Oligotrophic Water Bodies Research Articles

Ferrous-driven efficient removal of nitrate and various heavy metals by Zoogloea sp. ZP7 under oligotrophic conditions: Kinetics and heavy metal stress responses

Denitrification in surface water is affected by its oligotrophic characteristics and heavy metal pollution. In this study, a heterotrophic denitrifying bacterium Zoogloea resiniphila ZP7, which can utilize ferrous (Fe2+) as an additional electron donor under oligotrophic conditions, was isolated. Strain ZP7 achieved a 98.5 % nitrate (NO3−-N) removal efficiency (NRE) within 12 h using sodium acetate as carbon sources, with a Fe2+ concentration of 10.0 mg L−1, pH of 7.0, carbon to nitrogen ratio of 2.0, and NO3−-N concentration of 5.01 mg L−1, and no nitrite residue was observed. The denitrification performance and the removing ability of heavy metal by strain ZP7 were studied when exposed to copper (Cu2+), zinc (Zn2+), and cadmium (Cd2+) alone or in combination. When 1.0 mg L−1 Cu2+, Zn2+, and Cd2+ were added simultaneously, the strain ZP7 could achieve 91.3 % NRE in 14 h, and the removal efficiencies of Cu2+, Zn2+, and Cd2+ were 68.1, 89.2, and 83.5 %, respectively. The results of fluorescence region integration showed that the response of strain ZP7 to different heavy metal system stresses was different. Moreover, the changes in the content of extracellular polymeric substances (EPS) and humic acids indicated that they contributed to the enhancement of the resistance of strain ZP7 to heavy metals. Various characterization results showed that EPS and bio‑iron oxides were beneficial to remove heavy metals. In future studies, strain ZP7 can be considered to be immobilized in biomaterials to treat contaminated oligotrophic water bodies to explore its application prospects in actual contaminated water bodies.

Planted species influences soil phosphorus losses in a historically fertilized pasture system: A mesocosm study

AbstractThe gradual accumulation of phosphorus from historical fertilization can contribute to the eutrophication of surface waters by increasing the potential for subsurface leaching losses. Grazing lands areas are a priority for concern, and phytoremediation efforts in grazing lands have prioritized grasses that may be used as forage for cattle. This study investigated the influence of three different forage species—Paspalum notatum, Hemarthria altissima, and Cynodon nlemfuensis—on the loss of phosphorus in leachate from surface soils. The experiment used a nested pot mesocosm design that allowed us to monitor leachate volume and concentration biweekly over the course of 3 months. Pots containing P. notatum plants leached significantly more phosphorus than pots containing C. nlemfuensis or empty pots with no plants growing in them, despite losing an equivalent amount of water. H. altissima lost equivalent amounts of phosphorus in leachate water, but each H. altissima plant removed approximately 33.6 mg of phosphorus, approximately 2.5× that removed by P. notatum (13.4 mg). C. nlemfuensis had lower average leachate phosphorus concentrations at each biweekly sampling than either plant species (C. nlemfuensis‐P. notatum, padj = 0.001; C. nlemfuensis‐H. altissima, padj = 0.02), averaging only 0.110 ppm in leachate relative to 0.175 ppm and 0.200 ppm in pots beneath H. altissima and P. notatum, respectively. This, combined with C. nlemfuensis' slightly higher‐than‐average aboveground P content and overall aboveground biomass expression suggest it is the best possible phytoremediation candidate. As even minor leachate P loads can be critically threatening to neighboring oligotrophic water bodies, if the conservation of downstream environments is the priority, the short‐term threat of increased leachate must be considered. Further research is needed to explore the underlying mechanisms and field‐scale implications of these findings.

