Algal Decomposition Research Articles

Microalgal consortia for municipal wastewater treatment – Lipid augmentation and fatty acid profiling for biodiesel production

The present study investigates the phycoremediation potentials of two microalgal consortia (MAC1 and MAC2) for treating sewage water and producing biomass with high lipid, protein and chlorophyll contents. During the study, the microalgal strains were tested for lipid enhancement, biomass production and contaminant removal from wastewater. The microalgal consortia showed prolific growth in wastewater with 75% dilution and accumulated higher lipid content of 31.33% dry cell weight in MAC1. The maximum biomass (50% diluted wastewater) for both the consortia was 1.53 and 1.04 gL−1. Total chlorophyll (19.17–25.17 μg mL−1) and protein contents (0.12–0.16 mg mL−1) for both the consortia were found to be maximum in 75 WW. MAC1 was capable of removing 86.27% of total organic carbon and 87.6% of chemical oxygen demand. Approximately, 94% of nitrate and phosphate contents were removed from the initial contents of wastewater. Heavy metal removal efficiency was also found to be better and showed 85.06% Cu, 75.2% Cr, 98.2% Pb, and 99.6% Cd removal by the algal consortia. Pyrolytic decomposition of algal consortia was observed using thermogravimetric analysis. The stepwise decomposition of algae indicated distinct losses of functional groups. The gas chromatography-mass spectrometric analysis revealed the majority of saturated fatty acids followed by monounsaturated and polyunsaturated fatty acids. Thus, the present study proved that both the consortia show tremendous potential for the treatment of domestic wastewaters with successive lipid enhancement for biodiesel production.

S-type Dissolved Oxygen Distribution along Water Depth in a Canyon-shaped and Algae Blooming Water Source Reservoir: Reasons and Control.

Dissolved oxygen (DO) is a crucial indicator of water quality. DO usually shows a monotonic decrease along water depth during thermal stratification in reservoir, whereas metalimnetic oxygen minimum (MOM) is observed in some cases. Although MOM phenomena have been reported in different areas, the characteristics of different reservoirs are greatly different, and few comprehensive studies have been published regarding MOM in Chinese drinking water source reservoirs. The DO distribution along water depth was determined and the detailed reasons were clarified by two-years of field monitoring. In addition the effect of water lifting aerators (WLAs) on DO improvement was investigated in the Lijiahe Reservoir in Northwest China. A typical S-type DO distribution with two anaerobic water layers, below the epilimnion (10–25 m water depth) and above the sediment (bottom water), was observed derived from the decomposition of dead algae or organic matter and the restriction of DO vertical exchange. Moreover, after WLAs’ operation since 10 June 2018, the water body was completely mixed and DO was rich and uniform along water depth by eliminating the water stratification and inhibiting algae growth. The deep understanding of the DO distribution in a deep canyon-shaped reservoir and the technical support for reservoir restoration are meaningful for optimizing reservoir management.

Efficacy of dredging engineering as a means to remove heavy metals from lake sediments

Dredging is used worldwide to remove polluted sediments from water bodies. However, the dredging efficacy remains hard to identify. Here, we studied the efficacy of dredging engineering as a means to remove Cu, Cd, and Pb from polluted lake sediments, after six years of completion. Dissolved metals and DGT-labile metals were quantified in the non-dredged and post-dredged sediments by high-resolution dialysis (HR-Peeper) and diffusive gradients (DGT) in thin films techniques. April and July measurements showed that dredging was effectively remediate the polluted sediments. The dissolved Pb, Cd, and Cu contents decreased up to 30%, 44%, and 26%, and the DGT-labile contents decreased up to 51%, 27%, and 33% compared with the contents in the non-dredged zone. Dredging was thus proven efficient in decreasing the labile metal fractions, increasing the capacity of available solids to bind metals, and slowing the leaching of metals from available solids in the post-dredged sediments. In October and January, the dredging efficacy was counteracted by the decomposition of algae, which increased the dissolved and DGT-labile metal concentrations in the post-dredged zone.

