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Accurately identifying the species present in an ecosystem is vital to lake managers and successful bioassessment programs. This is particularly important when monitoring cyanobacteria, as numerous taxa produce toxins and can have major negative impacts on aquatic ecosystems. Increasingly, DNA-based techniques such as metabarcoding are being used for measuring aquatic biodiversity, as they could accelerate processing time, decrease costs and reduce some of the biases associated with traditional light microscopy. Despite the continuing use of traditional microscopy and the growing use of DNA metabarcoding to identify cyanobacteria assemblages, methodological comparisons between the two approaches have rarely been reported from a wide suite of lake types. Here, we compare planktonic cyanobacteria assemblages generated by inverted light microscopy and DNA metabarcoding from a 379-lake dataset spanning a longitudinal and trophic gradient. We found moderate levels of congruence between methods at the broadest taxonomic levels (i.e., Order, RV=0.40, p0.0001). This comparison revealed distinct cyanobacteria communities from lakes of different trophic states, with Microcystis, Aphanizomenon and Dolichospermum dominating with both methods in eutrophic and hypereutrophic sites. This finding supports the use of either method when monitoring eutrophication in lake surface waters. The biggest difference between the two methods was the detection of picocyanobacteria, which are typically underestimated by light microscopy. This reveals that the communities generated by each method currently are complementary as opposed to identical and promotes a combined-method strategy when monitoring a range of trophic systems. For example, microscopy can provide measures of cyanobacteria biomass, which are critical data in managing lakes. Going forward, we believe that molecular genetic methods will be increasingly adopted as reference databases are routinely updated with more representative sequences and will improve as cyanobacteria taxonomy is resolved with the increase in available genetic information.

As cities expand, urban ecosystems could either contribute to or impede conservation efforts. To maximize the potential for urban areas to support biodiversity, there is a need to understand how systems in an urban environment can sustain the natural history requirements of species. This study compared the relative importance of local-scale factors (plant communities and water quality) to landscape factors (surrounding land cover) in structuring assemblages of a recognized group of wetland bioindicators. Odonata (dragonflies and damselflies), at both the adult and larval life stages, along with plant communities, pond water quality and surrounding land cover types were sampled at 51 ponds across a north temperate metropolitan area. Plant communities (particularly of wetland species) consistently explained the largest amount of variation in both dragonfly and damselfly community structure at all life stages. Pond water quality was of secondary importance for both aquatic and terrestrial life stages, with dragonflies more negatively affected by urban contaminants than damselflies. Overall, surrounding land cover types in pond catchments explained less variation in Odonata community structure, especially in the case of damselflies. However, the presence of adjacent ponds and wetlands had a measurable effect. Plant, water quality and land cover variables together explained as much as half of the variation in Odonata community structure at ponds. Urban ponds could potentially provide high quality habitat for species when designed and managed to promote native wetland plant communities and water quality is maintained.

Agrochemicals, including fertilizers and herbicides, are significant contributors of non-point source pollution to surface waters and have the potential to negatively affect periphyton. We characterized periphyton communities using pigment markers to assess the effects of nutrient enrichment and the herbicide atrazine with in situ experimental manipulations and by examining changes in community structure along existing agrochemical gradients. In 2008, the addition of nutrients (20mg/L nitrate and 1.25mg/L reactive phosphate), atrazine (20μg/L) and a combination of both nutrients and atrazine had no significant effect on periphyton biomass or community structure in a stream periphytometer experiment. In 2009, similar experiments with higher concentrations of atrazine (200μg/L) at two stream sites led to some minor effects. In contrast, at the watershed scale (2010) periphyton biomass (mg/m2 chlorophyll a) increased significantly along correlated gradients of nitrate and atrazine but no direct effects of reactive phosphate were observed. Across the watershed, the average periphyton community was composed of Bacillariophyceae (60.9%), Chlorophyceae (28.1%), Cryptophyceae (6.9%) and Euglenophyceae (4.1%), with the Bacillariophyceae associated with high turbidity and the Chlorophyceae with nitrate enrichment. Overall, effects of nitrate on periphyton biomass and community structure superseded effects of reactive phosphate and atrazine.

Polar organic chemical integrative samplers (POCIS) were used to estimate atrazine contamination at 24 stream/river sites located across a watershed with land use ranging from 6.7 to 97.4% annual crops and surface water nitrate concentrations ranging from 3 to 5404 μg/L. A gradient of atrazine contamination spanning two orders of magnitude was observed over two POCIS deployments of 28 d and was positively correlated with measures of agricultural intensity. The metabolite desisopropyl atrazine was used as a performance reference compound in field calibration studies. Sampling rates were similar between field sites but differed seasonally. Temperature had a significant effect on sampling rates while other environmental variables, including water velocity, appeared to have no effect on sampling rates. A performance reference compound approach showed potential in evaluating spatial and temporal differences in field sampling rates and as a tool for further understanding processes governing uptake of polar compounds by POCIS.

