High Concentrations Of Chl Research Articles

Bayesian change point quantile regression approach to enhance the understanding of shifting phytoplankton-dimethyl sulfide relationships in aquatic ecosystems

Dimethyl sulfide (DMS) serves as an anti-greenhouse gas, plays multiple roles in aquatic ecosystems, and contributes to the global sulfur cycle. The chlorophyll a (CHL, an indicator of phytoplankton biomass)-DMS relationship is critical for estimating DMS emissions from aquatic ecosystems. Importantly, recent research has identified that the CHL-DMS relationship has a breakpoint, where the relationship is positive below a CHL threshold and negative at higher CHL concentrations. Conventionally, mean regression methods are employed to characterize the CHL-DMS relationship. However, these approaches focus on the response of mean conditions and cannot illustrate responses of other parts of the DMS distribution, which could be important in order to obtain a complete view of the CHL-DMS relationship. In this study, for the first time, we proposed a novel Bayesian change point quantile regression (BCPQR) model that integrates and inherits advantages of Bayesian change point models and Bayesian quantile regression models. Our objective was to examine whether or not the BCPQR approach could enhance the understanding of shifting CHL-DMS relationships in aquatic ecosystems. We fitted BCPQR models at five regression quantiles for freshwater lakes and for seas. We found that BCPQR models could provide a relatively complete view on the CHL-DMS relationship. In particular, it quantified the upper boundary of the relationship, representing the limiting effect of CHL on DMS. Based on the results of paired parameter comparisons, we revealed the inequality of regression slopes in BCPQR models for seas, indicating that applying the mean regression method to develop the CHL-DMS relationship in seas might not be appropriate. We also confirmed relationship differences between lakes and seas at multiple regression quantiles. Further, by introducing the concept of DMS emission potential, we found that pH was not likely a key factor leading to the change of the CHL-DMS relationship in lakes. These findings cannot be revealed using piecewise linear regression. We thereby concluded that the BCPQR model does indeed enhance the understanding of shifting CHL-DMS relationships in aquatic ecosystems and is expected to benefit efforts aimed at estimating DMS emissions. Considering that shifting (threshold) relationships are not rare and that the BCPQR model can easily be adapted to different systems, the BCPQR approach is expected to have great potential for generalization in other environmental and ecological studies.

Identification of Upwelling Area of the Western Territorial Waters of Indonesia From 2000 To 2017

The Western Waters of Indonesian (WWI) present a diverse interaction of ocean-atmosphere dynamics. One of them represents the event of Indian Ocean Dipole (IOD), El Niño–Southern Oscillation (ENSO), and upwelling. The objective of this study is to determine the dynamics of chlorophyll-a concentration (Chl–a), especially during IOD and ENSO. Also, this study is aimed to examine the temporal and spatial distribution of the upwelling area from 2000 to 2017. The data utilized consisted of Chl–a, wind stress, Sea Level Anomaly (SLA), and Sea Surface Temperature (SST). The technique used to determine the upwelling area was by examining the maximum conditions of Chl–a, the low temperature of SST, and SLA. The results showed the sea surface temperature had a relationship with the concentration of Chl–a. It was obtained if the Directional Movement Index (DMI) and N3.4 (Niño 3.4 Index) moved stably (not too fluctuation) resulting in high concentrations of Chl–a. High standard deviations of SST are recognized around the Sunda Strait (June – October). When the standard deviation of SST is high, there is also a tendency for high Chl–a concentrations, while the results of empirical calculations show that large areas of upwelling occurred in January and September respectively at 12,447.72 km2 and 8,146.20 km2. Based on the results of the analysis, it can be concluded that the upwelling does not only occur at the coastal area of Western Sumatra (coastal upwelling), but it also occurs in the eastern territorial waters of the Indian Ocean. In addition, the upwelling area has the same pattern as the Chl–a concentration in January - October.

Modeling phaeopigment concentrations in water from a shallow mesotrophic lagoon.

