Oligotrophic Lake Research Articles

Historical impacts of mink fur farming on chironomid assemblages from shallow lakes in Nova Scotia, Canada

Campbell J, Libera N, Smol JP, Kurek J. 2022. Historical impacts of mink fur farming on chironomid assemblages from shallow lakes in Nova Scotia, Canada. Lake Reserv Manage. XX:XX–XX. Mink fur farms in southwestern Nova Scotia, Canada, are a suspected source of nutrients that have likely contributed to water quality issues in nearby lakes. Despite a decade of water quality monitoring, the cumulative effects of mink farming are not fully known due to a lack of information regarding baseline conditions. We used sedimentary midge remains and visible reflectance spectroscopy of sedimentary chlorophyll a (VRS Chl-a) to assess environmental changes prior to and following the establishment and growth of the local mink farming industry. Study lakes include hypereutrophic Nowlans Lake, with mink farms near its shoreline, mesotrophic Porcupine Lake with mink farms upstream, and oligotrophic Clearwater Lake (reference lake) with no mink farms in the catchment. We recorded a significant compositional shift in midge assemblages at Nowlans Lake (ANOSIM: 0.63, P < 0.001) following an increase in VRS Chl-a and the growth of the industry ca. 1970. Midge assemblage changes were indicative of a deterioration of benthic habitat and included increases in taxa associated with productive environments (i.e., Glyptotendipes, Endochironomus, and Cricotopus). Porcupine and Clearwater lakes, however, showed no significant assemblage shifts, suggesting relatively stable benthic conditions. VRS Chl-a increased around the 1950s in Porcupine Lake, whereas VRS Chl-a in Clearwater Lake increased around the 1980s. Our findings indicate that impacts from mink farming should be considered from a site-specific context. This study highlights the complexity of shallow lake responses associated with human activities related to >50 yr of mink farming.

Assessing relationship of degradation of coastal zones and phytoplankton species structure of Lake Uvildy and Lake Turgoyak (South Ural, Russia)

The current paper aims at analyzing the species structure of the phytoplankton community of two reservoirs on the territory of South Ural. The given water bodies are of different trophicity, namely, oligotrophic Lake Turgoyak and oligomesotrophic Lake Uvildy. Both lakes, being natural monuments, are subject to intensive recreational use. A large flow of tourists is a serious problem for the ecological state of the water bodies coastal areas. Also, tourist activities can affect the state of aquatic biocenoses. In this work, the degree of recreational degression of the selected study sites was assessed. The analysis was carried out according to the state of landscapes, vegetation and trampledness of the surveyed area. Based upon the research the current paper reveals spatial patterns in the distribution of recreational load on the coastal geosystems and the level of anthropogenic transformation of the territory. Mainly due to the high density of recreational centres and camping areas, the coastal area is characterized by a high degree of regression. Some signs allow forecasting changes in the species composition of phytoplankton communities and the trophic status of the lakes depending on the degradation of the coastal zones. Diatoms (Bacillariophyta) have been dominant in plankton phytocoenosis of Turgoyak and Uvildy. At the same time, in the oligomesotrophic lake (Uvildy), the number of diatom species is significantly reduced in areas with a higher degree of regression. Thus, diatoms are sensitive indicators of anthropogenic impact on aquatic ecosystems. Green and blue-green algae biodiversity has grown in the water body. However, no relationship was found between their species diversity and the level regression. But the following tendency is observed for the oligotrophic Lake Turgoyak. The species diversity of green algae grows with an increase in the degression degree. To forecast the further state of the studied water bodies, the revealed patterns in the change of the phytoplankton species structure depending on the degradation level of the coastal territories can be used as eutrophication signs.