Biogeography of Planktonic and Benthic Bacterial Communities of Lake Khubsugul (Mongolia)

The bacterioplankton of Lake Khubsugl (Hövsgöl) has significant differences from that of large ancient and oligotrophic water bodies. The greatest similarity was noted, however, between the microbiomes of Lake Khubsugul and Lake Baikal, the lakes located in the same rift zone and connected by the river system, which emphasizes the similarity of microbiomes at the regional level. In the global aspect, geographical zonation had the greatest reliable significance in the microbial community biogeography, while depth had the lowest. Trophic status of the lakes, as well as their ancient origin, did not affect the clustering of microbiomes, with the seasonal factor playing the major part at the local and regional levels.

A sequence of weather‐driven hydrodynamic events stimulates the formation of harmful algal blooms on an oligotrophic lake

AbstractHarmful algal blooms (HABs) are common in many eutrophic lakes and frequently associated with nutrient excesses, warm waters, and calm conditions. While HABs can also occur in oligotrophic waterbodies, bloom‐stimulating factors remain elusive for these ecosystems. Here, using a high‐frequency sensor platform supported by hydrodynamic modeling, we document a clearly linked sequence of three hydrodynamic events that immediately preceded each HAB event on Skaneateles Lake, NY during 2018. HABs were first preceded by interactions between internal waves in the thermal structure of the lake with the northern slope of the lakebed. These interactions disturbed sediments resulting in upwelling of nutrient‐rich sediment and possibly cyanobacterial cells into the lower water column. Next, moderate winds stimulated Langmuir circulation which facilitated the transport of material from the lower water column to well‐lit surface waters. Finally, the sequence culminated with a calm wind period, which is often classically associated with surface HAB formation. While individual steps in this sequence occurred independently and repeatedly throughout the year, the complete sequence occurred only eight times, immediately preceding each of the eight documented HABs. We empirically derive thresholds for and timing of the sequence to independently predict HAB occurrence and elevated cyanobacteria levels in the lake. The discovery of this specific and repeated event sequence and the identified thresholds provides the potential for forecasting of HABs days in advance. Ongoing climate change impacts, including increasing water column thermal stratification and changing wind speeds may alter the frequency, timing, and duration of this sequence and consequent HAB formation.

Estimation of water quality variables based on machine learning model and cluster analysis-based empirical model using multi-source remote sensing data in inland reservoirs, South China

Reservoirs play important roles in the drinking water supply for urban residents, agricultural water provision, and the maintenance of ecosystem health. Satellite optical remote sensing of water quality variables in medium and micro-sized inland waters under oligotrophic and mesotrophic status is challenging in terms of the spatio-temporal resolution, weather conditions and frequent nutrient status changes in reservoirs, etc., especially when quantifying non-optically active components (non-OACs). This study was based on the surface reflectance products of unmanned aerial vehicle (UAV) multispectral images, Sentinel-2B Multispectral instrument (MSI) images and Landsat 7 Enhanced Thematic Mapper Plus (ETM+) by utilizing fuzzy C-means (FCM) clustering algorithm was combined with band combination (BC) model to construct the FCM-BC empirical model, and used mixed density network (MDN), extreme gradient boosting (XGBoost), deep neural network (DNN) and support vector regression (SVR) machine learning (ML) models to invert 12 kinds of optically active components (OACs) and non-OACs. Compared with the unclustered BC (UC) model, the mean coefficient of determination (MR) of the FCM-BC models was improved by at least 46.9%. MDN model showed best accuracy (R2 in the range of 0.60–0.98) and stability (R2 decreased by up to 13.2%). The accuracy of UAV was relatively higher in both empirical methods and machine learning methods. Additionally, the spatio-temporal distribution maps of four water quality variables were mapped based on the MDN model and UAV images, all platforms showed good consistency. An inversion strategy of water quality variables in various monitoring frequencies and weather conditions were proposed finally. The purpose of introducing the UAV platform was to cooperate with the satellite to improve the monitoring response ability of OACs and non-OACs in small and micro-sized oligotrophic and mesotrophic water bodies.

Relationship between Phytoplankton, Heterotrophic Plankton, and Planktivorous Fish Productions in Different Water Bodies.

