Changes In Phytoplankton Community Research Articles

The Influence of Diapycnal Nutrient Fluxes on Phytoplankton Size Distribution in an Area of Intense Mesoscale and Submesoscale Activity off Concepción, Chile

AbstractMesoscale and submesoscale processes that contribute to localized increases in nutrients in the sunlit layer can stimulate phytoplankton growth and community changes, but the mechanisms involved remain sparsely documented with in situ data in the case of Eastern Boundary Upwelling Systems (EBUSs) and of most ocean regions. The role of diapycnal mixing in providing nutrients to the upper layer and in influencing phytoplankton size structure was analyzed in an area of intense mesoscale and submesoscale activity during the coastal upwelling season off Concepción (~36–37°S), the Humboldt Current EBUS. Diapycnal nutrient fluxes based on conductivity, temperature, and depth vertical eddy diffusivity (Kz) values (the Thorpe scale method) and on nutrient gradients were assessed in association with size‐fractionated chlorophyll‐a and microdiatom abundance derived from in situ sampling in an area including a mesoscale intrathermocline eddy (ITE) adjacent to a coastal upwelling front (CUF). The indirect estimates of Kz values spanned between 0.01 and 4 × 10−4 m2 s−1, and maxima in diapycnal nitrate flux per station ranged between 0.08 and 19.1 mmol m−2 day−1. Maxima in the upward fluxes were detected at the subsurface (15–40 m depth) in the CUF and ITE areas, coinciding with maxima in the micro‐ and nano‐chlorophyll‐a fractions and in microdiatom abundance. These results suggest that ITE and CUF features, as well as their interaction, can generate intense diapycnal mixing and, thereby, contribute to increasing nutrient availability below the mixed layer. In turn, these processes enhance the contribution of larger phytoplankton cells in the coastal transition zone of EBUSs.

Drivers shaping episodic and gradual changes in phytoplankton community succession: Taxonomic versus functional groups

Describing temporal changes in phytoplankton communities is complicated owing to (i) multivariate environmental drivers, (ii) inter-specific relationships, and (iii) various species. With long-term research data from the lower Nakdong River from 1993 to 2016, we examined the temporal changes at two scales—episodic (from weekly to monthly) and long-term (yearly)—and screened the potential environmental drivers. Phytoplankton community component patterns were modeled with the drivers as covariates, using multivariate autoregressive state-space (MARSS) models, to assess their response to environmental drivers and biotic interactions. We assumed that compared to taxonomic classification, functional classification would obtain a better identification of community response to temporal variability. Over 24 years, the succession patterns of the dominant taxonomic and functional groups decreased in diversity, with the greatest decreases in biomass of Bacillariophyceae and group D (mainly the diatom Stephanodiscus hantzschii), and coincided with the introduction of group H1 (dinitrogen-fixing nostocaleans). The potential drivers for these changes were precipitation, water level, and total nitrogen (TN) for taxonomic groups and TN, total phosphorus, and euphotic zone depth for functional groups. The results of the MARSS model and temporal trends for each driver indicated that the increases in the water level and light availability were mostly related with the taxonomic and functional groups, respectively. The model for functional groups proposed a total of 24 significant inter-group relationships, where five relationships supported the succession patterns of dominant groups in the Nakdong River. Combined with the effects of increased light availability, a positive relationship between groups H1 and M (mainly Cyanobacteria and Microcystis aeruginosa) appears to induce cyanobacterial bloom development over a long period. These results can be fundamental information for river system management concerning the resulting cascading effects of changes in environmental drivers and inter-group relationships on the phytoplankton community composition.

A comparative study of phytoplankton community structure and biomass determined by HPLC-CHEMTAX and microscopic methods during summer and autumn in the central Bohai Sea, China

