Increase Of Chl-a Concentration Research Articles

Response of chlorophyll-a to rainfall event in the basin of the South China sea: Statistical analysis

Chlorophyll-a (Chl-a) is an essential ecological indicator, and affected by processes such as typhoons, mesoscale eddies, and Rossby waves. However, the impact of more frequent and widespread precipitation events on Chl-a seems to be overlooked. This study utilized remote sensing data and reanalysis data to investigate the response of Chl-a to 240 precipitation events in the central South China Sea from 2005 to 2019. The results indicate that precipitation events have a significant impact on Chl-a concentration. Following a precipitation event in 2019, the Chl-a concentration in the affected area increased by approximately 0.22 mg m−³ from the 3rd to the 7th day. The reasons for the increase in Chl-a concentration were the vertical mixing induced by wind stirring and the upwelling caused by wind stress curl, which transported nutrients to the euphotic zone, lowering the sea surface temperature and triggering a proliferation of phytoplankton. Additionally, dissolved nutrients in precipitation provided a nutrient source for Chl-a growth. The contributions of nutrient supply, wind speed, and wind stress curl to the increase in Chl-a concentration during precipitation events were 18%, 37%, and 45%, respectively. Precipitation events enhanced marine primary productivity, playing a crucial role in deepening our understanding of ocean-atmosphere interactions and their impact on marine ecosystem.

Remote impacts of low-latitude oceanic climate on coastal upwelling in a marginal sea of the Northwestern Pacific

Upwelling plays an important role in the physical processes and biological variability of coastal regions. Using 40-year-long hydrographic and climate data, the remote impacts of low-latitude oceanic climate on the upwelling along the east coast of Korea were investigated. During El Niño, the development of anomalously enhanced anti-cyclonic circulation over Northwestern Pacific resulted in relatively strong (∼1.1 m s−1) southerly winds, compared to La Niña. During El Niño, the mean upwelling index was 402 ± 106 kg m−1 s−1, and 10 °C isotherm was located at a depth of 32.7 m. During La Niña, they were 368 ± 95 kg m−1 s−1 and 39.9 m, respectively. During El Niño, in the approximation, the offshore Ekman transport by wind-induced upwelling and the vertical transport by isotherm were higher than those during La Niña. This finding can be explained by the increased sea surface height gradient, the subsequent enhanced geostrophic current, the decrease in onshore sea surface temperature, and the increase in chl-a concentration during El Niño. The intensity of upwelling tended to be stronger (weaker) during periods when El Niño (La Niña) and the PDO (Pacific Decadal Oscillation) were in phase than those when they were out of phase. These results suggest that low-latitude climate change could affect the coastal upwelling in the mid-latitude marginal sea through the teleconnection.

Long-term spatial-temporal monitoring of eutrophication in Lake Burdur using remote sensing data.

Lake eutrophication continues to be one of the major environmental challenges in lakes worldwide. This study is about using a remote sensing approach to monitor long-term chlorophyll-a (Chl-a) concentrations and the trophic state index (TSI) in Lake Burdur, Türkiye. Surface reflectance from Landsat 5, Landsat 7, and Landsat 8 satellite image collections were evaluated with an empirical equation to estimate a 38-year-long (1984-2021) time series of the lake's median Chl-a concentrations. Pixel quality masking was applied to retain only acceptable quality information and exclude images affected by cloud cover, icing, and other environmental factors from the analysis. The results were analyzed based on annual, seasonal, and monthly temporal averages. Over a period of 38 years, Chl-a concentrations were found to vary between 58.7 and 196.4 mg/m3. Notably higher concentrations were recorded in 2010 and 2021, while lower concentrations were observed between 1991 and 1993. A substantial increase in Chl-a concentration was evident from 2002 to 2010. The maximum concentration of Chl-a during the first two decades of the analysis was 130 mg/m3, which increased to 200 mg/m3 during the last two decades. Landsat-derived TSI values suggested that Lake Burdur has been mostly hypertrophic for the entire study period.

