The influence of environmental parameters on the phytoplankton community of two tropical reservoirs

Freshwater phytoplankton communities are currently experiencing multiple global change stressors, including increasing frequency and intensity of storms. An important mechanism by which storms affect lake and reservoir phytoplankton is by altering the water column's thermal structure (e.g., changes to thermocline depth). However, little is known about the effects of intermittent thermocline deepening on phytoplankton community vertical distribution and composition or the consistency of phytoplankton responses to varying frequency of these disturbances over multiple years. We conducted whole‐ecosystem thermocline deepening manipulations in a small reservoir. We used an epilimnetic mixing system to experimentally deepen the thermocline via five short (24–72 hr) mixing events across two summers, inducing potential responses to storms. For comparison, we did not manipulate thermocline depth in two succeeding summers. We collected weekly depth profiles of water temperature, light, nutrients, and phytoplankton biomass as well as bottle samples to assess phytoplankton community composition. We then used time‐series analysis and multivariate ordination to assess the effects of intermittent thermocline deepening due to both our experimental manipulations and naturally occurring storms on phytoplankton community structure. We observed inter‐annual and intra‐annual variability in phytoplankton community response to thermocline deepening. We found that peak phytoplankton biomass was significantly deeper in years with a higher frequency of thermocline deepening events (i.e., years with both manipulations and natural storms) due to altered thermal stratification and more variable depth distributions of soluble reactive phosphorus. Furthermore, we found that the depth of peak phytoplankton biomass was linked to phytoplankton community composition, with certain taxa being associated with deep or shallow biomass peaks, often according to functional traits such as optimal growth temperature, mixotrophy, and low‐light tolerance. For example, Cryptomonas taxa, which are low‐light tolerant and mixotrophic, were associated with deep peaks, while the cyanobacterial taxon Dolichospermum was associated with shallow peaks. Our results demonstrate that abrupt thermocline deepening due to water column mixing affects both phytoplankton depth distribution and community structure via alteration of physical and chemical gradients. In addition, our work supports previous research that phytoplankton depth distributions are related to phytoplankton community composition at inter‐annual and intra‐annual timescales. Variability in the inter‐annual and intra‐annual responses of phytoplankton to abrupt thermocline deepening indicates that antecedent conditions and the seasonal timing of surface water mixing may mediate these responses. Our findings emphasise that phytoplankton depth distributions are sensitive to global change stressors and effects on depth distributions should be taken into account when predicting phytoplankton responses to increased storms under global change.

Flood events can significantly affect the physical and biological processes of aquatic ecosystems in a short time, leading to rapid changes in phytoplankton community structure. The Huayanghe Lakes experienced extreme flooding in the summer of 2020, with the water level reaching 16.42 m. In order to understand the effects of flooding on phytoplankton diversity and community structure, eight samples were collected in the Huayanghe Lakes from 2019 to 2020. Water-level disturbance has a significant influence on lake-water quality and phytoplankton community structure. The results showed that the Secchi depth increased from 65.36 to 8.52 cm, while the concentration of total nitrogen (from 0.98 to 0.7 mg/L) and total phosphorus (from 0.04 to 0.031 g/L) decreased. In addition, flooding significantly increased the Shannon–Wiener diversity index, the Pielou index, and the Margalef richness index by an average of 43.5%, 36.7%, and 40.21%, respectively. The phytoplankton community structure in the Huayanghe Lakes changed due to the change of physicochemical environment caused by flood. While in the pre-flood period phytoplankton was composed of large diatoms (e.g., Aulacoseira granulata), cyanobacteria (e.g., Microcystis sp., Anabaena sp., and Aphanizomenon sp.) and other multicellular taxa, the flood period showed an increase in the proportion of chlorophytes and diatoms that quickly adapted to settle in new environments. Pearson correlations and redundancy analyses showed that water level fluctuation was the most significant environmental factor affecting the phytoplankton community between the regular hydrological cycle and flood periods. There are few studies on phytoplankton in the Huayanghe Lakes, and the present study provides basic data on phytoplankton diversity and community structure. In addition, it provides a theoretical basis for controlling water level change in the Yangtze River.

