Average Chlorophyll Research Articles

Two-photon excitation chlorophyll fluorescence lifetime imaging: a rapid and noninvasive method for in vivo assessment of cadmium toxicity in a marine diatom Thalassiosira weissflogii

We demonstrate that a two-photon excitation fluorescence lifetime imaging technology can rapidly and noninvasively assess the cadmium (Cd)-induced toxic effects in a marine diatom Thalassiosira weissflogii. The chlorophyll, an intrinsic fluorophore, was used as a contrast agent for imaging of cellular structures and for assessment of cell toxicity. The assessment is based on an imaging-guided statistical analysis of chlorophyll fluorescence decay. This novel label-free imaging method is physically based and free of tedious preparation and preprocessing of algal samples. We first studied the chlorophyll fluorescence quenching induced by the infrared two-photon excitation laser and found that the quenching effects on the assessment of Cd toxicity could be well controlled and calibrated. In the toxicity study, chlorophyll fluorescence lifetime images were collected from the diatom samples after exposure to different concentrations of Cd. The alteration of chloroplast structure at higher Cd concentration was clearly identified. The decay of chlorophyll fluorescence extracted from recorded pixels of high signal-to-noise ratio in the fluorescence lifetime image was analyzed. The increase of average chlorophyll fluorescence lifetime following Cd treatment was observed, indicating the Cd inhibition effect on the electron transport chain in photosynthesis system. The findings of this study show that the temporal characteristics of chlorophyll fluorescence can potentially be utilized as a biomarker for indicating Cd toxicity noninvasively in algal cells.

Phytoplankton Species Composition and Abundance in the Southwestern Caspian Sea

This study, accomplished is focused on the spatial and temporal distribution and species composition of phytoplankton in the southwestern Caspian Sea between January 2008 and December 2008. Samples were collected from 11 stations along three transects known as Lisar, Anzali and Sefidrood. This study identified 43 phytoplankton species comprised of diatoms (25 species), dinoflagellates (7 species), chlorophytes (6 species), cyanophytes (4 species), and euglenoids (1 species) were identified. The study showed, diatom Dactyliosolen fragilissimus and the dinofllagelate Prorocentrum cordatum numerically dominate the southwestern Caspian Sea. The annual average phytoplankton density was calculated as 2.35E+04 ± 1.63E+04 Cell L-1, with the maximum value recorded in the winter (4.50E+04 ± 3.90E+04 Cell L -1 ). Diatoms were dominant during the autumn and winter (77.0% and 96.0%, respectively), while dinoflagellates were prevalent during the spring and summer (89.0% and 86.0%, respectively). The annual average chlorophyll a was calculated as 9.26±3.54 μg L -1 , with the maximum values were recorded in the winter (16.9±5.60 μg L-1). This is supported by the Spearman rank correlation result between phytoplankton abundance and chlorophyll a (r=0.551). The high phytoplankton cell density and chlorophyll a concentration coincided with the poor species composition.

Effects of soil flooding on photosynthesis and growth of Zea mays L. seedlings under different light intensities

Soil flooding is one of the major abiotic stresses that repress maize ( Zea mays L.) growth and yield, and other environmental factors often influence soil flooding stress. This paper reports an experimental test of the hypothesis that light intensity can influence the responses of maize seedlings to soil flooding. In this experiment, maize seedlings were subjected to soil flooding at the two-leaf stage under control light (600 µmol m -2 s -1 ) or low light (150 µmol m -2 s -1 ) conditions. Under control light growth conditions, the average photosynthetic rate (PN), transpiration rate (E) and water use efficiency (WUE) were 70, 26 and 59%, respectively, higher in non-flooded than in flooded seedlings; and the average chlorophyll a (Chl a), chlorophyll b (Chl b) and Chl a+b were 31, 42 and 34%, respectively, higher in non-flooded than in flooded seedlings; and the average belowground biomass and total biomass were 52 and 34%, respectively, higher in non-flooded than in flooded seedlings. There was a slight decrease of seedling biomass in six days flooded seedlings under low light growth conditions. The effects of flooding on photosynthetic, seedling growth and shoot/root ratio were more pronounced under control light growth conditions than under low light growth conditions, which indicate that even for maize which is a C4 plant, relatively high light intensity still aggravated soil flooding stress, while low light growth condition mitigated soil flooding stress, and suggests that light effects should be considered when we study maize responses to soil flooding.

