Benthic Algal Communities Research Articles

Electron transport, light energy conversion and proteomic responses of periphyton in photosynthesis under exposure to AgNPs

Silver nanoparticles (AgNPs) including a mix of intact nanoparticle-Ag and ‘free’ Ag+ pose high risks to benthic photoautotrophs, but the photosynthetic responses of benthic microbial aggregates to AgNPs still remain largely unknown. Here, periphyton and Nostoc were used to elucidate the photosynthetic responses of benthic algae community to intact nanoparticle-Ag and Ag+. During exposure, both intact nanoparticle-Ag and Ag+ imposed negative effects on photosynthesis of benthic algae, but via different pathways. Specifically, Ag+ had stronger effects on damaging the oxygen-evolving complex (OEC) and thylakoid membrane than intact nanoparticle-Ag. Ag+ also suppressed electron transfer from QA to QB, and impaired phycobilisome. Intact nanoparticle-Ag inhibited the expression of PsbD and PsbL in PSII, but prompted the ROS scavenging capacity. In response to the stress of AgNPs, the benthic algae increased light energy absorption to maintain the electron transport efficiency, and up-regulated PSI reaction center protein (PsaA) to compensate the degraded PSII. These results reveal how intact nanoparticle-Ag and Ag+ influence electron transport, energy conversion and protein expression in the photosynthesis of periphyton, and provide deep insights into the responses of benthic photoautotrophs to different components of AgNPs.

A comparison of benthic algal and macroinvertebrate communities in a dammed and undammed Mediterranean river (Eel River watershed, California, USA)

AbstractFlow regulation by dams can reduce hydrologic variability, and subsequently, alter river food webs. This study compared the summer algal and macroinvertebrate assemblages from the mainstem Eel River (Mainstem) below Cape Horn Dam to that of the unregulated Middle Fork Eel River (Middle Fork). Despite above average rainfall in 2017, flow regulation produced a steeper spring flow recession limb with only 15.72 cubic meter per second in the dammed Mainstem in late May, which was about half the undammed Middle Fork's discharge of 32.28 cubic meter per second at the same time of year. Peak summer water temperatures in the Mainstem (mid‐August) were later relative to the Middle Fork (late July) based on past years of monitoring. The regulated Mainstem supported less Cladophora with lower mid‐summer algal richness, resulting in a macroinvertebrate community less reliant on Cladophora, with fewer key invertebrates such as Chironominae compared to the unregulated Middle Fork. Dam systems that reduce flow variation in Mediterranean rivers may shift the downstream community away from seasonal proliferation of dense green filamentous algae and invertebrate grazers typical of rivers in this climate, and towards adnate epilithic algae and cyanobacteria and generalist invertebrates, due to the encroachment of riparian vegetation and reduced thermal variation.

Identifying diatom indicator species of nutrient enrichment: An in situ nutrient enrichment experiment in subtropical upland streams

Nutrients are a fundamental determinant of broad scale patterns in the benthic algal community of stream ecosystems. Excessive inputs of nutrients such as nitrogen and phosphorus into upland streams may result in significant impacts on benthic algal communities. In upland streams, diatoms are the most abundant and diverse taxonomic group in benthic algal communities. In this study, benthic algal biomass and diatom community responses to in situ nitrogen and phosphorus enrichment were investigated by conducting an in-stream nutrient diffusing substrate experiment at high and low ambient nutrient concentration sites. Nitrogen was found to be the primary limiting nutrient across all sites, regardless of the ambient nutrient concentrations. In general, enrichment relieved nutrient limitation, promoting the dominance of a smaller suite of eutrophic species in the community. This was particularly evident in the low ambient nutrient sites where oligotrophic species initially dominated the community. This study identified diatom species with competitive advantage under nutrient enriched conditions and further the understanding of diatom species competition for multiple nutrients. Five diatom nutrient trait groups differentiate nutrient generalists and specialists and identifies potential indicator species based on their responses to specific enrichment treatments.