ЗООИНДИКАЦИЯ ВОДОЕМОВ НА ТЕРРИТОРИИ НЕФТЯНЫХ МЕСТОРОЖДЕНИЙ БОЛЬШЕЗЕМЕЛЬСКОЙ ТУНДРЫ

Intensive development of the oil and gas industry and accidents on oil pipelines become the reason of the environmental tension in the Pechora River basin (Nenets Autonomous District). Data on changes in water quality in five lakes and a small watercourse in the territory of oil fields of the Bolshezemelskaya tundra are presented. The bioindication indices (Berger-Parker (D), Shannon biodiversity (H '), Woodiwiss (W), Pantle-Buck (S), Balushkina (Kch)) were applied. The assessment of the state of water bodies in the Kolva River Basin (large lakes - Kolvaty and Nercheity), in the Laya River Basin (shallow lakes - Krugloye, Bezymyannoe 1, Bezymyannoe 2, stream) was done. The 28 samples of zoobenthos was processed by the standard method in July 2012 and 2019. A low diversity of benthic invertebrates was revealed for 5–20 taxa of the rank of families and orders. During the considered period, the changes have occurred in the structure and composition of the zoobenthos of water bodies. In 2019, the species diversity decreased in Kolvaty Lake (H'&lt;2). There are no species of the crustacean complex (Monoporeia affinis, Mesocyclops leuckarti, Heterocope borealis) and larvae of Trichoptera. Only Sphaeriidae and Chironomidae with a predominance of Psectrocladius psilopterus (D = 55%) were recorded. The species diversity in Nercheity Lake increased (H'&gt; 2) with a change in the dominant taxa: the larvae of the chironomids Ablabesmyia monilis (D = 44%) were found in 2012, the lower crustaceans (D = 47–51%) - in 2019. However, according to the totality of hydrobiological indicators, the quality of water in the lakes of the Kolva River Basin in 2019 compared to 2012 did not change significantly. The quality of water in the Krugloye and Bezymyannoe 1, Bezymyannoe 2 lakes (the Laya River Basin) has improved that is confirmed by a significant increase of species diversity. The most characteristic groups of benthic communities in these lakes are lower crustaceans (Cladocera, Copepoda, Ostracoda) and Chironomidae. The indicators of clean waters are o-β-mesosaprobic species Cladocera, Copepoda Heterocope appendiculata, Heterocope borealis (in the oligotrophic lakes), caddisfly Limnephilus stigma (in the Krugloe Lake), rotifer Polyarthra euryptera (in the Bezymyannoe 2 Lake), mayfly larvae Centroptilum luteolum. More resistant to organic pollution Copepoda began to prevail in abundance and diversity in Bezymyannoe 1 and Bezymyannoe 2 lakes, with a decrease in the taxonomic composition of Cladocera, which indicates the eutrophication of these water bodies. In most lakes, the water corresponds to the III quality class ("moderate pollution"), but in the Kolvaty lake and in the Bezymyanny stream (the Laya River basin) was recorded the biogenic pollution. Totally, insignificant taxonomic changes in zoobenthos structure took place in the lakes and the state of water bodies of the surveyed tundra remains relatively stable.

Unusual massive phytoplankton bloom in the oligotrophic Lake Tanganyika

Background and aims – Massive algae growth resulting in a phytoplankton bloom is a very rare event in the meromictic and oligotrophic Lake Tanganyika. Such a bloom was observed in the north of the lake in September 2018. Phytoplankton species composition during this bloom is compared to a documented bloom in 1955, and to the composition in September 2011–2013. Meteorological observations suggest hydrodynamics could explain the occurrence of the 2018 bloom.Material and methods – Phytoplankton net samples were taken in the pelagic and littoral zone near Uvira during five consecutive days of the bloom in 2018. For the period 2011–2013, quantitative phytoplankton samples were obtained during a weekly sampling at the same sites. Samples were analysed with an inverted microscope and relative abundances of the algal species were compared. Key results – Dolichospermum flosaquae (Cyanobacteria) initially dominated the bloom followed by high relative abundance of Limnococcus limneticus (Cyanobacteria) on the third sampling day in September 2018. In the pelagic zone an increase of Nitzschia asterionelloides (Bacillariophyta), and Dictyosphaerium and Lobocystis (Chlorophyta) was observed while in the littoral zone increasing abundances of dinophytes were noted. Dolichospermum flosaquae was also responsible for the bloom reported in 1955, but was only sporadically observed in the 2011–2013 samples. Although Limnococcus limneticus was present in 2011–2013, it never reached relative abundances as high as during the 2018 bloom. Meteorological data indicate that 2018 experienced different conditions compared to previous years: strong south-east winds from May to September with a more eastern direction of the wind, and a well-marked drop in atmospheric pressure between August and September.Conclusion – After a very windy season, the combination of strong hydrodynamics, calmer lake conditions, and high solar radiation and air temperature in September 2018 was favourable for a massive Cyanobacteria bloom in the north of Lake Tanganyika.