Catalytic conversion of Venice lagoon brown marine algae for producing hydrogen-rich gas and valuable biochemical using algal biochar and Ni/SBA-15 catalyst

This study investigated the catalytic behavior of two different types of materials: (i) algal biochar and (ii) 15 wt% Ni impregnated on SBA-15 support (Ni/SBA-15), in the thermochemical decomposition of Venice lagoon brown marine algae (Sargassum). First, non-catalytic pyrolysis tests were conducted in a temperature range of 400–800 °C in a dual-bed slow pyrolysis reactor. The optimum temperature for maximized liquid yield was at the temperature of 700 °C. Biochar catalyst exhibited excellent catalytic activity toward producing aromatic compounds via Diels-Alder-type reactions. However, Ni/SBA-15, because of interconnected pores provided easy passage for reactant and product during the catalytic pyrolysis process and resulted in an improvement in total gas yield (25.87 mmol/g Sargassum) and hydrogen-rich gas production (8.54 mmol/g Sargassum). The catalytic performances of both biochar and Ni/SBA-15 catalysts were compared to biochar-based catalysts derived from red and green macroalgae. High specific surface area, large pore volume, highly ordered pore structure, and narrow pore size distribution make SBA-15 a promising catalyst support in pyrolysis of biomass.

Switching Harmful Algal Blooms to Submerged Macrophytes in Shallow Waters Using Geo-engineering Methods: Evidence from a 15N Tracing Study.

Switching the dominance from algae to macrophytes is crucial for lake management of human-induced eutrophication. Nutrients from algal sources can be utilized in the process of transition from algal blooms to macrophytes, thereby mitigating eutrophication. However, this process rarely occurs in algal bloom dominated waters. Here, we examined the hypothesis that the transition of algal blooms to macrophytes and the transfer of nutrients from algae at different temperatures (8 and 25 °C) can be facilitated by using a geo-engineering method. The results showed that the combination of flocculation and capping treatment could not only remove Microcystis aeruginosa blooms from eutrophic waters but also facilitate algal decomposition and incorporation into a submerged macrophyte ( Potamogeton crispus) biomass. The flocculation-capping treatment could trigger algal cell lysis. As compared with the control groups, the photosynthesis and respiration rate of algae were inhibited and chlorophyll-a (Chl- a) concentrations were significantly reduced in the flocculation-capping treatment groups. The 15N tracing study revealed that 3.3% and 34.8% of algae-derived nitrogen could be assimilated by Potamogeton crispus at 8 and 25 °C, respectively. The study demonstrated that the flocculation-capping method can facilitate the switchover from algae- to the macrophyte-dominated state, which is crucial for restoring the aquatic ecosystem.

High sulfide production induced by algae decomposition and its potential stimulation to phosphorus mobility in sediment

This study is devoted to addressing the effects of algae blooms on sulfur cycle and the consequent phosphorus mobility in the sediments of freshwater lake ecosystems. A mesocosm experiment was conducted to investigate these effects through monitoring the dynamics of sulfur (S), iron (Fe) and phosphorus (P) in water and sediments, and their diffusion fluxes at the sediment-water interface (SWI). In addition, the abundance of sulfate-reducing bacteria (SRB) in the water column was also detected. The addition of the algae lead to an increase of SRB, a drastic decline of sulfate and a significant increase of total dissolved sulfide (ΣS2−, the peak value of near 3.0 mmol/L on day 6) in the water column. These results suggest the sulfate reduction was dramatically promoted during algae decomposition. Indeed the ΣS2− was 2 to 3 times of SO42− initial concentration, and higher ΣS2− was produced with higher algal biomass. Moreover, the diffusive flux of ΣS2− at the SWI was negative, indicating that diffusion of ΣS2− from water column toward sediment was occurring. These results indicated that algae decomposition might also be another important source of ΣS2− (termed “algae-derived ΣS2−”) in addition to sulfate reduction. The increase of Fe(II) in surface sediment pore-water was slightly delayed compared to the ΣS2− generation in the water column, which illustrated that Fe oxyhydroxides in sediments were transformed into Fe(II) through chemical reduction of ΣS2−. Concomitantly, the vertical distribution of PO43− in high amounts algae group suggested that desorption and release of iron oxides-bound PO43− occurred in sediments. Collectively, algae bloom can boost the lake eutrophication not only through direct release of nutrients but also through the high production of ΣS2−and indirect promotion of phosphorus mobility in sediment.

