Direct and indirect influence of parental bedrock on streambed microbial community structure in forested streams

A correlative study was performed to determine if variation in streambed microbial community structure in low-order forested streams can be directly or indirectly linked to the chemical nature of the parental bedrock of the environments through which the streams flow. Total microbial and photosynthetic biomass (phospholipid phosphate [PLP] and chlorophyll a), community structure (phospholipid fatty acid analysis), and physical and chemical parameters were measured in six streams, three located in sandstone and three in limestone regions of the Bankhead National Forest in northern Alabama. Although stream water flowing through the two different bedrock types differed significantly in chemical composition, there were no significant differences in total microbial and photosynthetic biomass in the sediments. In contrast, sedimentary microbial community structure differed between the bedrock types and was significantly correlated with stream water ion concentrations. A pattern of seasonal variation in microbial community structure was also observed. Further statistical analysis indicated dissolved organic matter (DOM) quality, which was previously shown to be influenced by geological variation, correlated with variation in bacterial community structure. These results indicate that the geology of underlying bedrock influences benthic microbial communities directly via changes in water chemistry and also indirectly via stream water DOM quality.     

Environmental degradation results in contrasting changes in the assembly processes of stream bacterial and fungal communities

Environmental degradation may have strong effects on community assembly processes. We examined the assembly of bacterial and fungal communities in anthropogenically altered and near‐pristine streams. Using pyrosequencing of bacterial and fungal DNA from decomposed alder Alnus incana leaves, we specifically examined if environmental degradation deterministically decreases or increases the compositional turnover of bacterial and fungal communities. Our results showed that near‐pristine streams and anthropogenically altered streams supported distinct fungal and bacterial communities. The mechanisms assembling these communities were different in near‐pristine and altered environments. Environmental disturbance homogenized bacterial communities, whereas fungal communities were more dissimilar in disturbed sites than in near‐pristine sites. Compositional variation of both bacteria and fungi was related to water chemistry variables in disturbed sites, further implying the influence of environmental degradation on community assembly. Bacterial and fungal communities in near‐pristine streams were weakly controlled by environmental factors, suggesting that the relative importance of niche‐based versus neutral processes in assembling microbial communities may strongly depend on the spatial scale and local environmental context. Our results thus suggest that environmental degradation may strongly affect the composition and β‐diversity of stream microbial communities colonizing leaf litter, and that the direction of the change can be different between bacteria and fungi. A better understanding of the environmental tolerances of microbes and the mechanisms assembling microbial communities in natural environmental settings is needed to predict how environmental alteration is likely to affect microbial communities.     

Bacterial Communities in Acidic and Circumneutral Streams

The relationship between pH and the abundance and activity of bacteria in streams was examined as part of a study of the effect of acidification on stream communities. Of the bacterial communities examined, the epilithic community appeared to be the most significantly affected by acidification. Microbial biomass, as quantified by measuring the ATP level, on rock surfaces was significantly correlated with pH. Also, bacterial production by the epilithic bacteria, indicated by incorporation of tritiated thymidine into DNA, was always higher at high-pH sites than at low-pH sites of the same stream order and elevation. Bacterioplankton concentrations varied between 0.53 × 10⁵ and 9.42 × 10⁵ cells · ml⁻¹ in the first- to fourth-order streams examined. The bacterioplankton concentration in one sample from a spring was 0.17 × 10⁵ cells · ml⁻¹. Bacterioplankton concentrations were not correlated with pH but were significantly correlated with seston concentrations. The correlation with seston is a result of increases in particle-associated bacteria at high seston concentrations. The proportion of bacterioplankton attached to particles varied from 0 to 70%. Bacterial numbers and production in the sediments were significantly correlated with the organic content of the sediment rather than with the pH of the overlying water. Thus, reduced abundance and activity of bacteria as a result of acidification could be detected only for the relatively active community on rock surfaces; this community was exposed to the low pH because of the unbuffered nature of its environment.     

