Aquatic Systems Research Articles

The oils adsorption potential of heat and sulfuric acid treated Chrysopogon zizanioides biomass through in-vitro approach

BackgroundFinding an environmentally sound solution for oil pollution remediation work is crucial because oil pollution in aquatic habitats is one of the most serious environmental issues. MethodsThis study aimed to assess the oil adsorption capability of powdered form of C. zizanioides biomass adsorbent, as untreated, heat and H2SO4 treated adsorbents. Significant FindingsThe SEM analysis revealed that the heat-treated adsorbent has porous microstructures which can interact with oil pollutants. According to the FTIR and EDS analyses, the heat-treated biomass adsorbent has a higher number of functional groups and a significant elemental composition. The heat-treated adsorbents have greater oil adsorption efficiency. Hence, the petrol adsorption competence of untreated, heat, and H2SO4 treated C. zizanioides biomass adsorbents was noticed as their weight enhanced up to several folds than their initial weight. Whenever the oil is compared, it is clear that absorption is preferred in the following order: diesel (10.63, 13.51, as well as 12.12 g) >oil (9.65, 14.85, and 11.85 g)>petrol (7.59, 14.24, and 11.53 g). The heat-treated C. zizanioides biomass outperformed than others in terms of adsorption and retention. Thus, it can be used to remediate the oil contamination from aquatic system.

Cigarette filter fibres as a source and sink of trace metals in coastal waters

Cellulose acetate fibres from cigarette filters represent a form of microplastic that has received little attention in the environment. In this study, a ground composite of spent, smoked filter material (FM) has been used to investigate the role of cellulose acetate fibres as a source and a sink of trace metals (Cd, Co, Cu, Ni, Pb and Zn) in coastal waters. FM suspended in river water and seawater and mixtures thereof representative of an estuarine gradient resulted in the leaching of pre-existent metals derived from the combustion of tobacco, with mean percentages of release ranging from about 40 for Pb to nearly 90 for Cd, Co and Zn. Addition of 40 μg L−1 of each metal to FM suspensions incubated for 48 h yielded mean partition coefficients (KDs) ranging from <10 L kg−1 for Co to > 100 L kg−1 for Cu, Pb and Zn, with Cu and Ni displaying a net increase in KD with increasing salinity. Adsorption is interpreted in terms of hydrophobic interactions between metal-organic complexes and the cellulose acetate surface, and in support of this assertion KDs exhibited a significant, positive relationship with published metal-humic acid binding constants. The findings of this study improve our understanding of the role of cellulosic microfibres more generally in transporting trace metals in aquatic systems.

Co-occurrence of organophosphate diesters and organophosphate triesters in daily household products: Potential emission and possible human health risk

Eight paired organophosphate diesters (Di-OPs) and organophosphate triesters (Tri-OPs) were investigated in wipes from analytical instruments and 47 material samples related to household products, including textiles, electrical/electronic devices, building/ decoration materials and children’s products. The total concentrations of Di-OPs ranged in 3577–95551 ng/m2 in the wipes and limit of detection–23002 ng/g in the materials. The Tri-OPs concentrations varied significantly in the ranges of 107218–1756892 ng/m2 and 2.13–503149 ng/g, respectively. Four industrial Di-OPs were detected in > 65% of the studied samples suggesting their direct application in the studied materials. Furthermore, we demonstrated for the first time that four non-industrial Di-OPs, e.g., bis(2-chloroethyl) phosphate, bis(1-chloro-2-propyl) phosphate, bis(1,3-dichloro-2-propyl) phosphate, and bis(butoxyethyl) phosphate, identified as degradation products of their respective Tri-OPs were also detected in these studied samples, which might act as important emission sources of Di-OPs in indoor environments. We estimated the burden of Di-OPs and Tri-OPs in a typical residential house and instrumental room, which both exhibited important contributions from furniture, building and decoration materials, and electrical/electronic devices. Limit health risk was posed to local people via air inhalation.

