Variability Of Chlorophyll-a Concentration Research Articles

Spatiotemporal Assessment of Water Quality and Quantity of the Kaptai Lake at Rangamati, Bangladesh - An Approach of Remote Sensing, Field Investigation and Laboratory Analysis

Monitoring water quality and quantity is essential for sustainable water resource management. This study investigates changes in the extent and water quality of Kaptai Lake using remote sensing, field measurements, and laboratory analysis. Analysis of Landsat TM/OLI images from 1989, 2000, 2010, and 2021 shows that the lake's water extent ranges from 380 km² (in 2010) to 435 km² (in 2021), with an average of 407.5 km². The extent of water decreased by approximately 3% from 1989 to 2010 and increased by about 5% from 2010 to 2021 due to changing rainfall patterns, dam operations, sedimentation, and land use changes. Seasonal variations in chlorophyll-a concentration and turbidity, analyzed using Sentinel 2B images from 2022 and 2023, indicate mesotrophic to eutrophic conditions and higher turbidity in post-monsoon. The study found that nutrient enrichment from untreated sewage, agricultural runoff, and algal growth affect chlorophyll-a levels, while development activities, excessive rainfall, and sedimentation influence turbidity. Linear regression analyses show strong positive correlation between field obtained and image derived values both for chlorophyll-a (R2 0.621) and turbidity (R2 0.698). Physico-chemical parameters such as pH, EC and temperature have been measured in the field and hydrochemical parameters including, cations and anions have been measured by laboratory analysis to assess the contemporary water quality status. The average values for pH, EC and temperature are 7.55, 119.85 µS/cm and 22.17 °C respectively. The cationic dominance in the studied segment of the Lake is in the order of Ca2+ > Na2+ > Mg2+>K+ > Fe2+ >Mn2+. On the other hand, the anions are in the order of HCO3- > SO42- > Cl- > NO3-. All the physico-chemical parameters of the lake water fall within the Bangladesh Drinking Water Limit (BDWL) and are not linked to chlorophyll-a and turbidity variations. The findings of this study can help mitigate the deterioration of Kaptai Lake by addressing water quality and extent issues, promoting effective and sustainable lake management strategies. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 13(1), 2024, P 121-139

Patterns in the temporal complexity of global chlorophyll concentration

Decades of research have relied on satellite-based estimates of chlorophyll-a concentration to identify oceanographic processes and plan in situ observational campaigns; however, the patterns of intrinsic temporal variation in chlorophyll-a concentration have not been investigated on a global scale. Here we develop a metric to quantify time series complexity (i.e., a measure of the ups and downs of sequential observations) in chlorophyll-a concentration and show that seemingly disparate regions (e.g., Atlantic vs Indian, equatorial vs subtropical) in the global ocean can be inherently similar. These patterns can be linked to the regularity of chlorophyll-a concentration change and the likelihood of anomalous events within the satellite record. Despite distinct spatial changes in decadal chlorophyll-a concentration, changes in time series complexity have been relatively consistent. This work provides different metrics for monitoring the global ocean and suggests that the complexity of chlorophyll-a time series can be independent of its magnitude.

Variations in chlorophyll-a concentration in response to hydrodynamics in a flow-through lake: Remote sensing and modeling studies

A convolution neural network (CNN) machine learning algorithm is established for Chlorophyll-a retrieval in Poyang Lake using in-situ Chlorophyll-a concentrations and concurrent satellite image data. For comparison, other machine learning methods, e.g., deep neural network, XGBoost, random forest, gradient boost, decision tree, and linear regression, are also employed, together with two empirical models. Accuracy analysis validates the robustness of the CNN algorithm, with the R2 of 0.97 and the mean absolute errors of 1.74 μgL−1, and its performance is better than other machine learning and empirical algorithms. The Chl-a in Poyang Lake is derived from Sentinel-2 Multi-Spectral Instrument (MSI) images based on the robust CNN algorithm. As a follow-through type, Poyang Lake has abundant hydrodynamics affecting the Chl-a in the lake water. Thus, the Delft3D Flexible Mesh (FM) model is employed in Poyang Lake to simulate the active hydrodynamics with a high spatial resolution (∼80 m) under the realistic forcing in the period from 1 October 2020 to 15 March 2022. The simulation results reveal that the flow speed is a significant factor modulating the lake Chl-a with a high concentration in summer and a low concentration in winter; the flow speed and water storage exceed the temperature and solar radiance in modulating the Chl-a. The jacking effect of the Yangtze River can slow down the flow speed in the lake’s north channel, therefore, augmenting the Chl-a by ∼20%, favoring phytoplankton blooms in Poyang Lake. The active eddies may significantly affect the lake Chl-a; cyclonic eddies enhance the local Chl-a, and anticyclonic eddies weaken the Chl-a. A detailed analysis indicates that the Coriolis force plays a vital role in the momentum balance, which may cause the lift (restriction) of bottom nutrients in the cyclonic (anticyclonic) eddy area, increasing (decreasing) the surface nutrient supply. This study uses Poyang Lake as an example to show that such eddies conventionally appearing in a flow-through lake may dramatically affect the ecological environment in the lake water.

