Relationships Between Coastal Bacterioplankton Growth Rates and Biomass Production: Comparison of Leucine and Thymidine Uptake with Single-Cell Physiological Characteristics

Specific growth rates of heterotrophic bacterioplankton have been frequently estimated from in situ bacterial production (BP) to biomass (BB) ratios, using a series of assumptions that may result in serious discrepancies with values obtained from predator-free cultures. Here, we used both types of approaches together with a comprehensive assessment of single-cell physiological characteristics (membrane integrity, nucleic acid content, and active respiration) of coastal bacterioplankton during a complete annual cycle (February 2007–January 2008) in the southern Bay of Biscay off Xixón, Spain. Both leucine and thymidine incorporation rates were used in conjunction with empirical tracer to carbon or cells conversion factors (eCFs) to accurately derive BP. Leu and TdR incorporation rates covaried year-round, as did the corresponding eCFs at 0 and 50 m depth. eCFs peaked in autumn, with mean annual values close to the theoretical ones (3.4 kg C mol Leu⁻¹ and 2.0 × 10¹⁸ cells mol TdR⁻¹). Bacterial abundance (0.2–1.5 × 10⁶ cells L⁻¹) showed a bimodal distribution with maxima in May and October and minima in March. Live (membrane-intact) cells dominated year-round (79–97%), with high nucleic acid cells (42–88%) and actively respiring bacteria (CTC+, 1–16%) showing distinct surface maxima in April and July, respectively. BB (557–1,558 mg C m⁻²) and BP (7–139 mg C m⁻² day⁻¹) presented two distinct peaks in spring and autumn, both of similar size due to a strong upwelling event observed in September. Specific growth rates (0.35–3.8 day⁻¹) were one order of magnitude higher in predator-free incubations than bacterial turnover rates derived from integrated BP:BB ratios (0.01–0.16 and 0.01–0.09 day⁻¹, for Leu and TdR, respectively) and were not correlated, probably due to a significant contribution of low activity cells to total standing stocks. The Leu:TdR molar ratio averaged for the water column (6.6–25.5) decreased significantly with higher integrated BB, indicating that low standing stocks tend to present unbalanced growth. Discrepancies about the true magnitude of specific growth rates must be solved before fully appreciating the role of bacteria in the ocean carbon cycle.     

Pharmacokinetics and Pharmacodynamic Effects of Flunixin after Intravenous,Intramuscular and Oral Administration to Dairy Goats

The pharmacokinetics and the prostaglandin (PG) synthesis inhibiting effect of flunixin were determined in 6 Norwegian dairy goats. The dose was 2.2 mg/kg body weight administered by intravenous (i.v.), intramuscular (i.m.) and oral (p.o.) routes using a cross-over design. Plasma flunixin content was analysed by use of liquid chromatography and the PG synthesis was evaluated by measuring plasma 15-ketodihydro-PGF_2α by a radioimmuno-assay. Results are presented as median (range). The elimination half-lives (t_1/2·λ) were 3.6 (2.0–5.0), 3.4 (2.6–6.8) and 4.3 (3.4–6.1) h for i.v., i.m. and p.o. administration, respectively. Volume of distribution at steady state (Vd_ss) was 0.35 (0.23–0.41) L/kg and clearance (CL), 110 (60–160) mL/h/kg. The plasma concentrations after oral administration showed a double-peak phenomenon with the two peaks occurring at 0.37 (0.25–1) and 3.5 (2.5–5.0) h, respectively. Both peaks were in the same order of magnitude. Bioavailability was 79 (53–112) and 58 (35%–120)% for i.m. and p.o. administration, respectively. 15-Ketodihydro-PGF_2α plasma concentrations decreased after flunixin administration independent of the route of administration.     

