Spatial Distribution Of Chlorophyll Research Articles

Enhanced Chlorophyll-a in the Coastal Waters near the Eastern Guangdong during the Downwelling Favorable Wind Period

Phytoplankton dynamics, which are highly sensitive to the ecosystem condition and change, are different in coastal waters and open ocean. Previous researches mainly focused on the open ocean dynamic in the South China Sea (SCS), but few research on the Eastern Guangdong (EGD), especially during a period of downwelling-favorable winds. In fact, the influence of topographic irregularities, downwelling, continental outflows, and cold, nutrient-rich currents from Fujian-Zhejiang coastal waters (ZFC) of the East China Sea (ECS) on the spatial distribution of Chlorophyll a (Chl a) in EGD coastal waters could be significant. This study utilized ocean color time series and meteorological and hydrographic data jointly from July 2002 to June 2020 to investigate the heterogeneous regional specific distribution pattern of Chl a in EGD and the environmental determinants in different regions subdivided by water depth. Then the temporal and spatial distribution pattern of Chl a in EGD in winter were discussed in detail by applying an Empirical Orthogonal Function (EOF) analysis, GaoFeng-1 (GF-1) satellite data and in situ measured dataset. The sea surface temperature (SST) in February was negatively related with Chl a in shallow coastal waters less than 60 m deep due to the nutrient-rich, cold waters from ZFC. The monthly mean photosynthetically active radiation (PAR) and precipitation showed significant effects on the phytoplankton growth over regions with a depth less than 10 m. An area with higher Chl a concentration in the downwelling zone were detected in winter. By an examining the temporal variability in meridional distribution of the mean Chl a at 22.41°N and 22.21°N, a symmetrical peak was observed. The coastal fronts extended southwestward from the southeastern coast of Guangdong Province to Dangan Island in the SCS. In addition, a cross-shelf filament was detected near the coast of Shanwei, Guangdong, China on 8 January 2020.

Study on the temporal and spatial distribution of chlorophyll a in Erhai Lake based on multispectral data from environmental satellites

Satellite remote sensing technology presents advantages of macroscopicity, timeliness and cost effectiveness and has been increasingly used in lake water quality monitoring. In this paper, an empirical model for the remote sensing inversion of the chlorophyll a (Chl-a) concentration in Erhai Lake was established using ground monitoring Chl-a concentration data and multispectral remote sensing data from environmental satellites from 2010 to 2017. The average absolute error and relative error were 1.92 mg/m3 and 22%, respectively. A 10-year remote sensing inversion of Erhai blooms identified the temporal and spatial distribution characteristics of blooms and showed that the occurrence frequency of blooms was 37%, and they were mainly in the form of light algal blooms at a local scale. Moderate and severe blooms occurred at a frequency of 42%, mainly from Oct. to Jan. Moderate algal blooms were distributed along the southern and northern coasts and in coastal areas, while severe algal blooms were distributed in the northern section and across the entire lake. During the bloom period, the growth rate of the bloom area reached 102 km2/d, which was faster than the reduction rate (90 km2/d). Bloom events generally lasted for 6–37 days. The inflow of pollution sources led to a higher frequency of blooms in the coastal zone than in the lake center, and the frequency in the northern section was nearly twice as high as that in the southern section. Most blooms in Erhai Lake occurred from late summer to winter (i.e., Jul. to Jan. of the following year) because of the higher average air temperature (AT) and lower wind speed (WS) in winter and spring and the amount of precipitation in summer and autumn. The remote sensing method captured the high-risk areas and the spatial-temporal evolution trend of algal blooms, and the model provided support for the prevention and control of lake algal blooms; however, this work should be complemented by ground monitoring data for cloudy days.

The Spatial Distribution of Chlorophyll in Leaves.

