Increase In Chl-a Research Articles

Understanding environmental drivers and trends in chlorophyll-a and related factors across equatorial Indian Ocean regions: implications for marine ecosystem dynamics and vulnerability

ABSTRACT We estimated the concentration of Chlorophyll-a (Chl-a) along with physical and biological factors including sea surface temperature (SST), wind speed and concentration of nitrate and phosphate in the Western, Central and Eastern Equatorial Indian Oceans (WEIO, CEIO and EEIO) using data from the Copernicus Marine Service and ERA-5 for the years 1994 to 2019. Our results show that along with the concentration of Chl-a, nitrate and phosphate have decreased, and sea surface temperature has increased in the EEIO. Due to coastal upwelling off the coast of Somalia and offshore Ekman transport throughout the summer, the southwest monsoon caused a significant increase in concentrations of Chl-a, nitrate, phosphate and wind speed in WEIO during June-July-August-September (JJAS) and October-November-December (OND). SST decreased at this time and deeper water interacted with surface water, increasing biological production. In EEIO, the upwelling zone is primarily maintained by wind-induced divergence throughout the year, whereas stratification in winter prevented surface Chl-a increase. High wind speed and low SST led to increased productivity in WEIO. Comparison of EEIO with WEIO and CEIO demonstrates low levels of Chl-a, phosphate and nitrate. The trends signify that these oceanic zones are highly vulnerable to developing into ecological deserts in the near future.

Impacts of droughts and human activities on water quantity and quality: Remote sensing observations of Lake Qadisiyah, Iraq

Water quantity and quality in lakes are closely linked to the compounding effects of climate change and human activities in their catchments, especially for lakes located in semi-arid and arid regions where water resources are scarce. Whilst knowledge gaps exist for these effects in semi-arid and arid region lakes due mainly to the lack of long-term in situ monitoring data. By using satellite remote sensing data, this study firstly investigated the variations of water level, chlorophyll-a concentration (Chl-a) and turbidity in Lake Qadisiyah, Iraq between 2000 and 2019. Results showed that the average water level was 138.3 m in 2000–2019, it decreased clearly in 2001, 2009, 2015 and 2018 with the lowest value of 120 m in July 2015. The mean Chl-a was 6.3 mg/m3 and it showed an overall increasing trend during 2000 and 2019. Turbidity showed extremely high values (>10 NTU) in 2009 and 2017–2018 compared to the mean value of 3.6 NTU in 2000–2019. The boosted regression tree (BRT) was then used to explore the relationship between those variations and El Niño-Southern Oscillation, droughts, meteorological factors and land use land cover changes in the catchment. Results revealed that water level declines were mainly associated with droughts led by La Niña events. Chl-a increase in the lake were mainly explained by built-up area increase and water area decrease in the catchment, with a relative contribution of 29.2 % and 28.6 % respectively. Water area changes in the catchment were the main factor influencing turbidity explaining 55.3 % of the variation. An exception water level decline in 2014–2016 was also observed when there was no drought, which was most likely caused by the cut off of water flow upstream and the release of water from the dam during periods of war. The findings in this study underscored the impacts of climate and human activities on water quantity and quality in semi-arid region lakes. Actions such as improving water use efficiency, establishing water storages, and enhancing cross-border cooperation are therefore recommended to deal with extreme events. Pollution control measures in the catchment are also suggested to prevent water quality deterioration in the lake.

Warming waters lead to increased habitat suitability for juvenile bull sharks (Carcharhinus leucas)