Mechanisms driving phosphorus release during algal blooms based on hourly changes in iron and phosphorus concentrations in sediments

Algal growth causes a drastic change in aquatic conditions over a diel cycle, which may induce sensitive feedback systems in sediments, causing P release. In this study, a microcosm experiment was performed using a suction sampler (Rhizon) to observe changes in soluble reactive phosphorus (SRP) and soluble Fe(II) concentrations in the top 20 mm sediment layer on a 3-h time interval, at different phases of harmful algal bloom (HAB) development. The results showed that the algal blooms prevailed up to 15 days after incubation, after which the process of bloom collapse proceeded until the 70th day. The concentrations of pore-water soluble Fe(II) and SRP increased throughout the incubation period. Compared to day 1, maximum increases of 214% in soluble Fe(II) and 387% in SRP were observed at night during the bloom and collapse periods, respectively. The diffusive fluxes of Fe and P at the sediment-water interface (SWI) generally corresponded to their changes in concentrations. Hourly fluctuation in soluble Fe(II) and SRP concentrations were observed with two distinct concentration peaks occurred at 21:00 p.m. and 06:00 a.m. (or 03:00 a.m.), respectively. These findings suggest that Fe-P coupling mechanisms are responsible for the release of P from sediments. During the collapse period, soluble Fe(II) concentrations were suppressed by the increase of labile S(-II) at night. Meanwhile, SRP concentrations were decoupled from Fe cycling with small fluctuations (<11% RSD) on an hourly timescale, and the decomposition of algae was a dominant source contributing to the release of P from sediments. These results significantly improved the understanding of processes and mechanisms behind the stimulated release of P from sediments during HABs.

The secretion of organics by living Microcystis under the dark/anoxic condition and its enhancing effect on nitrate removal

Recent studies indicated that the algal decomposition produces particulate and dissolved organic carbon (DOC), and can enhance denitrification in eutrophic lakes. However, the effects of the living cyanobacteria on nitrogen cycling in eutrophic lakes were still an unknown question. This study explores a new underlying mechanism of nitrate removal which is driven by living Microcystis. The results suggested that living Microcystis significantly enhanced the nitrate removal at sediment-water interface, with a nitrate removal rate of 0.54 d−1, which was 2.57 times higher than the nitrate removal rate in the treatment without the addition of Microcystis. Measurements of Chl a and Fv/Fm confirmed that Microcystis was tolerant to the dark/anoxic condition, and the recovery experiments suggested that Microcystis could survive under such stress conditions for at least seven days. Meanwhile, DOC secreted by living Microcystis reached to 4.55 mg C mg−1 Chl a. These secretions were biodegradable hydrophilic and contained carbohydrates and proteins. Our study indicated that during blooms, sinking Microcystis cells could directly provide DOC as carbon source, then consequently enhanced the denitrification at sediment-water interface, and the interactive relationship between living cyanobacteria and permanent nitrate removal should be taken into account while studying nitrogen cycling in aquatic ecosystem.

Correlation between hydrogen yield and product distribution in algae conversion through an isopropanol/water system.

This work reports a catalytic decomposition of algae to bio-oil over an isopropanol and water mixture system. The H2 yield was adjusted by changing the ratio between isopropanol and water. In this system, the introduction of formic acid was helpful to extend the yield range. Five noble metal supported catalysts were applied and Rh/C was proved to give the highest oil yield. A correlation was established between hydrocarbon yield and H2 yield. It was useful in predicting product distribution and helping to obtain desired products. EA, GC and GC-MS were applied in product analysis.