The importance of explicitly representing the streambed in watershed models

AbstractThe streambed is the critical interface between the aquatic and terrestrial systems and hosts important biogeochemical hot spots within river corridors. Although the streambed characteristics are significantly different from those of its surrounding soil, the streambed itself has not been explicitly represented in watershed models. Here, we explicitly incorporated a streambed layer into an integrated hydrologic model through model parameterization and discretization. We examined the hydrological effects of streambed characteristics, including hydraulic conductivity (K), layer thickness, and resolution, on the exchange fluxes across the streambed as well as the streamflow at the watershed outlet. The numerical experiments were performed in the American River Watershed, a headwater, mountainous watershed within the Yakima River Basin in central Washington. Despite having a negligible effect on the watershed streamflow, an explicit representation of the streambed with distinctive properties dramatically changed the magnitude and variability of the exchange flux. In general, a larger streambed K along with a thicker streambed layer induced larger exchange fluxes. The exchange flux was most sensitive to the streambed resolution. A finer streambed resolution increased exchange fluxes per unit area while reducing the overall exchange volumes across the entire streambed. The amount of baseflow decreased by 6% as the streambed resolution increased from 250 to 50 m. This finding is important because these hydrological changes may, in turn, affect the exchange of nutrients and contaminants between surface water and groundwater and the associated biogeochemical processes. Our work demonstrated the importance of representing streambeds in fully distributed, process‐based watershed models to better capture the exchange flow dynamics in river corridors.

Effect of Aquatic Plants as a Biofilter on Water Criteria and Common Carp Growth Performance in Aquaculture Intensive System

The experiment was conducted in the field of the College of Agriculture, University of Tikrit, for the period from 14/6/2022 to 14/8/2022 inside a semi-exposed building (gable) with four treatments. Each treatment included three replicates, and each replicate included (6) fishes in a closed bio-aquatic system, by weight 14.15±1.22, 13.8±0.72,13.9±0.78, 13.7±0.93g for T1, T2, T3 and T4 in 12 ponds respectively. On a filtration tank representing the biological and mechanical filter in an intensive aquatic system with a capacity of 100 liters each, three aquatic plants were grown (lentils, Azolla, Ceratophylom), except for the control treatment, which was similar to all treatments except for the presence of aquatic plants. The water was treated in a mechanical filter unit through thick sponge layer, then directing the water to the biological treatment by means of crushed gravel, in addition to the aquatic plants to filter the dissolved organic pollutants. The results showed a significant effect of aquatic plants at (p ≤0.05) on dissolved oxygen DO (mg / liter), pH, total dissolved salts (TDS), nitrate NO3, nitrite NO2, and ammonia. The biological characteristics of aquatic plants are impacted by modifications to the physicochemical properties of the water. There was a significant improvement in weight gain (G.W), relative growth (RGR), specific growth of fish (SGR), and feed conversion efficiency (FCR) for treatments T2, T3, and T4 compared with control treatment. There was a significant difference when using aquatic plant in the percentage of protein compared to the control treatment. No significant differences were observed on blood biochemical parameters. While the result of the correlation or interactions between water characteristics with growth parameters for Common carp fish showed significant effects at a significant level (P ≤0.05) and (P ≤0.01).

Differences in the Synergic Accumulation of Toxic Elements in Pelagic and Benthic Fish from Glacier-Fed Rivers of the Dzungarian Alatau

Abstract The determination of potentially toxic element concentrations in fish is an important topic from the point of view of both nature conservation and human consumption. The aim of this study was to assess the concentrations of S, K, Ca, Cr, Mn, Fe, Zn, Rb, Sr, Mo, and P in benthic and pelagic fish species in the Karatal river, which is fed by melting glaciers from the Dzungarian Alatau in Kazakhstan. In September 2022, 48 fish samples were collected. It has been demonstrated that the accumulation of chemical elements in fish species can be explained by both the physiological parameters of the fish species and the influence of glaciers that feed river habitats. The data presented in this study provide a synergistic view of pollutants affecting fish populations. Benthic fish contained more manganese and strontium than pelagic species, while the mutual accumulation of potassium, chromium, rubidium, and molybdenum was higher in pelagic fish. The synergistic concentration of calcium and phosphorus in pelagic fish was higher than that in benthic species, while the amount of zinc and sulfur was higher in benthic animals. Relatively elevated levels of mercury in fish were found. The study contributes to the discussion about the role of glacial environments in loading pollutants to aquatic systems.