Concentrations of phaeopigments (Pha) and chlorophyll a (Chl) were determined in surface waters from a temperate lagoon during six sampling campaigns at high and at low tide. In order to develop models for phaeopigment concentration in water, it was necessary to replace Chl with photosynthetic pigment concentration (Pt =Pha+Chl) as one of the explanatory variables. Under first approximation, food availability and water temperature (T) could be considered as independent variables. The concentrations of Pha were then determined following seasonal change of response curves of the consumer community on T. However, multiple regression models with Pt , T and, eventually, salinity as explanatory variables were better able to depict Pha. All equations, developed with Pt , were also solved using Chl as an input variable. Although part of the performance was lost, such back-transformed models can be used at low/medium T and moderate to high concentrations of Chl. The developed equations about middle to long-term variations of Pha could be applied to study the biogeochemistry of contaminants related to Pha and to evaluate the dependence on temperature of phytoplankton utilization by consumers. PRACTITIONER POINTS: Phaeopigment concentration depicted by chlorophyll (Chl), temperature (T), and salinity. Better results obtained at low to medium T and moderate to high Chl concentration. Multiple regression (MR) better for extrapolation than model (S) with variable separation. Thermal response of consumer community in mesotrophic lagoon studied using model S.

Comparison of Phytoplankton Communities Between Melt Ponds and Open Water in the Central Arctic Ocean

Climate warming has a significant impact on the sea ice and ecosystem of the Arctic Ocean. Under the increasing numbers of melt ponds in Arctic sea ice, the phytoplankton communities associated with the ice system are changing. During the 7th Chinese National Arctic Research Expedition cruise in summer 2016, photosynthesis pigments and nutrients were analyzed, revealing differences in phytoplankton communities between melt ponds and open water in the central Arctic. Photo synthetic pigment analysis suggested that Fuco (5-91 μg m-3 and Diadino (4-21 μg m-3) were the main pigments in the open water. However, the melt ponds had high concentrations of Viola (7-30 μg m-3), Lut (4-59 μg m-3) and Chl b (11-38 μg m-3), suggesting that green algae dominated phytoplankton communities in the melt ponds. The significant differences in phytoplankton communities between melt ponds and open water might be due to the salinity difference. Moreover, green algae may play a more important role in Arctic sea ice ecosystems with the expected growing number of melt ponds in the central Arctic Ocean.

Scale-Up Testing of a Novel Cleaning Method for Low-Pressure Hollow Fiber Membranes Treating High Algae Surface Waters

Abstract The objective of this study was to determine an optimum flux maintenance protocol for a hollow fiber membrane filtration, treating a surface water with high concentrations of algae and chl...

Influence of the oceanographic dynamic in size distribution of cephalopod paralarvae in the southern Mexican Pacific Ocean (rainy seasons 2007 and 2008)

The southern Mexican Pacific Ocean presents seasonal changes related to the rainy season and Tehuano winds, which generate mesoscale processes affecting biological productivity and marine biodiversity. Size distributions of squid paralarvae collected in this region during the rainy season (July 2007 and May-June 2008) were analyzed in relation to regional oceanography. Samples were collected through oblique hauls, and CTD casts were used to determine the structure of the water column. Between surveyed periods, there were no significant changes in the water temperature at 10 m, but there were significant variations in the mixed layer depth (MLD). The number of taxa, community composition and total abundance of paralarvae were similar between periods. However, in July paralarvae ≤2.0 mm were distributed along the margins of cyclonic and anticyclonic eddies associated with high temperatures. In May-June, the MLD and high concentrations of chlorophyll a (Chl- a ) determined the presence of a group of oceanic paralarvae and another of coastal paralarvae, separated by an upwelling front. The percentage of recently spawned paralarvae (≤2.0) nearly doubled during this period as a result of increased coastal sampling and high concentrations of Chl- a , indicating a coupling of adult reproduction with regional productivity. In the absence of winds, the mesoscale oceanographic complexity generates gradients and a differential effect on the distribution, transport and survival of cephalopod paralarvae. Normal 0 21 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabla normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Calibri,sans-serif; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} Normal 0 21 false false false EN-US X-NONE X-NONE