Reduced fouling and enhanced microbial inactivation during online sterilization of cheese whey using UV coil reactors in series

The effectiveness of coil UV reactor series for the online sterilization of cheese whey was compared to those of the single conventional and coil reactors at various flow rates (5–70 mL/min). The residence time varied from 168 to 12 min and from 48 to 24 min for the single and the series reactors, respectively. Hundred percent destruction efficiency could not be achieved in the single reactors whereas in the coil reactor series the destruction efficiency reached 100% at the flow rates of 35 and 40 mL/min. The rate of microbial destruction was described by polynomial equation for the single coil reactor and by exponential equations for the single conventional reactor and the coil reactor series. The temperature of the effluent decreased with the increase in flow rate in all the reactors. The maximum effluent temperatures in the single conventional reactor, single coil reactor and coil reactor series were 45.8, 46.1, and 36.4 °C (Δt = 20.8, 21.1, 11.4 °C), respectively. The flow in all the reactors was laminar (R _e = 1.39–20.10) and the Dean number was in the range of 1.09–15.41 in the coil reactors. Visual observation revealed less fouling on the UV lamps of coil reactors than on that of the conventional reactor due to the impact of Dean flow. The total operating time during which 100% destruction efficiency is achieved prior to the advent of fouling was 240 min in the coil reactor series compared to only 45 min in the conventional reactor.     

Determination of selenium in the human brain by graphite furnace atomic absorption spectrometry

For the investigation of neurological disorders, a development of simple and accessible methods for determining selenium in human brain samples is required. We devised a method of determining selenium using graphite furnace atomic absorption spectrometry (GFAAS). An electrodeless discharge lamp provided the sufficient sensitivity to determine brain selenium. The matrix interferences were avoided by using high temperature, a prolonged pyrolysis step, and a palladium matrix modifier. The technique of standard addition was used to evaluate the sample concentrations. The accuracy of the method was confirmed by a bovine liver reference material. The detection limit of selenium was 0.04 ng. The determined selenium concentrations of human brain cortex and white matter were higher than those of putamen (115–155 and 206–222 ng/g wet wt, respectively). These GFAAS values agreed with those obtained by fluorometric analysis (r=0.91,n=10). Moreover, the GFAAS values were compatible to those reported by other researchers (99–274 ng/g wet wt), in which selenium concentrations in putamen also tended to be higher than the other two regions. We conclude that GFAAS is useful for selenium analysis in brain samples.     

Fatigue-induced modulation of the H reflex of soleus muscle in humans

We studied the effect of fatigue of the mm. gastrocnemius-soleus on the H reflex elicited by transcutaneous stimulation of n. tibialis and recorded from the m. soleus; healthy 18-to 34-year-old volunteers were tested. Fatigue was evoked by long-lasting (6 to 9 min) voluntary tonic static sole flexion of the foot (ankle extension) with a force equal to 75% of the maximum voluntary contraction (MVC). The amplitude of H reflex significantly (P < 0.001) decreased to about 60% of the initial value immediately after the period of fatiguing effort. Within 2 to 3 min, it relatively rapidly recovered and reached about 90% of the control, and this was followed by a period of slow recovery to about 96–97% of the initial value 30 min after conditioning fatigue. We suppose that the initial period of suppression of the H reflex results to a considerable extent in an increase in the intensity of presynaptic inhibition of transmission from Ia afferents due to tonic activation of high-threshold (groups III and IV) afferent fibers induced by intensive fatigue-related metabolic changes in the muscles. More long-lasting (tens of minutes) changes are related to slow reverse development of direct effects of fatigue-induced biochemical shifts in the muscle. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 426–431, September–December, 2006.     

Cryopreservation of shoot-tips by droplet vitrification applicable to all taro (Colocasia esculenta var. esculenta) accessions

The application of the droplet vitrification cryopreservation technique to taro accessions from a range of Asia Pacific countries is presented. The optimum protocol involves excision of about 0.8 mm shoot-tips from in vitro plants, 20–40 min PVS2 exposure at 0°C followed by rapid plunge into liquid nitrogen. Thawing was done at room temperature (25°C) and shoot-tips inoculated on MS medium with 0.1 M sucrose regenerated into plantlets 4–6 weeks later. This new droplet vitrification protocol improved the mean post-thaw regeneration rates to 73–100% from 21–30% obtained with the previous cryo-vial vitrification protocol.     

