Phytoplankton Biovolume Research Articles

An evaluation of cyanobacterial occurrence and bloom development in Adirondack lakes

Cyanobacterial harmful algal blooms (cyanoHABs) have occurred in many low nutrient (oligotrophic) lakes in the northeastern United States. The Adirondack Park in New York is a large, mountainous region with many low nutrient lakes. There is a gap in understanding regarding whether cyanoHAB reporting data are truly reflective of the susceptibility of lakes to develop bloom conditions. We evaluated lakes with and without documented cyanoHABs for cyanotoxin synthetase gene quantification, phytoplankton community composition, and akinete abundance to identify conditions associated with the observation of cyanoHABs. We analyzed (1) contributions of cyanobacteria to the overall phytoplankton community, (2) differences in cyanobacterial communities and the presence of cyanotoxin synthetase genes, and (3) lake physical and geomorphological attributes as drivers of differences in cyanobacteria occurrence. Two sample types (water and sediment) were collected from 2 sample locations (nearshore and open water) in 5 lakes in 2021. We found cyanobacteria in all lakes and sample locations. Phytoplankton biovolume and cyanotoxin synthetase genes differed among lakes and by cyanoHAB history. Samples from lakes with documented blooms were associated with marginally higher total phosphorus. Nonmetric multidimensional scaling was used to identify which environmental factors influenced community structure. Our study demonstrates the importance of multifaceted approaches to detect cyanobacteria that may only be apparent during ephemeral bloom events and the similarities among lakes with and without a history of bloom reports. This work contributes to a better understanding of cyanoHAB occurrence in Adirondack lakes, and of conditions that may cause low nutrient lakes to be susceptible to cyanoHABs.

Stable phytoplankton community compositions in Lake Mead (Nevada-Arizona, USA) during two decades of severe drought

Lake Mead, a large reservoir on the Colorado River and a critical drinking water source for the southwestern United States, typically exhibits high water quality, characterized by low nutrient and chlorophyll-a concentrations. This stability persists despite the inflow of highly treated wastewater since the 1960s and significant water level declines since 2000, driven by the ongoing Megadrought and basin-wide consumptive use. Such environmental changes may alter phytoplankton communities, potentially leading to increased cyanobacteria abundance, which could negatively impact water quality and the aquatic ecosystem through harmful algal blooms and toxin production. Here we analyzed 17 years of phytoplankton community structure and chlorophyll-a concentrations in Lake Mead, alongside quantitative water quality data, including nutrients, temperature, and water clarity, to assess the effects of environmental changes on phytoplankton communities. Contrary to the hypothesis that cyanobacteria abundance would have increased throughout the reservoir, our results indicate that phytoplankton community structures have remained largely stable, except for shallow areas where increases in temperature or phosphorus levels were observed. Additionally, we evaluated machine learning models for predicting changes in phytoplankton community structures. While the models confidently predicted changes in total phytoplankton biovolume and chlorophyll-a concentrations within the input parameter boundaries, predictions of peak biovolume showed considerable uncertainty, emphasizing the importance of incorporating uncertainty analysis in forecasting and communicating results. This study underscores the current buffering capacity of large, oligotrophic reservoirs like Lake Mead to maintain stable phytoplankton communities despite environmental changes. However, it also highlights the potential for significant community shifts if this buffering capacity is exceeded.