Dynamics of Stoichiometric Autotroph-Mixotroph-Bacteria Interactions in the Epilimnion.

Autotrophs, mixotrophs and bacteria exhibit complex interrelationships containing multiple ecological mechanisms. A mathematical model based on ecological stoichiometry is proposed to describe the interactions among them. Some dynamic analysis and numerical simulations of this model are presented. The roles of autotrophs and mixotrophs in controlling bacterioplankton are explored to examine the experiments and hypotheses of Medina-Sánchez, Villar-Argaiz and Carrillo for La Caldera Lake. Our results show that the dual control (bottom-up control and top-down control) of bacteria by mixotrophs is a key reason for the ratio of bacterial and phytoplankton biomass in La Caldera Lake to deviate from the general tendency. The numerical bifurcation diagrams suggest that the competition between phytoplankton and bacteria for nutrients can also be an important factor for the decrease of the bacterial biomass in an oligotrophic lake.

Hydroclimatic drivers associated with an unusual bloom of Microcystis aeruginosa and increase of CyanoHABs in a deep oligotrophic lake

Abstract Hydroclimatic and anthropogenic factors in climate change scenarios contribute to ecological changes of harmful cyanobacterial algal blooms in lakes. This study describes the variability of the bathymetric and temporal distribution of cyanobacterial communities in a deep oligotrophic lake. An increase of two to nine in the detection of CyanoHABs potential was observed, likely linked to nitrogen contributions to Lake Rupanco during the last 36 years related to changes in land use and the cultivation of salmonids. We recorded an unusual bloom of Microcystis aeruginosa in winter, 2017 at 30 m during the total mixing period of the lake, associated with the highest N/P index (16.24), the increase of total nitrogen (75 μg/L) and climatic conditions that favored the availability of nitrogen of this cyanobacterium. This study provides information on the causes of increased cyanobacteria in a deep oligotrophic lake. Long-term information on the composition of cyanobacterial communities is very helpful in determining ecological changes.

Optimization of Landsat Chl-a Retrieval Algorithms in Freshwater Lakes through Classification of Optical Water Types

The application of remote sensing data to empirical models of inland surface water chlorophyll-a concentrations (chl-a) has been in development since the launch of the Landsat 4 satellite series in 1982. However, establishing an empirical model using a chl-a retrieval algorithm is difficult due to the spatial heterogeneity of inland lake water properties. Classification of optical water types (OWTs; i.e., differentially observed water spectra due to differences in water properties) has grown in favour in recent years over traditional non-turbid vs. turbid classifications. This study examined whether top-of-atmosphere reflectance observations in visible to near-infrared bands from Landsat 4, 5, 7, and 8 sensors can be used to identify unique OWTs using a guided unsupervised classification approach in which OWTs are defined through both remotely sensed reflectance and surface water chemistry data taken from samples in North American and Swedish lakes. Linear regressions of algorithms (Landsat reflectance bands, band ratios, products, or combinations) to lake surface water chl-a were built for each OWT. The performances of chl-a retrieval algorithms within each OWT were compared to those of global chl-a algorithms to test the effectiveness of OWT classification. Seven unique OWTs were identified and then fit into four categories with varying degrees of brightness as follows: turbid lakes with a low chl-a:turbidity ratio; turbid lakes with a mixture of high chl-a and turbidity measurements; oligotrophic or mesotrophic lakes with a mixture of low chl-a and turbidity measurements; and eutrophic lakes with a high chl-a:turbidity ratio. With one exception (r2 = 0.26, p = 0.08), the best performing algorithm in each OWT showed improvement (r2 = 0.69–0.91, p &lt; 0.05), compared with the best performing algorithm for all lakes combined (r2 = 0.52, p &lt; 0.05). Landsat reflectance can be used to extract OWTs in inland lakes to provide improved prediction of chl-a over large extents and long time series, giving researchers an opportunity to study the trophic states of unmonitored lakes.

