Underestimated methane production triggered by phytoplankton succession in river-reservoir systems: Evidence from a microcosm study

Authors

Haolian Xu, Hong Li, Zhenzhen Tang, Yi Liu Guo Li, Qiang He

The impoundment of dammed rivers accelerates phytoplankton succession from river-dominated to lake-dominated species. Little is known about the role of phytoplankton succession in methane (CH₄) production. In this study, we performed a 61-day microcosm investigation to simulate the collapse processes of Cyclotella meneghiniana (river-dominated algae) and Chlorella pyrenoidosa and Microcystis aeruginosa (lake-dominated algae). The results suggested that different methanogenic conditions were induced by the collapse of river-and lake-dominated algae. The rapid settlement of C. meneghiniana induced aerobic conditions in the water that inhibited anaerobic CH₄ production and intensified CH₄ oxidation as a result of an increase in pmoA. However, the decomposition of C. pyrenoidosa and M. aeruginosa depleted dissolved oxygen and provided abundant labile organic matter, which jointly elevated mcrA and the mcrA/pmoA ratio. Under this condition, anaerobic CH₄ production was the dominant pathway for the mineralization of algae-derived carbon. Finally, the CH₄ produced per unit of particulate total carbon (identified as the carbon content of the algal biomass) by C. pyrenoidosa and M. aeruginosa was 16.29-fold and 8.56-fold higher, respectively, than that produced by C. meneghiniana. These observations provided evidence that lake-dominated algae played a more vital role in CH₄ production than river-dominated algae when algal succession occurred. This discovery might be a new and vital, yet largely underestimated CH₄ emission pathway in river-reservoir systems, that should be considered when evaluating the effect of hydraulic projects on greenhouse gas emissions.

Modeling cyanobacterial blooms in tropical reservoirs: The role of physicochemical variables and trophic interactions

Authors

Cihelio Alves Amorim, Ênio Wocyli Dantas, Ariadne do Nascimento Moura

Understanding the importance of environmental variables on the dominance of cyanobacteria is crucial for appropriately managing water resources. Although studies about temperate and subtropical regions show a high influence of nutrients and temperature on blooms, this relationship is still unclear for the tropics. Accordingly, we hypothesized that nutrients and temperature are the main factors driving cyanobacterial blooms in tropical reservoirs, and those relationships are intensified by the zooplankton. To test these hypotheses, we constructed a structural equation model based on the monitoring of ten reservoirs from Northeast Brazil. We analyzed the effects of physicochemical variables and zooplankton on cyanobacterial blooms and the biomass of four morphotypes. Cyanobacterial biomass varied within the reservoirs, with bloom records (0.2–268.4 mg L⁻¹) in all of them, primarily constituted by the colonial morphotype, followed by picocyanobacteria, heterocyted, and non-heterocyted filaments. The cyanobacterial community was driven mainly by chemical variables (55.14% of the variation), followed by physical (48.28%), and zooplankton (39.47%). Through the structural equation model, we demonstrated that total cyanobacterial biomass, as well as the morphotypes, were mainly influenced by omnivorous crustaceans and total dissolved phosphorus. Solar radiation, air temperature, mixing zone, and salinity were important to explain the biomass of the morphotypes. The model explained most of the variation in the picocyanobacterial blooms (79.8%), followed by total cyanobacteria (62.4%), heterocyted filaments (59.1%), non-heterocyted filaments (58.2%), and coccoids (55.1%). Zooplankton groups were also influenced by the physicochemical variables, which presented direct and indirect effects on cyanobacteria. Given the predictions of increased eutrophication, warming, and salinization, cyanobacterial blooms will become more intense in tropical reservoirs. Thus, restoring measures must be adopted to reduce bloom development, such as external phosphorus and salt loadings, and biomanipulation.