Coastal ecosystems are highly vulnerable to the impacts of climate change and other stressors, including urbanization and overfishing. Consequently, distributions of coastal fish have begun to change, particularly in response to increasing temperatures linked to climate change. However, few studies have evaluated how natural and anthropogenic disturbances can alter species distributions in conjunction with geophysical habitat alterations, such as changes to land use and land cover (LU/LC). Here, we examine the spatiotemporal changes in the distribution of juvenile bull sharks (Carcharhinus leucas) using a multi-decadal fishery-independent survey of coastal Alabama. Using a boosted regression tree (BRT) modeling framework, we assess the covariance of environmental conditions (sea surface temperature, depth, salinity, dissolved oxygen, riverine discharge, Chl-a) as well as historic changes to LU/LC to the distribution of bull sharks. Species distribution models resultant from BRTs for early (2003–2005) and recent (2018–2020) monitoring periods indicated a mean increase in habitat suitability (i.e., probability of capture) for juvenile bull sharks from 0.028 to 0.082, concomitant with substantial increases in mean annual temperature (0.058°C/yr), Chl-a (2.32 mg/m3), and urbanization (increased LU/LC) since 2000. These results align with observed five-fold increases in the relative abundance of juvenile bull sharks across the study period and demonstrate the impacts of changing environmental conditions on their distribution and relative abundance. As climate change persists, coastal communities will continue to change, altering the structure of ecological communities and the success of nearshore fisheries.

Causal impact analysis of weir opening on cyanobacterial blooms and water quality in the Yeongsan River, Korea: A bayesian structural time-series analysis and median difference test

The construction of weirs in Korea's Four Major Rivers Project has led to an increase in cyanobacterial blooms, posing environmental challenges. To address this, the government began opening weirs in 2017. However, interpreting experimental results has proven to be complex due to the multifaceted nature of blooms. This study aimed to assess the impact of opening the Juksan Weir on cyanobacterial blooms and water quality in the Yeongsan River. Using a median difference test (MDT) and causal impact analysis (CIA) with Bayesian structural time-series (BSTS) models, changes in cyanobacterial cell density (Cyano) and chlorophyll a concentration (Chl-a) before (January 2013 to June 2017) and after (July 2017 to December 2021) the weir-opening event were analyzed. The MDT revealed no significant change in Cyano post-weir opening (p = 0.267), but Chl-a significantly increased by 48.1 % (p < 0.01). As a result of CIA, Cyano decreased, albeit statistically insignificantly (p = 0.454), while Chl-a increased by 59.0 % (p < 0.01). These findings contradict the expectation that Cyano decrease due to the increased flow velocity resulting from weir opening. The absence of changes in Cyano and the increase in Chl-a can be attributed to several factors, including the constrained and inadequate duration of full weir opening combined with conducive conditions for the proliferation of other algae such as diatoms and green algae. These findings suggest that the effectiveness of weir opening in controlling Cyano may have been compromised by factors influencing the overall aquatic ecosystem dynamics. Further analysis revealed that factors such as elevated water temperatures (≥ 30 °C) and reduced flow rates (< 37 m3/s) contributed to the flourishing of cyanobacteria, whose concentrations exceeded 10,000 cells/mL. In analyzing causal relationships in environmental management, especially when there are complex causal interactions, the application of MDT and CIA provides valuable insights.

Competition between ocean thermal structure and tropical cyclone characteristics modulates ocean environmental responses in the Yellow and Bohai Seas

To study the environmental responses of tropical cyclones (TCs) in continental shelf regions, TCs passing over the Yellow Sea and Bohai Sea (YBS) during 2002–2020 were investigated, with a special focus on how competition between ocean thermal structure and TC characteristics modulates ocean surface changes. The spatial distributions of the climatic mixed layer depth (MLD), accumulated wind forcing power index (WPi), accumulated sea surface temperature (SST) changes and accumulated chlorophyll (Chl-a) changes in the YBS were calculated. The linear regressions indicate that both the TC-induced SST cooling and TC-induced Chl-a increase are correlated with the TC wind speed rather than the translation speed, especially when the TC forcing depth (Zmixing) is greater than the MLD. Otherwise, both the changes in SST and Chl-a are correlated with the TC translation speed when Zmixing is shallower than the MLD. Further study has shown that whether TCs can break the MLD is also a key condition for oceanic responses. In the southern YBS, which has a deep-sea basin and MLD, the TC wind speed is the major factor affecting SST cooling and Chl-a increase, as TCs need more strength to reach the MLD. However, in the northern YBS, which has the shallowest sea basin and MLD, even weak TCs can easily break the MLD and reach the seabed; thus, ocean surface changes are associated mainly with the TC translation speed. The composite results reveal that both the maximum SST cooling center (1.64 °C) and the maximum Chl-a increasing center (0.14 log10(mg/m3)) are located on the right and behind the TC center, respectively. In addition, TC-induced SST cooling and Chl-a increase were initiated two days prior to TC passage and then reached their maximum values after 1 day. It takes approximately 7–8 days for the Chl-a concentration to recover, but it takes a much longer time (>15 days) for the SST to recover.

