Biotic connectivity between ecosystems can provide major transport of organic matter and nutrients, influencing ecosystem structure and productivity
, yet the implications are poorly understood owing ...to human disruptions of natural flows
. When abundant, seabirds feeding in the open ocean transport large quantities of nutrients onto islands, enhancing the productivity of island fauna and flora
. Whether leaching of these nutrients back into the sea influences the productivity, structure and functioning of adjacent coral reef ecosystems is not known. Here we address this question using a rare natural experiment in the Chagos Archipelago, in which some islands are rat-infested and others are rat-free. We found that seabird densities and nitrogen deposition rates are 760 and 251 times higher, respectively, on islands where humans have not introduced rats. Consequently, rat-free islands had substantially higher nitrogen stable isotope (δ
N) values in soils and shrubs, reflecting pelagic nutrient sources. These higher values of δ
N were also apparent in macroalgae, filter-feeding sponges, turf algae and fish on adjacent coral reefs. Herbivorous damselfish on reefs adjacent to the rat-free islands grew faster, and fish communities had higher biomass across trophic feeding groups, with 48% greater overall biomass. Rates of two critical ecosystem functions, grazing and bioerosion, were 3.2 and 3.8 times higher, respectively, adjacent to rat-free islands. Collectively, these results reveal how rat introductions disrupt nutrient flows among pelagic, island and coral reef ecosystems. Thus, rat eradication on oceanic islands should be a high conservation priority as it is likely to benefit terrestrial ecosystems and enhance coral reef productivity and functioning by restoring seabird-derived nutrient subsidies from large areas of ocean.
•This review focused on the generation of biohydrogen from macroalgae.•Key issues affecting H2 production via dark fermentation are presented.•Discussed various strategies for 5-HMF removal and ...detoxification.
(Red, green and brown) macroalgal biomass is a propitious candidate towards covenant alternative energy resources to be converted into biofuels i.e. hydrogen. The application of macroalgae for hydrogen fermentation (promising route in advancing the biohydrogen generation process) could be accomplished by the transformation of carbohydrates, which is a topic receiving broad attention in recent years. This article overviews the variety of marine algal biomass available in the coastal system, followed by the analyses of their pretreatment methods, inhibitor formation and possible detoxification, which are key-aspects to achieve subsequent H2 fermentation in a proper way.
Since 2008, macroalgal blooms of Ulva prolifera (also called green tides) occurred every summer in the Yellow Sea (YS), causing environmental and economic problems. A number of studies have used ...satellite observations to estimate the severity of the blooms through estimating the bloom size and duration. However, a critical bloom parameter, namely biomass, has never been objectively determined due to lack of measurements. In this study, laboratory experiments were conducted to measure U. prolifera biomass (wet weight) per unit area and the corresponding spectral reflectance, through which a robust relationship has been established to link biomass per area to the reflectance-based floating algae index (FAI). The lab-based model has been validated with in situ measurements, with an estimated relative uncertainty of <16% for algae with FAI values <0.2 (corresponding to ~2kg/m2 biomass and accounting for >99.5% of the algae-containing pixels in satellite images). The model was further transferred to MODIS Rayleigh-corrected reflectance (Rrc), where aerosol impacts on the model were simulated under various atmospheric conditions. The simulations showed an average of 6.5% (up to 12.3% for the extreme case) uncertainties in biomass estimates when MODIS Rrc data were used as the model inputs. The dry biomass per wet biomass and carbon and nitrogen contents per dry biomass were also determined through lab experiments, thus making their estimation possible from MODIS Rrc data. The model was then applied to time-series of MODIS observations over the YS between 2008 and 2015 to determine the inter-annual variability of these critical parameters. Results showed maximum daily biomass of >1.7milliontons during June 2015 and minimum daily biomass of <0.09milliontons during 2012. The ability to estimate U. prolifera biomass at given locations from the near real-time MODIS images is expected to significantly enhance the capacity of an existing monitoring system to provide quantitative information for decision making.