Spatial–temporal differentiation and control strategies of nitrogen environmental loss in China's coastal regions based on flow analysis

Nitrogen pollution emissions from human production and living activities in coastal regions are important topics in the management of environmental pollution in coastal waters. However, to date, there has been relatively little research systematically assessing the environmental loss of nitrogen (NEL) from human activities that negatively affect marine ecosystems. This study categorised emission sources into five subsystems, namely livestock, farming, aquatic, industrial, and residential. Through flow analysis, the anthropogenic emissions of nitrogen in the gas, liquid, and solid phases from 11 coastal provinces in China in 2011, 2015, and 2020 were determined. A nitrogen cost index was constructed by combining the social indicators of each province. The effectiveness of nitrogen emission control since the land-sea coordination and the future challenges for the coastal region were discussed from various perspectives. The results of the study showed that the total NEL that poses a potential threat to marine ecosystems in coastal areas of China has decreased from 18.93 TgN to 14.66 TgN since the proposal of land-sea coordination, with livestock systems and aquatic systems emitting the most. The Bohai and Yellow Seas area were most threatened by nitrogen pollution. Among the three oceanic pathways, liquid-phase nitrogen discharge from each subsystem was effectively controlled, and the control of gas-phase nitrogen emissions is still the most numerous NEL state, although it has had a significant effect. The results of the correlation analysis suggest that NEL flow can characterize the regional management of nutrient-based organic pollutants. Past management tools and environmental investments in China have been more effective in controlling emissions from point and line sources involving artificial facilities, but less direct effect on mariculture. How to control surface source pollution from livestock and aquaculture will be an important challenge to reduce reactive nitrogen emissions in the future.

Activating Illite kaolinite clay with CTAB for adsorbing Methylene blue: Isotherms, Kinetics, and thermodynamics studies

In this study, a stable multilayered adduct of maghemite surfactant and clay was created by sandwich-like electrostatic self-assembly of cationic polyelectrolytes of cetyltrimethylammonium bromide (CTAB) with illite kaolinite (IKaol) clay. The adsorptive property of IKaol/CTAB towards MB from . Aquatic system uptake was investigated. Its characteristics were analysed using X-ray powder diffraction, Fourier transform-infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and the zero point of charge. To attain higher performance of the IKaol/CTAB for MB adsorption, the primary key factors that influence the MB dye, such as (A: loading CTAB into the composite matrix of IKaol), adsorbent dose (B: 0.02–0.06 g), pH (C: 4–10), temperature (D: 30–60 °C), and time (E: 5–60 min) , were optimised using the Box–Behnken design method. The obtained results show that the highest MB removal efficiency of 86.24 % was observed at the following significant interactions: AB, BC, and AC and at optimum adsorption operation parameters (A: 0%, B: 0.06 g, C: 7, D: 45◦C, and E: 17.5 min). At these optimum conditions, the best adsorption capacity of MB dye (114.94 mg/g) was recorded at 45°C. The most effective isotherms and kinetic models were the Freundlich and pseudo-second-order kinetic models. The MB dye adsorption mechanism by IKaol can be assigned to several interactions, such as electrostatic attractions, n-π interaction, and hydrogen bonding interactions. The results of this study demonstrate the viability of IKaol as a promising precursor for the creation of an efficient adsorbent that can be used to remove cationic dye from an aqueous environment.

Modelling terrigenous DOC across the north west European Shelf: Fate of riverine input and impact on air-sea CO2 fluxes

Terrigenous carbon in aquatic systems is increasingly recognised as an important part of the global carbon cycle. Despite this, the fate and distribution of terrigenous dissolved organic carbon (tDOC) in coastal and oceanic systems is poorly understood. We have implemented a theoretical framework for the degradation of tDOC across the land to ocean continuum in a 3D hydrodynamical-biogeochemical model on the North West European Shelf. A key feature of this model is that both photochemical and bacterial tDOC degradation rates are age dependant constituting an advance in our ability to describe carbon cycling in the marine environment. Over the time period 1986-2015, 182±17 Gmol yr−1 of riverine tDOC is input to the shelf. Results indicate that bacterial degradation is by far the most important process in removing tDOC on the shelf, contributing to 73±6 % (132±11 Gmol yr−1) of the total removal flux, while 21±3 % (39±6 Gmol yr−1) of riverine tDOC was advected away from the shelf and photochemical degradation removing 5±0.5 % of the riverine flux. Explicitly including tDOC in the model decreased the air-sea carbon dioxide (CO2) flux by 112±8 Gmol yr−1 (4±0.4 %), an amount approximately equivalent to the CO2 released by the UK chemical industry in 2020. The reduction is equivalent to 62 % of the riverine tDOC input to the shelf while approximately 17 % of riverine input is incorporated into the foodweb. This work can improve the assumptions of the fate of tDOC by Earth System Models and demonstrates that the inclusion of tDOC in models can impact ecosystem dynamics and change predicted global carbon budgets for the ocean.

