Periphyton Community Composition Research Articles

The relationship between cellular protein content and selenium accumulation in freshwater microalgae.

Variability in the bioconcentration of selenium (Se) by primary producers at the base of the food web results in uncertainty in predictions of bioaccumulation and ecological risk to higher trophic level organisms. Water chemistry, speciation of Se, and periphyton community composition have all been suggested as factors that contribute to variability in bioconcentration by primary producers; however, the role of physiological composition of periphyton species in influencing the bioconcentration of Se has not been previously evaluated. To determine if a relationship exists between algal protein content and Se accumulation, Parachlorella kessleri, Chlorella vulgaris, and Raphidocelis subcapitata were exposed to Se (as selenate) and analyzed for total protein and tissue Se content in the exponential and stationary growth phases. Protein content and Se accumulation in R. subcapitata in the stationary phase were also measured under two light intensities. No relationship between cellular protein content and Se accumulation was found for algae in the exponential phase; however, a strong relationship was found in the stationary phase among species and for R. subcapitata under differing light intensities. Absolute Se accumulations by P. kessleri, C. vulgaris, and R. subcapitata in the stationary phase were statistically different; however, the concentrations of Se in protein were similar across species. These results suggest that cellular protein content in microalgae influences Se bioconcentration and that algal protein content may improve Se bioaccumulation modeling in food webs. Integr Environ Assess Manag 2024;00:1-10. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Spring peak flows control abundance of Cladophora in a Hydropower‐Impacted River

AbstractThe lower Deschutes River represents the 161‐km reach downstream of three hydroelectric dams flowing to its confluence at the Columbia River. We examined hydrology and nutrient chemistry from 2015–2017 to 2019 to determine factors affecting periphyton community composition and abundance following a change in the outlet structure and depth of release waters from the major upstream impoundment. The periphyton community composition was abundant and diverse in 2015 and 2016 and lower in 2017 and 2019. Filamentous chlorophytes were dominant in the first 2 years but were sparse in the subsequent years. Cyanophytes were dominant in 2017 and 2019. The expectation entering the study was that altered nutrient chemistry associated with the change in operations resulted in conditions more favorable for periphyton growth. Concentrations of total and soluble phosphorous are independent of reservoir operations, being high in all years because of natural weathering of P‐rich volcanic rocks in the basin. Concentrations of TN and DIN were low all study years, resulting in a system that was N‐limited, but with similar chemistry among the study years. The hydrology during 2015 and 2016, with abundant chlorophytes, exhibited low flow in the spring, whereas high spring flows were observed in the latter years. We conclude that high spring flows were far more influential in affecting the periphyton community composition in the lower Deschutes River compared to nutrient chemistry.

Differential selenium uptake by periphyton in boreal lake ecosystems

The largest and most variable step of selenium (Se) assimilation into aquatic ecosystems is the rapid uptake of aqueous Se by primary producers. These organisms can transfer more harmful forms of Se to higher trophic levels via dietary pathways, although much uncertainty remains around this step of Se assimilation due to site-specific differences in water chemistry, hydrological and biogeochemical characteristics, and community composition. Thus, predictions of Se accumulation are difficult, and boreal lake systems are relatively understudied. To address these knowledge gaps, five static-renewal field experiments were performed to examine the bioaccumulation of low, environmentally relevant concentrations of Se, as selenite, by naturally grown periphyton from multiple boreal lakes. Periphyton rapidly accumulated Se at low aqueous Se concentrations, with tissue Se concentrations ranging from 8.0 to 24.9 μg/g dry mass (dm) in the 1–2 μg Se/L treatments. Enrichment functions ranged from 2870 to 12 536 L/kg dm in the 4 μg Se/L treatment, to 11 867–22 653 L/kg dm in the 0.5 μg Se/L treatment among lakes. Periphyton Se uptake differed among the five study lakes, with periphyton from mesotrophic lakes generally accumulating more Se than periphyton from oligotrophic lakes. Higher proportions of charophytes and greater dissolved inorganic carbon in more oligotrophic lakes corresponded to less periphyton Se uptake. Conversely, increased proportions of bacillariophytes and total dissolved phosphorus in more mesotrophic lakes corresponded to greater periphyton Se uptake. Periphyton community composition and water chemistry variables were correlated, limiting interpretation of differences in periphyton Se accumulation among lakes. The results of this research provide insight on the biodynamics of Se assimilation at the base of boreal lake food webs at environmentally relevant concentrations, which can potentially inform ecological risk assessments in boreal lake ecosystems in North America.