Measuring and modeling the spatial distribution of chlorophyll within the leaf is critical for understanding the relationship between leaf structure and carbon assimilation, for defining the relative investments in leaf tissues from the perspective of leaf economics theory, and for the emerging application of in silico carbon assimilation models. Yet, spatially resolved leaf chlorophyll distribution data are limited. Here, we used epi-illumination fluorescence microscopy to estimate relative chlorophyll concentration as a function of mesophyll depth for 57 plant taxa. Despite interspecific variation due to differences in leaf thickness, mesophyll palisade fraction, and presence of large intercellular airspaces, the spatial distribution of chlorophyll in laminar leaves was remarkably well conserved across diverse lineages (ferns, cycads, conifers, ginkgo, basal angiosperms, magnoliids, monocots, and eudicots) and growth habits (tree, shrub, herbaceous, annual, perennial, evergreen, and deciduous). In the typical leaf, chlorophyll content increased gradually as a function of depth, peaking deep within the mesophyll. This chlorophyll distribution pattern is likely coupled to adaxial and abaxial intraleaf light gradients, including the relative enrichment of green light in the lower leaf. Chlorophyll distribution for the typical leaf from our dataset was well represented by a simple mathematical model (R2 = 0.94). We present chlorophyll distribution data and model equations for many ecologically and commercially relevant species and plant functional types (defined according to chlorophyll profile similarity, clade, and leaf thickness). These findings represent an advancement toward more accurate photosynthesis modeling and increase our understanding of first principles in intraleaf physiology.

The Effect of Air‐Sea Flux Products, Shortwave Radiation Depth Penetration, and Albedo on the Upper Ocean Overturning Circulation

AbstractWater mass transformation quantifies transport of matter between different density classes of the World Ocean. We present the first observationally based quantification of transformation rates due to air‐sea buoyancy fluxes, which considers different parameterizations of shortwave radiation depth penetration, including the influence of albedo and the Chlorophyll a concentration. The results provide a range of solutions that can be used to compare model‐based transformation rates against. We compared two air‐sea flux products with limited representation of ice dynamics at high latitudes. We find that variations in the air‐sea heat fluxes due to Chlorophyll a and its horizontal distribution are as important for water mass transformation rates than differences between the freshwater flux products. An accurate representation of the effects and spatial distribution of Chlorophyll a is required to obtain realistic transformation rates.

Multi-Spectral Remote Sensing of Phytoplankton Pigment Absorption Properties in Cyanobacteria Bloom Waters: A Regional Example in the Western Basin of Lake Erie

Phytoplankton pigments absorb sunlight for photosynthesis, protect the chloroplast from damage caused by excess light energy, and influence the color of the water. Some pigments act as bio-markers and are important for separation of phytoplankton functional types. Among many efforts that have been made to obtain information on phytoplankton pigments from bio-optical properties, Gaussian curves decomposed from phytoplankton absorption spectrum have been used to represent the light absorption of different pigments. We incorporated the Gaussian scheme into a semi-analytical model and obtained the Gaussian curves from remote sensing reflectance. In this study, a series of sensitivity tests were conducted to explore the potential of obtaining the Gaussian curves from multi-spectral satellite remote sensing. Results showed that the Gaussian curves can be retrieved with 35% or less mean unbiased absolute percentage differences from MEdium Resolution Imaging Spectrometer (MERIS) and Moderate Resolution Imaging Spectroradiometer (MODIS)-like sensors. Further, using Lake Erie as an example, the spatial distribution of chlorophyll a and phycocyanin concentrations were obtained from the Gaussian curves and used as metrics for the spatial extent of an intense cyanobacterial bloom occurred in Lake Erie in 2014. The seasonal variations of Gaussian absorption properties in 2011 were further obtained from MERIS imagery. This study shows that it is feasible to obtain Gaussian curves from multi-spectral satellite remote sensing data, and the obtained chlorophyll a and phycocyanin concentrations from these Gaussian peak heights demonstrated potential application to monitor harmful algal blooms (HABs) and identification of phytoplankton groups from satellite ocean color remote sensing semi-analytically.

