower biological integrity. In accordance with the European Water Framework Directive, our results indicate that the sites most impacted by agricultural land use should be restored and that the least-impacted forest sites could serve as reference conditions.     

Bird assemblages on Amazonian river islands: Patterns of species diversity and composition

The principles of island biogeography are rarely applied to the animal assemblages of Amazonian river islands. Here, we compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages were characterized by lower species richness and a higher abundance of a few dominant species. Additionally, the species composition of the islands was distinct from that of the mainland, including the nearby floodplain habitats. The number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbor an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial communities could be disproportionately threatened by river channel disturbances related to climate change or hydroelectric dam development. Abstract in Portughese is available with online material.     

Response of biota to land use changes and water quality degradation in two medium-sized river basins in southwestern Greece

To assess biotic responses to anthropogenic pressures, a seasonal monitoring of benthic macroinvertebrates, physicochemical and hydromorphological parameters has been applied in 11 sites along two highly impacted river basins in southwestern Greece, mainly during the year 2006. In the first river basin, the upper reaches were covered by thick riparian forest, replaced by intensive agriculture and livestock in the mid-reaches, while the lower parts were characterized mainly by agroindustrial activities. The second river basin was impacted by the discharge of raw cheese whey effluents in the mid-reaches, while the lower parts were protected by thick riparian vegetation. The mid- and lower parts of the first river basin (Peiros–Parapeiros rivers) were impaired by dam constructions, agricultural intensity and urbanization. In the second river basin (Vouraikos river), the 3/5 of the river length, located in the mid-reaches, was degraded due to the discharge of untreated cheese whey effluents. Water quality of the lower reaches was highly recovered due to the presence of thick riparian vegetation. Macroinvertebrate diversity was strongly correlated to pollution, as sites with major physicochemical and hydromorphological degradation presented low taxonomic richness and diversity values, while non-impacted sites were characterized by a considerable presence of E.P.T. taxa and higher diversity. The current study indicates the significant impact of land use changes to the water quality, which consequently influence the distribution of biota, pointing out the critical role of the riparian vegetation to the detoxification of surface waters.     

The fish populations of an industrial river in South Wales

The River Sirhowy, a trout river of the Ebbw System in south-east Wales still subject to sporadically high levels of suspended solids derived from the coal mining industry, was investigated over a three year period to assess its importance in the recolonization of a fishless river, the Ebbw Fawr, which is expected to recover from the effects of steelworks effluents discharged near its headwaters. Eight species of fish were recorded. Spawning areas for brown trout ( Salmo trutta L.) were limited by industrial and urban developments and the discharge of suspended solids. Small numbers of native trout were produced in the system and the growth of these fish was poor in the main river, confirming the need for regular stocking. Movements of stocked trout were limited except in the lower reaches of the river where the presence of a native population, high levels of suspended solids and flash floods may have increased the numbers of fish moving into the recovering Ebbw Fawr.     

Valley‐scale hydrogeomorphology drives river fish assemblage variation in Mongolia

River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley‐scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence‐ and abundance‐based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance‐based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley‐scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley‐scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.     

Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology

This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems. Handling editor: J. Trexler     

长江流域鱼类物种多样性大尺度格局研究

作者以长江流域鱼类编目数据库为基础数据,研究了长江流域鱼类物种多样性的大尺度格局。长江流域内共记录了鱼类378种(亚种),隶属于14目32科144属。其中淡水鱼338种(亚种),以鲤形目为主,达到269种(亚种),洄游鱼类11种,河口鱼类29种;流域内特有种和受威胁物种分别有162种(亚种)和69种(亚种)。根据鱼类分布特点,按水系将长江流域分为19个区域,除了江源区和金沙江中上游外,物种数和G-F多样性指数上游高于中下游,但各区域内差异不大,然而特有种比例从上游到下游随海拔降低而逐渐降低。利用Jaccard物种相似性系数对19个区域进行聚类分析,将整个流域分成三部分:(1)江源区和金沙江中上游,地理上属于青藏高原东南部波状平原部分和横断山区,(2)上游其他流域,地理上属于川西高原、云贵高原、四川盆地及秦巴山区,(3)中下游流域,地理上属于淮阳山地、江南丘陵和长江中下游平原,基本反映了流域内自然地理环境及我国大陆地势三级台阶变化的特点。     

