Photoinduced Intra- and Intermolecular Energy Transfer in Chlorophyll a Dimer

Applying nonadiabatic excited-state molecular dynamics, we investigate excitation energy transfer and exciton localization dynamics in a chlorophyll a (Chla) dimer system at the interface of two monomers of light-harvesting complex II trimer. After its optical excitation at the red edge of the Soret (B) band, the Chla dimer experiences an ultrafast intra- and intermolecular nonradiative relaxation process to the lowest band (Qy). The energy relaxation is found to run faster in the Chla dimer than in the Chla monomer. Once the molecular system reaches the lowest Qy band composed of two lowest excited states S1 and S2, the concluding relaxation step involves the S2 → S1 population transfer, resulting in a relatively slower relaxation rate. The strength of thermal fluctuations exceeds intraband electronic coupling between the states belonging to a certain band (B, Qx, and Qy), producing localized states on individual chromophores. Therefore, time evolution of spatial electronic localization during internal conversion reveals transient trapping on one of the Chla monomers participating in the events of intermonomeric energy exchange. In the phase space domains where electronic states are strongly coupled, these states become nearly degenerate promoting Frenkel-exciton-like delocalization and interchromophore energy transfer. As energy relaxation occurs, redistribution of the transition density on two Chla monomers leads to nearly equal distribution of the exciton among the molecules. For a single Chla, our analysis of excitonic dynamics reveals wave function amplitude transfer from nitrogen and outer carbon atoms to inner carbon atoms during nonradiative relaxation.Fil: Zheng, Fulu. Nanyang Technological University; SingapurFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Tretiak, Sergei. Los Alamos National Laboratory; Estados UnidosFil: Zhao, Yang. Nanyang Technological University; Singapu

Control of primary productivity and the significance of photosynthetic bacteria in a meromictic kettle lake.

During 1986 planktonic primary production and controlling factors were investigated in a small (A0 = 11.8 · 103 m2, Zmax = 11.5 m) meromictic kettle lake (Mittlerer Buchensee). Annual phytoplankton productivity was estimated to ca 120 gC · m–2 · a–1 (1,42 tC · lake–1 · a–1). The marked thermal stratification of the lake led to irregular vertical distributions of chlorophylla concentrations (Chla) and, to a minor extent, of photosynthesis (Az). Between the depths of 0 to 6 m low Chla concentrations (< 7 mg · m–3) and comparatively high background light attenuation (kw = 0,525 m–1, 77% of total attenuation due to gelbstoff and abioseston) was found. As a consequence, light absorption by algae was low (mean value 17,4%) and self-shading was absent. Because of the small seasonal variation of Chla concentrations, no significant correlation between Chla and areal photosynthesis (A) was observed. Only in early summer (June–July) biomass appears to influence the vertical distribution of photosynthesis on a bigger scale. Around 8 m depth, low-light adapted algae and phototrophic bacteria formed dense layers. Due to low ambient irradiances, the contribution of these organisms to total primary productivity was small. Primary production and incident irradiance were significantly correlated with each other (r2 = 0.68). Although the maximum assimilation number (Popt) showed a clear dependence upon water temperature (Q10 = 2.31), the latter was of minor importance to areal photosynthesis

Epilithic biomass in a large gravel-bed river (the Garonne, France): a manifestation of eutrophication?

In order to evaluate the impact of outputs of the city of Toulouse (740 000 inhabitants) on the epilithic communities colonizing pebble banks in the river Garonne, a large gravel-bed river (eighth order), dry mass (DM), ash-free dry mass (AFDM) and chlorophyll-a (chla) epilithic biomass per unit area were measured and autotrophic index (AI) (i.e. ratio AFDM/chla) was calculated at four stations. This river is morphologically characterized by a succession of pools and riffles and by highly fluctuating hydraulic conditions. At the four stations studied (223 km apart), the means of AFDM values varied between 17.1 and 31.1 g m−2 of colonized surface and the chla concentration varied between 112 and 254 mg m−2. However, there were no significant differences in AFDM per unit area between the parts of the river upstream and downstream of the Toulouse area (Mann–Whitney U-test statistic), nor between the four stations (Kruskal–Wallis test statistic), and the AI did not allow the description of changes in periphyton communities between sampling locations. This study showed that epilithic biomass should be considered as the typical microbial community of the river rather than as a manifestation of eutrophication

