Effects of hydropower-induced flow perturbations on mayfly (Ephemeroptera) richness and abundance in north Swedish river rapids

Mayfly species richness and abundance were investigated at 52 Swedish river rapids. These were either unregulated, or regulated with or without reduced discharge. Sites impacted by regulation had lower mayfly richness and abundances than unregulated reference sites. The relative importance of reduced discharge, daily fluctuations in flow, flow constancy, and the distance to nearest rapid (as a measure of isolation) was evaluated in multiple regression analyses. These indicated negative effects of diel fluctuations on both abundance and richness, whereas flow constancy was favourable for richness. Neither the distance to nearest rapid nor reduced flow were significantly related to mayfly richness and abundance. In total, 26 mayfly species were recorded. Only Baetis rhodani was found at all sites, but another five species were present at more than 40 sites. The strongest effects were found for species within the Heptageniidae. Nineteen of 20 mayfly species present in both the regulated (with unreduced flow) and unregulated reference rapids were on average more common in the unregulated ones. Mayfly assemblage structure was primarily influenced by regional factors and nutrient status, although daily fluctuations in flow together with rapids dimensions also had a significant influence. No rare species appears to be threatened by hydropower regulation though it is conceivable that depressed abundances in regulated rivers indirectly influence predators and periphyton.     

Response of fringing vegetation to flooding and discharge of hypersaline water at Lake Austin,Western Australia

Patterns and dynamics of the salt marsh vegetation that surrounds many of the salt lake systems of arid/semi-arid Australia are poorly known. Lake Austin is a very large salt lake with extensive areas of fringing salt marsh; it is located in the arid Yilgarn Region of Western Australia. In this study, the changes in this vegetation over a 4-year period (1998–2002), during which both a major flooding event and addition of hypersaline groundwater from a nearby mining operation occurred, are reported. The monitoring program, based on Before-After-Control-Impact (BACI) principles, was designed to detect impacts of discharging hypersaline water into the lake; however, the flooding event, the result of above average rainfall in early 2000, complicated the results. The rains of 2000 and subsequent inundation of the vegetation immediately fringing the lake bed and major inlet channels resulted in dramatic changes to the species composition of annual and short-lived species and growth of perennial species. Flooding resulted in substantial death and damage to perennial shrubs (particularly Halosarcia fimbriata) due most likely to a combination of several weeks/months of inundation and smothering by macroalgae and Ruppia, with smaller plants and those closer to the lake bed impacted upon to a greater degree. Seed germination and recruitment of new Halosarcia plants was substantial as floodwaters receded with the majority of these seedlings surviving some 2 years after flooding despite the severe drought that followed the flood. Growth rates of seedlings differed substantially and were linked to subtle differences in micro-topography. Recruitment following flooding was also demonstrated in in vitro experiments involving inundated soil cores, provided water was relatively non-saline (conductivity <30 mS cm⁻¹). A conceptual model is proposed to explain changes in fringing vegetation in response to frequency, depth, period and salinity of flooding in relation to micro-topography. Despite the profound effect of flooding, impacts of discharge were identified, with changes in topsoil pH and salinity greater in areas closer to the discharge than those further away. Impacts on vegetation characteristics were not detected. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Spatial variability in nitrification rates and ammonia-oxidizing microbial communities in the agriculturally impacted Elkhorn Slough estuary, California

Ammonia oxidation-the microbial oxidation of ammonia to nitrite and the first step in nitrification-plays a central role in nitrogen cycling in coastal and estuarine systems. Nevertheless, questions remain regarding the connection between this biogeochemical process and the diversity and abundance of the mediating microbial community. In this study, we measured nutrient fluxes and rates of sediment nitrification in conjunction with the diversity and abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing betaproteobacteria (β-AOB). Sediments were examined from four sites in Elkhorn Slough, a small agriculturally impacted coastal California estuary that opens into Monterey Bay. Using an intact sediment core flowthrough incubation system, we observed significant correlations among NO(3)(-), NO(2)(-), NH(4)(+), and PO(4)(3+) fluxes, indicating a tight coupling of sediment biogeochemical processes. (15)N-based measurements of nitrification rates revealed higher rates at the less impacted, lower-nutrient sites than at the more heavily impacted, nutrient-rich sites. Quantitative PCR analyses revealed that β-AOB amoA (encoding ammonia monooxygenase subunit A) gene copies outnumbered AOA amoA gene copies by factors ranging from 2- to 236-fold across the four sites. Sites with high nitrification rates primarily contained marine/estuarine Nitrosospira-like bacterial amoA sequences and phylogenetically diverse archaeal amoA sequences. Sites with low nitrification rates were dominated by estuarine Nitrosomonas-like amoA sequences and archaeal amoA sequences similar to those previously described in soils. This is the first report measuring AOA and β-AOB amoA abundance in conjunction with (15)N-based nitrification rates in estuary sediments.     

