Maximum Chlorophyll-a Research Articles

An analytical phytoplankton model and its application in the tidal freshwater James River

This study constructs an analytical model to understand the phytoplankton dynamics in a one-dimensional system by integrating physical and biological processes. We present an analytical solution of phytoplankton distribution along the longitudinal direction of a tidal river. The solution has two components: water age and accumulative growth. The water age represents the overall effect of physical transport due to advection, while the accumulative growth represents the accumulation of phytoplankton biomass due to biological processes during the transport. In addition, an alternative solution with nonlinear reaction term is given to account for the feedback mechanism of nonlinear processes that affect phytoplankton growth rate. The nonlinear reaction term can be also used to approximate the effect of physical mixing on phytoplankton distribution. The analytical solutions can be further used to predict the temporal variation and spatial distribution of phytoplankton along the tidal river. They also serve as a mathematical tool to unite different field phytoplankton observations. We applied the model in the Tidal Freshwater Region (TFR) of James River under different dynamic conditions and the model results match well with the observations, which validates the theory on different time scales. Furthermore, an analysis is conducted for the Local Chlorophyll-a Maximum (LCM) in the TFR. It shows that the condition for LCM is biologically controlled, but its location is regulated by river flow and river geomorphology.

Importance of mixotrophic flagellates during the ice-free season in lakes located along an elevational gradient

Mixotrophy seems to be widespread among phytoplankton, but whether this strategy is more relevant in oligotrophic lakes remains unclear. Here, we tested the hypothesis that the relative abundance of mixotrophic flagellates in lakes increases along an elevational gradient paralleling increasingly oligotrophic conditions. For this purpose, 12 lakes located between 575 and 2796 m above sea level were sampled in summer and fall to include two different seasonal windows in phytoplankton dynamics and environmental conditions. The degree of mixotrophy in phytoplankton was estimated in tracer experiments using fluorescently-labeled bacteria and done with composite samples collected in the euphotic zone and in samples obtained from the chlorophyll-a maximum. The results indicated the existence of a positive trend particularly in summer in the relative abundance of mixotrophic flagellates with elevation, however, this trend was not linear, and exceptions along the elevational gradient were found. Changes in the relative abundance of mixotrophic flagellates were related with significant changes in water transparency, DOC and phosphorus concentrations, as well as in bacterial and flagellate abundance. Overall, our results reveal that the harsh growth conditions found in oligotrophic high mountain lakes favor a mixotrophic trophic strategy among phytoplankton.

Spatial Distribution and Physical Controls of the Spring Algal Blooming Off the Changjiang River Estuary

The Changjiang River discharges huge amounts of nutrients, which cause frequent harmful algal blooms off its estuary. By analyzing historical and in situ observational data, this study aimed to determine the distribution and physical controls of these blooms. The results indicated that phytoplankton bloomed within the 30–50 m isobaths south of the Changjiang River mouth, with several high-value centers. South of the river mouth, the river plume front propagated along the coast as bottom-trapped river plume, which reached the bottom along the 25–30 m isobaths. The algae bloomed between the locations of the bottom and surface fronts. The surface front determined the seaward limit of the nutrient-rich river-influenced water and set the outer boundary of algal blooming; the latter separated the stratified (hence less turbid) offshore surface water from the well-mixed thus turbid nearshore surface water, forming the shoreward limit of the algal blooming due to high turbidity. The surface plume front was relatively unstable compared with the bottom. The surface plume front relaxes around the bathymetric irregularities, which enlarges the distance between the plume’s surface and bottom fronts, providing a larger area favorable to algal blooming. Consequently, several high chlorophyll-a centers developed around the bathymetric irregularities. East and northeast of the river mouth, the river plume floated above ambient seawater as a surface-trapped river plume. A subsurface chlorophyll-a maximum was observed above the pycnocline in the far-field plume area, which descended gradually to ~ 10 m in the offshore direction. The associated dynamical mechanism was also discussed.

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.