Geo-informatics Techniques for Assessing Physiological Status and Productivity of RRIC 121 Genotype of Hevea brasiliensis (Rubber) under Different Harvesting Systems

Abstract Rubber (Hevea brasiliensis) one of the main plantation crops in Sri Lanka is the only plant species cultivated commercially for natural rubber harvesting. Novel systems for harvesting have been introduced but spatial distribution of photosynthetic potential determining key factor for sustainable cultivation has not been properly explored. Use of such techniques such as Satellite Remote Sensing (RS) and Geographic Information System (GIS) to analyse spatial and biological factors related to the productivity of rubber plantation with different harvesting systems is the main objective of the present study. Quikebird high resolution satellite images were used for RS analysis. Chlorophyll content of rubber leaves was measured using a SPAD-502 chlorophyll meter. Chlorophyll content and satellite images were analysed using GIS and spatial statistical methods to determine the variation in different harvesting systems. Yield data were collected from the study site and yield parameters were correlated with chlorophyll content and Normalized Difference Vegetation Index (NDVI) values. Results revealed all systems exhibited promising yield performance without significant deviation but slightly higher yield per hectare per year (YPH) and dry rubber content of latex (DRC) were recorded in quarter spiral based once in three days (S/3 d4) and weekly (S/2 d1 2d7) harvesting systems. Chlorophyll content and rubber yield showed direct correlation in all systems. NDVI vs chlorophyll showed positive correlation r2=0.65 and spatial distribution of chlorophyll and NDVI values demonstrated sound physiological status of plants across the plantation with different harvesting systems. Cost effective LIH systems showed better production trend demonstrating relatively higher yield while reducing tapping cost and labour. Satellite based remote sensing technique is an easy and efficient tool to estimate productivity of rubber plantation over a large area. Keywords: Chlorophyll, NDVI, harvesting, Remote Sensing, Rubber.

Spatial variability of concentrations of chlorophyll a, dissolved organic matter and suspended particles in the surface layer of the Kara Sea in September 2011 from lidar data

The article presents results of underway remote laser sensing of the surface water layer in continuous automatic mode using the UFL-9 fluorescent lidar onboard the R/V Akademik Mstislav Keldysh during cruise 59 in the Kara Sea in 2011. The description of the lidar, the approach to interpreting seawater fluorescence data, and certain methodical aspects of instrument calibration and measurement are presented. Calibration of the lidar is based on laboratory analysis of water samples taken from the sea surface during the cruise. Spatial distribution of chlorophyll a, total organic carbon and suspended matter concentrations in the upper quasi-homogeneous layer are mapped and the characteristic scales of the variability are estimated. Some dependencies between the patchiness of the upper water layer and the atmospheric forcing and freshwater runoff are shown.

Spatial distribution of plankton from the upper and Middle Volga reservoirs in years with different thermal conditions

The spatial distribution of chlorophyll, as well as the structure and abundance of zooplankton, from three large Volga reservoirs (Rybinsk, Gorky, and Cheboksary Reservoirs) in the summers of 2008 and 2010 has been studied. Factors influencing the pigment content and zooplankton abundance have been analyzed. It has been shown that the concentration of chlorophyll and zooplankton in the abnormally hot 2010 exceeded those typical for the studied reservoirs. Changes in the zooplankton structure, decrease in the cladoceran fecundity and occurrence frequency of benthic species, and low density of Dreissena veligers have been registered.

Multispectral remote sensing of harmful algal blooms in Lake Champlain, USA.

This study developed satellite remote sensing models to detect cyanobacterial blooms via chlorophyll a in Lake Champlain. Landsat Enhanced Thematic Mapper Plus data was used to retrieve chlorophyll a concentrations, phytoplankton, and cyanobacteria biovolume by calibrating and validating with coincident observation data. Correlation analysis results showed that band 2 (green band) and the band ratio of 2/1 (green/blue) were most highly correlated to chlorophyll a concentration (r = 0.76 and 0.82, respectively). Multiple regression results identified band 2 and 3 (red), and band ratio of 2/1 and 3/1 (red/blue) as critical information to estimate chlorophyll a concentrations. The regression models accounted for 72 to 83% of the variability in chlorophyll a observations, allowing for estimates of phytoplankton and cyanobacteria levels in the lake. Satellite image processing results successfully showed the temporal and spatial distribution of chlorophyll a, phytoplankton, and cyanobacteria in the lake. This information can be used to evaluate the effect of pollution sources and weather conditions, and assist decision making for water management.

