Substrate Particle Size Research Articles

Developing environmental flow targets for benthic macroinvertebrates in large rivers using hydraulic habitat associations and taxa thresholds

Holistic environmental flows frameworks are built on our understanding of key flow-ecology relationships that support sensitive taxa and critical ecosystem functions under different flow and water level scenarios. Most research on flow-ecology relationships has typically focused on small systems, with less known about flow associations, indicator taxa, and environmental thresholds of assemblage change along hydraulic gradients of large non-wadeable rivers. We assessed benthic macroinvertebrate assemblage structure and applied Taxa Indicator Threshold ANalysis (TITAN) on biomonitoring data collected during a six-year period in the Wolastoq | Saint John River in Atlantic Canada. Flow velocity was strongly associated with the distribution and relative abundance of benthic macroinvertebrates in the river, and taxon associations reflected functional adaptations to flow. We identified 33 genus-level indicator taxa that were either positively or negatively associated with flow velocity. Weaker taxa responses were shown for the gradient in median substrate particle size where 22 negatively and positively responding taxa were identified. We predicted changes in indicator taxon abundance under different flow scenarios using a hydrodynamic model, and characterised the distribution and availability of suitable hydraulic habitat patches within a 20 km reach downstream of a large hydropower generating station. These observations set the stage for the development of ecologically-based flow targets to support holistic environmental flow management in large rivers.

OPTIMIZATION OF ASPERGILLUS TUBINGENSIS GROWTH FOR CELLULASE PRODUCTION

Celluloses are the basic component of plant cell walls which are difficult to break however, cellulase enzymes have the ability to degrade the cellulose into glucose. The use of celullase enzymes is spreading widely particularly in the paper, pulp and food industries to reduce biowaste. The purpose of this study was to optimize the production of cellulase enzymes by using fungal strain Aspergillus tubingensis. The fungal strain Aspergillus tubingensis was extracted from putrid fruits and vegetable samples collected from the local fruit market of Pattoki in the District Kasur. The identification of fungus was carried out using microscope. Corn Stover was used as a substrate for cellulase production. Different parameters were used for the optimization of fungus growth such as substrate level, substrate particle size, temperature, pH, moisture, urea and glucose. Cellulase enzymes were purified by salting out and gel filtration techniques. The optimum substrate level, substrate particle size, temperature, pH, glucose, urea and moisture were analyzed as 5g, 40mm, 40°C, 4.5pH, 0.5g, 0.04g and 60% respectively. The maximum activity reveled by cellulase enzyme at different optimized parameters were reported in U/mL/min. The cellulase molecular weight was determined 71 kDa by Dodecyl Sulphate Poly Acrylamide Gel Electrophoresis. It was concluded that the study will help to a way for the scientists for the maximum production of cellulase from Aspergillus tubingensis using Corn stover as substrate and most cost-effective Solid State Fermentation method.

Bioprocessing of Agro-Industrial Waste for Maximization of Pectinase Production by a Novel Native Strain Aspergillus cervinus ARS2 Using Statistical Approach

The demand for microbial pectinase has increased due to its vast applications in different industries. The current study dealt with the synthesis of pectinase by a novel native strain Aspergillus cervinus ARS2 using agro-industrial waste. Comparative studies conducted on pectinase production by submerged fermentation (SmF) and solid-state fermentation (SSF) showed that pectinase activity was more increased in SSF (44.51 ± 1.33 IU/mL) than in SmF (40.60 ± 1.15 IU/mL) when using orange peel as a substrate. Using SSF, one-factor-at-a-time (OFAT) studies were conducted, considering different process variables such as inoculum size, initial pH, incubation time, moisture content, incubation temperature, and substrate particle size, all of which affected the pectinase activity. OFAT results showed the highest pectinase activity at an inoculum size of 106 spores/mL (43.11 ± 1.06 U/mL), an incubation time of 6 days (43.81 ± 1.21 U/mL), a moisture content of 100% (44.30 ± 1.69 U/mL), a substrate particle size of 1.7 mm (42.06 ± 1.20 U/mL), an incubation temperature of 37 °C (45.90 ± 1.33 U/mL), and an initial pH of 4 (43.31 ± 0.89 U/mL). The identified significant process variables were then optimized by response surface methodology (RSM)-central composite design (CCD). The results showed optimum pectinase activity of 107.14 ± 0.71 IU/mL for a substrate particle size of 2 mm, an incubation temperature of 31.5 °C, an initial pH of 4.9, and a moisture content of 107%, which was obtained from the Minitab optimizer. By using statistical optimization, the pectinase production from the isolated novel fungal strain A. cervinus ARS2 was increased 2.38-fold. Therefore, the A. cervinus ARS2 strain can be further explored for large-scale pectinase production which could meet the growing industrial demands.

