Relative importance of periphyton and phytoplankton in turbid and clear vegetated shallow lakes from the Pampa Plain (Argentina): a comparative experimental study

We analyzed experimentally the relative contribution of phytoplankton and periphyton in two shallow lakes from the Pampa Plain (Argentina) that represent opposite scenarios according to the alternative states hypothesis for shallow lakes: a clear lake with submerged macrophytes, and a turbid lake with high phytoplankton biomass. To study the temporal changes of both microalgal communities under such contrasting conditions, we placed enclosures in the littoral zone of each lake, including natural phytoplankton and artificial substrata, half previously colonized by periphyton until a mature stage and half clean to analyze periphyton colonization. In the clear vegetated shallow lake, periphyton chlorophyll a concentrations were 3–6 times higher than those of the phytoplankton community. In contrast, phytoplankton chlorophyll a concentrations were 76–1,325 times higher than those of periphyton in the turbid lake. Here, under light limitation conditions, the colonization of the periphyton was significantly lower than in the clear lake. Our results indicate that in turbid shallow lakes, the light limitation caused by phytoplankton determines a low periphyton biomass dominated by heterotrophic components. In clear vegetated shallow lakes, where nitrogen limitation probably occurs, periphyton may develop higher biomass, most likely due to their higher efficiency in nutrient recycling.     

Interspecific Differences in the Direct and Indirect Effects of Two Neotropical Hylid Tadpoles on Primary Producers and Zooplankton

Herbivores can both consume and facilitate primary producers with important consequences for community structure. How differences in herbivore foraging ecology alter the relative importance of such effects is not well understood, especially in tropical lentic systems. To address this issue, we manipulated the density of two herbivores with different foraging strategies to evaluate their effects on primary producers and other consumers. Specifically, we examined the effects of the tadpoles of two common Neotropical hylid frogs at two densities on conspecific growth, periphyton and phytoplankton, and zooplankton. We found that the tadpoles of the pantless treefrog, Dendropsophus ebraccatus, reduced periphyton and increased phytoplankton abundances, whereas they had no affect on zooplankton. The red‐eyed treefrog, Agalychnis callidryas, also reduced periphyton and increased phytoplankton, but to a greater extent, and they also had strong impacts on zooplankton by altering the composition, size structure, and total abundances of the zooplankton community. Differences between both species' impacts on these food webs were independent of tadpole biomass, as size‐selective filter feeding and nutrient cycling seems to drive the impacts of A. callidryas on phytoplankton and zooplankton, while the role of D. ebraccatus is more limited. Species level differences in the strength and direction of top‐down and bottom‐up effects on food webs suggest that the ecological roles of tadpoles may be diverse and important to aquatic communities.     

Living in the litter: the influence of tree leaf litter on wetland communities

Empirical research in streams has demonstrated that terrestrial subsidies of tree leaf litter influence multiple community factors including composition, diversity and growth of individuals. However, little research has examined the importance of tree litter species on wetlands, which are ubiquitous across the landscape and serve as important habitats for a unique and diverse community of organisms. Using outdoor mesocosms, we assessed the impact of 12 litter monocultures and three litter mixtures (from both broadleaf and conifer trees) on pond communities containing gray tree frog tadpoles Hyla versicolor, periphyton, phytoplankton and zooplankton. We found that leaf litter species had substantial and differential impacts on all trophic groups in the community including effects on algal abundance, zooplankton density and amphibian growth. In many instances, patterns of responses were specific to individual litter species yet some responses, including both pH values and periphyton biomass, were generalizable to broad taxonomic groups. In addition, while most responses of litter mixtures were additive, we found evidence for antagonistic effects of litter mixing among responses of periphyton and amphibian body mass. Our results highlight the potential impact of human and naturally driven changes in forest composition on wetland communities through associated changes in leaf litter.     

Relationship between epipelon,epiphyton and phytoplankton in two limnological phases in a shallow tropical reservoir with high Nymphaea coverage

Macrophytes and phytoplankton are recognized as having roles in determining alternative stable states in shallow lakes and reservoirs, while the role of periphyton has been poorly investigated. Temporal and spatial variation of phytoplankton, epipelon and epiphyton was examined in a shallow reservoir with high abundance of aquatic macrophytes. The relationships between algae communities and abiotic factors, macrophyte coverage and zooplankton density were also analyzed. Monthly sampling was performed in three zones of the depth gradient of the reservoir. Two phases of algal dominance were found: a phytoplankton phase and epipelon phase. The phase of phytoplankton dominance was characterized by high macrophyte coverage. Rotifera was the dominant zooplankton group in all the zones. Flagellate algae were dominant in phytoplankton, epipelon and epiphyton. Macrophyte coverage was found to be a predictor for algal biomass. Changes in biomass and species composition were associated with macrophyte cover variation, mainly the Nymphaea. In addition to the abiotic factors, the macrophyte coverage was a determining factor for changes to the algal community, contributing to the alternation between dominance phases of phytoplankton and epipelon. The macrophyte–phytoplankton–periphyton relationship needs to be further known in shallow reservoirs, especially the role of epipelon as an alternate stable state.

