Macroalgal Biomass Research Articles

Pollution affects even oceanic marine protected areas in Southwestern Atlantic.

Reefs are facing a global decline with sewage pollution emerging as a significant and poorly understood threat. Inadequate wastewater management and disorderly urbanization contributes to water pollution globally. Tropical Southwestern Atlantic comprises a set of oceanic Marine Protected Areas (MPAs) including the Fernando de Noronha Archipelago in Brazil, which has experienced significant population growth without expanding the sewage infrastructure. We mapped and quantified marine pollution in these MPAs, characterizing pollution sources and evaluating their effects on benthic and fish communities in 13 reef sites. We quantified nutrients, metals and metalloid, microplastics, fecal sterols, and Polycyclic Aromatic Hydrocarbons (PAHs) in both water and sediment samples. We also used isotopic tracing on macroalgae to identify the origin of organic matter and characterized benthic and fish communities, and algae biomass at each site. Pollution was more pronounced in the multiple-use area but also affected no-take areas. Effluents from wastewater treatment plants did not meet legislative standards, and reefs in the multiple-use area were enriched in orthophosphate and ammonia compared to those in the no-take area. Nitrogen isotopes in macroalgae revealed sewage-derived nitrogen throughout the multiple-use area. Nutrient enriched sites exhibited higher abundances of fast-growing and opportunistic green macroalgae, and higher biomass of brown macroalgae. The port area, within the multiple-use area, showed high PAHs, coprostanol and metal(loid) concentrations, suggesting untreated sewage and nautical chemical pollution. Microplastics were widespread in sediment and water samples. We documented the pervasive impacts of marine pollution on reef habitats even within marine protected areas in oceanic regions, demonstrating that local pollution control, sewage management and regulating procedures in port areas are critical to protect marine ecosystems. Comparisons with previous studies suggest marine pollution has substantially increased in the Archipelago in the last ten years. This is the first comprehensive assessment of marine pollution in an oceanic environment in Southwestern Atlantic, showing these isolated environments are not immune to pollution impacts.

Conversion of Kappaphycus alvarezii macroalgae biomass enriched with fulvic acid into a foliar biostimulant for plant (Oryza sativa L.) growth and stress protection

BackgroundThe incorporation of circular economy into agricultural processes is necessary to improve the efficiency of agronomic practices in the future. The biomass of macroalgae as well as humic substances is sustainable options for stimulating the efficient use of nutrients in plants. This study aimed to evaluate the modes of action of a potential plant biostimulant composed of an aqueous extract of Kappaphycus alvarezii seaweed plus fulvic acid (KAF) applied to rice (Oryza sativa L.) leaves. The aqueous extract was obtained from the fresh biomass of the macroalga Kappaphycus alvarezii and the fulvic acid was extracted from a cattle manure vermicompost (FAVC). Both fractions (KAlv-sap and FAVC) were characterized using 1H NMR. The bioactivity of KAF was evaluated in experiments with four treatments: control (foliar application of water), FAVC (foliar application of FAVC), KAlv-sap (foliar application of seaweed extract), and KAF (foliar application of FA + KAlv-sap). In rice, the expression of genes related to K+ and N transport, plasma membrane H+-ATPases, and oxidative stress defense enzymes were evaluated. Metabolites and N, K, and P contents, as well as photosynthetic efficiency and root morphology, were quantified.ResultsThe 1H-NMR spectra showed that KAF is rich in organic fragments such as sugars, nitrogenous, aromatic, and aliphatic compounds in general. Foliar application of KAF resulted in a 7.1% and 19.04% increase in the dry mass of roots and leaves, respectively. These plants had 19% more roots and 11% more total root length. The application of KAF increased in the plant sheaths the N and K contents by up to 50% and 14%, respectively.ConclusionsThe mechanism of action by which KAF triggered these changes seemed to start with an improvement in the photosynthetic efficiency of plants and regulation through increased expression and suppression of genes related to K+, N, H+-ATPase transporters, and oxidative metabolism. KAF might become a sustainable plant biostimulant that promotes plant growth, development, and defense against abiotic stresses.Graphical