Episodic loadings of phosphorus influence growth and composition of benthic algae communities in artificial stream mesocosms

Phosphorus (P) is an essential macronutrient for algal communities, but in excess can exacerbate stream eutrophication. However, P loadings to streams vary temporally from continuous to episodic as a result of inputs from point and non-point sources, respectively. P loading pattern can thus alter the temporal availability of P and may influence effects of P enrichment on algal communities. We assessed how P loading pattern influences algal biomass and composition by conducting a 29-day P enrichment experiment in nine artificial streams exposed to either: (1) continuous P enrichment; (2) episodic P enrichment, or; (3) no P enrichment. P enrichment increased algal biomass accrual, but peak biomass did not differ between continuously and episodically enriched treatments. Maximum absolute growth rates were also comparable between P enriched treatments. However, episodic P additions sustained elevated rates of biomass accrual, whereas absolute growth rates in the continuously enriched communities declined towards the end of the experiment. P enrichment resulted in comparable increases in relative abundance of chlorophytes and decreased proportions of bacillariophytes and charophytes in algal communities for continuously and episodically enriched treatments. However, composition of bacillariophyte (diatom) assemblages differed significantly among all P enrichment treatments in accordance with species autecological attributes for P. Our results demonstrate that episodic and continuous P enrichment may augment algal biomass similarly. Yet, P loading pattern regulated the composition of algal communities. Thus, remedial management strategies for the control of nuisance algae production may require focus on the predominant source of P to streams. Finally, species specific responses of diatom assemblages to P enrichment and associated loading patterns suggests this taxonomic group may have potential as diagnostic indicators for identifying the presence of key nutrient sources associated with eutrophication of stream ecosystems.

Algal communities of the waterbodies of Schirmacher Oasis, East Antarctica

In continental waterbodies of Antarctic oases specific algal communities are forming. The structure and dominating complex of species of this communities due to different distance from the seashore and latitude, the composition of the constituent rocks, altitude and the presence in the past of periods of contact with sea water is unique for different oases. It may vary in different waterbodies within one oasis besides.Aim of the research is to describe different types of algal communities from the continental waterbodies of Schirmacher Oasis and it’s confinement to the different types of waterbodies.Samples were collected from 173 waterbodies: 151 with stagnant water and 22 streams.During the study 64 species of Cyanoprokaryotes were found, and this group usually dominated in communities. Also 14 most frequent species of Chlorophyta, 12 most frequent species of Bacillariophyta, 6 species of desmid algae, 2 species of Xanthophyceae, 1 species of Eustigmatophyceae were noted in benthos. Usually resting stages and in one case — life cells of Golden algae (Chrysophyceae, Synurophyceae) were found in mats on the bottom of big lakes. Plankton algae in most of the waterbodies had very low abundance and diversity and were strongly influensed by trophic level. Benthic algal communities were much more diverse and abundant. Eight sustainable types of benthic algal communities were revealed in continental waterbodyes of Schirmacher Oasis. Form, colour, and species composition of bentic films and mats strongly depended on temperature, conductivity and pH of the waterbody and its depth.

Friends or foes? The ecological relationships between micro- and macroalgae in low-order tropical streams

Streambeds are abundantly colonized by benthic algal assemblages. Environmental factors are the most assessed to find out predictable correlations between algal presence and habitat conditions, but biological interactions can also be important determinant of species composition in stream algae communities. Although there is plenty of information about algal ecology, the mechanisms leading their spatial distribution remain insufficiently clarified. Herein, we contribute to a better understanding regarding this latter issue, carrying out an experimental study to assess possible interactions between micro- and macroalgae during a successional process (75 days) in nine streams, using artificial substrates. The experimental analyses revealed the following main results: (i) streams with higher abundance of macroalgae also registered higher microalgal densities; (ii) the relative interaction index showed values greater than zero for all sampling dates, suggesting positive interaction between micro- and macroalgae during colonization process; and (iii) the multiple partial regression analyses (redundancy, pRDA) showed that environmental variables and microalgae density together explained 25% of macroalgal variation. These results indicate that interactions between stream micro- and macroalgae may contribute to shape the community structure during the successional process on the streambed. As observed previously, microalgae are early successional settlers and macroalgae are late successors, but both community components, besides their inherent competition, seem to cooperate in order to keep their coexistence. Based on this perspective, some typical ecological concepts related to the stream macroalgae, specially from tropical regions, may be expanded. For instance, studies have reported that the highest richness and abundance of lotic macroalgae in tropical/subtropical streams are determined basically by variation in climatic and environmental factors. Our results showed that, in addition to climatic and environmental factors, the increase in richness and abundance of stream macroalgae may also be affected by biotic interactions. In this context, our results suggest that the higher abundance of microalgae on the streambed seems to allow a better development of the benthic algal community, reaching to the later successional stages, in which the relative occurrence of larger and more complex algae (i.e., macroalgae) become more evident.