Reducing the water residence time is inadequate to limit the algal proliferation in eutrophic lakes

The eutrophication problem now threatens many lakes and reservoirs. To avoid the occurrence of algal blooms, some cities try to increase the flow rate or directly choose lakes or reservoirs with a short water residence time (WRT) as drinking water sources. However, up to now, whether such a strategy can achieve its goal is still unclear. In this study, a newly restored lake with a WRT of approximately 3 days was chosen to investigate algal growth potential as well as its responses to external nitrogen (N) and phosphorus (P) inputs. The results suggested that although the water quality of the lake could generally meet the environmental quality standards for surface water, dissolved inorganic nitrogen reached a high level with an average value of 1.58 mg/L. Meanwhile, a considerable increase in Chl-a concentration was observed across the flow direction. Especially, in July, Chl-a concentration at the site near the outlet was 8.1 times higher than that at the inlet, and cyanobacteria became the dominant species accounting for 83% of the total cell density. Nutrient enrichment experiments showed that algae could grow rapidly within 3 days with average specific growth rates (μ) of 0.36–0.42 d−1. The addition of N and P furtherly promoted the algal growth, and μ values of the treatments with P addition were the highest at 0.67–0.83 d−1. These results indicated that even if the WRT was reduced to 3 days, the risk of the occurrence of algal blooms still exists, and this undesirable trend would be enhanced by the short-term external nutrient input. Our findings indicated that the hydrodynamic control measures may not be entirely successful in protecting the drinking water source from algal blooms, especially when its influent has already been under eutrophication.

Analysis of Changes in River Water Quality Due to Weir Installation

There has been an increase in the amount of pollutants such as biochemical water and factory wastewater discharged from urban areas as a result of urbanization and industrialization. Therefore, research on securing water resources and improving water quality in rivers around cities is being actively conducted. This study analyzed the pattern of change of water quality due to the installation of overflow type weirs among the hand structures in the existing river. The target watershed was performed at Gilancheon, located in Andong-si, Gyeongsangbuk-do. The flow coefficient was calculated by analyzing the flow velocity and water level according to weir installation using the HEC-RAS. Afterwards, the QUALKO model was built, and the water quality analysis according to weir installation was performed by applying the flow coefficient calculated using HEC-RAS. As a result of the analysis, the flow rate was found to have decreased, and a stagnation section occurred due to the influence of weir installation, resulting in an increase in Chl-a. Due to the increase of Chl-a, BOD increased by 29%-32%, and T-N and T-P, which are nutrients for Chl-a, decreased. Therefore, an increase in Chl-a concentration due to weir installation can cause eutrophication due to the growth of green algae in the river, and it is believed that it can greatly affect the deterioration of water quality. Furthermore, it is considered that it will be able to help predict changes in water quality for the installation and operation of weirs in the future.

Validity evaluation of a machine-learning model for chlorophyll a retrieval using Sentinel-2 from inland and coastal waters

The MultiSpectral Instrument (MSI) on-board Sentinel-2 provides satellite images at spatiotemporal resolutions suitable for chlorophyll a (Chla) retrieval from inland and coastal waters. Machine-learning (ML) algorithms including light gradient boosting machine (LGBM) were employed for Chl a retrieval from MSI. The study area encompasses 78 lakes and estuaries located across four major river watersheds in South Korea. Matchup data between MSI overpass and near-concurrent in situ Chl a measurements from December 2018 to April 2021 were included. The remote sensing reflectance (Rrs) values of six single spectral bands and four two-band ratios were used as the input features. Despite the difficulty in Chla estimation in optically complex waters, ML algorithms showed overall reasonable accuracy. Among the ML algorithms, LGBM exhibited the best performance (R2 = 0.75, bias = -0.15, slope = 0.73, RMSE = 15.15 mg·m-3, MAE = 9.49 mg·m-3) over a wide range of trophic states. Post-hoc interpretations of the best performing LGBM using Shapley additive explanations indicated that Rrs(704)/Rrs(665) was the most important feature, while Rrs(739)/Rrs(704) and Rrs(492)/Rrs(560) played auxiliary roles in Chl a retrieval through interaction with Rrs(704)/Rrs(665). Among-lake spatial variations of Chla were explained by percent forest and agricultural area within the buffer zone at multiple scales (buffer widths of 50 m and 500 m). The associations between the modeled Chla and buffer land cover types, that is, increase in Chla concentration with increase in percent forest and decrease in percent agricultural area, were consistent with the established ecological knowledge. Overall, the model interpretations and spatial variations in Chla within and among lakes confirmed the validity of LGBM for retrieving MSI-derived Chla from lakes and estuaries. Our study can serve as the reference for evaluating the validity of complex ML models for inland water remote sensing.