Does glacial retreat impact benthic chironomid communities? A case study from Rocky Mountain National Park, Colorado

The aim of this study was to determine which environmental variables are responsible for modern benthic chironomid distributions in a glacial setting. The chironomid communities from nine alpine lakes were assessed, and forty-three individual taxa were extracted and identified. Surface water temperature and nitrate were strongly and negatively correlated (−0.82, p = 0.007), suggesting that glacial meltwater (the driver that explains both surface water temperature (SWT) (°C) and nitrate (NO3 + NO2-N)) is the environmental variable that explains the most variance (15%). On average, lakes receiving glacial meltwater were 2.62 °C colder and contained 66% more NO3 + NO2-N than lakes only receiving meltwater from snow. The presence of taxa from the tribe Diamesinae indicates very cold input from running water, and these taxa may be used as a qualitative indicator species for the existence of glacial meltwater within a lake catchment. Heterotrissocladius, Diamesa spp., and Pseudodiamesa were present in the coldest lakes. Chironomus, Diplocladius, and Protanypus were assemblages found in cold lakes affiliated with the littoral zone or alpine streams. The modern benthic chironomid communities collected from the alpine of subalpine lakes of Rocky Mountain National Park, Colorado, represent a range of climatic and trophic influences and capture the transition from cold oligotrophic lakes to warmer and eutrophic conditions.

Speciation of Dissolved Ferrous and Ferric Iron in Catamarasti Lake, Botosani (Romania)

The aquatic chemistry of iron involves many environmental aspects because dissolved iron is present as ferrous and ferric ion and the equilibrium between these two forms depends on many natural or antropogenic factors. This paper aims to provide a brief introduction to chemistry of iron in an oligotrophic lake, a new topic in this domain. A number of 28 sampling were taken from Catamarasti Lake, Botosani (Romania). The main physico-chemical properties showed that the acidity, dissolved oxygen, electrical conductivity and saturation satisfied the water quality criteria for this ecosystem. The results for dissolved iron species indicated that there is no strictly correlation with the variation of oxygen content. Thus, for the samples from NE shore, the contents of ferrous iron are bigger than of ferric iron, for the samples from SW shore the contents are almost equal, because of the low contents of oxygen. For the samples from the middle and from downstream of the lake, the contents of ferric iron are bigger than of ferrous iron, due to the oxygen content recorded.

Factors regulating lake periphyton biomass and nutrient limitation status across a large trophic gradient

Abstract Because of the historical focus of limnology on pelagic processes, the factors controlling lake periphyton growth and nutrient limitation are understudied compared to the phytoplankton. We deployed nutrient‐diffusing substrata at 28 sites spanning a wide trophic status gradient in Lakes Superior and Michigan to assess periphyton biomass accrual on control substrata and the response of periphyton to single and combined phosphorus (P) and nitrogen (N) additions. Periphyton growth was unimodally related to a composite metric of site trophic status, with highest biomass at mesotrophic sites and lower growth at oligotrophic and highly eutrophic sites. Contrary to expectations, P limitation was rare. Instead, several lines of evidence pointed to primary N or N + P co‐limitation of periphyton. Limitation extent was negatively related to site trophic status, with stronger nutrient limitation at oligotrophic sites. Our results support the hypothesis that phytoplankton and periphyton biomass respond differently to nutrient enrichment and suggest that different nutrients may limit pelagic and benthic primary production, even in the same system. Our findings also support the use of periphyton as an early warning indicator of nutrient pollution and help explain why large, oligotrophic lakes may be especially susceptible to localised benthic algal blooms.

