Yosef Z. Yacobi

Estimation of chlorophyll a from time series measurements of high spectral resolution reflectance in an eutrophic lake

We acquired high spectral resolution reflectance data in Carter Lake, a eutrophic oxbow on the Iowa–Nebraska border, from April 1995 to April 1996. Chlorophyll a, total seston, sestonic organic matter, Secchi depth, and nephelometric turbidity were determined for each respective spectral measurement. Changes in algal taxonomic structure and abundance coincided with the development and senescence of a midsummer through autumn bloom of Anabaena. Taxonomic structure was more diverse in late winter and spring when Synedra sp. (diatom) and several chlorophytes and dinoflagellates were present. Overall, chlorophyll a varied from about 20 to 280 μg·L−1, Secchi transparency from 18 to 74 cm, and seston dry weight from 11 to 48 mg·L−1 in February and September, respectively. Particulate matter completely dominated lake water light attenuation. Dissolved organic matter had low optical activity. The most sensitive spectral feature to variation in chlorophyll a concentration was the magnitude of the scattering peak near 700 nm. The 700‐nm peak correlated to chlorophyll concentration through the relationships between algal pigment absorption near 670 nm and the cell biomass and surface‐related scattering signal in the near infrared. An algorithm relating the height of the 700‐nm reflectance peak above a reference baseline between 670 and 850 nm to chlorophyll a was accurate and robust despite large variations in optical constituents caused by both strong seasonality in the algal system and short‐term variations in seston from wind‐induced sediment resuspension. The present algorithms were successfully used in other systems with different seasonality and productivity patterns. The coefficients of the models relating chlorophyll a and spectral reflectance variables appeared to be ecosystem specific: both the intercept and slope for the models in this study were moderately lower than for several other recently published results. We validated our algorithm coefficients with a second, independent dataset. The standard error for chlorophyll a prediction was ±28 μg·L−1.

Chlorophyll distribution throughout the southeastern Mediterranean in relation to the physical structure of the water mass

The spatial distribution of chlorophyll was recorded throughout the southern part of the Levantine Basin of the eastern Mediterranean and was related to patterns of the physical structure and nutrient concentrations. Chlorophyll a concentration in the upper 200 m of the water column ranged from 9.2 to 423 ng l−1, with an overall mean of 126 ± 85.6 (SD) ng l−1. The pattern of vertical distribution of chlorophyll was close to uniform throughout the basin, with a prominent deep chlorophyll maximum (DCM) of ca. 250 ng l−1 at 90–110 m. The values we report fall at the lower end of ranges reported from other oligotrophic seas, in accordance with the ultra-oligotrophic nature of the eastern Mediterranean. Throughout the basin more than 90% of the chlorophyll at the surface was confined to particles < 10 μ in diameter and more than 60% was found in particles < 2 μ. The proportion of chlorophyll in < 2 μ particles increased with depth between the surface and the DCM, as was also confirmed by flow cytometric analysis. Discontinuities of physical and chemical features were mostly confined to depths greater than 200 m, and had little impact on the distribution of chlorophyll. An exception was an anti cyclonic eddy south of Crete, within which chlorophyll (mostly > 100 μg l−1) was more evenly distributed with depth over the upper 200 m.

Chlorophyll distribution in Lake Kinneret determined from Landsat Thematic Mapper data

Abstract Chlorophyll distribution in Lake Kinneret was estimated at a time of low chlorophyll concentrations (3-7 mgm−3). Landsat Thematic Mapper (TM) data were acquired three days after the acquisition of high spectral resolution radiometric measurements in the range 400 to 750 nm, chlorophyll and suspended matter concentrations, and Secchi disk transparency at 22 stations. The radiometric data were used to create an algorithm for estimation of chlorophyll concentration from the TM data. The radiance in channel TM3 (620-690 nm) was primarily dependent upon non-organic suspended matter concentration. Radiance in this channel was substracted from radiance in TM1 (450-520 nm) to correct for the additional radiance caused by scattering of non-pigmented suspended particles and (TM1 – TM3)/TM2 was found to be a useful index for estimating chlorophyll concentration. The concentrations calculated from atmospherically corrected TM data were compared to chlorophyll extracted from lake water samples. The estimation...