As the largest inland sea of China, the Bohai Sea has confronted significant environmental changes in recent decades, and a shift of phytoplankton community from diatoms to dinoflagellates was observed by microscopic method in previous studies. However, the counting of some small-sized non-diatoms (e.g., flagellates and cyanobacteria) have long been neglected due to the limitation of this method. In this study, we measured the phytoplankton community structure and abundance in the central Bohai Sea in summer and autumn of 2015 by employing both microscopic method and high-performance liquid chromatography (HPLC) pigments – CHEMTAX analysis. The results of microscopic counting showed that the phytoplankton community was characterized by diatoms, dinoflagellates, and chrysophytes, which contained a total of 107 species. Dinoflagellates and diatoms co-dominated in summer while the latter became the dominant group in autumn. Compared with microscopic counting, CHEMTAX analysis allowed identification of a larger number of phytoplankton groups (including 8 phyla). The results of CHEMTAX analysis showed that besides diatoms and dinoflagellates, the small-sized non-diatoms (i.e., flagellates and cyanobacteria) also played an important role. Diatoms and cyanobacteria dominated the total Chl a (contributing 32.5% and 17.1%, respectively), followed by cryptophytes, dinoflagellates, and prasinophytes in the summer. A short-term summer to autumn variability of phytoplankton abundance and community was observed. Temperature and nutrient availability affected the succession of the phytoplankton community from diatoms and non-diatoms co-dominance in the summer to absolute diatoms dominance in the autumn. A direct comparison of algal cell abundance and CHEMTAX biomass showed that a significant positive correlation was observed only for dinoflagellates (P < 0.01) in the autumn. Our work provides some basic information on the dynamics of small-sized flagellates and cyanobacteria in this area, and also suggests that a combination of both the methods is needed in future investigations to better understand the current status as well as the future changes of phytoplankton community.

Succession Pattern of Phytoplankton and Its Drivers in Lake Luoma, Jiangsu Province

As a water storage lake for the South-to-North Water Diversion Project, it is crucial to examine changes in aquatic ecosystem structures in Lake Luoma, Jiangsu province. Field sampling was carried out in Lake Luoma monthly from 2014 to 2018 to study the relationship between the phytoplankton community structure and environmental factors. During the studied period, total nitrogen, permanganate index, and electrical conductivity in water column gradually increased, whereas fluoride content declined. The pattern of total phosphorus and dissolved oxygen was not distinct. A total of 71 genera of phytoplankton were identified from 2014 to 2018, and the average monthly biomass variation ranged from 0.16 to 5.51 mg·L-1. Bacillariophyta and Chlorophyta were the dominant phyla in the four years, followed by Pyrrophyta and Cryptophyta. The dominant genera were Synedra sp., Chroomonas spp., Aulacoseira spp., Dinobryon sp., Scenedesmus spp. , Fragilaria spp., Mougeotia sp. , Ankistrodesmus sp. , and Euglena spp. The results showed that the phytoplankton community structure significantly changed in the four years, which was mainly ascribed to the redistribution of biomass. Specifically, in addition to the dominance of Bacillariophyta and Chlorophyta, the dominance of Pyrrophyta and Cyanophyta increased during the last two years. Non-metric multidimensional scaling analysis showed that variation of the phytoplankton community in Lake Luoma was mainly related to total nitrogen, fluoride, water temperature, total phosphorus, dissolved oxygen, pH, conductivity, and permanganate index, among which the total nitrogen, water temperature, and fluoride concentration dominated the phytoplankton community change after the generalized additive model test. Water temperature is the driving factor affecting seasonal changes of the phytoplankton community. Total nitrogen and fluoride concentrations are the driving factors affecting the interannual variation in the phytoplankton community. Our study indicated that in recent years, the implementation of the ban on sand mining and demolition of the enclosed aquaculture in Lake Luoma has affected the water environment, resulting in a significant succession of the phytoplankton community.

Effects of phytoplankton community composition and productivity on sea surface pCO2 variations in the Southern Ocean

The Southern Ocean is a vast net sink for atmospheric carbon dioxide (CO2), with marine phytoplankton playing a crucial role in CO2 fixation. We assessed how changes in the dominant phytoplankton community and net primary productivity (NPP) affected variations in the partial pressure of CO2 in surface water (pCO2sw) in the Indian sector of the Southern Ocean during austral summer. pCO2sw was negatively correlated with total phytoplankton and diatom abundances, as estimated from pigment signatures, in the zone south of the Antarctic Circumpolar Current; however, pCO2sw was not correlated with haptophyte abundance. Additionally, a stronger correlation was found between pCO2sw and total phytoplankton NPP than between chlorophyll a concentration and pCO2sw. We reconstructed pCO2sw at inter-annual scale using satellite data and assessed the inter-annual variability of air-sea CO2 flux. Over the period from 1997 to 2007, the integrated CO2 fluxes over the study region showed very large variations from a small source to a strong sink. Variations in the integrated CO2 fluxes were also correlated with changes in satellite-derived phytoplankton community in the Indian sector of the Southern Ocean and changes in the dominant phytoplankton community may control CO2 dynamics in the marginal ice zone.

