How suitable is freshwater sponge Ephydatia fluviatilis (Linnaeus, 1759) for time-integrated biomonitoring of microbial water quality?

Faecal pollution of water by bacteria has a negative effect on water quality and can pose a potential health hazard. Conventional surveillance of microbial water quality relies on the analysis of low-frequency spot samples and is thus likely to miss episodic or periodic pollution. This study aimed to investigate the potential of filter-feeding sponges for time-integrated biomonitoring of microbial water quality. Laboratory trials tested the effects of different ratios of bacterial abundance and the sequence of exposure on bacterial retention by the freshwater sponge Ephydatia fluviatilis (Linnaeus, 1759) to establish its potential to indicate bacterial exposure. Gemmule grown sponges were simultaneously exposed to Escherichia coli and Enterococcus faecalis but at different ratios (Trial 1) or individually exposed to each bacterial species but in different sequential order (Trial 2). The E. coli and E. faecalis retained in each sponge was quantified by culture on selective agars. Data analysis was conducted using the Kruskal-Wallis test and/or the Mann-Whitney U test to compare between the numbers of bacteria retained in each treatment. Additionally, the Wilcoxon matched-paired signed-rank test was used for comparison of the different bacterial abundances retained within each individual sponge. Sponges from all trials retained E. coli and E. faecalis in small numbers relative to the exposure (<0.05 % Trial 1 and <0.07 % Trial 2) but exhibited higher retention of E. coli. Higher abundance of either bacterial species resulted in significantly lower (P<0.005) retention of the same species within sponges (Trial 1). An initial exposure to E. coli resulted in significantly higher (P=0.040) retention of both bacterial species than when sponges were exposed to E. faecalis first (Trial 2).Bacterial retention by sponges was neither quantitatively representative of bacterial abundance in the ambient water nor the sequence of exposure. This implies either selective filtration or an attempt by sponges to prevent infection. However, freshwater sponges may still be useful in biomonitoring as qualitative time-integrated samplers of faecal indicator bacteria as they detect different bacteria present in the water even if their quantities cannot be estimated.

Biological and synthetic surfactant exposure increases antimicrobial gene occurrence in a freshwater mixed microbial biofilm environment.

Aquatic habitats are particularly susceptible to chemical pollution, such as antimicrobials, from domestic, agricultural, and industrial sources. This has led to the rapid increase of antimicrobial resistance (AMR) gene prevalence. Alternate approaches to counteract pathogenic bacteria are in development including synthetic and biological surfactants such as sodium dodecyl sulfate (SDS) and rhamnolipids. In the aquatic environment, these surfactants may be present as pollutants with the potential to affect biofilm formation and AMR gene occurrence. We tested the effects of rhamnolipid and SDS on aquatic biofilms in a freshwater stream in Northern Ireland. We grew biofilms on contaminant exposure substrates deployed within the stream over 4 weeks. We then extracted DNA and carried out shotgun sequencing using a MinION portable sequencer to determine microbial community composition, with 16S rRNA analyses (64,678 classifiable reads identified), and AMR gene occurrence (81 instances of AMR genes over 9 AMR gene classes) through a metagenomic analysis. There were no significant changes in community composition within all systems; however, biofilm exposed to rhamnolipid had a greater number of unique taxa as compared to SDS treatments and controls. AMR gene prevalence was higher in surfactant-treated biofilms, although not significant, with biofilm exposed to rhamnolipids having the highest presence of AMR genes and classes compared to the control or SDS treatments. Our results suggest that the presence of rhamnolipid encourages an increase in the prevalence of AMR genes in biofilms produced in mixed-use water bodies.

Fine-scale quantification of stream bank geomorphic volume loss caused by cattle access.

Unrestricted cattle access to streams and rivers can be a significant source of pollution in fluvial systems, contributing to bank erosion and fine sediment inputs. Despite this pressure, observational data are scarce. This study quantified stream bank geomorphic modifications caused by cattle access at fine scale using motion-capture cameras and Terrestrial Laser Scanning (TLS) campaigns. Continuous monitoring of rainfall, discharge, conductivity and turbidity further augmented this dataset. The application of these techniques extended over a five-month grazing period in agricultural sub-catchments with intensive cattle production. At low flow, high-resolution water quality data showed that the frequency of cattle activity in and around stream margins was associated with elevated turbidity signals downstream. However, when elevated turbidity coincided with high flow events, it was not possible to distinguish between local erosion and upstream sediment transfers. TLS results indicated a loss of 0.141 m3 to 1.035 m3 stream bank material, which equates to 0.067 m3 m-2 - 0.092 m3 m-2 of stream bank area (between 27% and 41% in the <2 mm fraction) over the study period from sites with 130 to 1154 discrete cattle access hits. Multiple linear regression showed that the observed geomorphic volume loss could not be explained by natural processes alone (hydrometeorology), but was more significantly related to cattle-access frequency as the principal driver. The geomorphic volume loss had the potential to impact 29 m2 to 197 m2 of stream bed with fine sediment (<2 mm) from the three study sites. Grazing parcels adjacent to streams in the study sub-catchments were enumerated at 18.4 parcels km-2 and so the results of this investigation potentially scale to a considerable fine sediment risk. Regulations and time-limited incentives to exclude cattle access to stream channels should therefore expect to reduce sediment pressures where these measures are targeted at access points.