Evaluating the risk of fish stranding due to hydropeaking in a large continental river

AbstractWith the continuous development of hydropower on a global scale, stranding of freshwater fishes is of growing concern, and an understanding of the mechanisms and variables affecting fish stranding in hydropeaking rivers is urgently needed. In particular, a methodology is required to identify the magnitude and timing at which fish stranding occurs in relation to environmental conditions. Here, we studied fish stranding in three reaches downstream of a hydropeaking generation station in the Saskatchewan River, Saskatchewan, Canada, using an innovative remote photography approach with 45 trail cameras and traditional transect monitoring, conducting 323 transects. We observed that juvenile sport and commercial fish species are stranding at a higher proportion than small bodied fish species. The remote photography approach provided more precise fish stranding timing and associated the environmental and physical conditions with a given stranding event, but captured fewer fish and only rarely allowed species identification. The comparison of the two methodologies resulted in similar stranded fish densities, but the remote photography allowed for continuous observations whereas the transect monitoring was limited by the observer availability in the field. Remote photography allowed for additional information on the scavenging of stranded fish, with scavenging occurring on average within 240 minutes of the fish being stranded. The probability of fish stranding increased significantly with increasing water temperature and substrate particle size resulted in greater stranding on finer substrates. Our findings have important implications for hydroelectric flow management by introducing an innovative, standardized method to study the effects of hydropeaking events on fish stranding that can be applied to increase our understanding of the impacts of hydropeaking on fish communities.

Improved Properties of Li-Ion Battery Electrodes Protected By Al2O3 and ZnO Ultrathin Layers Prepared By Atomic Layer Deposition

Surface modification using thin layers grown by atomic layer deposition (ALD) is an effective strategy for performance improvement of Li-ion batteries. Ultrathin Al2O3 layers are the most studied coating material. In our contribution we compare properties of Al2O3 and ZnO ultrathin layers prepared by ALD on lithium-iron-phosphate (LFP) cathodes and Si-graphite anodes.Ultrathin Al2O3 and ZnO films were grown at 100 °C using trimethylaluminum (TMA) and diethylzinc (DEZ) precursors, respectively, with water vapors as reactant. The growth rates of the Al2O3 and ZnO films were about 0.1 nm/cycle on control flat Si substrates. ALD layers thickness in this study ranged from 5 to 20 cycles. A modified deposition recipe utilizing a prolonged precursor dwell time in the reactor chamber for coverage of the highly porous battery electrodes has been utilized. As TMA, DEZ and H2O all have rather high vapor pressures, we assume that significant part of the electrodes were coated.Porous LFP cathodes (NANOMYTE BE-60E, NEI Corp.) with the thickness of 70 μm were used as a substrate. The average particle size of the LFP substrate was ~ 2 μm with the specific surface area of 15 m2/g and active material loading of 7.3 mg/cm2. Experimental capacity C of the LFP electrode is 170 mAh/g in the voltage range 2.5 - 4.1 V using 0.1 charging/discharging c-rate.As an anode material porous silicon-graphite composite electrode sheets NANOMYTE BE-150E (NEI Corp) with the thickness of 65 μm and composition of active material 20% Si and 65 % graphite were used. The nominal capacity C of the silicon-graphite anode is 750mAh/g in the voltage range 0.05 - 1V using 0.05 charging/discharging c-rate.In our contribution we present specific discharge capacity of the electrodes as a function of charging/discharging cycles. For both pristine and Al2O3 protected LFP cathode sheets specific discharge capacity of 160 mAh/g was achieved at the c-rate of 0.2. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g at the c-rate 0.2 to about 90 mAh/g for the c-rate 1, while the electrode protected by 0.5 nm of Al2O3 saturated at 120 mAh/g. Properties of ZnO- protected LFP cathodes are compared to that covered by Al2O3.Electrochemical properties of the silicon-graphite anode were studied using low c-rate of 0.05. During the first cycles the specific capacity is relatively low due to the formation of the solid-electrolyte interface layer at the surface. After several cycles the capacity increased to the nominal value of 750 mAh/g. In our study we compare the charging/discharging capability of the pristine silicon-graphite anode and that of the electrodes covered by 5 -20 ALD cycles of Al2O3 and ZnO films during the first charging/discharging cycles. We discuss the effect of ALD protecting layers on the rate capability of the silicon-graphite anode. Finally, the results of the electrochemical measurements are compared to those obtained by X-ray photoelectron spectroscopy.