Dust storms increase the tolerance of phytoplankton to thermal and pH changes.

Aquatic communities are increasingly subjected to multiple stressors through global change, including warming, pH shifts, and elevated nutrient concentrations. These stressors often surpass species tolerance range, leading to unpredictable consequences for aquatic communities and ecosystem functioning. Phytoplankton, as the foundation of the aquatic food web, play a crucial role in controlling water quality and the transfer of nutrients and energy to higher trophic levels. Despite the significance in understanding the effect of multiple stressors, further research is required to explore the combined impact of multiple stressors on phytoplankton. In this study, we used a combination of crossed experiment and mechanistic model to analyze the ecological and biogeochemical effects of global change on aquatic ecosystems and to forecast phytoplankton dynamics. We examined the effect of dust (0-75 mg L-1 ), temperature (19-27°C), and pH (6.3-7.3) on the growth rate of the algal species Scenedesmus obliquus. Furthermore, we carried out a geospatial analysis to identify regions of the planet where aquatic systems could be most affected by atmospheric dust deposition. Our mechanistic model and our empirical data show that dust exerts a positive effect on phytoplankton growth rate, broadening its thermal and pH tolerance range. Finally, our geospatial analysis identifies several high-risk areas including the highlands of the Tibetan Plateau, western United States, South America, central and southern Africa, central Australia as well as the Mediterranean region where dust-induced changes are expected to have the greatest impacts. Overall, our study shows that increasing dust storms associated with a more arid climate and land degradation can reverse the negative effects of high temperatures and low pH on phytoplankton growth, affecting the biogeochemistry of aquatic ecosystems and their role in the cycles of the elements and tolerance to global change.

Storm characteristics influence nitrogen removal in an urban estuarine environment

Abstract. Sustaining water quality is an important component of coastal resilience. Floodwaters deliver reactive nitrogen (including NOx) to sensitive aquatic systems and can diminish water quality. Coastal habitats in flooded areas can be effective at removing reactive nitrogen through denitrification (DNF). However, less is known about this biogeochemical process in urbanized environments. This study assessed the nitrogen removal capabilities of flooded habitats along an urban estuarine coastline in the upper Neuse River estuary, NC, USA, under two nitrate concentrations (16.8 and 52.3 µM NOx, respectively). We also determined how storm characteristics (e.g., precipitation and wind) affect water column NOx concentrations and consequently DNF by flooded habitats. Continuous flow sediment core incubation experiments quantified gas and nutrient fluxes across the sediment–water interface in marsh, swamp forest, undeveloped open space, stormwater pond, and shallow subtidal sediments. All habitats exhibited net DNF. Additionally, all habitats increased DNF rates under elevated nitrate conditions compared to low nitrate. Structured habitats with high-sediment organic matter had higher nitrogen removal capacity than unstructured, low-sediment organic matter habitats. High-precipitation–high-wind-storm events produced NOx concentrations significantly lower than other types of storms (e.g., low-precipitation–high-wind, high-wind–low-precipitation, low-wind–low-precipitation), which likely results in relatively low DNF rates by flooded habitats and low removal percentages of total dissolved nitrogen loads. These results demonstrate the importance of natural systems to water quality in urbanized coastal areas subject to flooding.

Progress in Research on the Bioavailability and Toxicity of Nanoplastics to Freshwater Plankton

The present review critically examines the advancements in the past 5 years regarding research on the bioavailability and toxicity of the nanoplastics (NPLs) to freshwater plankton. We discuss the recent progress in the understanding of adsorption, absorption, trophic transfer, and biological effects in phyto- and zooplankton induced by NPLs exposure. The influence of plankton on NPLs’ bioavailability via the excretion of biomolecules and formation of eco-corona is also examined. Despite important research developments, there are still considerable knowledge gaps with respect to NPLs’ bioavailability and trophic transfer by plankton as well as a potential adverse effect in natural aquatic systems. As plankton play a critical role in primary production, nutrient cycling, and food web structure, understanding the interactions between NPLs and plankton is essential in assessing the potential implications of NPLs pollution for aquatic ecosystem biodiversity and services.