•Biomass (wet and dry weights, carbon, nitrogen) per area of U. prolifra measured•Model established and validated to relate biomass per area to reflectance•Model applied to MODIS 2008–2015 data to determine biomass distributions
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•Living algae were applied to concentrate and recover critical rare earth elements.•G. gracilis removed 70% of 500μgL−1 solutions of Y, Ce, Nd, Eu and La in 48h.•In mixtures, ...selectivity was not observed although removal of lanthanides improved.•Uptake of these emergent contaminants by algae followed the Elovich kinetic model.•Nearly 100% of all elements were recovered in a 300-fold more concentrated solution.
The experiments performed in this work proved the ability of Gracilaria gracilis to concentrate and recover Critical Rare Elements (CRE) from contaminated waters. The importance of recycling these elements is related to their very limited sources in Nature and progressive use in technologies. Moreover, their mining exploitation has negative environmental impact, and recent studies point them as new emerging pollutants. To the best of our knowledge, this is the first report on the application of living macroalgae for the removal and recovery of CRE. G. gracilis (2.5gL−1, fresh weight) was exposed to mono- and multi-element saline solutions of 500μgL−1 of Y, Ce, Nd, Eu and La. Removal was up to 70% in 48h, with bioaccumulation following Elovich kinetic model. In multi-element solutions, selectivity was not observed although removal of lanthanides improved comparatively to single-element solutions. No mortality or adverse effect on growth was registered. The subsequent macroalgae digestion allowed collecting virtually 100% of all elements in a 300-fold more concentrated solution. The overall results suggest the application of living macroalgae as a simple and effective alternative technology for removing and recovering CRE from wastewaters, contributing to an improvement of water quality and CRE recycling.
•Process water recycling of Laminaria hydrothermal carbonization was investigated.•The solid yield and high heating value of hydrochar increased during recirculation.•The inorganic salt and organic ...acids could catalyze hydrothermal carbonization.•Organic acids predominantly accumulated with the process water recirculation.•High proportion of organic acids in process water promoted methane production.
Hydrothermal carbonization (HTC) is a promising thermo-chemical technology to treat wet biomasses for production of hydrochars but produces excessive process water. In this study, recirculation of process water from HTC of macroalgae Laminaria was investigated for 12 rounds. Recycling process water increased the hydrochar yield, carbon recovery rate and high heating value from 13.3% to 17.1%, from 22.9% to 32.6%, and from 18.4 MJ/kg to 20.5 MJ/kg after 12 rounds, respectively. The process water recirculation could partly alleviate the toxicity of process water through seed germination test. Volatile fatty acids (VFAs) predominantly accumulate with process water recirculation. The increased proportion of VFAs on chemical oxygen demand could promote methane production of diluted process waters, a 12.3% increase was observed in the round 10, compared with initial process water. These results showed that recycling the process water could reduce water consumption significantly and enhance energy recovery efficiency.
Almond shell is one of the most abundant agricultural wastes in Kurdistan province of Iran. Conversion of almond shell into hydrogen-rich gas via supercritical water gasification (SCWG) was ...investigated in this study using a tubular batch micro-reactor system. Non-catalytic tests were carried out in different conditions to determine the optimum condition for H2 production. Maximum hydrogen yield of 7.85 mmol/g, was observed in the temperature of 460 °C, residence time (RT) of 10 min and feed/water ratio (F/W) of 0.01. Catalytic experiments were performed using hydrochars as solid residues remained after SCWG of Cladophora glomerata (C. glomerata) macroalgae and wheat straw. Hydrochars were characterized by ICP-OES, FESEM and BET methods. For catalytic experiments, hydrochars were added to the almond shell by the weight ratio of 0.4. Conversion of almond shell and hydrogen production, were more influenced by the presence of inorganic compounds in the hydrochars rather than the surface area and pore volume. The maximum hydrogen yields of 10.77 and 11.63 mmol/g, were observed for catalytic experiments in the presence of wheat straw and C. glomerata hydrochars, respectively.