Effects of low flow and co-occurring stressors on structural and functional characteristics of the benthic biofilm in small streams

Low flow and co-occurring stress is a more and more frequent phenomenon these years in small agricultural streams as a consequence of climate change. In the present study we explored short and longer term structural responses of the stream benthic algae community and biofilm metabolism to multiple stress in small streams applying a semi-experimental approach. We hypothesized that i) a reduction in flow in combination with secondary stress (nutrients and sediments) have immediate effects on the benthic algae community in terms of biomass (chlorophyll a, biovolume), taxonomic and trait (lifeform and size distribution) compositions as well as on metabolism (GPP and CR), and ii) that changes in the benthic algae community persist due to altered environmental settings but that functional redundancy among benthic algae species provides a high level of resilience in metabolism (GPP and CR). Overall, we found that stress imposed by nutrients was less pronounced than stress imposed by fine sediments under low flow, and that nutrient enrichment to some extent mitigated effects of fine sediments. Fine sediment deposition mediated a decline in the fraction of erect algae and/or algae with mucilage stalks but this did not happen under co-occurring stress from both sediments and nutrients. Additionally, fine sediment deposition mediated a decline in GPP of the biofilm, but again this did not happen under co-occurring stress from nutrients. We conclude that 1) the benthic algae community and biofilm metabolism displayed similar resilience to stress imposed by low flow and co-occurring stress from nutrients and sediments on a short and longer time scale and 2) as structure–function adaptations may occur at several trophic levels in the biofilm, more research is needed to explore mechanisms underlying mitigating effects of nutrients in response to sediment deposition under low flow.

Response of Microphytobenthos and Benthic Bacteria Viability to Eutrophication in a Benthic–Pelagic Coupling Mesocosm Experiment

Excessive primary productivity due to nutrient inputs is a potential problem in coastal areas when resulting in high organic matter sedimentation rates. Microphytobenthos and heterotrophic bacteria are two components of the benthic ecosystem that contribute to nutrient cycling and decomposition of organic matter. In this context, the effects of nutrient addition and the associated in situ produced organic matter on microphytobenthos community composition and benthic bacterial viability were assessed in a mesocosm experiment for 58 days. The experimental setup included triplicate mesocosms filled with sediment and water under three levels of nutrient addition (‘control’, ‘low’ and ‘high’). Benthic algal community composition was assessed using chemotaxonomy and bacterial viability was estimated using flow cytometry and a double-staining protocol. Multivariate analysis detected a significant effect of treatment and time on microphytobenthic community composition indicating a difference between control and low mesocosms and also between low and high treatments at Day 12 and Day 24 of the experiment. Nonetheless, microphytobenthos implied high resistance and redundancy of benthic algae to disturbance as all three treatments showed no significant difference in community structure between Day 0 and Day 58. Bacterial viability responded quickly to the high nutrient addition and was significantly lower than in the ‘control’ and ‘low’ treatments at Days 6 and 12. Both pelagic and benthic environmental variables were correlated to these changes in benthic community.