Bacterial Community Structure and Function along a Heavy Metal Gradient

The response of the planktonic, sediment, and epilithic bacterial communities to increasing concentrations of heavy metals was determined in a polluted river. None of the communities demonstrated a pollution-related effect on bacterial numbers (viable and total), heterotrophic activity, resistance to Pb or Cu, or species diversity as determined by either the Shannon-Wiener diversity index or rarefaction. The lack of correlation between concentrations of heavy metals and resistance in the sediment bacterial community was investigated and found to be due at least in part to the high pH of the river water and the resultant reduction in heavy metal toxicity. The three different communities demonstrated characteristic profiles based on the relative abundances of bacterial strains grouped according to functional similarities.     

流式细胞仪检测纳帕海高原湿地浮游病毒和浮游细菌丰度

【背景】浮游病毒是水体微生物群落中重要的组成成分,深入研究浮游病毒的时空分布有助于更好地保护和开发当地的微生物资源。【目的】对采集到的纳帕海高原湿地水样中的浮游病毒和浮游细菌进行计数,揭示纳帕海高原湿地浮游病毒的分布规律。【方法】采用流式细胞仪检测2013年12月和2014年9月纳帕海高原湿地7个水样的浮游病毒与浮游细菌丰度,并对影响浮游病毒丰度的因素,如细菌丰度、叶绿素a含量以及其他环境因子进行了相关性分析。【结果】季节分布上,雨季浮游病毒和浮游细菌丰度高于旱季;水平分布上,原水样品的浮游病毒高于湿地水和淤泥水。旱季水样的浮游病毒丰度受到细菌丰度及叶绿素a浓度的影响较大;雨季水样的浮游病毒丰度受到水体的p H值和温度的影响较大。【结论】纳帕海高原湿地的浮游病毒和浮游细菌是比较活跃的。浮游病毒丰度在不同季节、不同采样点受到细菌丰度和叶绿素a浓度等因素的不同影响。在旱季噬菌体而非噬藻体或浮游植物病毒是纳帕海高原湿地中浮游病毒的优势种群。     

Dynamic changes in microbial community structure in farming pond water and their effect on the intestinal microbial community profile in juvenile common carp (Cyprinus carpio L.)

Water quality parameter dynamics, gut, sediment and water bacteria communities were studied to understand the environmental influence on the gut microbial community of a new strain of Huanghe common carp. A total of 3,384,078 raw tags and 5105 OTUs were obtained for the gut, water and sediment bacteria. The water quality had a stronger influence on the water bacteria community than gut and sediment bacteria communities. The ambient water quality parameters also significantly influenced the water and sediment bacteria communities. Comparing the gut, sediment, and water microbial communities, a relationship was found among them. However, gut bacteria were more closely related to sediment bacterial communities than to water bacteria communities. The results showed that the top three bacterial taxa were identical in gut and sediment samples in the early days of rearing. Interestingly, bacterial communities in the carp gut, water, and sediment had different adaptabilities to variations in environmental factors.     

The effects of sewage-treatment-works effluent on epilithic bacterial and algal communities of three streams in northern england

The responses of epilithic bacterial and algal communities to sewage-treatment-works (STW) effluent were studied in three streams in North Yorkshire, England, using both conventional microbiological techniques and the techniques of molecular genomics. Cod Beck, Thornton Beck and the River Wiske, were visited in May–June 2000 and January 2001 and the epilithic communities on submerged stones were sampled to determine chlorophyll-a, leucine assimilation, bacterial abundance, identity and abundance of microalgae, and epilithon dry and organic weights. Additionally, DNA from the epilithon of stones, collected in March–April and November 2000, was extracted, and samples were amplified using universal primers appropriate, respectively, for bacteria [Muyzer et al., 1993. Applied and Environmental Microbiology 59: 695–700] and microscopic phototrophs [Nübel et al., 1997. Applied and Environmental Microbiology 63: 3327–3332] followed by DGGE (Denaturing Gradient Gel Electrophoresis). Differences in algal community composition and abundance were greater between streams than between sites upstream and downstream of the STW outfalls. DGGE banding profiles of bacterial communities revealed grouping according to stream, and not the formation of communities characteristic of downstream sites; seasonal variation was also evident. Thus the discharge of STW effluent to the streams did not bring about the development of communities that are characteristically associated with organic pollution. Changes in composition and structure of bacterial and micro-algal epilithic communities were detected, but the relatively high quality effluents had only mild effects, not altering the environments sufficiently to override the natural differences between the three streams.     