Modelling key variables for understanding the effects of grazing and nutrient recycling by zooplankton on the freshwater microbial loop

Abstract Pelagic microbial food webs are structured by zooplankton through grazing and nutrient recycling. Cladocerans and copepods are assumed to have different effects on the microbial loop by grazing on different prey sizes and releasing phosphorus (P) differentially. Here, we assessed this effect of differential zooplankton grazing and nutrient recycling on microbial loop dynamics using a combination of experimental and modelling approaches. We performed field incubation experiments in an oligotrophic mountain lake (north‐Patagonian Andes) using the natural microbial community and the two dominant zooplankton taxa: a cladoceran (Diaphanosoma chilense) and a copepod (Boeckella gibbosa). The effect of zooplankton grazing and nutrient recycling were assessed separately in different treatments with direct and indirect zooplankton presence, respectively. We built a mechanistic model to estimate zooplankton grazing and P recycling and prey P quotas. The model was parameterised with the results from our field experiment and with prior information from size‐based traits and zooplankton C:P using a Bayesian approach. Laboratory experiments for zooplankton P excretion were also performed to test the predictive accuracy of our model. Our model showed that copepods and cladocerans have contrasting effects on the microbial loop. Diaphanosoma chilense grazed mainly on picoplankton while B. gibbosa grazed on nanoflagellates and algae. Diaphanosoma chilense reduced the biomass and increased P quota of picoplankton, and reduced the P quota of nanoflagellates. In contrast, B. gibbosa released more P, increasing the picoplankton biomass and reducing the biomass of nanoflagellates, but increasing its P quota. Based on our experimental and model results, copepod grazing favours higher P acquisition rates for cladocerans by releasing more P for picoplankton. By contrast, cladocerans would have a mixed effect on the main food items of copepods by increasing P quotas of the strict osmotrophic algae but decreasing P quotas of nanoflagellates. Our mechanistic model is useful to quantitatively assess key planktonic variables, which are usually difficult to measure in the field, such as zooplankton P excretion rates and microbial P quotas, by using more conspicuous variables such as biomass of the different microbial compartments and dissolved and particulate P concentrations. The model presented here could be used to disentangle complex pathways in the microbial food web. The relative importance of phagotrophy and osmotrophy in P uptake, P quotas, and nutrient recycling by grazers result in key variables for understanding ecosystem matter flux and resource use efficiency.

Seasonality and distribution of cyanobacteria and microcystin toxin genes in an oligotrophic lake of Atlantic Canada.

Cyanotoxins are an emerging threat to freshwater resources worldwide. The most frequently reported cyanotoxins are the microcystins, which threaten the health of humans, wildlife, and ecosystems. Determining the potential for microcystin production is hindered by a lack of morphological features that correlate with microcystin production. However, amplicon-based methods permit the detection of microcystin biosynthesis genes and were employed to assess the toxin potential in Lake Utopia, NB, Canada, an oligotrophic lake that occasionally experiences cyanobacteria blooms. Samples collected at 2 week intervals from June 27th to September 27th, 2016, were screened by polymerase chain reaction (PCR) for the microcystin synthetase E gene (mcyE). The mcyE gene was present in some samples every sampling day, despite microcystin not being detected via ELISA, and was most frequently associated with the larger pore size fractions of the serially filtered samples. Further PCR surveys using primer sets to amplify genus-specific (e.g., Microcystis, Anabaena/Dolichospermum, and Planktothrix) mcyE fragments identified Microcystis as the only taxa in Lake Utopia with toxigenic potential. Sequencing of the 16S rRNA V3-V4 region revealed a community dominated by members of the order Synechococcales (from 38 to 96% relative abundance), but with significant presence of taxa from Cyanobacteriales including Microcystaceae and Nostocaceae. A persistent Microcystis population was detected in samples both testing positive and negative for the mcyE gene, highlighting the importance of identifying cyanotoxin production potential by gene presence and not species identity. To our knowledge, this study represents the first application of amplicon-based approaches to studying toxic cyanobacteria in an understudied region-Atlantic Canada.

