Pigment alterations in the brown mussel Perna perna

Potential sex and/or gametogenic stage differences in the metabolism of chlorophyll-a and carotenoids in the brown mussel Perna perna of southern Brazil were studied using high performance liquid chromatography (HPLC). Carotenoids derived directly from diet (phytoplankton) were fucoxanthin plus diatoxanthin (diatoms), alloxanthin (cryptophytes) and zeaxanthin (mainly cyanobacteria). Females accumulated carotenoid-diols and epoxides (~ 3–4 mg/g-dry wt.) while males had much lower concentrations (~ 0.7 mg/g-dry wt.). An antioxidant/free radical scavenging role is proposed for carotenoids in females. Mean ratios of chlorophyll plus derivatives (Chlns-a) to carotenoids for male and female P. perna were 50:1 and 4:1, respectively. The higher ratio in males relates to both higher carotenoid contents in females plus higher total Chlns-a in males (~ 22 mg/g-dry wt.), relative to the females (~ 4 mg/g-dry wt.). Chlorophyll-a metabolism in both sexes followed two distinct pathways. First, cyclization of pyropheophorbide-a gave 13², 17³-cyclopheophorbide-a-enol (CPPaE) which was further oxidized to hydroxy-chlorophyllone. Second, chlorophyll-a derivatives retaining the 13²-carbomethoxy moiety were oxidized to purpurin-18 which was hydrolyzed to chlorin-p₆. In both cases, metabolism of dietary chlorophyll-a was oxidative and derivatives could either serve as antioxidants or merely be the results of non-specific digestive processes.     

Light-harvesting properties of zinc complex of chlorophyll-<Emphasis Type="Italic">a</Emphasis> from <Emphasis Type="Italic">spirulina</Emphasis> in surfactant micellar media

Zn chlorophyll-a was prepareted from Mg chlorophyll-a from spirulina and the optical properties of the ground state and the photoexited state of Zn chlorophyll-a in aqueous surfactant micellar media were studied using UV-vis absorption, fluorescence emission spectra, electrochemical and fluorescence lifetime measurements. In comparison of the UV-vis absorption and fluorescence emission spectra of Zn chlorophyll-a and Mg chlorophyll-a, the blue-shift in the absorption bands and emission peak of Zn chlorophyll-a was observed. The energies of the first excited singlet state of Zn chlorophyll-a was 1.87eV. The first oxidation and reduction potentials of the photoexcited singlet state of Zn chlorophyll-a were −0.67 and 0.60V, respectively. Fluorescence lifetime of Zn chlorophyll-a was 9.0 ns in CTAB micellar solution. The fluorescence lifetime of Zn chlorophyll-a is shorter than that of Mg chlorophyll-a (9.8 ns). The photositability of Zn chlorophyll-a was superior to that of Mg chlorophyll-a in various pH conditions. Published online December 2004     

Drift-ice and under-ice water communities in the Gulf of Bothnia (Baltic Sea)

The algal, protozoan and metazoan communities within different drift-ice types (newly formed, pancake and rafted ice) and in under-ice water were studied in the Gulf of Bothnia in March 2006. In ice, diatoms together with unidentified flagellates dominated the algal biomass (226 ± 154 μg ww l⁻¹) and rotifers the metazoan and protozoan biomass (32 ± 25 μg ww l⁻¹). The under-ice water communities were dominated by flagellates and ciliates, which resulted in lower biomasses (97 ± 25 and 21 ± 14 μg ww l⁻¹, respectively). The under-ice water and newly formed ice separated from all other samples to their own cluster in hierarchical cluster analysis. The most important discriminating factors, according to discriminant analysis, were chlorophyll-a, phosphate and silicate. The under-ice water/newly formed ice cluster was characterized by high nutrient and low chlorophyll-a values, while the opposite held true for the ice cluster. Increasing trends in chlorophyll-a concentration and biomass were observed with increasing ice thickness. Within the thick ice columns (>40 cm), the highest chlorophyll-a concentrations (6.6–22.2 μg l⁻¹) were in the bottom layers indicating photoacclimation of the sympagic community. The ice algal biomass showed additional peaks in the centric diatom-dominated surface layers coinciding with the highest photosynthetic efficiencies [0.019–0.032 μg C (μg Chl-a ⁻¹ h⁻¹) (μE m⁻² s⁻¹)⁻¹] and maximum photosynthetic capacities [0.43-1.29 μg C (μg Chl-a ⁻¹ h⁻¹)]. Rafting and snow-ice formation, determined from thin sections and stable oxygen isotopic composition, strongly influenced the physical, chemical and biological properties of the ice. Snow-ice formation provided the surface layers with nutrients and possibly habitable space, which seemed to have favored centric diatoms in our study.     