Spatial distribution of chlorophyll a and its relationship with the environment during summer in Lake Poyang: a Yangtze-connected lake

Lake Poyang, a Yangtze-connected lake that is the largest freshwater lake in China, was studied in summer from 2009 to 2012. The primary objective was to investigate the spatial variability of chlorophyll a (chl a) on a whole-lake scale and to identify the key factors affecting phytoplankton growth. Stepwise multiple linear regression and Spearman’s rank correlation analyses showed that the shade index is the major factor determining the spatial distribution of chl a; nutrients don’t explain much variation in chl a, except in the east. The relationships between shade index and chl a varied regionally. Chl a varied inversely with the variation of the shade index, especially in the north and south, reflecting light limitation. However, the correlation was positive in the east due to high chl a concentration negatively affecting light availability, which was promoted by sufficient nutrients. In the center, no factor was found to have an obvious effect on phytoplankton growth, most likely because of human activities and high heterogeneity. These new data on the spatial variability of chl a and its relationship with light availability in Lake Poyang will be crucial to understand chl a regulation and contribute to the knowledge regarding phytoplankton in the Yangtze Basin.

The distribution of chlorophyll a in the tropical eastern Indian Ocean in austral summer

To study the effect of hydrographic factors on the spatial distributions of chlorophyll a (Chl a), an investigation was carried out in the tropical eastern Indian Ocean (80°-100°E along 7°S, and 7°-18°S along 80°E) in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at (0.168±0.095) mg/m3 s.d. (range: 0.034–0.475 mg/m3), concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower (0.034–0.066 mg/m3) in the region to the south of 16°S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant: correlation and regression analysis suggests that it was primarily affected by PO 4 3− , N(NO3-N+NO2-N) and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton (24.5%) and microphytoplankton (7.6%). The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature.

Multispectral Remote Sensing of Harmful Algal Blooms in Lake Champlain, USA

ABSTRACT This study developed satellite remote sensing models to detect cyanobacterial blooms via chlorophyll a in Lake Champlain. Landsat Enhanced Thematic Mapper Plus data was used to retrieve chlorophyll a concentrations, phytoplankton, and cyanobacteria biovolume by calibrating and validating with coincident observation data. Correlation analysis results showed that band 2 (green band) and the band ratio of 2/1 (green/blue) were most highly correlated to chlorophyll a concentration (r = 0.76 and 0.82, respectively). Multiple regression results identified band 2 and 3 (red), and band ratio of 2/1 and 3/1 (red/blue) as critical information to estimate chlorophyll a concentrations. The regression models accounted for 72 to 83% of the variability in chlorophyll a observations, allowing for estimates of phytoplankton and cyanobacteria levels in the lake. Satellite image processing results successfully showed the temporal and spatial distribution of chlorophyll a, phytoplankton, and cyanobacteria in the lake. This information can be used to evaluate the effect of pollution sources and weather conditions, and assist decision making for water management.

Comparison of temporal and spatial structures of chlorophyll derived from MODIS satellite data and ECOHAM3 model data in the North Sea

In this paper, we assess the ability of the three-dimensional physical–biological coupled model ECOHAM3 to reproduce the seasonal dynamics and the spatial distribution of chlorophyll in the greater North Sea area. We use chlorophyll products from MODIS and in situ measurements of chlorophyll from long-term monitoring as ground truths to validate the spatial and temporal phytoplankton dynamics for the year 2004. The MODIS diffusive attenuation coefficient showed that the depth up to which the chlorophyll concentration is integrated for the MODIS chlorophyll product seldom exceeds 10 m. The upper 10 m of the water column are represented by the top layer of the model. Monthly regional distributions show a large-scale overestimation by the model while 87% of the difference values lie in the interval of − 1 mg/m 3 and 1 mg/m 3. Only in the coastal regions the model underestimates the satellite data. For comparison of annual cycles and spatial gradients we used in situ observations to check the reliability of satellite and model data. On a transect through the North Sea the best agreement between the three data sets is achieved in the central and northern North Sea during winter and autumn. All data sets show an increase at the northern part of this transect during spring and summer. Averaged over the whole year the satellite data agrees well with in situ data. The model data exceeds the in situ and satellite data along the transect by 50% except for the coastal region where the in situ and satellite data have a much steeper slope and finally exceed the model data. The monthly mean values at a stratified station in the northern North Sea for both model and satellite data show a spring and autumn bloom and lie within the standard deviation of the in situ data during spring time. In the well mixed German Bight all three data sets show an increase of the chlorophyll concentration until April. In summer the data sets have different developments within the observed variability. An analysis of a Gaussian four-parameter fit to the weekly satellite and model time series describes the phytoplankton dynamics in stratified waters quantitatively. By considering the 576 (24 × 24 pixels) different annual chlorophyll cycles of the satellite data in a region of 1° by 1°, the extremely different biological evolution during spring bloom on such a high resolution becomes apparent, which is not reproduced by the model. The best agreement between the model and satellite data is achieved in the timing of the chlorophyll maximum concentration. This comparison of data sets is the first validation of the model with satellite data.