Substrate size modifies stream grazer-biofilm interactions in the presence of invertivorous fish.

When herbivore abundance is controlled by predators there may be an indirect positive effect on primary producers due to reduced grazing pressure, but the potential of predation refuges to modify such trophic cascades has rarely been studied. By experimentally manipulating substrate particle size and fish predation regime, we assessed the outcome of invertebrate grazer-biofilm interactions in streams. Locations at the center of larger substrate particles were predicted to pose a higher predation risk, and therefore be subjected to a lower grazing pressure. In our 52-day experiment in a New Zealand stream, small-sized substrates (terracotta tiles) remained virtually free of periphyton across their entire upper surface, whereas a thick periphyton mat was formed across large tiles with only edges remaining free. In channels containing fish (either native Galaxias vulgaris or exotic Salmo trutta), grazing on tiles was lower than in the absence of fish. A preference for grazing near to the edge of tiles was clearest in fish channels but was also evident even in the absence of fish, probably reflecting fish presence and/or fish kairomones in the stream from where the colonizing invertebrates had been derived. Total grazer density was similar across treatments with or without fish, suggesting that our results can be explained mostly by changes in the behavior of grazers. We suggest that refuge availability, interacting with grazer predator-avoidance behavior, may produce a context-dependent patchwork of trophic cascades in streams and other ecosystems.

Growth and Mechanical Characterization of Mycelium-Based Composites towards Future Bioremediation and Food Production in the Material Manufacturing Cycle.

Today’s architectural and agricultural practices negatively impact the planet. Mycelium-based composites are widely researched with the aim of producing sustainable building materials by upcycling organic byproducts. To go further, this study analyzed the growth process and tested the mechanical behavior of composite materials grown from fungal species used in bioremediation. Agricultural waste containing high levels of fertilizers serves as the substrate for mycelium growth to reduce chemical dispersal in the environment. Compression and three-point bending tests were conducted to evaluate the effects of the following variables on the mechanical behavior of mycelium-based materials: substrate particle size (with or without micro-particles), fungal species (Pleurotus ostreatus and Coprinus comatus), and post-growth treatment (dried, baked, compacted then dried, and compacted then baked). Overall, the density of the material positively correlated with its Young’s and elastic moduli, showing higher moduli for composites made from substrate with micro-particles and for compacted composites. Compacted then baked composites grown on the substrate with micro-particles provided the highest elastic moduli in compression and flexural testing. In conclusion, this study provides valuable insight into the selection of substrate particle size, fungal species, and post-growth treatment for various applications with a focus on material manufacturing, food production, and bioremediation.

Research status and development of microbial induced calcium carbonate mineralization technology.

