Algal epilithon and water quality of a stream receiving oil refinery effluent

Changes in epilithic algal communities colonizing introduced substrata were determined in a stream polluted with oil refinery effluent at Digboi (Assam, India). The number of algal taxa was reduced but the growth of blue-green algae, particularly two species ofOscillatoria, was encouraged. Epilithic biomass (as chlorophylla) also declined at polluted stations. The algal community of the upstream station was markedly different from the community occurring just after the confluence of effluent; however, the differences were gradually reduced downstream, indicating improvement in water quality. Of the various criteria tested for possible relationships with the level of pollutants, species richness, Shannon diversity and biomass showed significant relationships. The study demonstrates the usefulness of algal criteria for monitoring oil pollution in running waters.     

Epilithic cyanobacterial communities and water quality: an alternative tool for monitoring eutrophication in the Alberche River (Spain)

Changes in epilithic cyanobacterial communities were determined in a river characterized by variations in nutrient content. The cyanobacterial community composition of the upstream sites was different from that of the downstream communities, where anthropogenic influences lead to an increase in nutrients (principally soluble reactive phosphate, SRP). There was a general trend in downstream sites towards a decrease in species richness, abundance, and diversity of cyanobacteria. The reduced cyanobacterial species richness in downstream locations was due largely to a marked decrease in the number of heterocystous species, although the number of non-heterocystous species also decreased. Epilithic phycobiliprotein content was positively correlated with the number of cyanobacterial cells, implying that this pigment provides information about the abundance of the cyanobacteria community in the epilithon. The lowest concentrations of phycobiliprotein in the epilithon were observed where concentrations of phosphate were highest. Similarly, the number of heterocystous and non-heterocystous species tended to decrease as the SRP increased, and as the DIN:SRP ratio decreased. However, no relation was found with dissolved inorganic nitrogen (DIN). The differences among cyanobacterial communities could be interpreted as being a consequence of variations in nutrient composition. Finally, the usefulness of cyanobacteria as an alternative tool for assessing changes in water quality is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Bacterial Community Succession in Natural River Biofilm Assemblages

Temporal bacterial community changes in river biofilms were studied using 16S rRNA gene-based polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) followed by sequence analysis. Naturally occurring biofilms were sampled in 2001 during an undisturbed 7-month low-water period in the River Garonne (SW France). During the sampling period epilithic biomass exhibited a particular pattern: two 3-month periods of accumulation that resulted in two peaks in summer and fall, each at about 25 g ash-free dry mass per square meter. Bacterial community DGGE profiles differed between the summer and fall biomass peaks and shared only 30% common operational taxonomic units (OTUs), suggesting the influence of seasonal factors on these communities. During the second biomass accrual phase, bacterial richness and the appearance of new OTUs fitted a conceptual model of bacterial biofilm succession. During succession, five OTUs (corresponding to Dechloromonas sp., Nitrospira sp., and three different Spirosoma spp.) exhibited particular patterns and were present only during clearly defined successional stages, suggesting differences in life-history strategies for epilithic bacteria. Co-inertia analysis of DGGE banding patterns and physical–chemical data showed a significant relationship between community structure and environmental conditions suggesting that bacterial communities were mainly influenced by seasonal changes (temperature, light) and hydrodynamic stability. Within the periods of stability, analysis of environmental variables and community patterns showed the dominant influence of time and maturation on bacterial community structure. Thus, succession in these naturally occurring epilithic biofilm assemblages appears to occur through a combination of allogenic (seasonal) and autogenic changes.     