Patterns of variability of sea surface chlorophyll in the Mozambique Channel: A quantitative approach

We analyse the coupling between sea surface chlorophyll concentration (CC) and the physical environment in the Mozambique Channel (MZC) using statistical models. Seasonal and interannual patterns are studied along with the role of mesoscale dynamics on enhancement and concentration processes for phytoplankton. We use SeaWifs data for CC and two other remotely sensed data sets, TMMI for sea surface temperature (SST) and merged altimetry products for sea level anomaly and geostrophic current. Empirical Orthogonal Functions (EOF) on SSC and SST show strong seasonality and partition the MZC into three distinct sub-areas. The chlorophyll variability is mostly driven by seasonality, but more in the North (10°S–16°S) and South (24°S–30°S), and explains respectively 64% and 82% of the CC variance. In the Central part (16°S–24°S), the seasonal signal has less influence (60% variance). There, complex EOFs on Sea Level Anomaly (SLA) highlight the role of mesoscale activity (i.e. eddies and filament structures) in the spatial distribution of chlorophyll. Five mesoscale descriptors (shear, stretch, vorticity, deformation and eddy kinetic energy) are derived from the altimetry data to quantify the eddies-related physical patterns in the central region of the MZC. We use generalized Additive Models to explain the effect of those features on phytoplankton enhancement. The best model fit ( r 2 = 0.73) includes shear, stretch, vorticity and the latitude-longitude interaction as eddies are well structured in space. Cyclonic eddies associated with negative vorticity are conductive to phytoplankton enhancement by the effect of upwelling in the core notably during the spin-up phase. The interaction between eddies generate strong frontal mixing favourable to the production and aggregation of organic matter. The mesoscale activity is also affected by interannual variability with consequences on CC. We highlight a substantial reduction of the SLA pattern in 2000–2001 when the SOI positive phase is peaking (Nina-type pattern). The strong relationship between mesoscale eddies and SOI suggests that primary productivity in the MZC is also under the influence of distant forcing at a basin scale.

On-line determination of silver in natural waters by inductively-coupled plasma mass spectrometry: Influence of organic matter

We investigated interference effects on the analysis of silver in estuarine and oceanic waters using on-line high resolution inductively coupled plasma mass spectrometry (ICP-MS). A mini-column packed with a strong anion exchange resin (Dowex 1-X8) was used in a flow-injection system to separate and concentrate silver from the saline samples prior to on-line determination by ICP-MS. A series of analyses showed the concentrations of silver measured in San Francisco Bay estuary and the North Pacific that had been acidified (pH < 2) and stored for periods of 1–2 years were 10–70% lower than those measured in aliquots of those samples after ultraviolet (UV) irradiation. Additional silver released after UV irradiation of the estuarine waters, but not the ocean waters, was positively correlated ( r = 0.77, simple linear correlation) with chlorophyll- a concentrations, but not with dissolved organic carbon (DOC) concentrations. Spatial distributions of chlorophyll- a and UV-released silver also exhibited similar patterns along a salinity gradient in the San Francisco Bay estuary, suggesting an in situ biogenic source of the interferent for the silver measurements.

High-light stress and photoprotection in Umbilicaria antarctica monitored by chlorophyll fluorescence imaging and changes in zeaxanthin and glutathione.