Effects of Mississippi River water on phytoplankton growth and composition in the upper Barataria estuary, Louisiana

Diversion of river waters to adjacent estuaries may occur during wetland restoration, navigation channel development, or storms. We proposed that diversions of nitrogen- and phosphorus-enriched waters from the river to estuarine waters would result in increased phytoplankton biomass and shifts to noxious or harmful algal blooms. We tested this hypothesis by conducting four seasonal microcosm experiments in which Mississippi River water was mixed at different volume ratios with ambient estuarine waters of three lakes in the upper Barataria Basin, Louisiana, USA. These lakes included two brackish lakes that were in the path of diverted Mississippi River water, and a freshwater lake that was not. The results from the 3- to 8-day experiments yielded a predictable increase in phytoplankton biomass related to nutrient additions from Mississippi River water. The subsequent decreases in the dissolved nitrate + nitrite, soluble reactive phosphorus, and silicate concentrations explained 76 to 86% of the increase in chlorophyll a concentrations in the microcosms. Our experiments showed that cyanobacteria can successfully compete with diatoms for N and P resources even under non-limiting Si conditions and that toxic cyanobacteria densities can increase to bloom levels with increased Mississippi River water inputs to ambient waters in the microcosms. Diversions of Mississippi River into adjacent estuarine waters should be considered in relation to expected and, possibly, unexpected changes in phytoplankton communities to the receiving waters and coastal ecosystems.

Применение теории «соотношения ресурсов» при анализе структурных изменений морских сообществ фитопланктона

Применение теории «соотношения ресурсов» при анализе структурных изменений морских сообществ фитопланктона

Quantifying photosynthetic performance of phytoplankton based on photosynthesis\u2013irradiance response models

BackgroundClarifying the relationship between photosynthesis and irradiance and accurately quantifying photosynthetic performance are of importance to calculate the productivity of phytoplankton, whether in aquatic ecosystems modelling or obtaining more economical production.ResultsThe photosynthetic performance of seven phytoplankton species was characterized by four typical photosynthesis–irradiance (P–I) response models. However, the differences were found between the returned values to photosynthetic characteristics by different P–I models. The saturation irradiance (Isat) was distinctly underestimated by model 1, and the maximum net photosynthetic rate (Pnmax) was quite distinct from its measured values, due to the asymptotic function of the model. Models 2 and 3 lost some foundation to photosynthetic mechanisms, that the returned Isat showed significant differences with the measured data. Model 4 for higher plants could reproduce the irradiance response trends of photosynthesis well for all phytoplankton species and obtained close values to the measured data, but the fitting curves exhibited some slight deviations under the low intensity of irradiance. Different phytoplankton species showed differences in photosynthetic productivity and characteristics. Platymonas subcordiformis showed larger intrinsic quantum yield (α) and lower Isat and light compensation point (Ic) than Dunaliella salina or Isochrysis galbana. Microcystis sp., especially M. aeruginosa with the largest Pnmax and α among freshwater phytoplankton strains, exhibited more efficient light use efficiency than two species of green algae.ConclusionsThe present work will be useful both to describe the behavior of different phytoplankton in a quantitative way as well as to evaluate the flexibility and reusability of P–I models. Meanwhile we believe this research could provide important insight into the structure changes of phytoplankton communities in the aquatic ecosystems.

High-Frequency Dynamics of Water Quality and Phytoplankton Community in Inflowing River Mouth of Xin'anjiang Reservoir, China

