Maximum Chlorophyll-a Concentration Research Articles

Vertical and Horizontal Variability of Chlorophyll-a and Its Relationship with Environmental Parameters in the Waters of Sangihe and Talaud Islands, North Sulawesi, Indonesia

The chlorophyll-a is an important biological parameter that could act as a proxy to indicate the abundance of phytoplankton and the primary productivity of an aquatic ecosystem. This paper investigates the vertical and horizontal variability of chlorophyll-a in the waters of Sangihe and Talaud Islands, Indonesia, and its correlation with water environmental parameters. In this study, the distribution of chlorophyll-a, temperature, salinity, and nutrients (NO3 and PO4) from the surface to a depth of 200 m (photic zone) was measured at 29 research stations. The results showed that the distribution of chlorophyll-a in the waters of the Sangihe-Talaud Islands was varied vertically and horizontally. The waters around the Sangihe Islands generally exhibited a higher chlorophyll-a distribution and shallower Deep Chlorophyll Maxima compared to the water around the Talaud Islands. The concentration of chlorophyll-a varied between 0.0017 and 1.2155 mg.m-3, with most of the water column in Sangihe-Talaud considered oligotrophic, although some stations or depths were mesotrophic or slightly eutrophic. The maximum chlorophyll-a concentration was found in the sub-surface layer at depths between 46 and 101 m. The low N:P ratio (<16) and N:Si ratio (<1) indicate that the water columns of Sangihe-Talaud, up to a depth of 200m, were N-limited. Based on the GAM analysis, chlorophyll-a concentration in Sangihe-Talaud waters was primarily regulated by temperature, salinity, and the N:P ratio, with weak influence from phosphate and the N:Si ratio. The analysis also suggests that primary productivity in Sangihe-Talaud is sensitive to temperature changes, indicating its vulnerability to future warming events.

Revealing the seasonal cycles of Arctic phytoplankton: insights from year-round chlorophyll monitoring

Rapid Arctic Ocean warming has caused severe sea ice decline, impacting light distribution, phytoplankton blooms, and primary production. We investigated Arctic phytoplankton bloom timing using continuous chlorophyll-a fluorescence data obtained from three Korea Arctic Mooring Systems (KAMSs) deployed north of the East Siberian Sea (KAMS1), north of the Chukchi Sea (KAMS2), and the middle of the Northwind Ridge (KAMS4). Our findings revealed that the bloom initiation times were June 4 (±28 d) in KAMS1, June 24 in KAMS2, and May 21 (±6 d) in KAMS4, when the sea ice concentration (SIC) was >90% and the ice thickness was 1–2 m, indicating that the under-ice phytoplankton blooms (UIBs) developed 1–2 months before the sea ice retreated (mid-July, when SIC was <80%). Peak bloom and termination times were consistently observed in early August and mid-October, respectively. The average phytoplankton bloom lasted for approximately four months, longer than the open water periods at the mooring sites. However, the timing of the phytoplankton blooms from the biogeochemical model-based reconstructions was, on average, 6–10 weeks later than that deduced from the observed data. Furthermore, the maximum chlorophyll-a concentration observed during the bloom peak was approximately ten-times higher than that indicated by the biogeochemical model-based reconstructions (1.81 vs. 0.17 mg −3). The differences in chlorophyll-a concentrations and bloom timings indicate that biogeochemical models remain insufficient for simulating the phytoplankton dynamics of the Arctic Ocean, such as UIBs and the subsurface chlorophyll maximum layer. Based on the continuously observed chlorophyll-a concentrations, we gained a precise understanding of the seasonal cycles of Arctic phytoplankton, including UIBs. These valuable data will contribute to improving the accuracy of biogeochemical models of the Arctic Ocean.

