Population dynamics and body composition of the Arctic hyperiid amphipod Themisto libellula in Svalbard fjords

Population structure, growth and body composition (wet-, dry-, ash weight and total lipid) of the Arctic pelagic amphipod Themisto libellula were studied in four fjords on West Spitsbergen, Svalbard, from July to December 2000 and in April 2002. In one of the fjords, Kongsfjorden, growth of T. libellula was calculated as the change in mean length of the 0+ cohort from July to December. The young were released from the brood pouches in early spring (March–April). Summer growth was 3.5 mm month⁻¹, whereas growth during the autumn was only 0.6 mm month⁻¹. The size frequency distributions indicated a 2–2.5 year life-span. The size structure of the population in Hornsund, the southernmost fjord on Spitsbergen, indicated a delayed time of spawning. The storage of lipids in T. libellula occurred during late summer and towards the winter, when the food items contain the maximum amount of stored lipids.     

Spatial and seasonal patterns of periphyton biomass and productivity in the northern Everglades,Florida, U.S.A.

We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity, and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m⁻²) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of sawgrass,Cladium jamaicense (7–52 g AFDM m⁻²). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m⁻²) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality. Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m⁻²d⁻¹) and oligotrophic (1.75–11.49 g C m⁻²d⁻¹) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have important implications for efforts to manage this wetland in asustainable manner. This revised version was published online in July 2006 with corrections to the Cover Date.     

SPECIES COMPOSITION,BIOMASS, AND NUTRIENT CONTENT OF PERIPHYTON IN THE FLORIDA EVERGLADES1

Periphyton biomass, nutrient dynamics in the biomass, and species composition were studied in two Florida Everglades sloughs from August 1991 to August 1992. Periphyton biomass on macrophytes was strongly season-dependent. Maximum biomasses, 1180, 161, and 59 g dry mass.m^?2 on Eleocharis vivipara, E. cellulosa, and Nymphaea odorata, respectively, occurred in summer and early autumn; winter and spring periphyton biomass was very low (practically not measurable). Periphyton was dominated by blue-green algae (cyanobacteria) during the summer and autumn; diatoms dominated during the winter and spring. Green algae occurred mostly during the summer and autumn, but their growth was sparse and did not contribute significantly to periphyton biomass. Nitrogen-to-phosphorus ratios in the periphyton were very high (59–121:1), suggesting phosphorus limitation of periphyton growth. The periphyton contained large concentrations of calcium (up to 22.3% on dry mass basis) especially in late summer and autumn.     

Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades

Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations, water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic) and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic, they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton net production of 1.08 mg C AFDW⁻¹ h⁻¹ and periphyton whole system respiration of 0.38 mg C AFDW⁻¹ h⁻¹ rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean biomass over all our study sites was high, 1517.30 g AFDW m⁻². Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g⁻¹ and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely low mean water total phosphorus concentrations ( ≤ 0.21 μmol l⁻¹), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows. These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water source.     

Estimation of periphytic microalgae gross primary production with DCMU-fluorescence method in Yenisei River (Siberia, Russia)

Periphyton (epilithon) gross primary production (GPP) was estimated using the DCMU-fluorescence method in the Yenisei River. In the unshaded littoral zone, chlorophyll a concentration (Chl a) and GPP value varied from 0.83 to 973.74 mg m⁻²and 2–304,425 O₂ m⁻² day⁻¹ (0.64–95 133 mg C m⁻² day⁻¹), respectively. Positive significant correlation (r = 0.8) between daily GPP and periphyton Chl a was found. Average ratio GPP:Chl a for periphyton was 36.36 mg C mg Chl a m⁻² day⁻¹. The obtained GPP values for the Yenisei River have a high significant correlation with values predicted by a conventional empirical model for stream periphyton. We concluded that the DCMU-fluorescence method can be successfully used for measuring of gross primary production of stream phytoperiphyton at least as another useful tool for such studies.     

