Variability Of Chl Research Articles

Seasonal appearance of Chlorophyceae phytoplankton bloom by river discharge off Paradeep at Orissa Coast in the Bay of Bengal

Characteristics of the monsoonal bloom of phytoplankton at Orissa Coast in the Bay of Bengal were studied through bimonthly observation from April 2001 to December 2002. Three photosynthetic pigments chlorophyll-a (Chl a), chlorophyll-b (Chl b) and carotenoid (Car) were analyzed by absorption spectroscopic method. The seasonal variation of Chl a included phytoplankton bloom in the coastal area during monsoon period. The water column integrated Chl a reached to 68 mg m(-2) at the station-1(St1), and amounted to 20 mg m(-2) at 30 km off the river mouth during August 2001. In contrast the same amount was found at 15 km off the Mahanadi river mouth during August 2002. Salinity during this period varied from 5 psu at the St1 to 27 psu at the edge of the bloom area. The total amount of river discharge in the monsoon period calculated from daily river discharge data reported by Water Resources Department in India was 84 x 10(9) m(3) during 2001 and 20 x 10(9) m(3) during 2002. Both nitrate and phosphate concentrations showed negative quadratic relationship with salinity throughout the observation period. Extrapolated nitrate and phosphate concentration discharge from the Mahanadi river were 10.8 and 4 microg-at l(-1), respectively. Microscopic identification revealed dominance of fluvial Chlorophyceae and diatoms during the monsoon period showing influence of the freshwater discharge.

Generalised model of primary production in the southern Benguela upwelling system

We provide a proof-of-concept demonstration using a novel method for estimating depth-integrated distributions of chlorophyll from archives of data from ships, buoys or gliders combined with remotely sensed data of sea surface temperature (SST) and surface chlorophyll a (chl a) from satellites. Our area of application has contrasting hydrographic regimes, which include the dynamic southern Benguela upwelling system and the stratified waters of the Agulhas Bank, South Africa. The method involves using self-organising maps (SOMs), a type of artificial neural network, to identify 'typical' chl a profiles regardless of their statistical form, provided several of a similar shape have been found in the training set. These are arranged in a linear array, ranging from uniform profiles low in chl a to profiles with high surface or subsurface peaks. We then use generalised modelling to relate these characteristic profiles to remotely sensed surface features, viz. surface chl a and SST, as well as area, season, and water depth (a proxy for distance offshore). The model accounts for 87% of the variability in chl a profile and is used to predict the type of profile likely for each pixel in monthly remote sensing composites of SST and surface chl a and then to estimate integrated chl a and primary production with the aid of a light model. Primary production peaks in mid-summer, reaching 5 mgC m(-2) d(-1) locally, with an average over the whole area and all seasons of 1.4 mg C m(-2) d(-1). Seasonal variation is greatest in the southern part of the west coast, and lowest in the stratified southeast. Annual primary production for the southern Benguela region including the Agulhas Bank is ca. 156 million tC yr(-1). This is the most robust estimate of primary production in the Benguela system to date because it combines the spatial and temporal coverage provided by remote sensing with realistic vertical chl a profiles.

Satellite-data-based study of seasonal and spatial variations of water temperature and water quality parameters in Lake Ladoga

A satellite sensor nonspecific operational advanced algorithm is developed to simultaneously retrieve the concentrations of phytoplankton chlorophyll (chl), dissolved organics (doc) and suspended minerals (sm) in turbid and strongly absorbing natural waters (i.e., case II waters). Also, a new interpolation procedure is developed and used jointly with the advanced bio-optical and standard window-split algorithms to generate from SeaWiFS and AVHRR data the time series of spatial and temporal (seasonal and interannual) variations of chl, sm, doc and water surface temperature (TS) for the period 1998-2004 in Lake Ladoga, the largest European fresh water body. Obtained for the first time, the spaceborne fields of the above variables have revealed at an unprecedented time and space resolution some intrinsic features and interdependence of thermal and biogeochemical processes in the lake. Rates of thermobar displacement from the littoral zone to the central deep water area are quantified during periods of lake warming and cooling. From spring to mid-summer, the dynamics of phytoplankton biomass spatial distribution are evidenced to follow the retraction of the cold water zone bordered by the thermobar. Importantly, along with the thermobar dynamics, the zones of the most enhanced phytoplankton concentration are concurrently governed by the lake bathymetry, and thus gradually move from south to north along the eastern coast line. Brought with fluvial input, suspended minerals and allochthonous dissolved organics are not only restricted to the zones of major river deltas but also driven northward by coastal cyclonic currents prevailing in Lake Ladoga. The obtained space data allows the interplay of the above factors to be explicitly revealed and explains the observed interannual variations in the surficial expressions of biogeochemical processes inherent in Lake Ladoga.