Ecological Characteristic of Brown Algae Communities – Potential Aquaculture Objects

The benthic brown algae communities in coastal zone of southwest part of the Barents Sea have been studied. Research was carried out on the structure of benthic phytocenosis on the Murman coast in which edificators are brown seaweeds of the orders Fucales and Laminariales. The study focused on the dynamics of populations, size and age features against influence of the basic ecological factors on growth of commercial seaweeds - potential objects of mariculture. It is established that benthic phytocenosis on certain biotopes of littoral and sublittoral zones characterize by relativity high species diversity. The populations of commercial seaweeds form the multilevel structured benthic communities. The algae populations create topical, trophic and mediative connections which provide for steady stability of benthic communities. The use of plant community rather than individual algae species as biological indicators and biomonitors allows obtaining more complete information about the ecological state of benthic coastal ecosystem. The information collected can be used for the biological monitoring of marine bioresources in natural benthic communities, and also for cultivation of brown seaweeds under conditions of aquaculture.

Do leaf‐litter decomposers control biofilm primary production and benthic algal community structure in forest streams? Insights from an outdoor mesocosm experiment

Abstract 1. Forested headwater streams are generally considered to be light‐limited ecosystems where primary production is reduced, and the main source of energy and nutrients is composed of allochthonous detritus. We hypothesised that in these ecosystems, the development of primary producers might also be limited by (1) competition for nutrients with leaf‐litter decomposers (e.g. bacteria and fungi), and (2) leaf‐litter leachates or allelopathic compounds produced by aquatic fungi. 2. To test these hypotheses, a 48‐day mesocosm experiment was performed in 12 artificial streams containing stream water inoculated with epilithic biofilm suspensions collected from a forested headwater stream. Three different treatments were applied: control without leaf litter (C), microbially conditioned leaf litter added at the beginning of the experiment and left to decompose throughout the experiment (L), or leaf litter renewed three times during the experiment (RL). 3. We predicted that (1) the presence of litter, through microbial nutrient immobilisation and allelopathy, would reduce primary production and that (2) this effect would be amplified by litter renewal. We also predicted that nutrient competition would mean that (3) leaf‐litter decomposers will alter primary producer community composition and physiology. These predictions were tested by analysing biofilm development, physiology, stoichiometry, and benthic algal community structure. To distinguish between the effects of nutrient immobilisation and allelopathy, the biofilm responses to leaf‐litter leachates collected after different microbial conditioning durations were also measured in a parallel laboratory experiment. 4. Contrary to our expectations, by day 28, primary producer growth was higher in the mesocosms containing leaf litter (L and RL) despite the rapid decrease in dissolved nutrients when leaf litter was present. After 48 days, the lowest phototrophic biofilm development was observed when leaf litter was renewed (RL), whereas phototrophic biofilm development was similar in the C and L treatments. Biofilm stoichiometry indicated that this effect was most probably related to greater nitrogen limitation in the RL treatment. The presence of leaf litter also affected primary producers' photophysiology, which could be attributed to changes in taxonomic composition and to physiological adjustments of primary producers. 5. Laboratory measurements showed that despite a strong inhibition of primary producer growth by unconditioned leaf‐litter leachates, microbially conditioned leaf litter had either low or no effects on the development of primary producers. 6. These results reveal that leaf‐litter decomposers can have both positive and negative effects on primary producers underlining the need to consider microbial interactions when investigating the functioning of forested headwater streams.

Influence of water motion on the spatial distribution of Spirogyra in Lake Baikal

We investigated the diversity of benthic algal communities as well as phytoplankton in Lake Baikal. The structure of benthic algal communities changed in comparison to the period before 2000 due to intense development of filamentous algae, particularly Spirogyra. Percent cover of filamentous algae in different areas of the coastal zone varied from 0 to 100%. The lowest Spirogyra biomass was recorded in the surf and wave-breaking zones, whereas the highest biomass was observed in the area of the bottom less affected by waves. Fragments of Spirogyra thallomes were also recorded in the phytoplankton community of Lake Baikal's southern basin which is a new phenomena not previously recorded in the lake. Hydraulic characteristics of Spirogyra were similar to those of planktonic diatoms. Currents and wave effects on the bottom favored transfer and distribution of Spirogyra from locations with intense development to the coastal area of Lake Baikal. Spirogyra is now found throughout Lake Baikal.

