Algal Decomposition Research Articles

Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Oil Droplet Capture and Ingestion by Filter-Feeding Sabellid and Serpulid Polychaetes

Benthic filter-feeders form an essential role in marine food chains as they constitute the bridge between the microscopic primary producers and the consumers. Although filter-feeders mainly feed on solid particles, they also capture and ingest oil droplets. Usually, these microdroplets come from the decomposition of animals or algae or from petroleum oils that enter water via spills and leakages. Here, we used videography, TRITC fluorescence microscopy, and fluid mechanics to study the capture mechanisms of canola, fish, and four petroleum motor oil droplets by the filter feeding sabellid and a serpulid polychaetes. Schizobranchia insignis, Eudistylia vancouveri, Myxicola infundibulum and Serpula columbiana actively feed on waste motor oil droplets in seawater. A further experiment found that S. insignis fed on all types of oil droplets, demonstrating no selectivity based on type. The oil droplet capture mechanism of S. insignis were direct interception and sieving, like that of solid particles. The size range of droplets ingested was 10 to 300 µm in diameter, but these ranges differed depending on the density and viscosity of the oils. Higher density and viscous oils were captured at smaller droplet sizes. These results are the first to characterize the mechanics of oil droplet capture, transport and ingestion by benthic ciliary filter feeders, and contribute to understanding the behavior of animals in response to oil emulsions, and how oils enter marine food webs.

Driving effects of dissolved organic carbon on cadmium release of the sediments by cyanobacterial decomposition

The driving effects of dissolved organic carbon (DOC) on cadmium (Cd) release of the sediments by cyanobacterial decomposition were investigated, and the great shallow lakes (Taihu Lake, China) with the algae-type, grass-type, and grass-algal alternation areas were chosen as the study area. The results showed that DOC concentration in the overlying water and Cd content in sediments were the highest in the algae-type areas, amounting to 6.4 mg L−1 and 2.4 mg kg−1, respectively, while the DOC contents in the surface sediments showed higher in the algae-type and grass-type areas. The sediments from the grass-type and algal-type areas showed the strong Cd source state, and only the sediments from Zhushan Bay had the sink state. Most of the sediments had the low Cd release risk, and the values of the degree of Cd saturation (DCdS) and Cd release risk index (CdRI) showed a significant correlation with the DOC content in the sediments (P < 0.05). The Cd release contribution originated from the surface sediments, and F1 (the extractable state of Cd form) was the main Cd release form (the maximum value of 51 % from grass-type areas). Due to the algal decomposition and the complex external environment, the contribution values of F2 (the reducible state of Cd form) and F1 was similar (40 %–47 %) in the process of Cd release from the surface and bottom sediments in grass-algae alternation areas, as well as in some algae-type areas. This study provides theoretical foundation for Cd release control at the ecosystems level.

Algal Decomposition Accelerates Denitrification as Evidenced by the High-Resolution Distribution of Nitrogen Fractions in the Sediment–Water Interface of Eutrophic Lakes

This study investigates the decomposition process of algal blooms (ABs) in eutrophic lakes and its impact on the labile endogenous nitrogen (N) cycle. In situ techniques such as diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper) were employed to decipher the vertical distribution of N fractions within the sediment–water interface (SWI) in Taihu, China. Additionally, an annular flume was used to simulate regional differences in lake conditions and understand labile nitrogen transformation during AB decomposition. This study reveals that the NH4+-N fraction exuded from algae is subsequently converted into NO3-N and NO2-N through nitrification, resulting in a significant increase in the concentrations of NO3−-N and NO2−-N at the SWI. The decomposition of algae also induces a significant increase in dissolved organic matter (DOM) concentration, referring to humic acid and humus-like components; a seven-millimeter decrease in dissolved oxygen (DO) penetration depth; as well as a significant decrease in the pH value near the SWI, which consequently promotes denitrification processes in the sediment. Moreover, the decomposition process influences nitrogen distribution patterns and the role conversion of sediments between a “source” and a “sink” of nitrogen. This investigation provides evidence on the migration and/or transformation of N fractions and offers insights into the dynamic processes across the SWI in eutrophic lakes.