Vertical profiles of water and sediment denitrifiers in two plateau freshwater lakes

The present study investigated the abundance, richness, diversity, and community composition of denitrifiers (based on nirS and nosZ genes) in the stratified water columns and sediments in eutrophic Dianchi Lake and mesotrophic Erhai Lake using quantitative PCR assay and high-throughput sequencing analysis. Both nirS- and nosZ denitrifiers were detected in waters of these two lakes. Surface water showed higher nosZ gene density than bottom water, and Dianchi Lake waters had larger nirS gene abundance than Erhai Lake waters. The abundance of sediment nirS- and nosZ denitrifiers in Dianchi Lake was larger than that in Erhai Lake. nirS richness and diversity and nosZ richness tended to increase with increasing sediment layer depth in both lakes. The distinct structure difference of sediment nirS- and nosZ denitrifier communities was found between in Dianchi Lake and Erhai Lake. These two lakes also differed greatly in water denitrifier community structure. Moreover, phylogenetic analysis indicated the presence of several different groups of nirS- or nosZ denitrifiers in both lakes. The novel nirS denitrifiers were abundant in both Dianchi Lake and Erhai Lake, while most of the obtained nosZ sequences could be affiliated with known genera.

     

Agricultural Risk Factors Influence Microbial Ecology in Honghu Lake

Agricultural activities, including stock-farming, planting industry, and fish aquaculture,can affect the physicochemical and biological characters of freshwater lakes. However, the effects of pollution producing by agricultural activities on microbial ecosystem of lakes remain unclear.Hence, in this work, we selected Honghu Lake as a typical lake that is influenced by agriculture activities. We collected water and sediment samples from 18 sites, which span a wide range of areas from impacted and less-impacted areas. We performed a geospatial analysis on the composition of microbial communities associated with physicochemical properties and antibiotic pollution of samples. The co-occurrence networks of water and sediment were also built and analyzed. Our results showed that the microbial communities of impacted and less-impacted samples of water were largely driven by the concentrations of TN, TP, NO_3^--N, and NO_2^--N, while those of sediment were affected by the concentrations of Sed-OM and Sed-TN. Antibiotics have also played important roles in shaping these microbial communities: the concentrations of oxytetracycline and tetracycline clearly reflected the variance in taxonomic diversity and predicted functional diversity between impacted and less-impacted sites in water and sediment samples, respectively. Furthermore, for samples from both water and sediment, large differences of network topology structures between impacted and less-impacted were also observed. Our results provide compelling evidence that the microbial community can be used as a sentinel of eutrophication and antibiotics pollution risk associated with agricultural activity; and that proper monitoring of this environment is vital to maintain a sustainable environment in Honghu Lake.     

Using predictive models to estimate effects of flow regulation on net-spinning caddis larvae in North Swedish rivers

1. Effects of flow regulation on abundance and richness of net-spinning caddis larvae (Hydropsychoidea; Trichoptera) were examined in fifty-two North Swedish rivers. Models based on conditions at unregulated sites were used to predict densities at impacted sites and the residuals, i.e. the differences between observed and predicted numbers, were used as measures of the effects.
2. Two broad categories of impacted sites were identified. Sites with regulated but unreduced flow often have reduced seasonal flow variation and slightly enhanced short-term variation, while those with reduced flow usually have long periods of low and stable flow occasionally interrupted by short periods of violently fluctuating flow.
3. The abundance of net-spinning caddis larvae was significantly lower than predicted at both types of sites (reduction 30%), while richness was significantly reduced only at sites with reduced flow (reduction 20%).
4. A subsequent analysis of the relationship between the effects and variables altered by flow regulations, e.g. flow magnitude and flow variation, indicated that species richness was primarily affected by the occurrence of periods with zero flow, while negative effects of abundance were associated with high flow variability.
5. Significant negative effects on the abundance of individual taxa were observed for Cheumatopsyche lepida and Hydropsyche pellucidula at sites with regulated but unreduced flow.
6. Analyses of the relationships between the effects and regulation-related variables suggest that H. siltalai was significantly negatively affected by the occurrence of zero flow and that negative effects on Arctopsyche ladogensis were associated with flow reduction and high flow variability.     