     

Interactive multiple‐stressor effects of the antibiotic monensin,cattle effluent and light on stream periphyton

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Relationships between phytoplankton and periphyton communities in a central Iowa stream

Relationships between phytoplankton and periphyton communities were investigated in a central Iowa stream. Results generally support the hypothesis that the phytoplankton community arises from the epipelic periphyton community. A high correlation existed between the proportion of benthic diatoms composing the epipelon and phytoplankton. One dominant epipelic species (Nitzschia acicularis) showed a greater tendency to become planktonic than the grouped remainder of Nitzschia spp. There was a significant inverse relationship between the proportion of centric diatoms in the plankton and volume of flow. Centric diatoms were important members of the plankton only when volume of flow was less than 60 ft³ / sec (2.1 m³ / sec). Possible mechanisms explaining these phenomena are discussed.This study represents a portion of a dissertation submitted to the Graduate College, Iowa State University in partial fulfillment of requirements for the degree Doctor of Philosophy.     

Effects of dissolved organic matter and ultraviolet radiation on the accrual, stoichiometry and algal taxonomy of stream periphyton

1. We investigated the effects of dissolved organic matter (DOM) and ultraviolet‐B (UVB) radiation on periphyton during a 30‐day experiment in grazer‐free, outdoor artificial streams. We established high [10–12 mg carbon (C) L⁻¹] and low (3–5 mg C L⁻¹) concentrations of DOM in artificial streams exposed to or shielded from ambient UVB radiation. Periphyton was sampled weekly for ash‐free dry mass (AFDM), chlorophyll (chl) a , algal biovolume, elemental composition [C, nitrogen (N) and phosphorus (P)], and algal taxonomic composition. 2. Regardless of the UVB environment, increased DOM concentration caused greater periphyton AFDM, chl a and total C content during the experiment. Increased DOM also significantly increased periphyton C : P and N : P (but not C : N) ratios throughout the experiment. Algal taxonomic composition was strongly affected by elevated stream DOM concentrations; some algal taxa increased and some decreased in biomass and prevalence in artificial streams receiving DOM additions. UVB removal, on the other hand, did not strongly affect periphyton biomass, elemental composition or algal taxonomic composition for most of the experiment. 3. Our results show strong effects of DOM concentration but few, if any, effects of UVB radiation on periphyton biomass, elemental composition and algal taxonomic composition. The effects of DOM may have resulted from its absorption of UVA radiation, or more likely, its provision of organic C and nutrients to microbial communities. The strong effects of DOM on periphyton biomass and elemental composition indicate that they potentially play a key role in food web dynamics and ecosystem processes in forested streams.     

A comparison of algal periphyton composition on eleven species of submerged macrophytes

Summary The composition of algal periphyton was examined on eleven species of submerged macrophytes collected at a depth of 0.25 m in Sewell Lake, southwestern Manitoba, a shallow nitrogen and phosphorus rich lake. There were substantial differences in the periphyton on all macrophyte species. Diatom subcommunities were the most similar, while the green algal subcommunities were the most dissimilar on different plant hosts.Potamogeton zosteriformis differed the most from all other macrophytes with respect to the composition of its periphyton. These results and a comparison of the literature suggest that the composition and structure of periphyton communities on living substrates is a product of the interaction of many variables, determined by the characteristics of the host plant, the external environment and the algae themselves. Studies of periphyton at a given site must take into account the various substrates available.     