Rare plant communities of lakes and river estuaries of the Arkhangelsk Region

The problem of protecting rare communities in the vegetation cover still remains poorly studied. Currently, it is relevant for aquatic and coastal aquatic plant communities of lakes and river estuaries of the Arkhangelsk Region. Two critical criteria were used to distinguish rare communities: 1) protected species are cenosis-formers, 2) species that were first noted outside the northern border of the ranges are either cenosis-formers, or abundant in the composition of communities. The first criterion includes communities with species listed in the Red Data Books of the Russian Federation (2008) and the Arkhangelsk Region (), if these species are significant from the point of phytocenosis. The last includes taxa and plant populations of the Arkhangelsk Region that need special attention to their state in the natural environment and are recommended for bio-surveillance. The second criterion includes the communities of the Glycerietum fluitantis association located on the coast of the Pechora Inlet, which were described here for the first time.&#x0D; The communities’ habitats are water bodies that differ significantly in hydrological conditions. Lobelietum dsortmannae, Isoëto lacustris–Lobelietum dortmannii, Isoëto echinosporae–Lobelietum dortmannae, Lobelieto dortmannae–Phragmitetum australis, Lobelieto dortmannae–Caricetum rostratae, Fontinalieto dalecarlicae–Phragmitetum australis, Fontinalieto dalecarlicae–Nupharetum lutea associations are typical for oligotrophic and oligo-mesotrophic lakes of the hydrocarbonate class with low water salinity. Nympheto candidae–Nupharetum pumilae, Potamogeneto natantis–Nymphaeetum tetragonae, Chareto virgatae–Scirpetum lacustris associations are identified in eutrophic and mesotrophic lakes. Communities of Chareto strigosae–Charetum asperae, Charetum subspinosae, Chareto subspinosae–Phragmitetum australis charosum subspinosae associations develop in sulfate lakes with increased water salinity. Ruppietum maritimae, Glycerietum fluitantis purum, Hippurideto tetraphillae–Glycerietum, and Zannichellia pedunculata communities are typical for river estuaries.&#x0D; We have described most of the rare communities for specially protected natural areas of the Arkhangelsk Region: in the Kenozero National Park, the Onega Pomorie National Park, the Pinezhskiy Nature Reserve, the Nenetskiy Nature Reserve, and the Pakhanchenskiy Nature Reserve. At the end of the article, some recommendations for the protection of rare communities are given. They are useful for monitoring such species in protected areas. The protection of rare communities is based on the principle that any species that is part of the community is its integral part. The destruction of cenosis-forming species leads to the disappearance of both an integral unique community and protected species as a part of it, regardless of whether they are phytocenotically significant, or grow singularly within the community.

Periphyton diversity in two different Antarctic lakes assessed using metabarcoding

AbstractAntarctic lakes have generally simple periphyton communities when compared with those of lower latitudes. To date, assessment of microbial diversity in Antarctica has relied heavily on traditional direct observation and cultivation methods. In this study, sterilized cotton baits were left submerged for two years in two lakes on King George Island and Deception Island, South Shetland Islands (Maritime Antarctic), followed by assessment of diversity by metabarcoding using high-throughput sequencing. DNA sequences of 44 taxa belonging to four kingdoms and seven phyla were found. Thirty-six taxa were detected in Hennequin Lake on King George Island and 20 taxa were detected in Soto Lake on Deception Island. However, no significant difference in species composition was detected between the two assemblages (Shannon index). Our data suggest that metabarcoding provides a suitable method for the assessment of periphyton biodiversity in oligotrophic Antarctic lakes.

Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive Silurus glanis L. in a Deep, Large, and Oligotrophic Lake (Lake Maggiore, North Italy)

The ecological features of invasive alien species are crucial for their effective management. However, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore, where the species is present since 1990, but no scientific information is available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. The NPUE and BPUE (individuals (N) and biomass (B, in grams) per unit effort (m2), respectively) of catfish were generally higher in littoral (NPUE &gt; 0.01; BPUE &gt; 96) than in pelagic habitats (NPUE &lt; 0.009; BPUE &lt; 114), but the catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded, belonging to 12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad, and roach), whilst the diet of littoral catfish was more variable and dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.