柴达木盆地尕斯库勒盐湖区邻近水体对湖泊微生物群落的贡献

【目的】探究尕斯库勒盐湖生态系统中邻近水体对湖泊微生物的贡献。【方法】采集尕斯库勒盐湖区湖水、沉积物以及邻近的泉水、河水和盐田的水样,对其进行地球化学分析;通过16S rRNA基因的Illumina MiSeq高通量测序分析样品的微生物群落组成。【结果】尕斯库勒盐湖区水体和沉积物中的优势门是变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、放线菌门(Actinobacteria)和广古菌门(Euryarchaeota)。盐度和pH是影响尕斯库勒盐湖区群落组成的最主要环境因素。邻近水体对湖泊水体和沉积物的贡献分别为12.94%和7.53%。【结论】邻近水体对尕斯库勒盐湖微生物群落的贡献有限。     

A Century of Change in Macrophyte Abundance and Composition in Response to Agricultural Eutrophication

Clear Lake, Iowa, USA is a shallow, agriculturally eutrophic lake that has changed drastically over the past century. Eight macrophyte surveys since 1896 were pooled and examined to characterize long-term impacts of eutrophication on macrophyte community composition and relative abundance. Surveys in 1981 and 2000 revealed few submergent and floating-leaved species and a dominance in emergent species (Scirpus, Typha). Over the past century, however, species richness has declined from a high of 30 species in 1951 to 12 found today, while the community composition has shifted from submergent-(99%) to emergent-dominated floras (84%). Potamogeton praelongus was the first emergent species to disappear but was followed by several other clear water Potamogeton species. Several floating leaved and emergent genera increased in relative abundance with eutrophication, notably Nuphar, Nymphaea, Phragmites, Polygonum, Sagittaria, Scirpus, and Typha. P. pectinatus was present over the entire century due to its tolerance of eutrophic conditions. Macrophyte growth was generally light-limited, with 93% of the variance in relative abundance of submergent species explained by changes in water transparency. Clear Lake exhibits signs of alternative stable states, oscillating between clear and turbid water, coupled with high and low submerged species relative abundance. The maximum macrophyte richness occurred as the lake oscillated between submergent- and emergent-dominated states. Changes in the water level have also impacted macrophyte growth since the area of the lake occupied by emergent macrophytes was negatively correlated with water level. Strongest correlations indicated that macrophytes respond to water level variations with a 2-year time-lag.     

Patterns of chironomid body-size distribution in an effluent-impacted river in the Eastern Cape,South Africa

Body size is an important determinant of assemblage structure in rivers and streams impacted by elevated concentrations of pollutants such as salts and metals. In the present study, because of the larger surface-area-tovolume ratio of small-bodied chironomid species compared with large-bodied species, it was hypothesised that the relative abundance of the small-bodied species would decrease at the impacted sites by elevated concentrations of total dissolved solids compared with that at the less-impacted control site. The aim of this study was to analyse and compare patterns of chironomid final instar body-size classes at impacted sites with those at the control site. Chironomid larvae were sampled seasonally from August 2009 to September 2012 from one control site and three impacted sites (Sites 2, 3 and 4) in the Swartkops River, Eastern Cape. Site 2 was impacted by diffuse pollution sources, whereas Sites 3 and 4 were impacted by wastewater effluent discharges in addition to diffuse pollution sources. Small-bodied species dominated the assemblage at the control site and declined significantly at the impacted sites, suggesting that chironomid body size responds predictably to deteriorating water quality in the Swartkops River.     

