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PubMed2005

Current status and future tendency of lake eutrophication in China.

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes. Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now. Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.

Animals↗
PubMed1988

Mercury in fish in Swedish lakes.

The aim of this work has been to try to obtain a picture of the past, present and future mercury situation in fish in Swedish lakes, to make an estimate of the number of lakes threatened by 'blacklisting', and to see if the data can be used to reveal anything about the impact of liming on the Hg content in pike. The register contains a broad set of data from 1456 lakes. The main results are as follows. Trend analyses indicate that the Hg content in 1-kg pike seems to increase with time. This is interesting since there has been a significant decrease in mercury emissions from Swedish industries during the last two decades. High Hg contents in 1-kg pike appear in a very characteristic pattern, linked to specific sources of Hg emission. The data indicate that old Swedish 'sins' are still causing a lot of problems. The factors governing the leakage of Hg from soils to water ought to be a very important topic for further studies. The Hg content in pike shows the highest correlation with the following parameters: Hg in surficial sediments, pH, distance from point source and water hardness, lake water alkalinity and conductivity, water retention time, size of drainage area and lake surface. A formula which provides the best possible degree of explanation (r2 = 0.78) has been derived. At present there are about 250 lakes 'blacklisted' in Sweden due to high Hg content in fish. Our data show that there are at least 9400 lakes that ought to be 'blacklisted' today. A successful liming operation will alter the chemical conditions in lakes and also decrease the Hg content in fish.

Journal Article↗
PubMed2005

Phytoplankton community and chlorophyll a as trophic state indices of Lake Skadar (Montenegro, Balkan).

BACKGROUND, AIMS AND SCOPE: Phytoplankton, as a first step in trophic cascades of lakes, can be a good indicator of trophic states, considering that every environmental change affects this community and many species of this community are sensitive to changes, and that they response very quickly. In this study, we tried to assess and predict the trophic state of Lake Skadar according to phytoplankton data. METHODS: Water samples were collected using Ruttner sampling bottle. Temperature, dissolved oxygen, ph, conductivity and transparence were measured in situ using portable equipment. Nutrients and chlorophyll a were measured using standard spectrophotometric methods. A determination of phytoplankton species was performed using relevant keys and the counting of cells was performed using sedimentation methods. RESULTS AND DISCUSSION: The species composition of Lake Skadar revealed 95 taxa, with Chlorophyceae and Bacillariophyceae being represented best. According to an average chlorophyll a concentration of 5.9 pg/l, Lake Skadar belongs to the mesotrophic level of the trophic scale. Developed prediction equation for chlorophyll a revealed a good prediction (R2 = 0.71) and the parameter Secchi depth was primarily correlated with chlorophyll a concentration. Trophic state indices derived from chlorophyll a and transparency, were close together, but both were below the phosphorous index. Values of trophic state indices rank the Lake Skadar as being mesotrophic. This study also showed that indices of diversity based on phytoplankton are weak indicators of trophic status and that they can well characterize only differences between assemblages and associations. According to calculated saprobic indices (ranging from 1.5 to 2.15), Lake Skadar is on betamesosaprobic level of saprobity, which means that it is moderately polluted with organic compounds. CONCLUSIONS: Total phosphorus is not the main limiting factor for the phytoplankton community in Lake Skadar. Disagreements between chlorophyll and the transparency index, on the one hand, and the total phosphorus index, on the other, suggest that the phytoplankton in Lake Skadar is probably limited by other factors than phosphorus, such as nitrogen, toxic substances or intense zooplankton grazing. According to the majority of investigated parameters and indices derived from phytoplankton data, Lake Skadar is mesotrophic, with tendencies toward eutrophic levels during the summer period. RECOMMENDATIONS AND OUTLOOK: Long-term monitoring is required for a better estimation of state and the conditions of Lake Skadar. Further studies on factors influencing the phytoplankton community, especially zooplankton grazing and toxic substances, which were not included in this study, should be continued in the future to improve the efficiency of phytoplankton usage in estimating the ecological and trophic conditions of Lake Skadar.