Examination of 14 lake-type water bodies at various latitudes of the Northern Hemisphere showed that the efficiency of phytoplankton production transformation through heterotrophic bacterioplankton and non-predatory zooplankton to predatory zooplankton and planktivorous fish increases in the direction from eutrophic to oligotrophic water bodies. The highest ratios between autotrophic and heterotrophic organism production were observed in lakes and reservoirs where the contribution of allochthonous substances to the total energy flow is relatively high. Bacterioplankton utilizing allochthonous dissolved organic matter (DOM) provides an additional source of energy for zooplankton, which serves as food for planktivorous fish. Therefore, to predict the total biological productivity and production of the fish community, it is necessary to take into account the production of not only autotrophic plankton, but also that part of heterotrophic bacterioplankton that is specialized in utilizing DOM entering the water body from the outside.

Response of Dissolved Trace Metals to Dust Storms, Sediment Resuspension, and Flash Floods in Oligotrophic Oceans

AbstractTrace metals (TM) delivered by atmospheric dust play a key role in oceanic biogeochemical cycles. However, the impact of short‐term environmental perturbations such as dust storms and sediment resuspension events on the oceanic water column is poorly constrained due to the low temporal sampling resolution and episodic nature of these events. The Gulf of Aqaba (GoA), Red Sea, is a highly accessible deep oligotrophic water body featuring exceptionally high atmospheric deposition fluxes that provide the main source of TMs to the GoA surface water. Here, we present a 2‐year time series of dissolved manganese, cobalt, nickel, copper, zinc, cadmium, and phosphate concentration profiles sampled in the GoA. The study focuses on daily time scale dust storms and episodes of sediment resuspension to quantify the immediate impact of these events on dissolved TM cycling. Counter‐intuitively, upper mixed layer TM inventories decrease with increasing aerosol loads, with the effects of aerosol‐induced TM scavenging and dissolution peaking 5–6 days after aerosol deposition. Dust storms promote intense TM scavenging, with TM inventories decreasing by up to 44%, but seldom lead to TM enrichment. Similarly, sediment resuspension and flash flood events triggered significant TM scavenging. These findings highlight the potential dual role of atmospheric deposition in the oceans as a long‐term source of dissolved TMs and a short‐term sink. The in situ observations presented here may be used to understand and quantify the global impact of abrupt environmental events on oceanic chemical compositions.

Broadening the Taxonomic Composition of Diatoms (Bacillariophyta) in Tundra Water Bodies of Adjacent Territories of the Lena Delta Wildlife Reserve (Yakutia, Russia) Using Electron Microscopy<sup>1</sup>

Using the electron microscopy, 435 diatom algae from 78 genera of 14 different types of tundra water bodies located in the vicinity of the Ust-Lensky State Reserve, north of the Arctic Circle, on the northern exposure of the slope of the Primorsky Ridge (the eastern spur of the Kharaulakh Range of the Verkhoyansk Mountain system) 435 diatom algae from 78 genera were revealed. Among them, 24 taxa of the species rank and 1 of the generic rank are new to the flora of Russia. Most of the identified species, which are new to the flora of Russia, are found in Europe and are characteristic of oligotrophic water bodies and watercourses. Of all the species under study, 66 species belonging to 28 genera have been identified to the genus, with the largest number of them belonging to the genera Planothidium (7) and Gomphonema (10).

Features of Zoobenthos of Mesohumus Lakes of the Republic of Karelia in a Natural State

The results of studies of the current state of zoobenthic communities of lakes Sukkozero and Gimolskoye, located in the western part of the Republic of Karelia (Muezersky district), are presented. Under conditions of high color and low mineralization of waters, communities are formed with a predominance of chironomid larvae, caddisflies, mayflies, and oligochaetes. Biomass and abundance indicators in 2017–2018 were within 0.41–0.75 g/m2 and 315–685 ind./m2 in the lake Sukkozero and 0.41–0.93 g/m2 and 220–346 ind./m2 in the lake Gimolskoye. The highest values of abundance and biomass were noted in biotopes of silty soils (overgrown littoral and profundal), the lowest values in the biotope of sandy littoral. According to the level of quantitative development of zoobenthos, Sukkozero belongs to oligotrophic water bodies; Gimolskoye – mesotrophic. The experience of using common biotic indices for assessing the ecological quality of waters (Mayer, oligochaete, saprobity, chironomid) indicates that low mineralization and high humus content can affect their performance and distort the assessment of real organic pollution.