Population dynamics of zooxanthellae during a bacterial bleaching event

Each summer 80–90% of the colonies of Oculina patagonica undergo bleaching off the Mediterranean coast of Israel. To investigate fluctuations through a yearly bleaching cycle, monthly measurements of zooxanthella density, mitotic index and chlorophyll-a concentration were conducted. Results showed (1) a significant negative correlation between sea surface temperature (SST) and zooxanthella density; (2) both significantly lower zooxanthella mitotic index and higher chlorophyll-a per zooxanthella content during the bleaching season compared with the non-bleaching period; (3) prior to bleaching, a lag between the peak of zooxanthella density and chlorophyll-a concentration followed by a similar lag during recovery. Zooxanthella density declined significantly between March and May while chlorophyll-a concentration peaked in April, and then declined. Zooxanthella density increased significantly in November while chlorophyll-a concentration increased significantly in January. We conclude that during bacterial bleaching events, zooxanthellae are severely damaged. However, by the time of the following bleaching event the coral tissues regain their “normal” (pre-bleaching) zooxanthella population density.     

Implications of rapid changes in chlorophyll-<Emphasis Type="Italic">a</Emphasis> of plankton,epipelon, and epiphyton in a Pampean shallow lake: an interpretation in terms of a conceptual model

Biomass assessments of algae in wetlands usually include only the phytoplankton community without considering the contribution of other algal associations to total algal biomass. This omission prevents an accurate evaluation of the phytoplankton community as an integral part of the total ecosystem. In the present work, the biomass contributions (expressed as chlorophyll-a content per m² of lake) of phytoplankton, epiphyton on both submerged and emergent macrophytes, and epipelon were measured in Lacombe Lake, Argentina, for the purpose of (1) establishing the relative importance of the phytoplankton and (2) evaluating the entire contribution of algal biomass within the context of the Goldsborough & Robinson conceptual model. Our sampling was carried out monthly for a year in sites representative of different conditions with respect to water depth and type of macrophytes. Physicochemical analyses of water were performed following standard methods. Plankton was collected in a five-level profile at deeper stations and in subsurface samples at the shallow one. Samples of sediment obtained with corers were collected for epipelon sampling and segments of plants were cut at different levels, so as to obtain the epiphytes by scraping. Pigment was extracted with aqueous acetone and calculations were made by means of the Lorenzen equation. According to the Goldsborough & Robinson model, a Lake State developed here during the winter (phytoplankton maxima: 150 mg chlorophyll-a per m²). Then, through the subsequent growth of the submerged macrophytes, an Open State was observed, characterized by a maximum epiphyton biomass (at 3,502 mg chlorophyll-a per m²) along with lower levels of phytoplankton biomass. The epiphytic algae on the emergent macrophytes were always present but attained only relatively low biomass values (maximum: 120 mg of chlorophyll-a per m² in February). The epipelon biomass varied between 50 and 252 mg chlorophyll-a per m², registering a considerable contribution of settled algae from the water column (phytoplankton). This study contributes to our knowledge of wetland dynamics through its assessment of the rapid changes in the relative contributions of both planktonic and attached algae to the total algal biomass within the context of specific environmental factors. Guest editors: U. M. Azeiteiro, I. Jenkinson & M. J. Pereira Plankton Studies     

Dynamics and distribution of microphytobenthic chlorophyll-a in the Western Scheldt estuary (SW Netherlands)

The temporal dynamics and spatial distribution of microphytobenthic chlorophyll-a in the layer 0–1 cm were determined in the Western Scheldt estuary over the period 1991–1992. Connections between the annually averaged benthic chlorophyll-a and station elevation and sediment composition (as a measure of the hydrodynamic energy caused by currents and waves) were also examined.Microphytobenthic chlorophyll-a showed one main peak in early summer and a smaller peak in autumn. The mean chlorophyll-a concentration of 113 mg Chl-a m^–2 in the upper centimeter is of the same order of magnitude as in other estuarine areas. The average annual primary production of the microphytobenthos has been estimated at 136 g C m^–2 y^–1 The primary production of sediment inhabiting microalgae is at least 17% of the total primary production in the estuary.Considerable differences in annually averaged chlorophyll-a emerges between the stations. These differences are related mainly to the interaction between station elevation and clay content of the sediment.     