Albania↗
PubMed2006

LNG pool fire spectral data and calculation of emissive power.

Spectral description of thermal emission from fires provides a fundamental basis on which the fire thermal radiation hazard assessment models can be developed. Several field experiments were conducted during the 1970s and 1980s to measure the thermal radiation field surrounding LNG fires. Most of these tests involved the measurement of fire thermal radiation to objects outside the fire envelope using either narrow-angle or wide-angle radiometers. Extrapolating the wide-angle radiometer data without understanding the nature of fire emission is prone to errors. Spectral emissions from LNG fires have been recorded in four test series conducted with LNG fires on different substrates and of different diameters. These include the AGA test series of LNG fires on land of diameters 1.8 and 6m, 35 m diameter fire on an insulated concrete dike in the Montoir tests conducted by Gaz de France, a 1976 test with 13 m diameter and the 1980 tests with 10 m diameter LNG fire on water carried out at China Lake, CA. The spectral data from the Montoir test series have not been published in technical journals; only recently has some data from this series have become available. This paper presents the details of the LNG fire spectral data from, primarily, the China Lake test series, their analysis and results. Available data from other test series are also discussed. China Lake data indicate that the thermal radiation emission from 13 m diameter LNG fire is made up of band emissions of about 50% of energy by water vapor (band emission), about 25% by carbon dioxide and the remainder constituting the continuum emission by luminous soot. The emissions from the H2O and CO2 bands are completely absorbed by the intervening atmosphere in less than about 200 m from the fire, even in the relatively dry desert air. The effective soot radiation constitutes only about 23% during the burning period of methane and increases slightly when other higher hydrocarbon species (ethane, propane, etc.) are burning in the LNG fire. The paper discusses the procedure by which the fire spectral data are used to predict the thermal emission from large LNG fires. Unfortunately, no direct measurements of the soot density or smoke characteristics were made in the tests. These parameters have significant effect on the thermal emission from large LNG fires.

Air Movements↗
PubMed1994

Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida.

The reproductive development of alligators from a contaminated and a control lake in central Florida was examined. Lake Apopka is adjacent to an EPA Superfund site, listed due to an extensive spill of dicofol and DDT or its metabolites. These compounds can act as estrogens. Contaminants in the lake also have been derived from extensive agricultural activities around the lake that continue today and a sewage treatment facility associated with the city of Winter Garden, Florida. We examined the hypothesis that an estrogenic contaminant has caused the current failure in recruitment of alligators on Lake Apopka. Supporting data include the following: At 6 months of age, female alligators from Lake Apopka had plasma estradiol-17 beta concentrations almost two times greater than normal females from the control lake, Lake Woodruff. The Apopka females exhibited abnormal ovarian morphology with large numbers of polyovular follicles and polynuclear oocytes. Male juvenile alligators had significantly depressed plasma testosterone concentrations comparable to levels observed in normal Lake Woodruff females but more than three times lower than normal Lake Woodruff males. Additionally, males from Lake Apopka had poorly organized testes and abnormally small phalli. The differences between lakes and sexes in plasma hormone concentrations of juvenile alligators remain even after stimulation with luteinizing hormone. Our data suggest that the gonads of juveniles from Lake Apopka have been permanently modified in ovo, so that normal steroidogenesis is not possible, and thus normal sexual maturation is unlikely.

Alligators and Crocodiles↗
PubMed2001

Photodegradation of the pharmaceutical drug diclofenac in a lake: pathway, field measurements, and mathematical modeling.