Efficient and sustainable approach of heavy metal adsorption from wastewater using algal biomass of Hypnea valentiae (Turner) Montagne, 1841

The biosorption of heavy metals especially, Cd2+, Pb2+, and Zn2+ from wastewater were evaluated using the biomass of macroalgae, Hypnea valentiae found in coastal waters of Rameshwaram, Tamil Nadu, India. The probable functional groups involved in the biosorption process was analyzed by Fourier transform infrared spectroscopy. The specific surface area, pore volume and pore diameter of prepared biosorbent was determined by Brunauer–Emmett–Teller (BET) analysis and it was found to be 59.993 m2 g−1, 0.292 cc g−1 and 1.429 nm, respectively. The scanning electron microscopy images after the biosorption revealed that the heavy metals have been adsorbed on to the surface of biosorbent. The optimization study was performed using Box–Behnken design and the optimum parameters used were initial concentration of metal ions (10–500 mg L−1), biomass dose (5–25 g L−1), contact time (10–120 min), temperature (25–45 °C), agitation speed (60–120 rpm) and pH (2–14). The heavy metal uptake (biosorption) was assessed by isotherm models including Dubinin–Radushkevich (D–R), Freundlich and Langmuir models. The maximum sorption of metal ions was observed in Langmuir isotherm model (R L 0.1773 and K F 2.2030 L mg−1) with an R 2 value close to 0.99 clearly indicating the chemical mode of metal ion adsorption. Also, the sorption of Cd2+, Pb2+, and Zn2+ on to the surface of algal biomass followed pseudo-second-order kinetics with a rate constant, k2 being 9.627 × 10−3 g (mg min) −1 and qe being 93.98496 mg g−1, strongly supporting the chemisorption mechanism. The computed thermodynamic parameters (ΔG°, ΔH, and ΔS) demonstrated an endothermic, spontaneous biosorption that was feasible. The maximum removal efficiency was achieved for Pb (92.86%) followed by Cd (91.48%) and Zn (87.32%). The biosorbent can be reused and regenerated up to four cycles efficiently. There was a significant reduction in the biological oxygen demand, chemical oxygen demand, total dissolved solids, and pH of wastewater after treatment with the biosorbent. From this study, it is assessed that the biomass from red algae can be utilized for the biosorption of heavy metals from polluted water which is cost-effective and eco-friendly.

Pyrolysis of macroalgae biomass from Nitella hyalina and its thermokinetics

Pyrolysis of macroalgae biomass from Nitella hyalina and its thermokinetics

Techno-economic feasibility study of macroalgae for anaerobic digestion

The techno-economic feasibility of brown macroalgae biomass species Saccharina latissima (S. Latissima) for anaerobic digestion (AD) in North West Europe was investigated in this research. The feasibility of the biomass as a single feedstock and for co-digestion was tested. In the techno economic analysis, AD of S. Latissima as a single digestion feedstock was found to be economically not viable due to the relatively high price of the macroalgae biomass. However, co-digestion with sugar beet — vegetable mix combined with a gate fee of 29 Euros per tonne was found to be economically viable with the macroalgae biomass priced at 50 Euros per tonne.

The effects of voltage, particle size, and temperature on bio-oil yield produced via pyrolysis of Sargassum sp

Abstract The energy demand is increasing due to population growth and economic activities. Currently, global energy production, including in Indonesia, heavily relies on fossil fuels like petroleum, which are depleting day by day. One renewable energy form for the future is bio-oil, produced through pyrolysis using biomass as raw material. Macroalgae biomass, particularly Sargassum sp., is a sustainable and net-zero emission source for renewable energy. Pyrolysis is a promising technique to convert Sargassum sp. into high-value charcoal, gas, and bio-oil with less than 20% moisture content. Experimental research was conducted using a simple slow pyrolysis setup, using Sargassum sp. from Pantai Trenggole, Gunung Kidul. Proximate analysis showed Sargassum sp. contains ash, water, volatile matter (Vm), fixed carbon (FC), and calorific value of 15.428%, 6.032%, 40.222%, 38.318%, and 2161.758 cal/g respectively. Regarding the experiment results, the maximum bio-oil yield was obtained at 200 V with a yield of 27.289%. For the particle size variable, the maximum bio-oil yield was achieved with particles of 10-40 mesh, resulting in 27.289% yield. Regarding the temperature variable, the highest bio-oil yield was obtained at 600 °C with a yield of 29.362%.