Comparison of chlorophyll algorithms in the bohai sea of China

Empirical band-ratio algorithms and artificial neural network techniques to retrieve sea surface chlorophyll concentrations were evaluated in the Bohai Sea of China by using an extensive field observation data set. Bohai Sea represents an example of optically complex case II waters with high concentrations of colored dissolved organic matter (CDOM). The data set includes coincident measurements of radiometric quantities and chlorophyll a concentration (Chl), which were taken on 8 cruises between 2003 and 2005. The data covers a range of variability in Chl in surface waters from 0.3 to 6.5 mg m-3. The comparison results showed that these empirical algorithms developed for case I and case II waters can not be applied directly to the Bohai Sea of China, because of significant biases. For example, the mean normalized bias (MNB) for OC4V4 product was 1.85 and the root mean square (RMS) error is 2.26.

Reply to comment by Jinchun Yuan et al. on “Reduction of primary production and changing of nutrient ratio in the East China Sea: Effect of the Three Gorges Dam?”

[1] A brief discussion is presented here in response to Yuan et al.’s [2007] comment on our paper entitled ‘‘Reduction of primary production and changing of nutrient ratio in the East China Sea: Effect of the Three-Gorges Dam?’’ [Gong et al., 2006]. [2] First, we would like to point out that our research provides sufficient seasonal variations using accurate chlorophyll a (Chl a) data in the traditionally nutrient-rich (TNR) region of the East China Sea, as determined in several previous high-frequency sea-based investigations [Gong et al., 1996, 2003, 2006]. In contrast, Yuan et al. [2007] used questionable Chl a data (derived from the SeaWiFS OC4 algorithm: see second point) to study the inter-annual variations in Chl a in the entire East China Sea. This is clearly apparent in Figure 1 which illustrates the comparison between our average sea-based Chl a concentrations in the entire East China Sea (solid brown stars in Figure 1) and the SeaWiFS-derived Chl a data reported in Figure 2 of Yuan et al.’s comment. The results show that the SeaWiFS-derived Chl a data were substantially higher than our sea-based Chl a data. There can be no question that Yuan et al.’s [2007] data were invalid. [3] Second, we further question the accuracy of the SeaWiFS-derived Chl a data for the East China Sea which were used in Yuan et al.’s [2007] comments. Our reasons are as follows: [4] (1) It is widely believed that the standard SeaWiFSOC4 chlorophyll algorithm is only valid for ‘‘Case 1 waters’’ [O’Reilly et al., 1998; Carder et al., 1999]. But this type of global algorithm is flawed when it comes to ‘‘Case 2 waters’’ [Mueller and Austin, 1995; International Ocean-Colour Coordinating Group, 2000; Liew et al., 2001; Gong, 2004]. The key reason for the algorithmic failure in the case of ‘‘Case 2 waters’’ is that there is interference from the strong absorption of colored dissolved organic matter (CDOM) in the blue band that overlaps with phytoplankton chlorophyll absorption. When the absorption coefficient due to colored dissolved organic matter at 380 nm (acdom(l = 380 nm)) is greater than 0.1 m 1 [Mueller and Austin, 1995], the ocean waters are regarded as ‘‘Case 2 waters’’, and the use of the global satellite ocean-color OC4 algorithm is inappropriate. But unfortunately, Yuan et al. [2007] used the OC4 algorithm to process their Chl a data for the East China Sea, a region with ‘‘Case 2 waters.’’ [5] (2) O’Reilly et al. [1998] collected a large data set including coincident in-situ chlorophyll and remote sensing information to evaluate the performance of a wide variety of ocean color chlorophyll algorithms for SeaWiFS data. One of their conclusions is that, while the performance of the OC4 was superior to that of the OC2, it is not as suitable as the initial operational algorithm for SeaWiFS-derived Chl a data because its use requires accurate atmospheric correction and on-orbit calibrations in four bands (instead of two). They explain that this can only be assessed after the collection of sufficient data to validate and fine-tune sensor calibrations. It is currently widely known that atmospheric pollution in the shelf area of the East China Sea is very serious because of rapid industrial development in the coastal cities of China. Additionally, the high frequency of Asian dust storms has been observed in the East China Sea. As a result, the SeaWiFS-derived Chl a data are not likely very accurate without proper atmospheric correction. A second conclusion by O’Reilly et al. [1998] is that ‘‘Case 2 waters’’ present additional complications and challenges as their properties change depending on whether they are dominated by CDOM, nochlorophyllous particles, or a variable mix of both [Carder et al., 1989]. In short, specific algorithms or different parameterizations are required to process data from different regions. [6] (3) Gong [2004] presented CDOM data for four seasons from surface waters of the entire East China Sea. These data showed that the values of acdom(l = 325 nm) were higher than 0.2 m 1 (equivalent to acdom(l = 380 nm) = 0.1 m ) for most of the shelf waters year-round (Figure S1 of the auxiliary material). Figure S1 clearly shows that the values of acdom(l = 380 nm) in the TNR region are always higher than 0.1 m . These results support the optical classification of the TNR region as ‘‘Case 2 waters.’’ Additionally, a significant overestimation of the SeaWiFS-derived Chl a concentrations (2.3 mg m ) at a station located about 200 km east off the Changjiang River mouth (see star-symbol in Figure S1a) was found in