Response of planktonic foraminifera to seasonal and interannual hydrographic changes: Sediment trap record from the northern South China Sea

Foraminifera play an important role in the organic and inorganic carbon pumps of the ocean. Understanding their responses in seasonal and interannual time scales to the climate and seawater chemistry changes is important for studying carbon cycles and paleoclimatology. This study examined about 5.1-year continuous mass fluxes in 2013/9-2019/8 and 1.8-year planktonic foraminiferal shell fluxes in 2016/8-2019/8 census from ten and four sets of sediment traps, respectively, moored at the South East Asia Time-series Study (SEATS) site in the northern South China Sea (SCS), the world’s largest marginal sea. A total of four sets of sediment trap mooring with 11 common species were identified, spanning from August 2016 to August 2019 with 8-day and 16-day collecting periods, which provided access to evaluate the impact of the prevailing monsoon system and interannual climatic conditions. Our results show that the winter monsoon enhances the nutrient inventories in the euphotic zone, supporting the productivity and the mass and shell fluxes. In addition to seasonal cycles, the variation of chlorophyll-a concentration in the SCS shows a strong response to wind speed under the influence of El Niño–Southern Oscillation (ENSO). The reduction in wind speed and the intensification of Kuroshio intrusion during the ENSO warm phases reduces the productivity and mass and shell fluxes, and vice versa in the case of the ENSO cold phases. The imprint of an ENSO cold phase (La Niña event) in 2017 was signified by 2–3-fold higher values than the 3-year average of total mass and foraminiferal shell fluxes. Instead of the common dominance of Trilobatus sacculifer and Globigerinoides ruber among species composition, Neogloboquadrina dutertrei was the predominant species comprising over 40%–60% of total shells greater than 212 μm. Furthermore, the interval with an elevated abundance of N. dutertrei lasted throughout January 2018 (four collecting intervals). Foraminifera shell fluxes were the lowest during warm months (March-August) in 2019, which was coeval with the increase in proportions of Orbulina universa and Globigerinella calida. The unusual species composition might signify a weak ENSO warm phase (A weak El Niño event) between September 2018 and August 2019.

Application of remote sensing data for monitoring eutrophication of floodplain water bodies

The aim of this article was to investigate the influence of structural features of the floodplain water network on the spatial and temporal dynamics of chlorophyll-a concentration as an indicator of eutrophication. The research was conducted in the waters of the “Dnipro-Orilskiy” Nature Reserve. The geographic information base with polygonal objects which represented water bodies of the reserve was created on the basis of detailed geographical maps and the high resolution space images. The water bodies were characterized using such parameters as the distance of the water body centroid from the nearest shore of the Dnipro River, the area of the water body, the order of the water body and the connectivity of the water body. Chlorophyll-а concentration was estimated based on the surface algal bloom index. The information was obtained about 148 water bodies, 141 of which are water bodies in the floodplain of the Dnipro River. The area of floodplain water bodies within the reserve was 3.28 million m2. The area of floodplain water bodies ranged from 300–232,500 m2. Trophic State Index allows us to estimate the trophic level of Dnipro River waters as mesotrophic, water bodies of first and second order as eutrophic, and water bodies of third and fourth order as hypereutrophic. The dynamics of chlorophyll-a content in water followed the seasonal course of temperatures. The concentration was lowest in the cold period of the year and reached its maximum in the second half of summer. The autumn decrease occurred at the end of September. The seasonal course of air temperature was superimposed on the peculiarities of the temperature regime of a particular water body, which depended on its depth and flow rate. The time, water body area, distance from the Dnipro River channel, connectivity and order of water bodies were the statistically significant predictors of chlorophyll concentration in water and were able to explain 85% of the variation of this indicator. The increase in chlorophyll-a concentration with increasing order of a water body is due to a decrease in the intensity of water exchange and a decrease in the depth of water bodies of higher order. An increase in the order of a water body is accompanied by a branching network of water bodies, the ability of water bodies to clear sediments decreases. Sediment accumulation leads to a decrease in their depth. Warming of shallow ponds and accumulation of organic matter in them are factors of intensive growth of blue-green algae. The evacuation of surplus organic matter, which results from mass vegetation development with excessive nutrient inputs, is a key driver of the eutrophic regime of water bodies. The increasing importance of regulatory processes develops in agreement with an increase in chlorophyll-a concentration in a water body. The importance of the considered factors reaches the highest level in summer time, when simultaneous maximum warming of water bodies and minimum water level in them take place. Accordingly, the differences between deep and relatively cool water bodies and shallow water bodies that warm up quickly, which significantly stimulates the growth of organic mass, reach the greatest contrast. The spatial patterns of variation in chlorophyll-a concentration have a complex multiscale structure, indicating the multiple nature of the acting factors. The spatial variability was represented as a composition of broad-scale and medium-scale spatial processes. The broad-scale process is most dependent on connectivity, whereas for the medium-scale process the leading one is the effect of water body order.