Coupling of hydrography and bio-optical constituents in a shallow optically complex region using ten years of in-situ data

Using ten years of in-situ data from a shallow optically complex coastal ecosystem, this study unravels the coupling between bio-optical variability and seasonally changing hydrography. The data presented is novel, as these are long-term simultaneous measurements of bio-optical properties and constituents covering a wide range of hydrographic conditions at different sampling stations in riverine, estuarine, and coastal shelf. The data represent all three seasons experienced in the region, i.e., Indian Summer Monsoon (ISM), post-ISM, and pre-ISM. It allowed us to conduct a baseline study to characterize the bio-optical variability (absorption or scattering dominated) coupled with stratification for remote sensing applications on ecological health. Four groups of sampling stations, representing varying hydrography, were identified as riverine, maximum stratification, maximum chlorophyll-a (Chl-a) concentration, and estuarine/shelf. The maximum concentrations of total suspended matter (TSM) were always collocated with the strongest stratification site, while maximum Chl-a was always located downstream of maximum stratification. Surprisingly, colored dissolved organic matter (CDOM) values were negligible in the ISM season and increased manifold in other seasons. The source of CDOM (either land-derived or in situ generated) inferred from the spectral slope revealed the dominance of land-derived CDOM in the post-ISM season. Combining the entire data into the same groups showed that groups with maximum TSM and samples from estuarine locations were scattering-dominated. In contrast, the group with maximum Chl-a was absorption dominated. The analysis revealed that the optical behavior of the sampling locations being either absorption or scattering dominated depended on the state of stratification and contribution of Chl-a to the absorption budget.

Towards advanced nutrient removal by microalgae-bacteria symbiosis system for wastewater treatment

In this study, the microalgae-bacteria symbiosis (ABS) system by co-culturing Chlorella sorokiniana with activated sludge was constructed for pollutants removal, and the according interaction mechanism was investigated. The results showed that the ABS system could almost completely remove ammonia nitrogen, and the removal efficiency of total nitrogen and total phosphorus could accordingly reach up to 65.3 % and 42.6 %. Brevundimonas greatly promoted microalgal biomass growth (maximum chlorophyll-a concentration of 9.4 mg/L), and microalgae contributed to the increase in the abundance of Dokdonella and Thermomonas in ABS system, thus facilitating nitrogen removal. The extended Derjaguin-Landau-Verwey-Overbeek theory indicated a repulsive potential barrier of 561.7 KT, while tryptophan-like proteins and tyrosine-like proteins were key extracellular polymeric substances for the formation of flocs by microalgae and activated sludge. These findings provide an in-depth understanding of interaction mechanism between microalgae and activated sludge for the removal of contaminants from wastewater.

Chlorophyll maxima layer in a large subtropical reservoir (Xinanjiang Reservoir): Spatial development process and limitation by CO2 and phosphorus

In marine investigations, the maximum chlorophyll-a (Chla) concentration is often reported to occur at a specific depth below the ocean surface, a phenomenon known as subsurface Chla maxima (SCM). However, SCM has long been overlooked in artificial reservoirs, which may lead to a serious underestimation of the primary productivity level and trophic status of reservoirs. To better understand the temporal and spatial variability of SCM and the mechanisms leading to SCM development, this study conducted a detailed survey in a large subtropical reservoir (Xinanjiang Reservoir, XAJR) from September 2020 to August 2021. The seasonal thermal stratification, in situ variables (WT, pH, DO and Chla), nutrient concentrations (DSi, NO3−, DIP and DCO2), Chla maxima depth and magnitude of the riverine region (S1), transition region (S2) and the central part of the XAJR (S3 and S4) were all thoroughly investigated. Thermal stratification and SCM in XAJR exhibited significant seasonal and spatial heterogeneity. Phytoplankton biomass in the epilimnion was limited by dissolved CO2 from June to October in the warm seasons, while it was primarily limited by phosphorus in the other seasons, according to the nutrient limitation analysis. Along the water column, dissolved CO2 limitation occurred mainly above the SCM layer, and the water column below the SCM layer gradually transitioned from dissolved CO2 limitation to phosphorus limitation. Furthermore, as the thermal stratification developed, the upstream water mass moves along the middle of the water column as density flow toward the reservoir, providing nutrients for the development of the SCM. This research contributes to a better understanding of the temporal and spatial variation of SCM and nutrient supply in deep and large stratified reservoirs.