Ship-of-opportunity based phycocyanin fluorescence monitoring of the filamentous cyanobacteria bloom dynamics in the Baltic Sea

Distribution of cyanobacteria cannot be evaluated using chlorophyll a (Chl a) in vivo fluorescence, as most of their Chl a is located in non-fluorescing photosystem I. Phycobilin fluorescence, in turn, is noted as a useful tool in the detection of cyanobacterial blooms. We applied phycocyanin (PC) fluorometer in the monitoring of the filamentous cyanobacterial bloom in the Baltic Sea. For the bloom forming filamentous cyanobacteria Aphanizomenon flos-aquae and Nodularia spumigena, PC fluorescence maximum was identified using the excitation–emission fluorescence matrix. Consequently, the optical setup of our instrument was noted to be appropriate for the detection of PC, and with minor or no interference from Chl a and phycoerythrin fluorescence, respectively. During summer 2005, the instrument was installed on a ferryboat commuting between Helsinki (Finland) and Travemünde (Germany), and data were collected during 32 transects providing altogether 200 000 fluorescence records. PC in vivo fluorescence was compared with Chl a in vivo fluorescence and turbidity measured simultaneously, and with Chl a concentration and biomass of the bloom forming filamentous cyanobacteria determined from discrete water samples. PC fluorescence showed a linear relation to the biomass of the bloom forming filamentous cyanobacteria, and the other sources of PC fluorescence are considered minor in the open Baltic Sea. Estimated by PC fluorescence, cyanobacterial bloom initiated late June at the Northern Baltic Proper, rapidly extended to the central Baltic Proper and the Gulf of Finland, and peaked in the mid-July with values up to 10 mg l −1 (fresh weight). In late July, bloom vanished in most areas. During single transects, or for the whole summer, the variability in Chl a concentrations was explained more by PC fluorescence than by Chl a fluorescence. Thus, filamentous cyanobacteria dominated the overall variability in phytoplankton biomass. Consequently, we show that during the cyanobacterial blooms, the estimation of Chl a concentration using only Chl a in vivo fluorescence is not applicable, but PC in vivo fluorescence is required as a predictor as well.

Remote chlorophyll- a retrieval in turbid, productive estuaries: Chesapeake Bay case study