The tail of the reservoir is the unstable zone regarding water quality and phytoplankton community. Therefore, it is the crucial zone in aquatic ecosystem transitions. To understand the transition characteristics and driving mechanisms of water environment dynamics, high-frequency monitoring of the water environment and phytoplankton community in the tail of a deep and large reservoir, the Xin'anjiang Reservoir in southeast of China, was conducted using a water quality monitoring buoy and three-day interval water sampling during 18 months. Results show clear seasonal thermal and oxygen stratification in the river mouth of the reservoir. The nutrient and chlorophyll-a concentrations also show stratifying phenomena during the thermal stratification period. Heavy rain and inflow quickly consume the stratification. Nutrient concentrations were highly dynamic in the river mouth. The total phosphorus ranges from 0.011 mg·L-1 to 0.188 mg·L-1, and total nitrogen ranges from 0.75 mg·L-1 to 2.76 mg·L-1. Dissolved phosphorus comprised 56% of total phosphorus, and dissolved nitrogen occupied 88% of total nitrogen, respectively. Nutrient concentrations were influenced strongly by rainfall intensity and inflow rate. Total phosphorus and nitrogen concentrations were significantly related to the three-day accumulated rainfall. Nutrient concentrations in the flood season (March to June) were significantly higher than in the non-flood season (P<0.001). Seasonal phytoplankton proliferation also significantly influenced by total phosphorus concentration. The phytoplankton community changes significantly with seasons and flood events. Bacillariophytea was generally dominant throughout the year, with the predominant genus of Fragilaria spp., Cyclotella spp., Synedra spp., and Melosira spp. Cyanophyta biomass peaked in July, August, and September, with the dominant genus of Aphanizomenon spp., Microcystis spp., and Oscillatoria spp. Apart from the high temperature, storm inflow events also triggered Cyanophyta proliferation. The proliferation of Chlorophyta was similar to Cyanophyta, with the predominant genus of Pediastrum spp. and Closterium spp.. While the Cryptophyta biomass peaked during March to May, with the predominant genus of Cryptomonas spp.. Redundancy analysis shows that the influence factors of phytoplankton community dynamics include the inflow rate, temperature, water level, water transparency, total nitrogen, total phosphorus, and nitrogen to phosphorus ratio. The meteorological and hydrological factors were major factors for phytoplankton dynamics during later autumn and winter, while the nutrient will be the co-driving factors of phytoplankton community dynamics during summer and early autumn. The research confirmed the huge influence of the intensity rainfall event on the water environment in reservoirs and described the key environmental conditions for phytoplankton community dynamics. The research is useful for the design of the monitoring and forecasting system for water safety in drinking water source reservoirs.

Coccolithophore biodiversity controls carbonate export in the Southern Ocean

Abstract. Southern Ocean waters are projected to undergo profound changes in their physical and chemical properties in the coming decades. Coccolithophore blooms in the Southern Ocean are thought to account for a major fraction of the global marine calcium carbonate (CaCO3) production and export to the deep sea. Therefore, changes in the composition and abundance of Southern Ocean coccolithophore populations are likely to alter the marine carbon cycle, with feedbacks to the rate of global climate change. However, the contribution of coccolithophores to CaCO3 export in the Southern Ocean is uncertain, particularly in the circumpolar subantarctic zone that represents about half of the areal extent of the Southern Ocean and where coccolithophores are most abundant. Here, we present measurements of annual CaCO3 flux and quantitatively partition them amongst coccolithophore species and heterotrophic calcifiers at two sites representative of a large portion of the subantarctic zone. We find that coccolithophores account for a major fraction of the annual CaCO3 export, with the highest contributions in waters with low algal biomass accumulations. Notably, our analysis reveals that although Emiliania huxleyi is an important vector for CaCO3 export to the deep sea, less abundant but larger species account for most of the annual coccolithophore CaCO3 flux. This observation contrasts with the generally accepted notion that high particulate inorganic carbon accumulations during the austral summer in the subantarctic Southern Ocean are mainly caused by E. huxleyi blooms. It appears likely that the climate-induced migration of oceanic fronts will initially result in the poleward expansion of large coccolithophore species increasing CaCO3 production. However, subantarctic coccolithophore populations will eventually diminish as acidification overwhelms those changes. Overall, our analysis emphasizes the need for species-centred studies to improve our ability to project future changes in phytoplankton communities and their influence on marine biogeochemical cycles.

Changes in phytoplankton assemblage caused by anoxic conditions revealed with mesocosms in Omura Bay, western Japan

We artificially reproduced a scenario where the phytoplankton community changes under increased regeneration of nutrients from the sediment due to anoxic conditions using a mesocosm in Katagami Bay, one of many smaller bays in Omura Bay. Two instrumented mesocosms were used in the field experiment, whereas the surrounding waters acted as a control. The plastic bags used in the first mesocosm (M1) was completely transparent, whereas the second mesocosm (M2) was designed so that the bottom two-thirds of the plastic bag was opaque and only the top third was transparent. Photon flux density of M2 was about the same value in the surface layer as compared with M1 and Control, but it was approximately 1/2 in the middle layer and approximately 1/10 in the bottom layer. In M2, hypoxic water mass appears in the bottom layer on day 2 and then dissolved inorganic phosphate increased from day 3 to end of the experiment. At the start of the experiment, a diatom (Dactyliosolen flagilismus) was dominant in all compartments. Diatoms continued to dominate in M1 and the control, but in M2, a dinoflagellate (Heterocapsa circularisquama) became dominant at the end of the experiment. This study clearly shows that nutrient elution by water stratification can affect floral changes from diatom to flagellate dominance in summer in Omura Bay.