Stoichiometry and daily rhythms: experimental evidence shows nutrient limitation decouples N uptake from photosynthesis.

Diel variability in nutrient concentrations is common but not universal in aquatic ecosystems. Theoretical models of photoautotrophic systems attribute the absence of diel uptake variation to nutrient scarcity, such that diel variability in nutrient uptake disappears as nutrients become limiting. We tested this prediction in a mesocosm experiment, by exposing benthic algal communities to a range of nitrogen (N) and phosphorus concentrations and recording the rates of uptake during both day and night. We found that higher concentrations of N produced diel variability in uptake and that the difference between the day and night total mass uptakes approximately equaled N demand for observed primary production as seen in other studies. At lower concentrations of N, uptake rates during the day and night were indistinguishable. These results are the first empirical evidence to imply that diel nitrate patterns in streams and rivers indicate a release from N limitation and offer a new way to assess nutrient limitation.

Response of benthic algae to environmental conditions in an urban lake recovered from eutrophication, China

Benthic algae communities dominate the primary production in littoral zone of shallow lake. To understand the long-term effect of alteration in the composition of benthic algae community assemblage in such as a lake in China, we analyzed the benthic algae developments and indicators in the Donghu Lake in Wuhan, central China in 2004 and 2014. We compared the benthic algae biomass, compositions, and species richness of aquatic macrophytes and the changes of primary physicochemical parameters. The results show that in the 10-year period, chl a and conductivity declined significantly but nutrient level of the whole lake remained largely stable. The benthic algae biomass doubled and the relative proportion of green algae increased, whereas the benthic diatom ratio decreased. The benthic diatom assemblages and taxa differed in a number of ways, showing more epiphytic diatom species, and the relative abundance and species richness changed markedly. The number of aquatic macrophyte species increased from 3 in 2004 to 15 in 2014, presenting a remarkable recovery from previous eutrophication conditions. The changes of water level, chl a, and conductivity played a crucial role in governing aquatic macrophytes re-colonization in the littoral zones in the period. The ecological characteristics of littoral benthic diatoms reflect habitat coupling as indicated by redundancy analysis. Therefore, the close link between benthic algae and macrophyte recovery demonstrates that the benthic algae metrics are much more useful than nutrient levels to quantify the process of restoration in the lake.

Multiple-stressor effects of dicyandiamide (DCD) and agricultural stressors on trait-based responses of stream benthic algal communities.

Agricultural practices often result in multiple stressors affecting stream ecosystems, and interacting stressors complicate environmental assessment and management of impacted streams. The nitrification inhibitor dicyandiamide (DCD) is used for nitrogen management on farmland. Effects of leached DCD on stream ecosystems are still largely unstudied, even though it could be relevant as a stressor on its own or in combination with other agricultural stressors. We conducted two experiments in 128 outdoor stream-fed mesocosms to assess stressor effects on biomass, cell density, taxon richness, evenness and functional trait composition of benthic algal communities. First, we examined responses to a wide DCD gradient (eight concentrations, 0-31 mg L-1) and two additional stressors, deposited fine sediment (none, high) and nutrient enrichment (ambient, enriched). Second, we determined algal responses to four stressors: DCD, sediment, nutrients, and reduced flow velocity. Here DCD treatments included controls, constant application (1.4 mg L-1) and two pulsed treatments mimicking concentration patterns in real streams (peaks 3.5 mg L-1, 2.2 mg L-1). Sediment and nutrient enrichment were influential stressors in both experiments, with fine sediment having the most pervasive effects. In Experiment 2, reduced flow velocity had pervasive effects and stressor interactions were mainly restricted to two-way interactions. DCD had few, weak stressor main effects, especially at field-realistic concentrations (Experiment 2). At the highest concentrations in Experiment 1 (above levels observed in real streams), DCD effects were still rare but some significant stressor interactions occurred. Analyses of functional traits were helpful in identifying potential mechanisms driving changes in densities and community composition. These findings suggest that, while DCD on its own may be a minor stressor, it could have adverse effects on algal communities already exposed to other stressors, a scenario common in agricultural streams.