Macromolecular Size and Architecture of Humic Substances Used in the Dyes’ Adsorptive Removal from Water and Soil

Humic substances are naturally occurring materials composed of complex biogenic mixtures of substituted aromatic and aliphatic hydrocarbon core materials derived from the degradation and decomposition of dead plant and animal matter. They are ubiquitous in both terrestrial and aquatic systems constituting biotic pools and are characterized by unique properties; they are amphiphilic redox compounds with exceptional chelating features. Humic substances play a crucial role in both agriculture and the environment as carbon sequestrators, soil improvers, plant health promoters, as well as stabilizers of soil aggregates and regulators of organic/inorganic nutrients bioavailability. This review article attempts to summarize current knowledge about the molecular nature and characterization techniques employed for the study of humic substances worldwide as the chemistry of their components differs markedly and depends on natural processes, several abiotic and biotic factors, the origin of the organic matter, and their complexation with inorganic, e.g., metal-ion, compounds. This work is equally concerned with the association of humic substances with dyes, a notorious pollutant, responsible for various environmental issues generally arising from the discharge of untreated effluents into soils and water bodies. Azo dyes, in particular, negatively affect soil microbial communities, as well as plant germination and growth. The aim is to feature the potential contribution of humic substances as novel materials for environment-friendly and sustainable processes.

Magnesium oxide synthesized with Alpinia zerumbet leaf extracts as a sustainable alternative to zinc oxide in nitrile rubber compounds: A comparative vulcanization kinetics investigation

AbstractZinc oxide (ZnO) is the most widely used activator in the rubber industry; however, there is growing concern about its use as it can become toxic to the environment, particularly in aquatic systems. This study describes the synthesis of magnesium oxide (MgO) assisted by the Alpinia zerumbet extract, which is then used as an activator in the replacement of ZnO to vulcanize nitrile rubber (NBR) containing 33% and 45% acrylonitrile (ACN). The t90 for NBR‐33% and NBR‐45% are 20 and 15 min, respectively. This indicates a reduction of 5 min in t90 with an increase in ACN. In comparison, ZnO‐activated NBR compounds exhibit the opposite trend, with t90 increasing from 10 for NBR‐33% to 19 min for NBR‐45%. Furthermore, the decrease in activation energy (Ea) with the increase in conversion for 33%‐MgO and 45%‐MgO indicates that vulcanization with MgO is a complex process. This behavior is comparable to that of 45%‐ZnO, but not for 33%‐ZnO because its Ea remains oscillating at 80–90 kJ mol−1 in the entire conversion range. The crosslink densities of 33%‐MgO and 45%‐MgO are 5.87 and 4.78 mol cm−3, respectively. These values are slightly higher than those for 33%‐ZnO (5.77 mol cm−3) and 45%‐ZnO (4.38 mol cm−3).

Mercury deposition to lake sediments near historic gold mines in northern Canada

Mercury (Hg) contamination in aquatic systems can lead to adverse human and environmental health outcomes. Yellowknife, a city in Canada’s Northwest Territories, is a historic mining community, with two large gold mines (Giant Mine and Con Mine) that used Hg amalgamation methods to extract gold between ∼1938 and 1960. We analyzed dated sediment cores from 20 small lakes to investigate the spatial and temporal Hg deposition patterns within 50 km of Giant Mine. Breakpoint analysis of the within-lake z-score normalized anthropogenic Hg flux indicates two significant time periods of changing emission rates. The first is a significant increase in Hg deposition rate (∼1925) during the time of gold exploration in the region and onset of Hg amalgamation (1938) and the second is a significant decrease in deposition rate that begins around the time of the cessation of Hg amalgamation at Giant Mine (∼1959). Sediment Hg concentrations exceeded the Canadian Council for Ministers of the Environment Interim Sediment Quality Guideline (ISQG) for Hg (0.17 mg/kg dw) in 55% of the lakes (n = 11) during mining (1948–1999). All lakes within 5 km of the Giant Mine roaster stack exceeded CCME ISQG during mining (n = 8), with a 4-fold increase in total Hg concentration observed during mining at these near-field (<5 km from stack) sites. We observed evidence of enriched Hg in near-field, mid-field, and far-field sites. The elevated sedimentary Hg concentrations during mining in near-field sites would have posed a hazard to human and wildlife health during the height of emissions, however the significant decrease in Hg concentrations since the closure of mines in the region demonstrate the potential for recovery in these aquatic ecosystems.