Epilithic bacterial and algal colonization in a stream run, riffle, and pool: a test of biomass covariation

Epilithic bacterial and algal biomass were compared among a run, riffle, and pool along an open-canopy section of a third-order, temperate stream. Epilithic biofilms were sampled after 3, 7, 14, 21, 28, and 35 days colonization on unglazed ceramic tiles that were attached to plastic trays (n = 3) placed across each of the three habitats (i.e., run, riffle, pool). The diverse habitats and sampling regime were selected to provide a range in algal biomass so that potential covariation between epilithic bacterial and algal biomass could be assessed. There were significant differences among habitats and among trays within each habitat for both chlorophyll a and AFDM. Chlorophyll a and AFDM increased in the run and pool throughout the colonization period. In the riffle, chlorophyll a and AFDM increased rapidly early in colonization, then decreased. Epilithic bacterial biomass increased rapidly with no significant differences among the three habitats throughout colonization. Further, bacterial biomass did not correlate with either chlorophyll a or AFDM in any of the three habitats or on any of the sampling days. These results suggest that epilithic algal and bacterial biomass may be regulated by independent controls in some stream environments.     

Composition and dynamics of epilithic algae in a forest stream at Shillong (India)

The seasonal dynamics of epilithic algae in a third order pristine forest stream were analyzed over a period of 2 years. Stream water was slightly acidic and nutrient poor. Encrusting, filamentous flocs, and filaments were found. Algal standing crop was high (mean concentration of Chl a 16–43 mg m^–2) in spring. Filamentous algae contributed most to standing crop. Diatoms made up over 85% by number of the epilithon. Blue-greens were abundant upstream, and chlorophytes downstream. This shift was ascribed to greater light availability downstream. The community was more diverse during spring. Water current was the most important variable regulating epilithon structure. Total phosphorus (TP), orthophosphate (O-PO _inf4 ^su3– ), silica (Si⁴⁺), nitrate (NO _inf3 ^su– ) and conductance correlated negatively with flow rate. Green algae showed a positive correlation to phosphorus during low and stable flow. During rapid runoff, diatoms were the most resistant forms. Seasonal change in the epilithic community was mainly regulated by fluctuations in flow rate.     

Antarctic Stream Ecosystems: Variability in Environmental Properties and Algal Community Structure

The variability in physical, chemical and biological properties was examined for a number of glacier melt streams in south Victoria Land, Antarctica. Streams flowed for between one and two months. Stream water temperatures (range = 0–11°C) varied over short (hr) time scales whilst discharges varied considerably between streams (range 0.001–15 m³s⁻¹) and over diel cycles. Solar radiation and air temperature were major determinants of stream discharge. Variability in discharge was reflected in variability in nutrient chemistry and sediment load. Nitrogen and phosphorus varied considerably between streams; the meltwaters early in summer contained 10–20 times higher levels of dissolved N and P than later in the season. Within stream nutrient levels were modified by dense algal growths and penguin rookeries. Epilithic algal communities were made up predominantly of cyanophyceae which formed mats and crusts. Longitudinal and horizontal variability of species in the communities in selected streams is described. Analyses of algal cover and biomass (chlorophyll a) show that substrate type and flow rates are of greater importance than nutrients in influencing algal abundance and biomass. In some streams biomass values of over 20 μg Ch. a cm⁻² were recorded, much of which remains viable but inactive over the antarctic winter.     

The Stone Brusher, a New Sampler for Submerged Epilithic Material in Shallow Streams and Lakes

The Stone Brusher is designed to take qualitative or semi-quantitative samples of material attached to stones at 7–50 cm depth in running or stagnant waters. The epilithic material is dislodged from the stone surface with a rotating brush enclosed in a chamber and the material is drawn up directly into the sample bottle with an air-cylinder. The operator takes a sample quickly and without putting hands into the water. The sampling area is about 28 cm². The sampler is made of plastic, stainless steel and aluminium and weighs 3.1 kg. The equipment is robust and easily handled and it is constructed to meet the demand for standardized sampling for research and environmental monitoring and to improve working conditions for sampling personnel. The equipment allows sampling from bedrock and large stones that cannot be lifted from the bottom and it can be used for reliable sampling also in fast-flowing streams where the dislodged material is easily flushed away. Using Near-Infrared Spectroscopy and diatom analyses, this new sampler is evaluated in comparison to the recognized toothbrush method, which indicates that the Stone Brusher reduces sampling variability compared with the toothbrush method.     