Autumn drought drives functional diversity of benthic diatom assemblages of continental intermittent streams

Climate change is predicted to increase drought occurrence and severity in small continental watercourses. Here, we studied the structure and the functional diversity of benthic diatom assemblages in lowland intermittent and permanent watercourses of the Carpathian Basin. We assumed that the community structure of intermittent and permanent watercourses would be markedly different, and the functional diversity in both would be strongly influenced by autumn drought. We found that intermittent streams were primarily characterized by small-sized generalists and aerophilic taxa, while permanent watercourses were inhabited by large-sized planktic or fast moving groups. The functional richness was significantly lower in intermittent than in permanent streams. This decrease in the functional richness of benthic algal communities may negatively affect the functioning of lotic algal communities. We conclude that diatom assemblages in lowland intermittent watercourses are sensitive indicators of changes in ecosystem properties, and should be considered in appropriate evaluation and management of extreme climatic events on aquatic ecosystems.

Effects of water ecological environment on benthic algae in a water source reservoir

Several benthic plants and animals live in lakes and reservoirs. Benthic algae, mostly diatoms, can reflect the quality of the water environment. The indicative function of water quality by diatom community and basic principle of diatoms in-dexmethod was described. This paper investigates the benthic algal community in a water reservoir basin.in flood season (July) and non-flood season (November) respectively. A total of 129 species of benthic diatoms were collected in flood season (July) and non-flood season (November). By analyzing the generic index of Trophic Diatom Index (TDI), Index of Biological Diatom (IBD) and Specific Pollution Sensitivity Index (IPS) the status of aquatic ecological environment in this reservoir was evaluated, which indicates that the water quality of reservoir area is better.

Colonisation processes in benthic algal communities are well reflected by functional groups

Single-trait analyses are used to select the most appropriate species characteristics for an effective indication of changes in multiple stressors, but they are robust to detect fine-scale functional changes in biofilms. The combination of single traits may appropriately reflect ecological properties of changing benthic assemblages. We studied colonisation processes of benthic algal assemblages focusing on the changes in trait composition using life forms, type of attachments, cell size and mobility as single traits in a small lowland stream. We tested the descriptive power of single-trait groups (STGs) and also combined trait groups (CTGs). We assumed that STGs would be significantly affected by environmental factors, but compositional changes in biofilms would be described more easily by using CTGs rather than STGs. Our hypotheses were confirmed by the results. While some STGs correlated positively to environmental factors indicating disturbances, others correlated to environmental factors indicating the stable conditions. The fast settlement of large-sized groups was also relevant determining the compositional changes in the studied benthic community. Despite the strong correlation between STGs and environmental variables, CTGs analyses revealed important functional relations in the ecosystem, since CTGs display more sophisticated functional features of the organisms, which may provide more realistic responses.

Benthic Algal Community Structures and Their Response to Geographic Distance and Environmental Variables in the Qinghai-Tibetan Lakes With Different Salinity.

Uncovering the limiting factors for benthic algal distributions in lakes is of great importance to understanding of their role in global carbon cycling. However, limited is known about the benthic algal community distribution and how they are influenced by geographic distance and environmental variables in alpine lakes. Here, we investigated the benthic algal community compositions in the surface sediments of six lakes on the Qinghai-Tibetan Plateau (QTP), China (salinity ranging from 0.8 to 365.6 g/L; pairwise geographic distance among the studied lakes ranging 8–514 km) employing an integrated approach including Illumina-Miseq sequencing and environmental geochemistry. The results showed that the algal communities of the studied samples were mainly composed of orders of Bacillariales, Ceramiales, Naviculales, Oscillatoriales, Spirulinales, Synechococcales, and Vaucheriales. The benthic algal community compositions in these QTP lakes were significantly (p < 0.05) correlated with many environmental (e.g., dissolved inorganic and organic carbon, illumination intensity, total nitrogen and phosphorus, turbidity and water temperature) and spatial factors, and salinity did not show significant influence on the benthic algal community structures in the studied lakes. Furthermore, geographic distance showed strong, significant correlation (r = 0.578, p < 0.001) with the benthic algal community compositions among the studied lakes, suggesting that spatial factors may play important roles in influencing the benthic algal distribution. These results expand our current knowledge on the influencing factors for the distributions of benthic alga in alpine lakes.