Periphyton biomass and ecological stoichiometry in streams within an urban to rural land-use gradient

This study examined the effects land use on biomass and ecological stoichiometry of periphyton in 36 streams in southeastern New York State (USA). We quantified in-stream and land-use variables along a N–S land-use gradient at varying distances from New York City (NYC). Streams draining different landscapes had fundamentally different physical, chemical, and biological properties. Human population density significantly decreased (r = −0.739; P < 0.00001), while % agricultural land significantly increased (r = 0.347; P = 0.0379) with northing. Turbidity, temperature, conductivity, and dissolved Mg, Ca, SRP, pH, DOC, and Si significantly increased in more urban locations, but NO₃ ⁻ and NH₄ ⁺ did vary not significantly along the gradient. Periphyton biomass (as AFDM and Chl-a) in rural streams averaged one-third to one-fifth that measured in urban locations. Periphyton biomass in urban streams averaged 18.8 ± 6.0 g/m² AFDM and 75.6 ± 28.5 mg/m² Chl-a. Urban Chl-a levels ranging between 100 and 200 mg/m², are comparable to quantities measured in polluted agricultural streams in other regions, but in our study area was not correlated with % agricultural land. Periphyton nutrient content also varied widely; algal C varied >20-fold (0.06–1.7 μmol/mm²) while N and P content varied >6-fold among sites. Algal C, N, and P correlated negatively with distance from NYC, suggesting that periphyton in urban streams may provide greater nutrition for benthic consumers. C:N ratios averaged 7.6 among streams, with 91% very close to 7.5, a value suggested as the optimum for algal growth. In contrast, periphyton C:P ratios ranged from 122 to >700 (mean = 248, twice Redfield). Algal-P concentrations were significantly greater in urban streams, but data suggest algal growth was P-limited in most streams regardless of degree of urbanization. GIS models indicate that land-use effects did not easily fit into strict categories, but varied continuously from rural to urban conditions. We propose that the gradient approach is the most effective method to characterize the influence of land use and urbanization on periphyton and stream function.     

Spring-to-summer changes and regional variability of benthic processes in the western Canadian Arctic

Seasonal dynamics in the activity of Arctic shelf benthos have been the subject of few local studies, and the pronounced among-site variability characterizing their results makes it difficult to upscale and generalize their conclusions. In a regional study encompassing five sites at 100–595 m water depth in the southeastern Beaufort Sea, we found that total pigment concentrations in surficial sediments, used as proxies of general food supply to the benthos, rose significantly after the transition from ice-covered conditions in spring (March–June 2008) to open-water conditions in summer (June–August 2008), whereas sediment Chl a concentrations, typical markers of fresh food input, did not. Macrobenthic biomass (including agglutinated foraminifera >500 μm) varied significantly among sites (1.2–6.4 g C m⁻² in spring, 1.1–12.6 g C m⁻² in summer), whereas a general spring-to-summer increase was not detected. Benthic carbon remineralisation also ranged significantly among sites (11.9–33.2 mg C m⁻² day⁻¹ in spring, 11.6–44.4 mg C m⁻² day⁻¹ in summer) and did in addition exhibit a general significant increase from spring-to-summer. Multiple regression analysis suggests that in both spring and summer, sediment Chl a concentration is the prime determinant of benthic carbon remineralisation, but other factors have a significant secondary influence, such as foraminiferan biomass (negative in both seasons), water depth (in spring) and infaunal biomass (in summer). Our findings indicate the importance of the combined and dynamic effects of food supply and benthic community patterns on the carbon remineralisation of the polar shelf benthos in seasonally ice-covered seas.     