Microbial N Turnover and N-Oxide (N<Subscript>2</Subscript>O/NO/NO<Subscript>2</Subscript>) Fluxes in Semi-arid Grassland of Inner Mongolia

Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N₂O, NO and NO₂ were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R. China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other. Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were in a range of 0.5–4.1 mg N kg⁻¹ soil dry weight day⁻¹. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15% of the observed site differences in gross N turnover rates. N₂O and NO _x flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between plots. Mean values of N₂O fluxes varied between 0.39 and 1.60 μg N₂O-N m⁻² h⁻¹, equivalent to 0.03–0.14 kg N₂O-N ha⁻¹ y⁻¹, and were considerably lower than previously reported for the same region. NO _x flux rates ranged between 0.16 and 0.48 μg NO _x -N m⁻² h⁻¹, equivalent to 0.01–0.04 kg NO _x -N ha⁻¹ y⁻¹, respectively. N₂O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only less than 20% of the flux variance.     

Determining minimum ultimate size, setting size limits, and developing trophy standards and indices of comparable size for maintaining quality muskellunge (Esox masquinongy) populations and sports fisheries

Growth and ultimate size can provide important population insights and a sound biological basis for setting length limits, which can be the best single regulation for preventing overexploitation of muskellunge (Esox masquinongy) populations. A system was developed, using cleithral age and total length at age confidence limits (CL) data, to determine reproductive and growth potential (ultimate size) for calculating and setting increased size limits based on minimum reproductive size (upper 99% CL at age at first maturity + 2 year) and minimum ultimate size (MUS) calculated from the lower 99% CL—minimum ultimate size limit (MUSL). MUS also provides a trophy standard and an index of relative size for comparing trophy potential of individuals within and among populations. Guidelines are provided for determining minimum sample size (mean ± 95% confidence interval = 12 ± 4) and minimum age (8–10 ± 2.0 year) required to produce valid von Bertalanffy growth trajectories. MUS, MUSL, and trophy standards for both length and estimated weight are provided for female and male muskellunge from 14 Ontario sources. Mean MUS, or trophy standard, for females was 115 ± 10.3 cm (MUSL range 75–135) and 11.1 ± 2.6 kg (2.5–17.5) and for males was 95 ± 7.5 cm (66–110) and 6.1 ± 1.3 kg (1.9–9.2). These indices can precisely define growth and growth potential for muskellunge populations and individuals and can be used to better manage and maintain or improve the quality of muskellunge populations and fisheries. Dedicated to the late Dr. E.J. Crossman.     

Is protein folding rate dependent on number of folding stages? Modeling of protein folding with ferredoxin-like fold

Statistical analysis of protein folding rates has been done for 84 proteins with available experimental data. A surprising result is that the proteins with multi-state kinetics from the size range of 50–100 amino acid residues (a.a.) fold as fast as proteins with two-state kinetics from the same size range. At the same time, the proteins with two-state kinetics from the size range 101–151 a.a. fold faster than those from the size range 50–100 a.a. Moreover, it turns out unexpectedly that usually in the group of structural homologs from the size range 50–100 a.a., proteins with multi-state kinetics fold faster than those with two-state kinetics. The protein folding for six proteins with a ferredoxin-like fold and with a similar size has been modeled using Monte Carlo simulations and dynamic programming. Good correlation between experimental folding rates, some structural parameters, and the number of Monte Carlo steps has been obtained. It is shown that a protein with multi-state kinetics actually folds three times faster than its structural homologs.     

A nonlinear dynamical mechanism for bruit generation by an intracranial saccular aneurysm

 Intracranial saccular aneurysms have been clinically observed to emit a transient sound, a bruit, on each heartbeat. The mechanism causing the bruits has been a matter of contention. A qualitative analysis of the nonlinear dynamical properties of the Shah-Humphrey model for periodic pressure forcing of a thin-necked saccular aneurysm, using the Fung nonlinear constitutive model for the aneurysm material, shows that a small blood pressure jump on each beat, whether the pressure is weakly aperiodic or periodic, induces transients in the radial deformation response of the aneurysmal wall on each heartbeat. These transient vibrations, which have a component with frequency near the natural frequency of the system but are not resonant phenomena and which decay rapidly to a limit cycle during each distinct forcing pressure cycle, can generate the bruits. Received: 21 November 2000 / Revised version: 9 August 2001 / Published online: 23 August 2002 Mathematics Subject Classification (2000): 92B99, 70K40, 70K05 Key words or phrases: Intracranial saccular aneurysm – Bruit – Spectrum – Nonlinear dynamics – Transients – Vortex shedding – Fung model     