The relation of biotic and abiotic interactions to eutrophication in Tjeukemeer,The Netherlands

During the summer months of 1974–1985 chlorophyll-a and total P concentration, biomass of Daphnia hyalina, smelt Osmerus eperlanus, bream Abramis brema and pikeperch Stizostedion lucioperca, water temperature and water intake from lake IJsselmeer were monitored in Tjeukemeer. During this period there were manipulations with the bream and pikeperch stocks as a consequence of the termination of a gill-net fishery in 1977, and larval smelt immigrated each year from the large lake IJsselmeer and contributed largely to the yearly smelt recruitment.The correlation matrix of the nine variables mentioned above showed a positive correlation between bream and chlorophyll-a, but surprisingly a negative one between smelt and chlorophyll-a. The latter can only be explained when smelt is the dependent variable. In a multi-linear regression there was a negative effect of temperature, chlorophyll a and pikeperch on smelt and a positive effect of water intake. Daphnia hyalina was negatively influenced by the biomass of smelt and the water intake of lake IJsselmeer. The positive relation of Daphnia hyalina and chlorophyll-a was probably related to better survival chances of D. hyalina in an Oscillatoria-rich environment when smelt is the most important predator. An increasing biomass of bream coincided with higher total-P levels and probably contributed to higher chlorophyll-a levels.     

Extraction of chlorophylls a and b from phytoplankton using standard extraction techniques *

SUMMARY. Pigments extracted in methanol, acetone and ethanol from three cultures of green algae and one blue-green alga revealed different extraction efficiencies depending on the species, the extraction solvent used and the extraction time. Chromatographic identification and quantitative measurements of chlorophylls a and b were made from six green algae. When extraction of pigments was incomplete, chlorophyll-b was extracted faster than chlorophyll-a. This effect was more pronounced for acetone extractions, whereas methanol extractions gave the stable ratios of chlorophyll b/a after about 6–10 h. When green algae are frequent, a 6–10 h methanol extraction, without any extra manipulations, is sufficient to ensure reliable ratios of chlorophyll b/a and extraction of the major proportion of the chlorophylls without risk of induced destruction of the chlorophylls.     

Influence of ultraviolet radiation, copper, and zinc on microcystin content in Microcystis aeruginosa (Cyanobacteria)

Cyanobacterial toxin production is allied to some unknown trigger resulting in the production of toxins such as microcystin. We hypothesize that microcystins serve as metal ligands to control bioavailability and toxicity of ambient metals. Since ultraviolet radiation (UVR) promotes photo-oxidation of organic metal ligands and influences trace metal bioavailability, the present study aimed to investigate the influence of UVR, Cu, and Zn on specific growth rates, biomass, photosynthetic capacity, and microcystin content in Microcystis aeruginosa. Two toxigenic strains of Microcystis were cultivated using either Lake Erie filtered water or a chemically defined medium, with realistic concentrations of Cu and Zn combined with natural or artificial UVR exposure. Cu was more toxic than Zn on the basis of free ion concentration of trace metals in synthetic medium, although in Lake Erie water total added Zn (10 nM) or Zn plus Cu (10 nM) had a more detrimental effect on biomass and specific growth rate. Natural UVR delivered at 25% ambient levels caused no decrease on the parameters measured (chlorophyll-a, photosynthetic rate), yet artificial levels of UVR (up to 5.9 μmol UVB photons m⁻² s⁻¹) negatively affected biomass and specific growth rate. Cellular levels of microcystin (per unit chlorophyll-a) were concomitant with specific growth rather than being triggered in response either of these stressors (UVR, Zn, and Cu) alone or in combination, in agreement with a purported constitutive production of microcystins.     