Algae decomposition released dissolved organic matter subfractions on dark abiotic mercury methylation

To understand the mechanism of dark abiotic mercury (Hg) methylation by algae-derived dissolved organic matter (DOM) and effectively manage the environmental risks of mercury methylation in aquaculture areas, we investigated the influence of subfractions of DOM released from algae (Ulothrix sp.) decomposition on mercury methylation. The results showed that the hydrophobic basic component (HOB) in DOM exhibited the most substantial promotion effect on Hg methylation. The methylmercury (MeHg) production in the HOB treatment increased significantly, while the production rate of MeHg (%MeHg represented the concentration ratio of MeHg to THg) in the six subfractions treated solutions decreased significantly with the increase of Hg concentration. The change of the %MeHg was more evident at low Hg concentration, indicating the limited number of binding sites and methyl donors on DOM. As a consequence, Hg(Ⅱ) in the solution could not be converted into MeHg in equal proportion. Furthermore, the production of MeHg in solution was significantly reduced by the decomposed algae DOM, and its concentration was in the range of 0.017–0.085 ng·L−1 (significantly lower than undecomposed algal). The difference between the decomposed and the non-decomposed algae DOM reached a significant level (P < 0.05). When the DOM decayed for 20 and 30 days, the Hg methylation ability of DOM was weakened most obviously. During the decomposition process, considerable variations were observed among the subfractions, with HOB consistently playing a dominant role in Hg methylation. At the same time, the hydrophilic acid component exhibited a significant inhibitory effect on Hg methylation. Generally, the main components (e.g. HOB and HIA (hydrophilic acid component)) of DOM affecting mercury methylation were found in our study, which provided a better understanding of algae-derived DOM subfractions on the Hg methylation, in an attempt to prevent and control water pollution in aquaculture areas.

The decomposition of algae has a greater impact on heavy metal transformation in freshwater lake sediments than that of macrophytes

Heavy metal (HM) pollution is a major concern in freshwater ecosystem management. The different types of endogenous organic matter and the way their decomposition affects HM transformation in freshwater lakes is not well understood. An ex situ mesocosm study was conducted to compare HM transformation in sediments during anaerobic decomposition of cyanobacterial bloom biomass (CBB) and submerged cyanobacterial vegetation in Lake Taihu, known as Potamogeton malaianus (PM). Microbial community structures were examined through Illumina sequencing of 16S rDNA. Results indicate that Zn had a remarkably higher amount of potential mobile fraction than other heavy metals (Cr, Pb, Cu, Ni, and Cd) detected in sediments, especially in sediments collected from CBB-dominated areas (approximately 150 mg kg−1). CBB decomposition has caused a significant increase in exchangeable Zn content in sediments and a decrease in reducible Zn that was three times greater than PM decomposition. Additionally, oxidizable Zn content declined during CBB decomposition but increased during PM decomposition. Furthermore, the relative abundance of the main fermentative bacteria and some sulfate-reducing bacteria genera (e.g., Desulfomicrobium) were significantly associated with the HM content of exchangeable and reducible fractions during CBB decomposition. Overall, the findings indicate that Zn is more susceptible to endogenous organic matter decomposition than other metals in freshwater lakes, and the impacts of CBB decomposition on the transformation of heavy metals in sediment are greater than that of submerged macrophyte decomposition.