Vertical concentration profiles of diclofenac were measured in Lake Greifensee (Switzerland) under mixed (February/December) and stratified (July) lake conditions. The concentrations ranged from 1 to 12 ng/L and were lower in summer than in winter, especially near the lake surface, pointing to an efficient elimination of diclofenac by photodegradation in the lake. Laboratory experiments confirmed the rapid photodegradation of diclofenac in water when exposed to sunlight. First-order reaction rates varied seasonally according to actual solar radiation (half-lives, tau = 0.2-1.7 h). The initial photoproduct was 8-chlorocarbazole-1-acetic acid, which photodegraded even faster than the parent compound. Carbazole-1-acetic acid, previously reported as the main photoproduct, was only formed in the presence of a H-source, such as methanol. In the absence of a H-source and of air, hydroxycarbazole-1-acetic acid was formed. However, hydroxycarbazole-1-acetic acid was not observed in the presence of air and, thus, under conditions similar to those in a lake, likely because of its rapid further photooxidation. Computer simulations using a one-dimensional lake model taking actual solar radiation and flushing data of the lake into account confirmed that photolysis is the predominant elimination pathway for diclofenac in Lake Greifensee. These calculations further showed that the expected concentrations of the photoproduct 8-chlorocarbazole-1-acetic acid are less than the current detection limits of approximately 3 ng/L.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1991

Epidemiology of Great Lakes bald eagles.

Historical data are provided to support the hypothesis that organochlorine chemicals introduced into the Great Lakes ecosystem following World War II are the cause of reproductive loss among bald eagles (Haliaeetus leucocephalus) in the basin. This is supported with data on concurrent population fluxes of extrabasin North American bald eagle populations and the European white-tailed sea eagle (Haliaeetus albicillus) where the same chemicals were produced and released. Organochlorine chemicals appear as a unique stress on Great Lakes bald eagle populations when compared with stresses on successful populations of bald eagles continentwide. Shoreline birds bear significantly higher concentrations of these persistent toxics than inland birds. Association between contaminated prey and elevated concentrations of PCBs, DDT, and DDE in Great Lakes bald eagles are presented. A fledging ratio is used to support the hypothesis that maternal prezygotic exposure affects the viability of embryos and chicks. The ratio of the mean number of fledglings per successful territory to the mean number of fledglings per active territory, when the numerator is greater than 1.4, provides an index of exposure to contaminants by parental animals and affected offspring. When the ratio is greater than 2, parental exposure to organochlorine chemicals should be considered. The adverse effects of prezygotic exposure to the same contaminants in other animal species dependent upon Great Lakes fish, and extrabasin bald eagle populations dependent upon contaminated fish, provide consistency to the argument. The mechanism of action of the organochlorine chemicals further strengthens the causal argument indicting DDT, DDE, and PCBs. A strong association between DDT/DDE and bald eagle reproductive success is provided. However, the role of PCBs is not ruled out. Only data for total PCB concentrations in bald eagle tissue are available, and until specific PCB congeners are quantified there will be uncertainty concerning PCB's role in the Great Lakes bald eagle's lack of success.

Animals↗
PubMed1986

Oxygen budget of a perennially ice-covered Antarctic lake.

A bulk O2 budget for Lake Hoare, Antarctica, is presented. Five years of seasonal data show the lake to be persistently supersaturated with O2. Oxygen is carried into the lake in glacial meltstreams and is left behind when this water is removed as ice by ablation and sublimation. A diffusive loss of O2 from the lake through the summer moat is suggested. Measured values of the total O2 in the water column indicate that the time scale of O2 turnover is much longer than a year. Based on these results we suggest that the amount of O2 in the water does not change significantly throughout the year and that the lake is also supersaturated with N2.

Antarctic Regions↗
PubMed2003

Recovery from acidification of Finnish lakes: regional patterns and relations to emission reduction policy.