NIR-red reflectance-based algorithms for chlorophyll-a estimation in mesotrophic inland and coastal waters: Lake Kinneret case study

A variety of models have been developed for estimating chlorophyll-a (Chl-a) concentration in turbid and productive waters. All are based on optical information in a few spectral bands in the red and near-infra-red regions of the electromagnetic spectrum. The wavelength locations in the models used were meticulously tuned to provide the highest sensitivity to the presence of Chl-a and minimal sensitivity to other constituents in water. But the caveat in these models is the need for recurrent parameterization and calibration due to changes in the biophysical characteristics of water based on the location and/or time of the year. In this study we tested the performance of NIR-red models in estimating Chl-a concentrations in an environment with a range of Chl-a concentrations that is typical for coastal and mesotrophic inland waters. The models with the same spectral bands as MERIS, calibrated for small lakes in the Midwest U.S., were used to estimate Chl-a concentration in the subtropical Lake Kinneret (Israel), where Chl-a concentrations ranged from 4 to 21 mg m(-3) during four field campaigns. A two-band model without re-parameterization was able to estimate Chl-a concentration with a root mean square error less than 1.5 mg m(-3). Our work thus indicates the potential of the model to be reliably applied without further need of parameterization and calibration based on geographical and/or seasonal regimes.

Comparative reflectance properties of algal cultures with manipulated densities

A comparative study was conducted with representatives of four ecologically important freshwater algal phyla (Chlorophyta, Cyanophyta, Bacillariophyta and Pyrrophyta) in order to (1) analyze the relationship between reflectance spectral features and algal density, and (2) to elucidate and characterize possible diagnostic spectral reflectance features for identification of dominant groups in algal bloom states. Algae (two chlorophytes, a cyanophyte and a bacillariophyte) were cultured in mesocosm tanks and then their densities were reduced through dilution with clear water in four experiments. In a fifth experiment, use was made of the pyrrophyte Peridinium gatunense, which bloomed in Lake Kinneret, Israel, practically forming a unialgal ‘culture’. The basic quantitative procedures for spectroradiometeric measurements and support data collection (pigment concentrations) were consistent among the experiments. Several spectral reflectance characteristics were found to be common to all the species examined in the study: a depression between 440 and 500 nm, a salient trough around 670 nm, and prominent peaks centered around 570 nm and 700 nm. The increase in magnitude of a near infra-red peak and shift of its position towards longer wavelengths with increased chlorophyll- a concentration was found to be a common trait for all the species studied. Other specific spectral reflectance features were also found and are discussed here. Quantitatively different relationships of magnitude and position of spectral reflectance features with chlorophyll- a concentration reflect different optical properties of algae (their scattering and absorption). This may be useful for taxonomic characterization by remote sensing.

Chlorophyll estimation in the Southeastern Mediterranean using CZCS images: adaptation of an algorithm and its validation

Abstract Region-specific algorithm to derive chlorophyll concentration from Coastal Zone Color Scanner (CZCS) images was adopted following field measurements in the Southeastern Mediterranean Sea, in June 1992. Reflectance in the range 400 to 700 nm, chlorophyll concentration and seston dry weight were measured simultaneously at 21 stations. The optical model used based on algorithm for Case I waters, using shipboard simulation of CZCS channels for adaptation of parameters. The resulting model was validated with an independent data sets from series of cruises in the Southeastern Mediterranean (1981–1984). Concurrent CZCS images were used for retrieval of the radiance ratio Channel 1/Channel 3, for each station. The resulting ratios were then used to calculate chlorophyll concentrations. A comparison between those calculated concentrations and the actual chlorophyll measurements showed that an estimation error of chlorophyll as low as 0.013 mg m −3 was achieved.

Synoptic Measurements of Chlorophyll-a and Suspended Particulate Matter in a Transitional Zone from Polluted to Clean Seawater Utilizing Airborne Remote Sensing and Ground Measurements, Haifa Bay (SE Mediterranean)

Abstract The hyperspectral Compact Airborne Spectrographic Imager (CASI) sensor was implemented to monitor water quality in a transitional zone from polluted to clean seawater, in Haifa Bay and adjacent river estuaries, at the northern part of the Mediterranean coast of Israel. Synoptic measurements of optical data acquired from the airborne scanner were used to map chlorophyll- a (chl- a ) and suspended particulate matter (SPM) concentrations in surface waters in the study area. This airborne hyperspectral scanner was found as an expedient monitoring tool for the relatively small geographic area of the current study, as it enabled to reveal the patchy distribution, and sharp concentration changes of the mapped water characteristics. The distribution of SPM concentrations in Haifa Bay was mainly dictated by the polluted riverine inputs, with concentrations between 1 and 3 mg l −1 at its seaward border and higher by more than 1 order of magnitude at the river estuaries. The chl- a concentrations mapped and measured in this survey were unusually low ( −1 ) due to a long-period intermission of anthropogenic phosphate and nitrate input to the bay. SPM and chl- a spatial distributions along the lower rivers system exhibit variations which could be plausibly explained by the hydrological structure and geochemical impacts on the riverine water sources. The correlation between SPM and some particulate heavy metal concentrations was found as a useful tool for monitoring such environmental hazardous substances.