Hydrographic variation in a tropical coral reef system: The Veracruz Reef System, Gulf of Mexico

Three thousand forty-one profiles of temperature, salinity, density, dissolved oxygen, nitrogen and chlorophyll-a were used to study their seasonal variation on a tropical coral reef system, located in the central part, of the reef corridor of the southwestern Gulf of Mexico. The results revealed three seasons according to their hydrographic variations; the northerly wind season from September to April; the dry season from May to June; and the rainy season from July to August. The results of the density ratio during the dry season were ∼1.25 on average, while during the rainy season it had an average value of ∼0.62. Thus, the pycnocline was more influenced by the halocline during the rainy season and by the thermocline during the dry season. There was also an evident variation in chlorophyll-a concentration over the water column, which was not evident in the surface layer. During the summer (rainy season), dissolved oxygen was related to chlorophyll-a concentration; while, during the winter (northern wind season), these values were related to the vertical mixing of the water column due to wind stress. There was evidence of cooler ocean water intrusion into the Veracruz Reef System during the spring-summer season below ∼10 m. Finally, a second halocline, pycnocline, and nitrocline were found near ∼30 m depth during the rainy season.

Impact Assessment of PSBB on Variations of NO2, CO, and Chlorophyll-a Concentration in Java Island during the COVID-19 Pandemic based on Multi-satellite Imagery Data

The enactment of the PSBB (Large-scale Social Restriction) on April to May 2020 due to COVID-19 pandemic, has reduced residents’ activities, especially in Java Island, the most populous area in Indonesia with high anthropological activities. This policy may affect the conditions of atmospheric and water environment around the island of Java. NO<sub>2</sub> and CO concentrations in atmosphere along with chlorophyll-a concentrationin the ocean are environmental indicators that can be observed through satellite imagery. Satellite data TROPOMI and CMEMS were used to investigate the variation of those concentrations in the atmosphere and ocean during PSBB. Oceanographic and atmospheric daily data of each parameter over the Java Island region were retrieved and merged into gridded data with 1 km spatial resolution to be compared. Variations of chlorophyll-a concentration within the same month over the previous years were also taken into account. NO<sub>2</sub>, CO, and chlorophyll-a concentration were fluctuating during the PSBB period, but tended to decrease in the early phase of PSBB.The higher concentration of chlorophyll-a concentrated in the northern coastal areas of Java Island. In Jakarta and Surabaya, chlorophyll-a concentrations value during April-May 2020 were decreased by 48% and 27% compared to the previous three years’ averages. Human activities were thought to be the main factor influencing variations in the concentration of NO<sub>2</sub>, CO, and chlorophyll-a during PSBB enactment

Early Warning of Harmful Algal Bloom Risk Using Satellite Ocean Color and Lagrangian Particle Trajectories