Response of phytoplankton biomass to nutrient stoichiometry in coastal waters of the western Bay of Bengal

The hydro-biological parameters such as thermohaline structure, nutrients, and chlorophyll-a (chl-a) during pre-southwest monsoon (PRSWM) and post-southwest monsoon (POSWM) periods of 2017, was investigated and compared along a coastal transect in the western Bay of Bengal (BoB). The impact of cold-core and warm-core eddies on chl-a in the very near coastal waters of the western BoB was analyzed. During PRSWM period, the water column was recharged with phytoplankton growth-promoting nutrients entrained by cold-core eddies that resulted in an increment in chl-a concentration. A three-times increase in chl-a concentration was observed due to the cold-core eddy, whereas the presence of warm-core eddy reduced the chl-a concentration by 87%. However, during POSWM period, despite having higher nitrate concentration and adequate light in the water column, the surface chl-a was substantially lesser than PRSWM. The molar ratio of ambient inorganic macronutrients during POSWM period played a significant role resulting in lower chl-a concentration. Nitrogen to phosphate (N:P) and nitrogen to silicate (N:Si) ratios were less than the Redfield values. The chl-a concentration off Godavari, a biological hotspot, was the lowest during POSWM period. This study highlights phosphate limitation off Godavari during the high river discharge period.

Coastal upwelling and seasonal variation in phytoplankton biomass in the Pemba Channel

This study was conducted in the Pemba Channel off Tanga Region in northern Tanzania to investigate physical and chemical factors that drive changes in phytoplankton biomass. Three transects off Mwaboza, Vyeru and Sahare were selected. For each transect, ten stations were sampled. Phytoplankton biomass was determined as chlorophyll-a (Chl-a) concentration. Similarly, physico-chemical variables (temperature, salinity, dissolved oxygen, pH and nutrients) were determined. It was observed that the Chl-a concentration was significantly higher during the northeast monsoon (median 1.44 mg m-3) as compared to the southeast monsoon (median 1.19 mg m-3; W = 2216, p = 0.029). The higher productivity during the northeast monsoon is attributed to the presence of high-nutrient water caused by coastal upwelling. It is concluded that indication of upwelling, observed through relatively low temperatures during the northeast monsoon season, could be responsible for bringing nutrient-rich waters to the surface, which in turn stimulated the increase in Chl-a concentration.

Spatio-Temporal Variability in Bio-Optical Properties of the Southern Caspian Sea: A Historic Analysis of Ocean Color Data

Currently, satellite ocean color imageries play an important role in monitoring of water properties in various oceanic, coastal, and inland ecosystems. Although there is a long-time and global archive of such valuable data, no study has comprehensively used these data to assess the changes in the Caspian Sea. Hence, this study assessed the variability of bio-optical properties of the upper-water column in the Southern Caspian Sea (SCS) using the archive of the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS). The images acquired from SeaWiFS (January 1998 to December 2002) and MODIS Aqua (January 2003 to December 2015) satellites were used to investigate the spatial–temporal variability of bio-optical properties including Chlorophyll-a (Chl-a), attenuation coefficient, and remote sensing reflectance, and environmental parameters such as sea surface temperature (SST), wind stress and the El Nino-southern oscillation (ENSO) phenomena at different time lags in the study area. The trend analysis demonstrated an overall increase of 0.3358 mg m−3 in the Chl-a concentration during 1998–2015 (annual increase rate of 0.018 mg m−3 year−1) and four algal blooms and in turn an abnormal increase in Chl-a concentration were occurred in August 2001, September 2005, 2009, and August 2010. The linear model revealed that Chl-a in the northern and middle part of the study area had been influenced by the attenuation coefficient after a one-month lag time. The analysis revealed a sharp decline in Chl-a concentration during 2011–2015 and showed a high correlation with the turbidity and attenuation coefficient in the southern region, while Kd_490nm and remote sensing reflectance did a low one. Generally, Chl-a concentration exhibited a positive correlation with the attenuation coefficient (r = 0.63) and with remote sensing reflectance at the 555 nm (r = 0.111). This study can be used as the basis for predictive modeling to evaluate the changes of water quality and bio-optical indices in the Southern Caspian Sea (SCS).

