As blooms of cyanobacteria expand and intensify in freshwater systems globally, there is increasing interest in their ecological effects. In addition to being public health hazards, cyanobacteria ...have long been considered a poor quality food for key zooplankton grazers that link phytoplankton to higher trophic levels. While past laboratory studies have found negative effects of nutritional constraints and defensive traits (i.e., toxicity and colonial or filamentous morphology) on the fitness of large generalist grazers (i.e., Daphnia), cyanobacterial blooms often co-exist with high biomass of small-bodied zooplankton in nature. Indeed, recent studies highlight the remarkable diversity and flexibility in zooplankton responses to cyanobacterial prey. Reviewed here are results from a wide range of laboratory and field experiments examining the interaction of cyanobacteria and a diverse zooplankton taxa including cladocerans, copepods, and heterotrophic protists from temperate to tropical freshwater systems. This synthesis shows that longer exposure to cyanobacteria can shift zooplankton communities toward better-adapted species, select for more tolerant genotypes within a species, and induce traits within the lifetime of individual zooplankton. In turn, the function of bloom-dominated plankton ecosystems, the coupling between primary producers and grazers, the stability of blooms, and the potential to use top down biomanipulation for controlling cyanobacteria depend largely on the species, abundance, and traits of interacting cyanobacteria and zooplankton. Understanding the drivers and consequences of zooplankton traits, such as physiological detoxification and selective vs. generalist grazing behavior, are therefore of major importance for future studies. Ultimately, co-evolutionary dynamics between cyanobacteria and their grazers may emerge as a critical regulator of blooms.
Studies of the fate and toxicity of nanoparticles, including nanosilver (AgNPs), have been primarily conducted using bench scale studies over relatively short periods of time. To better understand ...the fate of AgNPs in natural aquatic ecosystems over longer time scales and ecological settings, we released suspensions of AgNPs (30-50 nm, capped with polyvinylpyrrolidone) into a boreal lake at the Experimental Lakes Area in Canada. Approximately 9 kg of silver was added from a shoreline point source from June to October 2014, which resulted in total Ag (TAg) concentrations of about 10 μg L-1 or less. In addition, dissolved Ag concentrations (DAg) were typically very low. Using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) analysis of grab samples, we found that the nanoparticles typically ranged in the 40-60 nm size class and were widely distributed throughout the lake, while larger aggregates (i.e. >100 nm) were infrequently detected. The highest occurrence of aggregates was found near the addition site; however, size distributions did not vary significantly among spatial locations or time suggesting rapid dispersal upon entry into the lake. Lake stratification at the thermocline was not a barrier to mobility of the AgNPs, as the particles were also detected in the hypolimnion. Environmental factors influenced Ag size distributions over sampling locations and time. Total dissolved phosphorus, bacterioplankton chlorophyll-a, and sampling time strongly correlated with aggregation and dissolution dynamics. AgNPs thus appear to be relatively mobile and persistent over the growing season in lake ecosystems.
Dissolved organic matter (DOM) composition in freshwater ecosystems is influenced by the interactions among physical, chemical, and biological processes that are controlled, at one level, by ...watershed landscape, hydrology, and their connections. Against this environmental template, humans may strongly influence DOM composition. Yet, we lack a comprehensive understanding of DOM composition variation across freshwater ecosystems differentially affected by human activity. Using optical properties, we described DOM variation across five ecosystem groups of the Laurentian Great Lakes region: large lakes, Kawartha Lakes, Experimental Lakes Area, urban stormwater ponds, and rivers (n = 184 sites). We determined how between ecosystem variation in DOM composition related to watershed size, land use and cover, water quality measures (conductivity, dissolved organic carbon (DOC), nutrient concentration, chlorophyll a), and human population density. The five freshwater ecosystem groups had distinctive DOM composition from each other. These significant differences were not explained completely through differences in watershed size nor spatial autocorrelation. Instead, multivariate partial least squares regression showed that DOM composition was related to differences in human impact across freshwater ecosystems. In particular, urban/developed watersheds with higher human population densities had a unique DOM composition with a clear anthropogenic influence that was distinct from DOM composition in natural land cover and/or agricultural watersheds. This nonagricultural, human developed impact on aquatic DOM was most evident through increased levels of a microbial, humic‐like parallel factor analysis component (C6). Lotic and lentic ecosystems with low human population densities had DOM compositions more typical of clear water to humic‐rich freshwater ecosystems but C6 was only present at trace to background levels. Consequently, humans are strongly altering the quality of DOM in waters nearby or flowing through highly populated areas, which may alter carbon cycles in anthropogenically disturbed ecosystems at broad scales.