Combining Lagrangian trajectories and satellite observations provides a novel basis for monitoring changes in water properties with high temporal and spatial resolution. In this study, a prediction scheme was developed for synthesizing satellite observations and Lagrangian model data for better interpretation of harmful algal bloom (HAB) risk. The algorithm can not only predict variations in chlorophyll-a concentration but also changes in spectral properties of the water, which are important for discrimination of different algal species from satellite ocean color. The prediction scheme was applied to regions along the coast of England to verify its applicability. It was shown that the Lagrangian methodology can significantly improve the coverage of satellite products, and the unique animations are effective for interpretation of the development of HABs. A comparison between chlorophyll-a predictions and satellite observations further demonstrated the effectiveness of this approach: r2 = 0.81 and a low mean absolute percentage error of 36.9%. Although uncertainties from modeling and the methodology affect the accuracy of predictions, this approach offers a powerful tool for monitoring the marine ecosystem and for supporting the aquaculture industry with improved early warning of potential HABs.

Insights from barium variability in a Siderastrea siderea coral in the northwestern Gulf of Mexico

Coral Ba/Ca is a proxy for seawater barium concentration that varies with upwelling, terrigenous input, and marine productivity whereas coral Sr/Ca varies with temperature. We examine monthly coral Ba/Ca and Sr/Ca before and during offshore oil exploration in a Siderastrea siderea coral from West Flower Garden Bank located on the continental shelf edge in the Gulf of Mexico. Coral Ba/Ca variations lack pulses driven by upwelling or river outflow and are not in sync with coral Sr/Ca that exhibit a different seasonal pattern. Seasonal variations in chlorophyll-a concentration negatively correlate with coral Ba/Ca explaining 25% of that variability. A significant increase in mean coral Ba/Ca of 1.76 μmol/mol between 1931–1944 and 1976–2004 corresponds to the increase in the United States barite production and consumption primarily used in offshore oil drilling, which escalated in the 1970s, suggesting oil drilling operations are increasing seawater Ba concentration in the Gulf of Mexico.

Phytoplankton bloom detection during the COVID-19 lockdown with remote sensing data: Using Copernicus Sentinel-3 for north-western Arabian/Persian Gulf case study

To examine whether a country-wide COVID-19 lockdown affected phytoplankton development, variability of chlorophyll-a concentrations in the north-western Arabian/Persian Gulf (Kuwait Bay) was investigated using remote sensing instruments Sentinel OLCI between 2018 and 2020 and compared to available in situ collected data. Satellite-retrieved chlorophyll concentrations considerably increased in inshore waters of Kuwait Bay, 1–2 months following the initiation of the 24/7 curfew. The extremely high concentrations of dissolved inorganic nutrients, especially ammonia, and coincided phytoplankton bloom were revealed in June-July 2020 by opportunity field sampling, supporting the satellite-derived bloom detection. Remote sensing operational monitoring with high spatial resolution sensors provides an exceptional opportunity for emergency analysis and decision making in conditions of natural or anthropogenic crises, which forces the development of regional remote sensing algorithms for the shallow marine environment of the Gulf.

Statistical tools for studying the temporal variations in chlorophyll-a concentration along the Southwest Bay of Bengal waters

Multivariate statistical analysis such as Multiple Linear Regression (MLR) and Principal Component Analysis (PCA) are used to study the effect of physico-chemical parameters on chlorophyll distribution along the southwest Bay of Bengal from January 2012 to June 2014. Physical properties recorded showed clear seasonal patterns in sea surface temperature (26.2 – 32.8 °C), salinity (24 – 36 PSU), pH (7.808 to 8.428), photosynthetic photon flux (522 – 1220.4 µM m-2s-1) with the minimum and maximum values during monsoon and summer seasons, respectively. In contrast, the chemical variables such as nitrite (0.15 to 2.35 µM), nitrate (1.02 to 6.58 µM), ammonia (0.11 – 5.22 µM), total nitrogen (1.04 to 11.58 µM), inorganic phosphate (0.16 – 2.97 µM), total phosphorus (0.55 – 8.60 µM) and reactive silicate (2.00 to 23.95 µM) showed the minimum and maximum concentration during summer and monsoon seasons, respectively. The high and low chlorophyll (0.10 to 6.92 µg l-1) and dissolved oxygen (4.07 and 7.884 mg l-1) concentrations are observed during summer and pre-monsoon seasons, respectively. PCA found that nitrogenous nutrients and chlorophyll are positively loaded and Sea Surface Temperature (SST) was negatively loaded in all the seasons except during summer season. Inter-comparison of modeled and in-situ chlorophyll-a (chl-a) concentration showed a significant correlation during monsoon season by 93 % of matchup with a R2 = 0.930, N = 60 and SEE = ±0.369 compared to other seasons. Regression analysis also predicted the positive influence of nitrate and ammonia and negative influence of SST with chl-a.