Effect of bio-regulators on vegetative parameters of Asiatic lily var Pavia under protected condition

An investigation on “Effect of bio-regulators on vegetative parameters of Asiatic lily var. Pavia under protected condition” was carried out at Department of Floriculture and Landscape Architecture, College of Horticulture, Mudigere (Under University of Agricultural and Horticultural sciences, Shivamogga), during 2018-19. The treatments comprised of, GA3 (100, 150 and 200 ppm), BA (150, 300 and 450 ppm), NAA (100,150 and 200 ppm) and CCC (1000, 1500 and 2000 ppm) and control. The results revealed that GA3 @ 200 ppm recorded minimum days to sprouting (3.33), maximum plant height (98.44 cm), number of leaves (80.93), leaf length (12.53 cm), leaf breadth (2.77 cm), leaf area (1704.60 cm2) and leaf area index (LAI) (5.68). The maximum number of days for sprouting (16.67), minimum plant height (21.93 cm), minimum number of leaves (31.77), minimum length of leaves (4.27 cm), breadth of leaves (1.37 cm), minimum leaf area (442.45 cm2) and minimum LAI (1.47) was recorded by BA @ 450 ppm. NAA @ 100 ppm recorded maximum chlorophyll-a, chlorophyll-b and total chlorophyll content (98, 0.50 and 1.48 mg per g fresh weight, respectively). Whereas BA @ 450 ppm was recorded minimum chlorophyll-a, chlorophyll-b and total chlorophyll content (0.63, 0.22 and 0.85 mg per g fresh weight, respectively).

Characterization of the Light Field and Apparent Optical Properties in the Ocean Euphotic Layer Based on Hyperspectral Measurements of Irradiance Quartet

Although the light fields and apparent optical properties (AOPs) within the ocean euphotic layer have been studied for many decades through extensive measurements and theoretical modeling, there is virtually a lack of simultaneous high spectral resolution measurements of plane and scalar downwelling and upwelling irradiances (the so-called irradiance quartet). We describe a unique dataset of hyperspectral irradiance quartet, which was acquired under a broad range of environmental conditions within the water column from the near-surface depths to about 80 m in the Gulf of California. This dataset enabled the characterization of a comprehensive suite of AOPs for realistic non-uniform vertical distributions of seawater inherent optical properties (IOPs) and chlorophyll-a concentration (Chl) in the common presence of inelastic radiative processes within the water column, in particular Raman scattering by water molecules and chlorophyll-a fluorescence. In the blue and green spectral regions, the vertical patterns of AOPs are driven primarily by IOPs of seawater with weak or no discernible effects of inelastic processes. In the red, the light field and AOPs are strongly affected or totally dominated by inelastic processes of Raman scattering by water molecules, and additionally by chlorophyll-a fluorescence within the fluorescence emission band. The strongest effects occur in the chlorophyll-a fluorescence band within the chlorophyll-a maximum layer, where the average cosines of the light field approach the values of uniform light field, irradiance reflectance is exceptionally high approaching 1, and the diffuse attenuation coefficients for various irradiances are exceptionally low, including the negative values for the attenuation of upwelling plane and scalar irradiances. We established the empirical relationships describing the vertical patterns of some AOPs in the red spectral region as well as the relationships between some AOPs which can be useful in common experimental situations when only the downwelling plane irradiance measurements are available. We also demonstrated the applicability of irradiance quartet data in conjunction with Gershun’s equation for estimating the absorption coefficient of seawater in the blue-green spectral region, in which the effects of inelastic processes are weak or negligible.