USING EPILITHIC ALGAL COMMUNITIES TO ASSESS TROPHIC STATUS IN IRISH LAKES1

Relationships between taxonomic composition of shallow epilithic algal communities and nine environmental variables in 32 lakes of different trophic states in Ireland were explored using gradient analysis. A canonical correspondence analysis using four representative environmental variables, alkalinity (correlated with pH and conductivity), maximum phytoplankton chl a (CHL_max) (correlated with total P, total N, and chl), turbidity, and water color explained 21% of the variance in taxa distributions. The first two axes were significant and accounted for 77% of the variance in the periphyton–environmental relationship. The first axis was strongly related to alkalinity and color, which reflected geology and land use in the watersheds. The second axis was most correlated with CHL_max, and separation of lakes corresponded to their Organization for Economic Cooperation and Development (OECD) trophic classification based on water chemistry. Eutrophic lakes were characterized by cyanobacteria taxa and Stigeoclonium sp. Diatoms and desmids were generally more abundant in oligotrophic and mesotrophic lakes. Values for diatom trophic indices were poor indicators of trophic state. Weighted averaging regression and calibration techniques were used to develop transfer functions between 84 taxa and total P, total N, and CHL_max. The total P inference model predicted OECD trophic classification correctly for 84% of the lakes. Values for taxa preferences resulting from such models can provide the foundation for biomonitoring schemes using extant periphyton communities. The turnover time of periphyton taxa should integrate changes in environmental conditions at a temporal scale intermediate to surface‐sediment fossil diatom assemblages and water column variables, which may be more appropriate for detecting annual changes.     

Physiological characteristics of inorganic nitrogen uptake by spatially separate algal communities in a nitrogendeficient lake

1. The physiological characteristics of nitrogen uptake by sublittoral and eulittoral (splash zone) epilithic periphyton as well as epipelic periphyton in N-deficient Castle Lake, California were determined by evaluating the half-saturation constants (K_t) and initial slopes (V_max/K_t) of uptake kinetics curves. These results were compared to similar studies of phytoplankton nitrogen uptake in this lake. 2. The strategies of nitrogen uptake differed among the various communities and were largely determined by the proximity of each to pools of available dissolved inorganic N (DIN). 3. The sublittoral algae did not have a high biological affinity for either NH₄ or NO₃ and depended on nitrogen fixation for their N supply. The eulittoral community showed an increased capacity for DIN uptake at low substrate concentration, but not as high as measured for the phytoplankton community. Epipelic algae live immediately adjacent to a large pool of interstitial sediment NH₄ and showed no physiological adaptations for surviving in a N-deficient environment. 4. K_t values for all benthic communities were approximately two orders of magnitude greater than ambient substrate levels. In contrast, the half-saturation constants for NH₄+ NO₃ uptake by phytoplankton were very similar to in situ levels of these nutrients.     

Submerged Macrophytes Mitigate Direct and Indirect Insecticide Effects in Freshwater Communities

Understanding how ecological interactions mitigate the impacts of perturbations such as pesticides in biological communities is an important basic and applied question for ecologists. In aquatic ecosystems, new evidence from microcosm experiments suggests that submerged macrophytes can buffer cladocerans from pulse exposures to the widely used insecticide malathion, and that mitigation increases with macrophyte density. However, whether these results scale up to more complex aquatic communities where ecological interactions such as competition can alter toxicity is unknown. Further, macrophyte abilities to mitigate different insecticide exposure scenarios (i.e. single versus repeated pulses) have never been tested. To address these gaps, we performed a factorial mesocosm experiment examining the influence of four macrophyte treatments (0, 10, 50, or 100 Elodea Canadensis shoots planted per mesocosm) crossed with three malathion exposure scenarios (no insecticide, single pulse, repeated pulses) on aquatic communities containing zooplankton, phytoplankton, periphyton, two snail species, and larval amphibians. In the absence of macrophytes, single malathion pulses caused short-term declines in cladoceran abundance followed by their rapid recovery, which precluded any indirect effects (i.e. trophic cascades). However, repeated malathion pulses caused cladoceran extinctions, resulting in persistent phytoplankton blooms and reduced abundance of one snail species. In contrast, with macrophytes present, even at low density, malathion had no effect on any taxa. We also discovered novel effects of macrophytes on the benthic food web. In the two highest macrophyte treatments, we observed trends of reduced periphyton biomass, decreased abundance of one snail species, and decreased amphibian time to and mass at metamorphosis. To our knowledge, this is the first evidence of negative submerged macrophyte effects on amphibians, a taxa of global conservation concern. Our findings suggest that facilitating macrophytes could be an important strategy for buffering freshwater communities from insecticides, though consideration of their impacts on animal species is necessary.     