Trends in tuna carbon isotopes suggest global changes in pelagic phytoplankton communities.

Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open-ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the world's oceans. Here, we use the carbon stable isotope composition of tuna to provide a first insight into the existence of global trends in complex ecosystem dynamics and changes in the oceanic carbon cycle. From 2000 to 2015, considerable declines in δ13 C values of 0.8‰-2.5‰ were observed across three tuna species sampled globally, with more substantial changes in the Pacific Ocean compared to the Atlantic and Indian Oceans. Tuna recorded not only the Suess effect, that is, fossil fuel-derived and isotopically light carbon being incorporated into marine ecosystems, but also recorded profound changes at the base of marine food webs. We suggest a global shift in phytoplankton community structure, for example, a reduction in 13 C-rich phytoplankton such as diatoms, and/or a change in phytoplankton physiology during this period, although this does not rule out other concomitant changes at higher levels in the food webs. Our study establishes tuna δ13 C values as a candidate essential ocean variable to assess complex ecosystem responses to climate change at regional to global scales and over decadal timescales. Finally, this time series will be invaluable in calibrating and validating global earth system models to project changes in marine biota.

Abiotic environmental factors override phytoplankton succession in shaping both free-living and attached bacterial communities in a highland lake

Bacterial communities are an important part of biological diversity and biogeochemical cycling in aquatic ecosystems. In this study, the relationship amongst the phytoplankton species composition and abiotic environmental factors on seasonal changes in the community composition of free-living and attached bacteria in Lake Erhai were studied. Using Illumina high-throughput sequencing, we found that the impact of environmental factors on both the free-living and attached bacterial community composition was greater than that of the phytoplankton community, amongst which total phosphorus, Secchi disk, water temperature, dissolved oxygen and conductivity strongly influenced bacterial community composition. Microcystis blooms associated with subdominant Psephonema occurred during the summer and autumn, and Fragilaria, Melosira and Mougeotia were found at high densities in the other seasons. Only small numbers of algal species-specific bacteria, including Xanthomonadaceae (Proteobacteria) and Alcaligenaceae (Betaproteobacteria), were tightly coupled to Microcystis and Psephonema during Microcystis blooms. Redundancy analysis showed that although the composition of the bacterial communities was controlled by species composition mediated by changes in phytoplankton communities and abiotic environmental factors, the impact of the abiotic environment on both free-living and attached bacterial community compositions were greater than the impact of the phytoplankton community. These results suggest that the species composition of both free-living and attached bacterial communities are affected by abiotic environmental factors, even when under strong control by biotic factors, particularly dominant genera of Microcystis and Psephonema during algal blooms.

Responses of marine phytoplankton communities to environmental changes: New insights from a niche classification scheme

Predicting changes of phytoplankton communities in response to global warming is one of the challenges of ecological forecasting. One of the constraints is the paucity of general principles applicable to community ecology. Based on a synecological analysis of a decadal-scale database, we created a niche habitat classification scheme relating nine phytoplankton groups to fifteen statistically refined realized niches comprised of three niche dimensions: temperature, irradiance, and nitrate concentrations. The niche scheme assigned the nine phytoplankton groups to three types of niches: a cold type, a warm type, and a type associated with high irradiance and high nitrate concentrations. The fact that phytoplankton groups in cold niches were governed by irradiance and those in warm niches by nitrate is consistent with general ecological theories, but the fact that diatoms were the only dominant group in high-irradiance, high-nitrate niches challenges the idea based on autecological studies that diatoms are generally better adapted to low-irradiance, high-nutrient conditions. When combined with an irradiance model, the niche scheme revealed that photoinhibition of Prochlorococcus, which is predicted from autecological studies, is a function of temperature. We used the niche scheme to predict the responses of phytoplankton communities to environmental changes due to seawater warming and eutrophication. The results of the study suggest that a synecological analysis of large databases from field studies facilitates identification of general principles of community ecology that can be used to forecast responses of biological communities to environmental changes.