Successful control of internal phosphorus loading after sediment dredging for 6 years: A field assessment using high-resolution sampling techniques

The effectiveness of sediment dredging for the control of internal phosphorus (P) loading, was investigated seasonally in the eutrophic Lake Taihu. The high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques were used to measure the concentrations of soluble Fe(II) and soluble reactive P (SRP) as well as DGT-labile Fe/P in the non-dredging and post-dredging sediments. The P resupply kinetics from sediment solids were interpreted using DGT Induced Fluxes in Sediments (DIFS) modeling. The results showed no obvious improvement in water and sediment quality after dredging for 6years, due to their geographical proximity (a line distance of approximately 9km). However, dredging significantly decreased the concentrations of soluble Fe(II)/SRP and DGT-labile Fe/P in sediments, with effects varying at different depths below the sediment-water interface; More pronounced effects appeared in January and April. The diffusive flux of pore water SRP from sediments decreased from 0.746, 4.08 and 0.353mg/m2/d to 0.174, 1.58 and 0.048mg/m2/d in April, July and January, respectively. DIFS modeling indicated that the P retention capability of sediment solids was improved in April in post-dredging site. Positive correlations between pore water soluble Fe(II) and SRP as well as between DGT-labile Fe and P, reflect the key role of Fe redox cycling in regulating dredging effectiveness. This effect is especially important in winter and spring, while in summer and autumn, the decomposition of algae promoted the release of P from sediments and suppressed dredging effectiveness. Overall, the high-resolution HR-Peeper and DGT measurements indicated a successful control of internal P loading by dredging, and the post-dredging effectiveness was suppressed by algal bloom.

Complete genome sequence and transcriptomic analysis of a novel marine strain Bacillus weihaiensis reveals the mechanism of brown algae degradation.

A novel marine strain representing efficient degradation ability toward brown algae was isolated, identified, and assigned to Bacillus weihaiensis Alg07. The alga-associated marine bacteria promote the nutrient cycle and perform important functions in the marine ecosystem. The de novo sequencing of the B. weihaiensis Alg07 genome was carried out. Results of gene annotation and carbohydrate-active enzyme analysis showed that the strain harbored enzymes that can completely degrade alginate and laminarin, which are the specific polysaccharides of brown algae. We also found genes for the utilization of mannitol, the major storage monosaccharide in the cell of brown algae. To understand the process of brown algae decomposition by B. weihaiensis Alg07, RNA-seq transcriptome analysis and qRT-PCR were performed. The genes involved in alginate metabolism were all up-regulated in the initial stage of kelp degradation, suggesting that the strain Alg07 first degrades alginate to destruct the cell wall so that the laminarin and mannitol are released and subsequently decomposed. The key genes involved in alginate and laminarin degradation were expressed in Escherichia coli and characterized. Overall, the model of brown algae degradation by the marine strain Alg07 was established, and novel alginate lyases and laminarinase were discovered.

Assessment of mobilization of labile phosphorus and iron across sediment-water interface in a shallow lake (Hongze) based on in situ high-resolution measurement

The internal loading of P is reported to be the main factor initiating algal blooms. However, there are only a few reports on the dynamic variation of labile P in the sediment and overlying water during the decomposition of algal. In addition, the widely perceived relationship between labile P and Fe was not supported by in situ obtained values in freshwater. Consequently, the in situ simultaneous measurement of diffusion gradients in thin-film techniques (DGT) was applied on a large scale to detect the mechanisms of labile P and Fe in a typical shallow lake (Lake Hongze). The newly developed ZrO-DGT and ZrO-Chelex DGT were combined to obtain the concentration of labile P and Fe. Results showed that decomposition of algal might be the main contributor for the concentration dots and peaks of labile P in sediment profiles, as well as for the high values on the horizontal heterogeneity index of labile P at the depth of 0–30 mm of the sediment. Moreover, there existed significant difference between the apparent diffusion fluxes of labile P and Fe across the sediment–water interface which obtained from June sampling and October sampling. The results of apparent diffusion flux in two periods indicated the sediments changed from “sink” to “source” for labile P, especially at Sites 4–8, 10, 13–14, and 18. However, the role of the labile Fe has no significantly variation in the values of the diffusion flux. This phenomenon also contributed to the poor relationship between labile P and Fe in the sediment which obtained from the October sampling. Accordingly, we conclude that algal decomposition might be essential for internal loading of P in this aquatic ecosystem, and that also be the reason for vicious circle of algal occurrence in the following year in the center of Lake Hongze.