Formation mechanism of organic-rich mixed sedimentary rocks in saline lacustrine basin, Permian Lucaogou Formation, Jimsar Sag, Junggar Basin, Northwest China

The organic-rich mixed sedimentary rocks deposited in a saline lacustrine environment are widespread in the Lucaogou Formation (P2l), Jimsar Sag, Junggar Basin. These rocks have complex lithology (mainly including mudstone, dolomitic mudstone and argillaceous dolomite) and significant changes in geochemical characteristics. Presently, the formation mechanism of organic-rich mixed sedimentary rocks in the P2l of the Jimsar Sag is obscure. To address these issues, the formation mechanism of mudstone, dolomitic mudstone and argillaceous dolomite is revealed by evaluating their sedimentary environment, primary productivity and sources of organic matter using organic petrology, organic geochemistry and inorganic geochemistry. The results show that the mixed sedimentary rocks of the P2l exhibit excellent hydrocarbon generation potential. The mixed sedimentary strata were mainly deposited in saline and suboxic to anoxic water column, and the main source of organic matter was aquatic organisms. During the changes from mudstone, dolomite mudstone to argillaceous dolomite deposition, the paleoclimatic condition varied from warm-humid to arid-hot with more frequent hydrothermal activity, which enhanced the salinity of the water column, leading to a higher proportion of halotolerant algae (cyanobacteria and green algae). The improvement in the paleoproductivity caused by volcanic activity was the most critical factor to promote the enrichment of organic matter in the mixed sedimentary rocks. In addition, the decomposition of algae and stratified water column were conducive to the formation of a stable and suboxic to anoxic bottom water environment, which improves the preservation conditions of organic matter, and also favored the organic matter enrichment in mixed sedimentary rocks. Therefore, the frequent changes in paleoclimatic conditions and periodic hydrothermal activity controlled the formation of different lithologies in the P2l. High primary productivity and good preservation conditions promoted the accumulation of organic matter in these mixed sedimentary rocks.

Algal organic matter inhibits methylmercury photodegradation in eutrophic lake water: A dynamic study

Algal organic matter (AOM) is a major component of dissolved organic matter (DOM) in eutrophic lakes and could impact the photodegradation of neurotoxic methylmercury (MeHg) in water. Predicting these effects, however, is challenging, largely due to the dynamic changes of AOM during algal decomposition. Here, we investigated the effects of AOM on MeHg photodegradation throughout the algal decomposition process and elucidated these effects by characterizing dynamic changes of AOM and exploring the respective roles of various reactive oxygen species (ROS). Our results reveal that AOM derived from algal decomposition significantly inhibits MeHg photodegradation, and the extent of this inhibition varies depending on the specific lakes (8–21 %, p < 0.05) and their eutrophication states (16–28 %, p < 0.05). The inhibitory effect gradually weakened as the decomposition progressed, which may be attributed to the dynamic changes in the quantity and quality of AOM. Moreover, hydroxyl radical (·OH) was found to be the main contributor in driving MeHg photodegradation (15–23 %) during the early stages of decomposition (day 0–3), while in the later stage (day 12–24), the role of singlet oxygen (1O2, 15–20 %) and (3DOM*, 21–30 %) gradually strengthened and these three ROS jointly drove MeHg photodegradation. Based on our findings and recent studies, we propose that AOM derived from algal decomposition plays a vital role in increasing the risk of MeHg in eutrophic lakes. It promotes MeHg formation while simultaneously inhibiting its photodegradation. Integrating AOM-MeHg interactions into Hg biogeochemical cycling models would reduce uncertainties when predicting MeHg risks.

Elevated methylmercury production in mercury-contaminated soil and its bioaccumulation in rice: key roles of algal decomposition

Elevated methylmercury production in mercury-contaminated soil and its bioaccumulation in rice: key roles of algal decomposition

Macrofauna Community Dynamics and Food Webs in the Canopy-forming Macroalgae and the Associated Detrital Subsidies