Meteorological feedback and eco-environmental impact of Asian dust: A simulation study

Wind-blown dust plays a crucial role in air quality, biogeochemical cycles, and climate change. In East Asia, one of the main dust source regions in the world, dust storms frequently engulf eastern China, with a substantial negative effect on air pollution and the ecological environment. By integrating multiple observations and the online coupled meteorology-chemistry model WRF-Chem, a severe dust storm event originating from the Gobi Desert in early May 2017 is comprehensively analyzed from the perspective of emission estimation, meteorological feedback, and the possible impact on the ecological environment. We optimize the size distribution of dust aerosol by applying local observations to better represent dust emission and regional transport in the model. Both the observations and simulations indicate that the dust storm broke out with PM10 concentrations exceeding 1500 μg/m3 in the source region of the Gobi Desert, and was quickly transported downwind, deteriorating the air quality of cities in northern and eastern China. Moreover, we find that the dust storm significantly perturbed the temperature stratification, since mineral dust is a radiatively active aerosol and can absorb both short- and long-wave radiation. The upper dust layer at an altitude of around 2–3 km became warmer by 1–2 °C while the surface temperature decreased by about 2 °C, making the planetary boundary layer more stable and indirectly aggravating local air pollution near the ground in eastern China. Furthermore, during this event, a large amount of dust deposition increased ocean primary productivity, with the maximum Chlorophyll-a concentration rising from 4 to 14 mg/m3 in the central area of the Yellow Sea. This study highlights the critical impact of Asian dust pollution on air quality and marine ecosystems in downwind areas.

Cyanobacteria and their secondary metabolites in three freshwater reservoirs in the United Kingdom

BackgroundBloom-forming cyanobacteria occur globally in aquatic environments. They produce diverse bioactive metabolites, some of which are known to be toxic. The most studied cyanobacterial toxins are microcystins, anatoxin, and cylindrospermopsin, yet more than 2000 bioactive metabolites have been identified to date. Data on the occurrence of cyanopeptides other than microcystins in surface waters are sparse.ResultsWe used a high-performance liquid chromatography–high-resolution tandem mass spectrometry/tandem mass spectrometry (HPLC–HRMS/MS) method to analyse cyanotoxin and cyanopeptide profiles in raw drinking water collected from three freshwater reservoirs in the United Kingdom. A total of 8 cyanopeptides were identified and quantified using reference standards. A further 20 cyanopeptides were identified based on a suspect-screening procedure, with class-equivalent quantification. Samples from Ingbirchworth reservoir showed the highest total cyanopeptide concentrations, reaching 5.8, 61, and 0.8 µg/L in August, September, and October, respectively. Several classes of cyanopeptides were identified with anabaenopeptins, cyanopeptolins, and microcystins dominating in September with 37%, 36%, and 26%, respectively. Samples from Tophill Low reservoir reached 2.4 µg/L in September, but remained below 0.2 µg/L in other months. Samples from Embsay reservoir did not exceed 0.1 µg/L. At Ingbirchworth and Tophill Low, the maximum chlorophyll-a concentrations of 37 µg/L and 22 µg/L, respectively, and cyanobacterial count of 6 × 104 cells/mL were observed at, or a few days after, peak cyanopeptide concentrations. These values exceed the World Health Organization’s guideline levels for relatively low probability of adverse health effects, which are defined as 10 µg/L chlorophyll-a and 2 × 104 cells/mL.ConclusionsThis data is the first to present concentrations of anabaenopeptins, cyanopeptolins, aeruginosins, and microginins, along with microcystins, in U.K. reservoirs. A better understanding of those cyanopeptides that are abundant in drinking water reservoirs can inform future monitoring and studies on abatement efficiency during water treatment.