Catchment-scale biogeography of riverine bacterioplankton

Lotic ecosystems such as rivers and streams are unique in that they represent a continuum of both space and time during the transition from headwaters to the river mouth. As microbes have very different controls over their ecology, distribution and dispersion compared with macrobiota, we wished to explore biogeographical patterns within a river catchment and uncover the major drivers structuring bacterioplankton communities. Water samples collected across the River Thames Basin, UK, covering the transition from headwater tributaries to the lower reaches of the main river channel were characterised using 16S rRNA gene pyrosequencing. This approach revealed an ecological succession in the bacterial community composition along the river continuum, moving from a community dominated by Bacteroidetes in the headwaters to Actinobacteria-dominated downstream. Location of the sampling point in the river network (measured as the cumulative water channel distance upstream) was found to be the most predictive spatial feature; inferring that ecological processes pertaining to temporal community succession are of prime importance in driving the assemblages of riverine bacterioplankton communities. A decrease in bacterial activity rates and an increase in the abundance of low nucleic acid bacteria relative to high nucleic acid bacteria were found to correspond with these downstream changes in community structure, suggesting corresponding functional changes. Our findings show that bacterial communities across the Thames basin exhibit an ecological succession along the river continuum, and that this is primarily driven by water residence time rather than the physico-chemical status of the river.     

Small and impoverished regional species pools constrain colonisation of restored river reaches by fishes

1. Using an extensive data set from 18 river restoration projects in the lower mountain ranges of Germany and 5462 river reaches in their surroundings, we estimated the spatial extent of the regional fish species pool from which restored river reaches are colonised. 2. Restoration resulted in a marginally significant increase in fish species richness; however, restored reaches still deviated markedly from natural reference conditions. Nearly all (96.6%) species occurring in restored reaches were present in reaches within a distance of 5 km up‐ or downstream of the restored reach. 3. Species richness in restored reaches was correlated with species richness within a 5‐km species pool. This relationship was more pronounced for common than for rare fishes and applied to both the total number of fish species at the restored reach and the number of additional fish species that were not present at unrestored conditions. 4. The richness of the regional species pools was greatly impoverished. On average, only 50% of all species considered to represent natural reference assemblages were present. The limited success in establishing natural fish assemblages in restored reaches was attributed to spatial limitation (e.g. due to fragmentation) and an impoverished regional species pools from which restored reaches recruit. 5. We recommend that integrated river restoration management should consider not only the abiotic prerequisites of successful restorations, but also the structure and quality of the regional species pool.     

Fish assemblage changes over half a century in the Yellow River,China

Riverine environments have been threatened by anthropogenic perturbations worldwide, whereby their fish assemblages have been modified by habitat changes and nonendemic species invasions. We assessed changes in fish assemblages by comparing the species presence in historical and contemporary fish data in the Yellow River from 1965 to 2015. The temporal change in species assemblages was found with increased nonendemic species and fewer natives. Fish species richness of the river declined 35.4% over the past fifty years. Moreover, the decreased mean Bray–Curtis dissimilarity among reaches suggested that the fish assemblages of different reaches in the Yellow River were becoming more similar over time. However, temporal patterns of fish assemblages varied among reaches. In the upper Yellow River, higher species richness and more invasive species were found than those in the historical record, while the lower reaches experienced significant species loss. Dam constructions, exotic fish invasions, and flow reductions played the vital role in structuring the temporal fish assemblages in the Yellow River. It is suggested that river basins which experienced different types and levels of stressors by anthropogenic perturbations can produce varied effects on their temporal trends of species assemblages.     