Influence of pyrolysis time on removal of heavy metals using biochar derived from macroalgal biomass (Oedogonium sp.)

In this study, pyrolysis was performed at different times to convert Oedogonium biomass into biochar. The physicochemical properties show that the pyrolysis time significantly impacts structural and morphological changes in biochar samples. The influence of pyrolysis time on the removal of multiple heavy metals was investigated. Owing to the presence of abundant functional groups, inorganic minerals and porous nature, biochar obtained from a 40 min pyrolysis time showed higher removal efficiency of heavy metals compared to biochars pyrolyzed at 20 mins and 60 mins even with higher concentrations of metal ions. The maximum adsorption capacity was observed 9.33, 10.74, 322.58, 13.70 and 9.11 mg/g with the biochar prepared at the pyrolysis time of 40 mins for Co, Ni, Cu, Zn and Cd, respectively. The adsorption isotherm is well fitted with the Langmuir adsorption model for heavy metals adsorption, and the kinetic study is well-defined by a pseudo second-order model.

Community gross primary production and respiration in epilithic macroalgae and Posidonia oceanica macrophytodetritus accumulation in the Bay of Revellata (Corsica)

We report estimates of community gross primary production (GPP), community respiration (CR), and net community production (NCP) based on the change of dissolved O2 during incubations over epilithic turf-forming macroalgae (Halopteris scoparia, Padina pavonica, and Dictyota dichotoma) on 7 occasions and in accumulations of Posidonia oceanica macrophytodetritus (i.e. litter) on 8 occasions in the Bay of Revellata (Corsica) from March 2009 to May 2011. In the epilithic macroalgae community, GPP ranged between 7.8 and 82.2 mmol O2 m−2 d−1, CR ranged between −108.5 and −13.6 mmol O2 m−2 d−1, and NCP ranged between −53.2 and −5.7 mmol O2 m−2 d−1. In the P. oceanica macrophytodetritus accumulation, GPP ranged between 5.7 and 91.6 mmol O2 m−2 d−1, CR ranged between −112.8 and −27.2 mmol O2 m−2 d−1, and NCP ranged between −46.8 and −9.9 mmol O2 m−2 d−1. GPP in both the epilithic macroalgae community and the P. oceanica macrophytodetritus accumulation peaked in summer and was lowest in fall, following the seasonal variation of incoming light. GPP correlated to macroalgal biomass but was unrelated to the biomass of living macroscopic plant material in the P. oceanica macrophytodetritus accumulation. The annual average of GPP was equivalent in the epilithic macroalgae and P. oceanica macrophytodetritus accumulation communities (17.6 and 19.4mol O2 m−2 yr−1). Both the epilithic macroalgae community and the P. oceanica macrophytodetritus accumulation were net heterotrophic with an annual average NCP of −6.1 and −8.8mol O2 m−2 yr−1, respectively. The NCP of the adjacent P. oceanica meadow at 10 m depth based on simultaneous measurements based on the open water O2 mass balance from moored O2 probes (optodes) was 28.9mol O2 m−2 yr−1. The potential export of dissolved organic carbon from the P. oceanica meadow could quantitatively meet the carbon demand to sustain the net heterotrophy of the adjacent epilithic macroalgae community in the Bay of Revellata. We also show the limitation and possibly over-estimation of extrapolating decay rates based on litter bag experiments with small quantities of material to “real” macrophytodetritus biomass densities.