Effect of algal bloom on phosphorus exchange at the sediment–water interface in Meiliang Bay of Taihu Lake, China

Taihu Lake, the third largest freshwater lake, is typical of many eutrophic lakes in China. In recent years, Taihu Lake is frequently suffering from extensive algal blooms which dramatically change the environmental conditions (e.g., oxygen concentration and pH) and thereafter may influence phosphorus (P) exchanges at the sediment–water interface. Here, we used the repeated ANOVA to compare the water P concentration either with or without algae addition by a mimic experiment. Over a period of 20 days of incubation, chlorophyll a (Chl-a), water temperature, dissolved oxygen (DO), oxidation–reduction potential (ORP), pH, nitrate (NO3 −), as well as the P fractions of overlying water and sediments were monitored. Results showed that compared with the Control treatment algal bloom significantly decreased DO, ORP, and pH and increased P concentration of overlying water. The first 7 days of incubation could be considered as a period of algal decomposition for the Algae treatment based on the decreased Chl-a concentration, as well as the black and smelly water. The increased total P (TP), dissolved total P (DTP), and soluble reactive P (SRP) during the initial 7 days mainly resulted from the P release from the decomposing algae when DO concentration was lower than 0.5 mg L−1, and NO3 − having a potential to suppress iron (Fe) reduction was up to 1.1 mg L−1. Subsequently, Chl-a concentration dramatically increased and reached at a maximum value on September 17, which indicated that algal growth became the dominant process. The increased P level during algal growth might result from the sediment Fe-bound P release when DO and NO3 − concentration was kept at low levels, which could be further confirmed by the lowest NaOH-extractable P (NaOH-P) in the sediments on September 19. The results indicate that influence of algal blooms on sediments P release cannot be neglected during algal decomposition as well as the followed period of algal growth in Meiliang Bay, the highly polluted region of Taihu Lake.

Physicochemical factors affecting the spatial variance of monomethylmercury in artificial reservoirs

The aim of this study was to identify how hydrologic factors (e.g., rainfall, maximum depth, reservoir and catchment area, and water residence time) and water chemistry factors (e.g., conductivity, pH, suspended particulate matter, chlorophyll-a, dissolved organic carbon, and sulfate) interact to affect the spatial variance in monomethylmercury (MMHg) concentration in nine artificial reservoirs. We hypothesized that the MMHg concentration of reservoir water would be higher in eutrophic than in oligotrophic reservoirs because increased dissolved organic matter and sulfate in eutrophic reservoirs can promote in situ production of MMHg. Multiple tools, including Pearson correlation, a self-organizing map, and principal component analysis, were applied in the statistical modeling of Hg species. The results showed that rainfall amount and hydraulic residence time best explained the variance of dissolved Hg and dissolved MMHg in reservoir water. High precipitation events and residence time may mobilize Hg and MMHg in the catchment and reservoir sediment, respectively. On the contrary, algal biomass was a key predictor of the variance of the percentage fraction of unfiltered MMHg over unfiltered Hg (%MMHg). The creation of suboxic conditions and the supply of sulfate subsequent to the algal decomposition seemed to support enhanced %MMHg in the bloom reservoirs. Thus, the nutrient supply should be carefully managed to limit increases in the %MMHg/Hg of temperate reservoirs.

The role of filamentous algae Spirogyra spp. in methane production and emissions in streams

Periphyton is an important primary producer in freshwater ecosystems. However, their effects on methane (CH4) production and emissions in streams and rivers are not fully understood. The purpose of this study was to investigate the effects of filamentous algae Spirogyra spp. on CH4 flux and to characterize the factors responsible for these effects. Sediments cores were collected from a stream in the suburbs of Shanghai and either inoculated with Spirogyra spp. in the laboratory or left uninoculated. CH4 flux, dissolved CH4 concentration, potential CH4 production rate and organic carbon in sediments and overlying water were measured for 2 months. Study results indicated that CH4 fluxes in algal treatment columns were significantly higher than in unvegetated sediments during initial algal decomposition, while potential CH4 production rates in algal treatment columns were significantly higher than in controls during both algal bloom and initial decomposition. The relationship between CH4 flux and environmental parameters was assessed and CH4 flux was found to exhibit a strongly positive relationship with dissolved organic carbon (DOC) concentration and potential CH4 production rate during experimental periods. It was concluded that Spirogyra spp. increased CH4 emissions in streams by providing algal carbon sources for methanogenesis and stimulating the CH4 production in sediments. These findings may facilitate understanding the roles of periphyton in aquatic methane dynamics and global greenhouse gas emissions.