Spatial-Temporal Variability of Chlorophyll-a Concentration in Cenderawasih Bay and Surrounding Waters

Chlorophyll-a is one of the parameters determining the primary productivity of water. In the fisheries sector, information on chlorophyll-a concentration in marine waters is very important for the prediction of fishing grounds. This study aims to analyze the variability of chlorophyll-a concentrations in Cenderawasih Bay and the surrounding waters, both spatial and temporal variability. Data from the Aqua-MODIS Level 3 monthly composite period from January to December 2019 was used to determine the concentration of chlorophyll-a. Time-series data are used to determine fluctuations of chlorophyll-a concentrations, while interpolation with the kriging method is used to determine the spatial distribution of chlorophyll-a. The analysis showed that the monthly average value of chlorophyll-a concentration in the study area ranged from 0.1988 – 0.3415 mg.m-3. The average value of chlorophyll-a concentration increases from March to June and then decreases in July or August. The highest average chlorophyll-a concentration was in March and the lowest in January. The maximum chlorophyll-a concentration in April and the minimum in August, which is around 9.1089 mg.m-3 and 0.0975 mg.m-3, respectively. The concentration of chlorophyll-a in Cenderawasih Bay and its surrounding waters is dominated by a low concentration, which ranges 0.1482 – 0.3158 mg.m-3. Generally, the variability of chlorophyll-a concentrations in the study area is influenced by seasons. The average chlorophyll-a concentration is high in the Transition I (West-east) and East seasons and will decrease in Transition II (East-West) until the West season. Spatially, chlorophyll-a concentrations in coastal areas are higher than in offshore waters. High chlorophyll-a concentrations are found around the border between Nabire Regency and Waropen Regency. The amount of run-off flow that supplies nutrients from the mainland greatly affects the high concentration of chlorophyll-a in the coastal area.

Predicting coral-reef futures from El Ni\xf1o and Pacific Decadal Oscillation events

El Niño Southern Oscillation (ENSO) events modulate oceanographic processes that control temperature and productivity in tropical waters, yet potential interactions with low frequency climate variability, such as the Pacific Decadal Oscillation (PDO), are poorly understood. We show that ENSO and PDO together predicted (i) maximum sea-surface temperatures (SST), which were associated with coral bleaching and declines in coral cover, and (ii) maximum chlorophyll-a concentrations, which were associated with high densities of coral-predatory Acanthaster starfish, across the tropical north Pacific Ocean since 1980. Asynchrony between the positive PDO and negative ENSO (i.e., La Niña) was associated with peaks in annual SST. By contrast, synchrony between the positive PDO and positive ENSO (i.e., El Niño) was associated with peaks in chlorophyll-a. Both conditions led to ecological disturbances and significant loss of coral cover, however, spatial models revealed where impacts to reefs were expected under varying climate scenarios. The 2015/17 ENSO event was coupled with a positive PDO and resulted in high SST and Acanthaster abundances in eastern Micronesia, while positive coral growth occurred in western Micronesia. Our novel approach for forecasting coral growth into the future may be applicable to other oceanic regions with differing oceanographic modulators.

Impact of abiotic factors on microbialite growth (Great Salt Lake, Utah, USA): a tank experiment

Microbialites are microbial communities that create a carbonate structure. They are abundant in the Great Salt Lake, a hypersaline lake in the arid Great Basin of the USA, where they contribute to overall primary production, seasonally up to 55%. While the microbial diversity of microbialites has been investigated, how abiotic factors affect the abundance of their primary constituents is not well understood. We examined how microbialite primary producers respond to varying levels of temperature, salinity, and nitrogen within ranges observed in the Great Salt Lake. All abiotic factors and their interactions significantly affected the maximum chlorophyll-a abundance, suggesting that these factors co-limit microbialite primary producers in the Great Salt Lake. Maximum chlorophyll-a concentrations increased with nitrogen additions and showed a parabolic relationship with salinity and temperature with peaks around 60 ppt and 20°C, respectively. While salinity had a strong effect on microbialite primary producers, we found that temperature and nitrogen were more impactful, accounting for 40 and 30% of the variance in maximum abundance, respectively, while salinity contributed just 15%. Our results show the importance of the interplay of abiotic factors on Great Salt Lake microbialites and highlight the need for increased study of benthic communities in inland saline lakes.