Hydrogen exchange and proteolytic degradation of ribonuclease A. The local splitting of the native structure and the conformation of loop segments

The limited proteolytic sites or nicksites are present only in one of the five loops of the RNase A molecule. The splitted loop 15–23 connects two structural domains in the hinge region of the interdomain contacts of the V-shaped molecule. The other four loops are inside two domains, 64–71 and 112–115 in the domain I (1–19, 47–81, 102–106) and 36–42 and 88–95 in the domain II (20–46, 82–101). Because of enhanced chain flexibility of the splitted loop in the pH-dependent conformational isomerization, deformation of its structure is slighter under the influence of the intermolecular contacts in the crystal lattice and more significant changes occur in loop conformation at the formation of the 3D swapped dimer of the RNase A molecule. The proteolytic splitting of the 15–23 loop proceeds due to the local fluctuation of the native protein structure.     

Dew and its effect on two heliophile understorey species of a tropical dry deciduous forest in Mexico

 A series of horizontal and vertical measurements of dew deposition and dew duration were carried out in a tropical dry deciduous forest in western Mexico (19° 30′ N, 105° 03′ W). The effect of dew on transpiration in heliophile species was also investigated. The amount of dew was very variable with no temporal or spatial pattern. The amount of dew measured at two horizontal transects (maximum and minimum) (at heights of 0.20 m and 1.30 m above ground level) was from 0.014 to 0.203 mm and from 0.013 to 0.061 mm in the middle and at the end of the dry season, respectively. Dew deposition at different vertical levels (0.50–12.5 m height) ranged from 0.04 to 0.36 mm. The duration of dew formation ranged between 60 and 129 min after sunrise above the canopy (a height of 11 m), and between 259 and 290 min after sunrise at a height of 2 m. Daily transpiration rates were 883 and 632 g m^–2 d^–1 in Coccoloba liebmannii and 538 and 864 g m^–2 d^–1 in Jacquinia pungens in January and April, respectively. Transpiration was restricted from sunrise to early afternoon in April, as a result of the pronounced midday closure of stomata in both species. The reduction of transpiration by dew ranged from 13.2 to 50.1 g m^–2 d^–1 and from 4.5 to 77.7 g m^–2 d^–1 for C. liebmannii and J. pungens, respectively. Dew can play an important role in enhancing the survival of heliophile species in the dry season by reducing transpiration rates during the morning. Received: 30 April 1998 / Accepted: 14 December 1998     

Systematics and distribution of theDiplophos taenia species complex (Gonostomatidae), with a description of a new species

For the systematic study of the gonostomatid fishes of theDiplophos taenia species complex, a total of 698 specimens was obtained from the three oceans. Four valid species were recognized:D. taenia Günther,D. proximus Parr,D. orientalis Matsubara, andD. australis sp. nov. The diagnostic characters are 90–100 total vertebrae (TV) (37–41 abdominal (AV) +52–60 caudal vertebrae (CV)) and 103–115 IC photophores (IC) for D.taenia, 85–90 TV (36–39 AV + 48–52 CV) and 98–104 IC forD. proximus, 83–86 TV (33–35 AV + 49–52 CV) and 92–100 IC for D.orientalis, and 84–91 TV (33–37 AV+ 50–54 CV) and 99–105 IC forD. australis. In addition to the above,D. proximus has larger orbital diameter (the proportion to head length 21–28%) than the other three species (15–23%) beyond 70mm in standard length. Due to wide distribution,D. taenia shows meristic variations: the numbers of TV, IC and anal fin rays (A) are smaller at lower latitudes and larger at higher ones in all oceans, and the number of A is smaller in the Atlantic (56–71) than in the other oceans (59–72) of the same latitude. Because of these variations, identification to species level is possible only area by area. The distribution of each of the four species is also distinct:D. taenia is a cosmopolitan between about 40° N and 30° S exclusive of the eastern tropical Pacific;D. proximus is endemic to the eastern tropical Pacific;D. orientalis is limited to the North Pacific transitional zone between about 30° and 40° N; andD. australis in a transitional zone of the Southern Ocean south of 20° S.     

