Microplastic (MP) pollution is an emerging issue in aquatic sciences. Little comparative information currently exists about the problem in coastal systems exposed to different levels of human impact. ...Here we report a year-long study on the abundance of MP in the water column of three estuaries on the east-coast of Australia. The estuaries are subject to different scales of human impact; the Clyde estuary has little human modification, the Bega estuary has a small township and single wastewater treatment works discharging to its waters, and the Hunter estuary which has multiple townships, multiple wastewater treatment plants, and heavy industry. MP abundance followed an expected pattern with the lowest abundance in the low-impact Clyde estuary (98 part. m3), moderate levels of MP in the moderately impacted Bega estuary (246 part. m3), and high MP abundance in the highly impacted Hunter estuary (1032 part. m3). The majority of particles were <200 μm and fragment-like rather than fiber-like. MP abundance was positively related to maximum antecedent rainfall in the Bega estuary, however there are no clear environmental factors that could explain MP variation in the other systems. MP were generally higher in summer and following freshwater inflow events. On the Hunter estuary MP abundance was at times as high as zooplankton abundance, and within the range of numbers reported in other highly impacted systems globally. The results confirm that higher levels of human impact lead to greater plastic pollution and highlight the need to examine aquatic ecosystems under a range of conditions in order to adequately characterize the extent of MP pollution in rivers and coastal systems.
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•Microplastic abundance increased in estuaries with increasing human impact.•68–76% of particles <200 μm.•The majority of microplastics were fragment-like rather than fibers.•Microplastic concentrations positively related to antecedent rainfall.
Microplastic abundance is higher in estuaries with higher human impact. The microplastic pool was dominated by fragment like particles <200 μm in size.
Cyanobacterial blooms are becoming more common in freshwater systems, causing ecological degradation and human health risks through exposure to cyanotoxins. The role of phosphorus and nitrogen in ...cyanobacterial bloom formation is well documented and these are regularly the focus of management plans. There is also strong evidence that trace metals are required for a wide range of cellular processes, however their importance as a limiting factor of cyanobacterial growth in ecological systems is unclear. Furthermore, some studies have suggested a direct link between cyanotoxin production and some trace metals. This review synthesises current knowledge on the following: (1) the biochemical role of trace metals (particularly iron, cobalt, copper, manganese, molybdenum and zinc), (2) the growth limitation of cyanobacteria by trace metals, (3) the trace metal regulation of the phytoplankton community structure and (4) the role of trace metals in cyanotoxin production. Iron dominated the literature and regularly influenced bloom formation, with 15 of 18 studies indicating limitation or colimitation of cyanobacterial growth. A range of other trace metals were found to have a demonstrated capacity to limit cyanobacterial growth, and these metals require further study. The effect of trace metals on cyanotoxin production is equivocal and highly variable. Better understanding the role of trace metals in cyanobacterial growth and bloom formation is an essential component of freshwater management and a direction for future research.
The growth of planktonic cyanobacteria in a weir pool on the Lower Darling River, Australia, downstream of the major regulated Menindee Lake system was examined. Blooms of the saxitoxin producing ...freshwater cyanobacterium Anabaena circinalis occurred for two summers out of four studied. Large cell numbers of other cyanobacteria including Aphanizomenon, Planktolyngbya and Merismopedia also occurred during the same summer periods as the Anabaena blooms. The growth events also coincided with periods of improved light climate. Flow releases from the regulated Menindee Lakes System were assessed for their ability to either suppress bloom development or to mitigate pre-existing blooms over this period. A discharge of 300 ML/day (flow velocity of 0.03 m/s) was found to be sufficient to prevent prolonged periods of persistent thermal stratification, which also suppressed the development of A. circinalis blooms. A flow release of 3000 ML/day was effective at removing an established cyanobacterial bloom, and total cyanobacterial numbers declined from over 100 000 to <1000 cells/mL within a week. In two summers without blooms, higher flows and decreased light availability prevented the development of cyanobacterial blooms. Flow releases were effective at mitigating cyanobacterial growth through either the suppression of persistent thermal stratification or through dilution and translocation of cells. Greater discharges also increased turbidity, which diminished the growth of cyanobacteria through reduced light availability under the mixed conditions, which also reduced the ability for surface migration through buoyancy regulation. The volume of water required for different management strategies varied and is considered in terms of environmental allocations.