Regulation of Spatial Changes in Phytoplankton Community by Water Column Stability and Nutrients in the Southern Yellow Sea

AbstractThe southern Yellow Sea (SYS) shows extensive spatial variations in water masses, particularly YS Warm Current Water (YSWCW) and YS Coastal Current Water in cold and YS Bottom Cold Water (YSBCW) and Changjiang Diluted Water in warm seasons. These hydrographic processes result in significant spatial changes in nutrients, stratification, and turbidity, which may highly regulate phytoplankton distribution in the SYS. Here, we provide high spatial resolution data sets of phytoplankton in the SYS in all seasons during 2011–2012. Diatoms thrived in eutrophic Changjiang Diluted Water and YS Coastal Current Water regions. Notably, benthic/meroplanktonic diatoms, including Paralia sulcata and Rhaphoneis spp., were dominant near the Changjiang Estuary and Subei Shoal. However, cryptophytes and haptophytes were dominant in oligotrophic offshore regions controlled by YSWCW and YSBCW. Phytoplankton abundance and chlorophyll a were considerably lower in the YSWCW and YSBCW than in other regions, and the community composition varied significantly among regions. Algal blooms were observed off the SYS coast in spring and near the Changjiang Estuary in summer, which were characterized by abundant nutrients, low turbidity, and a relatively stable water column. Canonical correspondence analysis demonstrated that stratification in cold and nutrients in warm seasons were most important variables correlated with phytoplankton community. Variation partitioning analysis confirmed that spatial changes in phytoplankton community composition were largely structured by nutrients rather than by physical factors in all seasons except winter. Our findings highlight the significance of water column stability and nutrients associated with water mass variation in shaping spatial changes of phytoplankton community in the SYS.

Climate exerts a greater modulating effect on the phytoplankton community after 2007 in eutrophic Lake Taihu, China: Evidence from 25 years of recordings

Long-term phytoplankton community changes indicate the trophic status under nutrient regulation conditions in eutrophic lakes, although the modulatory role of climate change scenarios in their indicative function has been underestimated. Hence, we analyzed the relative contributions of nutrient and climate factors to interannual and seasonal variations in the phytoplankton biomass and composition from 1992 to 2017 in Meiliang Bay, Lake Taihu, China. Discrete phytoplankton communities from five periods were classified according to their interannual features. Variations in the phytoplankton community composition were observed during the five periods, and these variations included a shift from exclusive cyanobacterial dominance before 2008 to diatom-cyanobacterial codominance in 2008–2010 and from cyanobacterial dominance in 2011–2014 to cyanobacterial-diatom codominance in 2015–2017. The phytoplankton biomass pattern typically peaked in summer, although peaks also occurred in winter 2008–2010 and autumn 2011–2014. Additionally, the phytoplankton biomass increased by threefold from 2015 to 2017, which might have been related to rising air temperatures and greater light availability. The variance in the phytoplankton community was significantly explained by nutrient (ammonium, nitrate and phosphate) and climatic (air temperature and wind speed) factors. However, the explaining effect of the factors varied among the five periods: nutrients strongly impacted the community composition from 1992 to 2007, whereas climatic variables became more important modulators after 2007. These results reveal that climatic factors play importance roles in shaping the phytoplankton community and cyanobacterial blooms and suggest that differences in the roles between specific climatic conditions should be considered. Future declines in cyanobacterial blooms require further dual nitrogen and phosphorus reduction and longer recovery times under current climate change scenarios in this and possibly other shallow eutrophic lakes.

Variation in spectral characteristics of dissolved organic matter in inland rivers in various trophic states, and their relationship with phytoplankton