Ponds that collect and process stormwater have become a prominent feature of urban landscapes, especially in areas recently converted to residential land use in North America. Given their increasing number and their tight hydrological connection to residential catchments, these small aquatic ecosystems could play an important role in urban biogeochemistry. However, some physicochemical aspects of urban ponds remain poorly studied. Here we assessed the frequency and strength of water column stratification, using measurements of vertical water temperature profiles at high spatial and temporal frequency, in 10 shallow urban stormwater management ponds in southern Ontario, Canada. Many of the ponds were well stratified during much of the summer of 2010 as indicated by relatively high estimates of thermal resistance to mixing (RTRM) indices. Patterns of stratification reflected local weather conditions but also varied among ponds depending on their morphometric characteristics such as maximum water depth and surface area to perimeter ratio. We found greater vertical nutrient gradients and more phosphorus accumulation in bottom waters in ponds with strong and persistent stratification, which likely results from limited particle resuspension and more dissolved phosphorus (P) release from sediments. However, subsequent mixing events in the fall diminished vertical P gradients and possibly accelerated internal loading from the sediment-water interface. Our results demonstrate that stormwater ponds can experience unexpectedly long and strong thermal stratification despite their small size and shallow water depth. Strong thermal stratification and episodic mixing in ponds likely alter the quantity and timing of internal nutrient loading, and hence affect water quality and aquatic communities in downstream receiving waters.

Size-fractionated (20–153 μm; 2–20 μm; and 0.2–2 μm) chlorophyll-a (Chl-a) specific growth and loss rates of phytoplankton size due to microzooplankton grazing were determined in the metalimnion and epilimnion at pelagic hydrographic stations across Lake Ontario in July 2008, in addition to rates of growth and grazing of phycoerythrin (PE)-rich picocyanobacterial populations measured using flow cytometry. Eight of the nine stations contained pronounced deep chlorophyll maxima (DCM) in the metalimnion, which corresponded to the base of the euphotic zone (approximately 17 m). DCM were composed primarily of the Heterokontophyta and Pyrrophyta, and frequently also contained smaller metalimnetic peaks of PE-rich cyanobacteria and Cryptophyta. Specific growth and grazing rates of all plankton size fractions suggested close coupling of growth and grazing rates. Using dilution assays, Chl- a -specific growth and grazing rates (per day; mean ± standard deviation) for total Chl- a (0.2–153 μm) were 0.42 ± 0.30 and 0.53 ± 0.24, respectively, in the epilimnion and 0.58 ± 0.74 and 1.03 ± 0.96 in the metalimnion. Rates for cell specific growth and grazing for PE-picocyanobacteria, the numerically dominant phytoplankton (10 7.1 to 10 8.1 cells/L), were much higher overall with growth exceeding grazing at all stations and depths when measured by both dilution assays and antibiotic assays. The results of this study suggest that the DCM is as active a layer as the epilimnion during the period of summer thermal stratification and should be included in estimates of primary and secondary production.

We tested the relative importance of physical versus chemical factors in explaining aquatic plant species diversity and community composition within a temperate lowland river. A total of 38 macrophyte species were identified at 33 sites along the 104 km length of the Rideau River, a National Heritage River of Canada. Species richness ranged from 0 to 15 species per site, and Shannon diversity from 0 to 2.98. Macrophyte species richness and Shannon diversity were significantly related to the physical characteristics of sites. For Shannon diversity, 77% of the increase was explained by an increase in sediment organic content and a decrease in water velocity. For species richness, 70% of the increase was explained by the latter factors in addition to an increase in the littoral zone (0–2 m depth contour) width and planktonic chlorophyll concentrations. River water chemistry did not explain any observed variation in either Shannon diversity or species richness in this moderately enriched system. In contrast to species richness, the physical and chemical variables measured failed to explain variation in community composition. Cluster analysis did not reveal any grouping of species into distinct communities. Canonical correlation analysis showed that environmental variables had minimal effect on the distribution of most species, with only floating-leaved species responding to water velocity. We conclude that physical factors can predict species diversity at the within river scale but not the species composition at a given site, underlying the need to preserve the geomorphological diversity of rivers to maintain plant diversity.

cited By 37; International audience; Concentrations of mercury and persistent organic pollutants in fish were examined in 11 lakes of the French Pyrénées spanning an elevation range of 2 km. All lakes were confined to a relatively small area within a 50-km diameter. Most of the lakes were within the Pyrénées National Park, which is restricted to recreational hiking, angling, and seasonal grazing of livestock, and are not subject to any known point sources of contaminants. Fish collected were mainly of 1 species (Salmo trutta fario), which is stocked regularly in the lakes. With increasing elevation, lake temperatures declined along with electrical conductivity and planktonic chlorophyll a. In contrast, water column nutrients (total phosphorus and total nitrogen) and epilithic periphyton biomass were not correlated with lake elevation. Of the global contaminants measured in fish, mercury, dicholorodiphenyltrichloroethane and its derivatives, and polybrominated diphenyl ethers showed the strongest positive correlation with elevation. Hg levels in some fish exceeded health consumption guidelines in these mountain lakes. Variation in fish contaminant levels was not related to differences in growth rate or to fish trophic position as determined using δ15N stable isotope measurements. This implies that the delivery and/or retention of many of these contaminants increase with lake elevation. © 2005 Elsevier Inc. All rights reserved.