An integrated approach to testing and assessment (IATA) to support grouping and read-across of nanomaterials in aquatic systems

Even small changes in physicochemical properties of nanoforms (NFs), can drive differences in their environmental fate and hazard. The large number of new materials being developed means it will not be feasible to test and characterise the fate, behaviour and (eco)toxicity of each individual NF. This is further amplified by transformations of NFs over their lifecycle, changing the processes governing their risk. A common complexity arises from dissolution, where the combined toxicity of the exposure arises from both the solutes and any remaining particles contribution to the overall toxicity of the exposure. For efficient and effective risk assessment, it is the most relevant form of the NF for a given exposure that should be targeted for testing and assessment. In aquatic systems, functional fate processes (including dissolution, dispersion stability and chemical and biological transformations) determine the NF’s exposure relevant form. Whilst transformations in the environment alter the initial properties of an NF, different NFs may follow a shared functional fate pathway and ultimately present a similar fate and hazard profile in the environment. Therefore, these processes may be used to scientifically justify grouping NFs and read-across for specific endpoints from data rich NF(s) to verified members of the group that have not been tested yet. Integrated Approaches to Testing and Assessment (IATA) have been used in other regulatory contexts to support the collection and integration of relevant existing information as well as the targeted generation of new data to support grouping and read-across. Here, a new IATA is presented consisting of decision nodes focused on dissolution, dispersion stability, chemical transformations and the relative contribution to toxicity of the particle and dissolved component of the overall exposure. The IATA focuses on the fate of NFs in aquatic systems outside of the body, but it can be considered a template for future assessment of in vivo kinetics, which will require further development. Guidance on tiered testing approaches and thresholds for grouping within each decision node are critically discussed. Worked examples for ecotoxicity of metal oxide NFs in aqueous systems (in microbial communities isolated from soils and for lettuce plants in hydroponic systems) demonstrate successful identification of the exposure relevant form of the NF in these case studies and allows for different grouping of NFs through application of the IATA.

Combination of multivariate data analysis and mixing modelling to assess tracer potential of contaminants of emerging concern in aquifers

Collected evidence has shown that contaminants of emerging concern (CECs) in conjunction with more conventional tracers (major ions, nutrients, isotopes etc.) can be used to trace pollution origin in aquatic systems. However, in highly mixed aquifer systems signals obtained from conventional tracers overlap diminishing their potential to be used as tracers. In this study, we present an approach that incorporates multivariate statistical analysis (principal component analysis (PCA) and Kohonen's Self-Organizing Map method (SOM)) and mixing modelling to identify the most suitable CECs to be employed as anthropogenic tracers. The study area is located in the Besòs River Delta (Barcelona, NE Spain) and represents the highly mixed aquifer system. A one-year monthly based monitoring campaign was performed to collect the information about the concentrations of 105 CECs as well as major and minor ions in the river and along the groundwater flow. The dimensionality of the obtained dataset was reduced to 25 CECs, based on their estimated health risk effects, for multivariate data analysis. The obtained results showed the overlap of conventional tracers' signals obtained from PCA. In case of CECs, PCA revealed differences in their distributions allowing the differentiation of the roles of natural attenuation processes, local and regional flows on their occurrence in different parts of the aquifer. This was not possible to do using solely CECs' distribution profiles. SOMs provided the lacking information about the modality of the distribution of each CECs, revealing their ability to represent factors controlling the groundwater hydrochemistry, which assist in defining their tracer potential. Based on the obtained results four identified persistent CECs, two with unimodal (lamotrigine and 5-Desamino-5-oxo-lamotrigine) and two with bimodal (carbamazepine and diazepam (higher modality was not revealed)) distributions, were selected to run a mixing model to compare their tracer performance.

Insects in the city: Determinants of a contained aquatic microecosystem across an urbanized landscape.