Photosynthetic activity of epilithic algal communities in sections of the Torna stream (Hungary) with natural and modified riparian shading

The photosynthetic activity of epilithon grown in the Torna-stream (Hungary) was studied. Samples were collected from natural sections with closed canopy and natural stream bed and from modified sections with trapezoid river bed and shores lacking riparian vegetation. We assumed that human modifications would have a significant impact on epilithic photosynthesis, and therefore expected to observe corresponding changes in photosynthesis–irradiance (P–I) parametric. The laboratory P–I measurements were carried out monthly between April 2008 and September 2009 with epilithon after 3 weeks of in situ colonization. The maximum rate of the photosynthesis (P _max) correlated positively with the chlorophyll a content of the samples. Natural sites had lower biomass and P _max values than modified sites, and the biomass differed substantially in spring and summer, the P _max differed significantly only in spring. Natural sections had higher biomass-specific photosynthesis values than modified sections in all seasons, but the difference was significant only in summer–autumn: in summer the samples from the natural sections had significantly higher photosynthetic efficiency. In spring and summer, the photoadaptation parameters (I _k ) of communities grown in modified sections were substantially higher than in natural sections. Light availability appeared to be the major factor regulating the seasonal photosynthetic activity of epilithic communities.     

Stream permanence influences microalgal food availability to grazing tadpoles in arid-zone springs

Primary production in many ephemeral waters peaks soon after inundation, but the extent to which the algal biomass generated by this process is immediately available to aquatic herbivores as a food source has not been extensively studied. To examine this, we exposed natural epilithon from two permanent and two recently rewetted temporary reaches of an intermittent stream to grazing by small, presumably newly hatched, Limnodynastes tasmaniensis tadpoles and compared the algal content of tadpole feces to that of the assemblages on which they grazed. Rocks from the temporary sites, one colonized by tadpoles and one not, supported relatively flocculent, diatom-rich (79.7–85.7%) epilithon of similar biomass and taxonomic content. Epilithon from the permanent sites (one with and one without tadpoles) were more cohesive, contained fewer diatoms (57.0–60.7%), and differed in species composition from that of the temporary sites, and from one another. Feces and epilithon were more taxonomically similar when epilithon originated from temporary reaches than from permanent sites. This implies that grazing tadpoles accessed a greater percentage of the algal assemblages from recently rewetted sites. Algal species differed in susceptibility to ingestion by small tadpoles, but these differences were not consistent among habitats; susceptibility to ingestion was not predictable based solely on species growth habit, but was likely also affected by physiognomic differences in mat structure among habitats. A large percentage of algal cells ingested by tadpoles survived gut passage. `Live' cells (those with full chloroplasts) comprised 43.8–66.6% of all diatoms from epilithic samples and 27.4–42.7% of those in feces of small tadpoles. In contrast, only 12.8–14.9% of the diatoms in feces produced by large L. tasmaniensis tadpoles collected from the two tadpole-colonized sites contained full chloroplasts, suggesting higher digestion efficiency in large tadpoles than in small ones. Distinct, gut-passage-induced transitions from `live' diatoms to empty frustules or single diatom valves (`dead' cells) were evident when grazed material originated from temporary reaches. In contrast, `live' diatoms in epilithon from permanent sites were more likely to emerge in tadpole feces with reduced or fragmented chloroplasts. Thus, algae from temporary reaches appeared to be more efficiently digested than those from permanent reaches. While digestibility of individual taxa varied among sites, some algae (e.g., Synedra ulna) were clearly more digestible than others. Our results suggest that temporary stream reaches in arid-zone catchments are important sources of readily digestible autotrophic biomass for anuran species in these regions. Received: 5 March 1998 / Accepted: 9 November 1998     