Plant community dynamics in a chain of lakes: principal factors in the decline of rooted macrophytes with eutrophication

Shoe Lake and East Graham Lake, part of a small chain of lakes in southeastern Michigan, USA, differ in nutrient loading and in the structure and productivity of their aquatic plant communities. A comparative study of species frequency and biomass distributions, nutrient contents, and responses to experimental nutrient enrichment and shading, was conducted to determine the principal factors controlling the macrophyte dynamics. A central objective was to address the question of why rooted macrophyte growth declines with eutrophication, and to test existing models designed to explain this phenomenon. In the more eutrophic Shoe Lake, diversity and productivity of rooted macrophytes were relatively low, restricted primarily by combined shading of phytoplankton, periphyton, and non-rooted macrophytes (principally Ceratophyllum demersum, along with Utricularia vulgaris and Cladophora fracta). In the less eutrophic East Graham Lake, lower nitrogen availability restricted the growth of all of these shading components, resulting in clearer water and higher productivity and diversity of rooted macrophytes. The macrophytes did not allelopathically suppress the phytoplankton in East Graham Lake. The results supported a direct relationship between nutrient loading, increasing growth of phytoplankton, periphyton and non-rooted macrophytes, and decline of rooted macrophytes.     

Seasonal variations of metal concentrations in periphyton and taxonomic composition of the algal community at a Yenisei River littoral site

The concentrations of metals K, Na, Ca, Mg, Fe, Mn, Zn, Cu, Ni, Pb, Co and Cr, in the water and periphyton (epilithic algal communities) were studied at a site in the middle stream of the Yenisei River (Siberia, Russia) during three years using monthly sampling frequencies. Despite considerable seasonal variations in aquatic concentrations of some metals, there was no correlation between metal contents in the water and in periphyton. Seasonal concentration variations of some metals in periphyton were related to the species (taxonomic) composition of periphytic microalgae and cyanobacteria. Enhanced levels of Ni and Co in periphyton in late autumn, winter, and early spring were likely caused by the predominance of cyanobacteria in the periphytic community, and annual maximum levels of K in periphyton in late spring and early summer were attributed to the domination of Chlorophyta, primarily Ulothrix zonata.     

Invertebrate communities associated with macrophytes in Lake Ladoga: effects of environmental factors

Littoral invertebrate communities (meio- and macrobenthos and zooplankton) were studied in seven types of macrophyte associations commonly encountered in Lake Ladoga: in reed (Phragmites) beds on sand, soft and hard bottoms, in associations with the prevalence of Potamogeton spp., Carex spp., and Equisetum fluviatile, and in diverse vegetation stands with e.g. Polygonum amphibium, Cicuta virosa, Typha latifolia and Eleocharis acicularis. Some of the studied habitats were affected by sewage pollution, others were in comparatively undisturbed areas. Statistically significant differences between invertebrate communities in the different macrophyte associations were found. In stepwise multiple linear regression analysis the following factors were identified as determinants of abundance of aquatic invertebrates in macrophyte associations: shoot density, plant dry weight biomass, periphyton biomass, periphyton chlorophyll a, periphyton primary production, and concentrations of Sr, Mg, Ca, P, Mn, Zn, Pb and Cu. Pollution was shown to have a minor effect on the composition of littoral invertebrate communities. It is not possible to determine one single principle factor responsible for the structure and density of invertebrates in macrophyte communities.     

Periphyton and phytoplankton associated with the tropical carnivorous plant Utricularia foliosa

The abundance and taxonomic composition of periphyton attached to the bladders and phytoplankton associated with the aquatic carnivorous plant Utricularia foliosa were quantified, to determine whether periphyton associated with U. foliosa would enhances predation success. Bladder size, periphyton abundance and periphyton richness together explained 76% of the variation observed in the number of prey captured by the bladders. The abundance and richness of periphyton followed the same pattern as phytoplankton, i.e., both increased as dissolved inorganic phosphate concentration rose. This nutrient concentration explained 84 and 74% of the variation observed in richness and abundance of periphyton, respectively. This suggests that abundance and richness of the periphyton associated with U. foliosa depend mostly on environmental conditions rather than on facilitation mechanisms displayed by the plant. In conclusion, if periphyton affects U. folisosa negatively due to the competition for light or nutrients, the plant is “fated to get along with the enemy” but apparently without the capacity to manipulate this “enemy” to its own advantage.     