In nature, biomineralization is a common phenomenon, which can be further divided into authigenic and artificially induced mineralization. In recent years, artificially induced mineralization technology has been gradually extended to major engineering fields. Therefore, by elaborating the reaction mechanism and bacteria of mineralization process, and summarized various molecular dynamics equations involved in the mineralization process, including microbial and nutrient transport equations, microbial adsorption equations, growth equations, urea hydrolysis equations, and precipitation equations. Because of the environmental adaptation stage of microorganisms in sandy soil, their reaction rate in sandy soil environment is slower than that in solution environment, the influencing factors are more different, in general, including substrate concentration, temperature, pH, particle size and grouting method. Based on the characteristics of microbial mineralization such as strong cementation ability, fast, efficient, and easy to control, there are good prospects for application in sandy soil curing, building improvement, heavy metal fixation, oil reservoir dissection, and CO2 capture. Finally, it is discussed and summarized the problems and future development directions on the road of commercialization of microbial induced calcium carbonate precipitation technology from laboratory to field application.

Study on carbon matrix composite bipolar plates with balance of conductivity and flexural strength

In order to balance the conductivity and flexural strength of graphite composite bipolar plates, the influence of conductive filler on the properties of graphite composite bipolar plate was comprehensively studied by using phenolic resin as binder, natural flake graphite as conductive substrate and functional carbon materials with different structures as auxiliary filler. The results show that the particle size of conductive substrate has an important influence on the conductivity enhancement of auxiliary filler. The influence of conductive particle size on auxiliary filler electrical conductivity improvement was first investigated in this research. The effects of various auxiliary filler concentrations on improving electrical conductivity and flexural strength were then examined. This research has substantial implications for the balance of electrical conductivity and flexural strength of graphite composite bipolar plates.

Statistical optimization of cellulase production by halophilic strains isolated from Tunisian Sebkhas using the renewable marine biomass waste, Posidonia oceanica, as a cellulosic substrate

Bio-based ethanol production from enzymatic lignocellulosic biomass degradation serves an efficient technology to combat the problem of depleting fossil fuels. High cost of the enzyme is the major obstacle in preventing the commercialization of this process. Thus, main objective of the present study was to optimize composition of culture parameters for enhancing cellulase production by two halophilic strains Oceanobacillus picture E50 and Bacillus vallismortis J77 using Posidonia oceanica waste (POW) as a substrate. A Plackett-Burman design was conducted to study and evaluate the weight of eight cultural variables on bacterial cellulase production. The optimal culture conditions for maximum enzyme yield were developed by maintaining the variables of POW concentration, NaCl concentration, POW liquor, bacterial strain and inoculum size at their higher levels, while keeping substrate particle size, glucose concentration and incubation time at their lower levels. The highest cellulase production in terms of CMCase activity was 950 U/L following this optimization process. Thus, the results obtained in this study demonstrated the potential of utilizing POW as a substrate for enhanced cellulase production by halophilic bacteria. B. vallismortis J77 produced the highest cellulase activity and therefore could be of great interest for saccharification of Posidonia oceanica biomass for biofuel and biorefinery applications.

Distribution Characteristics of Microplastics and Their Migration Patterns in Xiangxi River Basin

Microplastics as a prevalent pollutant in water bodies have recently attracted widespread attention. To investigate the spatial and temporal distribution characteristics of microplastics in freshwater rivers and their migration patterns, the surface water, sediments, and subsidence zone of the Xiangxi River, a tributary of the Yangtze River, were sampled and analyzed in November 2020 and April 2021, respectively. The results showed that the average abundance of microplastics in the surface water of Xiangxi River was (6.64±1.32) n·L-1 in flat water and (5.00±1.07) n·L-1 in dry water, the average abundance of microplastics in sediments was (0.56±0.13) n·g-1 in flat water and (0.41±0.09) n·g-1 in dry water, and the average abundance of microplastics in the subsidence zone was (0.53±0.15) n·g-1 in flat water and (0.68±0.18) n·g-1in dry water. There were significant differences in the abundance distribution of microplastics in the surface water, sediments, and subsidence zone (P<0.05). In the surface water and sediments, the particle size of microplastics was mainly distributed in the range of 0.1-0.5 mm, and in the subsidence zone, it mainly ranged from 1-5 mm. The color of microplastics was mainly transparent in the surface water and subsidence zone and blue in sediments. The morphology of microplastics in the Xiangxi River basin was mainly fiber, and the materials were mainly polyethylene (PE) and polypropylene (PP). There were many factors affecting the distribution of microplastics. The analysis results showed that the abundance of microplastics in the surface water was negatively correlated with the flow rate of the water body. The abundance of microplastics in the sediment was related to the substrate type of the riverbed and negatively correlated with the substrate particle size. Combined with the microplastic abundance data of each sampling site, it was found that there was a significant migration process of microplastics in the spatial distribution of the Xiangxi River in the watershed. Along the river longitudinal direction, the longitudinal migration of microplastics in the surface water was along the river direction, and in the vertical direction, it showed the mutual migration between the water body and the subsidence zone and the water body and sediments.