Cyanobacterial blooms in Ontario, Canada: Continued increase in reports through the 21st century

Favot EJ, Holeton C, DeSellas AM, Paterson AM. 2023. Cyanobacterial blooms in Ontario, Canada: Continued increase in reports through the 21st century. Lake Reserv Manage. XX:XXXXXX. The Ontario Ministry of the Environment, Conservation and Parks samples algal composition in response to public reports of suspected algal blooms, which have been tracked since 1994. In a previous analysis, Winter et al. noted a significant increase in the number of reports of confirmed algal blooms dominated by cyanobacteria from 1994 to 2009. Here, we determined that this increasing trend in the yearly number of confirmed cyanobacterial bloom reports (CCBRs) has persisted in Ontario over the intervening decade, to 2019. More than half of CCBRs were from waterbodies on the Precambrian Shield, in the Georgian Bay (5E) ecoregion, known for cottaging and water-based tourism. Data from the Ontario Lake Partner Program (LPP) was used to investigate total phosphorus (TP) concentrations in waterbodies with CCBRs. Approximately 44% of the waterbodies with a CCBR (mean TP 12.99 µg/L, n = 135) had average spring TP concentrations less than 10 µg/L, compared to 64% for LPP waterbodies with no reported or confirmed cyanobacterial blooms (mean TP 9.79 µg/L, n = 918). The most common taxon of cyanobacteria dominating bloom samples in inland waterbodies was Dolichospermum, followed by Aphanizomenon in waterbodies on the Precambrian Shield, and Microcystis in the Mixedwood Plains ecozone in southern Ontario. While an increase in public awareness cannot be ruled out in contributing to the rise in CCBRs across Ontario, the high proportion of cyanobacterial blooms occurring in oligotrophic waterbodies suggests that there may be a link to climate warming, rendering conditions more favorable for these blooms to occur.

Mineralization of autochthonous particulate organic carbon is a fast channel of organic matter turnover in Germany's largest drinking water reservoir

Abstract. Turnover of organic matter (OM) is an essential ecological function in inland water bodies and relevant for water quality. This is especially important for the potential of dissolved organic carbon (DOC) removal as well as for emissions of CO2. In this study, we investigated various phases of OM including DOC, autochthonous particulate organic carbon (auto-POC), allochthonous particulate organic carbon (allo-POC), and sedimentary matter (SED) in a temperate drinking water reservoir (Rappbode Reservoir, Germany) by means of dissolved inorganic carbon (DIC) concentrations and carbon stable isotope ratios. In order to best outline carbon turnover, we focused on the metalimnion and the hypolimnion of the reservoir, where respiration is expected to be dominant and hardly disturbed by atmospheric exchange or photosynthesis. DIC concentrations ranged between 0.30 and 0.53 mmol L−1, while δ13CDIC values ranged between −15.1 ‰ and −7.2 ‰ versus the VPDB (Vienna PeeDee Belemnite) standard. Values of δ13CDOC and δ13Cauto-POC ranged between −28.8 ‰ and −27.6 ‰ and between −35.2 ‰ and −26.8 ‰, respectively. Isotope compositions of sedimentary material and allochthonous POC were inferred from the literature and from measurements from previous studies with δ13CSED=-31.1 ‰ and δ13Callo-POC ranging from −31.8 ‰ to −28.6 ‰. Comparison of DIC concentration gains and stable isotope mass balances showed that auto-POC from primary producers was the main contributor to increases in the DIC pool. Calculated OM turnover rates (0.01 to 1.3 µmol L−1 d−1) were within the range for oligotrophic water bodies. Some higher values in the metalimnion are likely due to increased availability of settling auto-POC from the photic zone. Samples from a metalimnetic oxygen minimum (MOM) also showed dominance of respiration over photosynthesis. Our work shows that respiration in temperate lentic water bodies largely depends on auto-POC production as a major carbon source. Such dependencies can influence the vulnerabilities of these aqueous systems.