Seasonal phytoplankton response to physical processes in the southern Yellow Sea

The Yellow Sea (YS) is a semi-enclosed marginal sea in the West Pacific. As part of the China GLOBEC-IMBER program, the present study set out to investigate the mechanisms involved in the seasonal patterns of phytoplankton biomass and community structure in the southern YS. During four cruises in April and October 2006, and March and August 2007, the phytoplankton spring bloom, the Yellow Sea Warm Current (YSWC) and the Yellow Sea Cold Water Mass (YSCWM) were the most remarkable biogeochemical events in the study area, involving significantly different phytoplankton communities. During cold seasons nutrient-rich water was observed, coincident with the occurrence of the YSWC, which is considered to be warm and saline water from the northward Kuroshio branch current (Cheju Warm Current). However, low Chl a concentrations (<0.6mgm−3) and a high relative abundance of prasinophytes (29% of Chl a, average value of the euphotic zone, and the same below) were observed in the YSWC area in March. During April a spring bloom occurred with very high concentrations of Chl a (7.69mgm−3) and fucoxanthin (1.98mgm−3), and was dominated by diatoms. The mechanism and processes of the spring bloom in the central YS are very complex and possibly unique, and the YSWC affects the distribution of nutrients and hydrological environment for phytoplankton growth. Low Chl a biomass (0.2mgm−3) and a low contribution of diatoms, but a high contribution of cyanobacteria (36%) were observed in the stratified central YS in August when the YSCWM prevailed, and a high relative abundance of chrysophytes (38%) was observed in October when the YSCWM was decaying. In a word, significant seasonal variations of phytoplankton biomass and community structure were observed in the central rather than the coastal area. These results were considered as the physical–chemical–biological characteristics of the unique ecosystem in the central YS.

ESA-MERIS 10-Year Mission Reveals Contrasting Phytoplankton Bloom Dynamics in Two Tropical Regions of Northern Australia

The spatial and temporal variability of phytoplankton blooms was investigated in two tropical coastal regions of northern Australia using the MEdium Resolution Imaging Spectrometer (MERIS) full mission (2002–2012) reduced resolution dataset. Satellite-derived proxies for phytoplankton (Chlorophyll-a (Chl), Fluorescence Line Height (FLH), Maximum Chlorophyll Index (MCI)) and suspended sediment (Total Suspended Matter (TSM)) were jointly analyzed for two clusters of the Great Barrier Reef Wet tropics (GBRW; 15°–19.5°S; Queensland) and the Van Diemen Gulf (VDG; 9°–13°S; Northern Territory). The analysis of time-series and Hovmöller diagrams of the four MERIS products provided a unique perspective on the processes linking phytoplankton blooms and river runoff, or resuspension, across spatio-temporal scales. Both regions are characterized by a complex oceanography and seasonal inflows of sediment, freshwater and nutrients during the tropical wet season months (November to April). The GBRW is characterized by a great variability in water clarity (Secchi depth 0–25 m). A long history of agricultural land use has led to a large increase in the seasonal discharge of sediments and nutrients, triggering seasonal phytoplankton blooms (&gt;0.4 mg∙m−3) between January and April. In contrast, the VDG is a poorly flushed, turbid (Secchi depth &lt;5 m) environment with strong tidal-energy (4–8 m) and very limited land use. Phytoplankton blooms here were found to have higher Chl concentrations (&gt;1.0 mg∙m−3) than in the GBRW, occurring up to twice a year between January and April. Over the 10-year MERIS mission, a weak decline in Chl and TSM was observed for the VDG (Sen slope: −2.85%/decade, τ = −0.32 and −3.57%/decade, τ = −0.24; p 0.05), while no significant trend in those two satellite products was observed in the GBRW. Cyanobacteria surface algal blooms occur in both regions between August and October. The MCI and FLH products were found to adequately complement Chl, while TSM provided relevant insight for the assessment of sediment resuspension and river runoff.