Environmental monitoring of soil conditioner effects on photosynthetic parameters of Acer campestre L.

We evaluated photosynthetic reactions in Acer campestre L. in a multi-factorial field experiment near Hodonin, Southern Moravia, Czech Republic. In this experiment, selected plots were amended with three different supplementary soil substances, that is, zeolite, lignite, and hydroabsorbent Agrisorb , and were compared with unamended control plots. Microclimatic parameters, that is, temperature, relative humidity, soil moisture, and solar radiation were measured. In the spring of 2008, supplementary soil substances were applied, and in the autumn of the same year, experimental A. campestre L. plants were harvested. The basic physiological parameters, chlorophyll content and fluorescence, stomatal conductance, and sap flow were determined in the experimental plants. Determination of the above-mentioned parameters showed higher vitality of plants cultivated on plots supplemented by lignite, followed by zeolite. In comparison with the control plants, the application of lignite led to increase of average chlorophyll content and fluorescence by 37 and 20%, respectively, stomatal conductance by 29%, and sap flow by 44% in plants. In comparison with the control plants, the application of zeolite resulted in the enhancement of average chlorophyll content and fluorescence by 14 and 15%, respectively, stomatal conductance by 16%, and sap flow by 36% in plants. The monitored parameters of plants cultivated on plots supplemented with hydroabsorbent Agrisorb were similar to those measured in control plants. In addition, the results obtained are related to actual weather. Correlations between type of the applied supplementary soil substances, soil moisture, and physiological parameters were found. Data of short-time measurement of photosynthesis response correspond with data of long-time measurement of morphological characteristics. The highest height increments were determined in experimental group cultivated under lignite application, followed by zeolite. Statistically insignificant plant height increases were observed in plants cultivated on the soil supplemented with hydroabsorbent Agrisorb . Key words: Abiotic stress, soil conditions, microclimatic data, photosynthetic reactions, morphological characteristic, environmental sensors.

CURRENT STATUS OF AMBEWELA RESERVOIR OF SRI LANKA WITH SPECIALREFERENCE TO WATER POLLUTION

The water pollution trends in the Ambewela reservoir at the uppermost catchment of Kotmale River was assessed through a study on chemical and bio monitoring programme that carried out from March to October 2008.The mean average value (mean ± SD) of the nitrate, nitrite, phosphate and ammonia concentrations in Ambewela reservoir were 0.780 ± 1.386 mg/l, 0.103 ± 0.223mg/l, 0.051 ± 0.061mg/l and 0.218± 0.261 mg/l whereas values for the streams selected from Dambagasthalawa Oya were 0.985 ± 0.902 mg/l, 0.099 ± 0.207mg/l, 0.038 ± 0.026 mg/l and 0.085± 0.077 mg/l respectively. Average Chlorophyll- a values of the reservoir were 17.85 ± 17.858 mg/m3 and 8.30 ± 4.686 mg/m3for other two streams accordingly. Average BOD values of the reservoir were 8.06 ± 3.494 and 4.25 ± 2.251 for other two streams correspondingly.The bio monitoring studies also clearly showed sudden records of huge colonies of Hydra(approximately 258/cm3) in the reservoir from time to time. This phenomenon was found in relatively dry period that directly coincided with intensified use of agro chemicals. Moreover, steady population of Chironomid (average population density 208/cm3) that is commonly accepted pollution indicator was reported at Ambewela reservoir throughout the study period.Therefore, both chemical and bio monitoring studies indicate eutrophic condition in Ambewela reservoir in which long run might affect on the ecology of the entire ecosystem. Hence prompt mitigatory action should be implemented to avoid further depletion.Key Words: Ambewela Reservoir, Water Pollution, Physico-Chemical Parameters, Chlorophyll –a