The ability to directly measure and monitor poor nutrition in individual animals and ecological communities is hampered by methodological limitations. In this study, we use nutrigenomics to identify ...nutritional biomarkers in a freshwater zooplankter, Daphnia pulex, a ubiquitous primary consumer in lakes and a sentinel of environmental change. We grew animals in six ecologically relevant nutritional treatments: nutrient replete, low carbon (food), low phosphorus, low nitrogen, low calcium and high Cyanobacteria. We extracted RNA for transcriptome sequencing to identify genes that were nutrient responsive and capable of predicting nutritional status with a high degree of accuracy. We selected a list of 125 candidate genes, which were subsequently pruned to 13 predictive potential biomarkers. Using a nearest‐neighbour classification algorithm, we demonstrate that these potential biomarkers are capable of classifying our samples into the correct nutritional group with 100% accuracy. The functional annotation of the selected biomarkers revealed some specific nutritional pathways and supported our hypothesis that animal responses to poor nutrition are nutrient specific and not simply different presentations of slow growth or energy limitation. This is a key step in uncovering the causes and consequences of nutritional limitation in animal consumers and their responses to small‐ and large‐scale changes in biogeochemical cycles.
From 2013 to 2015, citizen scientist volunteers in Toronto, Canada were trained to collect and analyze water quality in urban stormwater ponds. This volunteer sampling was part of the research ...program, FreshWater Watch (FWW), which aimed to standardize urban water sampling efforts from around the globe. We held training sessions for new volunteers twice yearly and trained a total of 111 volunteers. Over the course of project, ~30% of volunteers participated by collecting water quality data after the training session with 124 individual sampling events at 29 unique locations in Toronto, Canada. A few highly engaged volunteers were most active, with 50% of the samples collected by 5% of trainees. Stormwater ponds generally have poor water quality demonstrated by elevated phosphate concentrations (~30μg/L), nitrate (~427μg/L), and turbidity relative to Canadian water quality standards. Compared to other urban waterbodies in the global program, nutrient concentrations in Toronto's urban stormwater ponds were lower, while turbidity was not markedly different. Toronto FWW (FWW-TO) data was comparable to that measured by standard lab analyses and matched results from previous studies of stormwater ponds in Toronto. Combining observational and chemical data acquired by citizen scientists, macrophyte dominated ponds had lower phosphate concentrations while phytoplankton dominated ponds had lower nitrate concentrations, which indicates a potentially important and unstudied role of internal biogeochemical processes on pond nutrient dynamics. This experience in the FWW demonstrates the capabilities and constraints of citizen science when applied to water quality sampling. While analytical limits on in-field analyses produce higher uncertainty in water quality measurements of individual sites, rapid data collection is possible but depends on the motivation and engagement of the group of volunteers. Ongoing efforts in citizen science will thus need to address sampling effort and analytical limits to fully realize the potential value of engaging citizen scientists in water quality sampling.
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•A global citizen science program was used to study urban stormwater ponds in Toronto.•Most samples collected by a small percentage of citizen scientist volunteers•Citizen scientist data was comparable to previous stormwater pond studies in Toronto.•Lower PO4 in macrophyte dominated ponds and lower NO3 in algae dominated ponds•Citizen scientists can be employed to study urban water quality.
As cyanobacterial blooms and herbicide pollution, which are often detected in eutrophic waters, can separately jeopardise zooplankton populations, there is an urgent and on‐going need to understand ...the strength and direction of their interactive effects. This is a crucial step toward realistic risk‐evaluation of agricultural pollution in eutrophic waterbodies.
In this study, we evaluated how the herbicide, atrazine (ATZ), alters the effects of cyanobacterial food on the zooplankter, Daphnia magna.
We found survival time of Daphnia decreased with increasing amounts of Microcystis in their diets, and the magnitude of this cyanobacterial effect was independent of ATZ. In contrast, ATZ exposure triggered faster growth and larger body size in Daphnia fed diets containing Microcystis compared to those fed the good‐food diet. Although toxic Microcystis reduced the overall reproductive output of Daphnia, the presence of ATZ, regardless of the type of food treatment, exhibited a masking effect by further significantly decreasing Daphnia's overall reproductive output, resulting in a low level of reproduction. Finally, we found an expression trade‐off at the molecular scale between growth and reproduction genes on one side, and antioxidation gene on the other, which could account in part for ATZ's influence on Microcystis toxicity to Daphnia at maturation stage.