Long-term study of phytoplankton dynamics in a supply reservoir reveals signs of trophic state shift linked to changes in hydrodynamics associated with flow management and extreme events

This study analyses over a decade (2009–2022) of monitoring data to understand the impact of hydrological characteristics on water quality and phytoplankton dynamics in Prospect Reservoir, a critical water supply for Greater Sydney, Australia, known for its excellent water quality. Water quality and phytoplankton dynamics were related to hydrodynamics, linked to flow management and the water quality of inflows. Phytoplankton biovolume increased after a prolonged drawdown and subsequent refill event, mainly driven by dinoflagellates, and corresponded to increases in total phosphorus and water temperature. The hydrological period following the 2019/2020 summer bushfires (post-bushfire) that impacted connected reservoirs, was marked by increased flow activity and nutrient loading, leading to significant shifts in the phytoplankton community. Functional group classification and ordination analysis indicated a transition from taxa typically dominant in oligotrophic conditions to meso‑eutrophic. This transition correlated with elevated nutrient levels and chlorophyll-a (Chl-a), and reduced Secchi depth and dissolved oxygen, providing evidence of eutrophication. Q index indicated good water quality post-bushfire, contrasting with a eutrophic status assessment using Chl-a. Our findings highlight the importance of analysing long-term datasets encompassing varied hydroclimatological conditions for a deeper understanding of reservoir behaviour. A comprehensive approach to water quality assessment is recommended, combining functional group classification, Q index and Chl-a measurements for effective reservoir health assessment. This research provides novel insights into the effects of disturbances such as bushfires, on water quality and phytoplankton dynamics in an underrepresented geographic region, offering valuable knowledge for managing water resources amidst growing climate variability.

Local environmental factors are the main drivers of phytoplankton biovolume in subtropical streams of Brazil

The ecological attributes of phytoplankton in freshwater environments are strongly influenced by limnological factors and temporal variability. In this study, we investigated the importance of local environmental and regional (spatial and landscape) predictors in structuring stream phytoplankton from the perspective of metacommunity theory. We seasonally sampled phytoplankton and abiotic variables from nine streams in three subtropical basins. Variation partitioning was used to investigate the influence of environmental, landscape, and spatial predictors on phytoplankton biovolume. Independent of the hydrological period (dry and rainy), the phytoplankton communities were predominantly structured by local environmental factors. In addition, the different land uses considered (landscape) showed weak significance during the dry season, with emphasis on the rural category. Biovolume values remained low, and diatoms and green algae were the most representative groups. Our findings are consistent with recognized ecological patterns for potamoplankton and emphasize local environmental filters as a fundamental regulator of phytoplankton biodiversity in lotic environments.

A pluviosidade aumenta a biomassa e impulsiona a variabilidade dos grupos taxonômicos e morfo-funcionais do fitoplâncton em um lago urbano subtropical

Abstract: Aim To explore the short-term effects of rainfall events on the biomass, density, and richness of the phytoplankton community during dry and rainy periods, as well as on the selection and response of Morphology-Based Functional Groups (MBFG). Methods The phytoplankton community and abiotic environmental variables were sampled over a short period in a subtropical urban lake during the dry and rainy seasons (2018-2019). Generalized Linear Models (GLMs) were generated to analyze the relationship between phytoplankton biovolume, density, and richness with abiotic variables. The predictability of phytoplankton functional groups was assessed using Redundancy Analysis (RDA). Results There was an increase in the density and biovolume of the phytoplankton community during the rainy period. Species richness decreased with increased rainfall. The lake exhibited a high dominance of Cyanobacteria (MBFG VIII), mainly represented by Raphidiopsis raciborskii (Woloszynska) Aguilera in both periods studied. Conclusions We found evidence supporting the hypothesis that rainfall events increase the density and biovolume of phytoplankton. Morphology-based functional groups served as efficient indicators of the lake's environmental conditions.

Zooplankton-phytoplankton biomass and diversity relationships in the Great Lakes.