A case study to determine the efficacy of ozonation in purification processes

The aim of this study was to determine the efficacy of ozone in water purification processes at the Midvaal Water Company, which uses the hypertrophic Middle Vaal River for source water. It was found that pre- and intermediate ozonation had no significant effect on pH, conductivity, dissolved organic carbon (DOC) and total organic carbon (TOC). Chlorophyll-a, total chlorophyll, spectral absorbance coefficient (SAC 254) and total algal cells were not influenced by pre-ozonation (as desired) but were greatly reduced after intermediate ozonation. The dissolved air flotation step which occurs after preozonation and prior to intermediate ozonation contributed to an average total chlorophyll removal of 74%. The effect of ozonation on the removal of manganese, iron and aluminium could not be determined during this study since these elements were present in relatively low concentrations in the source water. Intermediate ozonation had variable effects on the removal of Cyanophyceae, Dinophyceae, Euglenophyceae and Chlorophyceae, but Chrysophyceae, Bacillariophyceae and Cryptophyceae were greatly reduced after this stage.

On the use of the FluoroProbe®, a phytoplankton quantification method based on fluorescence excitation spectra for large-scale surveys of lakes and reservoirs

Although microscope analysis is very useful for studying phytoplankton community composition, it does not allow for high frequency (spatial and/or temporal) data acquisition. In an attempt to overcome this issue, fluorescence-based approaches that use selective excitation of pigment antennae have spread rapidly. However, the ability of spectral fluorescence to provide accurate estimates of phytoplankton biomass and composition is still debated, and only a few datasets have been tested to date.In this study, we sampled of a wide range of water bodies (n=50) in the Ile-de-France region (North Central France). We used the resulting extensive dataset to assess the ability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton community composition in lakes and reservoirs.We demonstrated that FP data yields better estimates of total phytoplankton biovolume than do spectrophotometric chlorophyll a measures and that FP data can be further corrected using the average chlorophyll a to biovolume ratio among phytoplankton groups. Overall, group-specific relationships between FP and biovolume data were consistent. However, we identified a number of cases where caution is required. We found that Euglenophytes are expected to depart from the global FP vs. biovolume relationship of the ‘green’ group due to varying Fv/Fm and pigment content in response to environmental conditions (photoautotrophic vs. photoheterotrophic growth). Then, it appears necessary to consider the composition of the Chromophytes community in order to obtain a good agreement between both biomass estimation methods. Finally, we confirmed the misattribution toward the ‘red’ group of phycoerythrin-containing cyanobacteria and the occurrence of a strong scattering in the relationship between the FP vs. biovolume of the ‘blue’ group that can be partly attributed to the occurrence of large colony-forming cyanobacteria (e.g., Microcystis spp, Aphanizomenon flos-aquae).We propose correcting procedures to improve the quality of data obtained from spectral fluorescence tools in the context of large-scale sampling of lakes and reservoirs.

Mercury effects on Thalassiosira weissflogii: Applications of two-photon excitation chlorophyll fluorescence lifetime imaging and flow cytometry

The toxic effects of inorganic mercury [Hg(II)] and methylmercury (MeHg) on the photosynthesis and population growth in a marine diatom Thalassiosira weissflogii were investigated using two methods: two-photon excitation fluorescence lifetime imaging (FLIM) and flow cytometry (FCM). For photosynthesis, Hg(II) exposure increased the average chlorophyll fluorescence lifetime, whereas such increment was not found under MeHg stress. This may be caused by the inhibitory effect of Hg(II) instead of MeHg on the electron transport chain. For population growth, modeled specific growth rate data showed that the reduction in population growth by Hg(II) mainly resulted from an increased number of injured cells, while the live cells divided at the normal rates. However, MeHg inhibitory effects on population growth were contributed by the reduced division rates of all cells. Furthermore, the cell images and the FCM data reflected the morphological changes of diatom cells under Hg(II)/MeHg exposure vividly and quantitatively. Our results demonstrated that the toxigenicity mechanisms between Hg(II) and MeHg were different in the algal cells.