Dissolved organic matter (DOM) plays an important role in aquatic ecosystems. This study aimed to reveal the variation in spectral characteristics of DOM in inland rivers in various trophic states, and understand the relationship between spectral characteristics of DOM and phytoplankton composition in various trophic states. Our investigation was carried out on the Weihe River in Shaanxi Province, China. Three humic-like substances and one protein-like substance were identified from the DOM by examination of three-dimensional (3D) fluorescence combined with parallel factor (PARAFAC) analysis and UV–Vis spectroscopy. The trophic states in this study area ranged from mesotrophic to hyper-eutrophic (37 < Trophic States Index (TSI) < 76). As the trophic states increased, the amount of phytoplankton rose, and the dominant phylum gradually changed from bacillariophyta to cyanophyta and chlorophyta. The UVA humic-like substance C1 (λEx/Em = 250(310)/400 nm) and the protein-like substance C4 (λEx/Em = 240(280)/338), frequently found in pure cultures of various phytoplankton species, were considered to be phytoplankton secretions. As the trophic state increased, the fluorescence intensity of C1 and C4 increased, along with the rising phytoplankton biomass. The UVC humic-like substance C2 (λEx/Em = 260/480 nm), derived from a terrestrial source, did not change significantly along with the increasing trophic state. The humic-like substance C3 (λEx/Em = 270/430 nm), produced by microbial decomposition, increased significantly in individual places as the trophic state increased. We concluded that the trophic state can increase the endogenous proportion of DOM by promoting phytoplankton growth, but that the changes in phytoplankton community affected by trophic state have no direct influence on the spectral characteristics of DOM.

Seasonal and Temporal Drivers Influencing Phytoplankton Community in Kuwait Marine Waters: Documenting a Changing Landscape in the Gulf

This assessment of environmental drivers and phytoplankton community in Kuwait (Arabian Gulf) arises from a scenario in which the rapid urbanisation in recent decades has caused significant changes from pre-industrial conditions. To present these changes, we have analysed a long-term water quality dataset (1984 – 2017) and explored potential changes in a sub-set of phytoplankton community data by analyzing ten years of phytoplankton data available (2007 – 2016) for Kuwait Bay and the Northern Gulf waters. The longer-term water quality data shows that dissolved nutrient concentration, with the exception of a recent fall in SiO4, have been increasing over 30 years but with a high degree of variability reflecting the changing rate of inputs from coastal pollution and the Shatt Al-Arab River. The correlative analysis between the environmental parameters and phytoplankton in the period from 2007 to 2016 show the seasonal variability of the phytoplankton are influenced by several factors stressors including higher temperatures, coastal sewage runoff, and changing salinity. Whilst the rapid and extended nutrient enrichment data move Kuwait coastal waters into a eutrophic state, the temporal patterns highlight that recent changes in phytoplankton community are more likely to be responding to cumulative pressures of eutrophication, climate and salinity changes. The seasonal and temporal changes in the coastal phytoplankton community, alongside long term deteriorating water quality present management challenges of managing local and external pressures. Continued declines in water quality within a system that is influenced by a warming climate can potentially have long-term consequences on the resilience of the Northern Gulf environment.

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth, maintenance, and dissipation phases of a Prorocentrum donghaiense bloom

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9–12 May), maintenance (13–18 May) and dissipation phases (19–20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H′) and Pielou evenness index (J′) were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (Fq'/Fm') and the maximum relative electron transport rate (rETRmax) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.

Gaussian decomposition and component pigment spectral analysis of phytoplankton absorption spectra

The absorption spectrum of phytoplankton is an important bio-optical parameter for ocean color hyperspectral remote sensing; its magnitude and shape can be affected considerably by pigment composition and concentration. We conducted Gaussian decomposition to the absorption spectra of phytoplankton pigment and studied the spectral components of the phytoplankton, in which the package effect was investigated using pigment concentration data and phytoplankton absorption spectra. The decomposition results were compared with the corresponding concentrations of the five main pigment groups (chlorophylls a, b, and c, photo-synthetic carotenoids (PSC), and photo-protective carotenoids (PPC)). The results indicate that the majority of residual errors in the Gaussian decomposition are <0.001 m−1, and R2 of the power regression between characteristic bands and HPLC pigment concentrations (except for chlorophyll b) was 0.65 or greater for surface water samples at autumn cruise. In addition, we determined a strong predictive capability for chlorophylls a, c, PPC, and PSC. We also tested the estimation of pigment concentrations from the empirical specific absorption coefficient of pigment composition. The empirical decomposition showed that the Ficek model was the closest to the original spectra with the smallest residual errors. The pigment decomposition results and HPLC measurements of pigment concentration are in a high consistency as the scatter plots are distributed largely near the 1:1 line in spite of prominent seasonal variations. The Woźniak model showed a better fit than the Ficek model for Chl a, and the median relative error was small. The pigment component information estimated from the phytoplankton absorption spectra can help better remote sensing of hyperspectral ocean color that related to the changes in phytoplankton communities and varieties.