Phytoplankton in extreme environments: importance and consequences of habitat permanency

Authors

Judit Padisák & Luigi Naselli-Flores

There is hardly any sunshine exposed surface on this Earth, be it water or terrain, which would not support some biota. Still, many habitats offer harsh conditions requiring specialized physiological adaptations to survive. These environments are referred to as extremes; often inhabited by extremophilic organisms. In this review, characteristic species and assemblage properties of phytoplankton inhabiting extreme environments (especially lakes and pools where planktic life is potentially possible and independently of their origin) in terms of alkalinity, acidity, DOC, salinity, temperature, light and mixing regime will be outlined. Lakes characterized by more than a single extreme are common (e.g. saline + alkaline; acidic + high DOC + high metal content + low light). At the edge of extremes (e.g. pH of 1; salinity over ~ 100–150 g l⁻¹) single species with appropriate physiological adaptation are selected and the phytoplankton is often dominated by a single species (monodominant) setting compositional diversity to zero. Under less extreme conditions permanent equilibria may persist; in many cases over several years in contrast to „average” lakes where equilibria are rare and ephemeral. Food webs depending on „extreme phytoplankton” are often atypical for example because the microbial loop is of prior importance or because birds are top predators.

 

Temporal heterogeneity of microbial communities and metabolic activities during a natural algal bloom

Authors

Jin Zhou, Yong-min Lao, Jun-ting Song, Hui Jin, Jian-ming Zhu, Zhong-hua Cai

Elucidating the interactions between algae and associated microbial communities is critical for understanding the mechanisms that mediate the dynamic of harmful algal blooms (HABs) in marine environment. However, the microbial functional profiles and their biogeochemical potential in HABs process remains elusive, especially during a complete natural HAB cycle. Here, we used pyrosequencing and functional gene array (GeoChip) to investigate microbial community dynamics and metabolic potential during a natural dinoflagellate (Noctiluca scintillans) bloom. The results shown that bacterioplankton exhibited significant temporal heterogeneity over the course of the bloom stages. Microbial succession was co-driven by environmental parameters and biotic interactions. The functional analysis revealed significant variations in microbial metabolism during matter cycling. At bloom onset-stage, metabolic potential associated with iron oxidation and transport was elevated. Carbon fixation and degradation, denitrification, phosphorus acquisition, and sulfur transfer/oxidation were significantly enhanced at the plateau stage. During the decline and terminal stages, oxidative stress, lysis of compounds, and toxin degradation & protease synthesis increased. This work reveal phycosphere microorganisms can enhanced organic C decomposition capacity, altered N assimilation rate and S/P turnover efficiency, and balancing of the Fe budget during HAB process. The ecological linkage analysis has further shown that microbial composition and functional potential were significantly linked to algal blooms occurrence. It suggest that structural variability and functional plasticity of microbial communities influence HAB trajectory.

Freshwater phytoplankton diversity: models, drivers and implications for ecosystem properties

Authors

Gábor Borics, András Abonyi, Nico Salmaso & Robert Ptacnik

Our understanding on phytoplankton diversity has largely been progressing since the publication of Hutchinson on the paradox of the plankton. In this paper, we summarise some major steps in phytoplankton ecology in the context of mechanisms underlying phytoplankton diversity. Here, we provide a framework for phytoplankton community assembly and an overview of measures on taxonomic and functional diversity. We show how ecological theories on species competition together with modelling approaches and laboratory experiments helped understand species coexistence and maintenance of diversity in phytoplankton. The non-equilibrium nature of phytoplankton and the role of disturbances in shaping diversity are also discussed. Furthermore, we discuss the role of water body size, productivity of habitats and temperature on phytoplankton species richness, and how diversity may affect the functioning of lake ecosystems. At last, we give an insight into molecular tools that have emerged in the last decades and argue how it has broadened our perspective on microbial diversity. Besides historical backgrounds, some critical comments have also been made.

 

Formation of algal-derived nitrogenous disinfection by-products during chlorination and chloramination