Accurate remote assessment of phytoplankton chlorophyll a (chl a) concentration is particularly challenging in turbid, productive waters. Recently a conceptual model containing reflectance in three spectral bands in the red and near infra-red range of the spectrum was suggested for retrieving chl a concentrations in turbid productive waters; it was calibrated and validated in lakes and reservoirs in Nebraska and Iowa. The objective of this paper is to evaluate the performance of this three band model as well as its special case, the two-band model to estimate chl a concentration in Chesapeake Bay, as representative of estuarine Case II waters, and to assess the accuracy of chl a retrieval. To evaluate the model performance, dual spectroradiometers were used to measure subsurface spectral radiance reflectance in the visible and near infra-red range of the spectrum. Water samples were collected concurrently and contained widely variable chl a (9 to 77.4 mg/m 3) and total suspended solids (7–65 mg/L dry wt). Colored dissolved organic matter (CDOM) absorption at 440 nm was 0.20 to 2.50 m − 1 ; Secchi disk transparency ranged from 0.28 to 1.5 m. The two- and three-band models were spectrally tuned to select the spectral bands for most accurate chl a estimation. Strong linear relationships were established between analytically measured chl a and both the three-band model [ R − 1 (675)– R − 1 (695)] × R(730) and the two-band model R(720)/ R(670), where R( λ) is reflectance at wavelength λ. The three-band model accounted for 81% of variation in chl a and allowed estimation of chl a with a root mean square error (RMSE) of less than 7.9 mg/m 3, whereas the two-band model accounted for 79% of chl a variability and RMSE of chl a estimation was below 8.4 mg/m 3. The three-band model with MERIS spectral bands allows accurate chl a estimation with RMSE below 9.1 mg/m 3. Two-band model with SeaWiFS bands and MODIS 667 nm and 748 nm bands can estimate chl a with RMSE below 11 mg/m 3. The findings underlined the rationale behind the conceptual model and demonstrated the robustness of this algorithm for chl a retrieval in turbid, productive estuarine waters.

VALVE-GAPE RESPONSE TIMES IN MUSSELS (MYTILUS EDULIS)-EFFECTS OF LABORATORY PRECEDING-FEEDING CONDITIONS AND IN SITU TIDALLY INDUCED VARIATION IN PHYTOPLANKTON BIOMASS

Many physiological processes in bivalves are influenced by the valve opening sate and thus the valve opening-closing response times of the experimental animals. Controlled laboratory studies using underwater video camera recording of valve-gape responses of mussels (Mytilus edulis) to presence or absence of algal cells in the ambient water have revealed that valve opening and closing responses are strongly influenced by the preceding feeding conditions. The observations indicate that the period during which mussels may “learn” or “forget” to respond to the presence or absence of algal cells can last for weeks in the laboratory. Further, the critical algal concentration below which mussels close their valves has been identified to be about 700 Rhodomonas sp. cells mL−1, or 0.9 μg chl a L−1. Such knowledge is essential for making allowance for possible deviation from natural-response times in mussels kept in the laboratory previous to experimental physiological studies. In situ simultaneous registrations of water flow, chl a and valve-opening degree of mussels were made within a dense mussel bed in a shallow, tidally dominated inlet to a Danish fjord. Phases of strong tidal flow brought ample supply of phytoplankton to the mussel bed, and it was observed that concentrations higher than about 1 μg chl a L−1 in the near-bed layer stimulated the mussels to keep their valves wide open, whereas tidal slack with slow flow resulting in near-bed concentrations below 1 μg chl a L−1 caused by grazing by the mussels, after some time led to shell closure, or reduced valve gapes of the mussels. The valve opening time from opening degree 50% to 100% and the valve closing time from opening degree 100% to 50% in response to variation in near-bed chl a concentration were on average 59 ± 22 and 50 ± 19 min, respectively, which is considerably faster than observed in unfed mussels in the laboratory.

Responses of the green algal foliose lichen Platismatia glauca to increased nitrogen supply

Nitrogen (N) availability and light exposure were manipulated under field conditions to study responses to altered resource supply in the green algal lichen Platismatia glauca. The lichen was fertilized with different concentrations and frequencies of ammonium, nitrate or glutamine under different light regimes for 2-3 months. Responses were followed from the intact thallus to the cellular level. Despite significant differences in overall light exposure, light conditions were not significantly different among treatments when the lichens were wet and active. Ammonium was the preferred N source, followed by glutamine and then nitrate. Thallus N concentration as well as the chlorophyll a (Chl a) concentration increased 3-4-fold at the highest ammonium concentration, while the mycobiont ergosterol concentration remained unaltered. Growth was significantly enhanced by the enhanced N supply, with the increase in dry weight varying from 3 to 30%. Variation in Chl a concentration explained 31% of this variation, suggesting a causal link to the increased growth rate. Platismatia glauca responded to increased N availability by increasing its growth rate and carbon assimilation capacity through increased investments in the photobiont cells. This suggests a tight regulation of resource investments and metabolic pathways between the symbionts of this lichen.