Dietary variability and the degradation and incorporation of macroalgae in key macroinvertebrate consumers were examined (1) in a monitoring field study including a natural attached canopy habitat and an adjacent habitat receiving natural accumulations of detritus, and (2) in a manipulative in situ experiment of macroalgal detritus at two different depths (3 and 6 m) in the archipelago of SW Finland. The monitoring field study, examining species-specific dietary responses across three sampling dates in natural macroalgal stands, showed that a pulse of drifting filamentous macroalgae shaped the dietary compositions of the abundant benthic macroinvertebrate consumers and that accumulations of drifting filamentous macroalgae were rapidly incorporated into the food web through epigrazers. The in situ field experiment simulating a natural accumulation event and the degradation process of Fucus vesiculosus during 60 days showed that algal decomposition progressed relatively slowly at both depths. Detectable increasing incorporation of Fucus-derived matter to epigrazers and detritivorous bivalves occurred after 2−3 weeks, while simultaneously the incorporation of filamentous algae decreased over time. Hence, the ecological role of decomposing F. vesiculosus might be more important in areas where the algal matter can accumulate for several months. The effect of depth influenced the food incorporation of typical epigrazers. The increasing depth from 3 to 6 m lowered the median proportion of Fucus-derived matter incorporated into the macrofauna community approximately by 10% points compared to the shallower depth of 3 m.

Contribution of the decomposition of a macroalgal bloom to methane production in sea cucumber culture

CH4 is one of the most important greenhouse gases responsible for climate change. The effect of algal decomposition on CH4 emission fluxes in aquaculture environments is unknown. This study determined the relative abundance of methanogens in aquaculture in northern China. We determined various parameters in the water and sediment after the decomposition of Chaetomorpha valida. The results showed that the relative abundance of methanogens increased significantly during the decomposition of C. valida. The average CH4 emission flux was 50.64 mg m-2 h-1 when the density of C. valida was 25 mg cm-3, which was 11 times higher than that at a density of 0 mg cm-3. The concentrations of dissolved oxygen (DO), nitrite, nitrate and sulfate in the aquaculture pond significantly decreased during the decomposition of C. valida. The formation of a strong anaerobic reduction environment promoted the formation and release of CH4. Our results confirmed that the decomposition of C. valida enhanced the CH4 emission flux. The average CH4 emission fluxes ranged from 4.62 to 50.64 mg m-2 h-1. It is particularly important to remove decomposed algae in a timely manner and control greenhouse gas emissions from aquaculture ponds to mitigate climate change.

Quantitative discrimination of algae multi-impacts on N2O emissions in eutrophic lakes: Implications for N2O budgets and mitigation

It is generally accepted that eutrophic lakes significantly contribute to nitrous oxide (N2O) emissions. However, how these emissions are affected by the formation, disappearance, and mechanisms of algal blooms in these lakes has not been systematically investigated. This study examined and determined the relative contribution of spatiotemporal N2O production pathways in hypereutrophic Lake Taihu. Synchronously, the multi-impacts of algae on N2O production and release potential were measured in the field and in microcosms using isotope ratios of oxygen (δ18O) and bulk nitrogen (δ15N) to N2O and to intramolecular 15N site preference (SP). Results showed that N2O production in Lake Taihu was derived from microbial effects (nitrification and incomplete denitrification) and water air exchanges. N2O production was also affected by the N2O reduction process. The mean dissolved N2O concentrations in the water column during the pre-outbreak, outbreak, and decay stages of algae accumulation were almost the same (0.05 μmol·L–1), which was 2–10 times higher than in lake areas algae was not accumulating. However, except for the central lake area, all surveyed areas (with and without accumulated algae) displayed strong release potential and acted as the emission source because of dissolved N2O supersaturation in the water column. The mean N2O release fluxes during the pre-outbreak, outbreak, and decay stages of algae accumulation areas were 17.95, 26.36, and 79.32 μmol·m–2·d–1, respectively, which were 2.0–7.5 times higher than the values in the non-algae accumulation areas. In addition, the decay and decomposition of algae released large amounts of nutrients and changed the physiochemical properties of the water column. Additionally, the increased algae biomass promoted N2O release and improved the proportion of N2O produced via denitrification process to being 9.8–20.4% microbial-derived N2O. This proportion became higher when the N2O consumption during denitrification was considered as evidenced by isotopic data. However, when the algae biomass was excessive in hypereutrophic state, the algae decomposition also consumed a large amount of oxygen, thus limiting the N2O production due to complete denitrification as well as due to the limited substrate supply of nitrate by nitrification in hypoxic or anoxic conditions. Further, the excessive algae accumulation on the water surface reduced N2O release fluxes via hindering the migration of the dissolved N2O into the atmosphere. These findings provide a new perspective and understanding for accurately evaluating N2O release fluxes driven by algae processes in eutrophic lakes.