Phosphorus uptake and turnover by periphyton in the presence of suspended clays

We investigated the effect of suspended bentonite and kaolinite clays on phosphorus uptake and turnover by lotic periphyton in laboratory microcosms. Clays were characterized for their phosphorus affinity using laboratory batch experiments. Periphyton cultivated on glass microscope slides was subjected to a 0.02 mg L⁻¹ radiolabeled soluble reactive phosphorus solution in which a 200-mg L⁻¹ clay load was suspended. A 1-h uptake experiment was followed by a 10-day turnover experiment. Biomass normalized phosphorus uptake, and turnover rates were described by mean rate constants ranging from 0.14 to 0.17 min⁻¹ for uptake and 0.04–0.07 days⁻¹ for turnover. Mean phosphorus concentrations were compared among treatments using repeated measures analysis of variance (ANOVA). Mean phosphorus concentrations among treatments were compared using one-way ANOVA. No significant differences were found among treatments for either analysis. Under laboratory conditions, these clays appear to have little or no short-term influence upon phosphorus uptake or turnover by periphyton.     

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.     

The influence of large water level fluctuations and hurricanes on periphyton and associated nutrient storage in subtropical Lake Okeechobee,USA

The abundance, community structure and nutrient content of periphyton, and the host plant taxa Chara, Hydrilla, Potamogeton, Vallisneria and Scirpus were studied in Lake Okeechobee, USA. Water levels were generally high during the study period (August 2002–January 2006), but substantial fluctuations occurred. All host plant biomass was seasonally variable but only Vallisneria biomass was spatially variable. All submerged plant beds disappeared after the passage of two hurricanes in September 2004, and a third hurricane passed over the lake in October 2005. Periphyton assemblages were statistically separated most by substrate and then by season. Prior to the hurricanes, annual maxima of periphyton biovolumes and those of summer submerged plant coverage coincided. During all study years, the diatom taxa dominated periphyton total biovolumes. Periphyton biomass was generally highest during the summer or prior to the hurricanes (in the case of epiphytes) and was spatially variable in the case of both Scirpus and Vallisneria. Epiphytic nutrient contents within each host plant group seasonally varied except for nitrogen and carbon in the Vallisneria epiphytes. Epipelic nutrient contents were spatially variable and seasonally variable for carbon. Nutrient contents in epipelon were significantly higher than that in Scirpus epiphytes and were similar but lower among all epiphytic communities. The total annual areal potential epiphytic phosphorus storage extrapolated during this study (2.0 × 10⁻⁴ metric tons ha⁻¹ year⁻¹) was underestimated because storage estimates for epipelon, Chara and Hydrilla-associated epiphytes were omitted. The Chara and Hydrilla-associated epiphytic nutrient storage values were omitted because of limited data, whereas the epipelic data may have not been spatially representative. For periphyton biovolume, host substrate type, water level fluctuation and hurricane impacts on host substrates appear to be more important than seasonal variation in such factors as temperature and nutrients. Epiphytic nutrient storage appears to be influenced most by water level fluctuation and hurricane-related impacts, while the host substrate type appears to be a less important factor than it is for periphyton biovolume. Maximum periphyton biomass and high nutrient storage in shallow subtropical and tropical eutrophic lakes may only occur at consistently lower water levels and during infrequent periods of disturbance, which enhance host substrate colonizable area.     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Periphyton nitrogenase activity as an indicator of wetland eutrophication: spatial patterns and response to phosphorus dosing in a northern Everglades ecosystem