Gaussian processes retrieval of leaf parameters from a multi-species reflectance, absorbance and fluorescence dataset

Biochemical and structural leaf properties such as chlorophyll content (Chl), nitrogen content (N), leaf water content (LWC), and specific leaf area (SLA) have the benefit to be estimated through nondestructive spectral measurements. Current practices, however, mainly focus on a limited amount of wavelength bands while more information could be extracted from other wavelengths in the full range (400–2500nm) spectrum. In this research, leaf characteristics were estimated from a field-based multi-species dataset, covering a wide range in leaf structures and Chl concentrations. The dataset contains leaves with extremely high Chl concentrations (>100μgcm−2), which are seldom estimated. Parameter retrieval was conducted with the machine learning regression algorithm Gaussian Processes (GP), which is able to perform adaptive, nonlinear data fitting for complex datasets. Moreover, insight in relevant bands is provided during the development of a regression model. Consequently, the physical meaning of the model can be explored. Best estimates of SLA, LWC and Chl yielded a best obtained normalized root mean square error of 6.0%, 7.7%, 9.1%, respectively. Several distinct wavebands were chosen across the whole spectrum. A band in the red edge (710nm) appeared to be most important for the estimation of Chl. Interestingly, spectral features related to biochemicals with a structural or carbon storage function (e.g. 1090, 1550, 1670, 1730nm) were found important not only for estimation of SLA, but also for LWC, Chl or N estimation. Similar, Chl estimation was also helped by some wavebands related to water content (950, 1430nm) due to correlation between the parameters. It is shown that leaf parameter retrieval by GP regression is successful, and able to cope with large structural differences between leaves.

Phytoplankton dynamics in southern Portuguese coastal lagoons during a discontinuous period of 40 years: An overview

Shallow coastal lagoons in southern Portugal, such as the Ria Formosa and Alvor, are considered to be highly important both ecologically and economically. Given the impact of phytoplankton in the ecosystem productivity, it is important to understand its dynamics and to consider them for the assessment of ecosystem health.All available phytoplankton data (chlorophyll a; selected species composition and abundance) within the period from 1967 to 2011 were compiled within the framework of a project to implement the Water Framework Directive. Chlorophyll a (chl a) measurements in Ria Formosa from 1967 to 1968, 1985 to 1986, 1991 to 1992, 2006 to 2008, and 2010 show similar monthly averages with some exceptions. In the 80's the monthly averages were less than half of what was observed in the 60's. In the 90's, the chl a concentrations increased significantly and in the period from 2006 to 2010, chl a concentrations ranged between the values found in the 80's. The decrease in chl a concentrations during the 80's is likely to be associated with a peak in shellfish production. Shellfish production was recorded to have decreased from 1990 onwards. Chl concentrations in Ria de Alvor are found to vary within the same range as in Ria Formosa. However, data are limited and does not allow a detailed historical comparison.During the most important chl a peaks, the phytoplankton community was characterized by coastal species, such as Pseudo-nitzschia sp., which may be associated with upwelling events. This was found in Ria Formosa both in the 90's and from 2000 onwards, as well as in the most recent data from Ria de Alvor. This clearly indicates the influence of the coastal dynamics in these lagoons. High chl outside the lagoon confirmed the influence of coastal waters. In addition, high chl concentrations were also observed at inner parts of the lagoon but not outside, suggesting the existence of an interior maximum. The community was mainly characterized by the existence of low salinity tolerant species, such as Kryptoperidinium foliaceum.Over the time intervals in this study, the 90th percentile values of chlorophyll a concentrations were 3.0 in Ria Formosa and 2.6 mg m−3 in the Ria de Alvor. In a five-fold classification of ecological quality from High to Bad, we propose chlorophyll a concentrations of 5.3 mg m−3 as a reference value, 8 mg m−3 for the boundary High/Good, and 12 mg m−3 for the boundary Good/Moderate. According to this, all water bodies were considered as in High status.