Quantifying the relationship between phytoplankton and zooplankton may offer insight into zooplankton sensitivity to shifting phytoplankton assemblages and the potential impacts of producer-consumer decoupling on the rest of the food web. We analyzed 18 years (2001-2018) of paired phytoplankton and zooplankton samples collected as part of the United States Environmental Protection Agency (U.S. EPA) Great Lakes Biology Monitoring Program to examine both the long-term and seasonal relationships between zooplankton and phytoplankton across all five Laurentian Great Lakes. We also analyzed effects of phytoplankton diversity on zooplankton biomass, diversity, and predator-prey (zooplanktivore/grazer) ratios. Across the Great Lakes, there was a weak positive correlation between total algal biovolume and zooplankton biomass in both spring and summer. The relationship was weaker and not consistently positive within individual lakes. These trends were consistent over time, providing no evidence of increasing decoupling over the study period. Zooplankton biomass was weakly negatively correlated with algal diversity across lakes, whereas zooplankton diversity was unaffected. These relationships did not change when we considered only the edible phytoplankton fraction, possibly due to the high correlation between total and edible phytoplankton biovolume in most of these lakes. Lack of strong coupling between these producer and consumer assemblages may be related to lagging responses by the consumers, top-down effects from higher-level consumers, or other confounding factors. These results underscore the difficulty in predicting higher trophic level responses, including zooplankton, from changes in phytoplankton assemblages.

Long-term adjustment of phytoplankton structure to environmental traits at timescales during lifetime development and over generations

Long-term ecological research of deep Lake Mondsee covers over more than six decades of phytoplankton observation. According to our study, phytoplankton groups of various phenological traits are suitable to address the impact of two major environmental stressors: nutrient surplus by eutrophication from 1968 to 1998 and warming by climate change. Here, we focus on phytoplankton biovolume, phytoplankton assemblage structure, net changes rates, and phytoplankton biodiversity. Biweekly net change-dependent persistence of phytoplankton assemblages followed a dome-shaped relationship of observations. A short-term persistence of taxonomic traits along weeks is predominant and contributes to the structural stabilization of phytoplankton assemblages. This short-term persistence is interpreted by the benefit of lifetime adjustment of phytoplankton organisms. The long-term development phytoplankton structure is discussed as an alignment of organisms over generations. Single key taxa, as Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis &Komárek 1988, which are omnipotent players in phytoplankton assemblages and occur during different environmental scenarios in the long-term, are most suitable for long-term ecological research. Our findings interpret that phytoplankton taxa are excellent organisms to track the impact of environmental constraints due to their short generation time (1), their lifetime adjustment (2), and the re-occurrence in the long-term over generations (3).

Effects of Algal Extracellular Polysaccharides on the Formation of Filamentous Manganese Oxide Particles in the Near-Bottom Layer of Lake Biwa.

Filamentous manganese (Mn) oxide particles, which occur in the suboxic zone of stratified waterbodies, are important drivers of diverse elemental cycles. These particles are considered to be bacteriogenic; despite the importance of biogeochemical implications, however, the environmental factor responsible for their formation has not been identified. The aim of this study was to demonstrate the involvement of algal extracellular polysaccharides in Mn oxide particle formation. Based on this study of laboratory cultures of a model Mn(II)-oxidizing bacterium, the supply of algal extracellular mucilage was shown to stimulate Mn(II) oxidation and thus the production of filamentous Mn oxide particles. This observation was consistent with the results obtained for naturally occurring particles collected from a near-bottom layer (depth of approximately 90 m) in the northern basin of Lake Biwa, Japan, that is, most Mn particles resembling δ-MnO2 were associated with an extracellular mucilage-like gelatinous matrix, which contained dead algal cells and was lectin-stainable. In the lake water column, polysaccharides produced by algal photosynthesis sank to the bottom layer. The analysis of the quality of water samples, which have been collected from the study site for 18 years, reveals that the annual average total phytoplankton biovolume in the surface layer correlates with the density of filamentous Mn particles in the near-bottom layer. Among different phytoplankton species, green algae appeared to be the key species. The results of this study suggest that algal extracellular polysaccharides serve as an important inducer for the formation of filamentous Mn oxide particles in the near-bottom layer of the northern basin of Lake Biwa.