Herbicide-Induced Shifts in the Periphyton Community Composition Indirectly Affect Feeding Activity and Physiology of the Gastropod Grazer Physella acuta.

Herbicides are well known for unintended effects on freshwater periphyton communities. Large knowledge gaps, however, exist regarding indirect herbicide impacts on primary consumers through changes in the quality of periphyton as a food source (i.e., diet-related effects). To address this gap, the grazer Physella acuta (Gastropoda) was fed for 21 days with periphyton that grew for 15 days in the presence or absence of the herbicide diuron (8 μg/L) to quantify changes in the feeding rate, growth rate, and energy storage (neutral lipid fatty acids; NLFAs) of P. acuta. Periphyton biomass, cell viability, community structure, and FAs served as proxies for food quality that support a mechanistic interpretation of the grazers' responses. Diuron changed the algae periphyton community and fatty acid profiles, indicating alterations in the food quality, which could explain differences in the snails' feeding rate compared to the control. While the snails' growth rate was, despite an effect size of 55%, not statistically significantly changed, NLFA profiles of P. acuta were altered. These results indicate that herbicides can change the food quality of periphyton by shifts in the algae composition, which may affect the physiology of grazers.

Ecological Mapping in Assessing the Impact of Environmental Factors on the Aquatic Ecosystem of the Arys River Basin, South Kazakhstan

Assessment of the water quality of the Arys River basin based on the spatial distribution of richness of phytoperiphyton communities and abiotic variables was given for the first time. Altogether, 82 species were revealed in phytoperiphyton, including Bacillariophyta of 51, Cyanobacteria of 20, Chlorophyta of 7, and Charophyta of 4. Cluster analysis revealed the uniqueness of the composition of periphyton communities related to the abiotic conditions. The environmental preferences of the algae indicated fresh organic pollution in the lower reaches of the Arys River and weak or moderate levels of organic pollution in the rest of the basin. The ecological mapping of chemical data generally confirmed this conclusion. According to the maps, the highest water quality was revealed in the upper stream of the basin. The middle part of the river basin had the lowest water quality in terms of transparency, nitrite-nitrogen, and nitrate-nitrogen. The downstream of the Arys was characterized by a secondary deterioration in water quality according to the Aquatic Ecosystem State Index (WESI) index. We revealed the complicated interaction between natural and anthropogenic factors that caused changes in water quality in the Arys River basin.

The Perifiton Alga Community in Masang Kecil River Receives Liquid Palm Oil Mill Waste in Kinali District, West Pasaman Regency

The study of the periphyton algae community in Masang Kecil River that received palm oil mill effluent in Kinali District, West Pasaman Regency was held from November 2017 to September 2018. This study aims to determine the composition and structure of periphyton communities in the Masang Kecil River in Kinali, West Pasaman. This study used purposive sampling method with a sampling location of 4 stations. Based on this study, 88 species of periphyton were classified as 3 classes i.e Bacillariophyceae (64 species), Chlorophyceae (15 species) and Cyanophyceae (9 species). The average density is 8.967 ind/ cm2. The highest relative density (KR) at stations 1,2 and 3 is Navicula lanceolata and station 4 is Fragilaria capucina. Species that are always found at each station (FK= 100%) are Fragilaria capucina, Navicula lanceolata and Synedra ulna. The diversity index in the Masang Kecil River is classified as medium (H’ = 2.87). Equitability index is evenly distributed (E= 0.64). Dominance index (C= 0.12) there is no dominant species. The similarity index is almost the same except between stations 1 and 3.

Periphyton development during summer stratification in the presence of a metalimnetic bloom of Planktothrix rubescens

Cyanobacterial blooms have become common all over the world, negatively affecting various ecosystem components. Planktothrix rubescens is a planktonic cyanobacterium that frequently causes blooms in temperate (mostly mesotrophic) lakes in Europe and, unlike other cyanobacteria, it is usually associated with ecosystem re-oligotrophication. The potential effects of P. rubescens on periphyton development have not been estimated in any recently published studies. The objective of the present paper was to assess how a Planktohrix rubescens bloom affects periphyton development in a temperate freshwater reservoir. A field study was performed in the Vrutci reservoir (western Serbia), where P. rubescens blooms have occurred since December of 2013. Periphyton was grown on glass slides that were incubated following lake stratification and sampled monthly from July to October of 2015. Dry mass, ash free dry mass and content of chlorophyll a, as well as composition of the community of developed periphyton, were estimated, together with P. rubescens biomass in the water column at the particular depths where substrates for periphyton were incubated. The metalimnetic bloom of P. rubescens induced calcite precipitation on the incubated substrates, which was reflected in obstructed colonization. The periphyton community composition was mainly determined by the depth gradient, which was potentially related to reduced light availability driven by shading effects caused by the P.rubescens bloom. Our results provide a significant update on periphyton ecology in relation to cyanobacterial blooms, elucidating complex interactions in the ecosystem. They also represent a stimulus for further studies on the capacity of P. rubescens for induction of calcium carbonate precipitation in lakes.