Elevated methylmercury production in mercury-contaminated paddy soil resulted from the favorable dissolved organic matter variation created by algal decomposition

Algae-derived organic matter (AOM) may considerably regulate methylmercury (MeHg) production and accumulation in the paddy fields by changing the soil-dissolved OM (SDOM) properties. In this study, a 25-day microcosm experiment was performed to compare the responding mechanisms of MeHg production in the Hg-contaminated paddy soil-water system to the input of algae-, rice-, and rape-derived OMs. Results showed that algal decomposition could release much more cysteine and sulfate than crop straws. Compared with crop straw-derived OMs, AOM input greatly increased the dissolved organic carbon concentrations in soil but resulted in a greater decrease in tryptophan-like fractions while accelerated the formation of high-molecular-weight fractions in soil DOM. Moreover, AOM input significantly increased MeHg concentrations in the pore water by 19.43%–3427.66% and 52.81%–5846.57% compared to rape- and rice-derived OMs, respectively (P < 0.05). And, a similar MeHg changing pattern was also observed in the overlying water (10–25 d) and the soil solid-phase particles (15–25 d) (P < 0.05). Correlation analysis revealed that MeHg concentrations in the AOM-added soil-water system had significantly negative and positive relationships with the tryptophan-like C4 fraction and molecular weight (E2/E3 ratio) of soil DOM, respectively (P < 0.01). These findings suggest that AOM has a higher capacity than crop straw-derived OMs to promote MeHg production and accumulation in the Hg-contaminated paddy soils by creating a favorable soil DOM variation and providing more microbial electron donors and receptors.

Sources, Migration, Transformation, and Environmental Effects of Organic Carbon in Eutrophic Lakes: A Critical Review.

Organic carbon (OC) plays a leading role in the carbon cycle of lakes and is crucial to carbon balances at regional and even global scales. In eutrophic lakes, in addition to external river inputs, the decomposition of endogenous grass and algae is a major source of organic carbon. Outbreaks of algal blooms (algal eutrophication) and the rapid growth of aquatic grasses (grass eutrophication) can lead to the accumulation and decay of large amounts of algae and aquatic grass debris, which increases the intensity of the carbon cycle of lakes and greatly impacts aquatic environments and ecosystems. The structures, decomposition processes, and distribution characteristics of algae and higher aquatic plant debris in eutrophic lakes are different from mesotrophic and oligotrophic lakes. Studying their accumulation dynamics and driving mechanisms is key to further understanding lake carbon cycles and their many interdependent pathways. This paper focuses on the carbon sources, tracing technologies, migration and transformation processes, and environmental effects of OC in eutrophic lakes. Based on the existing knowledge, we further combed the literature to identify the most important knowledge gaps preventing an in-depth understanding of the processes and driving mechanisms of the organic carbon cycle in eutrophic lakes.

Cyanate dynamics under algal blooms and sediment resuspension events in a shallow micro-tidal estuary in the lower Chesapeake Bay