Phytoplankton community composition was characterized over varying seasonal and river discharge conditions during 5 research cruises across the continental margin of the northern Gulf of Mexico (NGOM). The spatial and temporal patterns of variation in the composition of the algal community were examined using high performance liquid chromatography (HPLC) analyses of phytoplankton pigments in conjunction with classification using the CHEMTAX software (v.1.95). Cluster analysis and principal component analysis were used to identify different regimes and to understand the relationship of the phytoplankton community to biological and environ- mental variables. The large river dominated margin of the NGOM was characterized by (1) an estuarine and inner shelf regime dominated by diatoms, cryptophytes, cyanobacteria, and chloro- phytes; (2) midshelf waters, a transition zone between coastal river-influenced and oligotrophic slope waters, associated with a mixed phytoplankton composition; and (3) a slope water regime typical of oligotrophic ocean conditions with a surface community dominated by cyanobacteria, haptophytes, and prochlorophytes. A chlorophyll fluorescence maximum (CFM) was a regular feature at offshore stations and showed significant differences from that of surface waters in sea- sonal variability of phytoplankton pigment ratios and community composition. Our findings sup- port the view that large river outflows, along with other environmental variables such as wind forcing and stratification, have a profound influence on phytoplankton communities over a large regional extent in the continental margin waters of the NGOM.

Phytoplankton community structure is influenced by seabird guano enrichment in the Southern Ocean

Effects of climatic variability on phytoplankton community structure and bloom development in the eutrophic, microtidal, New River Estuary, North Carolina, USA

Spatial and temporal variation in phytoplankton community structure within a large flood-control reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production.

Hydrologic conditions, especially changes in freshwater input, play an important, and at times dominant, role in determining the structure and function of phytoplankton communities and resultant water quality of estuaries. This is particularly true for microtidal, shallow water, lagoonal estuaries, where water flushing and residence times show large variations in response to changes in freshwater inputs. In coastal North Carolina, there has been an increase in frequency and intensity of extreme climatic (hydrologic) events over the past 15 years, including eight hurricanes, six tropical storms, and several record droughts; these events are forecast to continue in the foreseeable future. Each of the past storms exhibited unique hydrologic and nutrient loading scenarios for two representative and proximate coastal plain lagoonal estuaries, the Neuse and New River estuaries. In this synthesis, we used a 13-year (1998–2011) data set from the Neuse River Estuary, and more recent 4-year (2007–2011) data set from the nearby New River Estuary to examine the effects of these hydrologic events on phytoplankton community biomass and composition. We focused on the ability of specific taxonomic groups to optimize growth under hydrologically variable conditions, including seasonal wet/dry periods, episodic storms, and droughts. Changes in phytoplankton community composition and biomass were strongly modulated by the amounts, duration, and seasonality of freshwater discharge. In both estuaries, phytoplankton total and specific taxonomic group biomass exhibited a distinctive unimodal response to varying flushing rates resulting from both event-scale (i.e., major storms, hurricanes) and more chronic seasonal changes in freshwater input. However, unlike the net negative growth seen at long flushing times for nano-/microphytoplankton, the pigments specific to picophytoplankton (zeaxanthin) still showed positive net growth due to their competitive advantage under nutrient-limited conditions. Along with considerations of seasonality (temperature regimes), these relationships can be used to predict relative changes in phytoplankton community composition in response to hydrologic events and changes therein. Freshwater inputs and droughts, while not manageable in the short term, must be incorporated in water quality management strategies for these and other estuarine and coastal ecosystems faced with increasing frequencies and intensities of tropical cyclones, flooding, and droughts.

Influences of pesticides, nutrients, and local environmental variables on phytoplankton communities in lentic small water bodies in a German lowland agricultural area.

Owing to the dynamic nature of nutrient‐phytoplankton interactions, ambient macronutrient concentrations reveal little about the impact of nutrient availability on phytoplankton biomass and community composition at any given point in time or space. Here, however, we examine a global dataset (n = 262) where phytoplankton community structure and biomass are related to ambient concentrations of dissolved inorganic nitrogen (DIN), phosphate (P), and silicate. The macroecological patterns emerging from the analysis suggests plausible causal relationships between nutrient availability and global phytoplankton community responses: When DIN and P are below ca. 5 μM and 0.5 μM, respectively, increases in the concentration of either nutrient correlate with increases in both biomass and the contribution of large cells to the total phytoplankton biomass. At higher concentrations, increasing DIN or P concentrations do not correlate with increases in biomass. However, the fraction of large phytoplankton continues to increase with increasing concentrations suggesting DIN and P availability to be important factors in controlling phytoplankton community composition over the entire spectrum of potential macronutrient availability in the open ocean. Ambient silicate concentrations were not strongly associated with phytoplankton community structure or biomass. Nor did the DIN/P ratio correlate with community structure indicating that this ratio is a poor descriptor of phytoplankton limitation at the community scale. No empirical evidence was found for commonly referred threshold values for nutrient limitation (i.e., 2 μM, 0.2 μM, and 2 μM for DIN, P, and silicate, respectively) suggesting that these threshold values may not contain any practical information.