Selenium oxyanion bioconcentration in natural freshwater periphyton

Selenium (Se) enrichment has been demonstrated to vary by several orders of magnitude among species of planktonic algae. This is a substantial source of uncertainty when modelling Se biodynamics in aquatic systems. In addition, Se bioconcentration data are largely lacking for periphytic species of algae, and for multi-species periphyton biofilms, adding to the challenge of modelling Se transfer in periphyton-based food webs. To better predict Se dynamics in periphyton dominated, freshwater ecosystems, the goal of this study was to assess the relative influence of periphyton community composition on the uptake of waterborne Se oxyanions. Naturally grown freshwater periphyton communities, sampled from five different water bodies, were exposed to environmentally relevant concentrations of selenite [Se(IV)] or selenate [Se(VI)] (nominal concentrations of 5 and 25 μg Se L−1) under similar, controlled laboratory conditions for a period of 8 days. Unique periphyton assemblages were derived from the five different field sites, as confirmed by light microscopy and targeted DNA sequencing of the plastid 23S rRNA gene in algae. Selenium accumulation demonstrated a maximum of 23.6-fold difference for Se(IV) enrichment and 2.1-fold difference for Se(VI) enrichment across the periphyton/biofilm assemblages tested. The assemblage from one field site demonstrated both high accumulation of Se(IV) and iron, and was subjected to additional experimentation to elucidate the mechanism(s) of Se accumulation. Selenite accumulation (at nominal concentrations of 5 and 25 μg Se L−1 and mean pH of 7.5 across all treatment replicates) was assessed in both unaltered and heat-killed periphyton, and in periphyton from the same site grown without light to exclude phototrophic organisms. Following an exposure length of 8 days, all periphyton treatments showed similar levels of Se accumulation, indicating that much of the apparent uptake of Se(IV) was due to non-biological processes (i.e., surface adsorption). The results of this study will help reduce uncertainty in the prediction of Se dynamics and food-chain transfer in freshwater environments. Further exploration of the ecological consequences of extracellular adsorption of Se(IV) to periphyton, rather than intracellular absorption, is recommended to further refine predictions related to Se biodynamics in freshwater food webs.

Effects of macroconsumers on benthic communities: Rapid increases in dry-season accrual of calcium in a tropical karst stream.

Species loss from upper trophic levels can result in some major changes in community structure and ecosystem functions. Here, we experimentally excluded macroconsumers (e.g., fish and shrimp) in a Brazilian karst tropical stream during the dry season to investigate if their loss affected the accrual of calcium, dry mass (DM) and ash-free dry mass (AFDM) of sediment, benthic invertebrates, and chlorophyll-a. We found that the exclusion of macroconsumers decreased accrual of calcium. The absence of fish and shrimp may have promoted increased grazing by mayflies and snails in the electrified treatment as expressed by the depressed calcium accrual and shift in periphyton community composition. However, the exclusion of macroconsumers had no effect on DM and AFDM, chlorophyll-a, or total abundance of invertebrates. Our findings shed new light on the impact of macroconsumer loss and consequences for calcium accrual in karstic streams.

Genetic Characterization of Periphyton Communities Associated with Selenium Bioconcentration and Trophic Transfer in a Simple Food Chain.