Phytoplankton communities and environmental variables as indicators of ecosystem productivity in a shallow tropical lake

The water quality and ecosystem productivity of a tropical lake in Ethiopia (Lake Arkiet) was evaluated using phytoplankton and environmental factors. This was to ascertaining the lake’s potential for various applications. Phytoplankton communities and some selected environmental variables were collected from two predefined sampling sites (open water and littoral) using a seasonal campaign between March to May (dry season) and June to August (wet season) in 2022. The analysis of the physicochemical characteristics of this study showed that the lake’s water was well-oxygenated (6.8–16.7 mg/L), warm (25.8–29.8 °C), turbid (154–317 NTU), had poor water transparency (4.3–16.1 cm), and was alkaline (pH = 7.29–11.31). The concentrations of inorganic nutrients (phosphate and nitrate) were notably high, ranging from 2.12–5.26 and 2.19–10.64 mg/L, respectively. A total of 34 phytoplankton taxa from four divisions were identified in Lake Arekit. Bacillariophyceae (18 taxa) and Chlorophyceae (10 taxa) were the major groups of phytoplankton which together represented the largest (82%) phytoplankton taxa. The total biovolume of phytoplankton in the lake was to be 384.15 mm3/L. Cyanobacteria contributed the largest (41%) phytoplankton biovolume followed by Bacillariophyta (32%). The highest biovolume (about 75%) was constituted in the Microcystis aeruginosa, Cylindrospermopsis raphidiopsis, Anabaena spiroides, Pediastrum duplex, Aulacoseira granulate, Navicula schroeteri, and Nitzschia palea. The distribution of environmental factors and phytoplankton communities showed greater seasonality. High phytoplankton biovolume was observed in the dry season at both sampling sites concurrently with high water transparency and low water temperature. Findings from this study revealed that Lake Arkeit was a moderately polluted but productive lacustrine ecosystem that can still support aquatic life, fish production, irrigation, and aquaculture. The primary source of the pollution is the entry of inorganic and organic wastes from a brewery and other water bottling industries nearby and around the lake, as well as possible excessive nutrient levels due to the lake’s geological background. It is advised that commercial factories stop producing or releasing waste in open spaces that are heavily washed and enter the lake via flooding and tributary rivers and streams. Additionally, the local government should work with the nearby communities to set up a buffer zone where people are prohibited from engaging in agricultural activities to protect and reduce pollution, which will help to preserve the lake’s water and ecosystem.

Effects of cyprinid removal and reintroduction: Diamond Lake, Oregon

Eilers J, Miller R, Loomis D, Vogel A. 2023. Effects of cyprinid removal and reintroduction: Diamond Lake, Oregon. Lake Reserv Manage. 39:156–173. Diamond Lake, located in the Oregon Cascade Range, was treated with rotenone in 2006 to remove invasive populations of cyprinids, Gila bicolor and Notemigonus crysoleucas. The treatment successfully removed all fish, and the lake was restocked in 2007 with rainbow trout (Oncorhynchus mykiss). The treatment resulted in large increases in transparency, large cladocerans (Daphnia pulicaria), and benthic invertebrates. The previous cyanobacterial blooms were comprised almost exclusively of Anabaena [Dolichospermum], whereas the current populations of cyanophytes include Gloeotrichia. Cyprinids were reintroduced into the lake and documented in 2008 (Notemigonus crysoleucas) and 2015 (Gila bicolor), likely contributing to a decline of several metrics of water quality. Piscivorous trout (Salmo trutta and Salmo trutta x Salvelinus fontinalis) were introduced into the lake starting in 2016 to control the introduced cyprinids. The cyprinid populations have stabilized, and most metrics of lake status (Secchi disk transparency, phytoplankton biovolume, abundance of large cladocerans, zoobenthic biomass, trout condition factor) indicate that the lake has improved substantially since the treatment and introduction of piscivorous trout. It is unclear whether the cyprinid populations are constrained by behavioral mechanisms associated with the introduction of the piscivorous trout or whether other factors currently keep the cyprinids in check. The success of this biomanipulation project requires continued monitoring and use of adaptive management strategies to respond to changes in fish composition.