Surface-flow wetlands are generally considered sinks for Fe and Mn but they may also export and affect the partitioning of these metals. This study was undertaken to evaluate the effect of a young constructed wetland on the retention and transformation of both dissolved and particulate Fe and Mn. Duplicate water samples were collected every three days at the inlet and outlet structures of the Monahan Wetland, Kanata, Ontario, from spring of 1997 to 1999. While on a yearly basis the wetland showed significant retention of the dissolved phase, the retention of total Fe and Mn was poor. There were strong seasonal differences in retention and, during the winter, the wetland was a source. The wetland transformed dissolved into particulate Fe and Mn from spring to fall whereas during the winter, dissolved Fe and Mn were released. Changes in pH, alkalinity and temperature could explain 11% and 40% of the outlet variation in the ratio of dissolved to total Fe and Mn respectively. Furthermore, from spring to late summer, planktonic algal biomass was negatively related to the ratio of dissolved to total Fe and Mn implying a role in Fe and Mn transformations in young wetlands where emergent and submerged vegetation have yet to dominate the system.

The first-order removal model is widely used in constructed wetland design. The suitability of this model was tested to predict metal retention in a young constructed wetland receiving agricultural and urban runoff. During two years, water samples for total and dissolved metal analyses were collected every third day at both the inlet and the outlet. The wetland retained metals best during summer and fall whereas during winter the retention of metals was significantly lower. The first-order removal model predicted Fe and Mn retention in the spring and dissolved Zn retention from spring to fall in both years. During those periods, hydraulic retention times (HRTs) greater than 7 days provided maximum retention for Fe, Mn, and dissolved Zn. However, first-order removal models failed to fit summer, fall and winter data for almost every metal under investigation (Fe, Mn, dissolved Cu, dissolved As) suggesting that HRTs (

Previous research on mercury (Hg) in lakes and rivers has identified pH, alkalinity, and organic carbon levels as the major environmental variables which predict Hg concentrations in fish and invertebrates. However, the factors that regulate accumulation in wetland systems and aquatic plants in particular have yet to be identified. Total Hg in sediments, water, and four species of aquatic macrophytes [yellow pond lily (Nuphar variegatum), eurasian water milfoil (Myriophyllum spicatum), common waterweed (Elodea canadensis), and curly leaf pondweed (Potamogeton crispus)] were measured in twenty-three wetlands along the St. Lawrence River. The total Hg concentration in N. variegatum ranged from 6.4 to 36.5 ng/g and remained fairly constant in relation to measured environmental variables (pH = 7.6 to 8.4; alkalinity = 1,217 to 3,128 eq/L Ca; DOC = 3 to 12 mg/L; organic content of the sediment = 0.9 to 49%). As well, water Hg (3 to 19 ng/L), and sediment Hg concentrations (15 to 882 μg/kg) showed no relationships with Nuphar Hg. Because the plant concentrations were lower than the sediment concentrations, it appears that Nuphar is an excluder of Hg. In contrast, Hg concentrations of the submerged species were significantly higher with the highest concentrations found in Myriophyllum (63 to 240 ng/g) followed by Elodea (58 to 225 ng/g) and Potamogeton (80 to 85 ng/g), and these species were often found to be Hg accumulators in the wetlands. However, as with Nuphar, no correlations were observed with environmental concentrations of Hg and the chemical variables measured. None of these macrophyte species appear to be good biomonitors of sediment Hg contamination.

PCB concentration and congener composition were examined in sediments and two species of macrophytes in the St. Lawrence River downstream of Cornwall, Ontario. Total PCBs in the macrophytes ranged from 37 to 585 ng/g dry weight, with biota to sediment accumulation factors ranging from 0.3 to 10. The floating-leaved species Nuphar variegatum had generally higher PCB concentrations than the submerged species Myriophyllum spicatum, but the latter had higher biota to sediment accumulation factors. N. variegatum also had a higher lipid content, but lipid levels were not a good predictor of plant PCB concentrations. Congener specific analysis showed congener patterns shifted between plants and sediments; macrophytes tended to have higher levels of tetrachlorobiphenyl congeners. Given that contaminant levels in plants reflect those found in the sediments, the high biomass of macrophytes within the river and particularly in Lake St. Francis represents an important reserve of PCBs which may be transferred to the herbivorous and detrital food webs.