Acoustic mapping reveals macroalgal settlement following a retreating glacier front in the High Arctic

Vegetated coastal marine ecosystems are projected to expand northwards in the Arctic due to climate change, but the mechanisms for this expansion are complex and nuanced. Macroalgal biomass in the littoral areas of Svalbard has been increasing, but data at the glacier fronts are very scarce. In this study, we use hydroacoustics and video validation from an unmanned surface vehicle to survey macroalgal bed distribution along the coast of a High Arctic fjord (Billefjorden, Svalbard), including river bays and land- and sea- terminating glacier fronts, as well as oceanographic measurements to indicate physical drivers of macroalgal settlement. We found high variation of macroalgal coverage along the fjord coastline, with virtually no macroalgae in the river bays but abundant coverage in areas with little terrestrial runoff. Furthermore, the presence of kelp was found at the land-terminating glacier front which has recently retreated from the sea, which suggests the potential for rapid macroalgal establishment in newly available substrate following glacial retreat. These findings suggest large ecological implications throughout the Arctic, in which macroalgal expansion may lead to significant changes in the underwater coastal landscape and ecosystem. This study shows that the use of remote autonomous vehicles and hydroacoustic mapping with video validation has a high potential for sustainable and efficient ecological monitoring.

Observing changes of fish community in a semi-arid subtropical coastal lagoon subject to ecological conservation

El Soldado is a semi-arid subtropical coastal lagoon subject to ecological conservation in the Gulf of California, where we reviewed the changes in the fish community structure before (1972; 1978–79; 1990–92) and after (cycle 1, 2018–2019; cycle 2, 2019–2020) the decree as a protected area, and we determined spatio-temporal changes between two consecutive annual cycles. We conducted monthly fish sampling cycles 1 and 2 with a small trawl net at three sites, where water and sediment variables were recorded, and drift macroalgae biomass was estimated. Results showed 99 fish species have been recorded in previous studies, and our study added 11 species. The fish assemblage (2018–2020) comprised 34 marine species and nine of them were dominant in both cycles. In general, higher fish abundance, richness, and diversity were observed in the cycle 1. Spatial changes, in both cycles, showed higher fish abundance, richness, and diversity in the innermost area of the lagoon, characterized by silty sediment and higher drift macroalgae biomass. Temporal changes showed higher fish abundance, richness, and diversity in summer-autumn during cycle 1, while during cycle 2, the higher values were in winter-autumn, mainly associated with seasonal variations in water temperature and the biogeographic affinity of fish species, but were also attributed to changes in the density of species classified as dominant. There was notable a drastic decrease of fish richness, diversity, and density during summer in cycle 2, which was attributed to be a warmer year. El Soldado fish community showed changes before and after the decree as a protected area, but also in the contiguous cycles. These changes include the addition of species, the prevalence of common species over 48 years, and the current dominant species that belong to indicator groups, which exhibit effectiveness in the conservation of this ecosystem.

Species-Specific Responses of Bloom-Forming Algae to the Ocean Warming and Acidification.

Macroalgal biomass blooms, including those causing the green and golden tides, have been rising along Chinese coasts, resulting in considerable social impacts and economic losses. To understand the links between the ongoing climate changes (ocean warming and acidification) and algal tide formation, the effects of temperature (20 and 24 °C), pCO2 concentration (Partial Pressure of Carbon Dioxide, 410 ppm and 1000 ppm) and their interaction on the growth of Ulva prolifera and Ulva lactuca (green tide forming species), as well as Sargassum horneri (golden tide forming species) were investigated. The results indicate that the concurrent rises in temperature and pCO2 level significantly boosted the growth and nutrient uptake rates of U. lactuca. For U. prolifera, the heightened growth and photosynthetic efficiency under higher CO2 conditions are likely due to the increased availability of inorganic carbon. In contrast, S. horneri exhibited negligible responsiveness to the individual and combined effects of the increased temperature and CO2 concentration. These outcomes indicate that the progressive climate changes, characterized by ocean warming and acidification, are likely to escalate the incidence of green tides caused by Ulva species, whereas they are not anticipated to precipitate golden tides.

Thermo-catalytic reforming pyrolysis of ensiled Saccharina latissima dominated macroalgal pellets for bioenergy production