Although an emerging component in the marine nitrogen (N) cycle, cyanate concentrations and cycling have not been examined in estuarine systems to date. To better understand controls on cyanate concentrations in estuaries, time series data of cyanate and nutrient concentrations in the Lafayette River, a micro-tidal, sub-tributary of the lower Chesapeake Bay, were examined between June and September 2018, and May to September 2019. Cyanate concentrations ranged from near the detection limit (0.4 nmol L−1) to 82.9 nmol L−1 in 2018, and 6.8–207.4 nmol L−1 in 2019. Variations in cyanate concentrations were highly correlated with chlorophyll biomass in the summer, biomass degradation in early fall, and sediment resuspension that occurred in response to meteorological forcing. Cyanate concentrations increased after Chl a concentrations decreased suggesting algal decomposition as a source of cyanate. High cyanate concentrations in bottom waters, corresponded to wind-induced sediment resuspension events in the Lafayette River, again suggesting organic matter decomposition as a source of cyanate. Cyanate concentrations in sediment pore water varied between years; in summer 2018, cyanate concentrations were up to 150 nmol L−1, while in 2019, they were three times lower. To confirm an algal source for cyanate, a degradation experiment was conducted using Lafayette River water collected during a bloom of Margalefidinium polykrikoides in 2018. In dark incubation bottles, cyanate was one of the first labile organic nitrogen products produced, suggesting the contention that high concentrations of cyanate in late summer and fall were the result of organic matter decomposition. Neither cyanate nor ammonium accumulated in light bottles suggesting production and uptake are tightly coupled and microbes have a high affinity for cyanate in the light. In dark bottles, cyanate production rates were 6.8 nmol L−1 d−1, while microbial removal rates during the late phase of degradation were 1.5 nmol L−1 d−1, suggesting that cyanate may not be a preferred nitrogen substrate for microbes (including nitrifiers) in dark bottles or that microbes have a lower affinity for cyanate in the dark, allowing cyanate to reach steady state at concentrations greater than the detection limit.

Metabolic activity on Biolog FF MicroPlate suggests organic substrate decomposition by Aspergillus terreus NTOU4989 isolated from Kueishan Island Hydrothermal Vent Field, Taiwan

Aspergillus terreus NTOU4989 was isolated from sulfur sediment collected at Kueishan Island Hydrothermal Vent Field, Taiwan, and was shown to be able to grow at 45 °C and pH 3 in seawater, characteristics of hydrothermal vent sites. Fungi are one of the major decomposers in the marine environment, and to find out whether A. terreus NTOU4989 can fulfill such a role at the site, this study investigated its metabolic activity using the Biolog FF MicroPlate™ under different growth conditions (45 °C/pH 3, 45 °C/pH 7, 25 °C/pH 3, 25 °C/pH 7) with/without addition of Al 3+ , Fe 2+ and Mn 2+ , major metal ions in the vent effluent. The greatest metabolic activity was observed at 25 °C/pH 3 with/without the metal ions based on substrate richness (R S , metabolic richness), average well colour development (AWCD, metabolic capacity) and average well turbidity development (AWTD, mycelial production). Significant low R S , AWCD and AWTD were observed at 45 °C, suggesting that A. terreus NTOU4989 is a thermotolerant fungus. The presence of the metal ions did not have a significant effect on its metabolic activity. Monomers of lignin, cellulose and hemicellulose, and common sugars and amino acids of algae were utilized in selected conditions, providing evidence of wood and algal decomposition by the fungus at the hydrothermal vent site.

Enhanced performance of algal decomposition of electrolysis under cavitation

A clean water system is single important building block of ecosystems and has an apparent relationship between healthy ecosystems and healthy people. The global water conditions have been deteriorated, the vital water resources should be kept clean. A development of new water purification technology is urgent nowadays, since the original biological treatments are not sufficient for the reason that they have some disadvantages, such as high cost and low efficiency. Thus, this paper presents the detailed experimental data about the development of the water purifier by a venturi-type nozzle with electrodes using electrochemical technology, called electrolysis. Several pairs of iridium/ruthenium-coated titanium plates were used as electrodes. Optimal applied current, number of electrodes and flow rate of water were decided for decomposition of representative solution(p-nitrosodimethylaniline). And the electrodes were installed in the tube with the venturi nozzle for generating cavitation. By the bubbly flow induced by electrolysis of the electrodes, the cavitation effect of water could be enhanced with relatively lower powered water pumps. Finally, the prototype of a water purifier with electrodes and venturi nozzle was developed and proved its advantages for decomposition of algal bloom. As a result, the energy saving high efficiency water purifier has been developed in this study.