The impact of hurricanes on the oceanographic conditions in the Exclusive Economic Zone of Cuba

In this work, we analysed the satellite-based responses of sea surface temperature (SST) and chlorophyll-a (chl-a) concentration in the waters of the Exclusive Economic Zone (EEZ) of Cuba to hurricanes that crossed the EEZ between 1998 and 2016 as well as the environmental drivers governing the post-storm responses. We considered two spatial scales to capture the spatially heterogeneous nature of the effects of hurricanes. A first more fine-grained one where we considered 120 km radius disks centered at every consecutive hurricane position within the EEZ (scale 1) and a second more coarse grained one enclosing the entire EEZ (scale 2). We conclude that the hurricanes induced a weak cooling since 75 and 85% of the SST anomalies at scale 1 and 2, respectively, were smaller than −1 °C. The sea surface cooling was mainly caused by wind-driven processes. The maximum chl-a responses were recorded in the first and second post-storm weeks, with 60% ranging between −0.01 and 0.04 mg m−3 at scale 1, and between −0.07 and 0.02 mg m−3 at scale 2. During those post-storm weeks SST and chl-a anomalies were 18 and 44% higher at scale 1 than at scale 2, respectively. We argue that the transport of chl-a from the deep chlorophyll maximum and/or the rich coastal waters are the dominant mechanisms determining the post-storm chl-a response in the EEZ. We also found that the magnitude of the Island Mass Effect (i.e., increase of chl-a concentration in waters surrounding islands) after the passage of the hurricanes was 89% higher in the EEZ than before its passage.

Investigations on the time-series partitioning of 210Pb, 207Bi and 210Po between marine particles and solution under different salinity and pH conditions

The long-lived progeny of radon-222, lead-210 (210Pb), polonium-210 (210Po) and bismuth-210 (210Bi), serve as a tool in the study of marine biogeochemical processes. Here, we report our investigations on the partitioning of 210Pb, 210Po and 210Bi (207Bi) between seawater and solids (twelve commonly-occurring mineral particles) under different values of pH, salinity and contact time. The Kd values of 210Pb and 207Bi for MnO2 varied widely between the synthetic and natural minerals, and thus the suitability of using synthetic material for their partitioning studies in marine system needs to be re-assessed. The Kd values of 210Pb in clay minerals were found to be in the order: smectite > illite > kaolinite. The sorption efficiencies (=the particulate activity divided by the sum of particulate and dissolved activity) of 210Pb, 207Bi and 210Po on illite were above 81% when the contact time was >2 h. These radionuclides were more soluble when pH was ≤5, but show more particle-reactive nature for pH of 6 to 8. The fractionation factor between 210Po and 210Pb (FPo/Pb) varied with salinity for different mineral components while the FBi/Pb was less affected by mineral components, salinity and pH. The in-situ experimental results showed that the FBi/Pb increased with increase in Chl-a concentration. Considering the much shorter half-life of 210Bi (5.0 d) and the high Kd values established in this study, we propose that 210Bi/210Pb activity ratio could potentially be used to estimate the particle export from phytoplankton bloom on time scale much shorter than 234Th or 210Po.