Dynamics of Redox Changes of Iron Caused by Light–dark Variations in Littoral Sediment of a Freshwater Lake

Depth profiles of oxygen concentration and the redox status of acid-extractable iron were measured in littoral sediment cores of Lake Constance incubated under a light–dark regimen of 12 h. While oxygen penetrated to 3.4±0.2 mm depth in the dark, photosynthetic oxygen production shifted the oxic–anoxic interface down to 4.0±0.2 mm or 5.9±1.6 mm depth, at low or high light intensity, respectively, and caused a net oxygen efflux into the water column. After a light–dark or dark–light transition, the oxygen concentration at the sediment surface reached a new steady state within about 20 min. The redox state of the bioavailable iron was determined in 1-mm slices of sediment subcores. After a dark period of 12 h, 85% of the acid-extractable iron (10.5 μmol cm⁻³ total) in the uppermost 8 mm was in the reduced state. Within 12 h at low or high light intensity, the proportion of ferrous iron decreased to 82 or 75%, respectively, corresponding to net rates of iron oxidation in the range of 244 and 732 nmol cm⁻³ h⁻¹, respectively. About 55 or 82% of the iron oxidation at low or high light intensity occurred in the respective oxic zone of the sediment; the remaining part was oxidized in the anoxic zone, probably coupled to nitrate reduction. The areal rates of iron oxidation in the respective oxic layer (21 or 123 nmol cm⁻² h⁻¹ at low or high light intensity, respectively) would account for 4 and 23% of the total electron flow to oxygen, respectively. Light changes caused a rapid migration of the oxic–anoxic interface in the sediment, followed by a slow redox reaction of biologically available iron, thus providing temporal niches for aerobic iron oxidizers and anaerobic iron reducers.     

Occurrence ofAlternaria andFusarium mycotoxins in winter wheat from domestic crop in year 2003

The aim of this study was a monitoring of the occurrence ofAlternaria andFusarium mycotoxins in winter wheat from domestic crop in the year 2003. Altenuene was determined in 56 (100%) samples of winter wheat, range 14.5–41 μg/kg, mean 25 μg/kg. Alternariol was determined in 16 (28.6%) samples of winter wheat, range 6.3–22.1 μg/kg, mean 5.7 μ/kg. DON was determined in 42 (100%) samples of winter wheat, range 250–3500 μg/kg, mean 330 μg/kg. T2-toxin was determined in 42 (100%) samples of winter wheat, range 25–337 μg/kg, mean 99 μg/kg. ZEA was not determined in samples of winter wheat. Presented at the 26^th Mykotoxin-Workshop in Herrsching, Germary, May 17–19, 2004 Financial support. Supported (one part of experiments, the determination of Fusarium mycotoxins) by the Ministry of Agricu ture of the Czech Rebublic (Propect No QF3121)     

Modeling of chromosome aberration response functions induced by particle beams with different LET

This study is based on our already published experimental data (Kowalska et al. in Radiat Environ Biophys 58:99–108, 2019) and is devoted to modeling of chromosome aberrations in human lymphocytes induced by 22.1 MeV/u 11B ions, 199 MeV/u 12C ions, 150 MeV and spread-out Bragg peak (SOBP) proton beams as well as by 60Co γ rays. The curvature of the dose–effect curves determined by the linear-quadratic model was considered in the frame of a simple analytical approach taking into account increase in the irradiation dose due to overlapping interaction regions of ion tracks. The model enabled to estimate effective interaction radius which could be compared with the physical expectations. The results were also compared to the Amorphous Track Structure Model of Katz which allows to get some additional information about the ion track structure. The analysis showed that the curvature of the experimental dose–effect curves mainly results from highly efficient repair processes of the DNA damage.     

Production of ligninolytic exoenzymes and14C-Pyrene mineralization byPleurotus sp. in lignocellulose substrate

Pleurotus sp. was grown in liquid medium and on a solid straw substrate, and activities of laccase and manganese-dependent peroxidase (MnP) were recorded. The activities were the highest in a rich, glucose corn-steep liquid medium. In straw cultures, laccase activity was about ten times lower. Under solid state conditions, MnP production was the highest during days 20–40, when laccase activity already had declined. In straw cultures, mineralization of¹⁴C-pyrene was measured as release of¹⁴CO₂. The highest rates of pyrene mineralization occurred during days 20–45,i.e. the period of high MnP activities, suggesting a role of this enzyme in PAH degradation. Within 60d, 24% of pyrene was mineralized.     

