Lentic Freshwater Ecosystems Research Articles

Trophic transfer patterns of arsenic in freshwater ecosystem layers in arsenic-endemic Ganges Delta and its potential human health risk.

Arsenic (As) is a toxic environmental contaminant with global public health concern. In aquatic ecosystems, the quantification of total As is restricted chiefly to the individual organisms. The present study has quantified the total As in different trophic layers (sediment-water-phytoplankton-periphyton-zooplankton-fish-gastropod-hydrophytes) of lentic freshwater ecosystems. As transfer pathways quantifying the transmission rate across trophic-level compartmental route were delineated using a novel model-based approach along with its potential contamination risk to humans. Lentic water bodies from Indo-Gangetic region, acore area of groundwater As, were selected for the present investigation. The study revealed that among the lower biota, zooplankton were the highest accumulator of total As (5554-11,564µgkg-1) with magnification (rate = 1.129) of the metalloid, followed by phytoplankton (2579-6865µgkg-1) and periphytic biofilm (1075 to 4382µgkg -1). Muscle tissue of zooplanktivore Labeo catla is found to store higher As (80-115µgkg-1 w.w.) compared to bottom-dwelling omnivore Cirrhinus mrigala (58-92µgkg-1 w.w.). Whereas, Amblypharyngodon mola has accumulated higher As (203-319µgkg-1 w.w.) than Puntius sophore (30-98µgkg-1 w.w.) that raised further concern. The hepatic concentration indicated arsenic-mediated stress based on As stress index (threshold value = 1). Mrigal and Mola showed significant biomagnification among fishes while biodiminution was observed in Catla, Bata, Rohu and Punti. All the studied fishes were under the arsenic mediated stress. In the 'sediment-water-periphytic biofilm-gastropod' compartment, the direct grazing accumulation was higher (rate = 0.618) than the indirect path (rate = 0.587). Stems of edible freshwater macrophytes accumulated lesser As (32-190µgkg-1 d.w.) than roots (292-946µgkg-1 d.w.) and leaves (62-231µgkg-1 d.w.). The target cancer risk (TCR) revealed a greater concern for adults consuming edible macrophyte regularly. Similarly, the varied level of target hazard quotient and TCR for adults consuming fishes from these waterbodies further speculated significant health concerns. The trophic transfer rate of environmental As in soil-water-biota level at an increasing trophic guild and consumer risk analysis have been unravelled for the first time in the Indo-Gangetic plains, which will be helpful for the strategic mitigation of As contamination.

Pollution patterns and their effects on biota within lotic and lentic freshwater ecosystems: How well contamination and response indicators correspond?

Aquatic environments are often severely polluted with chemical substances of anthropogenic origin, which can pose a potential threat to aquatic organisms and human health. In this study, patterns and sources of heavy metals (HMs, 6 metals) and polycyclic aromatic hydrocarbons (PAHs, 16 hydrocarbons), contamination indicators, environmental genotoxicity measures and metrics of ecological status in lotic and lentic ecosystems were collated for the first time. Chemical analysis has confirmed previously reported long-term contamination at certain study sites. The sediments of Lake Talkša, located in a city and characterized by exclusive anthropogenic pressure, exhibited the highest levels of contamination by both HMs and PAHs. Through positive matrix factorization (PMF) analysis, vehicle and industrial emissions were identified as the primary sources of HMs and PAHs. Our results revealed that frequencies of genotoxic aberrations were higher in river sites compared to lakes, with the highest genotoxic risk observed in the Nemunas River below industrial cities Alytus and Kaunas. Surprisingly, even the severely contaminated Lake Talkša showed only a "moderate" grade of genotoxic risk, highlighting the potential for adaptation of biota to long-term contamination especially in lentic ecosystems. The ecological quality status assessed by macroinvertebrate metrics, which may be sensitive to observed high biological contamination, appeared to be unrelated to contamination patterns. Consequently, to obtain the robust information on anthropogenic contamination and its effects, a combination of various assessment methods and metrics should be employed.

Mysterious microsporidians: springtime outbreaks of disease in Daphnia communities in shallow pond ecosystems.