The use of periphyton nitrogenase activity (biological N₂ fixation) as an indicator of wetland P impact was assessed using patterns of nutrient content (C, N, P, Ca, Mg, K, Fe, and Mn) and acetylene reduction (AR) in floating cyanobacterial periphyton mat (metaphyton) communities of a P-enriched portion of the Florida Everglades, USA (Water Conservation Area-2A, WCA-2A). Spatial patterns of nutrients indicate the enrichment of floating mat periphyton N, P, Fe, and K, and the reduction of Mn and TN:TP in enriched marsh areas. In highly enriched areas, floating mat periphyton AR was approximately threefold greater than that in less enriched, interior marsh zones. Multiple regression models indicated AR dependence on P in eutrophic WCA-2A areas while the AR of more interior marsh periphyton mats was more closely related to tissue levels of Ca and Fe. Nitrogenase activity of floating mat periphyton from P-loaded mesocosms revealed a significant enhancement of N₂ fixation in samples receiving approximately 2–3 mg P m⁻² of cumulative P dosing or with biomass TP content of 100–300 mg kg⁻¹. At P contents above the optimum, mat periphyton AR was suppressed possibly as a result of changes in species composition or increased levels of NH₄⁺. After 3 years of dosing, consistently high AR occurred only at low rates of P enrichment (0.4–0.8 g P m⁻² yr⁻¹), and the patterns appeared to be seasonal. These findings agree with the hypothesis that P availability is a key determinant of nitrogenase activity in aquatic systems, and thus, may support the use of periphyton nitrogenase to indicate P impacts in P-limited systems. These results also demonstrate the potential existence of a P threshhold for biogeochemical alteration of periphyton mat function in the Everglades, and that cumulative loading of limiting nutrients (i.e., P), rather than instantaneous concentrations, should be considered when evaluating nutrient criteria.     

Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient

Replicated, factorial mesocosm experiments were conducted across Europe to study the effects of nutrient enrichment and fish density on macrophytes and on periphyton chlorophyll a (chl-a) with regard to latitude. Periphyton chl-a densities and plant decline were significantly related to nutrient loading in all countries. Fish effects were significant in a few sites only, mostly because of their contribution to the nutrient pool. A saturation-response type curve in periphyton chl-a with nutrients was found, and northern lakes achieved higher densities than southern lakes. Nutrient concentration and phytoplankton chl-a necessary for a 50% plant reduction followed a latitudinal gradient. Total phosphorus values for 50% plant disappearance were similar from Sweden (0.27 mg L⁻¹) to northern Spain (0.35 mg L⁻¹), but with a sharp increase in southern Spain (0.9 mg L⁻¹). Planktonic chl-a values for 50% plant reduction increased monotonically from Sweden (30 μg L⁻¹) to València (150 μg L⁻¹). Longer plant growing-season, higher light intensities and temperature, and strong water-level fluctuations characteristic of southern latitudes can lead to greater persistence of macrophyte biomass at higher turbidities and nutrient concentration than in northern lakes. Results support the evidence that latitudinal differences in the functioning of shallow lakes should be considered in lake management and conservation policies.     

Distribution and characterization of dissolved and particulate organic matter in Antarctic pack ice

Distribution and composition of organic matter were investigated in Antarctic pack ice in early spring and summer. Accumulation of organic compounds was observed with dissolved organic carbon (DOC) and particulate organic carbon (POC) reaching 717 and 470 μM C, respectively and transparent exopolymeric particles (TEP) up to 3,071 μg Xanthan gum equivalent l⁻¹. POC and TEP seemed to be influenced mainly by algae. Particulate saccharides accounted for 0.2–24.1% (mean, 7.8%) of POC. Dissolved total saccharides represented 0.4–29.6% (mean, 9.7%) of DOC, while dissolved free amino acids (DFAA) accounted for only 1% of DOC. Concentrations of TEP were positively correlated with those of saccharides. Monosaccharides (d-MCHO) dominated during winter–early spring, whereas dissolved polysaccharides did in spring–summer. DFAA were strongly correlated with d-MCHO, suggesting a similar pathway of production. The accumulation of monomers in winter is thought to result from limitation of bacterial activities rather than from the nature of the substrates.     