Longitudinal changes in macroinvertebrate assemblages along a glacial river system in central Iceland

1. Macroinvertebrate assemblages were studied in the glacial river West-Jökulsá, originating from the Hofsjökull Ice Cap in central Iceland at an altitude of 860 m. Sampling sites were distributed from the source to 45 km downstream at 160 m a.s.l. Comparative studies were carried out on non-glacial rivers and tributaries in the area, at similar altitudes and distances from the glacial source.
2. Detrended correspondence analysis (DCA) demonstrated that species composition of benthic macroinvertebrates was related to the distance from the glacier. Assemblages at sampling sites furthest from the glacier were similar in species composition to sites in non-glacial rivers. Temporal variation was small compared with longitudinal zonation.
3. Based on canonical correspondence analysis (CCA) of data from the main glacial river, distance from the glacier, altitude, bryophyte biomass and the Pfankuch Index of channel stability were the measured explanatory variables having a significant effect on the structure of macroinvertebrate assemblages, accounting for 31% of the total variation in the data set. When data from all the rivers were analysed, altitude, bryophyte biomass, channel slope, suspended sediment concentration and maximum water temperature explained 21% of the variance.
4. Macroinvertebrate communities were in general agreement with the predictions of the conceptual model of Milner & Petts (1994) for the upstream reaches. The assemblages consisted mainly of Orthocladiinae and Diamesinae (Chironomidae), although other taxa such as Simuliidae, Plecoptera and Trichoptera were also found in low numbers. Shredders were lacking from the benthic communities, apparently because of continued glacial influence in the river even 45 km downstream from the glacier and lack of allochthononus inputs from riparian vegetation.     

Stream macroinvertebrate communities in a conifer‐afforested catchment in Ireland: relationships to physico‐chemical and biotic factors

1. The influence of land use and physico-chemical factors on stream macroinvertebrates was analysed at fifteen sites over a 2-year period in a single conifer-afforested catchment in Ireland, in an area subject to very low levels of atmospheric pollution. 2. Macroinvertebrate assemblages were classified using two-way indicator species analysis into five major groupings that were related to distance from headwaters and land use. Trends in macroinvertebrate community composition were related to changes in physico-chemical and biotic characteristics of the river and its tributaries using canonical correspondence analysis. 3. Local ecological factors (e.g. acid water, moss, shading or agricultural runoff), longitudinal trends in stream physico-chemistry (related to distance from headwaters, geology and land use) and season (related to life history patterns of the invertebrates) were the explanatory variables of spatio-temporal patterns in macroinvertebrate community composition in the catchment. 4. Spatial variation in macroinvertebrate density, taxon richness, diversity and evenness was investigated in relation to environmental characteristics of the study sites using Spearman’s rank correlation, principal components analysis and stepwise multiple regression. Invertebrate density and richness increased with distance from the headwater and associated increases in pH, water hardness and nutrients. Macroinvertebrate density and richness also increased with increasing moss weight. Invertebrate diversity and evenness increased with shading of the channel. 5. The increase in macroinvertebrate density and richness and changes in community composition were particularly marked over a relatively short (1.2 km) distance in one tributary, and were concurrent with a rapid increase in stream pH of 1.7 units. 6. Although macroinvertebrate communities at conifer-afforested sites were not impoverished in the same way as those in some other parts of Europe, they differed from the communities found above and below the plantation. This appeared to be owing to the primary importance of local ecological factors and the effect that the longitudinal position of these forest sites within the river system had on their physico-chemical and biotic nature.     

The influence of flow impoundment and river regulation on the distribution of riverine macroinvertebrates at Mammoth Cave National Park, Kentucky, U.S.A.

The effects of impoundment by a low-head dam and hypolimnetic release from a reservoir on benthic macroinvertebrate assemblages were studied in two lowland rivers. The first river (Green River) was initially divided into three zones (impounded, transitional, erosional) according to hydrological characteristics. The entire reach of the second river (Nolin River) was a regime unit. Only the Green River erosional zone was free-flowing with a linear sequence of riffle-run-pool reaches. A detrended correspondence analysis showed that the Green River impounded and transitional zones were taxonomically indistinguishable while the Green River erosional zone and the Nolin River were each distinct. A canonical correspondence analysis revealed that higher surface velocity, higher summer water temperatures and more turbid conditions, and lower water temperatures were contributing parameters to the separation of the Green River erosional zone, Green River transitional/impounded zones, and the Nolin River, respectively, in ordination space. A series of one-way ANOVA’s testing for differences of macroinvertebrates assemblages between the three Green River zones according to five metrics showed that the Green River erosional zone demonstrated significantly higher values and the transitional and impounded zones were ecologically similar.     