Nutrient and carbon dynamics under the water mass seasonality on the continental shelf at the South Brazil Bight

Abstract The enrichment of the euphotic zone and the production of organic matter (OM) are induced by wind-driven processes that change the water mass distribution in the central inner and mid continental shelf of Santa Catarina State (27°18′–27°37′S), South Brazil Bight (23–28.5°S). During austral summer, the Ekman transport by north-eastern winds is balanced by onshore bottom intrusions of the nutrient-rich South Atlantic Central Water (SACW), while during austral winter, the Plata Plume Water (PPW) reaches the region, which is pushed northward by south-eastern winds. Between 2014 and 2016, six oceanographic campaigns were conducted at the isobaths of 30 and 50 m, one in the early fall of 2014, others in the summers of 2015 and 2016, and in each winter of the stated years. The aim was to investigate the spatio-temporal variability of nutrients (nitrate + nitrite, ammonium, phosphate and silicate), and composition of the particulate organic matter (POM), i.e. particulate organic carbon and nitrogen, in relation to the water masses dynamics. In summer of 2015 and 2016, the SACW reached all over the bottom layers of the studied area, while in 2014, it only reached the outer stations. The SACW intrusion was reflected by relatively high phosphate (0.61 ± 0.29 μM), silicate (9.51 ± 4.34 μM), and notably high nitrate (4.21 ± 2.83 μM) concentrations. The POM composition revealed the deep chlorophyll-a maximum at intermediate and bottom layers, indicating new primary production associated with the nutrient-rich SACW. The denitrification was identified in bottom water by nitrogen loss (up to 9.66 μM) associated with the low dissolved oxygen saturation (DO%) (53.07 ± 7.8%). In winter, the PPW reached the region in the surface, especially in 2015 and 2016, with high silicate concentrations (8.36 ± 2.46 μM). Nitrate (1.69 ± 0.92 μM) and phosphate (0.46 ± 0.23 μM) were mainly related to regeneration processes in the bottom layers associated with low DO% (78.25 ± 7.55%). In summer, the SACW presented higher potential for biological production against Subtropical Shelf Water (STSW), while in winter, the STSW was higher than the PPW. Besides the new nutrient supply associated with wind-driven water mass dynamics, the nutrients regeneration contributed to the food chain structure via a regenerated primary production.

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.

Distribution of thiol, humic substances and colored dissolved organic matter during the 2015 Canadian Arctic GEOTRACES cruises

Abstract Organic sulfur and humics play a key role in the biogeochemistry of metals in natural waters but their distribution is not well understood. In this study, we measured the concentrations of thiol-like, humic substance (HS) -like and fluorescent dissolved organic matter (FDOM) during the 2015 Canadian Arctic GEOTRACES cruises in the Canada Basin and Canadian Arctic Archipelago (CAA). Concentrations of thiol-like (7–85 nM, expressed as equivalent to glutathione concentration) and HS-like (19 to 190 μg C/L) determined by cathodic stripping voltammetry (CSV) were congruent with previous marine CSV-based studies. Three humic-like (C1-C3) and one protein-like (C4) components identified and validated using excitation-emission matrix (EEM) and parallel factor analysis (PARAFAC) have been reported in previous ocean studies. The distributions of HS-like and humic-like components (C1 and C2) in the CAA were similar, whereas thiol-like and protein-like component C4 were closely related in the study area. Maximum CSV-based thiol-like levels were associated with chlorophyll-a maximum, confirming the biogenic origin of thiols . The distribution and concentrations of CSV-based thiol- and HS-like, and FDOM varied between four distinct water masses (i.e. surface waters, Arctic outflow waters, Arctic intermediate waters and North Atlantic deep waters) with the lowest levels associated with the surface waters, likely due to photobleaching and sea ice melt dilution. The concentrations in CSV-based HS-like and FDOM in the Arctic outflow waters decreased from western to eastern CAA, reflecting the influence of DOM-rich Pacific derived waters.