Phytoplankton Diversity Relates Negatively with Productivity in Tropical High-Altitude Lakes from Southern Ecuador

Tropical high-altitude lakes are vital freshwater reservoirs in the Andean regions. They are heavily threatened by human activities that may alter their functioning and hamper the provisioning of key ecosystem services such as water supply. Despite their ecological and social relevance, we know little about these waterbodies, especially regarding the factors influencing their functioning. Here, we explored the links between several environmental variables and phytoplankton productivity, measured as chlorophyll-a concentration and total phytoplankton biovolume. For this, we sampled twenty-four tropical high-altitude lakes located over three-thousand meters above sea level in Southern Ecuador. We found that four abiotic factors combined explained 76% of the variation in chlorophyll-a concentration amongst lakes. Contrary to what studies from temperate regions suggest, taxa richness was not related to either chlorophyll-a concentrations or total phytoplankton biovolume. Moreover, phytoplankton biovolume diversity was negatively correlated to both chlorophyll-a concentrations and total phytoplankton biovolume. This was due to a very uneven distribution of productivity amongst taxa in the more productive lakes. To the best of our knowledge, this is the first attempt to explore the determinants of phytoplankton functioning in tropical high-altitude lakes. We hope that this study will help to establish a baseline for evaluating the consequences of human activities in the ecology and functioning of this vital but fragile ecosystem. Our results suggest that by modifying the abiotic and biotic parameters of tropical high-altitude lakes, human activities can indirectly impact their functioning and their capacity to provide vital ecosystem services.

Data Mining of Spatio-Temporal Variability of Chlorophyll-a Concentrations in a Portion of the Western Atlantic with Low Performance Hardware

The contemporary scientific literature that deals with the dynamics of marine chlorophyll-a concentration is already customarily employing data mining techniques in small geographic areas or regional samples. However, there is little focus on the issue of missing data related to chlorophyll-a concentration estimated by remote sensors. Intending to provide greater scope to the identification of the spatiotemporal distribution patterns of marine chlorophyll-a concentrations, and to improve the reliability of results, this study presents a data mining approach to cluster similar chlorophyll-a concentration behaviors while implementing an iterative spatiotemporal interpolation technique for missing data inference. Although some dynamic behaviors of said concentrations in specific areas are already known by specialists, systematic studies in large geographical areas are still scarce due to the computational complexity involved. For this reason, this study analyzed 18 years of NASA satellite observations in one portion of the Western Atlantic Ocean, totaling more than 60 million records. Additionally, performance tests were carried out in low-cost computer systems to check the accessibility of the proposal implemented for use in computational structures of different sizes. The approach was able to identify patterns with high spatial resolution, accuracy and reliability, rendered in low-cost computers even with large volumes of data, generating new and consistent patterns of spatiotemporal variability. Thus, it opens up new possibilities for data mining research on a global scale in this field of application.

Removal of diatom Nitzschia sp. cells via ozonation process catalyzed by martite nanoparticles

Abstract Martite nanoparticles (MNPs) catalyzed ozonation process was utilized for rapid and effective degradation of diatom Nitzschia sp. cells. MNPs were produced using high-energy planetary ball milling technique from the natural martite particles (NMPs). Complete examination of the physical and chemical characteristics of NMPs, and MNPs were carried out by investigating the X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and atomic absorption spectroscopy (AAS) analyses. The role of MNPs was investigated by XPS analysis, calculating the synergistic factor, and monitoring the dissolved concentration of ozone and oxygen. The decreased dissolved ozone concentration and increased oxygen concentration accompanied with the increased synergistic factor confirmed the positive role of Fe2+ and Fe3+ species in MNPs. The progress of the process through indirect mechanism was determined using simple organic and inorganic compounds acting as ROSs scavengers. Accordingly, the process for the diatom removal was mainly fulfilled by successive attacks hydroxyl radicals ( OH) and superoxide radicals (O2− ). For identifying the effectiveness of the MNPs catalyzed ozonation process, the light microscopic along with SEM images, variation of chlorophyll-a concentration, GC–MS and COD analyses were studied. The results confirmed the destruction of complex structure of diatom cells to the simple structures. Also, the results proved the simultaneous degradation of diatom cells and their chlorophyll a content in the reaction media indicating the effectiveness of this process in comparison with other studied processes.