Identification of non-indigenous phytoplankton species dominated bloom off Goa using inverted microscopy and pigment (HPLC) analysis

An unusual phytoplankton bloom dominated by unidentified green coloured spherical algal cells (∼5 μm diameter) and dinoflagellates (Heterocapsa, Scripsiella and Gymnodinium) was encountered along the coast of Goa, India during 27 and 29 January, 2005. Pigment analysis was carried out using both fluorometric and HPLC methods. Seawater samples collected from various depths within the intense bloom area showed high concentrations of Chl a (up to 106 mg m −3 ) associated with low bacterial production (0.31 to 0.52 mg Cm −3 h −1 ) and mesozooplankton biomass (0.03 ml m −3 ). Pigment analyses of the seawater samples were done using HPLC detected marker pigments corresponding to prasinophytes, dinoflagellates and diatoms. Chlorophyll b (36–56%) followed by peridinin (15–30%), prasinoxanthin (11–17%) and fucoxanthin (7–15%) were the major diagnostic pigments while pigments of cryptophytes and cyanobacteria including alloxanthin and zeaxanthin formed <10%. Although microscopic analysis indicated a decline in the bloom, pheaophytin concentrations in the water column measured by both techniques were very low, presumably due to fast recycling and/or settling rate. The unique composition of the bloom and its probable causes are discussed in this paper.

Marine microbial ecology in the sub-Antarctic Zone: Rates of bacterial and phytoplankton growth and grazing by heterotrophic protists

The sub-Antarctic zone (SAZ) of the Southern Ocean is considered one of the largest sinks for atmospheric CO 2 and as such is an important region for climate change research. To determine the importance of micro- and nano-heterotrophs in controlling microbial abundance within this region, we determined microbial standing stocks and rates of herbivory and bacterivory in relation to changes in the water masses south of Tasmania. The SAZ-Sense (‘Sensitivity of the sub-Antarctic zone to environmental change’) cruise traversed the SAZ during mid-late austral summer and focussed on process stations to the southeast (45°S, 153°E) and southwest (46°S, 140°E) of Tasmania and at the Polar Front (54°S, 147°E). Growth and grazing mortality of phytoplankton and bacteria were estimated by the grazing dilution technique using seawater from 10 m depth at 15 sites along the survey, along with concentrations of heterotrophic nanoflagellates (HNF), microzooplankton, bacteria, cyanobacteria and size fractionated (pico-, nano- and micro-sized) chlorophyll a (Chl a). Rates of herbivory ranged from 0.12 to 1.39 d −1 and were highest in the north-eastern SAZ (NE-SAZ) where concentrations of prey (as indicated by Chl a) and microzooplankton were also highest. Rates of herbivory were correlated with total rates of phytoplankton growth, bacterial growth and concentrations of microzooplankton. On average 82%, 67% and 42% primary production d −1 was consumed by microzooplankton and HNF at process stations in the north-western SAZ (NW-SAZ), NE-SAZ and polar frontal zone (PFZ), respectively. In the NW-SAZ, grazing pressure was highest on the pico-sized Chl a fraction, whereas in the NE-SAZ, grazing pressure was more evenly distributed across all three size fractions of Chl a. Bacterivory removed 77%, 93% and 39% of bacterial production d −1 in the NW-SAZ, NE-SAZ and PFZ, respectively, and rates of bacterivory ranged from 0.12 to 1.03 d −1. Rates of bacterivory were highest in the NE-SAZ where concentrations of bacteria were significantly higher than elsewhere in the region and bacterivory was correlated with bacterial growth rates and rates of cyanobacterivory. Cluster analysis of the concentrations of marine microbes and their rates of growth and grazing mortality identified 5 groups of sampling sites that differed in community structure. Analysis distinguished between high nutrient, low Chl a (HNLC) communities in the NW-SAZ that were iron-limited; iron-limited low Chl a PFZ communities; and iron-replete NE-SAZ communities where high rates of remineralisation correlated with higher concentrations of Chl a. Our findings show that much of the carbon sequestered by photosynthesis in the SAZ during summer is reprocessed via the microbial loop rather than contributing to vertical flux, particularly to the southeast of Tasmania. This suggests strong seasonality in carbon export in the region and that future climate-driven changes in oceanography may reduce carbon export from the region in summer.