Authors

X. Li, N.R.H. Rao, K.L. Linge, C.A. Joll, S. Khan, R.K. Henderson

Algal cells and algal organic matter (AOM) are a source of high dissolved organic carbon (DOC) and nitrogen (DON) concentrations. This poses a possible health risk due to their potential to form disinfection by-products (DBPs), some of which may be of health concern, after disinfection. While several studies have focussed on the formation of carbonaceous DBPs from AOM, only a few studies have focussed on the formation of nitrogen containing N-DBPs from AOM. Hence, the main aim of this study was to thoroughly investigate the N-DBP formation potential of the AOM from a species of cyanobacteria commonly found in natural waters, Microcystis aeruginosa. Three haloacetonitriles, two halonitromethanes, two haloacetamides, and eight N-nitrosamines were analysed by gas chromatography-mass spectrometry after chlorination and chloramination of the extracted AOM. To provide further insight into the influence of changing DON character on N-DBP formation potential, the AOM from three other species, Chlorella vulgaris, Dolichospermum circinale and Cylindrospermopsis raciborskii, were also tested. Dichloroacetonitrile (DCAN) was the DBP formed in the highest concentrations for both chlorination and chloramination of bulk AOM from all the species. Furthermore, during chlorination and chloramination, the high molecular weight fraction (>1 kDa) of AOM from M. aeruginosa had a greater DCAN formation potential (normalised to DOC or DON) than the AOM in the low molecular weight fraction (<1 kDa) of M. aeruginosa, regardless of growth stage. N-Nitrosamine formation from the bulk AOM of all species occurred only after chloramination. The molar concentration of N-nitrosodimethylamine (NDMA) was lower than the other N-nitrosamines detected. However, NDMA formation increased with culture age for all four species, in contrast to most other N-nitrosamines whose formation remained consistent or decreased with culture age. Overall, algal growth could result in elevated concentrations of N-DBPs due to the increasing concentrations of high molecular weight algal DON in the AOM. It is suggested that the AOM comprises precursors containing long C-chain amine (R₁-NH-R₂) or cyclic N-containing amine structures. Comparisons to previously measured N-DBP concentrations in drinking water suggest that the AOM from the algae and cyanobacteria examined in this study are not likely to be a major source of precursors for either DCAN or NDMA in real waters. However, AOM may present a major precursor source for other N-nitrosamines.

Carbon and nutrients transfer from primary producers to lake sediments – a stoichiometric approach

Authors

Lech Kufel, Małgorzata Strzałek, Elżbieta Biardzka, Marcin Becher

We aimed to demonstrate different input of organic and inorganic carbon, nitrogen and phosphorus from three main groups of primary producers (phytoplankton, charophytes and vascular submerged macrophytes) to respective lake sediments. Studies were carried out in one eutrophic and two mesotrophic lakes. Samples of sediments were taken from profundal and from littoral zones, the latter divided into such overgrown by charophytes and others covered by vascular submerged macrophytes. We applied a stoichiometric approach to illustrate variable functional carbon to nutrients relationships. Among profundal sediments, the lowest organic to inorganic carbon ratio was found in sediments from the eutrophic lake due to precipitation of calcium carbonate during algal blooms. Extremely low inorganic carbon input to profundal sediment of one of the mesotrophic lakes may be explained by low phytoplankton production but also by dissolution of once deposited calcium carbonates. Charophyte-dominated littoral sediments contained significantly more inorganic carbon than other littoral and profundal sediments. Comparison of stoichiometric ratios between plant standing crop and underlying littoral sediments showed significant enrichment of sediments in nitrogen manifested by reduction of organic carbon to total nitrogen ratio during plant decomposition taking place both in charophyte and in vascular plant stands. We also attempted to divide phosphorus pool in sediments into organic P and calcium-bound P present in charophyte stands and in profundal sediments of eutrophic lake. In the former, calcium-bound P was estimated at 17–19% of the total P pool while in profundal sediments it amounted 42% of the total P. This difference suggests that calcium carbonate settling during algal blooms in a eutrophic lake may be more effective in P trapping than calcite encrustations covering charophyte plants in littoral sites. In conclusions, we underline the need of considering often neglected inorganic fractions of carbon and phosphorus to get better insight into carbon and nutrient burial in lake sediments.

The genome of Prasinoderma coloniale unveils the existence of a third phylum within green plants

Authors

Linzhou Li, Sibo Wang, Hongli Wang, Sunil Kumar Sahu, Birger Marin, Haoyuan Li, Yan Xu, Hongping Liang, Zhen Li, Shifeng Cheng, Tanja Reder, Zehra Çebi, Sebastian Wittek, Morten Petersen, Barbara Melkonian, Hongli Du, Huanming Yang, Jian Wang, Gane Ka-Shu Wong, Xun Xu, Xin Liu, Yves Van de Peer, Michael Melkonian & Huan Liu