A major source of uncertainty in predicting selenium (Se) distribution in aquatic food webs lies in the enrichment factor (EF), the ratio of Se bioconcentration in primary producers and microorganisms relative to the concentration of Se in the surrounding water. It has been well demonstrated that EFs can vary dramatically among individual algal taxa, but data are lacking regarding the influence of periphyton community composition on EFs for a given geochemical form of Se. Therefore, the goals of this study were first to assess whether different periphyton communities could be established in aquaria with the same starting inoculum using different light and nutrient regimes, and second, to determine if the periphyton assemblage composition influences the uptake of waterborne Se (as selenite) and subsequent Se transfer to a model macroinvertebrate primary consumer. Periphyton biofilms were grown in aquaria containing filtered pond water (from Saskatoon, SK) spiked with approximately 20 μg Se/L (mean measured concentration 21.0 ± 1.2 μg Se/L), added as selenite. Five different light and nutrient regimes were applied to the aquaria (three replicates per treatment) to influence biofilm community development. After 6 weeks of biofilm maturation, 40 to 80 immature cultured snails (Stagnicola elodes) were added to each aquarium. The bacterial and algal members of the periphyton community were characterized by targeted metagenomic analyses before and after addition of snails to ensure the snails themselves did not significantly alter the biofilm community. Samples were collected for Se analysis of water, periphyton, and whole-body snail. The nutrient and light treatments resulted in substantially different compositions of the periphytic biofilms, with each being relatively consistent across replicates and throughout the study. Although the aqueous concentration of dissolved Se administered to treatments was constant, uptake by the different periphytic biofilms differed significantly. Both the low-light (61.8 ± 12.1 μg Se/g d.w.) and high-light (30.5 ± 4.7 μg Se/g d.w.) biofilms, which were found to have high proportions of cyanobacteria, contained statistically higher concentrations of Se relative to the other treatments. Furthermore, the concentration of Se in bulk periphyton was predictive of Se bioaccumulation in grazing snails but as an inverse relationship, opposite to expectations. The trophic transfer factor was inversely correlated with periphyton enrichment factor (r = -0.841). A number of different bacterial and algal taxa were correlated (either positively or negatively) with Se accumulation in periphyton biofilm and snails. Recent advancements in genetic methods make it possible to conduct detailed characterization of periphyton assemblages and begin to understand the influence that periphyton composition has on Se biodynamics in aquatic systems.

Preliminary evaluation of an in vivo fluorometer to quantify algal periphyton biomass and community composition

The bbe-Moldaenke BenthoTorch (BT) is an in vivo fluorometer designed to quantify algal biomass and community composition in benthic environments. The BT quantifies total algal biomass via chlorophyll a (Chl-a) concentration and may differentiate among cyanobacteria, green algae, and diatoms based on pigment fluorescence. To evaluate how BT measurements of periphytic algal biomass (as Chl-a) compared with an ethanol extraction laboratory analysis, we collected BT- and laboratory-measured Chl-a data from 6 stream sites in the Indian Creek basin, Johnson County, Kansas, during August and September 2012. BT-measured Chl-a concentrations were positively related to laboratory-measured concentrations (R2 = 0.47); sites with abundant filamentous algae had weaker relations (R2 = 0.27). Additionally, on a single sample date, we used the BT to determine periphyton biomass and community composition upstream and downstream from 2 wastewater treatment facilities (WWTF) that discharge into Indian Creek. We found that algal biomass increased immediately downstream from the WWTF discharge then slowly decreased as distance from the WWTF increased. Changes in periphyton community structure also occurred; however, there were discrepancies between BT- and laboratory-measured community composition data. Most notably, cyanobacteria were present at all sites based on BT measurements but were present at only one site based on laboratory-analyzed samples. Overall, we found that the BT compared reasonably well with laboratory methods for relative patterns in Chl-a but not as well with absolute Chl-a concentrations. Future studies need to test the BT over a wider range of Chl-a concentrations, in colored waters, and across various periphyton assemblages.

Composition of Periphyton Community on Water Hyacinth (Eichhornia crassipes): In Analysis of Environmental Characteristics at Ejirin Part of Epe Lagoon in Southwestern Nigeria

The composition of periphyton community on water hyacinth was investigated at Ejirin, part of Epe Lagoon, in relation to environmental characteristics from December 2012 to May 2013. A total of 14,536 individuals of 104 species belonging to five divisions were identified, with Bacillariophyta (82.69%), Cyanobacteria (10.43%), Chlorophyta (5.63%), and Euglenophyta (1.15%). The total species abundance observed showed a strong correlation with rainfall (r = 0.745) and strongly significant correlation with TDS (r=0.836*;P >0.05). Biochemical oxygen demand value remained (BOD)≤4.8 mg/L while Shannon-Wiener index value remained (Hs)≤ 1.47. The presence of the following organisms could be used as an indicator of environmentally stressed aquatic ecosystem: euglenoids, blue green algae,Nitzschia palea,Surirellasp.,Pinnulariasp.,Gomphonema parvulum,Mougeotiasp.,Spirogyrasp.,Trachelomonas affinis(Lemm.), andT. ensifera Daday; T. gibberosaPlayf. andPhormidium articulatum;Lyngbya intermedia;Cymbella ventricosa;Eunotia arcus;Surirella linearisandClosterium parvulumNag.