Marine macroalgae is a biomass resource for the manufacture of fuels and chemicals, which can be sustainably harvested from seaweed farms or from man-made structures where it accumulates as a biofouling organism. However, in temperate regions farmed macroalgae can only be harvested between late Spring and early Summer, limiting year-round availability. Here we show that a conventional grass ensilage procedure preserves Saccharina latissima dominated biomass on the tonne scale for 30 months, enabling year-round use of this biomass. Following processing, the resulting dried and pelletised ensiled macroalgae material was subject to Thermo-Catalytic Reforming™, comprising sequential pyrolysis (450 °C) and either dry or steam catalytic reforming (700 °C) processes. Both processing methods produced a mixture of bio-oil (1.6–1.9 wt%) and hydrogen-rich permanent gases (30.9–31.1 wt%) with higher heating values of 34.8–35.4 MJ/kg and 18.0–24.2 MJ/m3, respectively, together with char (45.5–48.5 % wt). The permanent gases can be used directly for heat generation, while hydro-treatment of the bio-oil would afford a material that can be blended with traditional transport fuels. This work demonstrates that if operated at scale, the combined harvesting, ensilaging and Thermo-Catalytic Reforming™ of preserved macroalgal biomass offers a year-round decentralised energy resource.

Biorefinery of Beach Cast Seaweed in Brazil: Renewable Energy and Sustainability

Macroalgae are a natural oceanic resource of inexhaustible abundance for the biomass energy industry with growth rates that are three to four times greater than those of terrestrial plants. The objective of this study was to evaluate the sustainability of macroalgae as biomass for biorefining through two investigations. Firstly, the deposition of macroalgae was sampled through 28 collections on seven beaches in the city of Maceió, Brazil, over a two-year period using a zigzag sampling method, covering a deposition area of 135,000 m2. From this, it was estimated that daily collection would yield 5.03 t/ha of dry biomass. Secondly, the calorific values of macroalgal biomass energy and pellet compounds were calculated. The lower calorific value (8.82 MJ/kg) found from a compound of 13 species analyzed was similar to that of the main biomass used in Brazil to obtain energy, i.e., sugarcane bagasse, which has been evaluated as 8.91 MJ/kg. Macroalgal biomass in the form of condensed energy pellets was found to have a higher calorific value of 20.18 MJ/kg, i.e., 1.2% greater than the average for terrestrial biomass pellets. Based on the results obtained, it was observed that macroalgal biomass has the possibility of becoming a new renewable feedstock with potential for bioenergy. The estimates for the deposition of biomass show possibilities for producing biofuels from marine algal raw material, which provides scope for creating another sustainable alternative for global energy issues with a reduction in environmental problems.

Biosorption of reactive amoxicillin antibiotic on Pithophora macroalgae in aqueous solution: Equilibrium and kinetic studies

The removal of antibiotics is a significant environmental concern due to their complex structure. Therefore, scientists are working on novel and efficient techniques for removing antibiotic compounds from aqueous solutions. The current research aims to utilize green Pithophora macroalgae for extracting the antibiotic amoxicillin (AMX). An investigation into the kinetics and equilibrium mechanism of the biosorption of reactive AMX on macroalgae biomass in aqueous solutions has been conducted. The effects of operating factors such as initial AMX concentration, contact time, biosorbent dosage, agitation speed, and pH were investigated. FT-IR, SEM, and point of zero charge pH (PZC) techniques were used to characterize the biosorbent. The Langmuir and Freundlich isotherms were examined to determine which model better fits the experimental data. The experimental data best matches the Langmuir isotherm model for AMX biosorption, with a maximum sorption capacity of 25.83 mg g-1. The kinetic model for the experimental results follows the pseudo-second order (R2 = 0.9992). According to this study, the biomass of the macroalgae Pithophora has been shown to be a promising biosorbent for the biosorption of AMX antibiotics, making it suitable for practical water and wastewater treatment applications.

Responses at various levels of ecological hierarchy indicate acclimation to sequential sublethal heatwaves in a temperate benthic ecosystem.

Marine heatwaves have caused massive mortality in coastal benthic ecosystems, altering community composition. Here, we aim to understand the effects of single and sequential sublethal heatwaves in a temperate benthic ecosystem, investigating their disturbance on various levels of ecological hierarchy, i.e. individual physiology, trophic groups' biomass and ecosystem carbon fluxes. To do so, we performed a near-natural experiment using outdoor benthic mesocosms along spring/summer, where communities were exposed to different thermal regimes: without heatwaves (0HW), with one heatwave (1HW) and with three heatwaves (3HWs). Gastropods were negatively impacted by one single heatwave treatment, but the exposure to three sequential heatwaves caused no response, indicating ecological stress memory. The magnitude of ecosystem carbon fluxes mostly decreased after 1HW, with a marked negative impact on mesograzers' feeding, while the overall intensity of carbon fluxes increased after 3HWs. Consumers' acclimation after the exposure to sequential heatwaves increased grazing activity, representing a threat for the macroalgae biomass. The evaluation of physiological responses and ecological interactions is crucial to interpret variations in community composition and to detect early signs of stress. Our results reveal the spread of heatwave effects along the ecological hierarchical levels, helping to predict the trajectories of ecosystem development.This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