The survival of aquatic biota in stream ecosystems depends on both water quantity and quality, and is particularly susceptible to degraded water quality in regulated rivers. Maintenance of ...environmental flows (e-flows) for aquatic biota with optimum water quantity and quality is essential for sustainable ecosystem services, especially in developing regions with insufficient stream monitoring of hydrology, water quality and aquatic biota. Few e-flow methods are available that closely link aquatic biota tolerances to pollutant concentrations in a simple and practical manner. In this paper a new method was proposed to assess e-flows that aimed to satisfy the requirements of aquatic biota for both the quantity and quality of the streamflow by linking fish tolerances to water quality criteria, or the allowable concentration of pollutants. For better operation of water projects and control of pollutants discharged into streams, this paper presented two coefficients for streamflow adjustment and pollutant control. Assessment of e-flows in the Wei River, the largest tributary of the Yellow River, shows that streamflow in dry seasons failed to meet e-flow requirements. Pollutant influx exerted a large pressure on the aquatic ecosystem, with pollutant concentrations much higher than that of the fish tolerance thresholds. We found that both flow velocity and water temperature exerted great influences on the pollutant degradation rate. Flow velocity had a much greater influence on pollutant degradation than did the standard deviation of flow velocity. This study provides new methods to closely link the tolerance of aquatic biota to water quality criteria for e-flow assessment. The recommended coefficients for streamflow adjustment and pollutant control, to dynamically regulate streamflow and control pollutant discharge, are helpful for river management and ecosystems rehabilitation. The relatively low data requirement also makes the method easy to use efficiently in developing regions, and thus this study has significant implications for managing flows in polluted and regulated rivers worldwide.
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•We present a new e-flows assessment method linking fish tolerances to pollutant criteria.•Requirements of fish for both quantity and quality of streamflow were well addressed.•The method is not data-intensive especially suitable for data-scarce rivers.•It provides new ways to link tolerance of aquatic biota to water quality concentrations.•It has significant implications for managing flows in polluted, regulated rivers worldwide.
To reveal the occurrence and mechanisms for dispersal of antibiotic resistance (AbR) among the microbial assemblages inhabiting impacted coastal environments, we performed a weekly, two-year duration ...time-series study at two urban beaches between 2014 and 2016. We combined quantitative PCR and multiplex PCR/reverse line blot techniques to track patterns in the occurrence of 31 AbR genes, including genes that confer resistance to antibiotics that are critically important antimicrobials for human medicine. Patterns in the abundance of these genes were linked to specific microbial groups and environmental parameters by coupling qPCR and 16S rRNA amplicon sequencing data with network analysis. Up to 100-fold increases in the abundance of several AbR genes, including genes conferring resistance to quinolones, trimethoprim, sulfonamides, tetracycline, vancomycin and carbapenems, occurred following storm-water and modelled wet-weather sewer overflow events. The abundance of AbR genes strongly and significantly correlated with several potentially pathogenic bacterial OTUs regularly associated with wastewater infrastructure, such as Arcobacter, Acinetobacter, Aeromonas and Cloacibacterium. These high-resolution observations provide clear links between storm-water discharge and sewer overflow events and the occurrence of AbR in the coastal microbial assemblages inhabiting urban beaches, highlighting a direct mechanism for potentially significant AbR exposure risks to humans.
•Storm-water events augment antibiotic resistance genes in coastal receiving waters.•Several antibiotic resistance genes remain elevated 1–2 weeks following rainfall.•Beach swimmers could be exposed to antibiotic resistant microbes and their genes.
Phosphorus (P) limitation has been regarded as the rule in freshwater systems and the basis for phytoplankton growth management. We hypothesised that P would be the limiting nutrient for ...phytoplankton growth in Grahamstown Dam, a shallow, mesotrophic reservoir, across different seasons and on different experimental time scales. Seven fully factorial microcosm assays with additions of nitrogen (N) and P were conducted in situ during different seasons. The influence of longer experimental duration was examined in two 18-day mesocosm assays. Additions of N and P in combination evoked significantly higher phytoplankton biomass and biovolumes of individual algal genera compared with controls and other treatments in both types of experiment. There were some significant responses to P additions in the microcosm assays in winter. Some genera first responded to combined P and N addition and then to P only addition during the mesocoms assays. Our results show that P was not the limiting nutrient across all seasons but that phytoplankton was mostly co-limited by N and P. A longer experimental time scale did not change this outcome at the biomass level. This implies that input of N as well as of P should be considered in the management of phytoplankton growth.