Remotely Sensed Chlorophyll: A Putative Trophic Link for Explaining Variability in Indian Oil Sardine Stocks

The landing of Indian oil sardines, Sardinella longiceps Valenciennes, 1847, along the southwest coast of India is highly variable. A few physical parameters and processes correlated with sardine landing could not establish a flawless connection and explain the phenomena of interannual variability. Earlier research has indicated that the probable appearance and disappearance of sardines is an active movement in search of food and favourable conditions. But no specific study has been carried out to explain the variability of sardine catch based on chlorophyll availability on a synoptic scale. An attempt is made in this study to correlate variability in chlorophyll a with sardine landings along the waters of the southwest coast of India. We have estimated monthly averaged surface phytoplankton biomass along the waters of the southwest coast of India from the shoreline up to the 200-m isobath for 10 years from SeaWiFS ocean-colour data. This estimation is compared with the biological calendar of Indian oil sardines. The average chlorophyll a for the bloom initiation month (1998–2006) matches very well with oil sardine landings. The results imply that the concentration of chlorophyll during the bloom initiation month can be used to assess the quantity of fish that recruit into the population. Finer scale spatial variations in the chlorophyll along the coastal waters help in deciphering the migratory pattern of sardines during their active breeding phase. This study shows that 39% of interannual variability in fish landings is related to availability of chlorophyll a during the bloom initiation month.

There’s more to the picture than meets the eye: Sampling microphytobenthos in a heterogeneous environment

Distributions of microphytobenthos are highly heterogeneous at scales as small as a few centimetres. However, the sampling protocols currently used for the absolute determination of microphytobenthos biomass through chlorophyll a concentration measurements in surface sediments are too limited to take this variability into account, typically relying on 3-5 samples taken within a randomly located 1 m 2 quadrat in a given environment. We address this issue by objectively and quantitatively inferring the minimum number of samples required to obtain reliable estimates of microphytobenthos biomass on the basis of high-resolution sub-sampling (225 regularly spaced samples) within each of nine 1 m 2 quadrats at an unvegetated sheltered intertidal sandbank of the Gold Coast (Queensland, Australia). The results were generalised using data obtained in previous studies on an exposed sandy shore and on sheltered estuarine sandy muds of the Eastern English Channel. Estimates of chlorophyll a concentration exhibited a high degree of heterogeneity, both between and within quadrats. The number of samples needed to estimate the average chlorophyll a concentration, and hence mean microphytobenthos biomass with 95% confidence intervals, ranged from 15 to 115, and mainly depended on the presence of global and local gradients within the quadrats. These results have major implications for intertidal ecology by implying a possible systematic bias in the measurement of both microphytobenthos biomass and production of up to 40%. Finally, we emphasise that this issue can be circumvented using field spectrometry or PAM fluorescence measurements coupled with traditional sediment sampling techniques, and urge for unified protocols to be adopted for the routine use of these combined methods.

Comparison of chlorophyll a concentration detected by remote sensors and other chlorophyll indices in inhomogeneous turbid waters

A new analytical approach for retrieval of the vertically weighted chlorophyll a concentration (<linear span>Chl<linear span>(rs)) detected by remote sensors is presented. Model calculations were carried out for the turbid waters of Lake Kinneret, Israel, and showed that <linear span>Chl<linear span>(rs) may be replaced by the average chlorophyll a concentration (<linear span>Chl<linear span>(p)) within the upper "penetration layer" 0-Z(p). The study also showed a high correlation between <linear span>Chl<linear span>(rs) and Chl concentration averaged in the other depth layers, namely, the 0-1 m layer, the euphotic layer (0-Z(e)), and the production layer (0-Z(pr)). Our findings are closely related to models developed for the world ocean, with the exception of periods when the dinoflagellate Peridinium gatunense blooms in the lake. We showed the effect of the pattern of vertical Chl distributions within the penetration layer on the difference between <linear span>Chl<linear span>(rs) and other Chl indices was conspicuous when the Chl maximum was in the uppermost 0- m layer of the water column. We assume that the presented approaches are instrumental for further development of optimal, locally adapted algorithms for remote sensing of Chl in any type of natural waters.

Iodine containing species in the remote marine boundary layer: A link to oceanic phytoplankton

[1] Iodine containing species have been measured in the particle phase (PM2.5) and the gas phase during a ship campaign between January and February 2007 in the South Atlantic marine boundary layer (MBL). Methyl iodide (CH3I) in the gas phase and soluble iodine species, i.e. iodide, iodate and an unidentified organic iodine species (UOI), in PM2.5 were measured. Temporal variations of gaseous and particulate iodine species were investigated. The exposure of the sampled air masses to phytoplankton along the back-trajectories was studied using a lagrangian transport model and satellite observations of oceanic chlorophyll-a concentration. Significant correlations were found between the concentrations of iodine species and the average chlorophyll exposure along back-trajectories, indicating an emission from phytoplankton in the open ocean. Good correlations were found when the ship approached or crossed the active biological region in the West-southern Atlantic. These results strongly suggest a connection between iodine species and the phytoplankton in the ocean. This study was extended to examine the relation of the iodine measurements to satellite derived phytoplankton distributions. We show that specific phytoplankton species may have impact on different iodine containing species.