Cities can have profound impacts on ecosystems, yet our understanding of these impacts is currently limited. First, the effects of the socioeconomic dimensions of human society are often overlooked. Second, correlative analyses are common, limiting our causal understanding of mechanisms. Third, most research has focused on terrestrial systems, ignoring aquatic systems that also provide important ecosystem services. Here we compare the effects of human population density and low-income prevalence on the macroinvertebrate communities and ecosystem processes within water-filled artificial tree holes. We hypothesized that these human demographic variables would affect tree holes in different ways via changes in temperature, water nutrients, and the local tree hole environment. We recruited community scientists across Greater Vancouver (Canada) to provide host trees and tend 50 tree holes over 14 weeks of colonization. We quantified tree hole ecosystems in terms of aquatic invertebrates, litter decomposition, and chlorophyll a (chl a). We compiled potential explanatory variables from field measurements, satellite images, or census databases. Using structural equation models, we showed that invertebrate abundance was affected by low-income prevalence but not human population density. This was driven by cosmopolitan species of Ceratopogonidae (Diptera) with known associations to anthropogenic containers. Invertebrate diversity and abundance were also affected by environmental factors, such as temperature, elevation, water nutrients, litter quantity, and exposure. By contrast, invertebrate biomass, chl a, and litter decomposition were not affected by any measured variables. In summary, this study shows that some urban ecosystems can be largely unaffected by human population density. Our study also demonstrates the potential of using artificial tree holes as a standardized, replicated habitat for studying urbanization. Finally, by combining community science and urban ecology, we were able to involve our local community in this pandemic research pivot.

The status of COI and 12S rRNA DNA barcode reference libraries for freshwater fish in South Africa: Implications for future eDNA projects

Environmental DNA metabarcoding (eDNA) is a rapidly emerging field in which high-throughput sequencing is used to catalogue the biodiversity of ecosystems through the amplification of DNA extracted from environmental samples (water, air, faeces and soil). Although eDNA has strong links to DNA barcoding, the molecular marker most often used to detect vertebrates in eDNA studies is a portion of the mitochondrial 12S ribosomal RNA (12S rRNA) and not the standard cytochrome oxidase I (COI) marker used in traditional DNA barcoding. eDNA methods rely on a comprehensive reference library to link sequence data to species, which are often lacking in hyper-diverse countries such as South Africa. In this study, we review the present state of DNA barcode reference databases for both 12S rRNA and COI for freshwater fish (native and introduced) found in South African aquatic systems. Analysis of DNA records available on GenBank and the Barcode of Life Database (BOLD) revealed incomplete records of the examined taxa for both markers. Our findings showed that 34 species, 6 genera and 0 families of native South African freshwater fish lack COI barcode records, while 86 species, 22 genera and 8 families lack 12S rRNA records. Unlike the native freshwater fish, the non-native fish all had barcode records available for both COI and 12S rRNA. Producing comprehensive reference libraries for both markers is an important first step in developing an eDNA protocol for the non-invasive monitoring of native and non-native freshwater fish in South Africa.

Taxonomic and environmental distribution of bacterial amino acid auxotrophies

Many microorganisms are auxotrophic—unable to synthesize the compounds they require for growth. With this work, we quantify the prevalence of amino acid auxotrophies across a broad diversity of bacteria and habitats. We predicted the amino acid biosynthetic capabilities of 26,277 unique bacterial genomes spanning 12 phyla using a metabolic pathway model validated with empirical data. Amino acid auxotrophy is widespread across bacterial phyla, but we conservatively estimate that the majority of taxa (78.4%) are able to synthesize all amino acids. Our estimates indicate that amino acid auxotrophies are more prevalent among obligate intracellular parasites and in free-living taxa with genomic attributes characteristic of ‘streamlined’ life history strategies. We predicted the amino acid biosynthetic capabilities of bacterial communities found in 12 unique habitats to investigate environmental associations with auxotrophy, using data compiled from 3813 samples spanning major aquatic, terrestrial, and engineered environments. Auxotrophic taxa were more abundant in host-associated environments (including the human oral cavity and gut) and in fermented food products, with auxotrophic taxa being relatively rare in soil and aquatic systems. Overall, this work contributes to a more complete understanding of amino acid auxotrophy across the bacterial tree of life and the ecological contexts in which auxotrophy can be a successful strategy.