Modeling curtain weirs for controlling algal blooms in the largest tributary of the Three Gorges Reservoir, China

Curtain Weirs (CWs) are hydraulic structures that act as a barrier to the flow and diffusion of heat across the width of a water body. Algal blooms occur frequently in Xiangxi Bay (XXB), which is one of the largest tributaries of the Three Gorges Reservoir (TGR). Numerical modeling has become a widely accepted tool for predicting and diagnosing hydrodynamic problems. A laterally averaged two-dimensional hydrodynamic and water quality model (CE-QUAL-W2) was used to simulate the CWs and the hydrodynamics, temperature and chlorophyll-a concentrations for XXB. The developed model was calibrated using data collected in XXB from January to December in 2010. The results indicated that the maximum chlorophyll-a concentrations was observed 154 mg/m3 at sampling sites XX09, XX06 and XX01. The CWs led to a marked reduction of the overall chlorophyll-a concentrations 30–85% because of the CWs height and locations. Therefore, the proposed CWs represent a potential method of reducing algal blooms and improving water quality in XXB of the TGR.

Long-term trend and environmental determinants of phytoplankton biomass in coastal waters of northwestern Bay of Bengal.

The present study is focused on understanding long-term trend in distribution of chlorophyll-a and its association with water quality parameters in coastal waters of northwestern Bay of Bengal. In situ observations were carried out in monthly frequency during January 2009 to March 2017 at two ecologically important study sites, off Gopalpur and off Visakhapatnam. A bimodal distribution of chlorophyll-a was observed off Gopalpur with primary and secondary peak during pre- and post-monsoon, respectively. In contrast, maximum chlorophyll-a concentration was noticed in monsoon irrespective of sporadic higher magnitudes during pre-monsoon in coastal waters off Visakhapatnam. The pivotal role of river influx and coastal upwelling was discerned in enriching coastal waters off Gopalpur with macronutrients and in turn on chlorophyll-a distribution. Adequate availability of silicate signified favorable condition for diatom growth in coastal waters off Gopalpur leading to preponderance. Influence of coastal upwelling and nutrient-controlledgrowth of phytoplankton was observed in coastal waters off Visakhapatnam.

Modeling Effects of Floating Curtain Weirs and Controlling Algal Blooms in a Subtropical Reservoir of China

Algal blooms occur frequently in Xiangxi Bay (XXB), which is one of the largest tributaries of the Three Gorges Reservoir (TGR). Floating curtain weirs (FCWs) are hydraulic structures that act as a barrier to divert density currents and diffuse heat across the width of the water body. Numerical modeling of FCWs is become a widely accepted method for controlling algal blooms. A laterally averaged two-dimensional hydrodynamic and water quality model (CE-QUAL-W2) was used to simulate the effects of FCWs, including those on water temperature, hydrodynamics and chlorophyll-a concentrations, for XXB. The developed model was calibrated using data collected in XXB from January to December 2010. The results indicated that the maximum chlorophyll-a concentrations observed were 74-154 mg/m3 at the XX09, XX06 and XX01 sampling sites. The performance of the FCWs suggests that the overall chlorophyll-a concentrations are markedly reduced by more than 85% as a function of the FCW heights and locations. Seasonally, an algal bloom reduction rate of more than 62% was observed in the summer. FCWs with heights of 3, 5, and 7 m reduced algal blooms by up to 99% at XX09 during March 26-28, April 24-27, July 18-26, August 5-20, and 23-28, and September 3-8 and 12-16, respectively. Therefore, the proposed FCWs can reduce algal blooms and improve water quality to save domestic water and aquatic ecosystems in XXB.

Modeling Effects of Bottom Curtain Weirs and Controlling Algal Blooms in Xiangxi Bay, Three Gorges Reservoir, China