Genome analysis of the pico-eukaryotic marine green alga Prasinoderma coloniale CCMP 1413 unveils the existence of a novel phylum within green plants (Viridiplantae), the Prasinodermophyta, which diverged before the split of Chlorophyta and Streptophyta. Structural features of the genome and gene family comparisons revealed an intermediate position of the P. coloniale genome (25.3 Mb) between the extremely compact, small genomes of picoplanktonic Mamiellophyceae (Chlorophyta) and the larger, more complex genomes of early-diverging streptophyte algae. Reconstruction of the minimal core genome of Viridiplantae allowed identification of an ancestral toolkit of transcription factors and flagellar proteins. Adaptations of P. coloniale to its deep-water, oligotrophic environment involved expansion of light-harvesting proteins, reduction of early light-induced proteins, evolution of a distinct type of C₄ photosynthesis and carbon-concentrating mechanism, synthesis of the metal-complexing metabolite picolinic acid, and vitamin B₁, B₇ and B₁₂ auxotrophy. The P. coloniale genome provides first insights into the dawn of green plant evolution.

Relative importance of top‐down vs. bottom‐up control of lake phytoplankton vertical distributions varies among fluorescence‐based spectral groups

Authors

Mary E. Lofton, Taylor H. Leach, Beatrix E. Beisner, Cayelan C. Carey

The relative importance of top‐down vs. bottom‐up control of phytoplankton biomass in aquatic ecosystems has been long debated and studied. However, few studies have considered the relative importance of top‐down vs. bottom‐up control on phytoplankton vertical distributions and characteristics of deep chlorophyll maxima (DCMs), and fewer still have investigated the importance of these drivers for multiple phytoplankton groups. We examined depth profiles of four phytoplankton spectral groups and a suite of top‐down (zooplankton) and bottom‐up (nutrients, temperature, and light) drivers from 51 north temperate lakes varying on gradients of size, trophic state, light availability, and thermal stratification. We used regression trees to identify the most important drivers of different vertical distribution metrics for each phytoplankton spectral group. The relative importance of top‐down vs. bottom‐up control varied across spectral groups and was related to the characteristics of the dominant taxa within each spectral group, as assessed by microscope counts. Zooplankton biomass was the most important driver of brown algae vertical distributions, likely because this group contained highly edible taxa (primarily chrysophytes), while thermal stratification predicted vertical distributions of buoyancy‐regulating cyanobacteria. Our work highlights the importance of examining phytoplankton community composition to improve understanding of DCM characteristics and top‐down vs. bottom‐up control of phytoplankton in aquatic systems.

The case for research integration, from genomics to remote sensing, to understand biodiversity change and functional dynamics in the world’s lakes

Authors

Stephen J. Thackeray, Stephanie E. Hampton

Freshwater ecosystems are heavily impacted by multiple stressors, and a freshwater biodiversity crisis is underway. This realization has prompted calls to integrate global freshwater ecosystem data, including traditional taxonomic and newer types of data (e.g., eDNA, remote sensing), to more comprehensively assess change among systems, regions, and organism groups. We argue that data integration should be done, not only with the important purpose of filling gaps in spatial, temporal, and organismal representation, but also with a more ambitious goal: to study fundamental cross‐scale biological phenomena. Such knowledge is critical for discerning and projecting ecosystem functional dynamics, a realm of study where generalizations may be more tractable than those relying on taxonomic specificity. Integration could take us beyond cataloging biodiversity losses, and toward predicting ecosystem change more broadly. Fundamental biology questions should be central to integrative, interdisciplinary research on causal ecological mechanisms, combining traditional measures and more novel methods at the leading edge of the biological sciences. We propose a conceptual framework supporting this vision, identifying key questions and uncertainties associated with realizing this research potential. Our framework includes five interdisciplinary “complementarities.” First, research approaches may provide comparative complementarity when they offer separate realizations of the same focal phenomenon. Second, for translational complementarity , data from one research approach is used to translate that from another, facilitating new inferences. Thirdly, causal complementarity arises when combining approaches allows us to “fill in” cause–effect relationships. Fourth, contextual complementarity is realized when together research methodologies establish the wider ecological and spatiotemporal context within which focal biological responses occur. Finally, integration may allow us to cross inferential scales through scaling complementarity . Explicitly identifying the modes and purposes of integrating research approaches, and reaching across disciplines to establish appropriate collaboration will allow researchers to address major biological questions that are more than the sum of the parts.