Parasites can play key roles in ecosystems, especially when they infect common hosts that play important ecological roles. Daphnia are critical grazers in many lentic freshwater ecosystems and typically reach peak densities in early spring. Daphnia have also become prominent model host organisms for the field of disease ecology, although most well-studied parasites infect them in summer or fall. Here, we report field patterns of virulent microsporidian parasites that consistently infect Daphnia in springtime, in a set of seven shallow ponds in Georgia, USA, sampled every 3-4weeks for 18months. We detected two distinct parasite taxa, closely matching sequences of Pseudoberwaldia daphniae and Conglomerata obtusa, both infecting all three resident species of Daphnia: D. ambigua, D. laevis, and D. parvula. To our knowledge, neither parasite has been previously reported in any of these host species or anywhere in North America. Infection prevalence peaked consistently in February-May, but the severity of these outbreaks differed substantially among ponds. Moreover, host species differed markedly in terms of their maximum infection prevalence (5% [D. parvula] to 72% [D. laevis]), mean reduction of fecundity when infected (70.6% [D. ambigua] to 99.8% [D. laevis]), mean spore yield (62,000 [D. parvula] to 377,000 [D. laevis] per host), and likelihood of being infected by each parasite. The timing and severity of the outbreaks suggests that these parasites could be impactful members of these shallow freshwater ecosystems, and that the strength of their effects is likely to hinge on the composition of ponds' zooplankton communities.

Fish Biozonation in the Balkan Peninsula, Especially in Bulgaria: A Challenge

Fish are important elements of aquatic ecosystems. Their communities naturally follow the river continuum and have been well described in the western European freshwater watersheds. In regions of higher endemism, such as the Balkan Peninsula, the widely accepted fish zonation of Illies is doubtfully relevant. In this study, a more suitable categorization of lotic and lentic freshwater ecosystems in Bulgaria is proposed, based on 389 multimethodological and multihabitat fish sampling occasions. Referent-type communities have been determined for 33 types of recognized water bodies. Adapted zonation of Illies is a rough estimation of the real distribution of fish assemblances in the country; moreover, sensitive and/or endemic species are generally of restricted distribution and abundance. In view of the lentic ecosystems, they can be divided into salmonid and cyprinid, at approximately 1500 m above sea level.

Biogeochemical Distinctiveness of Peatland Ponds, Thermokarst Waterbodies, and Lakes

AbstractSmall lentic freshwater ecosystems play a disproportionate role in global biogeochemical cycles by processing large amounts of carbon (C), nitrogen (N), and phosphorus (P), but it is unlikely that they behave as one homogenous group for the purpose of extrapolation. Here, we synthesize biogeochemical data from >12,000 geographically distinct freshwater systems: lakes, peatland ponds, and thermokarst waterbodies. We show that peatland ponds are biogeochemically distinct from the more widely studied lake systems, while thermokarst waterbodies share characteristics with peatland ponds, lakes, or both. For any given size or depth, peatland ponds tend to have dissolved organic carbon concentrations several‐fold higher and are 100‐fold more acidic than lakes because of the organic matter‐rich settings in which they develop. The biogeochemical distinctiveness of freshwater ecosystems highlights the need to account for the fundamental differences in sources and processing of organic matter to understand and predict their role in global biogeochemical cycles.

Extreme Weather Events Enhance DOC Consumption in a Subtropical Freshwater Ecosystem: A Multiple-Typhoon Analysis.

Empirical evidence suggests that the frequency/intensity of extreme weather events might increase in a warming climate. It remains unclear how these events quantitatively impact dissolved organic carbon (DOC), a pool approximately equal to CO2 in the atmosphere. This study conducted a weekly-to-biweekly sampling in a deep subtropical reservoir in the typhoon-prevailing season (June to September) from 2004 to 2009, at which 33 typhoons with distinctive precipitation (<1~362 mm d−1) had passed the study site. Our analyses indicated that the phosphate (i.e., DIP; <10~181 nMP) varied positively with the intensity of the accumulated rainfall 2-weeks prior; bacteria growth rate (0.05~3.68 d−1) behaved as a positive function of DIP, and DOC concentrations (54~119 µMC) changed negatively with bacterial production (1.2~26.1 mgC m−3 d−1). These implied that the elevated DIP-loading in the hyperpycnal flow induced by typhoons could fuel bacteria growth and cause a significant decline of DOC concentrations. As the typhoon’s intensity increases, many mineral-limited lentic freshwater ecosystems might become more like a CO2 source injecting more CO2 back to the atmosphere, creating a positive feedback loop that might generate severer extreme weather events.