Temperature driving vertical stratification regulates phytoplankton community structure in the Bohai Sea and Yellow Sea

Identification of major environmental factors driving phytoplankton community succession before and after the regime shift of Erhai Lake, China

A consistent structure of phytoplankton communities across the warm–cold regions of the water mass on a meridional transect in the East/Japan Sea

This study investigates the relationships between the spring phytoplankton community and environmental factors in the Brazil-Malvinas confluence region. Phytoplankton community composition was determined by the high performance liquid chromatography/CHEMTAX approach, complemented with microscopic examination. Abiotic factors included temperature, salinity, dissolved inorganic macronutrients (ammonium, nitrite, nitrate, phosphate and silicate), water column stability and upper mixed layer depth (UMLD). These environmental variables were reasonably informative to explain the variability of the phytoplankton communities (44% of variation explained). Cluster and canonical correspondence analyses allowed discrimination of four zones (coastal, Sub-Antarctic, tropical and intermediate zones), also identifiable in the T–S diagrams and in the nutrient spatial distribution patterns. The presence of nutrient-rich Sub-Antarctic waters was a major oceanographic feature, associated with diatoms and dinoflagellates. However, in the Sub-Antarctic zone, biomass was particularly low, probably as a result of grazing pressure, as suggested by chemical and biological indicators. In contrast, in oligotrophic tropical waters, phytoplankton was mainly composed by small nanoflagellates and cyanobacteria. A large intermediate zone was also dominated by nanoflagellates, mainly Phaeocystis antarctica, probably favored by strong water column stability. The coastal zone exhibited fairly similar conditions to those in the intermediate zone, but with deeper UMLD, a favorable condition for diatom growth. These results emphasize the importance of the properties of water masses and also biological processes such as grazing in structuring phytoplankton communities in the region.

Key-words: limnology, habitats, phyotplankton, community, Chatla floodplain wetland Phytoplankton diversity was investigated over a period of two years (2006 to 2008) in Chatla floodplain wetland in Barak valley, Assam, North-East India. Site 1 and site 2 are two inlets and site 3 is a lentic system associated with vegetation cover of Calamus tenuis and Baringtonia acutangula. The floodplain has a unique hydrology because of the presence of different types of habitats (inlets, fisheries, beels and outlets) which maintains a network among the floodplains, rivers and streams. Phytoplankton community composition, density and diversity were studied in relation to environmental variables.All the variables were estimated by following standard methods. Phytoplankton was collected by plankton net and quantitative estimation was made by using Sedgwick Rafter counting cell. Phytoplankton community comprised 53 taxa represented by Chlorophyceae (31), Cyanophyceae (11), Bacillariophyceae (7), Euglenophyceae (1) and Dinophyceae (3). Phytoplankton taxa was dominated by Volvox sp.,Nostoc sp., Eunotia sp., Navicula sp., Euglena spp. and density was found highest in site 3 and lowest in site 1. Shannon diversity index (H � ) for phytoplankton community varied between 2.4 to 2.65 indicating fairly high species diversity. The varying magnitude of correlationship among environmental variables and phytoplankton species density as shown by Canonical correspondence analysis (CCA) indicated that some of the environmental variables (water temperature, transparency, rainfall, nitrate and ammonia) are the driving factors for governing the phytoplankton species assemblages in Chatla floodplain wetland. Fluctuation of phytoplankton density and community composition in different habitats indicated various niche apportionment as well as anthropogenic influences.

The phytoplankton community composition, structure, and biomass were investigated under stratified and oligotrophic conditions during summer for three consecutive years in the Mediterranean Sea. Our results reveal that the phytoplankton community structure was strongly influenced by vertical stratification. The thermocline separated two different phytoplankton communities in the two layers of the euphotic zone, characterized by different nutrient and light availability. Picoplankton dominated in terms of abundance and biomass at all the stations sampled and throughout the photic zone. However, the structure of the picoplanktonic community changed with depth, with Synechococcus and heterotrophic prokaryotes dominating in surface waters down to the base of the thermocline, and Prochlorococcus and picoeukaryotes contributing relatively more to the community in the deep chlorophyll maximum (DCM). Light and nutrient availability also influenced the communities at the DCM layer. Prochlorococcus prevailed in deeper DCM waters characterized by lower light intensities and higher picophytoplankton abundance was related to lower nutrient concentrations at the DCM. Picoeukaryotes were the major phytoplankton contributors to carbon biomass at surface (up to 80%) and at DCM (more than 40%). Besides, contrarily to the other phytoplankton groups, picoeukaryotes cell size progressively decreased with depth. Our research shows that stratification is a major factor determining the phytoplankton community structure; and underlines the role that picoeukaryotes might play in the carbon flux through the marine food web, with implications for the community metabolism and carbon fate in the ecosystem.