Patterns in the Composition of Microbial Communities from a Subtropical River: Effects of Environmental,Spatial and Temporal Factors

Microbes are key components of aquatic ecosystems and play crucial roles in global biogeochemical cycles. However, the spatiotemporal dynamics of planktonic microbial community composition in riverine ecosystems are still poorly understood. In this study, we used denaturing gradient gel electrophoresis of PCR-amplified 16S and 18S rRNA gene fragments and multivariate statistical methods to explore the spatiotemporal patterns and driving factors of planktonic bacterial and microbial eukaryotic communities in the subtropical Jiulong River, southeast China. Both bacterial and microbial eukaryotic communities varied significantly in time and were spatially structured according to upper stream, middle-lower stream and estuary. Among all the environmental factors measured, water temperature, conductivity, PO₄-P and TN/TP were best related to the spatiotemporal distribution of bacterial community, while water temperature, conductivity, NO_x-N and transparency were closest related to the variation of eukaryotic community. Variation partitioning, based on partial RDA, revealed that environmental factors played the most important roles in structuring the microbial assemblages by explaining 11.3% of bacterial variation and 17.5% of eukaryotic variation. However, pure spatial factors (6.5% for bacteria and 9.6% for eukaryotes) and temporal factors (3.3% for bacteria and 5.5% for eukaryotes) also explained some variation in microbial distribution, thus inherent spatial and temporal variation of microbial assemblages should be considered when assessing the impact of environmental factors on microbial communities.     

Microbial leaf degraders in boreal streams: bringing together stochastic and deterministic regulators of community composition

1. Leaves that fall into the water represent a new habitat for microorganisms to colonise in streams, providing an opportunity to study colonisation and the subsequent regulation of community structure. We explored community composition of bacteria and fungi on decomposing alder leaves in nine streams in central Sweden, and describe their relationship with environmental variables. Succession of the microbial community was studied in one of the streams for 118 days. Microbial community composition was examined by denaturing gradient gel electrophoresis on replicate samples of leaves from each stream. 2. During succession in one stream, maximum taxon richness was reached after 34 days for bacteria and 20 days for fungi respectively. Replicate samples within this stream differed between each other earlier in colonisation, while subsequently such variation among replicate communities was low and remained stable for several weeks. Replicate samples taken from all the nine streams after 34 days of succession showed striking similarities in microbial communities within‐streams, although communities differed more strongly between streams. 3. Canonical analysis of microbial communities and environmental variables revealed that water chemistry had a significant influence on community composition. This influence was superimposed on a statistical relationship between the properties of stream catchments and microbial community composition. 4. The catchment regulates microbial communities in two different ways. It harbours the species pool from which the in‐stream microbial community is drawn and it governs stream chemistry and the composition of organic substrates that further shape the communities. We suggest that there is a random element to colonisation early in succession, whereas other factors such as species interactions, stream chemistry and organic substrate properties, result in a more deterministic regulation of communities during later stages.     

Diversity of Planktonic and Attached Bacterial Communities in a Phenol-Contaminated Sandstone Aquifer