Agricultural land use and pond management influence spatial-temporal variation of CH4 and N2O emission fluxes in ponds in a subtropical agricultural headstream watershed

Small water bodies are hotspots of biogeochemical cycles with large spatial and temporal heterogeneity of their greenhouse gas emission fluxes. To reveal the spatial and temporal variabilities of methane (CH4) and nitrogen dioxide (N2O) emission fluxes in small water bodies in subtropical agricultural headwater watersheds, monthly measurements of CH4 and N2O fluxes were performed in 53 ponds from May 2018 to July 2020. Results showed that the fluxes of CH4 and N2O exhibited distinct spatial and temporal variations, and generally showed a trend of high emission rate in summer and low emission rate in winter. Agricultural land use and pond management had important impacts on CH4 and N2O emission fluxes in ponds. The CH4 and N2O emission fluxes were significantly higher in the ponds with the landscape of farmland, tea plantation and residential area than those of forest, which might be relevant to the eutrophication of pond water bodies. The mean N2O emission flux in intensive fishing ponds was much higher than that in grass-fed fishing ponds and no fishing ponds. Moreover, the sustained-flux global warming potential (SGWP) in the eutrophic pond water bodies of farmland, tea plantation and residential area are significantly higher than that in oligotrophic water bodies of forest ponds. Our CH4 and N2O emission results suggest that the reduction potential of 4.98 kg C ha−1 y−1 for CH4 and 0.42 kg N ha−1 y−1 for N2O will occur in future if ecological management measures are implemented to improve the pond water quality from eutrophication to oligotrophic conditions.

Dissolved aluminium dynamics in response to dust storms, wet deposition, and sediment resuspension in the Gulf of Aqaba, northern Red Sea

Dissolved aluminium (Al) is a primary tracer of atmospheric deposition to the open ocean. However, the impact of short-term environmental perturbations such as dust storms, sediment resuspension and rainfall events on the oceanic water column is poorly constrained due to the typically low temporal resolution sampling in open ocean settings. The Gulf of Aqaba (GoA), northern Red Sea, is a highly accessible deep oligotrophic water body featuring exceptionally high atmospheric deposition fluxes delivered by dust storms, which constitutes as the main terrigenous input to the GoA surface water.Here, we present a time series of dissolved Al and silicate (Si) concentration profiles sampled during 2017 and 2018, with a particular focus on daily time scale dust storms, episodes of sediment resuspension and rain events. We evaluate the results in conjunction with high temporal resolution measurements of airborne aerosols and sediment trap -based water column sinking particulate fluxes.Dissolved Al and Si concentrations ranged between 22 and 91 nmol kg−1 and 0.6 and 3.2 µmol kg−1, respectively. These two elements correlated at depth but decoupled in the upper water column. Counter intuitively, mixed layer Al (AlML) inventories decrease with increasing aerosol loads, with dust storms promoting intense Al scavenging, causing scavenging rates to surpass dissolution rates and abruptly driving down AlML by up to 14 %. Concurrently, post dust storm AlML change rates increase linearly with increasing theoretical dissolution rates and thus net dissolution is predicted for higher dust loads than observed in this study. However, low seawater particle loads during low magnitude dust storms and deep mixing depths will result in conditions that favor scavenging. Similarly, a sediment resuspension event triggered a decrease of 34 % in the Al water column inventory. By contrast, wet deposition may enhance the soluble Al flux from mineral dust by a factor of 11. Atmospheric deposition flux estimates (29.8 ± 4.4 g m−2 year−1) calculated using long-term average AlML and mixed layer depths agree with independent flux estimations. Conversely, fluxes calculated using discrete profiles yielded a wide range of values (8–93 g m−2 year−1).The combined results demonstrate that atmospheric deposition in the oceans acts as a long-term source for Al while concomitantly serving as a short-term sink through scavenging. The in-situ rates and insights presented here may be used to understand and quantify the true impact of abrupt environmental events on water column chemical compositions.