Effects of desiccation duration on the community structure and nutrient retention of short and long-hydroperiod Everglades periphyton mats

Responses of periphyton communities to different relevant durations of dry down were assessed. Long-hydroperiod sites within Everglades National Park remain wet for greater than 8 months of the year while short-hydroperiod mats are wet for fewer than 4 months of the year. Dry down duration of long and short-hydroperiod Everglades periphyton was manipulated from 0 to 1, 3, or 8 months after which periphyton was rewetted 1 month and examined for algal species composition. The effects of desiccation and rewetting on periphyton nutrient retention were also assessed. Relative abundance of diatoms declined from an average of 47% in the long-hydroperiod community at the start of the experiment to 24% after 1 month of desiccation and only 12% after 8 months of desiccation. Short-hydroperiod periphyton contained a lower proportion of diatoms at the outset (3%), which declined to less than 1% after the 8-month desiccation treatment. A significant increase in the filamentous cyanobacteria Schizothrix calcicola occurred in long-hydroperiod periphyton mats during this same period, but not in short-hydroperiod mats. Long-hydroperiod periphyton communities had a greater response to desiccation overall, but short-hydroperiod community structure responded to desiccation more rapidly. Because short-hydroperiod communities dry frequently, they appear to cope better to desiccating conditions than long-hydroperiod periphyton communities. This is indicated by the dominance of desiccation resistant algal taxa such as the cyanobacterial filaments S. calcicola and Scytonema hofmanni. Long-hydroperiod periphyton mat communities converge compositionally to short-hydroperiod periphyton communities after prolonged desiccation. Desiccation and rewetting caused long-hydroperiod periphyton to flux greater concentrations of nutrients than short-hydroperiod periphyton. Significant increases in efflux occurred from 1 to 8 months for total phosphorus (TP) and from 1 to 3 and 8 months for total nitrogen (TN) and total organic carbon (TOC). Thus, changes in periphyton mat community structure and function with altered hydroperiod may have long-term ecosystem effects.     

Cadmium and lead toxicity on tropical freshwater periphyton communities under laboratory-based mesocosm experiments

Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l⁻¹ Cd and 0.033 and 0.1 mg l⁻¹ Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l⁻¹) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l⁻¹) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems.     

Photosynthesis in thick cyanobacterial films: a comparison of annual and perennial antarctic mat communities

Annual and perennial cyanobacterial mats from streams on Signy Island, Antarctica, show similar areal concentrations of chlorophyll-a and areal rates of photosynthesis. Maximum rates of photosynthesis were temperature dependant over the range 0–14 C, with a Q₁₀ of approximately 2.5. Rates of photosynthesis per unit chlorophyll-a were comparable to other Antarctic mat communities but low compared to phytoplankton from upstream lakes. Areal rates of photosynthesis were however much higher than for phytoplankton. Low chlorophyll-specific rates of photosynthesis are interpreted as the effect of self shading within the mats. It is hypothesised that these mats rapidly attenuate incoming radiation and that photosynthesis in most of the mat is effectively light-limited. This situation is likely to occur in all thick periphyton films.     

Snail–periphyton interactions in a prairie lacustrine wetland

This study examined the effects of nutrients and macrophytes on snail grazers and periphyton in a prairie wetland food web. Snails (Gyraulus circumstriatus) and periphyton in large enclosures in a lacustrine wetland, Delta Marsh, MB, Canada were subjected to two experimental treatments, nutrient addition (nitrogen, phosphorus) and macrophyte exclusion (using a porous geotextile carpet) during July and August. Snail biomass and periphyton biomass (on both artificial substrata and submerged macrophytes) increased over time in all treatments, representing seasonal growth. Snail biomass was three times higher on macrophytes than on artificial substrata. In response to nutrient addition, snail biomass was significantly elevated over time on macrophytes but not on artificial substrata. Conversely, periphyton biomass was higher on artificial substrata but not on macrophytes in response to nutrient addition. Snail biomass and periphyton biomass on artificial substrata showed no response to macrophyte exclusion. Snail biomass on all substrata was inversely correlated with turbidity, whereas periphyton biomass showed no relationship with turbidity. Timing of nutrient additions to wetlands may influence whether the response occurs primarily in phytoplankton or in periphyton and macrophytes.     

Phytoplankton and periphyton responses to in situ experimental nutrient enrichment in a shallow subtropical lake

Experiments were performed in situ in shallow, subtropical LakeOkeechobee (Florida. USA) to quantify and compare the responsesof phytoplanklon (in 20 I clear polycarbonate carboys) and periphyton(on nutrient-diffusing clay substrates) to additions of nitrogenand/or phosphorus. During early and late summer. 1994, bothassemblages were nitrogen limited or co-limited by nitrogenand phosphorus, indicating the potential for competition betweenbenthic and planktonic communities. During late summer, therewas evidence that high phytoplankton biomass reduced light penetrationthrough the water column and may have suppressed periphytongrowth. The similar phytoplankton and periphyton taxonomic structures,both dominated by Lyngbya sp. and pennate diatoms, suggestedthat in shallow regions of this lake, resuspended meroplanktonmight account for a large portion of phytoplankton biomass.This phenomenon has been observed in other shallow, wind-drivenFlorida lakes.