Designation of Reference Areas for Turkish Lakes Based on the Estimations of Phytoplankton Quality Element

Phytoplankton is the most suitable quality element for assessing the ecological status of standing surface water bodies such as lakes and reservoirs. In order to evaluate changes in these water bodies, it is important to determine the reference areas (REFS) and maximum ecological potential areas (MEPS) so as to explain the deviations from the reference conditions and maintain or improve the ecological condition of the water bodies. This study explains the methodology used in the designation of the REFS and MEPS based on the phytoplankton quality element in inland surface waters by the Project for the Establishment of a Reference Monitoring Network in Türkiye. For this purpose, a total of 275 lakes and reservoirs were investigated in three sampling periods and at several sampling points according to lake size from eight basins in 2017, nine basins in 2018 and eight basins in 2019. The evaluation of phytoplankton was mainly based on phytoplankton and cyanobacteria biovolumes. Phytoplankton biovolume metrics (PT-BV and CY-BV) have been developed for the sampled shallow and deep standing water bodies. A total of 79 lakes and reservoirs from eighteen typologies were determined as REFS and MEPS according to phytoplankton. In addition, the approaches and precautions taken to protect the reference areas are explained.

Experimental additions of allochthonous dissolved organic matter reveal multiple trophic pathways to stimulate planktonic food webs

Abstract There is still considerable debate as to whether the allochthonous (terrestrial) dissolved organic matter (DOM) mobilised during large flow events plays an important role in supporting secondary production in riverine food webs. Understanding how food webs respond to large pulses of terrestrial DOM (tDOM) is important for conceptualising the relative importance of energy sources supporting food webs. A mesocosm experiment (1,000 L) using three concentrations of leachate (1, 4, 8 mg C/L and a control) made from floodplain DOM was run for 34 days in a dam filled with water from Gunbower Creek in Northern Victoria, Australia. Nutrients, phytoplankton, zooplankton and stable isotope (δ13C signatures) data were collected to examine how floodplain nutrients affected growth and community structure within the lower food web typical of an Australian lowland river. All leachate additions led to very high concentrations of zooplankton and mixotrophic algae compared to the control. Mixotrophs dominated the algal biovolume of all leachate additions until Day (D)20 and appeared to drive changes in δ13C signatures of particulate organic matter (POM) which were significantly related to changes in zooplankton δ13C signatures. tDOM additions did not significantly suppress obligate autotroph growth which also appeared important as a food source, as reflected in the δ13C signatures of zooplankton and POM after D10. These results show the ability of phytoplankton and zooplankton communities in lowland rivers to respond quickly to changes in resource availability and quality. Mixotrophs appeared to provide an important trophic link between allochthonous carbon and primary consumers, and increased complimentarily to autotrophic production. This resulted in large net increases to phytoplankton biovolume and potentially played a significant role in driving changes in zooplankton growth. We suggest that allochthonous DOM may be highly bioavailable and support production through several different trophic pathways, offering a large boost to production via both autotrophy and heterotrophy. Furthermore, we contend that mixotrophy may be an important pathway for allochthonous organic matter to enter riverine food webs and support secondary production.

Controlling factors of phytoplankton distribution in the river–lake transition zone of a large lake

