Mercury methylation and demethylation rates were measured in periphyton biofilms growing on submerged plants from a shallow fluvial lake located along the St. Lawrence River (Quebec, Canada). Incubations performed situ within macrophytes beds using low-level spikes of (199)HgO Me(200)Hg stable isotopes as tracers. To determine which microbial guilds are playing role these processes, methylation/demethylation experiments absence presence different metabolic inhibitors: chloramphenicol...

We have developed a protocol for the cytometric enumeration of bacterioplankton in lakes with nucleic acid stain SYTO 13; our can be used any standard bench‐top flow cytometer equipped an argon laser excitation at 488 nm. The performs well range bacterial densities from 10 5 to 6 ml −1 . Estimates abundance using technique ranged 72 141% epifluorescence estimates DAPI staining. average C.V. replicate counts was 2.4%, and water samples 6.7%. precision 10‐fold higher than corresponding counts,...

A precise oxygen method was used to measure primary production, community respiration and determine the importance of exogenous organic carbon as an energy source planktonic communities in epilimnion 12 oligotrophic mesotrophic Shield lakes. Median photosynthetic parameters observed with were up twice high those measured 14 C other Gross photosynthesis almost always larger than respiration, a median P : R ratio 1.7. We strong relationships between gross photosynthesis, but could not detect...

ABSTRACT The response to arsenate in growth and phosphate uptake by five algae culture varied considerably. rates of Melosira granulata var. angustissima O. Müll, Ochromonas vallesiaca Chodat were depressed 1 μM arsenale. Chlamydomonas reinhardtii Dang. required 10 for the same degree depression, while rules Cryptomonas eroasa Ehr. Anabaena variabilis Kütz. unaffeted up 100 μM. However, following depletion phosphate, cultures later two began die at higher concentrations arsenale tested....

The uptake of mercury by microorganisms is a key step in the production methylmercury, biomagnifiable toxin. Mercury complexation low-molecular-weight (LMW) thiols can affect its bioavailability and thus methylmercury. Freshwater biofilms were sampled summer using artificial Teflon substrates submerged for over year to allow natural community colonization littoral zone Boreal Shield lake. Inside biofilms, concentrations different extracellular thiol species (thioglycolic acid,...

Eleven headwater lakes in Alberta's Boreal Plain were monitored for nutrients and plankton 2 years before after variable watershed harvesting (harvesting mean 15%, range 0-35%). After harvesting, variations annual precipitation resulted lake water residence times that differed by an order of magnitude from one year to the next. During first posttreatment year, total phosphorus concentrations increased (overall 40%) most lakes; however, response was consistent shallow column mixed or weakly...

Methylation rates by periphyton growing on the rocky shore of a remote boreal shield lake were measured over diurnal cycles at temperatures representative summer and fall conditions. The measurements carried out in vitro with natural communities grown artificial Teflon substrates submerged along lake's for 1−2 years. At above 20 °C, epilithon Hg methylation fast reached steady state within 12 h upon exposure to 2 ng L-1 inorganic mercury. A variety inhibitors used identify which...

The influence of macrophyte habitat and architecture on macroinvertebrate biomass, abundance, richness was investigated in Lake St. Pierre, a large fluvial lake the Lawrence River (Quebec, Canada). A lake-wide estimate biomass associated with different habitats also calculated order to assess quantitative effects vegetation changes communities. For two years during ice-free period, phytophilous macroinvertebrates were sampled beds comprising more than ten species plants three (emergent,...

(1981). Ecological significance of phenolic compounds Myriophyllum spicatum. SIL Proceedings, 1922-2010: Vol. 21, No. 3, pp. 1492-1496.

A review of headwater lakes in undisturbed watersheds on the Boreal Plain, with indirect gradient analyses chemical data, indicated a clear separation between those wetland-dominated (57–100% wetland variable proportions bog, fen, swamp, and marsh cover) upland-dominated (0–44% cover). In former, percentage cover watershed was positively correlated total phosphorus (TP, r 2 = 0.78, primarily bog), nitrogen (TN, 0.50), dissolved organic carbon (DOC, 0.74) concentrations. Rich fens appeared to...

To accurately assess the flux of mass and energy to higher trophic levels in a food web using stable isotopes, isotopic signature basal sources is required. When studying aquatic webs, it difficult obtain for algae because challenges associated with isolating small organisms from bulk sample. In this study, we compared freshwater algal δ 13 C values obtained five approaches literature. Results indicated that signatures derived primary consumer such as Daphnia sp., particulate organic carbon...