Fish assemblage–environment relationships suggest differential trophic responses to heavy metal contamination

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A spatio‐temporal framework for efficient inventories of natural resources: A case study with submersed macrophytes

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Challenges in estimating past plant diversity from fossil pollen data: statistical assessment, problems, and possible solutions

Fossil pollen data from sediment cores may be used as a measure for past plant diversity. According to the theory of probability, palynological richness is positively related to the pollen count. In a low pollen count, only common taxa are detected, whereas rare taxa are only detected by chance. The detection of all pollen taxa requires a very high pollen count, which is time-consuming. In regular palynological investigations, the detected richness in pollen spectra varies with the pollen count. Rarefaction analysis estimates palynological richness in an exactly equal-sum count for all samples, so that comparison between samples is meaningful. However, the over-representation of some taxa suppresses the detection probability of rare taxa; low total pollen abundance in a sample enhances the detection probability of rare taxa and long-distance transported pollen grains. These factors bias the observed palynological richness and distort comparisons. Palynological richness in a pollen count proportional to its pollen influx may be one proxy for reconstructing diversity trends through time. The use of this proxy overcomes most problems encountered in rarefaction analysis, but is constrained by inaccuracy in estimating pollen influx due to the imprecise time control of sediment cores. Estimating palynological richness by mathematical methods may be another way of reconstructing pollen diversity. Pollen data tend to reflect diversity on a regional scale. Sites from small basins have the advantage of recording diversity at both local and regional scales, if the detection of each taxon is independent. By associating one site from a large basin with a series of sites from very small basins (e.g. forest-hollows), information about both regional and local diversity may be obtained. Entomophilous pollen taxa may have to be measured using a different strategy than anemophilous taxa.     

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鄱阳湖湿地水土环境中微塑料的时空分布及多源性

淡水湿地中日益严重的微塑料(MPs)污染已引起全球关注。为了解鄱阳湖典型湿地微塑料的时空动态特征,相继于丰水期和枯水期采集鄱阳湖流域五河入湖段和鄱阳湖汇入长江出湖段的水体和沉积物样品,分别采用消解抽滤法和浮选分离-消解抽滤法分离水体和沉积物中的微塑料,采用显微镜、傅里叶变换红外光谱仪和扫描电镜鉴定分析微塑料表征。结果表明: 鄱阳湖各区域丰水期水体和沉积物微塑料丰度范围分别为32.1～127.3 n·L^-1和533.3～1286.6 n·kg^-1,枯水期分别为87.1～295.5 n·L^-1和460.0～1368.0 n·kg^-1,与其他淡水湿地相比,鄱阳湖具有较高的微塑料丰度,且各区域间呈时空差异性。研究区微塑料的主要形态有微球、碎片、薄膜和纤维等,相应聚合物成分主要为聚苯乙烯(PS)、聚丙烯(PP)和聚乙烯(PE)等;水体中微塑料以微球类(丰水期35.7%,枯水期52.0%)为主要形态,沉积物中以碎片类(丰水期45.8%,枯水期69.7%)为主要形态;两个水期水体和沉积物中均以小粒径(<0.1 mm)微塑料占优势(>50%),不同粒径微塑料丰度随粒径增大呈减少趋势。鄱阳湖湿地微塑料的潜在主要来源包括工业废水排放、城乡生活污水处理厂排放、农业和渔业活动以及生活垃圾处理不当。     

Nitrogen transformations at the sediment–water interface across redox gradients in the Laurentian Great Lakes

The capacity of a lake to remove reactive nitrogen (N) through denitrification has important implications both for the lake and for downstream ecosystems. In large oligotropic lakes such as Lake Superior, where nitrate (NO₃ ^?) concentrations have increased steadily over the past century, deep oxygen penetration into sediments may limit the denitrification rates. We tested the hypothesis that the position of the redox gradient in lake sediments affects denitrification by measuring net N-fluxes across the sediment–water interface for intact sediment cores collected across a range of sediment oxycline values from nearshore and offshore sites in Lake Superior, as well as sites in Lake Huron and Lake Erie. Across this redox gradient, as the thickness of the oxygenated sediment layer increased from Lake Erie to Lake Superior, fluxes of NH₄ ⁺ and N₂ out of the sediment decreased, and sediments shifted from a net sink to a net source of NO₃ ^?. Denitrification of NO₃ ^? from overlying water decreased with thickness of the oxygenated sediment layer. Our results indicate that, unlike sediments from Lake Erie and Lake Huron, Lake Superior sediments do not remove significant amounts of water column NO₃ ^? through denitrification, likely as a result of the thick oxygenated sediment layer.     