A study on anticancer and antioxidant ability of selected brown algae biomass yielded polysaccharide and their chemical and structural properties analysis by FT-IR and NMR analyses

The study was conducted to determine the chemical and structural properties of polysaccharides extracted from the marine macroalgae Nemalion cari-cariense. Furthermore, evaluate the anticancer and free radical scavenging activity of purified N. cari-cariense polysaccharide. Approximately 41.6% (w/w) of crude polysaccharide was extracted from N. cari-cariense macroalgae biomass. After deproteinization, the purified polysaccharide's major chemical composition was found to be 92.6%, with all protein content removed. The purified polysaccharide had ash and moisture % of 23.01% and 4.03%, respectively. The C, H, and N of the test polysaccharide were analyzed using GC-MS, with results of 39.21%, 5.87%, and 4.29%, respectively. Furthermore, this analysis also revealed the monosaccharide composition such as glucose, galactose, mannose, xylose, and rhamnose glucose, galactose, mannose, xylose, and rhamnose 54.62%, 29.64%, 2.8%, 5.9%, and 6.8% respectively. The molecular weight of purified polysaccharide was found as 49 kDa through PAGE analysis. The FT-IR analysis revealed that the presence of functional groups exactly attributed to polysaccharide and 1H and 13C-NMR analyses confirmed the structural properties of N. cari-cariense polysaccharide. The free radicals scavenging ability of purified N. cari-cariense polysaccharide was investigated by various assays such as total antioxidant assay (22.3%–72.5% at 50–250 μg mL−1), DPPH assay (23.6%–76.9% at 10–160 μg mL−1), OH radical scavenging assay (13.6%–70.2% at 50–250 μg mL−1 dosage, and SO radical scavenging assay (27.6–68.41% at 50–250 μg mL−1 concentration). The polysaccharide demonstrated 82.63% anticancer activity towards the A549 lung cancer cell line at 1000 μg mL−1 dosage. The findings suggest that this polysaccharide has biological applications.

Enteromorpha compressa Macroalgal Biomass Nanoparticles as Eco-Friendly Biosorbents for the Efficient Removal of Harmful Metals from Aqueous Solutions

This study focuses on the biosorption of harmful metals from aqueous solutions using Enteromorpha compressa macroalgal biomass nanoparticles as the biosorbent. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD) were employed to characterize the biosorbent. The effects of pH, initial metal ion concentration, biosorbent dosage, and contact time on the biosorption process were investigated. The maximum biosorption capacity for metals was observed at a pH of 5.0. The experimental equilibrium data were analyzed using three-parameter isotherm models, namely Freundlich, Temkin, and Langmuir equations, which provided better fits for the equilibrium data. A contact time of approximately 120 min was required to achieve biosorption equilibrium for various initial metal concentrations. Cr(III), Co(II), Ni(II), Cu(II), and Cd(II) demonstrated distinct maximum biosorption capacities of 24.99375 mg/g, 25.06894 mg/g, 24.55796 mg/g, 24.97502 mg/g, and 25.3936 mg/g, respectively. Different kinetic models were applied to fit the kinetic data, including intraparticle diffusion, pseudo-second-order, and pseudo-first-order versions. The pseudo-second-order model showed good agreement with the experimental results, indicating its suitability for describing the kinetics of the biosorption process. Based on these findings, it can be stated that E. compressa nanoparticle demonstrates potential as an effective biosorbent for removing targeted metals from water.