Peaks and transient dynamics of ecological and biogeochemical variables following impoundment in boreal reservoirs

Across the globe, reservoirs represent nearly 10 % of the world's freshwater. River impoundment strongly alters the hydrological regime of aquatic ecosystems which subsequently affect the ecological (e.g., primary production, fish biomass) and biogeochemical variables (e.g., nutrient, mercury, and carbon cycles which includes Green House Gas emissions; GHG). We examined the transient dynamics and co-variation of biogeochemical and ecological variables from unique long-term time series (40 years of data) from Hydro-Québec boreal reservoirs, with data before and after impoundment. To do so, we applied curve fitting analysis on the data from eight plausible scenarios and model selection. Following impoundment, most variables increased, peaked, and then decreased over time (clear hump-shaped patterns; six over eight variables). Model predictions peaked between three- and 11-years post-impoundment and returned to pre-impoundment levels after about nine- to 40-years. Variables also followed a clear sequence where GHG emissions (CO2, CH4) peaked first, immediately after impoundment, followed by an increase in phosphorus and Chl-a. Total mercury in fish peaked a few years later for non-piscivorous fish and was followed closely by piscivorous fish. This work provides the first comprehensive and holistic description of the transitory nature and co-variation of ecological and biogeochemical variables following reservoir impoundment.

A decade-long chlorophyll-a data record in lakes across China from VIIRS observations

Chlorophyll-a (Chl-a) is one of the optically active constituents in waters, and its concentration is frequently utilized as a proxy for lake trophic levels. However, generating a large-scale, long-term, and consistent data record of Chl-a in lakes from satellite images has been a challenging undertaking due to the limitations of conventional algorithms in monitoring inland waters spanning various optical properties. Here, we develop a practical deep neural network (DNN) model to generate a long-term Chl-a series (2012−2021) in 217 large lakes (> 50 km2) across China from the Visible Infrared Imaging Radiometer Suite (VIIRS) imagery. The assessment showed that the NOAA operational VIIRS remote sensing reflectance (Rrs(λ)) products were reliable over 28 of China's examined lakes (N = 340, bias = −12%, mean absolute percentage error [MAPE] = 38%), particularly at bands ranging from the green to near-infrared domain. The DNN model performed satisfactorily on Chl-a retrievals (bias = 5%, MAPE = 32%) in 79 lakes over three orders of magnitude (0.1–300 μg L−1) spanning clear/deep to turbid/shallow waters, with significant improvements compared with the existing algorithms and other machine learning algorithms. The algorithm was applied to VIIRS images to produce a data record of spatial and temporal variations in Chl-a for China's large lakes over the past decade. The VIIRS-derived data record showed that China's lakes have an average Chl-a of 9.5 μg L−1 and are to 45.5% eutrophic. The results revealed a spatial trend of lower Chl-a in the western deep lakes than that in the eastern shallow lakes. In addition, we observed a significant increase in Chl-a in the lakes of the China East Plain but a decreasing trend of Chl-a in the Tibetan Plateau. This study highlights the feasibility of a machine learning approach based on synchronous matchups to derive Chl-a data in various lakes from satellite images. Our results provide a comprehensive understanding of overall changes to the optical conditions of China's lakes and enable scientists to elucidate the roles of climate and human activities in regulating lake productivity.