Ferry wakes increase seaweed richness and abundance in a sheltered rocky intertidal habitat

Because hydrodynamic regimes influence community assemblages, commercial ferry traffic can directly affect neighboring marine ecosystems by altering water movement. One of the largest ferry fleets in the world traverses the calm, protected waters of the Canadian Gulf Islands (British Columbia). To address the effects of ferry wakes on rocky marine intertidal communities, we examined community assemblages in sites impacted by ferry wakes (N?=?5) relative to geographically similar control sites not directly exposed to ferry wakes (N?=?6). Intertidal communities were significantly different between wake-influenced and control sites. Further analyses revealed that community level differences resulted from differences in seaweed assemblages, while invertebrate assemblages were similar. Sites exposed to ferry traffic displayed significantly greater overall seaweed abundance and seaweed species richness. Nitrate and nitrite concentrations, salinity, fetch, and tidal zonation were not significantly different between wake-impacted and control sites. However, dissolution blocks revealed that wake-impacted sites experienced increased overall water movement. Furthermore, block dissolution was negatively associated with distance from nearest ferry route and not fetch. Although dissolution block cannot disentangle effects of increased flow versus waves resulting from ferry wakes, we conclude that increased overall water movement from frequent and proximate ferry traffic stimulates primary production in rocky intertidal marine seaweeds by ameliorating mass transfer limitation.     

Dynamics of Nutrient Contents (Phosphorus,Nitrogen) in Water,Sediment and Plants After Restoration of Connectivity in Side‐Channels of the River Rhine

During the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.     

Macrophyte communities of European streams with altered physical habitat

The impact of altering hydro-morphology on three macrophyte community types was investigated at 107 European stream sites. Sites were surveyed using standard macrophyte and habitat survey techniques (Mean Trophic Rank Methodology and River Habitat Survey respectively). Principal Components Analysis shows the macrophyte community of upland streams live in a more structurally diverse physical habitat than lowland communities. Variables representing the homogeneity and diversity of the physical environment were used to successfully separate un-impacted from impacted sites, e.g. homogeneity of depth and substrate increased with decreasing quality class for lowland sites (ANOVA p < 0.05). Macrophyte attribute groups and structural metrics such as species richness were successfully linked to hydro-morphological variables indicative of impact. Most links were specific to each macrophyte community type, e.g., the attribute group liverworts, mosses and lichens decreased in abundance with increasing homogeneity of depth and decreasing substrate size at lowland sites but not at upland sites. Elodea canadensis, Sparganium emersum and Potamogeton crispus were indicative of impacted lowland sites. Many of the indicator species are also known to be tolerant to other forms of impact. The potential for a macrophyte tool indicative of hydro-morphological impact is discussed. It is concluded one could be constructed by combining indicator species and metrics such as species richness and evenness.     

The role of <Emphasis Type="Italic">Campsurus notatus</Emphasis> (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

About 30% of the total area of Lake Batata (Amazon) was impacted by the disposal of bauxite tailings originated from the process of washing bauxite. This effluent, composed by fine particles of clay and water, settled on top of the natural sediment, originating a new substratum with a different physical and chemical composition. This phenomenon created a new distinct habitat (impacted sediment) influencing the benthic community. The aim of this study was to evaluate the impact of bioturbation by Campsurus notatus (Ephemeroptera: Polymitarcytidae) on potential gas fluxes in the sediment of natural and impacted areas of the lake. The natural sediment had a significantly higher methane concentration when compared to the impacted one. In incubated sediment cores, the presence of C. notatus nymphs resulted in a significant increase in oxygen consumption and methane and carbon dioxide release to the water column. The effect of the presence of nymphs on methane was ambiguous. The C. notatus nymphs strongly decreased methane concentration in natural sediment samples, probably because of the enhancement of the oxic sediment area. However, this effect was not observed in impacted samples. Finally, the new substratum of Lake Batata decreased methane concentration in sediment and water column. C. notatus nymphs demonstrated to have a significant role on gas flux (methane and CO₂) from sediment to water column as well as on oxygen consumption in Lake Batata, consequently influencing the carbon cycle in this lake. Handling editor: S. M. Thomaz