Polluted aquifers contain indigenous microbial communities with the potential for in situ bioremediation. However, the effect of hydrogeochemical gradients on in situ microbial communities (especially at the plume fringe, where natural attenuation is higher) is still not clear. In this study, we used culture-independent techniques to investigate the diversity of in situ planktonic and attached bacterial communities in a phenol-contaminated sandstone aquifer. Within the upper and lower plume fringes, denaturing gradient gel electrophoresis profiles indicated that planktonic community structure was influenced by the steep hydrogeochemical gradient of the plume rather than the spatial location in the aquifer. Under the same hydrogeochemical conditions (in the lower plume fringe, 30 m below ground level), 16S rRNA gene cloning and sequencing showed that planktonic and attached bacterial communities differed markedly and that the attached community was more diverse. The 16S rRNA gene phylogeny also suggested that a phylogenetically diverse bacterial community operated at this depth (30 mbgl), with biodegradation of phenolic compounds by nitrate-reducing Azoarcus and Acidovorax strains potentially being an important process. The presence of acetogenic and sulphate-reducing bacteria only in the planktonic clone library indicates that some natural attenuation processes may occur preferentially in one of the two growth phases (attached or planktonic). Therefore, this study has provided a better understanding of the microbial ecology of this phenol-contaminated aquifer, and it highlights the need for investigating both planktonic and attached microbial communities when assessing the potential for natural attenuation in contaminated aquifers.     

Effects of whole-tree harvest on epilithic bacterial populations in headwater streams

Bacteria attached to rock and glass surfaces were studied in streams draining a whole-tree harvested watershed (WTH) and a nonharvested (CONTROL) watershed in the Hubbard Brook Experimental Forest, New Hampshire, U.S.A. Seasonal trends in numbers of cells/cm², mean cell volume, cell size-frequency distribution, and bacterial biomass were determined using 46-diamidino-2-phenylindole (DAPI) epifluorescent microscopy and scanning electron microscopy (SEM); the response of these parameters to decreased pH and increased nitrate concentration in the WTH stream was assessed via controlled manipulation of stream water chemistry in artificial channels placed in the CONTROL stream. Bacterial distribution varied significantly between the two streams and seasonally within each stream in apparent response to differential availability of dissolved organic carbon from algae and autumn-shed leaves. Decreased pH similar to that in the WTH stream had a significant effect on cell numbers, mean cell volume, and biomass in the CONTROL stream. Decreased pH accounted for some aspects of the altered bacterial distributions observed in the WTH stream. Nitrate at concentrations similar to those in the WTH stream had no effect on bacterial distribution in the CONTROL stream suggesting that headwater stream epilithic bacteria were carbon limited.     

Detrital processing in streams exposed to acidic precipitation in the Central Appalachian Mountains

Continuing high rates of acidic deposition in the eastern United States may lead to long-term effects on stream communities, because sensitive catchments are continuing to lose anions and cations. We conducted a two-year study of the effects of pH and associated water chemistry variables on detrital processing in three streams with different bedrock geology in the Monongahela National Forest, West Virginia. We compared leaf pack processing rates and macroinvertebrate colonization and microbial biomass (ATP concentration) on the packs in the three streams. Breakdown rates of red maple and white oak leaf packs were significantly lower in the most acidic stream. The acidic stream also had significantly lower microbial and shredder biomass than two more circumneutral streams. Shredder composition differed among streams; large-particle detritivores dominated the shredder assemblages of the two circumneutral streams, and smaller shredders dominated in the acidic stream. Within streams, processing rates for three leaf species were not significantly different between the two years of the study even though invertebrate and microbial communities were different in the two years. Thus, macroinvertebrate and microbial communities differed both among streams that differed in their capacity to buffer the effects of acidic precipitation and among years in the same stream; these differences in biotic communities were not large enough to affect rates of leaf processing between the two years of the study, but they did significantly affect processing rates between acidic and circumneutral streams.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.     