CHLOROPHYLL-A CONCENTRATIONS AFFECTED BY FRESHWATER INFLOW AND CLIMATE CONDITIONS IN GALVESTON BAY, TEXAS

As transition zones between river and ocean, estuaries face increasing pressure on their ecosystem health due to changes of freshwater quantity and quality – especially under the impacts of population growth, land use/land cover change, and climate change. Located southeast of Houston, Galveston Bay is of particular social and economic importance for the State of Texas. Its freshwater inflow primarily arises from the San Jacinto River and the Trinity River. While it is well recognized that Chlorophyll a (chla) concentration – an indicator of ecosystem health – is closely linked to river inflows and other environmental factors, no quantitative relationships have been established. The objectives of this study are to identify the spatial-temporal variations of chla, and to investigate the impacts of freshwater inflow and climatic factors on chla variability – so that prediction models can be developed for chla forecasting in Galveston Bay. A 10-year validated remote sensing chla dataset is used in this study. Spatially, there are two spots with low chla concentration compared with other places, locations close to the river mouths and the area of the bay where Houston Ship Channel located. Temporally, chla tends to be higher in wet years than in dry years. Similarly, the seasonal fluctuations of chla are more significant during the wet months (from February to May) than the dry months (especially from August to December). Chla concentrations in different segments of Galveston Bay are determined by different factors during different seasons. Discharge from the Trinity River is the main driver of chla in JFM (January, February, March), AMJ (April, May, June) and JAS (July, August, September) in all segments, expect West Bay (where the chla concentration is mainly determined by climatological variations). Also, water temperature plays a significant role in regulating chla, especially in JFM. Based on these analyses, a chla prediction model is developed and tested. Despite its limitations, this empirical model offers seasonal forecasts of chla which could support decision making in Galveston Bay

From chlorophyll a towards bacteriochlorophyll a: Excited-state processes of modified pigments

By means of fluorescence spectroscopy and nonlinear absorption experiments, excited-state processes of the modified pigments [3-acetyl]-chlorophyll a, [31-OH]-bacteriochlorophyll a and [3-vinyl]-bacteriochlorophyll a were investigated and compared with those of chlorophyll a and bacteriochlorophyll a

Enhancement of primary production in the North Atlantic outside of the spring bloom, identified by remote sensing of ocean colour and temperature

Peer reviewedPublisher PD

Investigating Changes in Chlorophyll a and Other Water Chemistry Variables in Response to Global Environmental Change

Changes in water quality are influenced by climate change and other anthropogenic stressors. We 1) assessed changes in water quality in lakes in the Laurentian Great Lakes region, and 2) compiled water quality data for lakes across the world to assess global patterns in chlorophyll a. We found that at the regional scale water quality (specifically chlorophyll a, total phosphorus, total nitrogen, and dissolved organic carbon) were influenced by temperature, precipitation, morphology, and the presence of dreissenids. We also compiled chlorophyll a and water chemistry data together with morphometric characteristics for 8557 lakes worldwide. This global dataset will allow researchers to associate global water quality patterns to different pressures such as changes climate or land use

Recent progress in the identification and determination of freshwater phytoplankton in the natural environment

The biomass of the phytoplankton and its composition is one of the most important factors in water quality control. Determination of the phytoplankton assemblage is usually done by microscopic analysis (Utermöhl's method). Quantitative estimations of the biovolume, by cell counting and cell size measurements, are time-consuming and normally are not done in routine water quality control. Several alternatives have been tried: computer-based image analysis, spectral fluorescence signatures, flow cytometry and pigment fingerprinting aided by high performance liquid chromatography (HPLC). The latter method is based on the fact that each major algal group of taxa contains a specific carotenoid which can be used for identification and relative quantification of the taxa in the total assemblage. This article gives a brief comparative introduction to the different techniques available and presents some recent results obtained by HPLC-based pigment fingerprinting, applied to three lakes of different trophic status. The results show that this technique yields reliable results from different lake types and is a powerful tool for studying the distribution pattern of the phytoplankton community in relation to water depth. However, some restrictions should be taken into account for the interpretation of routine data

Sea Surface Temperature Dan Chlorophyll-a Concentration Variabilities of Jakarta Bay and Its Surrounding Waters

Variability of sea surface temperature (SST) and the concentration of chlorophyll-a (Chla) in Jakarta Bay and its surrounding waters were analyzed based on the time series data of monthly mean SST and Chla estimated by NOAA AVHRR, SeaWiFS, and MODIS satellites for 17 years (1997 to 2014). Generally, the monthly mean SST values fluctuated seasonally with the semi-annual pattern with the maximum value occurred in the second transitional season (Oct-Nov) and relatively high in the first transitional season (Mar). In contrast, the minimum of monthly mean SST values was found during the east season (Jul) and relatively low during the west season (Des-Jan). SST variabilities were generally associated with the sun position, sea water circulation, and rainfall. Based on MODIS data, the minimum-maximum of monthly mean SST ranged of 28.39°C-32.58°C. Seasonal fluctuations with the semi-annual pattern also occurred in the monthly mean Chla values with the maximum value occurred during the west season (Des-Jan) and relatively high values occurred during the east season (Jun). In contrast, the minimum of the monthly mean Chla was found during the second transition season (Sep-Oct) and relatively low during the first transitional season (March-Apr). The minimum-maximum of monthly mean Chla ranged of 0.09 mg/m3-2.50 mg/m3. Chla fluctuations were generally associated with the variabilities of rainfall, river water discharge, and sea water circulation of the Java Sea. Anomalous climatic factors such as El Nino Southern Oscillation (ENSO) and La Nina produced a significant impact on the SST and Chla interannual variability. Generally, the ENSO phenomenon lo-wers the value SST and Chla, while La Nina events tended to increase Chla values