Response of macroinvertebrates to blooms of iron-depositing bacteria

In field measurements and laboratory experiments we assessed the influence of high levels of iron, manganese, and concurrent blooms of iron-depositing bacteria, Leptothrix ochracea, on macroinvertebrates. Macroinvertebrate communities in five of six streams were depauerate inside blooms. Reasons for the decreased abundance vary among taxa, with our experiments demonstrating the importance, for one or more species, of (1) direct toxic effects, and,/or smothering, (2) behavioral avoidance of bacterial-coated substrates, and (3) an inability to use bacteria as food. Three mayfly species showed increased mortality when caged inside the blooms, but five trichopterans and one plecopteran did not. Five invertebrates avoided Leptothrix-coated substrate in choice trials, while three did not. Stenonema fuscum could not ingest Leptothrix, and Neophylax nacatus had reduced growth feeding on it, but Heptagenia umbratica grew equally well on diets of Leptothrix or diatoms. This study demonstrates the important role epilithic organisms play in modifying substrates, and how these changes may act to influence benthic abundance and distribution in streams.     

COMMUNITY DYNAMICS AND METABOLISM OF BENTHIC ALGAE COLONIZING WOOD AND ROCK SUBSTRATA IN A FOREST STREAM

Colonization dynamics and metabolism of algal communities on wood (small pieces of Douglas fir) and artificial rock (tiles) substrata were investigated in an open reach in Mack Creek, Cascade Mountain Range, Oregon, for 42 days. Chlorophyll a concentration was not significantly different between the two algal communities (ANOVA, P = 0.119). Even though differences in cell densities were not significantly different between the two algal communities (ANOVA, P = 0.063), biovolume and diversity were greater in epixylic than in epilithic communities (ANOVA, P = 0.011 and 0.002, respectively). The same algal taxa occurred on both substrata, but some of them (e.g. Ceratoneis arcus Grun., Cymbella minuta Hilse ex Rabh., Zygnema sp.) were more numerous on wood, whereas a few others preferred tiles (e.g. Achnanthes lanceolata (Bréb.) Grun.). Scanning electron microscopy revealed a much higher surface roughness on wood, which likely led to a patchy distribution of the algae and the development of stalked diatom species. However, adnate species adapted much better to the mainly flat surfaces of tiles. Net community primary productivity (NCPP) measured in 42-day-old substrata was moderate on tiles but negative on wood. Community respiration (CR) was significantly higher on wood than on tiles. Epixylic algal communities exhibited greater nitrogen demand than epilithic communities after ammonium addition. NCPP shifted to positive values on wood but did not increase on tiles. Despite metabolic differences, the variations between the two communities are more closely related to the physical characteristics of the substrata and the attachment abilities of the algal taxa.     

The impact of substrate and lake trophy on the biomass and nutrient status of benthic algae

Algal biomass, C:N:P (carbon:nitrogen:phosphorus) ratios and APA (biomass specific alkaline phosphatase activity) were measured in benthic algal communities on living substrates (mussels and macrophytes) and on rocks and stones (epilithon) in three lakes of different trophy. Benthic algal communities on living substrates had lower C:N:P ratios than epilithon, whereas algal biomass was highest on rocks and stones. Benthic algal biomass increased with the trophic level of a lake despite an increase of C:N:P ratios in the benthic community. The differences in C:N:P ratios and algal biomass between lakes of different trophy were higher on inert substrates than on macrophytes and mussels, probably because algae on living substrates could compensate a poor nutrient supply from lake water with substrate nutrients. However, the substrate was not, as expected, the most important nutrient supply in the oligotrophic lake, but in the eutrophic lake. Therefore, differences between inert and living substrates in a single lake were highest in the eutrophic lake. APA values of the oligotrophic lake were very high especially for benthic algae on stones, indicating an ability of the community to take up nutrients from organic sources. In conclusion, living substrates were an important nutrient source for benthic algae and the importance of this nutrient supply did not decrease with increasing lake trophy.     