Algal-based biochar and hydrochar: A holistic and sustainable approach to wastewater treatment

Biochar and hydrochar are carbon-rich solid products of algal and terrestrial biomass obtained through various thermochemical processes, mainly hydrothermal liquefaction, pyrolysis, and hydrothermal carbonization. Both are regarded as economical, potent, and environmentally friendly adsorbents for wastewater remediation. The versatile applicability of biochar and hydrochar, which is due to their enhanced surface physicochemical properties, includes efficient metal biosorption, soil fertility enhancement, and carbon sequestration. Consequently, there has been an increase in research for producing and exploiting biochar and hydrochar from algae. Both micro- and macro-algal biomass have strong potential due to their sustainability footprint and distinct properties. This review focuses on a comprehensive account of the synthesis of algal biochar and hydrochar and use in wastewater treatment to develop innovative solutions for efficient mitigation of several aqueous pollutants and heavy metal ions. The review discusses the various thermochemical production routes, biophysical characterization techniques, and modes of mechanism for wastewater bioremediation. Algal-based biochar and hydrochar are reported to have higher porosity and more diverse functional groups such as amines, hydroxyl, and carboxyl compared to their cellulosic and waste-derived counterparts, demonstrating an increased wastewater remediation efficiency. In addition, presence of inorganic metal including sodium, potassium, magnesium, and phosphorus in algal chars facilitates the formation of mesopores and graphite structures, improving their cation exchange capacity. Moreover, algal chars may exhibit pH buffering capacity, which could help stabilize the pH during wastewater treatment processes. Notably, the low O/C content of algal hydrochars enhances the binding and removal of organic pollutants including toxic dyes and antibiotics. The review highlights the development of modified algal chars to enhance the porosity, surface area, structural integrity, and adsorption capacity enabling a higher bioremediation potential.

Quantifying intertidal macroalgae stocks in the NW Iberian Peninsula using unmanned aerial vehicle (UAV) multispectral imagery

Intertidal macroalgae play a fundamental role in providing various ecosystem services, and they must be managed effectively for conservation purposes. Using remote sensing techniques to monitor macroalgae is a promising way of optimizing efforts in relation to logistics and personnel. This study aimed to quantify the cover and biomass of the predominant macroalgae in a rocky intertidal zone (of area 5.9 ha) in NW Spain. Drone monitoring with multispectral sensors, in situ photography and biomass sampling were conducted in June and July, 2021 (i.e. in summer, when macroalgae are most abundant in the study area). The macroalgae were classified using Minimum Distance, Spectral Angle Mapping and Maximum Likelihood algorithms, the latter of which proved the most accurate. The fresh weight of macroalgae determined in the quadrat sampling was regressed on the cover of July to enable subsequent estimation of biomass from the classification maps. The area occupied by brown algae (phylum Ochrophyta) in July 2021 was estimated to be 5574 m2 with a biomass of 28.5 t. The remote sensing method, which did not require in-depth knowledge of programming, proved to be a rapid, effective means of estimating macroalgal cover. The method may be useful for managing commercial macroalgal stocks and monitoring protected marine areas.

Kelp forest community structure and demography in Kongsfjorden (Svalbard) across 25 years of Arctic warming.

The Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience a continuous increase in seawater temperature and glacial melt while sea-ice cover declines. In 1996/1998, 2012-2014, and 2021 macroalgal biomass and species diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen) in order to identify potential changes over time. In 2021, we repeated the earlier studies by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0, 2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m-2 at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the depth transect in 2021 was not significantly different compared to 2012/2013, the digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed into an Alaria esculenta-dominated kelp forest. Consequently, a pronounced shift in kelp forest structure occurred over time as we demonstrate that biomass allocation to thallus parts is kelp species-specific. Over the past decade, kelp demography changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth limits of all dominant brown algae declined noticeably over the last 25 years while the red algal flora abundance remained unchanged at depth. We propose that the major factor driving the observed changes in the macroalgal community are alterations in underwater light climate, as insitu data showed increasing turbidity and decreasing irradiance since 2012 and 2017, respectively. As a consequence, the interplay between kelp forest retreat to lower depth levels caused by coastal darkening and potential macroalgal biomass gain with increasing temperatures will possibly intensify in the future with unforeseen consequences for melting Arctic coasts and fjord ecosystem services.