Tidal resuspension of microphytobenthic chlorophyll a in a Nanaura mudflat, Saga, Ariake Sea, Japan: flood–ebb and spring–neap variations

The resuspension of microphytobenthic chlorophyll a (chl a) and suspended particulate matter (SPM) from the upper intertidal flat was studied at Nanaura, Ariake Sea, Japan, and a spatial comparison of chl a and SPM in the northern Ariake Sea is presented here. A 15 d time series of chl a and SPM records (measured at 15 cm above the bottom) revealed that resuspension was clearly asso- ciated with flood-ebb and spring-neap tidal characteristics, where significant resuspension was found during early flood, particularly in the high-energy period (viz. spring tide). The peaks of resus- pended chl a and SPM during 28 tidal periods were observed to consistently occur shortly after the current velocity reached a maximum and when the threshold current velocity was found to be ca. 15 cm s -1 . Much more highly fluctuating, irregular peaks of chl a and SPM were occasionally observed, these were attributable to high wind speeds, ≥3 m s -1 . Computation of chl a and SPM fluxes showed clear spring-neap variation, and time-integrated fluxes denoted predominant offshore residual transport during the observation period. Benthic chl a measured in the surficial sediment (top 0.5 cm) during 13 exposure periods showed a decreasing trend from spring to neap tide, similar to spring-neap variations of chl a in the water column during the semi-lunar tidal period. The daily mean percentage of resuspended chl a in the water column relative to the amount of benthic chl a was estimated to be ca. 10 to 70% (mean = 33%), implying that a certain portion of the microphyto- benthos is resuspended during high tide and partly contributes to the total biomass in the water column of the upper intertidal flat.

Remote estimation of chlorophyll concentration in hyper-eutrophic aquatic systems: Model tuning and accuracy optimization

Accurate assessment of phytoplankton chlorophyll a (chl a) concentration by remote sensing is challenging in turbid hyper-eutrophic waters. This paper assessed methods to resolve this problem. A hand-held spectroradiometer was used to measure subsurface spectral reflectance ( R) in the visible and near infrared range of the spectrum. Water samples were collected concurrently and contained variable chlorophyll a concentration (chl a from 107 to more than 3000 mg/m 3) and turbidity (from 11 to 423 NTU) levels. The conceptual three-band model [ R − 1 ( λ 1) − R − 1 ( λ 2)] × R( λ 3) and its special case, the two-band model R( λ 3)/ R( λ 1), were spectrally tuned in accord with optical properties of the media to optimize spectral bands ( λ 1, λ 2 and λ 3) for accurate chlorophyll a estimation. Strong linear relationships were established between analytically measured chl a and both the three-band [ R − 1 (650) − R − 1 (710)] × R(740) and the reflectance ratio model R(714)/ R(650). The three-band model accounted for 7% more variation of chl a concentration than the ratio model (78 vs. 71%). Assessment of the model accuracy in dense algal blooms is hampered by the spatial and temporal inhomogeneity of algal distributions—in these waters, non-random algal distributions accounted for more than 20% spatial and up to 8% temporal variation in chlorophyll a concentration. The findings underlined the rationale behind the conceptual model and demonstrated the robustness of the algorithm for chl a retrieval in very turbid, hyper-eutrophic waters.

Top down control from the bottom: Regulation of eutrophication in a large river by benthic grazing

We use a 15‐yr record from a 100‐km stretch of the tidal, freshwater Hudson River to examine the controls of phytoplankton biomass. Across years, seasonal mean chlorophyll a (Chl a) and maximum Chl a varied by approximately 15‐fold, with mean growing‐season Chl a as high as 24 mg L−1 and maximum Chl a as high as 120 mg L−1. For 3 of the 15 yr the river would be classified as eutrophic on the basis of lake standards for Chl a. Year‐toyear variation in Chl a was not closely related to either nutrients (phosphorus or nitrogen concentrations) or hydrologic flow. Annual variation in grazing by the invasive zebra mussel (Dreissena polymorpha) explained 90% of the variation in mean Chl a; however, the maximum Chl a reached during the growing season was not significantly related to grazing and, even with high grazing, blooms of phytoplankton that contained high proportions of potentially toxic cyanobacteria occurred. Further, zebra mussels decreased dissolved oxygen concentrations even while increasing production of submersed aquatic vegetation. The results from the Hudson add to a growing literature that suggests that ecosystem changes linked with high phytoplankton biomass depend on a diverse range of system characteristics as well as whether phytoplankton are controlled by top‐down or bottom‐up mechanisms