Recurring seasonal dynamics of microbial communities in stream habitats

Recurring seasonal patterns of microbial distribution and abundance in three third-order temperate streams within the southeast Pennsylvania Piedmont were observed over 4 years. Populations associated with streambed sediments and rocks (epilithon) were identified using terminal restriction length polymorphism (tRFLP) and sequencing of 16S rRNA genes selectively amplified with primers for the bacterial domain. Analyses of the relative magnitudes of tRFLP peak areas by using nonmetric multidimensional scaling resolved clear seasonal trends in epilithic and sediment populations. Oscillations between two dominant groups of epilithic genotypes, explaining 86% of the seasonal variation in the data set, were correlated with temperature and dissolved organic carbon. Sequences affiliated with epilithic phototrophs (cyanobacteria and diatom chloroplasts), a Rhodoferax sp., and a Bacillus species clustered in the summer, whereas sequences most closely related to "Betaproteobacteria" (putative Burkholderia sp.), and a putative cyanobacterium clustered in the fall/spring. The sediment genotypes also clustered into two groups, and these explained 85% of seasonal variation but correlated only with temperature. A summer tRFLP pattern was characterized by prevalence of "Betaproteobacteria," "Gammaproteobacteria," and a Bacillus sp., whereas the winter/spring pattern was characterized by phylotypes most closely related to "Firmicutes," "Gammaproteobacteria," and "Nitrospirae." A close association between these headwater streams and their watersheds was suggested by the recovery of sequences related to microbial populations provisionally attributed to not only freshwaters but also terrestrial habitats.     

How will increased temperature and nutrient enrichment affect primary producers in sub‐Arctic streams?

1. Spring‐fed streams, with temperatures ranging from 7.1 to 21.6 °C, in an alpine geothermal area in SW Iceland were chosen to test hypotheses on the effects of nutrients and temperature on stream primary producers. Ammonium nitrate was dripped into the lower reaches of eight streams, with higher reaches being used as controls, during the summers of 2006 and 2007. Dry mass of larger primary producers, epilithic chlorophyll a and biovolumes of epilithic algae were measured. 2. Bryophyte communities were dominated by Fontinalis antipyretica, and biomass was greatest in the warmest streams. Jungermannia exsertifolia, a liverwort, was found in low densities in few samples from cold streams but this species was absent from the warmest streams. 3. Nutrient enrichment increased the biomass of bryophytes significantly in warm streams. No effects of the nutrient addition were detected on vascular plants. The biomass of larger filamentous algae (mainly Cladophora spp.) was significantly increased by nutrient enrichment in cold streams but reduced by nutrients in warm streams. Thalloid cyanobacteria (Nostoc spp.) were not affected by nutrients in cold streams but decreased with nutrient addition in warm streams. Epilithic algal chlorophyll a was increased by nutrients in all streams and to a greater extent in 2007 than in 2006. Nutrient addition did not affect the epilithic chlorophyll a differently in streams of different temperatures. 4. There were small differential effects of nutrients, influenced by pH and conductivity, on different epilithic algal groups. 5. As global temperatures increase, animal husbandry and perhaps crop agriculture are likely to increase in Iceland. Temperature will directly influence the stream communities, but its secondary effects, manifested through agricultural eutrophication, are likely to be much greater.     

Characterizing seasonal changes in physicochemistry and bacterial community composition in hyporheic sediments

The hyporheic zone of stream ecosystems is a critical habitat for microbial communities. However, the factors influencing hyporheic bacterial communities along spatial and seasonal gradients remain poorly understood. We sought to characterize patterns in bacterial community composition among the sediments of a small stream in southern Ontario, Canada. We used sampling cores to collect monthly hyporheic water and sediment microbial communities in 2006 and 2007. We described bacterial communities terminal-restriction fragment length polymorphism (TRFLP) and tested for spatial and seasonal relationships with physicochemical parameters using multivariate statistics. Overall, the hyporheic zone appears to be a DOC, oxygen, and nitrogen sink. Microbial communities were distinct from those at the streambed surface and from soil collected in the adjacent watershed. In the sediments, microbial communities were distinct between the fall, spring, and summer seasons, and bacterial communities were more diverse at streambed surface and near-surface sites compared with deeper sites. Moreover, bacterial communities were similar between consecutive fall seasons despite shifting throughout the year, suggesting recurring community assemblages associated with season and location in the hyporheic zone. Using canonical correspondence analysis, seasonal patterns in microbial community composition and environmental parameters were correlated in the following way: temperature was related to summer communities; DOC (likely from biofilm and allochthonous inputs) influenced most fall communities; and nitrogen associated strongly with winter and spring communities. Our results also suggest that labile DOC entering the hyporheic zone occurred in concert with shifts in the bacterial community. Generally, seasonal patterns in hyporheic physicochemistry and microbial biodiversity remain largely unexplored. Therefore, we highlight the importance of seasonal and spatial resolution when assessing surface- and groundwater interactions in stream ecosystems.     