River–lake transition zones have been identified as major drivers of phytoplankton growth. With climate change reducing the frequency of complete lake overturns, it is expected that the Rhône River, the main tributary to Lake Geneva (France/Switzerland), will become the major source of nutrients for the lake euphotic zone. The river–lake transition zone was hence examined at the mouth of the Rhône River with the aim of understanding the complexities and controls of phytoplankton distribution in this specific deltaic ecosystem. Two field campaigns were carried out in which water samples were collected from longitudinal and transversal transects across the transition zone. These samples were analyzed for both nutrient and phytoplankton concentrations, while the fraction of Rhône River water in a lake sample was determined by the stable isotope composition of the water. The results indicate contributions in P and Si related to the Rhône intrusion into the lake. Furthermore, this river–lake transition zone appears to be a dynamic area that can locally present optimal conditions for phytoplankton growth. In early spring, a wind event broke the early and weak stratification of the lake, forcing the Rhône River and its turbidity plume to intrude deeper. Thus, this sharp drop of the turbidity within the euphotic zone allowed an increase in the phytoplankton biovolume of 44%. In early fall, outside of the turbid near field of the river mouth, the Rhône interflow, located just below the thermocline, promoted a local deep chlorophyll maximum.

High-frequency monitoring through in-situ fluorometric sensors: A supporting tool to long-term ecological research on lakes

Lake Maggiore is a site of the Long-Term Ecosystem Research (LTER) network, belonging to the deep subalpine Lake District in Northern Italy. Studies on the physical, chemical, and biological features of the lake have been performed continuously since the 1980s. The lake recovered from eutrophication reaching the present oligotrophic condition. In the last decade, climate change represents the main driving factor for the long-term evolution of the lake, affecting its hydrodynamics, nutrient status, and biological communities. In 2020 a high-frequency monitoring (HFM) system was deployed, with the aim to integrate long-term monitoring based on discrete sampling and analysis. The system consists of a buoy equipped with sensors for limnological variables and algal pigments. The high-frequency monitoring program is part of a cross-border project between Italy and Switzerland focusing on lake quality monitoring as a critical input for successful lake management. In this paper we focus on Chlorophyll-a data, with the aim to test whether in-situ fluorescence measurements may provide a reliable estimate of lake phytoplankton biovolume and its seasonal dynamic. Sensor’s performance was regularly tested comparing chlorophyll-a data taken by the in-situ fluorescent sensors (Cyclops7, Turner Design), data from laboratory fluorescence analysis (FluoroProbe, BBE Moldaenke), values obtained from chlorophyll-a analysis by UV-VIS spectrophotometry and data from phytoplankton microscopy analysis. We found a general good agreement between the Chlorophyll-a data obtained with the different methods, confirming the use of in-situ sensors as a reliable approach to measure algal pigments, especially to assess their variability in the short-term, but also to describe the seasonal pattern of phytoplankton biovolume. However, phytoplankton community composition played a substantial role in the performance of the different methods and in the reliability of in-situ data as a tool to assess algal biovolume. This study demonstrates that high-frequency monitoring (HFM), used in conjunction with discrete chemical and biological monitoring, represents an important advance and support in the long-term monitoring of freshwaters and is a useful tool to detect ecological changes. Regular checking and validation of the sensor readings through laboratory analyses are important to get trustworthy data.

Copepod Feeding Responses to Changes in Coccolithophore Size and Carbon Content

Phytoplankton stoichiometry and cell size could result from both phenology and environmental change. Zooplankton graze on primary producers, and this drives both the balance of the ecosystem and the biogeochemical cycles. In this study, we performed incubations with copepods and coccolithophores including different prey sizes and particulate carbon contents by considering phytoplankton biovolume concentration instead of chlorophyll a level (Chl a) as is usually performed in such studies. The egestion of fecal pellet and ingestion rates were estimated based on a gut fluorescence method. The latter was calibrated through the relationship between prey Chl a level and the biovolume of the cell. Chl a/biovolume ratio in phytopkanton has to be considered in the copepod gut fluorescent content method. Both coccolithophore biovolume and particulate inorganic/organic carbon ratios affect the food foraging by copepods. Finally, we observed a non-linear relationship between ingestion rates and fecal pellet egestion, due to the presence of calcite inside the copepod’s gut. These results illustrate that both prey size and stoichiometry need to be considered in copepod feeding dynamics, specifically regarding the process leading to the formation of fecal pellets.