Examination of effects of acid and metals on benthic algae in streams using chemical diffusing substrata

Acid mine drainage environments have multiple stressors, making it difficult to isolate effects of individual contaminants on benthic algal communities in situ in order to develop more specific indicators. Additionally, responses to AMD contaminants may be dependent on the abiotic and biotic conditions within the affected stream. We examined the efficacy of using chemical diffusing substrata (CDS) to determine how acid and metals interact to affect benthic algae in 2 streams with different trophy. CDS containing Mn, Fe, Al, acid, Mn + acid, Fe + acid, and Al + acid were deployed in a flow-through system to determine flux from the liquid media. Flux values for metals ranged from 1.0 to 18.1 µg/cm2/d for 5 days, and 0.5–7.4 µg/cm2/d for 21 days. Flux values for H+ were 467 (5 day) and 212 (21 day) µg/cm2/d. Corresponding water column concentrations that would produce the same flux as CDS metal treatments were estimated to be in the low to mid toxicity range for Al, low range for Fe, and nontoxic range for Mn. Acid treatments were estimated to be equivalent to a stream pH of 2.1–2.5. Five replicates of each CDS treatment, and a water control, were placed into a high-alkalinity, eutrophic stream (Wolf Creek) for 5 days and a low-alkalinity, oligotrophic stream (Silver Creek) for 21 days, respectively. In Silver Creek, all treatments except circumneutral Fe and circumneutral Mn had significantly lower algal cell densities than control treatments. Cell densities were significantly lower on Al + acid and Mn + acid than on the acid-only treatment, indicating synergistic effects. Cell densities were not significantly different among treatments in Wolf Creek. Higher alkalinity, nutrients, and productivity in this stream likely increased neutralization and detoxification processes within the biofilm. However, significantly lower chlorophyll a and higher phaeophytin concentrations of communities on treatments containing acid indicated sublethal effects. Significantly more acid tolerant taxa occurred on treatments with acid in Silver Creek, and significantly more metal-tolerant taxa occurred on metal treatments in Wolf Creek. However, treatment effects on taxonomic composition appeared to be constrained by the species pool within each stream, as these indicator taxa made up less than 4% of any community. Although equating CDS flux of contaminants to water column concentrations requires assumptions, and flux decreases over the exposure period, this study indicates that in situ experiments using CDS can separate out effects of individual toxic components on benthic algae, and determine context-dependent responses.

Effects of stream grade control structures on benthic algal communities in a subtropical stream

Stream grade control structures (GCSs) can have strong effects on stream habitat and communities. While most studies of GCSs have examined their impacts on fish and macroinvertebrate assemblages, few have focused on their impacts on benthic algae. Thus, this research studied effects of GCSs by comparing benthic algal communities in a forested stream section with those in a GCS section in a subtropical stream of central Taiwan. We included habitat and water quality surveys and an algal growth experiment with 3 treatments: forested, GCS, and shaded GCS. The GCS section had a greater stream wetted width, percentage of pool area, and algal biomass indicated by chlorophyll a, algal biovolume, and density than the forested section, whereas the forested section had a higher canopy cover, substratum size, and habitat diversity. Filamentous green algae were the dominant group in the GCS section, whereas diatoms were dominant in the forested section. Experimental results showed that GCSs strongly elevated algal biomass and changed community compositions. The shaded treatment significantly reduced >80% of the algal biomass in the GCS section, close to the reduction in the forested treatment. Considering all variables altered by the GCS, canopy cover might be the primary responsible factor. We suggest considerations on design and construction of GCSs.