An extraordinary chlorophyll-a enhancement event jointly induced by two sequential tropical cyclones in the Kuroshio region south of Japan

We used Biogeochemical-Argo (BGC-Argo) float observation profiles and satellite data to investigate the physical-biogeochemical processes of a phytoplankton biomass rise in the Kuroshio region south of Japan during a period of two sequential tropical cyclones (TCs)—Hagibis and Neoguri—in October 2019. During TC Hagibis, prominent sea surface cooling and surface chlorophyll-a (Chl-a) increase occurred within a pre-existing cyclonic eddy (CE) south of Japan. Because of TC-induced mixing and upwelling, the maximum cooling happened at the depth of 57 m where water temperature dropped by 6°C. The dramatic mixing and upwelling redistributed chlorophyll-a vertically (reducing subsurface Chl-a and increasing surface Chl-a) with little augment of depth-integrated Chl-a in the upper ocean above 160 m depth. Meanwhile, the mixing and upwelling transported nutrients from the subsurface to the surface layer. In the week after Hagibis, the depth-integrated Chl-a greatly increased. Subsequently, TC Neoguri obviously enhanced the augment of phytoplankton biomass although it was weaker than Hagibis. The upwelling induced by Hagibis increased nutrients in the water below 80 m, providing a very favorable condition for the subsequent TC Neoguri to further promote the growth of phytoplankton. The intense precipitation accompanying with Neoguri brought the coastal water with rich terrestrial material to offshore ocean, increasing nutrients and decreasing salinity in the subsurface layer. These both contributed to the marked increase in Chl-a during Neoguri. Our results demonstrated that the two sequential TCs worked together with a cyclonic eddy to cause a drastic and complex Chl-a enhancement event in the Kuroshio region south of Japan.

Summer Chlorophyll-a Increase Induced by Upwelling off the Northeastern Coast of Hainan Island, South China Sea

There are generally high chlorophyll-a concentrations (Chl-a) where upwelling is prevalent. High Chl-a is often observed in upwelling areas of the northeastern coast of Hainan Island during the summer. Using the satellite remote sensing data, including sea surface temperature, sea surface wind and Chl-a data from 2009 to 2022, we analyze the spatial-temporal and inter-annual variation of Chl-a on the northeastern coast of Hainan Island. Then, the possible influence of environmental factors on Chl-a are further examined by using satellite data, as well as Ekman transport and Ekman pumping velocity derived from the wind products. Finally, the key factors affecting the changes of Chl-a are discussed by correlation analysis. The results show the significant interannual variation of Chl-a in the region, with the maximum of summer Chl-a during the prevalent period of upwelling. The correlation analyses reveal that there is a higher correlation coefficient between the summer Chl-a and the upwelling index (i.e., upwelling regional temperature anomaly), suggesting the role played by upwelling in the summer high Chl-a is more important than the other environmental factors. It is speculated that the summer Chl-a increase is not only influenced by wind-induced upwelling but also by the upwelling caused by tidal mixing, large-scale circulation, topographic changes, and typhoon events.

Chlorophyll-a prediction in tropical reservoirs as a function of hydroclimatic variability and water quality.

The study goal was to determine spatiotemporal variations in chlorophyll-a (Chl-a) concentration using models that combine hydroclimatic and nutrient variables in 150 tropical reservoirs in Brazil. The investigation of seasonal variability indicated that Chl-a varied in response to changes in total nitrogen (TN), total phosphorus (TP), volume (V), and daily precipitation (P). Therefore, an empirical model for Chl-a prediction based on the product of TN, TP, and normalized functions of V and P was proposed, but their individual exponents as well as a general multiplicative factor were adjusted by linear regression for each reservoir. The fitted relationships were capable of representing algal temporal dynamics and blooms, with an average coefficient of determination of R2 = 0.70. The results revealed that nutrients yielded better predictability of Chl-a than hydroclimatic variables. Chl-a blooms presented seasonal and interannual variability, being more frequent in periods of high precipitation and low volume. The equations demonstrate different Chl-a responses to the parameters. In general, Chl-a was positively related to TN and/or TP. However, in some cases (22%), high nutrient concentrations reduced Chl-a, which was attributed to limited phytoplankton growth driven by light deficiency due to increased turbidity. In 49% of the models, precipitation intensified Chl-a levels, which was related to increases in the nutrient concentration from external sources in rural watersheds. Contrastingly, 51% of the reservoirs faced a decrease in Chl-a with precipitation, which can be explained by the opposite effect of dilution of nutrient concentration at the reservoir inlet in urban watersheds. In terms of volume, in 67% of the reservoirs, water level reduction promoted an increase in Chl-a as a response to higher nutrient concentration. In the other cases, Chl-a decreased with lower water levels due to wind-induced destratification of the water column, which potentially decreased the internal nutrient release from bottom sediment. Finally, applying the model to the two largest studied reservoirs showed greater sensitivity of Chl-a to changes in water use classes regarding variations in TN, followed by TP, V, and P.