Assessing uncertainty of hydrological and ecological parameters originating from the application of an ensemble of ten global-regional climate model projections in a coastal ecosystem of the lagoon of Venice, Italy

With increasing evidences of climate change affecting coastal waters, there is a strong need to understand future climate conditions and assess the potential responses of delicate coastal ecosystems. Results of climate change studies based on only one GCM-RCM combination should be interpreted with caution as results are highly dependent on the assumptions of the selected combination. In this study we examined the uncertainty in the hydrological and ecological parameters of the Zero river basin (ZRB) – Palude di Cona (PDC) coastal aquatic ecosystem generated by the adoption of an ensemble of climate projections from ten different combinations of General Circulation Model (GCM) – Regional Climate Model (RCM) under two emission scenarios (RCP4.5 and RCP8.5) implemented in the hydrological model (SWAT) and the ecological model (AQUATOX). The baseline period of 1983–2012 was used to identify climate change variations in two future periods: mid-century (2041–2070) and late-century (2071–2100) periods. SWAT outputs from the ensemble indicate a summer reduction in inorganic nitrogen loadings of 1–22% and a winter increase of 1–19%. Inorganic phosphorus loadings indicate a yearly increase of 32–61%. AQUATOX outputs from the ensemble show major changes in the summer period, with an increase in Chl-a concentration of 9–56%, a decrease in diatoms of 74–98% and an increase in cyanobacteria of 421–3590%. Obtained results confirm that the use of multiple GCM-RCM projections can provide a more robust assessment of climate change impacts on the hydrology and ecology of coastal waters, but at the same time highlight the large uncertainty of climate change-related impact studies, which can affect the decision-making processes regarding the management and preservation of sensitive aquatic ecosystems such as those in coastal areas.

The Impact of Summer Arctic Cyclones on Chlorophyll-a Concentration and Sea Surface Temperature in the Kara Sea

In recent years, the intensity of Arctic cyclones has remarkably increased and the impact on the Arctic ecosystem has become more prominent. The Kara Sea is a Russian marginal sea with wide shelf, high productivity of phytoplankton, and abundant resources, and has a very important strategic position and research significance. We have used multiple datasets, including satellite remote sensing data and model reanalysis, to obtain the spatial–temporal distribution of Chlorophyll-a (Chl-a) concentration and sea surface temperature (SST) before and after the passage of the Arctic cyclone over the Kara Sea in summer, to explore basic processes and the ecosystem response to the cyclone. The results indicated that after the passage of the Arctic cyclone, the Chl-a concentration in different regions of the Kara Sea increased at different levels, and the SST decreased briefly. The increase of Chl-a concentration (0.49 mg/m3) caused by the Arctic cyclone happened in Kara Sea in July 2012. The nearshore Chl-a concentration increased more than that on the continental shelf, the continental shelf increases in turn being greater than the deep sea; however, the nearshore response time was shorter than that on the shelf and the deep sea. Compared with nearshore SST, which decreased more than 2 °C, the SST on the continental shelf and in the deep-sea area decreased slightly less. Besides, the left side of the cyclone cooled faster than the right side.

Mathematical Modelling as a Tool for the Assessment of Impact of Thermodynamics on the Algal Growth in Dam Reservoirs – Case Study of the Goczalkowice Reservoir

Abstract Depending on climate conditions, bathymetry, basin morphology, management practices and other factors, some reservoirs are more or less prone to stratification, which can strongly affect both chemical and biological status of water. In the Goczalkowice Reservoir (the biggest dam reservoir in the south of Poland), water quality parameters, such as chlorophyll a concentration, change very dynamically. In the presented study, the Estuary, Lake and Coastal Ocean Model (ELCOM) was applied to simulate water thermodynamics in a period of summer and autumn when the highest concentrations of chlorophyll a were observed, based on the continuous water monitoring in the ZiZOZap project (Łaszczyca et al., 2011). The purpose of the application of ELCOM was to simulate the thermal stratification in the reservoir and to prepare a basis for analyses of the relationship between water thermodynamics and quality. Simulations allowed the identification of several short water mixing events in summer and the final mixing event at the end of summer. The study also included the first application of model results to analyse the relation of changes in water temperature with observed concentration of chlorophyll a (ChlA). Analysis confirmed that each water mixing event was followed by a significant increase in ChlA concentration.