The regional-scale response of Finnish headwater lakes to changes in acidifying deposition loads was studied using data from a national deposition monitoring network (19 stations), acidification monitoring lakes (163 lakes) and results of a statistically based national lake survey (873 lakes). Data from 1990 to 1999 were used for statistical trend analysis. A deposition model was used to assess changes in S and N deposition for the year 2010, assuming emission reductions according to two international agreements. The deposition of sulfate and H(+) showed statistically significant (Kendall-tau, P<0.05) decreasing trends at nearly all deposition stations. For N compounds, nearly all slopes were negative, but rarely statistically significant. Sulfate concentrations have declined in all types of small lakes throughout Finland in the 1990s (significant decline in 64-85% of the lakes in three different lake regions), indicating a clear response to S emission reductions and declined sulfate deposition. Base cation concentrations decreased in both deposition and lake water, especially in southern Finland, but to a lesser extent than sulfate concentrations. The median slope of the trend for Gran alkalinity in lakes ranged between 0.98 and 2.1 microeq l(-1) a(-1). Some 1400 (27%) of Finnish headwater lakes of size 4-100 ha were estimated to show statistically significant increases in Gran alkalinity (recovery). No large changes were observed in the lake water TOC concentrations. The reduction in S deposition is the main driving factor for the lake acidification recovery process in Finland. Deposition model calculations showed that further large reductions in S deposition beyond the 1999 level are not likely to occur by the year 2010, particularly for southeastern Finland. The mean estimated S deposition change by 2010 for the three lake regions in Finland was only between -0.9 and -6.6% for the two policy scenarios (UN/ECE Gothenburg protocol, EU NEC-directive), respectively. A slower acidification recovery of the lake ecosystems is, therefore, anticipated in the future.

Acid Rain↗
PubMed2001

Factor analytical study on water quality in Lake Saimaa, Finland.

Multivariate data analysis methods (4-way Candecomp-PARAFAC model solved with Multilinear Engine (ME-1)) were used to interpret the data of over two decades to study the changes in the water of Lake Saimaa in Finland. Earlier studies have shown that it is difficult to extract the natural background from the other sources of variation. By using the multilinear model three interpretable factors representing natural and anthropogenic processes could be extracted. The natural long-term variation, seasonal fluctuation and dilution of discharges in the recipient area could be extracted into their own factors, which could be easily visualized. The variation could be also presented with estimated variation in the water quality parameters caused by each of these natural or anthropogenic processes.

Factor Analysis, Statistical↗
PubMedDate not supplied

How do fish ectoparasites Argulus spp. (Crustacea: Branchiura) match with their hosts at the behavioural and ecological scales?

Features of the Argulus foliaceus and A. coregoni life cycles including spatial distribution and hatching patterns of the resting eggs as well as their host searching behaviour were analyzed on the basis of field and experimental data obtained in lakes and a fish farm in the Central Finland. Published data on behaviour and ecology of these parasites were also used. The main point of this analysis was an ecological adjustment of the life cycles of parasites to that of their fish hosts at different spatial and temporal scales. Due to different spatial distribution of overwintering eggs, the newly hatched larvae of A. coregoni are more likely to attach to salmonids, which are their main hosts, while A. foliaceus to percids and cyprinids. The main peak of argulid hatching occurs in late spring-early summer and coincides with the period when most of freshwater fishes concentrate close to the shore, either for spawning, or, foraging. Nevertheless, despite the general coincidence, the parasite-host encounter rate could still be very low. The main peak of hatching is followed by a long "tail". We suggest that under fluctuating and uncertain environmental conditions characterised by both abiotic stochasticity and poor predictability of the hosts, an optimal recruitment strategy is to hedge a bet, with a proportion of eggs synchronously hatching and a proportion remaining dormant and hatching at much lower rate during an extended period. One of the main behavioural adaptations to match with the hosts is all-over-the-day searching activity of argulids. The boreal A. coregoni relies primarily on vision, which is most effective in transparent waters during long polar days in summer. Vision is also important in the behavioural repertoire of the temperate A. foliaceus in the light, but olfaction and mechanoreception in the dark provide the highest host searching rate. The two generally sympatric species of argulids segregated on the finer habitat scale. Partially overlapping on salmonid hosts, they prefer ecologically distinct categories of fish, and use different microhabitats for egg laying and searching for hosts.

Animals↗
PubMed2005

Lessons learned: geographic information systems and farmworkers in the Lake States.