Elevated nano-α-Fe2O3 enhances arsenic metabolism and dissolved organic carbon release of Microcystis aeruginosa under a phytate environment.

Little information is available on the effects of nano-α-Fe2O3 on arsenic (As) metabolism of algae and potential associated carbon (C) storage in As-contaminated water with dissolved organic phosphorus (DOP) as a phosphorus (P) source. In this study, Microcystis aeruginosa (M. aeruginosa) was used to investigate impacts of nano-α-Fe2O3 on cell growth and As metabolism of algae under a phytate (PA) environment as well as potential associated C storage. Results showed that nano-α-Fe2O3 had a subtle influence on algal cell growth in a PA environment. Herein, algal cell density (OD680) and chlorophyll a (Chla) were inhibited at elevated nano-α-Fe2O3 levels, which simultaneously limited the decrease of Yield. As suggested, the complexation of PA with nano-α-Fe2O3 could alleviate the negative influence on algal cell growth. Furthermore, the elevated nano-α-Fe2O3 increased As methylation in the PA environment due to higher monomethylarsenic (MMA) and dimethylarsenic (DMA) concentrations in the test media. Additionally, microcystins (MCs) in the media changed consistently with UV254, both of which were relatively lower at 10.0 mg·L-1 nano-α-Fe2O3. Enhanced As(V) methylation of algal cells was found to simultaneously reduce the release risk of As(III) and MC while increasing dissolved organic carbon (DOC) content in media, suggesting unfavorable C storage. Three-dimensional fluorescence analysis revealed that the main DOC constituent was the tryptophan-like component in aromatic proteins. Correlation analysis showed that decreases in pH and the zeta potential and an increase in Chla may lead to metabolic As improvements in M. aeruginosa. The obtained findings highlight the need for greater focus on the potential risks of DOP combined with nano-α-Fe2O3 on algal blooms as well as the biogeochemical cycling processes of As and C storage in As-contaminated water with DOP as the P source.

Evaluating the Performance of Sentinel-3A OLCI Products in the Subarctic Northeast Pacific

The subarctic northeast Pacific (SNEP) is a high-nitrate, low-chlorophyll (HNLC) region in the ocean, where phytoplankton growth and productivity are limited by iron. Moreover, there is a limited application of high spatial (300 m) and temporal resolution (daily) ocean color (OC) satellite imagery in studying the phytoplankton dynamics in this region. To address this issue, we aim to validate the remote sensing reflectance (Rrs; sr−1(λ)) and chlorophyll-a (Chla) concentration derived from the Polymer atmospheric correction algorithm against in situ data for the SNEP obtained during 2019 and 2020. Additionally, we performed qualitative analysis using weekly binned surface Chla maps to determine whether the product reflects the general pattern over a latitudinal and longitudinal domain. We processed the daily Level-1 image using Polymer and binned them weekly using Graphic Processing Tool (GPT). The validation results indicate that Polymer exhibits higher radiometric performance in the blue and green bands and fails to represent in situ Rrs in the red band. Furthermore, the Polymer slightly over- and underestimates reflectance between 0.0012 and 0.0018 sr−1 in the green band. On the other hand, excellent agreement was found between satellite-derived versus in situ Chla, followed by a slight overestimation of in situ Chla in the range from 0.17 to 0.28 mg/m3. The weekly binned Chla spatial map revealed a spatially homogeneous distribution of surface Chla in Central Alaska, but a substantial increase in Chla (≥0.7 mg/m3) was recorded toward Southeast Alaska (SEA) and the British Columbia (BC) shelf. Furthermore, Chla derived from latitudinal and longitudinal transects indicates high Chla toward 57°N and −135°W, respectively. Overall, the results of this study emphasize the need to obtain high-quality matchups from under-sampled oligotrophic waters, which are crucial for satellite validation, in addition to highlighting the importance of using high spatial and temporal resolution satellite imagery to study phytoplankton dynamics in the SNEP.