Different responses of chlorophyll-a concentration and Sea Surface Temperature (SST) on southeasterly wind blowing in the Sunda Strait

During southeast monsoon, along the western coast of Sumatra Island and southern coast of Java Island are known as the coastal upwelling areas denoted by the occurrence of Sea Surface Temperature (SST) cooling and chlorophyll-a blooming. Located between Sumatra and Java Islands, Sunda Strait waters may give different response to the southeasterly wind blowing above. Using SST and chlorophyll-a data obtained from daily MODIS level 3 during 2006–2016, this study demonstrated the evidence on how bathymetry and topography modified the effect of southeasterly wind on the spatial variability of SST and chlorophyll-a. All datasets were composed into monthly and monthly climatology. The area in the center of Sunda Strait had the lowest chlorophyll-a concentration and the warmest SST during the peak of upwelling season. The deep bottom topography and the absence of barrier land prevented the generation of wind driven coastal upwelling. However, the chlorophyll-a concentration in this area had the highest correlation with the wind speed which means that the variation of chlorophyll-a concentration in this area was highly depended on the variability of wind. On the other hand, the areas with shallow bathymetry and in front of Panaitan and Java Islands had higher chlorophyll-a concentration and cooler SSTs.

Preparation of martite nanoparticles through high-energy planetary ball milling and its application toward simultaneous catalytic ozonation of two green algae

Abstract The efficiency of heterogeneous catalytic ozonation in the presence of martite nanocatalyst was studied as a novel method for the thorough and in situ removal of Oocystis sp and Cosmarium sp green algae. High-energy planetary ball milling was utilized to prepare martite nanoparticles (MNPs) from natural martite particles (NMPs). X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR) analysis, X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) were carried out to determine the physical and chemical characteristics of NMPs, and MNPs. The mechanism of heterogeneous catalytic ozonation was investigated in the presence of different reactive oxygen species (ROSs) scavengers. The degradation process was accomplished via the continuous attacks of hydroxyl radicals (•OH) and superoxide radicals (O2−•). The variation of chlorophyll-a concentration and the morphologies of the algae cells were investigated. The results obtained from chlorophyll-a content, light microscopic and SEM images revealed the complete degradation of the algae cells. Moreover, the main elements of algae structure and intermediates, generated during the degradation process were identified using EDX and GC–MS analysis. The mineralization efficiency of the proposed catalytic ozonation process was investigated using of COD results.

Variability of chlorophyll-a concentration in the Gulf of Guinea and its relation to physical oceanographic variables

The Gulf of Guinea represents a wide tract of the African coast with complex and rich coastal ecosystems undergoing various pressures. The seasonal variations of chlorophyll-a concentration (Chla) along the Gulf of Guinea (GoG) and their relations with physical oceanographic variables were analyzed using satellite observations covering the period 2002–2012. The effects of sea surface temperature (SST), sea level anomalies (SLA), winds, geostrophic currents, eddy kinetic energy (EKE), mesoscale eddies and fronts were considered on a monthly time scale. The analysis for each unit area was carried out on a chlorophyll index (IChla) computed as the product of the mean distance from the coast to the eutrophic threshold (1mgm−3 isoline) and the average Chla in the eutrophic area. The study, based on satellite-derived Chla, was allowed by the unprecedented coverage given by the products distributed by the ESA Ocean Colour Climate Change Initiative (OC_CCI) resulting from the merging of data from several satellite missions. The physical variables served as potential predictors in a statistical Boosted Regression Tree (BRT) model. To account for the heterogeneous nature of the GoG, the analysis was conducted on eight systems that made up a partition of the whole region defined on the basis of the BRT model results and climatological properties. The western-most domain, from Guinea-Bissau to Sierra Leone, was associated with upwelling properties in boreal winter and appeared to share some characteristics with the overall Northwest African upwelling system. The region of Ivory Coast and Ghana also had upwelling properties but the main upwelling season was in boreal summer. In general upwelling conditions with cold SST, negative SLA, fairly strong frontal activity, and moderate winds, appeared as the environmental window most favorable to high IChla values. For these systems, the BRT model fitted the IChla data well with a percentage of explained total deviance D2 between 70% and 91% when using only physical oceanographic variables. Finally, the systems associated with the coasts of Nigeria to Gabon showed some mixed properties, with D2 values of 54–60%. Among these systems, a common feature seemed to be the importance of river discharge to explain IChla variations. Where possible (for the Niger River in the Nigeria system), the addition of river data as predictor in the BRT model resulted in a significant increase of D2 to 75%. Further progress is needed to understand the observed relationships and to predict how they can evolve in the face of climate change.