Comparison of spatiotemporal carbon, nitrogen, and phosphorus burial in two plateau lacustrine sediments: implication for N and P control.

The long-term accumulation, burial and release of nutrients, such as carbon (C), nitrogen (N), and phosphorus (P) in lacustrine sediments are responsible for the global lake eutrophication. Interpretation of the spatiotemporal sedimentary record of nutrients (C, N, and P) in contrasting trophic level of lakes is helpful for understanding the evolutionary process of water eutrophication. Based on the radiochronology of 210Pbex and 137Cs, a comparative study of spatial and temporal concentrations, burial of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP), the sources of organic matter were conducted using sediment cores from two plateau lakes Dianchi (DC) and Fuxian (FX) of SW China. Results showed that concentrations and burial of C, N, and P in sediments of DC, a shallow hypertrophic lake with the maximum depth of 5.8 m, were both higher than those in FX, an oligotrophic deep lake with the maximum depth of 155.0 m. For both lakes the molar ratio of TOC/TN increased in the sediments moving from north to south. The values of TOC/TN molar ratios increased over time in DC and were higher than in FX. The extremely high values of TOC/TN appeared in the central and southern parts of FX, indicating the impacts of accumulation effect and sediment focusing in the deeper region and indirect supplement from the Lake Xingyun (XY), an adjoining lake connected with FX via the Gehe River. Time-integrated sources identification in DC indicated the contribution of allochthonous sources was dominant over the past few decades, which contributed to the increased trophic level of the lake. The comparison of relationships of carbon accumulation rates (CAR), nitrogen accumulation rates (NAR), and phosphorous accumulation rates (PAR), the ratios of N/P and the utilizations of N and P fertilizer between DC and FX implied that both of N and P inputs should be limited for reducing the trophic level, but N control was predominant in comparison with P for both lakes. The results indicated that caution is required in plateau lakes to limit transition from oligotrophic to eutrophic in these lakes.

Effects of ultraviolet radiation removal on algal communities in three high-elevation Brazilian (ultra)oligotrophic lakes

ABSTRACT Ultraviolet (UV) radiation is a major constraint to aquatic photosynthetic organisms. Freshwater algae dwelling in natural high altitudinal ponds and lakes must tolerate high UV radiation exposure, especially in oligotrophic waters. Here, we investigated the in situ physiological short-term response of three algal communities to UV removal in lakes at high-elevation in Brazil, by measuring photosynthesis, carotenoid and phenolic contents, nutrient concentration and antioxidant enzymatic activities. Rancho Queimado (RQ), Lagoa do Roncador (LR) and Lagoa Bonita (LB), located in southern and central Brazil, were classified as oligo and ultraoligotrophic and presented species-rich algal communities dominated by species of the class Zygnematophyceae. The algal communities presented different short-term metabolic strategies to circumvent the stressful effects of the UV, influenced by species composition. At RQ, photosynthesis was negatively affected by UV removal, suggesting that photoprotection may be triggered by this radiation; at this site, the algae relied mainly on an efficient superoxide dismutase response. LR algae exhibited a higher contribution of catalase but prioritized the non-enzymatic antioxidant defences (phenolics and carotenoids) as their background and primary barrier against reactive oxygen species, which contributed to the development of higher net photosynthesis than that of the other sites and showed no variation to light treatments. LB algae appeared to be impaired by the increase in the temperature and highly variable irradiance throughout the day, which affected the net photosynthesis and activity of antioxidant enzymes. However, similar to LR, carotenoids and phenolic compounds acted as protagonists against oxidative damage.