Physical and biogeochemical variability in Todos Santos Bay, northwestern Baja California, derived from a numerical NPZD model

A physical-biogeochemical Nitrate-Phytoplankton-Zooplankton-Detritus (NPZD) numerical model is used to study the variability of coastal phytoplankton biomass in northwestern Baja California and the Todos Santos Bay (TSB), a region of high socioeconomic importance located in the southern California Current System. The model reproduces adequately the most important oceanographic features of the study area, like the coastal chlorophyll-a (Chl-a) maxima and thermal gradients in the regions of enhanced coastal upwelling. The variability of Chl-a in the TSB is influenced by the activity of El Niño-Southern Oscillation (ENSO) and decadal modes of the Pacific, e.g., the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). From de multi-year model simulation (2004–2011), this large-scale influence is remarkable in two contrasting anomalous years. The year 2006 was anomalously warm and with low Chl-a levels, associated with warm phases of ENSO and PDO and a weakening of the NPGO. These climatic anomalies caused a strong stratification and weak upwelling around the TSB, which induced a poor nutrient input into the Bay and a deep and weak subsurface Chl-a maximum (SCM) during summer. The year 2011, on the other hand, was a cold year with enhanced upwelling during the spring, associated with cold phases of ENSO and PDO and an intensification of the NPGO. These conditions also caused a weak stratification and an intense nutrient transport into the TSB and hence a shallower and stronger SCM.

Seasonal variation of zooplankton abundance and community structure in Prince William Sound, Alaska, 2009–2016

Large calanoid copepods and other zooplankters comprise the prey field for ecologically and economically important predators such as juvenile pink salmon, herring, and seabirds in Prince William Sound (PWS).​ From 2009–2016, the Gulf Watch Alaska program collected zooplankton 5–10 times each year at 12 stations in PWS to establish annual patterns. Surveys collected 188 species of zooplankton with Oithona similis, Limacina helicina, Pseudocalanus spp., and Acartia longiremis as the most common species present in 519 samples. Generalized additive models assessed seasonal abundance and showed peak abundance in July (mean: 9826 no. m−3 [95% CI: 7990–12,084]) and lowest abundance in January (503 no. m−3 [373 to 678]). Significantly higher zooplankton abundance occurred in 2010 (542 no. m−3 ± 55 SE) and lowest in 2013 (149 no. m−3 ± 13). The species composition of communities, determined via hierarchical cluster analysis and indicator species analysis, produced six distinct communities based on season and location. The winter community, characterized by warm-water indicator species including Mesocalanus tenuicornis, Calanus pacificus, and Corycaeus anglicus, diverged into four communities throughout the spring and summer. The first spring community, characterized by copepods with affinities for lower salinities, occurred sound-wide. The second spring community, comprised of planktonic larvae, appeared sporadically in PWS bays in 2011–2013. Spring and summer open water stations were defined by the presence of large calanoid copepods. A summer community including the most abundant taxa was common in 2010 and 2011, absent in 2013, then sporadically appeared in 2014 and 2015 suggesting interannual variability of zooplankton assemblages. The zooplankton community shifted to a uniform assemblage characterized by cnidarians in the early autumn. Community assemblages showed significant correlations to a set of environmental variables including SST, mixed layer depth, location, depth of chlorophyll-a max, mixed layer average salinity, chlorophyll-a maximum, and bottom depth (ρ = 0.24, p < 0.05). The disappearance of the summer community coincided with the appearance of the Gulf of Alaska warm water anomaly known as “The Blob”. A shift in zooplankton community composition during critical grazing periods for predators such as juvenile Pacific herring (Clupea pallasi) could have energetic consequences for overwintering success.

Stoichiometry of natural bacterial assemblages from lakes located across an elevational gradient

Heterotrophic bacteria are thought to be phosphorus-rich organisms with relatively homeostatic stoichiometry, but the elemental composition of natural bacterial communities has rarely been assessed. Here we tested whether bacterial stoichiometry changes with the trophic status of lakes by assessing the elemental composition of the bacterial-dominated (hereafter microbial) fraction together with that of the dissolved and seston fractions in 11 lakes situated along an elevational gradient. The stoichiometry of these three size-fractions was analyzed during the thermal stratification and mixing periods in composite water samples and in the water layer of the deep chlorophyll-a maximum. In addition, we analyzed the relative abundance of the most common bacterial groups in the lakes. Our results show that the microbial fraction was always enriched in phosphorus compared to the dissolved fraction, irrespectively of the lake trophic status. Further, they indicate that the elemental composition of bacteria in mountain lakes is at least seasonally very dynamic, resulting not only from changes in the nutrient ratios of the resource itself, but probably from changes in the composition of the dominant bacterial taxa too, though at the taxonomic level analyzed, we did not find evidence for this.