Year-long monitoring of phytoplankton community, toxigenic cyanobacteria, and total microcystins in a eutrophic tropical dam supplying the Mexico megacity

The Valle de Bravo dam is an important source of drinking water supply for the Mexico City Conurbation (>26 million inhabitants) and is also a hotspot for nautical sports, recreational fishing, and tourism. However, anthropogenic pressures in the upper reaches of the basin have led to increased eutrophication and numerous harmful cyanobacterial blooms (HCBs). To determine the effect of abiotic variables on the characteristics of the phytoplanktonic community, as well as their influence on the diversity of toxigenic cyanobacteria and related cyanotoxins, we evaluated monthly variations in environmental factors, phytoplankton biovolume and composition and total microcystins in Valle de Bravo dam during the year of 2019. Overall, 75 phytoplanktonic species were identified, mostly belonging to the divisions Cyanobacteria, Chlorophyta, and Bacillariophyta. Cyanobacteria presented the highest biomass throughout the year, with water temperature and rainfall being the best correlated factors. The highest concentrations of total microcystins were recorded from July to September (maximum of 71 μg L−1), associated with the dominance of species such as M. smithii, M. aeruginosa, M. viridis M. flos-aquae, Aphanocapsa planctonica, and Dolichospermum crassum, and environmental factors such as rainfall, total dissolved solids, water temperature, and specific trace metals. In all months except December, the total cyanobacterial biovolume was above the World Health Organization alert level two, indicating potentially high risks to human health. The predominance of cyanobacteria and high biovolumes classified water quality as poor to very poor during most of the year. To avoid the development of HCBs in this dam, the contribution of nutrients by the tributary rivers and sewage must be controlled, since the poor-quality conditions of the water threaten the aquatic biota, the sports and recreation activities and affect the potable water supply.

Phytoplankton biomass and community composition in three Texas estuaries differing in freshwater inflow regime

Because many estuaries worldwide are experiencing large-scale alterations in freshwater inflows due to climatic and human influences on watersheds, it is critical to understand ecosystem-level responses to freshwater inflow conditions and variability. This study compared environmental conditions and phytoplankton biomass/community composition among three Texas estuaries with differing freshwater inflow regimes to understand the impacts of freshwater inflow magnitude on phytoplankton communities. It was hypothesized that: 1) nutrient concentrations and phytoplankton biomass would be highest in San Antonio Bay (SA), the high inflow estuary and lower in Nueces-Corpus Christi Bay (NC) and Baffin Bay (BB) due to lower average inflows, and 2) the phytoplankton community would be dominated by large and/or fast-growing taxa in SA, with a greater fraction of small and/or slow-growing taxa in NC and BB. Highest inorganic nutrient concentrations were generally observed in SA, while high organic nutrient concentrations were found in BB. Chlorophyll a was relatively high in both SA and BB (mean 16.9–18.5 μg L−1) while phytoplankton biovolume was highest in BB. Despite distinct freshwater inflow, salinity and nutrient regimes, differences in phytoplankton community composition were less pronounced. Nano- or microplankton were the dominant size class of phytoplankton in each system, and diatoms were the dominant functional group, accounting for 27–49% of total biovolume on average. There were indications that the phytoplankton community was more diverse in SA, especially following inflow events, providing evidence that inflow may act as a disturbance that leads to greater phytoplankton diversity. Results from this study also showed that while freshwater inflow is important for nutrient delivery, low inflow estuaries such as BB are still susceptible to effects of eutrophication due to long residence times and nutrient retention/recycling. Overall, the differing responses of each of these ecosystems to freshwater inflow highlight the importance of system-specific management plans and consistent monitoring programs in coastal estuaries.