Compressive behaviour of anisotropic mycelium-based composites

Mycelium based composites (MBC) exhibit many properties that make them promising alternatives for less sustainable materials. However, there is no unified approach to their testing. We hypothesise that the two-phase particulate composite model and use of ASTM D1037 could provide a basis for systematisation. An experimental series of MBC were produced using four substrate particle sizes and subjected to compression testing. We report on their effect over Young’s modulus and ultimate strength. We extend the study by investigating three anisotropic substrate designs through orientated fibre placement as a strategy for modifying compressive behaviour. We find that the two-phase particulate model is appropriate for describing the mechanical behaviour of MBC and that mechanical behaviour can be modified through anisotropic designs using orientated fibres. We also confirm that fibre orientation and particle size are significant parameters in determining ultimate strength.

Metal-enhanced fluorescence of graphene oxide sheets.

Graphene oxide (GO) is an excellent chemical tunable optical platform for imaging and sensing. The photoluminescence (PL) quantum yield of GO is relatively low, which limited the application of the intrinsic and tunable fluorescence from GO. Here, we report the first case of metal-enhanced fluorescence (MEF) of GO. A significant enhancement (~10-fold) in fluorescence intensity is observed from GO on the Ag substrate as compared to that on the glass. FL, Raman, and SEM images are used to investigate the MEF behavior and are coincident with each other. The influence of the metal particle size of Ag substrate is investigated. The fluorescence is also found to be responsive when adding different metal ions into GO solution. GO contacting directly with metal substrate exhibits strong MEF without quenching, which makes it possible to use GO sheets for three-dimension optical imaging and sensing.

Identifying potential drivers of distribution patterns of invasive Corbicula fluminea relative to native freshwater mussels (Unionidae) across spatial scales.

This study aimed to identify the importance of ecological factors to distribution patterns of the invasive Clam (Corbicula fluminea) relative to native mussels (family: Unionidae) across seven rivers within the Mobile and Tennessee basins, Southeast United States. We quantitatively surveyed dense, diverse native mussel aggregations across 20 river reaches and estimated mussel density, biomass, and species richness along with density of invasive C. fluminea (hereafter Corbicula). We measured substrate particle size, velocity, and depth in quadrats where animals were collected. Additionally, we characterized reach scale environmental parameters including seston quantity and quality (% Carbon, % Nitrogen, % Phosphorous), water chemistry (ammonium [NH4+], soluble reactive phosphorous [SRP]), and watershed area and land cover. Using model selection, logistic regression, and multivariate analysis, we characterized habitat features and their association to invasive Corbicula within mussel beds. We found that Corbicula were more likely to occur and more abundant in quadrats with greater mussel biomass, larger substrate size, faster water velocity, and shallower water depth. At the reach scale, Corbicula densities increased where particle sizes were larger. Mussel richness, density, and biomass increased with watershed area. Water column NH4+ increased at reaches with more urban land cover. No land cover variables influenced Corbicula populations or mussel communities. The strong overlapping distribution of Corbicula and mussels support the hypothesis that Corbicula are not necessarily limited by habitat factors and may be passengers of change in rivers where mussels have declined due to habitat degradation. Whether Corbicula is facilitated by mussels or negatively interacts with mussels in these systems remains to be seen. Focused experiments that manipulate patch scale variables would improve our understanding of the role of species interactions (e.g., competition, predation, facilitation) or physical habitat factors in influencing spatial overlap between Corbicula and native mussels.