Indicators of ozone effects on Fagus sylvatica L. by means of spectroradiometric measurements

In this paper optical indices calculated from leaf reflectance measurements, acquired with a high resolution spectroradiometer, were investigated to monitor Ostress on Fagus sylvatica L. from the strain phase to the damage phase when visible symptoms occur (e.g. chlorosis, leaf browning). The CI (Chlorophyll Index) was the most sensible index to a wide range of chlorophyll (Chl) concentrations (R 2 =0.93), the simple ratio R 695 /R 740 (Ctr2) was the most correlated to carotenoids/chlorophyll (Car/Chl) ratio (R 2 =0.65), while YI (Yellowness Index) was sensible to Car/Chl ratio and to low Chl values but tends to saturate at moderate to high Chl concentrations. PRI (Photochemical Reflectance Index ) was correlated with the physiological parameters NPQ (Non Photochemical Quenching) and ∆F/ ' Fm confirming this index is a good indicator of photosynthetic efficiency. Results from this experiment showed that CI, Ctr2 and PRI were reliable indices of O � effects on Fagus sylvatica L. before visible symptoms occurred, while YI was able to detect the senescence anticipation when visible symptoms already spread. These results were confirmed by physiological parameters measured in field (F v /F m, NPQ and / ' F Fm D ).

Chloroplastid pigment contents and chlorophyll a fluorescence in Amazonian tropical three species

Plants react to changes in light and hydrological conditions in terms of quantity and composition of chloroplastidic pigments, which affects the photosynthetic properties and consequently the accumulation of plant biomass. Thus, the chloroplastidic pigment concentration and chlorophyll a fluorescence of three Amazonian species (Bertholletia excelsa, Carapa guianensis e Dipteryx odorata) were investigated in sun and shade leaves form the tree crown collected during two distinct periods of precipitation (dry and rainy seasons). Pigment contents were determined by spectrophotometry and fluorescence variables were determined using a portable fluorometer. The results demonstrated that the species showed high concentrations of Chl a, Chl b e Chl total during the wet season in relation to the dry season, especially in shade leaves. A higher concentration of carotenoids was found in B. excelsa, when compared with leaves of C. guianensis and D. odorata. In leaves of B. excelsa and D. odorata no significant difference was found in relation to the photochemistry of photosystem II (Fv/Fm) between the wet and dry seasons. In conclusion, the three species react differently to variations in the light and precipitation conditions regarding light capture, aspects that might be considered in the management of forest plantations.

Influence of the Pearl River estuary and vertical mixing in Victoria Harbor on water quality in relation to eutrophication impacts in Hong Kong waters

This study presents water quality parameters such as nutrients, phytoplankton biomass and dissolved oxygen based on 11 years of water quality data in Victoria Harbor and examined how the Pearl River estuary discharge in summer and year round sewage discharge influenced these parameters. Nutrients in Victoria Harbor were strongly influenced by both the Pearl River and sewage effluent, as indicated by the high NO 3 inputs from the Pearl River in summer and higher NH 4 and PO 4 in Victoria Harbor than both its sides. N:P ratios were low in the dry season, but increased to >16:1 in the wet season, suggesting that P is potentially the most limiting nutrient in this area during the critical period in the summer. Although there were generally high nutrients, the phytoplankton biomass was not as high as one would expect in Victoria Harbor. In fact, there were high concentrations of chl near the bottom well below the photic zone. Salinity near the bottom was lower in Victoria Harbor than at the two entrances to Victoria Harbor, suggesting strong vertical mixing within Victoria Harbor. Therefore, strong vertical mixing and horizontal advection appear to play an important role in significantly reducing eutrophication impacts in Victoria Harbor. Consequently, dissolved oxygen near the bottom was low in summer, but only occasionally dipped to 2 mg L −1 despite the high organic loading from sewage effluent.