Assessing the impact of gold mining in headwater streams of Eastern Amazonia using Ephemeroptera assemblages and biological traits

Whilst the biological traits composition of invertebrate assemblages has been successfully used to monitor temperate rivers, it has been seldom tested in tropical areas. We compared the trait composition of Ephemeroptera assemblages (five traits, 21 modalities) in three categories of headwater streams of FG: reference (undisturbed) sites, sites formerly impacted by gold-mining, and sites currently impacted by gold-mining. Differences in macroinvertebrate assemblage according to environmental characteristics and disturbance were evaluated using correspondence analysis and MANOVA. Among the considered traits, food acquisition, respiration and locomotion detected both past and current disturbance associated with gold-mining in headwaters. A fuzzy correspondence analysis showed a significant segregation of currently gold-mined, formerly gold-mined, and reference sites according to species traits. Shifts in trait composition were mostly related to changes in assemblage composition. Interestingly, no significant decline in diversity indices was observed in formerly gold-mined sites compared to the reference sites, 2 years after abandonment, while the taxonomic and trait composition of communities changed at these sites. These results support the case for further fundamental quantification of species traits, and for the inclusion of sensitive, trait-related metrics in upcoming multimetric indices for the assessment of river health.     

Habitat associations of imperilled fishes after conservation intervention in the Cape Fold Ecoregion,South Africa

The aim of this study was to examine the habitat associations of a native cyprinid community of the recovering Rondegat River in the Cape Fold Ecoregion of South Africa as part of a long-term native fish abundance monitoring project. Relative abundance data were extracted from underwater video camera footage across the longitudinal gradient of the river in three sampling instances. Using multivariate methods the authors assessed community composition with respect to habitat, its overlap with a protected area and species-specific abiotic predictors of relative abundance. Distance from the uppermost site in the river was the most significant predictor of species abundance, indicating spatial segregation and varying overlap between species. The protected status of sites in the upper reaches, vegetated substrates and the size of individual sites were the most impactful on the relative abundance of the endangered fiery redfin Pseudobarbus phlegethon. The results of this study indicate that underwater video monitoring is an effective and low-cost approach that can inform conservation recommendations. Reducing agricultural runoff and sedimentation in the lower reaches may be useful further interventions to maintain key habitats of submerged vegetation.     

Functional diversity and trait–environment relationships of stream fish assemblages in a large tropical catchment

1. The species composition of stream fish assemblages changes across the longitudinal fluvial gradient of large river basins. These changes may reflect both zonation in species distributions and environmental filtering of fish traits as stream environments change from the uplands to the lowlands of large catchments. Previous research has shown that taxonomic diversity generally increases in larger, lowland streams, and the River Continuum Concept, the River Habitat Template and other frameworks have provided expectations for what functional groups of fishes should predominate in certain stream types. However, studies addressing the functional trait composition of fish assemblages across large regions are lacking, particularly in tropical river basins. 2. We examined functional trait–environment relationships and functional diversity of stream fish assemblages in the Río Grijalva Basin in southern Mexico. Traits linked to feeding, locomotion and life history strategy were measured in fishes from streams throughout the catchment, from highland headwaters to broad, lowland streams. Relationships between functional traits and environmental variables at local and landscape scales were examined using multivariate ordination, and the convex hull volume of trait space occupied by fish assemblages was calculated as a measure of functional diversity. 3. Although there were a few exceptions, functional diversity of assemblages increased with species richness along the gradient from uplands to lowlands within the Grijalva Basin. Traits related to swimming, habitat preference and food resource use were associated with both local (e.g. substratum type, pool availability) and landscape‐scale (e.g. forest cover) environmental variables. 4. Along with taxonomic structure and diversity, the functional composition of fish assemblages changed across the longitudinal fluvial gradient of the basin. Trait–environment relationships documented in this study partially confirmed theoretical expectations and revealed patterns that may help in developing a better understanding of general functional responses of fish assemblages to environmental change.