Spatio-temporal variation of periphyton biomass and accumulation in a temperate spring-fed stream

Spatio-temporal variation of plant populations often can demonstrate synchronous patterns, particularly within highly connected landscapes. Periphyton biomass (chlorophyll a) and net accumulation were measured at five sites in a spring-fed fourth-order stream located in central Pennsylvania with a mixed land-uses watershed (Spring Creek, USA) to characterize longitudinal variation within the stream. Samples were collected at three-week intervals over one year to describe seasonal patterns of periphyton biomass and net production (n = 17 per site). Spring Creek periphyton biomass and net accumulation increased dramatically from the headwaters to downstream (range 10–1,000 mg/m²). The downstream reaches had exceptionally large algal biomass (chlorophyll a > 300 mg/m²) and potential for rapid turnover. Varying degrees of seasonality were observed among the sites, with upstream sites showing more temporal variation but no distinct seasonal pattern. Despite this, large-scale disturbances within the watershed seem to promote synchrony among sites throughout the stream as reflected by close correlations in chlorophyll values (Pearson correlation coefficient r > 0.50).     

Bacterioplankton of the Gdansk Basin,Baltic Sea

The numbers, biomass, and production of bacterioplankton were determined in the Russian Sector of the Gdansk Basin (Baltic Sea) in 2007–2009. Significant spatial and temporal variations were determined. During the year, bacterial activity increased with increasing water temperature and higher availability of organic substrates. The lowest bacterial production (0.01–31.63 mg C m⁻³ day⁻¹) was observed in late winter and late autumn, while the highest (0.17–341.70 mg C m⁻³ day⁻¹) occurred in spring and summer. Since bacterial numbers and biomass were found to depend on the weather conditions and the terrigenous inflow, significant variations were observed from year to year. The highest and lowest numbers and biomass of bacterioplankton determined in summer were 0.09–1.10 × 10⁶ cells mL⁻¹ and 2–22 mg C m⁻³ for July 2007 and 1.96–11.23 × 10⁶ cells mL⁻¹ and 23–123 mg C m^–3 for July 2009. The values of these parameters were the highest along the coast and decreased towards the open sea.     

Catabolic diversity of periphyton and detritus microbial communities in a subtropical wetland

The catabolic diversity of wetland microbial communities may be a sensitive indicator of nutrient loading or changes in environmental conditions. The objectives of this study were to assess the response of periphyton and microbial communities in water conservation area-2a (WCA-2a) of the Everglades to additions of C-substrates and inorganic nutrients. Carbon dioxide and CH₄ production rates were measured using 14 days incubation for periphyton, which typifies oligotrophic areas, and detritus, which is prevalent at P-impacted areas of WCA-2a. The wetland was characterized by decreasing P levels from peripheral to interior, oligotrophic areas. Microbial biomass and N mineralization rates were higher for oligotrophic periphyton than detritus. Methane production rates were also higher for unamended periphyton (80 mg CH₄-C kg⁻¹ d⁻¹) than detritus (22 mg CH₄-C kg⁻¹ d⁻¹), even though the organic matter content was higher for detritus (80%) than periphyton (69%). Carbon dioxide production for unamended periphyton (222 mg CO₂-C kg⁻¹ d⁻¹) was significantly greater than unamended detritus (84 mg CO₂-C kg⁻¹ d⁻¹). The response of the heterotrophic microbial community to added C-substrates was related to the nutrient status of the wetland, as substrate-induced respiration (SIR) was higher for detritus than periphyton. Amides and polysaccharides stimulated SIR more than other C-substrates, and methanogenesis was greater contributor to SIR for periphyton than detritus. Inorganic P addition stimulated CO₂ and CH₄ production for periphyton but not detritus, indicating a P limitation in the interior areas of WCA-2a. Continued nutrient loading into oligotrophic areas of WCA-2a or enhanced internal nutrient cycling may stimulate organic matter decomposition and further contribute to undesirable changes to the Everglades ecosystem caused by nutrient enrichment.     