Determination of chlorophyll content of small water bodies (kettle holes) using hyperspectral airborne data

This study presents an approach for chlorophyll content determination of small shallow water bodies (kettle holes) from hyperspectral airborne ROSIS and HyMap data (acquired on 15 May and 29 July 2008 respectively). Investigated field and airborne spectra for almost all kettle holes do not correspond to each other due to differences in ground sampling distance. Field spectra were collected from the height of 30–35cm (i.e. area of 0.01–0.015m2). Airborne pixels of ROSIS and HyMap imageries cover an area of 4m2 and 16m2 respectively and their spectra are highly influenced by algae or bottom properties of the kettle holes. Analysis of airborne spectra revealed that chlorophyll absorption near 677nm is the same for both datasets. In order to enhance absorption properties, both airborne hyperspectral datasets were normalized by the continuum removal approach. Linear regression algorithms for ROSIS and HyMap datasets were derived using normalized average chlorophyll absorption spectra for each kettle hole. Overall accuracy of biomass mapping for ROSIS data was 71%, and for HyMap 64%. Biomass mapping results showed that, depending on the type of kettle hole, algae distribution, the ‘packaging effect’ and bottom reflection lead to miscalculations of the chlorophyll content using hyperspectral airborne data.

Seasonal variability of chlorophyll a in the Mid-Atlantic Bight

For this manuscript we use a 9-year time series of Sea-viewing Wide Field of view Sensor (SeaWiFS), HF radar, and Webb Glider data to assess the physical forcing of the seasonal and inter-annual variability of the spatial distribution in phytoplankton. Using Empirical Orthogonal Function (EOF) analysis, based on 4-day average chlorophyll composites, we characterized the two major periods of enhanced chlorophyll biomass for the MAB in the fall–winter and the spring. Monthly averaged data showed a recurrent chlorophyll biomass in the fall–winter months, which represented 58% of the annual surface chlorophyll for the MAB. The first EOF mode explained ∼33% of the chlorophyll variance and was associated with the enhanced phytoplankton biomass in the fall–winter found between the 20 and 60 m isobaths. Variability in the magnitude of the enhanced chlorophyll in fall–winter was associated with buoyant plumes and the frequency of storms. The second EOF mode accounted for 8% of the variance and was associated with the spring time enhancements in chlorophyll at the shelf-break/slope (water depths greater than 80 m), which was influenced by factors determining the overall water column stability. Therefore the timing and the inter-annual magnitude of both events are regulated by factors influencing the stability of the water column, which determines the degree that phytoplankton are light-limited. Decadal changes observed in atmospheric forcing and ocean conditions on the MAB have the potential to influence these phytoplankton dynamics.

Extraction method influences the recovery of phytoplankton pigments from natural assemblages

Phytoplankton pigment samples are routinely collected by filtering water and storing filters at −20°C before extraction and fluorometric analyses. Although pigment loss on frozen filters has been demonstrated for phytoplankton cultures, its effect on taxonomically diverse, natural assemblages is unknown. We examined the effect of freezing filters on pigment measurements from weekly field samples collected for 1 y from Narragansett Bay, RI. Over 1000 filters representing the total and &lt; 20 µm size fractions were collected. One set of filters was treated with MgCO3 and stored at −20°C for ≤ 200 d before extraction. Another set was immediately extracted following filtration and not treated with MgCO3. A third subset was treated without MgCO3 and frozen for ≤ 70 d. Frozen storage decreased the annual average Chlorophyll a concentration by 51%. Pigment loss was greatest in samples dominated by the &gt; 20 µm size class, such as during the winter‐spring bloom peak when 62% of Chl a was lost from frozen samples. Freezing filters reduced analytical precision, increasing the coefficient of variation of Chl a measurements from 3.4% using immediate extraction to 13.1% using frozen filter storage. Correction factors created from regression analyses were applied to the year‐long frozen storage dataset and brought the annual average Chl a concentration to within 4% of the value determined using the immediate extraction technique. The application of correction factors to the Narragansett Bay Long‐Term Monitoring Program from 1999–2007 resulted in an average Chl a concentration that was 94% greater than the historical average.