Clogging in Vertical Flow Constructed Wetlands: Causes for Clogging and Influence of Decontamination

Abstract With the continuous operation of constructed wetlands, substrate clogging is issue. In order to solve the problem, there is practical significance to understand the causes for clogging in constructed wetlands. Two pilot-scale vertical flow constructed wetlands were established, namely, CW-B and CW-C. By studying the relationship between the accumulation of different substances and the banked-up water area, it was found that the accumulation of non-filter substances and total solids was an important reason for the clogging of the substrate, and the accumulation degree of non-filter inorganic substances was more obvious than that of non-filter organic substances, and the blockage was mainly located in the 10-20 cm layer. In the vertical flow constructed wetland with river sand as the main substrate, water accumulation will occur when the content of total solid and non-filter substances exceeds 67.233 g and 101.228 g per cubic meter of substrate, respectively. Therefore, it is important to pay attention to the substrate particle size matching of 0-20 cm layer to reduce the clogging in the vertical flow constructed wetland. The clogging has little effect on chemical oxygen demand (COD) removal, but great effect on total phosphorus (TP) removal. Compared with the control wetland (CW-C), the biomass content in the CW-B with biochar increased by 334.26 nmol P/g, which can improve the removal efficiency of total nitrogen (TN) and total phosphorus (TP), but also increase the risk of clogging in the vertical flow constructed wetland. Future research should try to combine the anti-blocking research results of biochar constructed wetlands to improve the purification effect, which is of great significance to promote the sustainable development of constructed wetlands.

Bioprocessing of Agricultural Waste (Banana Pseudostem) by Solid-State Fermentation (SSF) for Production of Cellulase

Cellulase was produced by Cellulomonas uda utilizing banana stem waste by solid state fermentation (SSF). The different parameters effects considered like particle size of substrate, pH(incubation and extraction), incubation period, temperature (incubation and extraction), media components (yeast extract and peptone) and moisture of substrate on the production of cellulase was investigated. The optimum activity of cellulase produced by Cellulomonas uda on banana waste for particle size (6.97 IU/min for 1mm), extraction pH (7.13 IU/min for pH 7), incubation pH(6.97 IU/min for pH 7), extraction temperature (7.10 IU/min for 500C), incubation temperature (7.20 IU/min for 450C), incubation period (7.20 IU/min on 3rd day), moisture content (7.12 IU/min for 100% ), peptone content ( 7.23 IU/min for 0.5 gm) and yeast extract content (7.18 IU/min for 0.30gm) was recorded. The cellulase produced by Cellulomonas uda by using banana stem waste indicates the socio-econic utilization of agricultural waste. After purification and characterization; cellulase enzyme can be used in industrial processes.

Modelling the effects of particle size pretreatment method on biogas yield of groundnut shells.

Optimising biogas yields from anaerobic digestion of organic wastes is significant to maximum energy recovery in the biodigestion process and has become an important topic of interest. Substrate particle size is an important process parameter in biogas production, and it precedes other pretreatments methods for the majority of the lignocellulose materials. Optimisation of biogas yield using Response Surface Methodology (RSM) was done, and temperature, hydraulic retention time and particle size were considered variables to develop the predictive models. Pretreatment of groundnut shells was investigated using particle size reduction of mechanical pretreatment methods. After pretreatment, 30 samples were digested in a batch digester at mesophilic temperature. The experimental results showed that the temperature, hydraulic retention time and particle size had significant effects of interaction (p < 0.05). The optimum experimental and predicted yields are: 44.70 and 42.92 (lNkgoDM) organic dry matter biogas yield, 20.80 and 19.09 (lN/kgFM) fresh mass biogas yield, 24.00 and 22.68 (lNCH4oDM) organic dry methane yield and 12.30 and 15.59 (lNCH4FM) fresh mass methane yield, respectively. The R2 recorded for the four yield components were 0.6268, 0.5875, 0.6109 and 0.5547. These values seem to be lower and a sign of the average fit of the model. Biogas production from groundnut shells was significantly improved with statistical optimisation and the pretreatment method.