The contribution of epipelon to total sediment microalgae in a shallow temperate eutrophic loch (Loch Leven, Scotland)

Benthic microalgae are known to perform important ecosystem functions in shallow lakes. As such it is important to understand the environmental variables responsible for regulating community structure, positioning and biomass. We tested the hypothesis that the positioning (across a depth gradient of 2–22 m overlying water depth) and relative biomass (determined using bulk and lens tissue harvested chlorophyll (Chl) a concentrations) of the epipelon community would vary independently with season (12 monthly samples) and across natural gradients of light and habitat disturbance relative to the total benthic algal community (i.e. all viable microalgae in the surface sediments) in a shallow eutrophic loch. Total sediment microalgal Chl a concentrations (TS-Chl; range: 5–874 μg Chl a g⁻¹ dw) were highest in winter and in the deepest site (20 m overlying water depth), apparently as a result of phytoplanktonic settling and sediment focussing processes. Epipelic Chl a concentrations (Epi-Chl; range: <0.10–6.0 μg Chl a g⁻¹ dw) were highest in winter/spring, a period when water clarity was highest and TS-Chl lowest. Principal components analysis highlighted strong associations between Epi-Chl and sites of intermediate depths (2.5–5.5 m) in all seasons except autumn/winter. Autumn/winter represented the season with the highest average wind speeds preceding sampling, during which the highest Epi-Chl concentrations were associated with the deepest sites. Epi-Chl was associated with intermediate light and habitat disturbance during spring/summer and summer/autumn and varied positively with habitat disturbance, only, in autumn/winter and winter/spring. The epipelon community structure also varied with depth; diatoms dominated shallow water sediments, cyanobacteria dominated deep water sediments, and sediments at sites of intermediate depth returned the highest biovolume estimates and the most diverse communities. This study has strengthened the hypothesis that the structure and biomass of benthic microalgal communities in lakes are regulated by habitat disturbance and water clarity, both of which are expected to respond to climate change and eutrophication. The degree to which these structural responses reflect functional performance requires clarification.     

Factors determining periphytic algae succession in a tropical hypereutrophic reservoir

The objectives of this study were to evaluate the effect of cyanobacterial blooms on periphyton algal succession and to identify the factors determining community dynamics in a tropical hypereutrophic reservoir. A variety of factors affecting periphytic community structure were identified at two different sites with domestic sewage and spring water inflows and two climatic periods. Microscope glass slides were used to assess periphyton growth. Sampling was carried out at short regular intervals (3–5 days) over 30 days. Climatic periods were limnologically distinct. The rainy period was characterized by an intense cyanobacterial bloom and the dry period by a less intense bloom. Periphyton biomass and growth tended to increase with colonization time during the dry period. Cyanobacteria and Bacillariophyceae were the most representative groups in the rainy period whereas Bacillariophyceae was dominant in the dry period. Community species had successional patterns in both climatic periods. The successional trajectory for sites 1 (domestic sewage) and 2 (spring water) was different in the dry period but similar in the rainy period. We concluded that the community structure over 30 days of colonization under hypereutrophic conditions was primarily determined by seasonal scale (bloom intensity), followed by successional scale (autogenic), and, finally, by the local scale (spring water and sewage inflow). Positive periphyton biological response (higher biomass and algal growth, dominance of diatoms, Cyanobacteria reduction) during small variations of bloom intensity may indicate rapid re-establishment of the community during recovery of the ecosystem.     

Small scale vertical gradients of Arctic ice algal photophysiological properties

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (F _v/F _m), maximum relative electron transport rate (rETR_max), photosynthetic efficiency (α), and the photoadaptive index (E _k). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0–5 cm from ice–water interface) expressed low F _v/F _m (0.331–0.426) and low α (0.098–0.130 (μmol photons m⁻²s⁻¹)⁻¹) in December. F _v/F _m and α increased in March and May (0.468–0.588 and 0.141–0.438 (μmol photons m⁻²s⁻¹)⁻¹, respectively) indicating increased photosynthetic activity. In addition, increases in rETR_max (3.3–16.4 a.u.) and E _k (20–88 μmol photons m⁻² s⁻¹) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).