Internal phosphorus loading from sediments causes seasonal nitrogen limitation for harmful algal blooms

It is proposed that the internal loading of phosphorus (P) from sediments plays an important role in seasonal nitrogen (N) limitation for harmful algal blooms (HABs), although there is a lack of experimental evidence. In this study, an eutrophic bay from the large and shallow Lake Taihu was studied for investigating the contribution of internal P to N limitation over one-year field sampling (February 2016 to January 2017). A prebloom-bloom period was identified from February to August according to the increase in Chla concentration in the water column, during which the ratio of total N to total P (TN/TP) exponentially decreased with month from 43.4 to 7.4. High-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) analysis showed large variations in the vertical distribution of mobile P (SRP and DGT-labile P) in sediments, resulting in the SRP diffusion flux at the sediment-water interface ranging from −0.01 to 6.76mg/m2/d (minus sign denotes downward flux). Significant and linear correlations existed between SRP and soluble Fe(II) concentrations in pore water, reflecting that the spatial-temporal variation in mobile P was controlled by microbe-mediated Fe redox cycling. Mass estimation showed that the cumulative flux of SRP from sediments accounted for 54% of the increase in TP observed in the water column during the prebloom-bloom period. These findings are supported by the significantly negative correlation (p<0.01) observed between sediment SRP flux and water column TN/TP during the same period. Overall, these results provide solid evidence for the major role of internal P loading in causing N limitation during the prebloom-bloom period.

Impact of two typhoons on the marine environment in the Yellow Sea and East China Sea

This study investigated the effects of two typhoons (Nari and Wipha) on sea surface temperature (SST) and chlorophyll-a (Chl-a) concentration. Typhoons Nari and Wipha passed through the Yellow Sea on September 13, 2007 and the East China Sea (ECS) on September 16, 2007, respectively. The SST and Chl-a data were obtained from the Aqua/Terra MODIS and NOAA18, respectively, and the temperature and salinity in the southeast of the study area were observed in situ from Argo. The average SST within the study area dropped from 26.33°C on September 10 to a minimum of 22.79°C on September 16. Without the usual phenomenon of ‘right bias’, the most striking response of SST was in the middle of the typhoons’ tracks, near to coastal waters. Strong cooling of the upper layers of the water column was probably due to increased vertical mixing, discharge from the Changjiang River estuary, and heavy rainfall. During the typhoons, average Chl-a increased by 11.54% within the study area and by 21.69% in the offshore area near to the southeast ECS. From September 1 to 13, average Chl-a was only 0.10 mg/m3 in the offshore waters but it reached a peak of >0.17 mg/m3 on September 18. This large increase in Chl-a concentration in offshore waters might have been triggered by strong vertical mixing, upwelling induced by strong typhoons, and sedimentation and nutrient influx following heavy rainfall.

Anomalous increase of chlorophyll concentrations associated with earthquakes

Recent studies have shown land, ocean, atmosphere and ionospheric anomalies prior to earthquakes. The optical and microwave sensors onboard satellites are now capable of monitoring land, ocean, atmosphere and ionosphere which provide changes associated with natural hazards. In this paper, we have analyzed remote sensing data of the ocean coasts lying near the epicenters of recent four major earthquakes (Gujarat of January 26, 2001, Andaman of September 13, 2002, Algeria of May 21, 2002 and Bam, Iran earthquake of December 26, 2003), our detailed analysis shows increase of Chlorophyll-a (Chl-a) concentration associated with these recent earthquakes. The increase of Chl-a concentration is due to the change in sea surface temperature (SST) associated with the changes in stress regime in the epicentral region which is responsible for modifying the in situ thermal structure of the water and enhancing the upwelling of nutrient-rich water. The increase of Chl-a concentration also shows one to one relation with the increase of surface latent heat flux (SLHF) which is found to increase significantly prior to the earthquake events. Due to cloud cover, it has not been possible to quantify the effect of the chlorophyll concentrations associated with the earthquake events for each successive day during an event. However, the limited data from the adjacent oceanic regions provide strong evidence of the increase in Chl-a concentration. The monitoring of chlorophyll concentrations with higher spatial and temporal resolutions may provide early information about impending coastal earthquakes.