A long-term monitoring study of chlorophyll, microbial contaminants, and pesticides in a coastal residential stormwater pond and its adjacent tidal creek

Stormwater ponds are commonly used in residential and commercial areas to control flooding. The accumulation of urban contaminants in stormwater ponds can lead to water-quality problems including nutrient enrichment, chemical contamination, and bacterial contamination. This study presents 5years of monitoring data assessing water quality of a residential subdivision pond and adjacent tidal creek in coastal South Carolina, USA. The stormwater pond is eutrophic, as described by elevated concentrations of chlorophyll and phosphorus, and experiences periodic cyanobacterial blooms. A maximum monthly average chlorophyll concentration of 318.75μg/L was measured in the stormwater pond and 227.63μg/L in the tidal creek. Fecal coliform bacteria (FCB) levels were measured in both the pond and the tidal creek that exceeded health and safety standards for safe recreational use. A maximum monthly average FCB level of 1,247CFU/100mL was measured in the stormwater pond and 12,850CFU/100mL in the tidal creek. In addition, the presence of antibiotic resistant bacteria and pathogenic bacteria were detected. Low concentrations of herbicides (atrazine and 2,4-D: ), a fungicide (chlorothalonil), and insecticides (pyrethroids and imidacloprid) were measured. Seasonal trends were identified, with the winter months having the lowest concentrations of chlorophyll and FCB. Statistical differences between the stormwater pond and the tidal creek were also noted within seasons. The tidal creek had higher FCB levels than the stormwater pond in the spring and summer, whereas the stormwater pond had higher chlorophyll levels than the tidal creek in the summer and fall seasons. Chlorophyll and FCB levels in the stormwater pond were significantly correlated with monthly average temperature and total rainfall. Pesticide concentrations were also significantly correlated with temperature and rainfall. Pesticide concentrations in the stormwater pond were significantly correlated with pesticide concentrations in the adjacent tidal creek. Chlorophyll and FCB levels in the tidal creek, however, were not significantly correlated with levels in the pond. While stormwater ponds are beneficial in controlling flooding, they may pose environmental and human health risks due to biological and chemical contamination. Management to reduce residential runoff may improve water quality in coastal stormwater ponds and their adjacent estuarine ecosystems.

Biochemical and structural characteristics of Scots pine (Pinus sylvestris L.) in an alkaline environment

Investigations in a 75-85-year-old Scots pine stand were performed on a territory influenced over 40 years by alkaline dust pollution (pH 12.3-12.7) emitted from a cement plant. Sample plots were located at distances of 2, 3, and 5 km E of the emission source and a control sample plot was selected on an unpolluted territory 38 km W of it. We studied soil properties and the anatomical structure, mineral nutrition, and pigments in Scots pine needles. The alkaline dust pollution has affected the biogeochemical cycling in the forest ecosystem, increasing the pH and total Ca, K, Fe, Mn, and Mg and decreasing N, C, organic matter, and C/N compared to the unpolluted soils. Alkalization and changes in the nutrient composition of soil had caused serious disbalances in nutrient availability and in the mineral composition of trees. Deficiency in foliar N and Mn and excess of K, Ca, and Fe contents had caused a decrease in the average chlorophyll concentrations. Carotenoids seemed to be more tolerant both to changes in soil and needle nutrient composition. The Chl a/Chl b ratio in needles was found to have declined. With the alkalization of the environment the total area of the needle cross-section, needle thickness, and mesophyll area had also decreased compared with control. Differences in the anatomical characteristics of needles between the polluted and unpolluted areas were significant in the oldest needles. The decrease of mesophyll was associated with the content of chlorophylls and correlated with N concentrations in needles.