Wind driven nutrient and subsurface chlorophyll-a enhancement in the Bay of La Paz, Gulf of California

Nutrient and chlorophyll-a distributions in the Bay of La Paz, Gulf of California, Mexico were analyzed during the late spring of 2004 to assess their relations to hydrography and circulation patterns. The results show the presence of both Gulf of California Water and Subtropical Subsurface Water. Water circulation was dominated by wind stress driven cyclonic circulation along f/H contours (f is planetary vorticity and H is depth), and upwelling resulting from the divergence shows a vertical velocity of ∼0.4 m d−1. Nutrient concentrations were higher in the center of the cyclonic pattern, where a rise in the nutricline contributed nutrients to the euphotic layer as a result of Ekman pumping. The vertical section showed the presence of a chlorophyll-a maximum at the thermocline shoaling to a depth of only 12 m. Along the surface, two peaks of chlorophyll-a were observed, one at Boca Grande and another off San Juan de la Costa, associated with upwelling and mixing derived from current interactions with abrupt topographies. The chlorophyll-a maximum increased from 0.8 mg m−3 in the external part of the cyclonic pattern to 2.0 mg m−3 in its center. The vertically integrated chlorophyll-a concentrations followed a similar pattern, rising from 10 to 20 mg m−2 and reaching their highest values in the center of the cyclonic circulation pattern. A schematic model was developed to describe processes that occur in late spring: the wind stress driven cyclonic structure promotes upward nutrient flux, which in turn drives an enhancement of chlorophyll-a. Upwelling was found to be the main mechanism of fertilization responsible for the enhancement of productivity levels by means of nutrient transport into the euphotic zone during spring. Other chlorophyll enhancement areas point to the occurrence of additional fertilization processes that may derive from interactions between cyclonic circulation patterns and the topography off of San Juan de la Costa, where phosphate mining occurs.

Reproductive patterns in demersal crustaceans from the upper boundary of the OMZ off north-central Chile

Pleuroncodes monodon (Crustacea: Munididae) supports one of the main trawling fisheries over the continental shelf off Chile between 25°S and 37°S within the upper boundary of the oxygen minimum zone (OMZ). Although the reproductive cycle of P. monodon has been described, the relationship between this key biological process and the variability of the OMZ has not been comprehensibly addressed neither for P. monodon nor for other OMZ resident species. In this study a set of 14 quasi-monthly oceanographic cruises carried out between June 2010 and November 2011 were conducted over the continental shelf off Coquimbo (30°S) to investigate the temporal variability of: i) dissolved oxygen concentration, temperature and chlorophyll-a at relevant depths ii) the presence and proportion of occurrence of P. monodon ovigerous females and juveniles from benthic trawls; iii) the presence of different stage larvae in the plankton, and iv) similar biological data for other species from the OMZ and shallower depths crustaceans. During summer months oxygen levels and bottom temperature were lower than in winter, while chlorophyll-a concentration was maximum in summer coinciding with an active (but not maximum) upwelling season. P. monodon maximum egg carrying occurred in winter during periods of increased oxygenation. Egg carrying females were never found at depths where oxygen concentration was below 0.5mlL−1, while over 50% of the autumn and spring cohorts of juveniles occurred at oxygen concentrations below that level. The depth range occupied by ovigerous females was more restricted than the rest of the population and their depth of occurrence followed the variability of the upper OMZ. The larval release period of OMZ resident species extends over late winter and spring, and its main peak precedes that of coastal species (spring) and the spring-summer chlorophyll-a maximum. We propose that for OMZ resident species, brood carrying during warmer and more oxygenated conditions in the adult benthic environment, might favor embryonic development, so OMZ seasonal variability could be acting as a selective pressure to synchronize reproductive periods.

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.