Lay Abstract Wind mixing is one of the main factors controlling ecology lakes. Large, deep lakes, as well small, shallow ones, can develop a seasonal thermal stratification. Because both light and heat come from above, warm illuminated surface layer develops above colder, darker, heavier bottom water under influence gravity. Gravity also controls tendency for microscopic plants that make up floating plankton—the phytoplankton, which are bit than water—to fall top to layer, where they die...

Stable carbon isotope mixing models were combined with inventories of macroinvertebrate biomass to quantitatively assess the trophic base three contrasting lotic ecosystems in a boreal forest drainage system spring/early summer. In second-order partially shaded stream and fourth-order unshaded river, 13 C/ 12 C ratios autochthonous allochthonous food sources distinct, allowing use isotopic equations calculate relative contribution both consumer biomasses. small lake outlet, compositions...

The impact of fish predation on epibenthic organisms at different trophic levels was studied in a series replicated experimental outdoor channels fed by boreal forest stream (Québec, Canada). Brook trout (Salvelinus fontinalis) were introduced into five 10 according to randomized block design. Periphyton biomass (expressed as total chlorophyll and organic matter) macroinvertebrate measured four times during the summer. small insects such Chironomidae always higher presence than absence fish,...

Experiments were performed to compare 14 C uptake, dissolved O 2 and CO change, microelectrode techniques for measuring benthic primary productivity community metabolism at a site on the South Saskatchewan River, Saskatchewan. The highest estimates of obtained with microelectrodes (two four times higher than simultaneous from bulk-water measurements), presumably because measurements are biased toward active communities under optimal conditions photosynthesis. In daytime experiments lasting...

Pelagic and benthic algal biomass pelagic community structure were measured in Boreal Shield lakes impacted by forest harvesting wildfires (Haute-Mauricie, Québec). Sixteen reference which the watershed has been unperturbed for at least 40 years, seven harvested lake watersheds (logged 1995), nine burnt 1995 sampled 3 years following or wildfires. From 1996 to 1998, repeated-measures ANOVA showed significant effects between treatment sampling chlorophyll a (Chl a) biomass, but 1997-1998 Chl...

Unlike large dams which favor methylation of Hg in flooded soils over long periods, run-of-river are designed to flood a limited area and therefore not expected significantly affect mercury (Hg) cycling or carbon processing. We studied the cycles within food webs from several sectors along Saint-Maurice River, Quebec, Canada, that differ how they influenced by two other watershed disturbances. observed peak concentrations fish five-year postimpoundment, but these levels were reduced three...

The latitudinal variation (35° to 28°N) in the rate of diffusive nitrate supply across thermocline and associated uptake ammonium Central Atlantic was studied. calculated flux showed a sharp gradient, with lowest (0.00037 μ mol m −3 d −1 ) South subtropical gyre highest values (23.5 between Equator 15°N. inhibited at high irradiance most stations. Both rates were (about 3 10 umol , respectively) southern end transect increased 20 55 towards Equator, this increase being much greater for than...

Pelagic and benthic algal biomass pelagic community structure were measured in Boreal Shield lakes impacted by forest harvesting wildfires (Haute-Mauricie, Québec). Sixteen reference which the watershed has been unperturbed for at least 40 years, seven harvested lake watersheds (logged 1995), nine burnt 1995 sampled 3 years following or wildfires. From 1996 to 1998, repeated-measures ANOVA showed significant effects between treatment sampling chlorophyll a (Chl a) biomass, but 1997-1998 Chl...

The potential difficulties of testing for nutrient limitation in turbid mixed layers are illustrated by comparing the outcome three different approaches (in vitro bioassays, limnocorrals, and whole-lake fertilization) subtropical Paraná floodplain. Bioassays planktonic communities consistently suggested acute N limitation, no or P depending on time at which we chose to terminate experiment. Enclosures (17 m2) deployed one lake indicated but increased sedimentation water transparency...

The recent discovery that N 2 fixation rates by the feather moss carpet of boreal Scandinavian forests increases with stand maturity has put into question paradigm is negligible in mature forest. was attributed to a previously unknown association between Nostoc sp., -fixing cyanobacteium and Pleurozium schreberi (Brid.) Mitt., abundant worldwide Here we report for first time this also exists Canadian We discovered, however, found growing not only on but two other species ( Hylocomnium...