The effect of high light on spatial distribution of chlorophyll (Chl) fluorescence parameters over a lichen thallus (Umbilicaria antarctica) was investigated by imaging of Chl fluorescence parameters before and after exposure to high light (1500 micro mol m (-2) s (-1), 30 min at 5 degrees C). False colour images of F (V)/F (M) and Phi (II) distribution, taken over thallus with 0.1 mm (2) resolution, showed that maximum F (V)/F (M) and Phi (II) values were located close to the thallus centre. Minimum values were typical for thallus margins. After exposure to high light, a differential response of F (V)/F (M) and Phi (II) was found. The marginal thallus part exhibited a loss of photosynthetic activity, manifested as a lack of Chl fluorescence signal, and close-to-centre parts showed a different extent of F (V)/F (M) and Phi (II) decrease. Subsequent recovery in the dark led to a gradual return of F (V)/F (M) and Phi (II) to their initial values. Fast (30 min) and slow (1 - 22 h) phase of recovery were distinguished, suggesting a sufficient capacity of photoprotective mechanisms in U. antarctica to cope with low-temperature photoinhibition. Glutathione and xanthophyll cycle pigments were analyzed by HPLC. High light led to an increase in oxidized glutathione (GSSG), and a conversion of violaxanthin to zeaxanthin, expressed as their de-epoxidation state (DEPS). The responses of GSSG and DEPS were reversible during subsequent recovery in the dark. GSSG and DEPS were highly correlated to non-photochemical quenching (NPQ), indicating involvement of these antioxidants in the resistance of U. antarctica to high-light stress. Heterogeneity of Chl fluorescence parameters over the thallus and differential response to high light are discussed in relation to thallus anatomy and intrathalline distribution of the symbiotic alga Trebouxia sp.

Patterns and dynamics of coastal waters in multi-temporal satellite images: support to water quality monitoring in the Archipelago Sea, Finland

The Archipelago Sea in the northern Baltic is a coastal region with a highly dynamic water flow regime, where the need for a methodology to monitor water quality accurately is encountered. In order to contribute to the development of an appropriate strategy to meet this need, the dynamics of the surface waters in the region were analysed using data from six Landsat TM/ETM+ images from the late 1990s. Single images were enhanced by principal component transformation and multi-temporal image combination was based on unsupervised classification. The visual patterns discernible in the single images as well as the classification result of the multi-temporal data were compared with the reference data from long-term water quality analyses (Secchi disk depth and chlorophyll- a). The satellite images confirmed dynamic surface flow patterns in the region, indicating gradual and abrupt gradients in water quality, flow directions and forms. These patterns suggest short-term variability in the surface water quality within the region, presenting a challenge for water monitoring. The average Secchi depths increased gradually from the mainland coast until ca. 3–5 m near the open sea. The spatial distribution of chlorophyll- a was found to be more homogeneous, ca. 2–4 μg l −1. The importance of evaluating the location of an in situ sampling site in relation to the surrounding hydrographic realm is pronounced in regions where field sampling and other monitoring methods remain insufficient in their ability to reflect water quality patterns credibly. In such areas, accurate and cost-effective water quality monitoring and forecasting require an integrated monitoring system, consisting of space and airborne surveillance, field surveys and hydrodynamic modelling.

Seasonal and spatial distribution of chlorophyll- a concentrations and water conditions in the Gulf of Tonkin, South China Sea