Agencies serving the estimated 42,000 to 137,000 migrant and seasonal farmworkers in the Lake States (Wisconsin, Michigan, and Minnesota) face distinct challenges, including inadequate access to farmworker data to address their needs. This project developed and evaluated a geographical information system (GIS) database for compiling and displaying existing farmworker data in the Lake States. A three-step study was conducted in the Lake States: (1) a preliminary resource and needs assessment was conducted among agencies serving farmworkers, (2) a GIS product was created using data available from state agencies, and (3) the GIS product was evaluated by an advisory board of qualified occupational health and safety representatives for appropriateness, applications, and ease of use. Agencies participated by sharing their available farmworker data. The GIS product consisted of a CD-ROM with data displayed in a graphic format and downloadable spreadsheet files consolidated by county demographic, crop, housing, and migrant health clinic information. Evaluators of the GIS product found it to be an accessible, unique clearinghouse for farmworker-related data. The GIS product can become a valuable tool for agencies serving farmworkers and those researching farmworker-related issues. Agencies and health professionals require useful and comprehensive databases to track and serve farmworkers, and a multi-agency partnership using GIS technology could provide this capability. Further research is required with improved definitions and resources to apply the GIS product.

Agricultural Workers' Diseases↗
PubMedDate not supplied

Modeling surface water critical loads with PROFILE: possibilities and challenges.

The critical load concept has become a valuable tool for policymakers in the European negotiations on emission reductions. Despite the international acceptance, ongoing validation of critical load methodology is of the utmost importance to avoid a situation where the calculation results are difficult to defend. In this paper we explore the potential of using the steady state soil chemistry model PROFILE as an alternative to the Steady State Water Chemistry (SSWC) method for calculating critical loads of acidity. The hypothesis is that the uncertainty in prediction of preindustrial leaching of base cations is reduced when soil properties instead of lake chemistry are used as input data. Paleolimnological reconstructions of preindustrial lake chemistry are used to test PROFILE. As PROFILE requires soil data that are not generally available on a catchment level, we used distributions of crucial parameters from soil survey data within the vicinity of five lakes for which paleoecological pH reconstructions were available. An important concern is the characterization of catchment hydrology. A calibration of the "effective" soil depth, needed to give PROFILE predictions that coincided with paleolimnology, suggested that approximately 0.6 m of the total soil depth was hydrologically active in supplying acid neutralizing capacity (ANC) to runoff through weathering. At present, there is insufficient evidence to either recommend or reject the PROFILE model for surface water critical loads. Before such a judgement can be made, the approach presented here has to be tested for other regions, and the definition of catchment hydrology needs to be investigated further.

Acid Rain↗
PubMed2006

Physical background of the development of oxygen depletion in ice-covered lakes.

The effect of the heat interaction between a water column and sediments on the formation, development, and duration of existence of anaerobic zones in ice-covered lakes is estimated based on observational data from five frozen lakes located in northwestern Russia and North America. A simple one-dimensional model that describes the formation and development of the dissolved oxygen deficit in shallow ice-covered lakes is suggested. The model reproduces the main features of dissolved oxygen dynamics during the ice-covered period; that is, the vertical structure, the thickness, and the rate of increase of the anaerobic zone in bottom layers. The model was verified against observational data. The results from the verification show that the model adequately describes the dissolved oxygen dynamics in winter. The consumption rates of DO by bacterial plankton and by bottom sediments, which depend on the heat transfer through the water-sediment interface, are calculated. The results obtained allow the appearance of potentially dangerous anaerobic zones in shallow lakes and in separate lake areas, which result from thermal regime changes, to be predicted.

Anaerobiosis↗
PubMed2001

Comparison of two inversion techniques of a semi-analytical model for the determination of lake water constituents using imaging spectrometry data.

In this study, two different inversion techniques for the determination of chlorophyll-a in water were compared by a sensitivity analysis: (i) a matrix inversion method, and (ii) a curve-fitting routine. Adding white noise to the reflectance spectrum led to clearly better results for the curve-fitting routine. If, however, the atmospheric parameter visibility was not exactly known, both methods behaved similarly well. The analyses implied that the performance depended on the quality of the input spectra, the knowledge of model parameters, and also on the inversion methods, even if they were based on the same semi-analytical model. Of course, not only the uncertainties of model parameters had to be considered for the testing of the performance, but also other factors, such as processing time, implementation of the inversion algorithm, number of relevant parameters, and the application of the method to different times and different lakes.