Seawater quality and microbial communities at a desalination plant marine outfall. A field study at the Israeli Mediterranean coast.

Global desalination quadrupled in the last 15 years and the relative importance of seawater desalination by reverse osmosis (SWRO) increased as well. While the technological aspects of SWRO plants are extensively described, studies on the environmental impact of brine discharge are lacking, in particular in situ marine environmental studies. The Ashqelon SWRO plant (333,000 m(3) d(-1) freshwater) discharges brine and backwash of the pre-treatment filters (containing ferric hydroxide coagulant) at the seashore, next to the cooling waters of a power plant. At the time of this study brine and cooling waters were discharged continuously and the backwash discharge was pulsed, with a frequency dependent on water quality at the intake. The effects of the discharges on water quality and neritic microbial community were identified, quantified and attributed to the different discharges. The mixed brine-cooling waters discharge increased salinity and temperature at the outfall, were positively buoyant, and dispersed at the surface up to 1340 m south of the outfall. Nutrient concentrations were higher at the outfall while phytoplankton densities were lower. Chlorophyll-a and picophytoplankton cell numbers were negatively correlated with salinity, but more significantly with temperature probably as a result of thermal pollution. The discharge of the pulsed backwash increased turbidity, suspended particulate matter and particulate iron and decreased phytoplankton growth efficiency at the outfall, effects that declined with distance from the outfall. The discharges clearly reduced primary production but we could not attribute the effect to a specific component of the discharge. Bacterial production was also affected but differently in the three surveys. The combined and possible synergistic effects of SWRO desalination along the Israeli shoreline should be taken into account when the three existing plants and additional ones are expected to produce 2 Mm(3) d(-1) freshwater by 2020.

Carbon:chlorophyll a ratio, assimilation numbers and turnover times of Lake Kinneret phytoplankton

Carbon to chlorophyll a (C:Chl) ratios, assimilation numbers (A.N.) and turnover times of natural populations of individual species and taxonomic groups were extracted from a long-term database of phytoplankton wet-weight biomass, chlorophyll a concentrations, and primary production in Lake Kinneret, Israel. From a database spanning more than a decade, we selected data for samples dominated by a single species or taxonomic group. The overall average of C:Chl was highest for cyanophytes and lowest for diatoms, while chlorophytes and dinoflagellates showed intermediate values. When converting chlorophyll a to algal cellular carbon this variability should be taken into account. The variability in C:Chl within each phylum and species (when data were available) was high and the variability at any particular sampling date tended to be greater than the temporal variability. The average chlorophyll a-normalized rate of photosynthetic activity of cyanophytes was higher and that of the dinoflagellates lower than that of other phyla. Turnover time of phytoplankton, calculated using primary productivity data at the depth of maximal photosynthetic rate, was longest in dinoflagellates and shortest in cyanophytes, with diatoms and chlorophytes showing intermediate values. The more extreme C:Chl and turnover times of dinoflagellates and cyanobacteria in comparison with chlorophytes and diatoms should be taken into consideration when employed in ecological modeling.

High performance liquid chromatography detection of phototrophic bacterial pigments in aquatic environments

Pigment extracts of phototrophic bacteria isolated from Lake Kinneret (Rhodopseudomonas palustris, Thiocapsa roseopersicina, Prosthecochloris aestuaris andChlorobium phaeobacteroides) were studied by means of high performance liquid chromatography (HPLC). An absorption wavelength of 360 nm provided the best resolution among the pigments of the species tested and between them and chlorophylla. Signature pigments were identified for each of these species, and their presence was thereby monitored in lake water samples.C. phaeobacteroides, which was observed in the anaerobic hypolimnion and predominated in the metalimnion, was recognized by a characteristic cluster of major chlorophyllous pigment peaks. The spectral qualities of these pigments were close but not identical to published data on bacteriochlorophylle, presumably due to the use of different solvents for extraction. The intensity of these pigment peaks was employed to determine the depth of the greatest phototrophic bacterial biomass, which was not related to that of algae.