Monitoring and estimating coastal upwelling using Sentinel-3 satellite imagery (case study: The Caspian Sea)

Delineation of upwelled zones is critical for the economy and physical processes of the coastal areas. The upwelling process is accompanied by vertical water motion, resulting in a surface with lower water temperature and increased chlorophyll-a contents (Chl-a). Since such patterns can be monitored using remote sensing technologies, this research investigates the potential of newly launched Sentinel-3 satellite imagery to gather information about the causes of summer upwelling in the Caspian Sea in 2017 and 2021. The upwelling spatial extent was determined using a Fuzzy C-means Clustering (FCM) approach. The UIwind index was also calculated to identify Ekman transport's involvement as an upwelling triggering factor. The results showed that during summer, the middle and south Caspian Sea had three upwelling cells, one in the eastern (cell 1) and two in the western regions (cells 2 and 3). FCM analysis revealed up to a 10 °C decline in SST, a 5 mg/m3 increase in Chl-a, and 70 km width during the upwelling events.

Differential response of chlorophyll-a concentrations to explosive volcanism in the western South Pacific

When it is deposited in the ocean, volcanic ash has the potential to release iron and other nutrients into surface water to stimulate ocean productivity. In the western South Pacific Ocean (SPO), one of the most important volcanic ash deposition regions, occasional widespread transport of volcanic ash may supply the nutrients not only locally around source islands but also within the wider the western SPO, accompanied by phytoplankton response. Through a comparative analysis of satellite and reanalysis data for the past 19 years (2004–2022), this study reveals that four explosive volcanic eruptions, Rabaul volcano, Papua New Guinea (October, 2006), Ambae volcano, Vanuatu (July, 2018), Ulawun volcano, Papua New Guinea (June, 2019), and Hunga volcano, Tonga (January, 2022), had the most strong stratospheric injection (&amp;gt;15 km) and mass loading of volcanic materials over the wider the western SPO (covering an area of &amp;gt;765,000 km2). The transport of 2006, 2018, 2019 volcanic emissions, was not likely associated with significant ash deposition over the western SPO. However, the Hunga eruption led to the deposition of ash-laden volcanic plumes over a wide area (~2,000 km from source), and was followed by the increase in chlorophyll-a concentrations (Chl-a) in the region (~70% increase). Minor changes related to other nutrient sources (e.g., hydrothermal input) suggest a link between the increase in Chl-a and 2022 Hunga ash falls over the western SPO. Our results indicate that volcanic ash deposition has implications for phytoplankton productivity in the western SPO, and highlights the need for further research into understanding how nutrient supply alleviated limitations of phytoplankton at the community level.

Regulation of CO2 by the sea in areas around Latin America in a context of climate change.

Anthropogenic activities are increasing the atmospheric carbon dioxide (CO2); around a third of the CO2 emitted by these activities has been taken up by the ocean. Nevertheless, this marine ecosystem service of regulation remains largely invisible to society, and not enough is known about regional differences and trends in sea-air CO2 fluxes (FCO2), especially in the Southern Hemisphere. The objectives of this work were as follows: first to put values of FCO2 integrated over the exclusive economic zones (EEZ) of five Latin-American countries (Argentina, Brazil, Mexico, Peru, and Venezuela) into perspective regarding total country-level greenhouse gases (GHG) emissions. Second, to assess the variability of two main biological factors affecting FCO2 at marine ecological time series (METS) in these areas. FCO2 over the EEZs were estimated using the NEMO model, and GHG emissions were taken from reports to the UN Framework Convention on Climate Change. For each METS, the variability in phytoplankton biomass (indexed by chlorophyll-a concentration, Chla) and abundance of different cell sizes (phy-size) were analyzed at two time periods (2000-2015 and 2007-2015). Estimates of FCO2 at the analyzed EEZs showed high variability among each other and non-negligible values in the context of greenhouse gas emissions. The trends observed at the METS indicated, in some cases, an increase in Chla (e.g., EPEA-Argentina) and a decrease in others (e.g., IMARPE-Peru). Evidence of increasing populations of small size-phytoplankton was observed (e.g., EPEA-Argentina, Ensenada-Mexico), which would affect the carbon export to the deep ocean. These results highlight the relevance of ocean health and its ecosystem service of regulation when discussing carbon net emissions and budgets.