Mix-cultured aerobic denitrifying bacteria augmented carbon and nitrogen removal for micro-polluted water: Metabolic activity, coexistence and interactions, and immobilized bacteria for reservoir raw water treatment

Less attention has been paid on the oligotrophic water body nitrogen treatment with mix-cultured aerobic denitrifying bacteria (Mix-CADB). In this study, three Mix-CADB communities were screened from the sediments of reservoirs. The nitrate and dissolved organic carbon (DOC) removal efficiencies of Mix-CADB communities were higher than 92 % and 91 %, respectively. Biolog results suggested that Mix-CADB communities displayed excellent carbon source metabolic activity. The nirS gene sequencing indicated that Pseudomonas sp. and Pseudomonas stutzeri accounted for more proportions in the core species of three Mix-CADB communities. The network model revealed that Pseudomonas sp. and Pseudomonas stutzeri mainly drove the total nitrogen and DOC removal of Mix-CADB communities. More importantly, the immobilized Mix-CADB communities could reduce >91 % nitrate in the adjusted reservoir raw water. Overall, this study showed that the three Mix-CADB communities could be regarded as potential candidates for the nitrogen treatment in oligotrophic water body ecosystems.

Potential influence of overwintering benthic algae on water quality

Overwintering benthic algae not only directly impact drinking water safety, but also affect the algae recruitment in warm spring seasons. Thus, understanding the characteristics of overwintering benthic algae can provide scientific references for formulating preventative strategies of reasonable water resource. However, they have received less attention. In this study, the spatiotemporal variation of benthic algae and their harmful secondary metabolites were studied from autumn to summer in Qingcaosha Reservoir. Benthic algae (picophytobenthos accounting for 55.42%) had a high biomass during overwintering, and the groups of overwintering benthic algae included pico-Cyanobacteria, pico-Cryptomonas, pico-Chlorophyta, pico-Diatoms, Cyanobacteria, Chlorophyta, Cryptomonas and Diatoms, which were consistent with the planktonic algae species in warm seasons. In oligotrophic or mesotrophic water bodies, micronutrients of iron and manganese were key nutrient factors influencing the biomass of benthic algae. Furthermore, picophytobenthos were important potential contributors of harmful secondary metabolites. The content of microcystins, anatoxin-a, geosmin and 2-methylisoborneol in sediment were 15.75 µg/kg·FW, 48.16 µg/kg·FW, 3.91 ng/kg·FW, and 11.76 ng/kg·FW during winter, which had potential to be released into water bodies to impact water quality. These findings indicate that water quality monitoring programs need to consider sediment in winter as a potential source of toxins and preventative measures to prevent excessive proliferation of algae should be implemented in winter.

Summer temperatures and environmental dynamics during the Middle Würmian (MIS 3) in the Eastern Alps: Multi-proxy records from the Unterangerberg palaeolake, Austria