•Hydrothermal gasification of almond shell for hydrogen-rich gas production.•Characterization of Cladophora glomerata and wheat straw hydrochars.•H2 and CO2 promotion in the presence of hydrochars as catalysts.•Higher catalytic activity of the algal hydrochar than agricultural hydrochar.
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•The removal of Hg from water by living algae was investigated at realistic levels.•All seaweeds showed huge accumulation capabilities, reaching up to 209μgHgg−1.•U. lactuca achieved ...99% of removal, leading to Hg levels in seawater below 1μgL−1.•Bioaccumulation was more advantageous than biosorption in terms of efficiency.•The volatilization of Hg or its conversion to organometallic forms was negligible.
This study aimed to assess and explore the bioaccumulation capabilities of three different macroalgae species, Ulva lactuca (green), Gracilaria gracilis (red) and Fucus vesiculosus (brown), very common on temperate coasts and estuaries, for the removal of mercury (Hg) from contaminated waters (with high salinity), using environmentally realistic concentrations of metal (10–100μgL−1). Levels of Hg accumulated by all seaweeds ranged between 20.8 and 208μgg−1, corresponding to bioconcentration factors of c.a. 2000. A comparative evaluation of bioaccumulation (living biomass) and biosorption (dried biomass) was performed for U. lactuca, which had displayed the best performance in accumulating Hg. The removal conducted by the living seaweed (mmacroalgae/Vsolution≈500mgL−1), although slower, was more promising since all Hg levels were reduced by about 99%, fulfilling the European criteria for drinking water quality. Pseudo-second-order and Elovich models described quite well the experimental data, assuming a process essentially of chemical nature. Determination of total Hg content in algal biomass over time, allowed to confirm and to follow the uptake of this metal by the living organism. Volatilization of Hg or its conversion to organo-metallic forms (0.02–0.05%) was negligible during the decontamination process.
Overall, the results are a contribution for the development of an efficient and cost-effective water remediation biotechnology, based on the use of living macroalgae to promote the removal of Hg.
Global outlook of biofuels turns out to be a full-fledged search focusing the viability and sustainability assets. The present day option for immediate and sustainable alternate fuels lies with algal ...biofuels. Algae are the most sustainable fuel resource in terms of food security and environmental issues. Inefficient and unsustainable biofuel derived from food crops twosome food security issues thus increasing interests towards algal energy. CO2 mitigation, quick biomass accumulation accomplishing simultaneous bioremediation have gathered progressive attention. Cultivation of biomass, harvesting, processing and fuel production by chemical/biochemical reactions are the sequential stages in algal biofuel production. Currently, biofuels produced from algal biomass is not economical since biomass cultivation, processing and separation of fuel products appears costly although certain advancements in culturing techniques have been recently unearthed. Further improvements with the biomass processing strategies may step up the third-generation biofuel concept a profitable one in the near future. This article reviews various cultivation methods, processing techniques and stages in algal biofuel production thereby extensively investigating their potential application in biofuel refineries.
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•Fe0 nanoparticles (Fe0 NPs) could improve H2 production from macroalga.•Hydrogen production was enhanced by 6.5 times comparing to control test.•Fe0 NPs promoted hydrogen production ...and acid accumulation.•Fe0 NPs enriched Clostridium and Terrisporobacter sp.
In this work, effect of Fe0 nanoparticles (Fe0 NPs) on macroalgae fermentation was explored. Hydrogen production was significantly enhanced by 6.5 times comparing with control test, achieving 20.25 mL H2/g VSadded with addition of 200 mg/L Fe0 NPs. In-depth analysis of substrate conversion showed that both hydrogen generation and acids accumulation were promoted with Fe0 NPs supplementation. Microbial analysis demonstrated that both hydrogen-producing strains belonging to genus Clostridium and Terrisporobacter sp. favorable for acids formation were enriched with Fe0 NPs supplementation, while species Acinetobacter lwoffii beneficial to organics mineralization was eliminated. Complex substrate compositions resulted in more prevalent cooperative relationships among species in the system. This study suggested that Fe0 NPs plays a crucial role in macroalgae fermentation by affecting the microbial distribution, subsequently influencing the products distribution and energy conversion.
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