The Gulf of Tonkin is a semi-closed gulf northwest of the South China Sea, experiencing reversal seasonal monsoon. Previous studies of water conditions have been conducted in the western waters of the gulf, but very few studies of the Chlorophyll- a (Chl- a) distribution have been carried out for the entire gulf. The present study investigates seasonal and spatial distributions of Chl- a and water conditions in the Gulf of Tonkin by analyzing Sea-viewing Wide Field-of-View Scanner (SeaWiFS) derived Chlorophyll- a (Chl- a), in situ measurements, sea surface temperatures (SST), and other oceanographic data obtained in 1999 and 2000. The results show seasonality of Chl- a and SST variations in the Gulf of Tonkin, and reveal phytoplankton blooming events in the center part of the gulf during the northeast monsoon season. In summer, Chl- a concentrations were relatively low (<0.3 mg m −3) and distributed uniformly throughout most of the area, with a belt of higher Chl- a concentrations along the coast, particularly the coast of Qiongzhou Peninsula; in winter, Chl- a concentration increased (0.5 mg m −3) in the entire gulf, and phytoplankton blooms offshore-ward from the northeast coast to the center of the gulf, while Chl- a concentrations reached high levels (0.8–1 mg m −3) in the center of the blooms. One peak of Chl- a concentrations was observed during the northeast monsoon season in the year. SST were high (27–29 °C) and distributed uniformly in summer, but lower with a large gradient from northeast (17 °C) to southwest (25 °C) in winter, while strong northeast winds (8–10 m/s) were parallel to the east coast of the gulf. Comparison of Chl- a values shows that SeaWiFS derived Chl- a concentrations match well with in situ measurements in most parts of the gulf in May 1999, but SeaWiFS derived Chl- a are higher than in situ data in river mouth waters. The seasonal variation of Chl- a concentrations and SST distribution were associated with the seasonally reversing monsoon; the winter phytoplankton blooms were related to vertical mixing and upwelling nutrients drawn by the northeast wind.

Ocean Color Satellite Imagery and Shipboard Measurements of Chlorophyll a and Suspended Particulate Matter Distribution in the East China Sea

Satellite-derived ocean color data of Coastal Zone Color Scanner (CZCS) on board the Nimbus-7 and Ocean Color and Temperature Scanner (OCTS) on board the Advanced Earth Observing Satellite (ADEOS) are jointly used with historical in situ data to examine seasonal and spatial distributions of chlorophyll a (Chl-a) and suspended particulate matter (SPM) concentrations in the East China Sea. Ocean color imagery showed that Chl-a concentrations on the continental shelf were higher than those of the Kuroshio area throughout the year. Satellite-derived Chl-a concentrations are generally in good accordance with historical in situ values during spring through autumn (although no shipboard in situ measurement was conducted at nearshore areas). In contrast, ocean color imagery in winter indicated high Chl-a concentrations (4–10 mg m−3) on the continental shelf where bottom depth was less than 50 m when surface water was turbid (2–72 g m−3 of SPM at surface), while historical in situ values were usually less than 1 mg m−3. This suggests that resuspended bottom sediment due to wind-driven mixing and winter cooling is responsible for the noticeable overestimation of satellite-derived Chl-a concentrations. The algorithm for ocean color needs to be improved urgently for turbid water.

Microbial Metabolism and Nutrient Cycling in the Mississippi and Atchafalaya River Plumes

Spatial distributions of chlorophyll, bacterial abundances and production, community respiration, and dissolved C, N, P and Si were measured in the Mississippi River (MRP) and Atchafalya River (ARP) plumes during July 1993. Dark bottle incubations were used to estimate net flux rates of inorganic nutrients, community respiration, and changes in chlorophyll concentrations in unfiltered water samples. Concentrations of total dissolved N (TDN) and soluble reactive P (SRP) in the Mississippi River were 55μM and 3μM higher, respectively, compared with those in the Atchafalaya River. Concentrations of dissolved organic carbon (DOC) and nitrogen (DON) in the Atchafalaya River, however, were 35 and 11μM higher, respectively than in the Mississippi River. Elevated chlorophyll concentrations, bacterial abundances and production, and community respiration rates were observed at intermediate (5–25) salinities of both plumes. Property-salinity plots indicated net sinks of dissolved N, P and Si at intermediate salinities consistent with photosynthetic utilization of these substances within the plumes. The distribution of dissolved P, N and chlorophyll suggested phytoplankton-mediated transformation of riverine-NO−3 to DON at intermediate salinities of the MRP, and a similar transformation of riverine SRP to dissolved organic P (DOP) at intermediate salinities of the ARP. Net regeneration of dissolved Si and NH+4 was observed in regions of elevated chlorophyll concentrations and net removal rates in both plumes. Nitrification rates in the MRP were c. 10-fold higher than in the ARP. Estimates of C fixation by nitrifying bacteria equalled or exceeded heterotrophic bacterial C production in the low salinity region of the MRP, but were negligible compared to heterotrophic bacterial production in the ARP. Dissolved inorganic N:P, Si:P and DOC:DON:DOP ratios suggested the potential for P limitation in both plume systems during the period investigated.