Several millennial-scale warm phases perturbed the glacial climate during Marine Isotope Stage 3 (MIS 3, ca. 57–29 ka BP). Little is known about the impact of these climatic changes on Alpine ecosystems due to the sparsity of undisturbed sediment records in the Alps and their foreland. In this study, multiple sediment-archived proxies (sediment geochemistry, stable oxygen and carbon isotopes of autochthonous carbonate, and subfossil remains of macrophytes and aquatic invertebrates) were examined in five drill cores from an ancient inner-Alpine lake at Unterangerberg (Eastern Alps) to reconstruct the palaeolake environment and to estimate summer temperature changes for the first half of MIS 3. The lacustrine sedimentation in the basin began ca. 54.6 ka, tentatively correlated with the start of Greenland Interstadial (GI) 14. We identified three distinct phases in the development of the lake. (1) A cold, oligotrophic water body influenced by snow/glacier meltwater ca. 54.6–52.2 cal ka BP. (2) A clear-water, macrophyte-dominated, productive lake ca. 52.2–44.9 cal ka BP. Submerged macrophytes were dominated by the charophyte alga Chara hispida and chironomid assemblages – by Corynocera ambigua, which is absent from the present-day fauna of the Alpine region. (3) A turbid-water, less productive lake ca. 44.9–41.5 cal ka BP. This shift towards a turbid-water state, as evidenced by the drastic reduction in the abundance of submerged macrophytes and associated invertebrates, likely occurred due to increased input of meltwater. The regime shift is tentatively correlated with the start of GI 11, for which the highest temperatures of the studied MIS 3 interval are inferred. Chironomid-based reconstructions of mean July air temperatures provide interstadial temperature estimates between ca. 11 and 12.5°C (i.e. ca. 5–6°C below present-day values), which concurs with reconstructions available from the northern Alpine foreland. Cooler July temperatures (ca. 9–10°C) are reconstructed for MIS 3 stadials. The Unterangerberg lacustrine records provide valuable new insights into MIS 3 climate dynamics inside the Eastern Alps and contribute to a better understanding of the effects of climate change on the Alpine environment.

The Simulation of the dynamics of 137Cs accumulation by freshwater fish

The study aimed to simulate the dynamics of 137Cs accumulation by freshwater fish under conditions of hypothetical radioactive contamination of water reservoirs in different seasons. The subject of research is the regularities of 137Cs accumulation by non-predatory fish species in eutrophic and oligotrophic water bodies. The dynamics of the 137Cs content in freshwater fish was calculated according to the content of radionuclides in water masses. The results of modeling the volumetric activity of 137Cs in water masses were used as an input parameter for the radionuclide accumulation in fish model. The fish organism was represented in the form of 3 independent related only by the balance equation; seasonal changes in the fish feeding intensity were taken into account in the modeling. The parameter that takes into account the contribution of the feeding intensity to the process of 137Cs intake into the fish organism has been determined. The features of the dynamics of 137Cs accumulation in eutrophic and oligotrophic water bodies fish are analyzed for cases of a hypothetical accidental input of 137Cs into ecosystems at the beginning of different periods of the annual life cycle of fish: 1st - from 1 to 31 March; 2nd - from 1 to 30 April; 3rd - from May 1 to September 19; 4th - from September 20 to October 19; 5th - from October 20 to November 30; 6th (freeze-up period) - from December 1 to February 28. The study has found that for a eutrophic water body the highest levels of 137Cs content in peaceful fish will be formed in the case of 137Cs entering ecosystems in spring (options 1–3). The maximum levels of 137Cs content in fish will be observed in the contamination period mentioned in option 3. Under hypothetical pollution in the autumn-winter period (options 4–6), the levels of 137Cs in peaceful fish will be approximately 2 times lower than in the case of pollution of the reservoir in spring. It has been found that the maximum value of the specific activity of 137Cs in fish from an oligotrophic water reservoir is not related to the season of pollution. However, the levels of fish pollution in the oligotrophic reservoir will be 1.5–2 times higher than those of the eutrophic one in options 1–3 and 3–4 times higher in options 4–6 . In the event of an emergency density of 137Cs fallout at the level of 4 kBq /m2 on the surface of different types of closed water reservoirs, its specific activity in peaceful fish will exceed the currently established permissible levels of fish products contamination. If the fallout density is twice as low (2kBq/ m2), the accumulation levels 137Cs by fishes of eutrophic water bodies will exceed the permissible standards in case of emergency inflows in spring. For oligotrophic water reservoirs, the guaranteed non-excess of the established standards in fish products is possible if the 137Cs fallout density is under 0.5 kBq /m2. Key words: fish, modeling, 137Cs, specific activity, hypothetical pollution, reservoirs of different trophic status.