Photo-oxidative Degradation of Chlorophyll-a and Unsaturated Lipids in Liposomal Dispersions at Low-Temperature

Liposomal dispersions in water were used as a tool to study photo-oxidation of chlorophyll-a and photo-oxidation of unsaturated lipids at 1 or 4°C. The presence of monogalactosyl diglyceride stimulated chlorophyll-a degradation. In addition the level of linolenic acid was decreased in liposomal dispersions containing chlorophyll-a, dipalmitoyl phosphatidyl choline, and monogalactosyl diglyceride, indicating that monogalactosyl diglyceride and chlorophyll-a were coupled in the preparations. In liposomal dispersions containing equal (molar) quantities of a-tocopherol, monogalactosyl diglyceride, and chlorophyll-a, a-tocopherol fully protected linolenic acid against photo-oxidative degradation, while chlorophyll-a degradation was only slightly reduced. In liposomal preparations containing a-tocopherol, chlorophyll-a and phosphatidyl choline, a-tocopherol catalyzed degradation of chlorophyll-a. Absorption spectra of the liposomal dispersions showed that the presence of a-tocopherol caused increased absorption in red light, which was attributed to structural changes in the liposomal preparations and thus could explain the noted effects. Tocopherol itself was rapidly degraded in chlorophyll-a containing liposomal preparations. Complex formation between chlorophyll-a and monogalactosyl diglyceride in chloroplasts is suggested and protection by a-tocopherol against photo-oxidation in chilling-sensitive plants; a suggestion which is founded on the similarities that exist between chloroplast preparations and liposomal preparations containing chlorophyll-a and monogalactosyl diglyceride as regards photo-oxidative degradation of chlorophyll-a, a-tocopherol and linolenic acid.     

Revisiting the total maximum daily load total phosphorus goal in Lake Okeechobee

In 2000, a total maximum daily load (TMDL) total phosphorus (TP) goal of 40 µg/L was established for Lake Okeechobee, Florida. The goal was selected to reduce the “imbalance to flora and fauna” caused by excessive phosphorus loading in the lake. We recalculate the TMDL TP goal using a water quality data series of TP and chlorophyll-a concentrations from 1986 to 2018 for the original 30 in-lake stations plus an additional 29 stations. Using the cross-tabulation approach used to generate the original TMDL TP goal, we determined a new goal of 42 µg/L, nominally different from the original. We also reevaluate the goal’s ability to maintain an implicit goal of 11.5% bloom frequency. We conclude substantial changes in the frequency and scope of the water quality sampling scheme prevent a determination on the effectiveness of the TMDL TP goal. The implementation, however, appears to have failed as the median TP concentration has increased by 93 µg/L to 133 µg/L and bloom frequency, after correcting for the declining sampling frequency, has increased from 1986 to 2018. An increased sampling frequency of TP and chlorophyll-a sampling is needed, or else tracking responses of chlorophyll-a to future TP reductions will be virtually impossible.

     

Extraction of chlorophyll and carotenoid pigments from Antarctic benthic mats for analysis by HPLC

The efficiency of 9:1 acetone-water, DMSO and boiling 9:1 ethanol-water in extracting chlorophyll and carotenoid pigments from benthic cyanobacterial mats from Antarctica for HPLC (high performance liquid chromatography) analysis was examined. Considerable breakdown of chlorophylla was observed after 5 min extraction in boiling ethanol and 2 h extraction in DMSO. Over 50% of the chlorophylla was degraded to chlorophyllidea and there was substantial loss of carotenoids after a 15 h exposure of ground cells to cold 9:1 acetone-water.Mild sonication of ground mat material in 9:1 acetone-water followed by a 4 h extraction at 4 ° C was found to minimise chlorophylla breakdown and dramatically improved the extraction efficiency of chlorophylla, myxoxanthophyll and -carotene.     

Effects of planktivore abundance on chlorophyll-a and Secchi depth

We used two analyses to test the hypothesis that planktivore abundances contribute to the residual variations of Secchi depth or chlorophyll-a plotted with respect to mean summer epilimnetic total phosphorus. The first analysis involved 15 lake years of data from six lakes. The data set comprised mark-recapture assessments of piscivore and planktivore numbers and estimates of mean summer chlorophyll-a, total phosphorus and Secchi depth. We found that residual chlorophyll-a variation was not significantly (p>0.05) correlated with planktivore densities, but that planktivore densities did contribute (p<0.02) to the residual variation of Secchi depth on mean total phosphorus. The second analysis included all of the data used in the first plus an additional 13 lake years of data from the literature. These data showed that the percentage of the total fish community comprising planktivores did not significantly (p>0.05) contribute to the residual variation in chlorophyll-a with respect to mean summer total phosphorus. Together, our results suggest that planktivore abundance has a significant cascading impact on water clarity, but no long term statistically significant impact on mean summer chlorophyll-a concentration.     

Selective ingestion of phytoplankton by the bivalvesMytilus edulis L. andCerastoderma edule (L.)