Effects of different forms of soil disinfection on soil physical properties and cucumber growth

Experiments were conducted to study the effects of three soil disinfection methods (ridge and furrow soil solarization with plastic film mulch, calcium cyanamid with stalk, dazomet fumigation) on soil physical properties and the growth of cucumber in greenhouse conditions. The results show that ridge and furrow solarization with plastic film mulch has no visible effect on soil physical properties. While the content of coarse silt decreases by 9.5% compared to CK, the contents of two diameter of sands (0.1～0.5 mm, 0.5～1.0 mm) increase by 39.4%, 117.7% respectively compared to CK. No significant changes are noted in the re-maining components. The content of clay in soil treated with calcium cyanamid and stalk increases by 163%, the contents two di-ameter of fine silts (0.001～0.005 mm, 0.005～0.01 mm) increase by 52.1%, 116.8% respectively compared to CK. Clay content of soil treated by dazomet fumigation decreases by 65.8%, the contents of two diameter of fine silt in soil decrease by 33.0%, 32.2% respec-tively compared to CK. Different soil disinfection treatments exert different inhibitions on soil aggregation. Calcium cyanamid with stalk treatment is most effective, followed by dazomet fumigation treatment. Ridge and furrow soil solarzation with plastic film mulch is least effective. The three soil disinfection treatments increase average plant height, leaf number, chlorophyll content and yield of cucumber. Ridge and furrow soil solarization with plastic film mulch not only significantly increases the biological indices of cucumber, but also promotes cucumber yield.

Microbial processes in a high-latitude fjord (Kongsfjorden, Svalbard): II. Ciliates and dinoflagellates

The composition and ecological role of ciliates and dinoflagellates were investigated at one station in Kongsfjorden, Svalbard, during six consecutive field cam- paigns between March and December 2006. Total ciliate and dinoflagellate abundance mirrored the seasonal progression of phytoplankton, peaking with 5.8 9 10 4 cells l -1 in April at an average chlorophyll a concentration of 10 l gl -1 . Dinoflagellates were more abundant than ciliates, dominated by small athecates. Among ciliates, aloricate oligotrichs dominated the assemblage. A large fraction ((60%) of cil- iates and dinoflagellates contained chloroplasts in spring and summer. The biomass of the purely heterotrophic fraction of the ciliate and dinoflagellate community (protozooplankton) was with 14 l gCl -1 highest in conjunction with the phytoplankton spring bloom in April. Growth experiments revealed similar specific growth rates for heterotrophic cil- iates and dinoflagellates (\0-0.8 d -1 ). Food availability may have controlled the protozooplankton assemblage in winter, while copepods may have exerted a strong control during the post-bloom period. Calculations of the potential grazing rates of the protozooplankton indicated its ability to control or heavily impact the phytoplankton stocks at most times. The results show that ciliates and dinoflagellates were an important component of the pelagic food web in Kongs- fjorden and need to be taken into account when discussing the fate of phytoplankton and biogeochemical cycling in Arctic marine ecosystems.

Distribution of quagga mussel veligers, Dreissena bugensis, in the reservoirs of the Colorado River Aqueduct

This study examined the distribution of quagga mussel veligers, Dreissena bugensis, in Copper Basin Reservoir and Lake Mathews, the 2 deepest reservoirs on the Colorado River Aqueduct system in California. Density stratification, driven by temperature differences, was a critical factor in controlling vertical distribution of veligers within the water column. Copper Basin Reservoir had the strongest stratification from May to August, with veliger concentrations higher than 80/L near the thermocline but much lower in the epilimnion and hypolimnion. Veliger concentrations were also elevated near the thermocline in Lake Mathews in late summer 2008 and spring 2009, although operation of a bubble aeration system later in 2009 eliminated the strong thermocline and may have influenced veliger abundance generally present there. Average chlorophyll a concentrations were low (<5 μg/L) in both reservoirs, although an increase in chlorophyll a concentration (to ∼10 μg/L) was observed within the spring thermocline in Lake Mathews; a chlorophyll a maximum near the thermocline was not present in Copper Basin Reservoir. These observations suggest that stratification, and not chlorophyll a concentration, determined the vertical distribution of veligers. The thermocline is a zone of increasing density that often concentrates particles. Statistically significant horizontal gradients in veliger concentrations were absent, suggesting that lateral currents mix and distribute veligers across these basins.