Remote Sensing-Based Study on the Temporal Variations in Chlorophyll-a Concentration After Confo Oil Spill in Bohai Sea

The satellite-derived chlorophyll-a concentration was used to measure the impact of oil contamination on marine environment after the oil spill on June 4, 2011 in the Bohai Sea. The chlorophyll-a concentration and sea surface temperature was derived from MODIS images with 38.47 % and 7.63 % uncertainty, respectively. The impacts of oil spill on aquatic environments can be divided into three stages: (1) the beginning stage (0–7 weeks), during which the toxicity of other pollutants besides the oil exceeds the tolerance of most algae in the Bohai Sea; (2) the self-repairing stage (7–51 weeks), during which the petroleum hydrocarbon concentration is diluted by the physical and chemical degradation process of aquatic ecology and petroleum hydrocarbon becomes one an important carbon source for algal growth; and (3) long-term toxic affecting stage (>1 year). However, there is currently little knowledge about the long-term toxic effect of oil spill on the natural assemblages of marine phytoplankton. In this study, we determined that the process for delivering nutrients required for algal growth from seabed to water column is slowed by the ‘oil-packaged’ suspended particles above the seabed. These results may be helpful for oil spill response, ecological remediation, and environment monitoring.

Determinants of chlorophyll-a concentration in tropical reservoirs

Predictive models for chlorophyll-a concentration are the most common ecological tools for water-quality management. However, the interactions among factors driving eutrophication processes remain poorly understood. In addition to nutrient concentrations, other variables such as, for instance, hydrology, land use and biotic interactions may also be included as explanatory variables. Here, we compared a set of a priori models (which included local, morphological, and landscape variables) with respect to their power to predict chlorophyll-a concentration in 21 reservoirs of central Brazil. The best model, selected according to the Akaike information criterion, explained 67.7% of the variation in chlorophyll-a concentration, and indicated a positive relationship with total phosphorus concentration (the main predictor in our model) and depth. Turbidity was negatively correlated with chlorophyll-a concentration. Contrary to recent studies indicating the importance of landscape predictors, our results suggested a preponderance of local factors in determining chlorophyll-a concentration, and that the control of phosphorus sources in tropical reservoirs is as important as it is in temperate ecosystems. We also detected a substantial uncertainty regarding the best model, suggesting that further studies should focus on explicitly modeling the variation in the strength of the relationships between chlorophyll-a and explanatory variables.

The regional impacts of climate change on coastal environments and the aquaculture of Japanese scallops in northeast Asia: case studies from Dalian, China, and Funka Bay, Japan

Climate changes affect coastal environments and aquaculture, threatening food security and economic growth. Japanese scallop (Mizuhopecten yessoensis) culture is economically important for the coastal communities of Dalian, China, and Funka Bay, Japan. In this study, we combined satellite remote-sensing data, in situ observations, and a suitable aquaculture site selection model to explore the interactions between marine environments and climate variability over a recent 10-year period (2003–2012). Our selection of appropriate zones in these two Far Eastern regions and our analyses of climatic event (Arctic Oscillation (AO), winter East Asian monsoon (EAM), and El Niño/La Niña Southern Oscillation (ENSO)) and meteorological (precipitation, temperature, and wind) data allowed us to determine the impacts of climate change on regional coastal environments and prospects for scallop aquaculture. These analyses showed that AO and EAM strongly influenced the aquaculture areas on the Dalian coast through their effects on temperature during winter. We also determined that wind was the main driving force behind regional environmental changes during spring. Conversely, ocean conditions and suitable areas in Funka Bay changed rapidly relative to oceanic and atmospheric circulation. In Funka Bay, areas appropriate for scallop aquaculture and variations in chlorophyll-a concentration (which reflect the availability of algal food for scallops) were strongly correlated with ENSO, precipitation, and air temperature. These correlations demonstrate the influence of oceanic and atmospheric parameters on the productivity of scallop aquaculture in Funka Bay. Adaptation to oceanic and atmospheric changes should be considered when developing plans and management strategies for coastal scallop aquaculture in northeast Asia.