Assessing ecological status in karstic lakes through the integration of phytoplankton functional groups, morphological approach and environmental DNA metabarcoding

Phytoplankton is one of the key Biological Quality Elements within the Water Framework Directive, used to assess the ecological status of surface water bodies. Water samples for phytoplankton identification were collected from April to September at a total of eight sampling sites in all six Croatian natural karstic lakes with an area greater than 0.5 km2. The main objective was to show the comparability of environmental DNA metabarcoding (Illumina sequencing using the hypervariable V9 region of the eukaryotic SSU rRNA gene) with morphologically based assessment and its applicability in assessing the ecological status of lakes. The value of Hungarian lake phytoplankton index (HLPI) indicating the final ecological status was calculated for both datasets using biomass and composition metrics. Chlorophyll a concentration measured using Ultra-High-Performance Liquid Chromatography and Spectrophotometer giving two biomass metrics along with the functional group approach (FG) as the composition metric for the complete taxa/operational taxonomic units (OTUs) lists as well as for the taxa/OTUs that contributed more than 5% to the total biomass/number of amplicons gave four to four HLPI values per sample. HLPI values from both approaches were highly correlated (Pearson's r > 0.92) and classified into good or high ecological status, although different compositions and proportions of FGs were recorded, thus giving the important role to the equal or similar factors assignment to different FGs with similar ecological demands and favourable habitats. In 89% of the samples, HLPI values indicate an equal range of ecological status and most differences were found due to different methods of Chlorophyll a measurement. Different composition metrics between approaches showed significant differences (p < 0.05) only in lakes Prošće and Crniševo. This study showed the applicability of the V9 region of 18S rRNA in ecological status assessment for oligotrophic and mesotrophic lakes due to the comparable results between approaches, but further development and standardization of eDNA metabarcoding are needed for the implementation in routine monitoring programs.

Daily vertical distribution of zooplankton in two oligo-mesotrophic north Patagonian lakes (39° S, Chile).

The zooplankton communities often exhibit daily vertical migrations to avoid natural ultraviolet radiation and/or fish predation. However there is no information on this topic in Chilean North Patagonian lakes up to date. Therefore, this study deals with a first characterization of plankton crustacean daily vertical migration in two temperate, oligotrophic lakes (Villarrica and Panguipulli lakes, 39°S) in Southern Chile. Zooplankton were collected at different depths intervals (0-10m, 10-20 m, 20-30m, 30-40m) at early morning, middle day, evening and night in the studied site. The results revealed that zooplankton species (Daphnia pulex, Ceriodaphnia dubia, Neobosmina chilensis, Mesocyclops araucanus, and Tropocyclops prasinus) are abundant in surface zones at night, early morning and evening, whereas at middle day the zooplankton abundances are high at deep zones. The results agree with observations for Argentinean and North American lakes where these daily migration patterns in crustacean zooplankton species were reported due mainly natural ultraviolet radiation exposure, whereas for northern hemisphere lakes the vertical migration is due to combined effect of natural ultraviolet radiation and fish predation exposure.

Taxonomic and functional differences between winter and summer crustacean zooplankton communities in lakes across a trophic gradient

AbstractDespite increasing interest in winter limnology, few studies have examined under-ice zooplankton communities and the factors shaping them in different types of temperate lakes. To better understand drivers of zooplankton community structure in winter and summer, we sampled 13 lakes across a large trophic status gradient for crustacean zooplankton abundance, taxonomic and functional community composition and C/N stable isotopes. Average winter zooplankton densities were one-third of summer densities across the study lakes. Proportionally, cladocerans were more abundant in summer than winter, with the opposite pattern for calanoids and cyclopoids. In green (eutrophic) lakes, zooplankton densities were higher under the ice than in brown (dystrophic) and blue (oligotrophic) lakes, suggesting better conditions for zooplankton in productive lakes during winter. Overall, zooplankton communities were more similar across lakes under the ice than during the open water season. Feeding group classification showed a decrease in herbivore abundance and an increase in predators from summer to winter. C/N stable isotope results suggested higher lipid content in overwintering zooplankton and potentially increased reliance on the microbial loop by winter zooplankton. Our results show substantial variation in the seasonality of zooplankton communities in different lake types and identify some of the factors responsible for this variation.