Phosphorus control and dredging decrease methane emissions from shallow lakes

Freshwater ecosystems are an important source of the greenhouse gas methane (CH4), and their emissions are expected to increase due to eutrophication. Two commonly applied management techniques to reduce eutrophication are the addition of phosphate-binding lanthanum modified bentonite (LMB, trademark Phoslock©) and dredging, but their effect on CH4 emissions is still poorly understood. Here, this study researched how LMB and dredging affected CH4 emissions using a full-factorial mesocosm design monitored for 18 months. The effect was tested by measuring diffusive and ebullitive CH4 fluxes, plant community composition, methanogen and methanotroph activity and community composition, and a range of physicochemical water and sediment variables. LMB addition decreased total CH4 emissions, while dredging showed a trend towards decreasing CH4 emissions. Total CH4 emissions in all mesocosms were much higher in the summer of the second year, likely because of higher algal decomposition and organic matter availability. First, LMB addition lowered CH4 emissions by decreasing P-availability, which reduced coverage of the floating fern Azolla filiculoides, and thereby prevented anoxia and decreased surface water NH4+ concentrations, lowering CH4 production rates. Second, dredging decreased CH4 emissions in the first summer, possibly it removed the methanogenic community, and in the second year by preventing autumn and winter die-off of the rooted macrophyte Potamogeton cripsus. Finally, methanogen community composition was related to surface water NH4+ and O2, and porewater total phosphorus, while methanotroph community composition was related to organic matter content. To conclude, LMB addition and dredging not only improve water quality, but also decrease CH4 emissions, mitigating climate change.

The variations of labile arsenic diffusion driven by algal bloom decomposition in eutrophic lake ecosystems

The vertical labile arsenic (As) concentration and diffusion pattern variations in eutrophic lakes were investigated using in situ techniques of diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper) in the typical eutrophic system of Lake Taihu in China. In addition, simulation experiments were used to reveal labile As distributions in sediment profiles under the influence of algae blooms and wind fluctuations. Our results indicated that eutrophication could lead to the migration and transformation of As fractions, including increased As bioavailability, as well as varied diffusion patterns. The sulfate released from algae decomposition reduced to H2S and formed FeS, which weak adsorbability contributed to the increased mobility of the As fractions. Meanwhile, further decomposition released a large quantity of algae-derived organic matter which competed with the adsorbed As, leading to more endogenous As migrating to the overlying water. Accordingly, the H2S production presented a likely explanation for the changed distribution of labile As and contributed to labile As concentrations in the sediment profiles significantly increasing at depths of −20 mm to −60 mm in the early stages of the simulation experiment. Moreover, the areas of enhanced diffusion patterns with high concentrations of As obviously expanded. However, following the complete decomposition of the algae, the organic matter component significantly changed, suggesting an explanation for the variations in distribution of labile As. All the diffusion pattern variations showed similar trends. Consequently, variation of labile As diffusion patterns could indicate the decomposition and eutrophication levels of freshwater ecosystems.

A Mathematical Study on Rising Pressures of Carbon Emissions and Acidity in Aquatic Bodies

Contamination of water bodies is one of the alarming concerns of today’s times calling for immediate attention and action. Accelerated industrialization and other human-driven activities have given way to abrupt spike in the carbon emissions. These carbon emissions are absorbed by the water bodies. As a resultant of this absorption, the carbon reacts with oxygen present in water, forming carbonic acid and causes the pH level of water to decrease, thus, causing water acidification. The acidity of water also increases due to discharge of wastes and pollutants into aquatic bodies. Also, the carbon induced global warming leads to an increase in the temperature of water which further leads to a decline in level of dissolved oxygen in aquatic bodies. Besides, these phenomena cause a rise in the growth of algal bloom, which depletes the dissolved oxygen concentration in water due to consumption of dissolved oxygen in algal decomposition process. To investigate these impacts of increasing acidity and rising carbon emissions on the aquatic populations, a non-linear mathematical model is proposed and analysed. Numerical simulations using MATLAB are performed in order to support the analytical results.