Chlorophyll content and fluorescence responses cannot be used to gauge reliably phytoplankton biomass, nutrient status or growth rate

To consider the relationship between chlorophyll a (Chl a) content and phytoplankton growth and nutrient status, four phytoplankton species were grown in nitrogen (N)-limited [and, for one species, phosphorus (P)-limited] culture and measurements were made of CNP biomass, in vivo and in vitro Chl a content, the ratio of variable to maximum fluorescence (FV/FM) and the performance index for photosynthesis, PIABS (a derivative of the O-J-I-P analysis of photosystem II functionality). Interspecies differences plus the development of intraspecies differences during nutrient stress produced c. 10-fold variations in Chl : C. Estimates of C from in vivo Chl content were better than those from extracted Chl content, as the decline in Chl : C during nutrient stress was offset in part by increased Chl fluorescence. FV/FM was not a robust indicator of nutrient status or relative growth rate. Responses of FV/FM in cells re-fed the limiting nutrient showed no consistent pattern with which to gauge nutrient status. PIABS showed some promise as an indicator of nutrient status and relative growth rate. Chl a content and fluorescence parameters do not deserve the unquestioned status they usually enjoy as indicators of biomass and physiological status.

Chlorophyll Response to Nutrients and Non-algal Seston in Missouri Reservoirs and Oxbow Lakes

When unaggregated summer chlorophyll data (Chl) from 184 Missouri reservoirs are plotted against total phosphorus (TP) a ‘bow’ in the distribution develops among a group of points with low Chl:TP ratios (averaging <0.05). Low Chl:TP is mostly associated with turbid, nutrient-rich inflows in reservoirs across the entire trophic range. Non-algal seston (NAS) is our best metric of these inflows and is a co-variable in Chl-TP regressions. This influence is most prominent in years of high runoff and is distinctly seasonal, being most prevalent in early summer prior to full stratification. In late summer, inflows typically enter as subsurface density currents, and nitrogen accounts for more variation in Chl-TP than NAS. Neither variable, however, greatly influences the long-term relation between Chl and TP, which is linear, relatively consistent, and matches the global pattern. In several oxbow lakes, high NAS caused by sediment resuspension is a chronic condition; it seems neither light nor flushing greatly influence Chl: TP in these shallow systems, and values approximate the statewide average. Temporal variation in Chl:TP is demonstrated by daily samples (n=1676) from a single reservoir, with average variability, that covers about 94% of the statewide Chl and about a third of the TP range. The Chl-TP pattern in over half of Missouri reservoirs deviates somewhat from predictions based on cross-system regression models. Nonetheless, for 97% of the study reservoirs, long-term Chl is within a factor of two above or below model predictions, and most are within ±25%. Such differences are modest when compared to the temporal variation measured in an intensively studied reservoir.

In-pixel variations of chl a fluorescence in the Northern Gulf of Mexico and their implications for calibrating remotely sensed chl a and other products

Remote sensing instruments such as SeaWiFS and MODIS are often calibrated or tested by comparison with in situ data. These comparisons are based on the premise that there is uniform in-pixel variation of the standard deviation of in situ properties. To evaluate some of the errors resulting from this assumption, we conducted an analysis of in-pixel variation of chl a fluorescence by examining fluorescence data from a flow-through system on an underway vessel mapping surface properties for 10 days on the continental shelf in the vicinity of the Mississippi River delta. Significant variations of in-pixel standard deviation of chl a fluorescence were observed, which indicate that this uniformity assumption is not valid in the Northern Gulf of Mexico. Furthermore, our analysis indicates that a large apparent error by the remote sensor is generated if uniformity of standard deviation is assumed. Our results suggest that one should take into account both in-pixel mean and standard deviation when comparing remotely sensed ocean color data with in situ measurements. Similar measures should be taken when comparing other remotely sensed products with field determinations.