Study of Structural and Optical Properties of Electrodeposited Silicon Films on Graphite Substrates.

Silicon (Si) films were deposited on low-cost graphite substrates by the electrochemical reduction of silicon dioxide nanoparticles (nano-SiO2) in calcium chloride (CaCl2), melted at 855 °C. Cyclic voltammetry (CV) was used to analyze the electrochemical reduction mechanism of SiO2 to form Si deposits on the graphite substrate. X-ray diffraction (XRD) along with Raman and photoluminescence (PL) results show that the crystallinity of the electrodeposited Si-films was improved with an increase of the applied reduction potential during the electrochemical process. Scanning electron microscopy (SEM) reveals that the size, shape, and morphology of the Si-layers can be controlled from Si nanowires to the microcrystalline Si particles by controlling the reduction potentials. In addition, the morphology of the obtained Si-layers seems to be correlated with both the substrate materials and particle size of the feed materials. Thus, the difference in the electron transfer rate at substrate/nano-SiO2 interface due to different applied reduction potentials along with the dissolution rate of SiO2 particles during the electrochemical reduction process were found to be crucial in determining the microstructural properties of the Si-films.

Response of sub-Antarctic streams to urbanization: Relevance of assemblage structure and independent reference areas

Andean Patagonia is experiencing sudden changes due to unorganized urban expansion. Despite being known for its wilderness areas, southern Patagonian urban streams have been increasingly studied during the last decade, using reference-impact gradients within urbanizing watersheds. Here, we assess urbanization effects on stream integrity by comparing environmental characteristics on independent reference streams vs. urban streams, and the benthic macroinvertebrate community structure along three stream reaches in an urbanization gradient. In comparison to reference sites, urban streams had higher nutrient concentrations, temperature, turbidity, stream flow, and total primary producer biomass, accompanied by lower dissolved oxygen concentrations, substrate particle size, mainly along mid and downstream areas. These variables were the main factors structuring macroinvertebrate assemblage ordination analysis. Macroinvertebrate assemblages from areas upstream from the urbanization differed from their counterparts in reference streams, but not from downstream reference areas. Environmental characteristics and biotic assemblage structure were altered in urban streams, even in reaches located upstream from urbanization, compared to independent upstream reference reaches. This study highlights the importance of a community and comparative vision towards independent areas with low impact to serve as reference values and establish appropriate goals or baselines when assessing ecological conditions and potential restoration.

Statistical optimization of arachidonic acid synthesis by Mortierella alpina CBS 754.68 in a solid-state fermenter.

Arachidonic acid (ARA) is an omega‐6 fatty acid that plays a major role in human health. The present study optimizes the production of ARA by the soil fungus Mortierella alpina CBS 754.68 on oil cakes. In the first step, the best substrate was chosen from four oil cakes, namely soybean, sunflower, olive, and colza oil cakes, of which sunflower oil cake showed the highest yield. In the next step, screening tests were performed using the Plackett‐Burman design. Seven variables (substrate particle size, moisture content, time, temperature, yeast extract, glucose, and glutamate) were investigated (each taking values of +1 and −1). Among these variables, time, temperature, and substrate particle size significantly affected ARA production (p < .05), so they were further investigated in the optimization step. The optimal fermentation time, temperature, and substrate particle size calculated by response surface methodology were 8.75 days, 18.5°C, and 1.3 mm–1.7 mm, respectively. Under these conditions, M. alpina was predicted to produce 4.19 mg of ARA/g dry weight of substrate (DWS). The actual yield, determined in evaluation tests, was 4.48 ± 0.16 mg ARA/g DWS, which shows the accuracy of the model. In the final step, the effect of the aeration rate on producing ARA was investigated in a packed‐bed solid‐state fermenter under the determined optimal conditions. In this stage, the highest ARA yield was 10.13 ± 0.26 mg/g DWS, approximately double that of the optimization step, and this confirms that aeration increases ARA production by M. alpina.