Réponses et stratégies d'adaptation des communautés algales épilithiques à différents régimes hydrologiques

Responses of epilithic algal communities were studied in a regulated river presenting two different hydrological regimes. Upstream of the Escale reservoir, the hydrological regime is characterized by a flow compensation with discharge continuous release responsible for the most significant disturbances occurring in the regulated River Durance. Downstream of this reservoir, the river presents a stable and low compensation flow. The analysis of the epilithic algal communities submitted to contrasting flow regimes has shown responses at different levels: a) at the level of the whole community, a global response by changes in species richness and abundance, as well as in community structure; b) at the level of the particular taxonomic groups, such as, for instance, a more important development of filamentous green algae, observed in the downstream reach; c) at the species level: the acquisition, by some diatoms, of an architectural type adapted to the flow regime.     

The effects of disturbance on a herbivore-epilithon interaction in an upland stream

Two experiments were performed in an upland stream to determine the effects of the frequency of physical disturbance on the relationship between an abundant glossosomatid trichopteran (Agapetus monticolus; Banks) and the epilithon upon which it feeds. Artificial cobbles with an established epilithic community were tumbled either every 1, 2 or 4 weeks. The first experiment failed to detect any significant effects of rock tumbling on the abundance of A. monticolus or the epilithon: a result due to several spates. The first experiment did reveal that disturbances may disrupt the ability of A. monticolus to locate patches of abundant food. The second experiment found that although the abundance of A. monticolus was not affected by the disturbances, periphyton abundance was significantly reduced. Increasing the frequency of disturbance did not magnify this effect. Comparisons of these results with other studies of disturbance in streams indicate that the effects of disturbance on herbivory may be highly variable. A variety of factors, such as the relative resistances of the herbivores and the epilithon, need to be examined before the effects of disturbances on lotic herbivorous interactions can be completely understood.     

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.     

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.     

Seasonal variations in bacterial communities in adirondack streams exhibiting pH gradients

Measurements of microbial biomass, bacterial numbers, and microbial production were determined for three small woodland streams located in the Adirondack Mountain region of New York State, USA. These streams exhibited spatial and temporal gradients in water pH ranging from a high of 7.0 to a low of 4.5. Twelve sites along these streams were used for comparative analyses of the effects of pH and related water chemistry parameters on the planktonic, sedimentary, and epilithic bacterial communities. The planktonic bacterial communities were not influenced by water pH or related water chemistry parameters. For sedimentary populations, the organic content of the sediment was more important than the chemistry of the overlying water. The epilithic bacterial communities, however, were influenced significantly by the pH of the water column, showing decreased bacterial production at lower pH.     

An improved epilithon sampler and its evaluation in two acid lakes

An improved epilithon sampler is described which allows for in situ substrate sampling and multiple washing of the sample surface. Good sample replication indicates minimal loss of detached epilithic material during collection. The sampler is evaluated in two acid lakes between which a significant difference in both the total cover of epilithic material and in diatom standing crop is demonstrated. The relevance of quantitative measurements of diatom epilithon abundance to palaeolimnology is emphasized.     

COLONIZATION AND STANDING CROPS OF EPILITHIC ALGAE IN THE SUSQUEHANNA RIVER,PENNSYLVANIA1

A SCUBA diver, using a bar-clamp sampler, collected quantitative epilithic algae samples from artificial substrates (slate and acrylic plates) and river stones at two stations on the Susquehanna River bottom in 1974. At Falls, Pennsylvania, algal colonization on monthly plates (submerged for ca. 30 day periods) was most rapid between September and October. In winter, when algal density on cumulative plates (submerged 2–13 mo) and on stones present in the river peaked at 18,100 and 21,900 units/ mm², respectively, colonization of clean monthly plates nearly ceased. Similar colonization patterns were observed in a portion of the river polluted by coal mine drainages (SSES), but expansion of the algae population at SSES was inhibited by iron in the effluents, and densities never exceeded 2,400 units/mm² on stones or plates. Diatoms composed 95% of the overall standing crop at Falls and 65% at SSES.