Regional, vertical and seasonal distribution of phytoplankton and photosynthetic pigments in Lake Baikal

A 3-year phytoplankton study was carried out in Lake Baikal (Siberia) as part of the CONTINENT project and in conjunction with a 60-year long monitoring programme by the Irkutsk State University. A combination of microscopy and high performance liquid chromatography (HPLC) pigment analysis was used. All over the lake, the dominant functional group (by biovolume) was the vernal diatom blooms, due to the dominance of endemic Cyclotella species. Chlorophyll a (Chl a) was significantly highest at the Selenga and Barguzin inflows (2.39 ± 0.34 and 2.49 ± 0.18 nmol L–1, mean ± 95% CI, respectively) and higher in the South than in the North (1.43 ± 0.26 and 0.96 ± 0.13 nmol L−1). This variation of Chl a reflected changes in the phytoplankton composition. Diatoms and Chrysophyceae were the major contributors to the total Chl a except in the South (Chlorophyceae) and Selenga Delta (cyanobacterial picoplankton). There were also indications of species composition changes due to enhanced P-loading from the Selenga River. However, canonical analyses indicated that temperature and stratification were the major driving forces for regional distribution patterns and seasonal succession. It seems likely that further global warming will cause a shift in the species and group composition towards small cells at the expense of the large endemic diatom flora.

SeaWiFS retrievals of chlorophyll in Chesapeake Bay and the mid-Atlantic bight

This paper presents three years (1998–2000) of chlorophyll a (chl a) data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) for Case 2 waters of Chesapeake Bay and the middle Atlantic bight (MAB) to describe phytoplankton dynamics on seasonal to interannual time scales. We used extensive data on inherent and apparent optical properties in conjunction with satellite retrievals to: (1) characterize the bio-optical properties of the study area relevant to processing and interpreting SeaWiFS data; (2) test the applicability of the SeaWiFS bio-optical algorithm (OC4v.4) for the estuarine and coastal waters; (3) evaluate the accuracy of the SeaWiFS remote sensing reflectance ( R RS) and chl a products on regional and seasonal bases using in situ observations. The characteristically strong absorption by chromophoric dissolved organic matter ( a cdom) and non-pigmented particulate matter ( a d) in estuarine and coastal waters contributed to overestimates of chl a using OC4v.4 applied to in situ radiances for the Bay (mean ratio 1.42±1.20) and the MAB (2.60±1.36). Values of R RS from SeaWiFS in the blue region of the spectrum were low compared to in situ R RS, suggesting that uncertainties remain in atmospheric correction. Direct comparisons of SeaWiFS retrievals of chl a with in situ chl a for the Bay showed larger biases and uncertainties (mean ratio 1.97±1.85) than for chl a estimated from OC4v.4 applied to in situ R RS. The larger biases were attributed to errors in SeaWiFS radiances and the larger uncertainties to time-space “aliasing” of satellite observations and in situ measurements. To reduce the time differences between SeaWiFS and in situ data, we compared chl a obtained from continuous underway fluorometric measurements on selected ship tracks to SeaWiFS chl a and showed that SeaWiFS captured phytoplankton dynamics in much of the Bay. The agreement of SeaWiFS chl a with in situ chl a was strongest in the mid- (regions 3, 4) to lower Bay (regions 1, 2), and deteriorated toward the upper Bay (regions 5, 6), in part due to a reduction of sensitivity and an increase of noise for SeaWiFS products in the highly absorbing, low R RS waters of the upper Bay. A three-year time-series of SeaWiFS and in situ data showed that SeaWiFS accurately and reliably captured seasonal and interannual variability of chl a associated with variations of freshwater flow. Significant short-term variability of chl a in summer that was unresolved with shipboard data was detected in the SeaWiFS time-series and the implications are discussed. The overall performance of SeaWiFS in the mid- to lower Bay and the MAB, combined with high spatial (∼1 km 2) and temporal (∼100 clear scenes per year) resolution, indicate current SeaWiFS products are valuable for quantifying seasonal to interannual variability of chl a in estuarine and coastal waters.