Shifts in amphibian population dynamics in response to a change in the predator community

AbstractPredation can affect prey behavior, demography, abundance, and distribution, particularly in lentic freshwater ecosystems. Fish are predators known to reduce the abundance of their prey and to restrict the distribution of species. Using time series which spanned 43 and 22 yr, respectively, we analyzed the effect of a change in the fish predator community on the dynamics of two pond‐breeding amphibian populations (Rana temporaria and Rana dalmatina). Specifically, we used a state‐space time series model which allows for density dependence and observation error, to ask whether the change in predation risk affects population growth rate and the return point around which the populations fluctuate. The results showed that the type of observation error assumed did not affect the biological parameters. We found evidence for density dependence in both populations. The effect of the change in fish predation on population growth rate and the return point was strong in the population where fish invaded a previously fish‐free pond. The effect was weaker in the population where the change was from cyprinid fish to pike. The results showed that fish predation can have strong effects on amphibian population dynamics. The observed population dynamical pattern is phenomenologically similar to alternative stable states.

Differential use of artificial habitats by native and non-native fish species in Neotropical reservoirs

The use of artificial habitats as tool for management and conservation of lentic freshwater ecosystems has been most studied in North America, with dominance of Centrarchidae fish. Contrary to north temperate ecosystems, Cichlidae species appear to be prevalent on artificial habitats in Neotropical reservoirs. Currently, due to the rapid expansion of non-native fish introductions globally, these two fish families are increasingly expected to coexist in the same environments. This study aimed to test experimentally the use of artificial habitats by fish in two Neotropical reservoirs between: (i) kind of habitats, (ii) Cichlidae and Centrarchidae, (iii) native and non-native species, and (iv) size classes. The results showed a higher number of individuals and species in pipes and rocks habitats. The dominance of Cichlidae over Centrarchidae in pipes, rocks and control habitats suggests a kind of partitioning between these groups. Native Cichlidae (< 80 mm) were predominant in pipes whereas native and non-native species seemed to share tree and rock habitats. Artificial habitats can potentially increase local abundance and diversity of fish species, however, it is essential to consider the species’ origin (i.e. native or non-native) associated with each kind of artificial habitat in order to prevent invasive species from benefiting of artificial structures deployment in freshwater systems.

Factors shaping community patterns of protists and bacteria on a European scale.

Factors shaping community patterns of microorganisms are controversially discussed. Physical and chemical factors certainly limit the survival of individual taxa and maintenance of diversity. In recent years, a contribution of geographic distance and dispersal barriers to distribution patterns of protists and bacteria has been demonstrated. Organismic interactions such as competition, predation and mutualism further modify community structure and maintenance of distinct taxa. Here, we address the relative importance of these different factors in shaping protists and bacterial communities on a European scale using high-throughput sequencing data obtained from lentic freshwater ecosystems. We show that community patterns of protists are similar to those of bacteria. Our results indicate that cross-domain organismic factors are important variables with a higher influence on protists as compared with bacteria. Abiotic physical and chemical factors also contributed significantly to community patterns. The contribution of these latter factors was higher for bacteria, which may reflect a stronger biogeochemical coupling. The contribution of geographical distance was similar for both microbial groups.

Altitudinal gradients in Magellanic sub-Antarctic lagoons: the effect of elevation on freshwater macroinvertebrate diversity and distribution

BackgroundThe study of altitudinal gradients provides insights about species diversity, distribution patterns and related drivers. The Magellanic sub-Antarctic ecoregion has a steep elevational gradient, peaking at around 1,000 m a.s.l., and marked changes in temperature and landscape composition can be observed over relatively short distances.MethodsThis study assessed freshwater macroinvertebrate diversity associated with lakes and ponds along the altitudinal gradient of a Magellanic sub-Antarctic watershed.ResultsA monotonic decline in species richness was observed with increasing elevation, with simpler and more even community composition at higher altitude. This pattern differs from the mid-peak trend found in streams of the same watershed. Functional feeding group structure also diminished with increasing elevation.DiscussionThe study provides a descriptive baseline of macroinvertebrate community structure associated with lentic freshwater ecosystems in the Magellanic sub-Antarctic ecoregion, and confirms that elevation has substantial effects on community structure, function and environmental features, even in these relatively low elevation mountain ranges. The harsh environmental conditions of this ecoregion increase freshwater macroinvertebrate development time, as well as decreasing habitat availability and food supply, supporting simple but well adapted communities. In conjunction with previous research, this study provides a watershed-scale platform of information underpinning future long-term research in the region.