Detecting multimodality in saccadic reaction time distributions in gap and overlap tasks

In many cases the distribution of saccadic reaction times (SRT) deviates considerably from a unimodal distribution and may often exhibit several peaks. We present a statistical approach to determining the number and form of the individual peaks. The overall density of the reaction times f _i (t), i=1…M obtained in M different experiments with the same subject is described as the sum of K basis functions x _k (t),k=1…K with different weights and an error term. A change in the experimental conditions is assumed to cause a change in the weights, not in the basis functions. We minimize the square of the difference (measured data minus approximation), divided by the error of the data. Incrementing K step by step we determine the necessary number of basis functions. This method is applied to data of six subjects tested in different saccade tasks. We detect five different modes: two in the range 80–140 ms (express modes), two in the range 145–190 ms (fast-regular mode) and one at about 230 ms (slow-regular mode). These modes are located at about the same positions for different subjects. The method presented here not only proves statistically the existence of several modes in SRT distributions but also allows the distributions to be described by a few characteristic numbers that go beyond the mean values and standard deviations. Received: 24 March 1997 / Accepted: 5 December 1997     

Shielding of relativistic protons

Protons are the most abundant element in the galactic cosmic radiation, and the energy spectrum peaks around 1 GeV. Shielding of relativistic protons is therefore a key problem in the radiation protection strategy of crewmembers involved in long-term missions in deep space. Hydrogen ions were accelerated up to 1 GeV at the NASA Space Radiation Laboratory, Brookhaven National Laboratory, New York. The proton beam was also shielded with thick (about 20 g/cm²) blocks of lucite (PMMA) or aluminium (Al). We found that the dose rate was increased 40–60% by the shielding and decreased as a function of the distance along the axis. Simulations using the General–Purpose Particle and Heavy-Ion Transport code System (PHITS) show that the dose increase is mostly caused by secondary protons emitted by the target. The modified radiation field after the shield has been characterized for its biological effectiveness by measuring chromosomal aberrations in human peripheral blood lymphocytes exposed just behind the shield block, or to the direct beam, in the dose range 0.5–3 Gy. Notwithstanding the increased dose per incident proton, the fraction of aberrant cells at the same dose in the sample position was not significantly modified by the shield. The PHITS code simulations show that, albeit secondary protons are slower than incident nuclei, the LET spectrum is still contained in the low-LET range (<10 keV/μm), which explains the approximately unitary value measured for the relative biological effectiveness.     

Distribution of dissolved organic carbon and dissolved fulvic acid in mesotrophic Lake Biwa, Japan

The dissolved organic carbon (DOC) concentrations in mesotrophic Lake Biwa were determined by a total organic carbon (TOC) analyzer, and DOC molecular size distributions were determined by size exclusion chromatography (SEC) using a fluorescence detector at excitation/emission (Ex/Em) levels of 300/425 nm with the eluent at pH 9.7. The fluorescence wavelengths for detection were chosen from the result of excitation–emission matrix spectrometry (EEM) analysis for dissolved fulvic acid (DFA) extracted from Ado River (peak A, Ex/Em = 260–270/430–440 nm; peak B, Ex/Em = 300–310/420–430 nm). Ado River DFA was eluted with a retention time (RT) of 7.4–8.9 min and the apparent molecular weight was estimated at 22–87 kDa based on the elution curve for the spherical protein molecular weight standard. A DFA peak eluted at the same retention time as Ado River DFA also appeared in all the samples of Lake Biwa water. From the linear relationship between the peak areas with an RT of 7.4–8.9 min by SEC analysis and DOC values of DFA by TOC analysis of a series of DFA samples (r² = 0.9995), the concentrations of DFA in the lake water were roughly calculated. DFA was distributed within the range 0.25–0.43 mg C l⁻¹ and accounted for 15%–41% of DOC, with the highest ratios observed at a depth of 70 m in August and the lowest at 2.5 m in May.