Chlorophyll-a concentration climatology, phenology, and trends in the optically complex waters of the St. Lawrence Estuary and Gulf

The spatiotemporal distribution of phytoplankton biomass drives the marine ecosystem. Chlorophyll-a concentration (Chla) is a biomass index for microalgae in seawater that is commonly used to study phytoplankton by means of satellite remote sensing. The St. Lawrence Estuary and Gulf (SLEG), in Eastern Canada, is a highly dynamic subpolar environment characterized by complex marine optical properties that make it difficult to distinguish Chla from the background signal caused by a strong freshwater discharge. In this study, we implement an inverse model based on a set of in situ Chla processed through a principal component analysis, making it specifically designed for the local marine optical conditions. We used this model to convert a multi-mission remote sensing reflectance dataset to daily Chla between 1998 and 2019 at a 4 km spatial resolution. From the resulting Chla time series, we computed the climatology, phenology and trend over the SLEG. The Chla climatology reveals the presence of relatively high Chla in the Gaspé Current, along the Gulf's North Shore and in areas of strong tidal mixing. Important differences in the phytoplankton phenology between the various subregions are found, with a prevailing shift towards earlier spring blooms of larger intensity. Finally, we found a positive mean Chla increase of 1.1% yr −1 over the SLEG, with strong positive trends in the Magdalen Shallows and west of the Anticosti Island. This description of the surface Chla in the SLEG provides important baseline information for the marine ecosystem. • Our regional algorithm produces realistic chlorophyll-a in the St. Lawrence Estuary and Gulf. • Chlorophyll-a is higher in coastal areas with upwellings or freshwater input. • Spring blooms develop from south to north, with the estuarine portion last. • Between 1998 and 2019, chlorophyll-a increased by 1.1% yr −1 .

Possible Mechanism of Phytoplankton Blooms at the Sea Surface after Tropical Cyclones

Although previous studies have recorded that tropical cyclones cause a significant increase in chlorophyll a concentration (Chl-a), most of these results were only based on surface Chl-a observed by satellite data. Using satellite, reanalysis and model data, this study investigated the response of the upper ocean and sea surface Chl-a to three different levels of tropical cyclones in the South China Sea. In our results, the severe tropical storm (STS) did not cause an increase in surface Chl-a or depth-integrated Chl-a in the short term (i.e., ~2 days); the typhoon (TY) increased the surface Chl-a from 0.12 mg·m−3 to 0.15 mg·m−3 in the short term, but the depth-integrated Chl-a did not increase significantly; the super typhoon (STY) caused the surface Chl-a to increase from 0.15 mg·m−3 to 0.37 mg·m−3 in the short term, and also increased the depth-integrated Chl-a from 40.41 mg·m−2 to 42.59 mg·m−2. These results suggest that the increase in the surface Chl-a after TY and STY were primarily caused by physical processes (e.g., vertical mixing). However, the increase in the depth-integrated Chl-a of STY may be due to the entrainment of both nutrients and phytoplankton through upwelling and turbulent mixing under the influence of STY.