Evaluating improvements to exposure estimates from fate and transport models by incorporating environmental sampling effort and contaminant use

Widespread chemical contamination represents one of the largest threats of the Anthropocene. The Pesticide in Water Calculator (PWC) is a fate and transport model used by the Environmental Protection Agency and Health Canada to estimate pesticide exposures in lentic freshwater ecosystems and make pesticide registration decisions. Here, we show that maximum measured concentrations of 31% of herbicides and 42% of insecticides exceeded maximum estimated environmental concentrations (EECs) produced by the PWC, suggesting that EECs often do not represent worst-case exposure as they have been purported to do. Based on this observation, we generated statistical models using EECs and over 600,000 field measurements of 31 common insecticides and herbicides to document if the congruence of EECs and maximum field measurements could be improved by accounting for environmental sampling effort (number of times a pesticide is sampled) and contaminant application, factors commonly ignored in most fate and transport models. For lentic systems, variance in pesticide field measurements explained by EECs increased by 50% when sampling effort was included. For lotic systems, variance explained increased by only 4%, most likely because lotic systems are sampled over 4.9 times as much as lentic systems. Including use more than doubled the ability of the EECs to predict maximum pesticides concentrations in lentic systems. Our results suggest that exposure characterization in risk assessment can likely be improved by considering sampling effort and use, thus providing more defensible environmental standards and regulations.

Feeding inhibition tests as a tool for seston quality evaluation in lentic ecosystems: salinization impact

Environmental disturbance on freshwater ecosystems significantly impacts all levels of the trophic web. Salinity in lentic freshwater ecosystems, as a consequence of climatic changes, is rising concern in the scientific community. These alterations affect water quality, the composition and diversity of the aquatic communities. This study aimed to assess the seston quality of two lentic ecosystems, Crestuma reservoir and lake Vela, and evaluate the effects of salinity on food performance of Daphnia magna and Daphnia longispina (isolated from the referred ecosystems). Feeding inhibition tests were used to conduct these two evaluations. Physical and chemical water classification revealed a poor or good ecological potential of the two lentic ecosystems, according to WFD approach. To evaluate seston quality, filtered and unfiltered water samples from the lentic ecosystems were used as treatments. Although only summer samples from Crestuma presented good water quality, the results from the feeding inhibition tests showed that seston from lake Vela presented more nutritional quality. Concerning the assay to evaluate the salinity effect on Daphnia spp., a significant reduction in the filtration rate was observed. The NOEC value was 0.7 g/L NaCl and 0.8 g/L NaCl for D. magna and D. longispina C and V, respectively. The LOEC value was also distinct between species, being 1.0 g/L and 0.9 g/L, respectively. This work allowed to verify that feeding inhibition tests are not sensitive enough for assess the quality of natural waters. However, these tests are economically viable and have high sensitivity to evaluate NaCl effects on Daphnia spp.

Distribution and attachment characteristics of Sida crystallina (O.F. Müller, 1776) in lentic freshwater ecosystems of South Korea

Macrophytes are commonly utilised as habitat by epiphytic species; thus, complex macrophyte structures can support high diversities and abundances of epiphytic species. We tested the hypothesis that the presence of aquatic macrophytes is an important factor determining Sida crystallina (O.F. Muller, 1776) distribution. An ecological survey was conducted in 147 lentic freshwater bodies. S. crystallina was frequently observed, and its density was strongly associated with macrophyte abundance. S. crystallina was found on emergent plant species such as Phragmites australis and Paspalum distichum, attached to the stem surfaces by adhesive substances secreted by the nuchal organ. Thus, S. crystallina was more strongly attached to macrophytes than to other epiphytic cladoceran species. We found higher densities of S. crystallina in filtered water with increased macrophyte shaking effort (i.e. 10, 20, 40, or 80 times). S. crystallina attachment was not related to fish predation. Stable isotope analysis showed that S. crystallina utilises epiphytic organic matter (EOM) on macrophytes as a food source. Consequently, S. crystallina seems to have a strong association with species-specific macrophyte biomass than with other cladoceran species, which may contribute to this species’ predominance in various freshwater ecosystems where macrophytes are abundant.