Catchment urbanisation and increased benthic algal biomass in streams: linking mechanisms to management

Summary1. Urbanisation is an important cause of eutrophication in waters draining urban areas. We determined whether benthic algal biomass in small streams draining urban areas was explained primarily by small‐scale factors (benthic light, substratum type and nutrient concentrations) within a stream, or by catchment‐scale variables that incorporate the interacting multiple impacts of urbanisation (i.e. variables that describe urban density and the intensity of drainage or septic tank systems).2. Benthic algal biomass was assessed as chlorophyll a density (chl a) in 16 streams spanning a rural–urban gradient, with both a wide range of urban density and of piped stormwater infrastructure intensity on the eastern fringe of metropolitan Melbourne, Australia. The gradient of urban density among streams was broadly correlated with catchment imperviousness, drainage connection (proportion of impervious areas connected to streams by stormwater pipes), altitude, longitude and median phosphorus concentration. Catchment area, septic tank density, median nitrogen concentration, benthic light (photosynthetically active radiation) and substratum type were not strongly correlated with the urban gradient.3. Variation in benthic light and substratum type within streams explained a relatively small amount of variation in log chl a (3–11 and 1–13%, respectively) compared with between‐site variation (39–54%).4. Median chl a was positively correlated with catchment urbanisation, with a large proportion of variance explained jointly (as determined by hierarchical partitioning) by those variables correlated with urban density. Independent of this correlation, the contributions of drainage connection and altitude to the explained variance in chl a were significant.5. The direct connection of impervious surfaces to streams by stormwater pipes is hypothesised as the main determinant of algal biomass in these streams through its effect on the supply of phosphorus, possibly in interaction with stormwater‐related impacts on grazing fauna. Management of benthic algal biomass in streams of urbanised catchments is likely to be most effective through the application of stormwater management approaches that reduce drainage connection.

High frequency and mesoscale variability in SeaWiFS chlorophyll imagery and its relation to other remotely sensed oceanographic variables

In its typical use for the study of large scale and relatively slow variability of phytoplankton biomass, ocean-color imagery is often binned in space and in time, and variability within the bin is discarded as noise. Since small- to mesoscale processes at time scales as short as a day may play a significant role in global cycles of carbon and nutrients, characterizing variability at these scales is necessary. With the first four years of nearly continuous daily imagery from the SeaWiFS instrument, we investigated patterns of variability at the mesoscales, operationally defined as that within a 2 � 2-degree neighborhood. We show that mesoscale variability of chlorophyll concentration (Chl) is high near the coasts, in dynamically active areas, and at the oligotrophic centers of subtropical gyres. High apparent variability over the oligotrophic ocean is a surprising contrast to the low variability in composite imagery at the same locations and may be due to increased relative noise at low mean Chl. Low correlation between pairs of images as little as 1 day apart in the oligotrophic ocean is consistent with a noise artifact, or alternatively may indicate that the observed variability is due to high-frequency phenomena. Spatial patterns of variability observed when data are binned into narrow ranges of mean Chl, suggest oceanographic origins. Patterns of variability in Chl and in sea-surface height have little correlation, suggesting that eddy pumping or turbulent diffusion along temporarily slanted isopycnal surfaces are not the major sources of Chl variability. The correlation between mesoscale anomalies of Chl and sea-surface temperature is not always negative as would have been the case if anomalies were produced mainly by the entrainment of colder, nutrientrich thermocline waters into the euphotic layer. Instead, we find roughly zonal bands of alternating negative and positive correlations determined by the relative directions of the background gradients of Chl and SST. Thus the most obvious influence of mesoscale motion on the distribution of Chl is advection of the existing gradients. Both long-term means and local anomalies of scatterometric winds from QuikSCAT are also correlated with mean Chl. Much of this correlation appears to be due to changes in the relationship between surface roughness and wind speed, brought on by factors like surface films, thermal stability of the air column, and surface currents. Our analyses show the feasibility of using ocean-color imagery to study mesoscale variability but also identify areas where there is room for major

The effect of axial Mg 2+ ligation and peripheral hydrogen bonding on chlorophyll a

Model systems of the chlorophyll a (Chl a) molecule were studied using density functional theory. Dependence of structure variation of Chl a on the polarity of ligand was described. The hydrogen bonding (H-bond) donated to the 13 1-keto carbonyl oxygen favors the ionic resonance structure of the 13 1-keto carbonyl bond. Such a H-bond causes spin density redistribution in anion, and charge transfer in cation from donor of H-bond to the porphyrin plane of Chl a because of orbital admixing, which indicates that the spin density of chlorophyll cation could be easily regulated by its peripheral H-bond.