Fluorescence-Based Approach to Estimate the Chlorophyll-A Concentration of a Phytoplankton Bloom in Ardley Cove (Antarctica)

A phytoplankton bloom occurred in Ardley Cove, King George Island in January 2016, during which maximum chlorophyll-a reached 9.87 mg/m3. Records show that blooms have previously not occurred in this area prior to 2010 and the average chlorophyll-a concentration between 1991 and 2009 was less than 2 mg/m3. Given the lack of in situ measurements and the poor performance of satellite algorithms in the Southern Ocean and Antarctic waters, we validate and assess several chlorophyll-a algorithms and apply an improved baseline fluorescence approach to examine this bloom event. In situ water properties including in vivo fluorescence, water leaving radiance, and solar irradiance were collected to evaluate satellite algorithms and characterize chlorophyll-a concentration, as well as dominant phytoplankton groups. The results validated the nFLH fluorescence baseline approach, resulting in a good agreement at this high latitude, high chlorophyll-a region with correlation at 59.46%. The dominant phytoplankton group within the bloom was micro-phytoplankton, occupying 79.58% of the total phytoplankton community. Increasing sea ice coverage and sea ice concentration are likely responsible for increasing phytoplankton blooms in the recent decade. Given the profound influence of climate change on sea-ice and phytoplankton dynamics in the region, it is imperative to develop accurate methods of estimating the spatial distribution and concentrations of the increasing occurrence of bloom events.

Modelling Dissolved Oxygen/Sediment Oxygen Demand under Ice in a Shallow Eutrophic Prairie Reservoir

Dissolved oxygen is an influential factor of aquatic ecosystem health. Future predictions of oxygen deficits are paramount for maintaining water quality. Oxygen demands depend greatly on a waterbody’s attributes. A large sediment–water interface relative to volume means sediment oxygen demand has greater influence in shallow systems. In shallow, ice-covered waterbodies the potential for winter anoxia is high. Water quality models offer two options for modelling sediment oxygen demand: a zero-order constant rate, or a sediment diagenesis model. The constant rate is unrepresentative of a real system, yet a diagenesis model is difficult to parameterise and calibrate without data. We use the water quality model CE-QUAL-W2 to increase the complexity of a zero-order sediment compartment with limited data. We model summer and winter conditions individually to capture decay rates under-ice. Using a semi-automated calibration method, we find an annual pattern in sediment oxygen demand that follows the trend of chlorophyll-a concentrations in a shallow, eutrophic Prairie reservoir. We use chlorophyll-a as a proxy for estimation of summer oxygen demand and winter decay. We show that winter sediment oxygen demand is dependent on the previous summer’s maximum chlorophyll-a concentrations.

Seasonal and interannual phytoplankton dynamics and forcing mechanisms in the Northern Benguela upwelling system

Seasonal phytoplankton blooms are one of the key features of the productive northern Benguela upwelling system (nBUS), however they are not well described thus far. In this study twelve years (2000–2012) of in situ chlorophyll-a data from a monitoring transect off the Namibian coast were analysed to assess the long-term and seasonal variability in chlorophyll-a as a measure of phytoplankton biomass and the occurrence of phytoplankton blooms. On the shelf, low chlorophyll-a concentrations were identified in 2001/2002, 2005/2006, and 2011/2012. The concentrations on the shelf were highest in 2008/2009 and 2010/2011. Major phytoplankton blooms defined at chlorophyll-a concentrations >18mgm−3 occurred in five of the 12years (2002/2003, 2004/2005, 2008/2009, 2009/2010 and 2010/2011) while minor blooms (>13mgm−3) occurred in almost every year. The calculated climatology of the chlorophyll-a time series revealed a clear seasonality. Three chlorophyll-a maxima typically develop inshore over the year: an austral winter peak (August), an early austral summer peak (December) and a late summer/autumn peak (April). The analysis of synoptic hydrographic, nutrient and wind data revealed three different forcing mechanisms that all initiate an influx of nutrients into the surface mixed layer.