Lentic and lotic habitats as templets for fungal communities: traits, adaptations, and their significance to litter decomposition within freshwater ecosystems

Decomposition of plant matter is a key ecosystem process and considerable research has examined plant litter decay processes in freshwater habitats. Fungi are common inhabitants of the decomposer microbial community and representatives of all major fungal phyla have been identified within freshwater systems. Development and application of quantitative methods over the last several decades have firmly established that fungi are central players in the decomposition of plant litter in freshwaters and are important mediators of energy and nutrient transfer to higher trophic levels. Despite the critical roles that fungi play in carbon and nutrient cycling in freshwater ecosystems, there are notable differences in the types and adaptations of fungal communities between lotic and lentic habitats. These differences can be explained by the wide range of hydrologic, physical, chemical and biological conditions within freshwater systems, all of which can influence the presence, type, and activity of fungal decomposers and their impact on litter decomposition. This paper seeks to provide a brief overview of the types, adaptations, and role of fungi within lotic and lentic freshwater ecosystems, with a particular emphasis on their importance to litter decomposition and the key environmental conditions that impact their growth and decay activities. This discussion will specifically focus on fungal dynamics occurring on plant litter in forested headwater streams and emergent freshwater marshes, since published data concerning their role in these systems is considerably more abundant in comparison to other freshwater habitats.

Zooplankton Community Dynamic in Lentic Freshwater Ecosystems in the Nakdong River Basin

Zooplankton Community Dynamic in Lentic Freshwater Ecosystems in the Nakdong River Basin

Detecting response patterns of zooplankton to environmental parameters in shallow freshwater wetlands: discovery of the role of macrophytes as microhabitat for epiphytic zooplankton

Abstract Freshwater macrophytes improve the structural heterogeneity of microhabitats in water, often providing an important habitat for zooplankton. Some studies have focused on the overall influence of macrophytes on zooplankton, but the ef-fects of macrophyte in relation to different habitat characteristics of zooplankton (e.g., epiphytic and pelagic) have not been intensively studied. We hypothesized that different habitat structures (i.e., macrophyte habitat) would strongly af-fect zooplankton distribution. We investigated zooplankton density and diversity, macrophyte characteristics (dry weight and species number), and environmental parameters in 40 shallow wetlands in South Korea. Patterns in the data were analyzed using a self-organizing map (SOM), which extracts information through competitive and adaptive properties. A total of 20 variables (11 environmental parameters and 9 zooplankton groups) were patterned onto the SOM. Based on a U-matrix, 3 clusters were identified from the model. Zooplankton assemblages were positively related to macrophyte characteristics (i.e., dry weight and species number). In particular, epiphytic species (i.e., epiphytic rotifers and cladocer -ans) exhibited a clear relationship with macrophyte characteristics, while large biomass and greater numbers of macro-phyte species supported high zooplankton assemblages. Consequently, habitat heterogeneity in the macrophyte bed was recognized as an important factor to determine zooplankton distribution, particularly in epiphytic species. The results indicate that macrophytes are critical for heterogeneity in lentic freshwater ecosystems, and the inclusion of diverse plant species in wetland construction or restoration schemes is expected to generate ecologically healthy food webs.

Short-term thermal stratification and partial overturning events in a warm polymictic reservoir: effects on distribution of phytoplankton community.

In lentic freshwater ecosystems, patterns of thermal stratification play a considerable part in determining the population dynamics of phytoplankton. In this study we investigated how these thermal patterns and the associated hydrodynamic processes affect the vertical distribution of phytoplankton during two consecutive diel cycles in a warm polymictic urban reservoir in the metropolitan region of São Paulo, Brazil. Water samples were taken and physical, chemical and biological data collected at half-meter intervals of depth along a water column at a fixed site, every 3 hours throughout the 48-hour period. Two events of stratification, followed by deepening of the thermocline occurred during the study period and led to changes in the vertical distribution of phytoplankton populations. Aphanocapsa delicatissima Nägeli was the single dominant species throughout the 48-hour period. In the second diel cycle, the density gradient induced by temperature differences avoided the sedimentation of Mougeotia sp. C. Agardh to the deepest layers. On the other hand, Pseudanabaena galeata Böcher remained in the 4.0-5.5 m deep layer. The thermal structure of the water was directly affected by two meteorological factors: air temperature and wind speed. Changes in the cell density and vertical distribution of the phytoplankton were controlled by the thermal and hydrodynamic events.

Timing matters: Sensitivity of Daphnia magna dormant eggs to fenoxycarb exposure depends on embryonic developmental stage