Algorithms↗
PubMed1994

Copper, zinc, manganese, iron, lead, cadmium, mercury and arsenic in fish from Lake Tanganyika, Burundi.

Atomic absorption spectrometric determination of copper, zinc, manganese, iron, lead, cadmium, mercury and arsenic in two fish species from Lake Tanganyika, Burundi, provide values that are lower than most literature data, especially for cadmium, arsenic and mercury. Tissue analysis of Lates stapersii reveals that liver accumulates the highest amount of most elements. The data illustrates that Lake Tanganyika is still a non-polluted area at the time of analysis.

Animals↗
PubMed2005

Comparison of microbial community between two shallow freshwater lakes in middle Yangtze basin, East China.

In order to investigate the role of the microbial community in aquatic ecology and nutrient transformations in the development of eutrophication in large shallow freshwater lakes along Yangtze River, the microbial community in the depth-related sediment in Lake Chaohu and Lake Longganhu were compared. Lake Chaohu is one of the three most polluted lakes in China. However, the neighboring Lake Longganhu, a mesotrophic lake, is relatively pristine. The total phosphorous (TP) and total nitrogen (TN) concentration in water was detected at 0.193 mgl(-1) and 3.035 mgl(-1) for Lake Chaohu, 0.051 mgl(-1) and 0.774 mgl(-1) for Lake Longganhu, respectively. The population of the microorganisms with various ecological nutrient transforming functions (e.g. phosphate solubilizing, denitrifying and cellulose decomposing) and a batch of environmental parameters concerning the nutrient accumulating and transforming (e.g. total organic carbon, total nitrogen, and total phosphorous concentrations) were assayed in the depth-related sediment samples from several defined points in both lakes. The sediment samples from Lake Chaohu showed higher density of actinomycetes (P<0.05) and phosphate-solubilizing bacteria (P<0.001) and less profusion of denitrifying bacteria (P<0.05) and cellulolytic microbes (P<0.001), compared with those of Lake Longganhu. The data suggested that the current microbial community in the sediment of Lake Chaohu is in favor of sustaining or further accelerating the process of the lake eutrophication. A possible positive feedback loop which consists of sustained growth of microorganisms and gradual decline of lake eutrophic status is worth further discussing.

Actinobacteria↗
PubMed2006

Ferrous iron oxidation rates in the pycnocline of a permanently stratified lake.

Ferrous iron was found year round at 2-4 mM in the anoxic hypolimnion of the Halls Brook Holding Area (HBHA), a small lake in eastern Massachusetts. Oxygenated epilimnion waters always had total iron concentrations of <80 nanomolar, implying nearly complete oxidation of ferrous iron as it mixed upward across the lake's pycnocline. Assuming conductivity was a conservative parameter, and using data on the lake's water balance, upward advection rates (0.02-0.05 m d(-1)) and vertical eddy diffusion coefficients (0.007-0.05 m2 d(-1)) were determined for the lake's pycnocline on five dates. Using the same advection and diffusion parameters, corresponding pseudo first-order rate coefficients for ferrous iron oxidation, k(ox) (s(-1)), on those dates were calculated (0.0004-0.007 s(-1)). The values of k(ox) (s(-1)) were always too large to reflect only homogeneous solution reactions; and on at least four dates they appeared too fast to be due to heterogeneous catalysis on iron oxyhydroxides. This suggested that ferrous iron oxidation in this lake's pycnocline was primarily due to catalysis by microorganisms, and this was supported by comparison of azide-poisoned vs. untreated batch tests. As a result of their continuous production, iron oxyhydroxide precipitates and any associated sorbates/coprecipitates are most likely continuously settling back into the lake's deep water and bed sediments, except when episodic storm events flush these solids out of the pycnocline and downstream via the Aberjona River.

Boston↗