Blue mussles (Mytilus edulis) and cockles (Cerastoderma edule) were collected in the Oosterschelde estuary (SW Netherlands) and exposed to diets consisting of the diatomPhaeodactylum tricornutum and silt. Algal concentrations were kept constant (20.10³ cells.ml^–1), and silt concentrations were varied between 3–80 mg.l^–1 (mussel experiments) and 20–120 mg.l^–1 (cockle experiments). Chlorophyll-a concentrations in the pseudofaeces were reduced compared to the diets, indicating selective ingestion of the algae. It was estimated that the mussels increase the ingestion of chlorophyll-a 2.0 times, and the cockles increase the chlorophyll-a ingestion 2.8 times, compared to the ingestion rate without selection. The selection coefficients were not affected by the SPM concentrations used. Phaeophytin-a concentrations in the faeces showed an increase as a consequence of the digestion of the ingested algae. Digestive efficiencies of chlorophyll-a varied between 36–92% The digestive efficiencies decreased with increasing SPM concentrations.Communication no. 541 of the Delta Institute for Hydrobiological Research.     

Optimization of variable fluorescence measurements of phytoplankton communities with cyanobacteria

Excitation–emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence. In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from community fluorescence under blue excitation (450–470 nm) with high accuracy (R ² = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red excitation in the 590–650 nm range (R ² = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow (up to 10 nm) and centred on PSII chlorophyll-a emission (~683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation in PSII in the range of 0.65–0.7.     

River–reservoir transition zones are nitrogen fixation hot spots regardless of ecosystem trophic state

Reservoir hydrodynamics may create heterogeneity in nitrogen (N) fixation along the riverine–transition–lacustrine gradient. In particular, N fixation may be highest in reservoir transition zones where phytoplankton biomass is also expected to be relatively high. We investigated spatial patterns of N fixation in three Texas (USA) reservoirs of varying trophic state. We sampled 6–9 stations along the longitudinal axes of the major inflows and measured N fixation using the acetylene reduction method. Total N, total phosphorus (P), and algal biomass (as chlorophyll-a) were also measured at each sample location. Measurable N fixation was observed in all reservoirs and was light-dependent. Nitrogen fixation was consistently low in the riverine zone, highest in the transition zone, and low in lacustrine zone of all reservoirs. The absolute magnitude of N fixation was similar in two relatively unproductive reservoirs and an order of magnitude higher in the eutrophic reservoir. A similar pattern was observed in mean nutrient and chlorophyll-a concentrations among reservoirs. However, chlorophyll-a concentrations were highest in the riverine zone of each reservoir and exhibited a monotonic decrease in the downstream direction. Maximum chlorophyll-a concentrations did not coincide with maximum N fixation rates. Results of our study indicate that reservoir transition zones can be biogeochemical hot spots for planktonic N fixation, regardless of trophic state. Therefore, transition zones may be the most at risk locations for water quality degradation associated with increased reservoir productivity. Water quality managers and aquatic scientists should consider the spatial heterogeneity imposed by unique hydrodynamic controls in reservoir ecosystems. Handling editor: Luigi Naselli-Flores     

Biological degradation of algae and microcystins by microbial enrichment on artificial media

The removal efficiency of algae and microcystins (MCs) of a pilot setup based on biological degradation of enrichment microbes by artificial media was studied. The results showed that when chlorophyll-a in Lake Taihu was 3.76–266.1 μg L⁻¹, 62.8% of chlorophyll-a could be removed within a hydraulic retention time of 6–7 days. High-performance liquid chromatography (HPLC) analysis for the detection of MCs was applied. When total microcystins RR and LR (TMC-RR and TMC-LR) and extracellular microcystins RR and LR (EMC-RR and EMC-LR) were 0.23–8.93, 0.14–4.73, 0.12–1.15, 0.02–0.17 μg L⁻¹, respectively, and in source water, the average removal efficiencies of TMC-RR, TMC-LR, EMC-RR, EMC-LR were 67.0%, 40.5%, 40.0% and 66.0%, respectively. The polymerase chain reaction (PCR) electrophoresis chart revealed that there was a large amount of algae-lysing bacteria such as Pseudomonas spp. and Bacillus spp. on the artificial medium. The protozoa number in the assembled medium was higher than in lake water. Enrichment microbes on the artificial medium could effectively degrade algae and microcystins in Lake Taihu.     