SPATIAL AND TEMPORAL DYNAMICS OF PHYTOPLANKTON IN A HIGHLY IMPACTED TROPICAL MONTANE RIVER

Rivers, as most bodies of water, are subject to eutrophication and water contamination, mainly from domestic sewage and industrial discharges from urban centers and agricultural areas. These growing human impacts result in a gradual loss of water quality and changes in biotic communities, including phytoplankton. Analyzing the dynamics of phytoplankton is important to understand how, in addition to hydrography and the physical, chemical and biological variables, human impact can be a controlling factor in this dynamic. In this study, we analyzed abiotic variables and zooplankton abundance to identify the factors controlling different phytoplankton attributes at six sampling points, in two climatic periods and three years, in the Piabanha River, a slowly flowing stream with to strong human impact beginning in its upper course, in a mountain region in southeastern Brazil. The results showed homogeneous environmental variables and different phytoplankton attributes along most of the stretch analyzed, except for sampling point 1, located in a preserved forest area but with nutrient concentrations limiting phytoplankton growth. The difference in flow between the two climatic periods (dry and wet) was not sufficient to change the total phytoplankton biovolume. Temperature seemed to strongly affect the phytoplankton response, with larger relative contributions from cyanobacteria in the wet period, with higher temperatures, and from phytoflagellates in the dry period, with lower temperatures. As expected, zooplankton showed no influence on phytoplankton dynamics, with a large contribution from small rotifers. In this tropical montane river, with slow flow and intense human impacts, nutrient concentrations and temperature were the main drivers of the spatial and temporal dynamics of phytoplankton, respectively

Phytoplankton dynamics in a drinking water catchment zone at the Amazon River mouth

Phytoplankton is formed by photosynthesizing microorganisms that act as primary producers in distinct water bodies. These include microalgae and cyanobacteria. It is essential to know the phytoplankton in water catchment areas intended for drinking water treatment once their excessive density may result in problems, such as taste and odor in the water, toxin production, filter clogging, and other damages. This study investigated the phytoplankton dynamics and the environmental factors that may influence phytoplankton density in the drinking water catchment zone of Macapá, a city located on the Amazon River mouth. The sampling was carried out monthly from April/2015 to March/2016. The study reports the first detailed information on the phytoplankton in the study area since previously published studies regarded only cyanobacteria. The species Limnothrix planctonica and Aulacoseira granulata may substantially influence the water treatment due to their great abundance in the study area, especially in July and November, when their density peaks occur, respectively. Nevertheless, Aulacoseira granulata is the primary constituent of the phytoplankton biovolume. This study provides biological and sanitary information to guide public administration towards improving the quality and safety of water supply services, and also to increase the biodiversity knowledge of Amazonian phytoplankton.

Interannual variability of water quality conditions in the Nyanza Gulf of Lake Victoria, Kenya

The Nyanza Gulf of Lake Victoria is considered eutrophic with degrading water quality, as shown by harmful algal blooms formed by cyanobacteria of the genus Microcystis. The dilution of gulf water occurs mainly through the wide Rusinga Channel, whereas the much narrower and shallower Mbita Channel was reopened in May 2017. Specific conductivity and phytoplankton biovolume composition were monitored monthly from July 2017 to July 2018 at three stations and compared with records during 2008 – 2009, when higher eutrophication was observed, in the west gulf (WG, closely located to the Mbita Channel), the mid gulf (central part of the gulf), and the east gulf (EG, close to Kisumu City). As previously observed, conductivity showed a distinct increase from the WG to the EG but compared with records 2008–2009 it had decreased. Water level fluctuations, resulting from wind possibly causing water exchange with the main basin, were related to the decrease in conductivity at the EG. When all three stations were compared, the environmental variable transparency was positively related to most phytoplankton genera, whereas the genera Dolichospermum, Microcystis, and Aulacoseira were related to eutrophication. Compared with the period 2008–2009, the proportion of Microcystis decreased, while the proportion of Aulacoseira increased. Compared with the period 2008–2009, the observed dilution at the EG was primarily related to the overall increased water level in the main basin. The observed dilutional influence might have led to a decline in nuisance phytoplankton and overall improved water quality conditions.