Phytoplankton and water quality of Lake Kuchane (Pskov region, Russia)

The phytoplankton communities of Lake Kuchane, located in the Mikhailovskoye Museum-Reserve, were studied during different 2016–2017 seasons for the first time. 213 specific and intraspecific taxa from 9 phylums were identified in the phytoplankton, namely: Bacillariophyta, Chlorophyta, Chrysophyta, Euglenophyta, Cyanobacteria, Dinophyta, Cryptophyta, Charophyta, and Xanthophyta. The ratio of the main phylums of microalgae during the studied seasons was similar. The floristic complex of the lake's algoflora consisted of diatoms (36.6%), green (27.2%) and golden (10.8%) algae. Most of the phytoplankton genera contained one species taxon only. The specific composition of the phytoplankton community in 2017 was similar from spring to autumn. The minimum specific similarity of the phytoplankton communities was noted in July, 2016, and August, 2017. According to the level of biomass of planktonic algae, the lake belongs to oligotrophic water bodies. The planktonic algoflora of Lake Kuchane is characterized by the predominance of cosmopolitan freshwater forms of microalgae. In relation to pH, the predominant representatives preferred slightly alkaline waters. The Milius trophic index varied in the range 18.0–39.6 with a maximum value in summer. The Pantle–Bukk saprobity index almost did not change during the entire study. The waters of Lake Kuchane corresponded to the betamesosaprobic self-purification zone, quality class III.

Adsorption of phosphate ions from aqueous solutions by amorphous silica obtained by acid decomposition of nepheline

Amorphous silica (AS) was obtained by acid decomposition of nepheline and characterized by the BET and BJH methods. It was found that the material has a predominantly mesoporous structure with cylindrical and wedge-shaped pores and a specific surface area of ~195 m2/g. The process of phosphate ion sorption by the synthesized sample was studied. The experimental data were processed using the sorption equations by Freundlich and Langmuir, which demonstrated that the sorption process is described quite reliably by both equations, while the Langmuir monomolecular adsorption equation is to be preferred in calculations. Adsorbed monolayer capacity of the synthesized sample with respect to PO43- ion and the adsorption equilibrium constant were found. Based on the data obtained, various sorption treatments of municipal wastewater were assessed allowing to bring PO43- ion to the threshold values adopted in the Russian Federation when discharging treated water into oligotrophic water bodies. The number of wastewater treatment stages required for the maximum phosphorus recovery was found.

Hydrobiological and ichthyological features of the Shirokovsky Reservoir

The characteristic of Shirokovsky Reservoir by communities of phytoplankton, zooplankton, benthic invertebrates, and fish is given. It is the first investigation of the reservoir since the building time of 1948. All levels of the ecosystem are impoverished as species compositions as functional groups. A considerable part of all communities is presented by riverine oxyphilous species. Any invasion species of algae, invertebrates, and fish haven’t registered. The maximal species richness and quantitative parameters of phytoplankton have been registered in the upper riverine part of the reservoir and were determined by Bacillariophyta (primarily centric species). The zooplankton complexes’ dominants were Bosmina longirostris, Daphnia galeata, and Mesocyclops leuckarti. Maximal quantity of zooplankton has been shown in the middle part of the waterbody. The species of oligochaetes Limnodrilus hoffmeisteri and chironomids Parakiefferiella coronata were the most important in benthic communities’ structure. Benthofauna species richness and quantity of benthic invertebrates have been maximal in the lower part of the reservoir. The most common fish species at the current period are dace, perch, and Siberian roach. The fish quantity has been the richest in the middle part of the reservoir with lots of shallow areas. Assessing the quantitative values, the Shirokovsky Reservoir was classified as an oligotrophic waterbody at present.