Light increases energy transfer efficiency in a boreal stream.

Periphyton communities of a boreal stream were exposed to different light and nutrient levels to estimate energy transfer efficiency from primary to secondary producers using labeling with inorganic 13C. In a one-day field experiment, periphyton grown in fast-flow conditions and dominated by opportunistic green algae were exposed to light levels corresponding to sub-saturating (forest shade) and saturating (open stream section) irradiances, and to N and P nutrient additions. In a two-week laboratory experiment, periphyton grown in low-flow conditions and dominated by slowly growing diatoms were incubated under two sub-saturating light and nutrient enrichment levels as well as grazed and non-grazed conditions. Light had significant positive effect on 13C uptake by periphyton. In the field experiment, P addition had a positive effect on 13C uptake but only at sub-saturating light levels, whereas in the laboratory experiment nutrient additions had no effect on the periphyton biomass, 13C uptake, biovolume and community composition. In the laboratory experiment, the grazer (caddisfly) effect on periphyton biomass specific 13C uptake and nutrient content was much stronger than the effects of light and nutrients. In particular, grazers significantly reduced periphyton biomass and increased biomass specific 13C uptake and C:nutrient ratios. The energy transfer efficiency, estimated as a ratio between 13C uptake by caddisfly and periphyton, was positively affected by light conditions, whereas the nutrient effect was not significant. We suggest that the observed effects on energy transfer were related to the increased diet contribution of highly palatable green algae, stimulated by higher light levels. Also, high heterotrophic microbial activity under low light levels would facilitate energy loss through respiration and decrease overall trophic transfer efficiency. These findings suggest that even a small increase in light intensity could result in community-wide effects on periphyton in boreal streams, with a subsequent increase in energy transfer and system productivity.

Climate warming and agricultural stressors interact to determine stream periphyton community composition.

Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate.

How periphytic algae respond to short-term emersion in a subtropical floodplain in Brazil

Algarte V.M., and Rodrigues L. 2013. How periphytic algae respond to short-term emersion in a subtropical floodplain in Brazil. Phycologia 52: 557–564. DOI: 10.2116/12-112.1Changes in hydrometric levels caused by dam operations can alter community structure in aquatic environments. We investigated the effects of a short-term emersion on a periphyton community in a lentic environment in a subtropical floodplain in Brazil. Our goals were to identify variations in periphyton community structure and composition during a period of 21 days subsequent to a short-term emersion and to identify taxa associated with periphyton after the emersion event. In situ, we simulated 15 hours of emersion of the periphyton community during the climax stage and investigated the effects of emersion on the structure and composition of this community over 21 days. Periphyton was removed by scrubbing randomly chosen glass slides from the support controls and the treatments. The structure and composition of the periphyton community showed variations soon after emersion, e.g. new taxa were recorded, the diatoms and oedogoniophyceans were lost; furthermore, the community did not return to its initial successional phase after the disturbance. Canonical ordination analysis showed a variation in community composition and structure throughout the successional period, and axis two indicated variation in the community soon after the emersion disturbance occurred in the control and treatment periphyton. Similarities between the control and treatment periphyton communities were lower soon after emersion and higher after the fifth day after emersion. Loosely attached species characterised the treatment periphyton after the disturbance. Recovery of the periphyton community may have been influenced by the reproduction of persistent species and by recruitment from the regional species pool. Short-term emersion affected the structure and composition of the periphyton community in the Upper Paraná floodplain; however, its rapid recovery to pre-disturbance conditions suggested that it is already adapted to the intensified variations that occur in this system because of dam operations.

Influence of Changing Water Sources and Mineral Chemistry on the Everglades Ecosystem

Human influences during the previous century increased mineral inputs to the Florida Everglades by changing the sources and chemistry of surface inflows. Biogeochemical responses to this enrichment include changes in the availability of key limiting nutrients such as P, the potential for increased turnover of nutrient pools due to accelerated plant decomposition, and increased rates of mercury methylation associated with sulfate enrichment. Mineral enrichment has also been linked to the loss of sensitive macrophyte species, although dominant Everglades species appear tolerant of a broad range of mineral chemistry. Shifts in periphyton community composition and function provide an especially sensitive indicator of mineral enrichment. Understanding the influence of mineral chemistry on Everglades processes and biota may improve predictions of ecosystem responses to ongoing hydrologic restoration efforts and provide guidelines for protecting remaining mineral-poor areas of this peatland.