Microbial communities show parallels at sites with distinct litter and soil characteristics

Plant and microbial community composition in connection with soil chemistry determines soil nutrient cycling. The study aimed at demonstrating links between plant and microbial communities and soil chemistry occurring among and within four sites: two pine forests with contrasting soil pH and two grasslands of dissimilar soil chemistry and vegetation. Soil was characterized by C and N content, particle size, and profiles of low-molecular-weight compounds determined by high-performance liquid chromatography (HPLC) of soil extracts. Bacterial and actinobacterial community composition was assessed by terminal restriction fragment length polymorphism (T-RFLP) and cloning followed by sequencing. Abundances of bacteria, fungi, and actinobacteria were determined by quantitative PCR. In addition, a pool of secondary metabolites was estimated by erm resistance genes coding for rRNA methyltransferases. The sites were characterized by a stable proportion of C/N within each site, while on a larger scale, the grasslands had a significantly lower C/N ratio than the forests. A Spearman's test showed that soil pH was correlated with bacterial community composition not only among sites but also within each site. Bacterial, actinobacterial, and fungal abundances were related to carbon sources while T-RFLP-assessed microbial community composition was correlated with the chemical environment represented by HPLC profiles. Actinobacteria community composition was the only studied microbial characteristic correlated to all measured factors. It was concluded that the microbial communities of our sites were influenced primarily not only by soil abiotic characteristics but also by dominant litter quality, particularly, by percentage of recalcitrant compounds.     

Relationships between stream acidity and bacteria,macroinvertebrates, and fish: a comparison of north temperate and south temperate mountain streams,USA

A comparative study of relationships between stream acidity and bacteria, macroinvertebrates, and fish in the Adirondack Mountains of upper New York state and in the Southern Blue Ridge Mountains of eastern Tennessee, USA, was conducted. Although the study sites in both regions spanned a pH range from approximately 4.5 to 6.4, considerably greater seasonal variability in pH and higher monomeric Al concentrations characterized the Adirondack sites. Relationships between several biological characteristics and stream water acidity were similar in both regions, including lower production of epilithic bacteria and bacteria on decomposing leaves, lower leaf decomposition rates, lower density and generic richness of scraper/grazer macroinvertebrates, particularly Ephemeroptera, and lower fish abundance and survival in more acidic streams. Densities of total macroinvertebrates and densities of macroinvertebrates and bacteria inhabiting or closely associated with stream sediments were generally not related to stream water acidity.Regional differences occur in some of the relationships between biological characteristics and stream water acidity. Negative correlations between bacterial production on rocks and pH, between bacterial production on decomposing leaves and pH, and between densities of Ephemeroptera and scrapers and pH were stronger in the Adirondacks than in the Southern Blue Ridge. Higher Al concentrations in the Adirondacks may be responsible for the stronger relationships with pH there. The steeper slopes of the relationships between Ephemeroptera density and all forms of Al in the Adirondacks compared with the Southern Blue Ridge suggests that there may be some adaptation among a few acid/aluminum-tolerant species in the seasonally more constant acidic Southern Blue Ridge streams. Fish bioassays indicated longer survival times in acidic streams in the Adirondacks compared with the Southern Blue Ridge, but these results may be an artifact associated with the use in the Southern Blue Ridge of rainbow trout as the test species which is known to be more acid sensitive compared with brook trout, the test species used in the Adirondacks.     