Changes in the mesozooplankton community associated with the hydrography off the northwestern Iberian Peninsula

Abstract Changes in the mesozooplankton community were investigated along the northwestern coast of the Iberian Peninsula during OMEX II cruises in August 1998, under upwelling conditions, and in October 1999, when there was a saline, warm poleward current flowing along the slope. Six stations, located at both the shelf break and in oceanic waters, were sampled for mesozooplankton by day and by night. Samples were grouped in accordance with their species abundance levels, and the resulting groups were compared with salinity, integrated chlorophyll a, and sea surface and average temperatures. The analysis discriminated stations from different cruises into different groups, and detected the influence of hydrographic structures. The abundance of species linked to high concentrations of Chl a and low temperature increased during the upwelling session, whereas species related to warmer water were more abundant during the 1999 cruise. Further, the analysis revealed differences in the mesozooplankton composition between coastal and oceanic sites, which were influenced to different degrees by the upwelling and the poleward current.

Growth Environment and Leaf Anatomy Affect Nondestructive Estimates of Chlorophyll and Nitrogen in Citrus sp. Leaves

Correlations between extractable leaf chlorophyll (Chl) concentration and portable, nondestructive leaf “greenness” meter readings imply that such estimates can be used as surrogate measurements of leaf nitrogen (N) status. However, few studies have actually found a direct relationship between Chl meter readings and leaf N. We evaluated the utility of two handheld transmittance-based Chl content meters (SPAD-502, Minolta Corp. and CCM-200, Opti-Sciences) and one reflectance-based meter (Observer, Spectrum Technologies), in estimating Chl and N concentrations in intact leaves of several citrus cultivars. Total Chl determined analytically, correlated well with nondestructive Chl meter readings (r2: 0.72 to 0.97; P &lt; 0.0001), but regression models differed among cultivars using the same meter and also among meters for a given cultivar. The relationships were generally more linear and stronger at low Chl concentrations (&lt;0.5 mmol·m-2) than at higher Chl concentrations, reflecting increased variability in Chl meter readings with increasing leaf Chl. Significant relationships between Chl meter readings and measured leaf N concentrations were also found in all the cultivars tested (r2: 0.23 to 0.69; P &lt; 0.01), but the data were more variable than those for Chl. Field-grown leaves were significantly thicker and had higher Chl meter readings than greenhouse-grown leaves of similar Chl or N concentrations. The results suggest that nondestructive Chl content meters can overestimate Chl and N in thicker leaves and/or leaves with high Chl concentrations. A single prediction equation derived from a wide range of Chl or N concentrations could be applicable across the range of citrus cultivars when grown in the same environment. Potential limitations associated with leaf thickness as influenced by environmental factors may necessitate the development of more specific calibration equations.

Topographically generated fronts, very nearshore oceanography, and the distribution of chlorophyll, detritus, and selected diatom and dinoflagellate taxa

At four sites (Sunset Bay, Miller's Cove, and Shore Acres 43° 20.13′ N; 124° 22.40′ W, Nellies Cove 42° 44.75′ N; 124° 29.75 W) along the Oregon coast, USA, relationships between fronts associated with shore-parallel foam lines and the distributions of chlorophyll, selected phytoplankters, and detritus were investigated. Sampling dates at the study sites were as follows: Sunset Bay, 1 August 1997, 25 June 1999 and 20 July 1999; Miller's Cove, 24 August 2000; Shore Acres, 19 July 1999 and 16 August 2000; Nellies Cove 17 August 2000 and 31 August 2000. Conductivity, temperature and depth data were used to describe the water masses on either side of the fronts, and vertical plankton tows with a 53-μm mesh net were used to describe the distribution of selected phytoplankters and detritus. At the cove sites during upwelling, fronts marked the presence of warm water within the bay and cooler water offshore. Chlorophyll a (Chl a) and phytoplankton concentrations were generally lower within the coves than seaward while detritus concentrations were higher. From 3 July 2000 to 15 September 2000, a period when upwelling winds from the north prevail, a time series of samples was collected at Sunset Bay. The front was only present during periods of upwelling favorable winds. During these periods there were significantly higher concentrations of Chl a, Pseudo-nitzschia spp., and Protoperidinium spp. seaward of the front than landward. During downwelling winds the front was absent and there were no significant differences in the concentrations inside and outside the mouth of the bay. At Shore Acres, an exposed, relatively straight stretch of shoreline, the shore-parallel front appears to be formed by boundary mixing. Chl a and phytoplankton from the coastal ocean spread well shoreward of the boundary-mixing front. When present, the front at the mouth of the coves and bay indicated the presence of water masses with distinct physical and biological characteristics, but not at Shore Acres. Alongshore differences in the very nearshore oceanography, by altering the availability of continental shelf phytoplankton production, may affect both the growth rates of intertidal benthic suspension feeders and community structure.