A bottom curtain weir (BCW) is a hydraulic structure that acts as a barrier to the flow and diffusion of heat across the width of a water body. Algal blooms occur frequently in the largest tributary of Xiangxi Bay (XXB) of the Three Gorges Reservoir (TGR). A laterally averaged two-dimensional hydrodynamic and water quality model was used to simulate BCWs, including water temperature, hydrodynamics and chlorophyll-a concentrations, for XXB. The numerical models show that BCWs are a much more attractive, much less expensive and time-saving algal bloom controlling technique for subtropical reservoirs. The developed model was calibrated using data collected in XXB from January to December 2010. The maximum chlorophyll-a concentrations observed were 125-154 mg/m3 according to sampling sites such as XX09, XX06 and XX01. Overall chlorophyll-a concentrations were markedly reduced by 4-44% as a function of BCWs height and location. A seasonal algal bloom reduction rate of more than 37% was observed in summer. In some periods, such as May 27-31, June 2-4, June 16-18, August 16-18 and August 23-24, BCWs with heights of 3 m, 5 m and 7 m reduced algal blooms by up to 99% at XX09 and XX06 in XXB. Therefore, the proposed BCWs can reduce algal blooms and improve water quality to save domestic water and aquatic ecosystems in XXB of TGR.

Chlorophyll-a vertical distribution patterns during summer in the Bay of La Paz, Gulf of California, Mexico

An understanding of chlorophyll-a vertical distribution patterns is essential for evaluating the productive potential of the oceans and implications for food webs. Based on high-resolution in-situ observations for conductivity, temperature and fluorescence of chlorophyll-a made at 30 stations during a multidisciplinary research cruise, this paper aims to assess the vertical distribution of chlorophyll-a in the Bay of La Paz, Gulf of California, Mexico, during the summer of 2009. The maximum chlorophyll-a concentration was 3.03 mg m−3 with a vertical distribution consistent with two patterns: 1) a peak closely related with the seafloor at the stations in the shelf area, close to the coast, and 2) a peak related with the thermocline and pycnocline, either above or below, in the central region of the bay. These patterns might have several implications for food webs, particularly for grazers, recently reported in high abundances in the bay. On the basis of these observations, a zonal trend would be expected for summer, whereby the two vertical patterns described above can be observed.

Enhanced Microalgal Lipid Production in Internally Illuminated Airlift Photobioreactor

AbstractInternal illumination systems are being considered for use as an alternative light supply technique in microalgal products. The main goal of the study was to analyze the roles of different light wavelengths in internally illuminated airlift photobioreactors (PBRs) providing the light energy in an efficient way for the biomass production, lipid yield, and fatty acid composition of Amphora capitellata. The maximum chlorophyll-a concentration per unit biomass (2.62 ± 0.16 mg L−1) was obtained under red light, which was only 14% higher than under blue light in internally illuminated airlift PBR, whereas low chlorophyll-a content was found under white light. Maximum specific growth rate of 0.317 day−1, which corresponded to a doubling time of 2.185 days, was obtained under red light for A. capitellata. It was found that lipid content increased with decreasing growth rate for A. capitellata. Palmitic acid (C16:0) and palmitoleic acid (C16:1) were the principal fatty acids accounting for between 31%‐33% and 31%‐32% of total fatty acids, respectively. It is important to underline that red and blue light spectrum ranges contribute to improved biomass growth, whereas white light has the potential to support lipid content of diatoms.

The environmental feasibility of low-cost algae-based sewage treatment as a climate change adaption measure in rural areas of SADC countries

Employing specific algae treatment to treat municipal domestic wastewater effluent presents an alternative practice to improving water quality effluent of existing rural pond systems in Southern Africa. In the present study, domestic wastewater was treated by using existing infrastructure and inoculated specific selected algae strains in a pond system treatment plant. The objective was to determine through a field pilot study if algae nutrient treatment efficiencies in current traditional water-stabilisation ponds can be optimised by manipulating the existing natural consortium of algae through mass inoculation of specific algae strains of Chlorella spp. The reduction of total phosphorus in the unfiltered water (contain algae) after specific algae treatment was 74.7 and 76.4% for water-stabilisation ponds 5 and 6, while total nitrogen removal was 43.1 and 35.1%, respectively. Chlorella protothecoides was the dominant algal species in ponds 4, 5 and 6 after specific algae treatment. The maximum algae abundance (4.6 × 106 cells mL−1 in pond 4 and 6.1 × 106 cells mL−1 in pond 5) were observed in August 2016, while the maximum chlorophyll-a concentration of 783 μg L−1 was measured in pond 5 after 2 months of specific algae inoculation. Although the present study showed that inoculation of specific algal strains can potentially enhance the treatment efficiencies of existing rural domestic sewage pond systems, it was also evident from the algae-treated effluent analysis that the algae biomass in the upper surface water layer must be harvested for maximum treatment results.