High Bacterial Diversity in Epilithic Biofilms of Oligotrophic Mountain Lakes

Benthic microbial biofilms attached to rocks (epilithic) are major sites of carbon cycling and can dominate ecosystem primary production in oligotrophic lakes. We studied the bacterial community composition of littoral epilithic biofilms in five connected oligotrophic high mountain lakes located at different altitudes by genetic fingerprinting and clone libraries of the 16S rRNA gene. Different intra-lake samples were analyzed, and consistent changes in community structure (chlorophyll a and organic matter contents, and bacterial community composition) were observed along the altitudinal gradient, particularly related with the location of the lake above or below the treeline. Epilithic biofilm genetic fingerprints were both more diverse among lakes than within lakes and significantly different between montane (below the tree line) and alpine lakes (above the tree line). The genetic richness in the epilithic biofilm was much higher than in the plankton of the same lacustrine area studied in previous works, with significantly idiosyncratic phylogenetic composition (specifically distinct from lake plankton or mountain soils). Data suggest the coexistence of aerobic, anaerobic, phototrophic, and chemotrophic microorganisms in the biofilm, Bacteroidetes and Cyanobacteria being the most important bacterial taxa, followed by Alpha-, Beta-, Gamma-, and Deltaproteobacteria, Chlorobi, Planctomycetes, and Verrucomicrobia. The degree of novelty was especially high for epilithic Bacteroidetes, and up to 50?% of the sequences formed monophyletic clusters distantly related to any previously reported sequence. More than 35?% of the total sequences matched at <95?% identity to any previously reported 16S rRNA gene, indicating that alpine epilithic biofilms are unexplored habitats that contain a substantial degree of novelty within a short geographical distance. Further research is needed to determine whether these communities are involved in more biogeochemical pathways than previously thought.     

A comparison of bacterial,ciliate and macroinvertebrate indicators of stream ecological health

We evaluate the reliability of communities of bacteria and ciliated protozoa as indicators of freshwater ecological health. Samples of epilithic biofilm were taken from 18 freshwater streams, impacted by varying types and degrees of catchment modification. Communities of bacteria and ciliates were characterised using DNA fingerprinting techniques (automated ribosomal intergenic spacer analysis and terminal restriction fragment length polymorphism, respectively) and macroinvertebrate data also obtained, for comparison. Similar to the macroinvertebrates, the taxa richness of ciliate communities was reduced in more developed stream catchments; significant differences in the evenness of ciliate communities were also detected. We could identify no significant relationship between the richness of bacterial taxa and the percentage catchment development. However, a significant trend was detected between bacterial community structure and the predominant catchment land use (rural vs. urban) using a Bray–Curtis measure of similarity, a relationship not detected for the ciliate and macroinvertebrate communities. These findings indicate that stream bacterial, ciliate and macroinvertebrate communities each respond differently to various catchment conditions and highlight the potential of microbial communities to provide novel, alternative indicators of stream ecosystem health.     

Developing and Testing Diatom Indicators for Wetlands in the Casco Bay Watershed, Maine, USA

Diatom indicators of wetland condition were developed and tested by assessing human disturbance, water chemistry, and species composition of benthic, epiphytic, and planktonic diatoms from 20 wetlands sampled for 2 years. One sample from each site was randomly selected to form a development data set, while the rest were used as the test data set. Human disturbance indicated substantial differences among wetlands in hydrologic modification, impervious surface, and potential for non-point source contamination. These landscape alterations were related to increases in pH, non-nutrient ions, and nutrients and decreases in dissolved organic carbon and water color. Pre-existing diatom indicators, calculated with autecological information from lakes and aquatic habitats, correlated highly to relevant water chemistry and human disturbance scores. Weighted average models (WAM) of Cl⁻, conductivity, pH, and alkalinity derived with the Maine development data set correlated to relevant water chemistry and human disturbance of the test wetlands. Diatom assemblage attributes that correlated with human disturbance were selected to combine into a multimetric index of biotic condition (IBC). IBCs and WAMs from benthic and epiphytic diatoms were usually more precisely related to relevant environmental factors than planktonic diatoms. These results showed that human disturbance alkalized wetlands, enriched them with nutrients, and diatom assemblages responded to these changes. Indicator development protocols for streams can be readily adapted for use in wetlands.