On the limits of applicability of spectrophotometric and spectrofluorimetric methods for the determination of chlorophyll a/b ratio

The concentration limits for spectrophotometric and spectrofluorimetric determinations of the chlorophyll (Chl) a/b ratio in barley leaves were studied using 80% acetone extracts at room temperature. The optimum sample absorbances (at 663.2 nm – maximum of the QY) band of Chl a) for the Chl a/b determination were determined. For given spectrometers and sample positions, these absorbances ranged between 0.2 and 1.0 and 0.008–0.1 for the absorption and fluorescence methods, respectively. Precision of the measurements and the distorting effects are discussed. The lower limits of both absorption and fluorescence methods depend on sensitivity of the spectrometers for the Chl b detection. The spectrophotometric determination of Chl a/b ratio at higher Chl concentrations can be distorted by the chlorophyll fluorescence signal. The extent of this distortion depends on sample-detector geometry in any given type of the spectrometer. The effect of inner filter of Chl molecules and the detection instrumental function affect the value of the upper limit for the spectrofluorimetric method. Both methods were applied to estimate the Chl a/b ratio in pigment extracts from greening barley leaves, which are characterized by a low Chl concentration and a high Chl a/b ratio at the beginning of greening process.

Phytoplankton pigment distributions and associated fluxes in the Bellingshausen Sea during the austral spring 1992

Pigment distribution patterns were investigated in the marginal ice zone of the Bellingshausen Sea and across the Drake Passage during the austral spring of November/December 1992. Elevated chlorophyll a (chl a) and fucoxanthin levels were observed at the Sub-Antarctic and Polar Fronts in the Drake Passage and at the Southern Polar Front in the Bellingshausen Sea. Investigations at 5 stations along 85°W in the Bellingshausen Sea between 70.3°S and 67.5°S revealed high concentrations of chl a (up to 24 000 ng l −1 ice melt) and fucoxanthin in hard pack ice samples and very low levels of pigments in the underlying water column (<100 ng l −1). At two ice melt stations, pigment concentrations in the ice were considerably lower and chl a in the upper mixed layer ranged from 120–250 ng l −1, with increased levels of hexanoyloxyfucoxanthin and chlorophyll b (chl b). In open water, the high chl a band at the Southern Polar Front (up to 2400 ng l −1) was associated with elevated fucoxanthin concentrations. Integrated concentrations, pigment ratios and a conversion of accessory pigments to chl a equivalents indicated that diatoms (fucoxanthin) were the most important group in the ice (>70%), although prymnesiophytes (hexanoyloxyfucoxanthin) and green algae (chl b) were present in smaller proportions. Diatoms dominated at the open water stations (>60%) and were prominent in the water column under the pack ice (52–61%). However, at the ice melt stations, prymnesiophytes (40–45%), green algae (11–13%) and, to a lesser extent, cryptophytes (4–6%; alloxanthin) collectively contributed more to the chl a biomass than the diatoms (37–42%). Budgeting the proportions of chloropigments indicated an increase in chlorophyllide a and phaeopigments from the ice to the northern open water stations, with chlorophyllide a being prominent in the upper water column and in the ice. Export fluxes of phytoplankton–carbon and phytodetritus in the upper 100 m were estimated from chloropigment inventories and residence times of 210 Po radionuclide reported by Shimmield et al. (1995) [Shimmield, G.B., Ritchie, G., Fileman, T.W., 1995. The impact of marginal zone processes on the distribution of 210 Pb , 210 Po and 234 Th and implications for new production in the Bellingshausen Sea Antarctica. Deep-Sea Res. II, 42 (1995) 1313–1335], revealing very low fluxes at the ice stations and up to 29 mg phyto-C m −2 day −1 at the open water high chlorophyll locality.