The effects of copper and zinc on biomass and taxonomic composition of algal periphyton communities from the River Gharasou, Western Iran

The effects of copper and zinc on biomass and taxonomic composition of algal periphyton communities from the River Gharasou, Western Iran Indoor artificial streams were used to evaluate the short-term (24 day) influence of copper and zinc, individually and in combination, on the biomass and taxonomic composition of algal periphyton communities. The effects of Cu (50 μg 1-1) and Zn (1 mg 1-1) were assessed using measurements of biomass, ash-free dry mass (AFDM), chlorophyll-a concentration, taxonomic composition and biovolume. In artificial streams with Cu, Zn and Cu+Zn, there were significant (p > 0.05) reductions of chlorophyll-a concentrations, dry mass and AFDM, and also changes in the species diversity and relative abundances of periphyton species. In artificial streams containing both Cu and Zn the taxonomic composition shifted from a Cyanophyceaen dominated community to one consisting mainly of Chlorophyceae, whilst the relative contribution of Bacillariophyceae was not significantly altered.

Effects of a thermal discharge from a nuclear power plant on phytoplankton and periphyton in subtropical coastal waters

Effects of elevated water temperatures and residual chlorine from a thermal discharge at a coastal nuclear power plant on the biomass and productivity of periphyton and phytoplankton were determined in subtropical Taiwan. Phytoplankton chlorophyll a, but not productivity, was significantly lower in the outlet region than in the intake region. Periphyton chlorophyll a was significantly greater in the outlet region than in the intake region. Nevertheless, periphyton productivity was negatively correlated with water temperature in the outlet region. A distinct difference in periphyton community composition was also detected between the two regions. Chlorination experiments showed that a chlorine concentration of 0.2 ppm greatly suppressed phytoplankton productivity, regardless of whether the water temperature was elevated or not. However, periphyton productivity was little influenced by a chlorine concentration of < 0.5 ppm. Our results suggest that phytoplankton productivity was greatly affected by residual chlorine, but periphyton productivity was more affected by elevated water temperatures.

人工水路において添加された微細粒子の堆積が付着藻類の群落構造に与える影響

付着藻類群落の発達過程に及ぼす微細懸濁物質堆積の影響を，人工水路を用いた実験により調べた。化学的に安定な微細炭化珪素粒子を添加した人工水路および添加していない人工水路において発達した付着藻類群落の，クロロフィルa 量，種組成および立体構造を比較した。水路に設置した基板を1，3，9-12，20-23日後に回収して観察し，計6回の繰り返し実験を行った。微細懸濁物質の有無は付着藻類群落の種組成とクロロフィルa量に大きな違いをもたらさなかった。一方，群落の発達過程および立体構造には違いが見られた。クロロフィルa量は微細粒子を添加していない水路では9-12日目から20-23日目の間に，減少することが多かったのに対して，微細粒子を添加した水路では引き続き増加した。微細粒子を添加した水路では，微細粒子が藻類細胞と共に堆積し，間隙の少ない密な構造が形成されていた。この構造が，光合成による気泡の発生および水流による付着藻類の剥離を抑えたと考えられる。

Effects of the antifouling compound, Irgarol 1051, on a simulated estuarine salt marsh ecosystem

Toxicity effects of the antifouling compound, Irgarol 1051, were examined using a simulated estuarine salt marsh ecosystem. The 35 day mesocosm exposure incorporated tidal flux and contained seawater, sediments, marsh grass, and estuarine biota. Irgarol (10.0 microg/l) caused a significant reduction in phytoplankton biomass and primary productivity. HPLC pigment analysis indicated significant effects of irgarol on both phytoplankton and periphyton community composition, with decreased concentrations of pigments representative of diatom species. There was also a significant decrease in dissolved oxygen levels in the 10.0 microg/l irgarol treatment. Growth of the hard shell clam was significantly reduced in the 1.0 and 10.0 microg/l irgarol treatments. The effects observed occurred at irgarol concentrations greater than those typically measured in the environment. Prolonged exposure, the accumulation of irgarol in sediments, plant, or animal tissues, and the interaction of irgarol with other chemicals in the environment; however, could increase risk.