Although Daphnia magna is a key species in many lentic freshwater ecosystems and is commonly used as model organism in ecology and ecotoxicology, very little is known about the effects of chemicals on their dormant life stages. Dormant eggs (ephippia) are produced when environmental conditions deteriorate, and Daphnia switch from clonal to sexual reproduction. Ephippia produced over different growing seasons can accumulate in the sediment of ponds and lakes, where they can be exposed to pesticides and other (anthropogenic) stressors. In the present study, we have investigated the effects of pesticide exposure on dormant eggs at different embryonic developmental stages and evaluated the degree of protection against pollution provided by the ephippial case. We therefore conducted a hatching experiment in which decapsulated and encapsulated dormant eggs were exposed to an insect growth regulator (fenoxycarb) at different stages during their development, both before and after activation of the eggs. In addition, we developed an analytical method to measure fenoxycarb concentrations in the dormant eggs. Fenoxycarb negatively affected development and hatching success and changed the timing of hatching in activated and in dormant eggs. Hatching characteristics as well as fenoxycarb concentrations inside the eggs differed significantly between exposure treatments. Final stages of embryonic development were most sensitive to pesticide exposure and had the highest tissue concentrations of fenoxycarb. Tissue concentrations did not differ significantly between decapsulated and encapsulated eggs, suggesting that the ephippial case offers limited or no direct protection against pesticide exposure. With this study we provide new evidence showing that pesticides can bioconcentrate in and affect D. magna dormant eggs. The severity of the effects on developing embryos depends on the timing of pesticide exposure. Our results stress the importance of considering the full life-cycle of model organisms used in ecotoxicological studies, since these are ultimately aimed at assessing risks of chemical exposure on natural aquatic ecosystems.

Role of macrophytes as microhabitats for zooplankton community in lentic freshwater ecosystems of South Korea

Zooplankton community distribution depends largely on the microhabitat characteristics of the water body. It has been reported that macrophytes provide microhabitats for zooplankton (e.g., space and food resources). To date, studies have focused on the overall influence of macrophytes on zooplankton (e.g., positive relationships with zooplankton diversity); however, the morphological characteristics of macrophytes have not been intensively studied. To fill this gap in knowledge, we investigated zooplankton abundance and diversity, macrophyte characteristics (types, dry weight, and species number), and physicochemical parameters (water temperature, dissolved oxygen, pH, conductivity, and chlorophyll a) by using the 1×1m quadrat method. We surveyed 164 wetlands in South Korea during spring (May to June), prior to the summer monsoon. Patterning zooplankton distribution was accomplished using a Self-organizing map (SOM). We used 34 input variables (zooplankton genera) to train the model. The distribution of five plant habit parameters (no plant, emergent, free-floating, floating-leaved, and submerged) was investigated with a trained SOM plane, by environment data masking. Based on a U-matrix, three clusters were identified from the model. Zooplankton assemblages were positively related to macrophyte characteristics (i.e., dry weight, species number, and plant type). In particular, free-floating plants supported rotifers, such as Testudinella, and cladocerans, such as Alona, Chydorus, Diaphanosoma, and Ilyocryptus (mostly epiphytic). Submerged plants were associated with planktonic rotifers, such as Filinia, Ploesoma, Synchaeta, cladocerans, such as Daphnia, and copepods, such as Eucyclops and Macrocyclops. On the basis of these results, we suggest that the microhabitat structure, created by macrophytes, is an important factor in determining the diversity and abundance of zooplankton communities, because the different species compositions of macrophytes support diverse zooplankton genera in these habitats. The results indicate that macrophytes are the key components of lentic freshwater ecosystem heterogeneity, and the inclusion of diverse plant species in wetland construction or restoration schemes will result in ecologically healthy food webs.

Comparison of primer sets for the study of Planctomycetes communities in lentic freshwater ecosystems

In search of a primer set that could be used to study Planctomycetes dynamics in lakes and especially via fingerprinting methods, e.g. denaturing gradient gel electrophoresis (DGGE), three existing specific primer sets, developed for marine and soil systems, have been tested on water samples from four freshwater ecosystems. The first primer set (PLA46F/PLA886R) allowed PCR amplification of Planctomycetes sequences in only one of the four ecosystems, whereas the second primer set (PLA40F/P518R) amplified Planctomycetes sequences in all the studied ecosystems but with a low specificity, since sequences belonging to Verrucomicrobiales and Chlamydiales clades were also amplified. Finally, the third primer set (PLA352F/PLA920R) allowed amplification of Planctomycetes sequences in the four ecosystems with a very high specificity. It amplified all known Planctomycetes genera and yielded the highest Operational Taxonomic Unit (OTU) richness and diversity estimates. In silico analyses supported these results. Further experiments comparing PLA352F/PLA920R to PLA46F/P1390R (a primer set generating a longer PCR fragment, also used to study Planctomycetes) yielded very similar results. Our findings suggest that the primer set PLA352F/PLA920R provides good estimates of Planctomycetes richness and diversity compared with other, and can thus be used to study Planctomycetes dynamics in lentic freshwater ecosystems.