These results demonstrated that ATZ can reshape Daphnia's responses to Microcystis, predominantly with effects on growth and reproductive traits. These trait‐dependent responses were found to be closely linked to the regulation of key metabolic pathways.
Collectively, our study enhances current knowledge regarding the potential interaction between fundamental trophic levels in cyanobacteria‐dominated lakes around farmlands, and is helpful to achieve more realistic environmental risk management of agricultural pollution in eutrophic waterbodies.
Consumer body stoichiometry is a key trait that links organismal physiology to population and ecosystem-level dynamics. However, as elemental composition has traditionally been considered to be ...constrained within a species, the ecological and evolutionary factors shaping consumer elemental composition have not been clearly resolved. To this end, we examined the causes and extent of variation in the body phosphorus (P) content and the expression of P-linked traits, mass specific growth rate (MSGR), and P use efficiency (PUE) of the keystone aquatic consumer Daphnia using lake surveys and common garden experiments. While daphnid body %P was relatively constrained in field assemblages sampled across an environmental P gradient, unique genotypes isolated from these lakes showed highly variable phenotypic responses when raised across dietary P gradients in the laboratory. Specifically, we observed substantial inter- and intra-specific variation and differences in daphnid responses within and among our study lakes. While variation in Daphnia body %P was mostly due to plastic phenotypic changes, we documented considerable genetic differences in daphnid MSGR and PUE, and relationships between MSGR and body P content were highly variable among genotypes. Overall, our study found that consumer responses to food quality may differ considerably among genotypes and that relationships between organismal life-history traits and body stoichiometry may be strongly influenced by genetic and environmental variation in natural assemblages.
Declines in environmental calcium (Ca) and phosphorus (P) concentrations have occurred over the past 30 yrs in lakes across the Canadian Shield in southern Ontario, and these reductions appear to be ...placing strong constraints on populations of Daphnia in this region. Here, we report results from a factorial manipulation of Ca concentrations and food P content under controlled laboratory conditions where we measured resulting changes in daphnid elemental content, individual growth and survival, and life history traits related to population growth. We found significant effects of Ca- and P-limitation on all variables measured; however, dietary P explained a majority of the variation in daphnid nutrient content and growth. Dietary effects of low P high food carbon (C): P ratios on individual Daphnia life-history traits also translated into significant population level effects. Dietary P also explained relatively more experimental variation in population level responses than Ca concentrations. Experimental Ca concentrations most strongly altered daphnid survival partly due to the use of a lethally low Ca concentration in our experiment. Although recent work examining shifts in zooplankton communities in this region mainly focuses on the effects of Ca-limitation, we show that Ca concentrations and food nutrient content, at levels commonly found on the Canadian Shield, are both likely to strongly alter Daphnia life-history and populations dynamics. Our results underscore the need to more fully examine how multielemental limitation (e.g., Ca, N, P) affects consumer physiology and life-history given the plausible translation of these effects on the community structure of lake zooplankton.
As urban ecosystems are known to be phosphorus (P)-rich environments, the sources of this nutrient and its biogeochemistry within human-dominated landscapes remain in need of study. Specifically, ...very little is known about how different P species vary within and among urban aquatic environments. In this study, we examined the phosphorus dynamics in urban stormwater ponds that are embedded in residential landscapes. Water samples were collected from stormwater ponds located in southern Ontario, Canada during the summer of 2012. We measured several P types: total P; TP, particulate P; PP, and dissolved inorganic P; DIP as well as two classes of DOP (phosphomonoesters (MP) and phosphodiesters (DP)) in the surface water samples. In most ponds, PP in outflowing water were found at concentrations higher (up to 12 times) than those measured in incoming stormwater. With respect to DOP, DP increased and became more abundant in outflowing compared to inflowing waters while MP concentrations decreased within ponds. The magnitude of these spatial changes from pond inlets to outlets was strongly linked to recent periods of rainfall and the hydrological condition of pond inflows. Elevated MP was found adjacent to inlets especially during periods of more frequent rainfall, which indicates that MP is derived from terrestrial sources and delivered by stormwater. In contrast, DP production was more related to internal biological activity in ponds as its concentrations increased during relatively dry conditions with low stormwater flow. Our results demonstrate that stormwater ponds have significant influence on the quantity and types of P moving through these highly human-modified environments.
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