Effects of electron acceptors on soluble reactive phosphorus in the overlying water during algal decomposition.

Endogenous phosphorus (P) release from sediments is an important factor to cause eutrophication and, hence, algal bloom in lakes in China. Algal decomposition depletes dissolved oxygen (DO) and causes anaerobic conditions and therefore increases P release from sediments. As sediment P release is dependent on the iron (Fe) cycle, electron acceptors (e.g., NO3 (-), SO4 (2-), and Mn(4+)) can be utilized to suppress the reduction of Fe(3+) under anaerobic conditions and, as such, have the potential to impair the release of sediment P. Here, we used a laboratory experiment to test the effects of FeCl3, MnO2, and KNO3 on soluble reactive phosphorus (SRP) concentration and related chemical variables in the overlying water column during algal decomposition at different algal densities. Results showed that algal decomposition significantly depleted DO and thereby increased sediment Fe-bound P release. Compared with the control, addition of FeCl3 significantly decreased water SRP concentration through inhibiting sediment P release. Compared with FeCl3, addition of MnO2 has less potential to suppress sediment P release during algal decomposition. Algal decomposition has the potential for NO3 (-) removal from aquatic ecosystem through denitrification and by that alleviates the suppressing role of NO3 (-) on sediment P release. Our results indicated that FeCl3 and MnO2 could be efficient in reducing sediment P release during algal decomposition, with the strongest effect found for FeCl3; large amounts of NO3 (-) were removed from the aquatic ecosystem through denitrification during algal decomposition. Moreover, the amounts of NO3 (-) removal increased with increasing algal density.

Dynamics of phosphorus–iron–sulfur at the sediment–water interface influenced by algae blooms decomposition

This study addresses the previously unknown effects of algae blooms on the dynamics of phosphorus (P), iron (Fe) and sulfur (S) across a lacustrine sediment-water interface (SWI). A mesocosm experiment was conducted in-situ to investigate these effects based on two recently-developed diffusive gradients in thin-films techniques (DGT). Soluble P, Fe(II), and S(-II) exhibited similar changing trends in a water column subject to the algae addition. Peak concentrations appeared on day 7 of the 16-day experiment. The lowest Eh occurred at the experiment’s midway point indicating a strong algae degradation. A maximum increase in DGT-labile S appeared on day 8 near the SWI, while the DGT-labile P and Fe exhibited persistent increases almost to the end of experiment. Significantly positive correlations of labile P were observed switching from between labile Fe and labile S in sediments, suggesting a significant change in original Fe-coupled dynamics of P under algae decomposition. Apparent fluxes were calculated based on DGT profiles where a simultaneous release of P and S occurred from degraded algae, resulting in bidirectional diffusion fluxes from sediment to overlying water. In contrast, sediment acted as a major source of labile Fe due to added depth and apparently positive fluxes.

Precontrol of algae-induced black blooms through sediment dredging at appropriate depth in a typical eutrophic shallow lake