Investigation of the Phycoremediation Potential of Freshwater Green Algae Golenkinia radiata for Municipal Wastewater

Recent developments in the removal of pollutants from wastewater show that phycoremediation to wastewater treatment and reuse wastewater may provide sustainable biosolutions. This work investigated the performance of the green microalgae Golenkinia radiata Chodat 1984 (Chlorophyceae) in terms of N, P, and COD removal at different treatment stages of municipal wastewater, reusability of remediated wastewater and wastewater-based biomass production. Water samples were taken from different wastewater units (presettling basin effluent, active sludge basin effluent, and discharge channel) of a municipal wastewater treatment plant (İzmir, Turkey). In the 7-day experiments, Chl-a, Chl-b, DO, pH, and T (°C) were also measured alongside the pollutant analyses. The results in Chl-a (1803 ± 75.9 µg L−1) and biomass yield (7.66 ± 0.05 g L−1) in the primary effluent (P) were quite impressive. Additionally, the results showed that the correlation between the increase in Chl-a and the residual concentrations of pollutants was remarkable. NH4-N, NO3-N, NO2-N, PO4-P, and COD treatment efficiencies were in the ranges of (74.6–83.0%), (15.35–70.4%), (0.00–47.22%), (80.67–86.27%), and (77.22–87.53%), respectively. The final concentrations of pollutants (E) were found to comply with EU legislation. The results also reveal that green microalgae G. radiata may be a strong candidate for microalgae-based wastewater treatment.

Upper Ocean Responses to the Tropical Cyclones Ida and Felicia (2021) in the Gulf of Mexico and the Eastern North Pacific

Tropical cyclones (TCs) are a significant component of ocean–atmosphere interactions and the climate system. These interactions determine both the development and strength of TCs, as well as various biogeochemical processes in the upper oceans, including vertical mixing and primary production. We investigated the impact of the TCs Felicia and Ida that emerged in 2021 in the eastern North Pacific and the Gulf of Mexico, respectively, using satellite observations of sea-surface temperature (SST) and surface chlorophyll a (chl-a) concentrations, and vertical profiles of temperature and salinity derived from Argo floats. Observations differed between the two study areas. Cooling of SST associated with TC Ida was observed throughout the Gulf of Mexico (&lt;0.5 °C), except for warming in a region off the Mexican coast east of Ida’s track (by about 0.5 °C). The passing of TC Felicia cooled SST in the eastern region (15°N, 115°W) and a central region (15°N, 125°W) by 0.5 °C and 0.36 °C, respectively. The passing of the TCs caused enhanced vertical mixing of the upper ocean layer in the Gulf of Mexico, with a deepening of the mixed layers from 38 m to 68 m (TC Ida). In contrast, the mixed layer in the eastern North Pacific decreased from 50 m to 20 m. For the eastern North Pacific, mixing could be related to an increase in surface chl-a and thus enhanced phytoplankton biomass was observed for 2 months after the passing of TC Felicia with a chl-a increase of 0.15 mg m−3. In the Gulf of Mexico, however, TC Ida caused the injection of a coastal phytoplankton bloom into the open Gulf, resting for more than a month after the cyclone had passed. Our findings contribute to the understanding of potential SST cooling, destratification, and enhanced primary production due to the passage of TCs in two distinct ocean regions, i.e., the open eastern North Pacific and the semi-enclosed Gulf of Mexico.

Worldwide moderate-resolution mapping of lake surface chl-a reveals variable responses to global change (1997–2020)

Anthropogenic activity is leading to widespread changes in lake water quality—a key contributor to socio-ecological health. But, the anthropogenic forces affecting lake water quality (climate change, land use change, and invasive species) are unevenly distributed across lakes, across the seasonal cycle, and across space within lakes, potentially leading to highly variable water quality responses that are poorly documented at the global scale. Here, we used 742 million chlorophyll-a (chl-a) estimates merged over 6 satellite sensors (daily, 1 to 4 km resolution) to quantify water quality changes from 1997 to 2020 in 344 globally-distributed large lakes. Chl-a decreased across 56% of the cumulative total lake area, challenging the putative widespread increase in chl-a that is expected due to human activity. 19% of lakes exhibited both positive and negative chl-a trends (p-value &lt; 0.1) across different locations or times of the year. This spatiotemporal complexity demonstrates the value of moderate resolution mapping of lake chl-a to inform water management decision-making and to determine the local ecological consequences of human activity.