Coupled hydrodynamic and water quality simulation of algal bloom in the Three Gorges Reservoir, China

Patterns of spatial and temporal variability of algal bloom in the Three Gorges Reservoir (TGR) of China were investigated using Semi-implicit Eulerian-Lagrangian Finite Element (SELFE) model, an unstructured grid, 3-dimensional, hydrodynamic model fully coupled with an extended version of Water Quality Analysis Program (WASP) and the Carbon and Nutrients DIagenesis (CANDI) model. The coupled model was driven by the discharge, operational water level of the TGR, nutrients and phytoplankton from the upstream, climate condition included the solar radiation, heat fluxes and precipitation observed in the hydrometric and meteorological stations. The simulations were conducted to study the dynamic process of the algal blooms occurred in September 2007 and June 2008, and the modeling results agreed well with the field data included nutrients, chlorophyll-a concentrations in the TGR. The results indicated that the nutrients and chlorophyll-a concentrations showed obvious difference in the mainstream and the tributaries affected by the diurnal evolution of the phytoplankton during the algal bloom period. The location of algal bloom in the tributary Xiangxi River where the maximum chlorophyll-a concentration was greater than 30 μg/L was about 20 km from the river mouth, which coincided with the position of backwater tail controlled by the operation of the TGR. Meanwhile, the nutrients concentration near the river bed reached nearly 10 times of the concentration near the water surface after considering the nutrients released from the re-suspended sediment and the biogeochemical process in the river bed sediment. Finally, the climate change affected the aquatic ecosystem in the TGR was investigated and the countermeasure to inhibit the algal bloom in the tributary was suggested through the scenario modeling.

The effect of climate change on the distribution of a tropical zoanthid (Palythoa caribaeorum) and its ecological implications.

Palythoa caribaeorum is a zoanthid often dominant in shallow rocky environments along the west coast of the Atlantic Ocean, from the tropics to the subtropics. This species has high environmental tolerance and is a good space competitor in reef environments. Considering current and future scenarios in the global climate regime, this study aimed to model and analyze the distribution of P. caribaeorum, generating maps of potential distribution for the present and the year 2100. The distribution was modeled using maximum entropy (Maxent) based on 327 occurrence sites retrieved from the literature. Calcite concentration, maximum chlorophyll-a concentration, salinity, pH, and temperature range yielded a model with the smallest Akaike information criterion (2649.8), and were used in the present and future distribution model. Data from the HadGEM2-ES climate model were used to generate the projections for the year 2100. The present distribution of P. caribaeorum shows that parts of the Brazilian coast, Caribbean Sea, and Florida are suitable regions for the species, as they are characterized by high salinity and pH and small temperature variation. An expansion of the species’ distribution was forecast northward under mild climate scenarios, while a decrease of suitable areas was forecast in the south. In the climate scenario with the most intense changes, P. caribaeorum would lose one-half of its suitable habitats, including the northernmost and southernmost areas of its distribution. The Caribbean Sea and northeastern Brazil, as well as other places under the influence of coastal upwellings, may serve as potential havens for this species.

Eutrophication control decision making using EFDC model for Shenzhen Reservoir, China

The three-dimensional hydrodynamic and eutrophication model was implemented based on EFDC to help eutrophication control decision making of Shenzhen Reservoir. Model calibration and validation were conducted with two set of independent observed data in 2009 and 2010–2011. The model represented the hydrodynamic process and the spatial and temporal distribution of water quality well. Subsequently, three eutrophication control scenarios were configured, included removing 100% nutrients from all tributaries, increasing by 50% of water flows, and removing 50% nutrients from Dongjiang. As results shown, the maximum chlorophyll-a concentrations were decreased by 1, 16.4 and 46.3%, the average chlorophyll-a concentrations were decreased by 1.3, 29.8 and 29.9%. Increasing water flows and removing nutrients from Dongjiang can significantly improve water quality and effectively reduce risk of water bloom.