β-N-methylamino L-alanine (BMAA) is a neurotoxin linked to high incidences of neurodegenerative disease. The toxin, along with two of its common isomers, 2,4-diaminobuytric acid (2,4-DAB) and ...N-(2-aminoethyl)glycine (AEG), is produced by multiple genera of cyanobacteria worldwide. Whilst there are many reports of locations and species of cyanobacteria associated with the production of BMAA during a bloom, there is a lack of information tracking changes in concentration across a single bloom event. This study aimed to measure the concentrations of BMAA and its isomers through the progression and end of a cyanobacteria bloom event using liquid chromatography-triple quadrupole-mass spectrometry. BMAA was detected in all samples analysed, with a decreasing trend observed as the bloom progressed. BMAA’s isomers were also detected in all samples, however, they did not follow the same decreasing pattern. This study highlights the potential for current sampling protocols that measure a single time point as representative of a bloom’s overall toxin content to underestimate BMAA concentration during a bloom event.
•Flow management changes affect water quality and phytoplankton dynamics.•Major bushfire and subsequent heavy rainfall triggered eutrophication.•Manganese associated with phytoplankton productivity ...(Chl-a and cyanobacteria).•Functional grouping and Q index improved water quality assessment.
This study analyses over a decade (2009–2022) of monitoring data to understand the impact of hydrological characteristics on water quality and phytoplankton dynamics in Prospect Reservoir, a critical water supply for Greater Sydney, Australia, known for its excellent water quality. Water quality and phytoplankton dynamics were related to hydrodynamics, linked to flow management and the water quality of inflows. Phytoplankton biovolume increased after a prolonged drawdown and subsequent refill event, mainly driven by dinoflagellates, and corresponded to increases in total phosphorus and water temperature. The hydrological period following the 2019/2020 summer bushfires (post-bushfire) that impacted connected reservoirs, was marked by increased flow activity and nutrient loading, leading to significant shifts in the phytoplankton community. Functional group classification and ordination analysis indicated a transition from taxa typically dominant in oligotrophic conditions to meso‑eutrophic. This transition correlated with elevated nutrient levels and chlorophyll-a (Chl-a), and reduced Secchi depth and dissolved oxygen, providing evidence of eutrophication. Q index indicated good water quality post-bushfire, contrasting with a eutrophic status assessment using Chl-a. Our findings highlight the importance of analysing long-term datasets encompassing varied hydroclimatological conditions for a deeper understanding of reservoir behaviour. A comprehensive approach to water quality assessment is recommended, combining functional group classification, Q index and Chl-a measurements for effective reservoir health assessment. This research provides novel insights into the effects of disturbances such as bushfires, on water quality and phytoplankton dynamics in an underrepresented geographic region, offering valuable knowledge for managing water resources amidst growing climate variability.
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Micronutrients play key roles in numerous metabolic processes in cyanobacteria. However, our understanding of whether the micronutrient cobalt influences the productivity of freshwater systems or the ...occurrence of cyanobacterial blooms is limited. This study aimed to quantify the concentration of Co necessary for optimal cyanobacterial growth by exposing Microcystis aeruginosa to a range of Co concentrations under culture conditions. Extended exposure to concentrations below ˜0.06 μg · L−1 resulted in notable inhibition of M. aeruginosa growth. A clear negative relationship was observed between Co concentration in solution and intracellular Fe quota of M. aeruginosa, possibly due to decreased transport of Fe at higher Co concentrations. Cyanocobalamin and any Co within the structure of cyanocobalamin appears to be non‐bioavailable to M. aeruginosa, instead they likely rely on the synthesis of a structural variant – pseudocobalamin, which may have implications for the wider algal community as the variants of cobalamin are not necessarily functionally exchangeable. To evaluate the likelihood of Co limitation of cyanobacterial growth under field conditions, a survey of 10 freshwater reservoirs in South‐Eastern Australia was conducted. Four of the ten sites had dissolved Co concentrations below the 0.06 μg · L−1 threshold value. All four of these sites rarely undergo cyanobacterial blooms, strengthening evidence of the potential for Co to limit growth, perhaps either alone or in combination with phosphorus.
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