Algae-induced black blooms, which trigger both the collapse of lake ecosystems and crises in urban water supplies, have become a serious ecological problem in numerous eutrophic shallow lakes. Therefore, preventing and suppressing the outbreak of black blooms is critical for maintaining the health of lake ecosystems. In this study, sediment dredging was employed as a black bloom precontrol method, and the effects of different dredging depths (0cm, 7.5cm, 12.5cm, and 22.5cm) were compared regarding the prevention of black bloom formation. Drained algae (mostly cyanobacteria) were added to these treatments at a density of 5000g/m2. The main physical and chemical characteristics of the water and sediment important for black blooms were analyzed during the study. The results showed that dredging was unable to suppress the offensive odor of the algal bloom. High concentrations of volatile organic sulfur compounds due to algal decomposition were detected in all of the added-algae treatments. Black blooms occurred in the undredged (UDR), 7.5cm dredged (7.5DR), and 12.5cm dredged (12.5DR) treatments but did not occur in the 22.5cm dredged (22.5DR) treatment. Therefore, black blooms can be suppressed by sediment dredging at an appropriate depth (22.5cm in the current study). The ∑H2S concentrations in the water samples of the 22.5DR treatment were remarkably lower than in the other added-algae treatments during the experiment. Hence, ∑H2S, as compared to DO, Eh, pH, and Fe2+, was considered as the most important limiting factor in the overlying water for black blooms. Two major reasons may have caused the low ∑H2S concentrations and suppressed the black blooms: (a) low levels of acid-volatile sulfide in the sediment after dredging (22.5cm) may have reduced the release of hydrogen sulfide to the overlying water, and (b) the low porosity (≤60.5%) observed after dredging is unconducive to pollutant diffusion and migration in sediments, which may have suppressed the release of Fe2+ and ∑H2S into the overlying water.

Algal decay, temperature and body size influencing trophic behaviour of wrack consumers in sandy beaches

Drift macroalgae detached from rocky substrate frequently strand on the shoreline, supplying food and habitat to a number of coastal species and sustaining important ecological processes, such as consumption and biogeochemical processing. Large amounts of algal wrack subsidies in open-coast sandy beaches follow the consumption pathway through the activity of upper shore crustaceans. The potential effect of the consumer population on the fate of algal subsidies depends on the rate at which these allochthonous inputs are exploited. Consumption in turn depends on the edibility of the stranded wrack and the environmental conditions that affect both consumers and consumed materials. The degradative process of algal wrack through the consumption pathway was analysed in a set of laboratory and field experiments where the effect of temperature and decomposition level was tested. Pre-weighted fragments of Saccorhiza polyschides and Sargassum muticum were supplied in independent containers harbouring groups of small, medium and large size classes of Talitrus saltator, a common supratidal amphipod widely distributed along the NE Atlantic and Mediterranean sandy beaches. To check the influence of primary environmental variables, such as temperature, assays were performed along the range of expected temperatures in the region, at 5, 10, 15, 20, 25, 30 and 35 °C. The influence of unpredictable natural events that are endured by the algal material once stranded on the beach was evaluated by mimicking macroalgae drying, burying and ageing along different time lapses. Consumer behaviour in the field was tested by adding individuals and algal fragments into experimental containers, as well as in manipulative assays where algal fragments were deployed on the drift line, by night at low tide, following the peak of consumer abundance on the beach. The consumption rate on fresh material depended on temperature and body size. Both low and high temperatures drastically reduced the consumption of algal material, with the feeding rate increasing with decreasing body size. Decomposition of algae enhanced the consumption, with maximum rates obtained when algae decayed in a wet environment. Consumption rose with increasing algal humidity, with deterrent molecules (such as phenolics) playing a minor role once the decomposition evolved with time.

Pressurized thermal and hydrothermal decomposition of algae, wood chip residue, and grape marc: A comparative study

Pressurized thermal decomposition of two marine algae, Pinus radiata chip residue and grape marc using high temperature, high pressure reactions has been studied. The yields and composition of the products obtained from liquefactions under CO of a mixture of biomass and H2O (with or without catalyst) were compared with products from liquefaction of dry biomass under N2, at different temperatures, gas pressures and for CO runs, water to biomass ratios. Thermochemical reactions of algae produced significantly higher dichloromethane solubles and generally higher product yields to oil and asphaltene than Pinus radiata and grape marc under the reaction conditions used. Furthermore, the biofuels derived from algae contained significant concentrations of aliphatic hydrocarbons as opposed to those from radiata pine and grape marc which were richer in aromatic compounds. The possibility of air transport fuel production from algae thus appears to have considerable advantages over that from radiata pine and grape marc.