Comparison of water level and eutrophication indicators during the wet and dry period in a eutrophic urban lake

Eutrophication modifies lakes' ecological balances and threatens its viability. To date, eutrophication management strategies have been related to nutrient reduction in the lakes' water column. However, nutrient reduction strategies are complicated by the variations of the lake's water level, nutrient concentration, and eutrophication symptom, which are primarily known to be influenced by the local rainfall patterns. Therefore, this study aimed to compare the variability of water level, total phosphorus, and total chlorophyll-a concentrations in Slim River Lake during wet and dry seasons. In this study, water sampling and depth measurements were carried out from six sampling points for 1 year. Water samples were used to quantify total phosphorus and total chlorophyll-a. Our results showed that mean water levels in the studied lake ranged from 1.36 m to 5.46 m in the wet season and from 1.31 m to 5.41 m in the dry season, which implicated no significant difference (p > .05) between seasons in most sampling points. Total phosphorus present at concentrations exceeding 10 mg/L and showed small variations between wet and dry seasons. Mean total phosphorus concentrations varied from 10.55 mg/L to 26.66 mg/L in the wet season and 10.77 mg/L to 21.76 mg/L in the dry season and showed no significant difference between seasons. In addition, mean chlorophyll-a concentrations ranged from 14.35 mg/m³ to 180.13 mg/m³ and from 14.15 mg/m³ to 39.27 mg/m³ in wet and dry seasons, respectively. Chlorophyll-a concentrations showed significant differences (p < .05) between seasons in the deepest sampling points in the lake. The observed seasonal variations in total chlorophyll-a suggest the importance of algae monitoring during the wet season even when no apparent surge of phosphorus concentration is detected.     

Temporal and spatial distributions of dissolved organic carbon and nitrogen in two small lakes on the Southwestern China Plateau

Temporal and spatial distributions of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chlorophyll-a and inorganic nitrogen were investigated in two small mountainous lakes (Lake Hongfeng and Baihua), on the Southwestern China Plateau, based on almost 2 years’ field observation. DOC concentrations ranged from 163 μM to 248 μM in Lake Hongfeng and from 143 μM to 308 μM in Lake Baihua, respectively, during the study period. DON concentrations ranged from 7 μM to 26 μM in Lake Hongfeng and from 14 μM to 47 μM in Lake Baihua. DOC showed vertical heterogeneity with higher concentrations in the epilimnion than in the hypolimnion during the stratification period. The DON concentration profiles appeared to be more variable than the DOC profiles. Apparent DON maxima occurred in the upper layer of water. In Lake Hongfeng, DOC concentration in the surface water was highest at the end of spring and early summer. DON concentration was 2–5 μM higher in May 2003 and in June 2004 than in adjacent months. DOC and chlorophyll-a concentrations were significantly correlated (r = 0.79, P < 0.05). The period of highest concentrations of DOC in Lake Hongfeng was also the season of concentrated rainfall. Algae activity and allochthonous input might result in an increase of DOC and DON concentrations together. In Lake Baihua, the maximum concentrations of DOC and DON in the surface water occurred simultaneously in May 2003 and February 2004. DOC concentrations were significantly correlated with DON (r = 0.90, P < 0.01), indicating the common sources. Allochthonous input, biological processes, stratification and mixing were the most important factors controlling the distributions and cycling of dissolved organic matter (DOM) and inorganic nitrogen in these two lakes. Inference from the corresponding vertical distributions of DOM and inorganic nitrogen indicated that DOM played potential roles in the internal loading of nitrogen and metabolism in the water body in these small lakes. The carbon/nitrogen (C/N) ratio showed a potential significance for tracing the source and biogeochemical processes of DOM in the lakes. These results are of significance in the further understanding of biogeochemical cycling and environmental effects of DOM and nitrogen in lake ecosystems.     

The use of high-spectral-resolution radiometer data for detection of low chlorophyll concentrations in Lake Kinneret

Chlorophyll distribution in Lake Kinneret was estimated in aperiod of low chlorophyll-a concentrations (3–7 mg m^–3)using remotely sensed data. The data set included high-spectral-resolutionradiometric measurements in the range 400–750 nm, chlorophylland suspended matter concentrations, Secchi disk transparencyand vertical attenuation coefficients at 20 stations. The spectroradiometricdata were used to create the algorithms suitable for quantitativedetermination of chlorophyll content. The present paper presentsexperimental field evidence showing that fluorescence can besuccessfully used for remote monitoring of chlorophyll-a content(with an estimation error <0.5 mg m^–3) in productiveinland waters with a background of variable and relatively highsuspended matter concentration.