Prioritization Approaches for Substances of Emerging Concern in Groundwater: A Critical Review.

Risks from emerging contaminants (ECs) in groundwater to human health and aquatic ecology remain difficult to quantify. The number of ECs potentially found in groundwater presents challenges for regulators and water managers regarding selection for monitoring. This study is the first systematic review of prioritization approaches for selecting ECs that may pose a risk in groundwater. Online databases were searched for prioritization approaches relating to ECs in the aquatic environment using standardized key word search combinations. From a total of 672, 33 studies met the eligibility criteria based primarily on the relevance to prioritizing ECs in groundwater. The review revealed the lack of a groundwater specific contaminant prioritization methodology in spite of widely recognized differences between groundwater and surface water environments with regard to pathways to receptors. The findings highlight a lack of adequate evaluation of methodologies for predicting the likelihood of an EC entering groundwater and knowledge gaps regarding the occurrence and fate of ECs in this environment. The review concludes with a proposal for a prioritization framework for ECs in groundwater monitoring that enables priority lists to be updated as new information becomes available for substances with regard to their usage, physicochemical properties, and hazards.

Transfer of antibiotic resistance genes between Enterococcus faecalis strains in filter feeding zooplankton Daphnia magna and Daphnia pulex.

Antibiotic resistant bacteria from faecal pollution sources are pervasive in aquatic environments. A facilitating role for the emergence of waterborne, multi-drug resistant bacterial pathogens has been attributed to biofiltration but had not yet been substantiated. This study investigated the effect of filtration and gut passage in Daphnia spp. on conjugal transfer of resistance genes in Enterococcus faecalis. In vivo conjugation experiments involved a vancomycin-resistant donor strain bearing a plasmid-borne vanA resistance gene, and two vancomycin-susceptible and rifampicin-resistant recipient strains in the presence of Daphnia magna or Daphnia pulex. Results showed successful transfer of the vanA resistance gene from donor to recipient; gene identity was confirmed by PCR and DNA sequencing. There was no significant difference in the number of transconjugants recovered from D. magna and D. pulex. However, transconjugant numbers differed by one order of magnitude between recipient strains. Transconjugant numbers from D. magna were also significantly different between treatments with ingestion of individual phytoplankton species before filtration of bacteria. The highest transfer efficiency calculated from excreted transconjugants was 2.5 × 10-6. This proof of concept for facilitation of horizontal gene transfer by a filter feeding organism provides evidence that Daphnia can disseminate antibiotic resistant transconjugants in the environment.

An assessment of the performance of municipal constructed wetlands in Ireland.

While performance assessments of constructed wetlands sites around the world have appraised their capacity for effective removal of organics, a large variance remains in these sites' reported ability to retain nutrients, which appears to depend on differences in design, operation and climate factors. Nutrient retention is a very important objective for constructed wetlands, to avoid eutrophication of aquatic environments receiving their effluents. This study assessed the performance of constructed wetlands in terms of nutrient retention and associated parameters under the humid conditions of Ireland's temperate maritime climate. A review of the performance of 52 constructed wetland sites from 17 local authorities aimed to identify the best performing types of constructed wetlands and the treatment factors determining successful compliance with environmental standards. Data analysis compared effluent results from constructed wetlands with secondary free surface flow or tertiary horizontal subsurface flow, hybrid systems and integrated constructed wetlands with those from small-scale mechanical wastewater treatment plants of the same size class. Nutrient concentrations in effluents of constructed wetlands were negatively correlated (p < .01) with specific area, i.e. the ratio of surface area and population equivalents. The latest generation of integrated constructed wetlands, which had applied design guidelines issued by the Department of the Environment, performed best. Storm management design features improved treatment performance of constructed wetlands significantly (p < .05) for total suspended solids concentrations and exceedance frequency of limit values for total nitrogen. Mechanical wastewater treatment plants, secondary free surface water and tertiary horizontal subsurface flow wetlands showed a very large variance in effluent concentrations for organic and nutrient parameters. E. coli numbers in effluents were lowest for integrated constructed wetlands with an arithmetic mean of 89 MPN/100 ml. Despite Ireland's humid climate, some constructed wetland sites achieved long or frequent periods of zero effluent discharge and thus did not transfer any waterborne pollution to their receptors during these periods.

Field and laboratory tests of flow-proportional passive samplers for determining average phosphorus and nitrogen concentration in rivers.

Flow responsive passive samplers offer considerable potential in nutrient monitoring in catchments; bridging the gap between the intermittency of grab sampling and the high cost of automated monitoring systems. A commercially available passive sampler was evaluated in a number of river systems encapsulating a gradient in storm response, combinations of diffuse and point source pressures, and levels of phosphorus and nitrogen concentrations. Phosphorus and nitrogen are sequestered to a resin matrix in a permeable cartridge positioned in line with streamflow. A salt tracer dissolves in proportion to advective flow through the cartridge. Multiple deployments of different cartridge types were undertaken and the recovery of P and N compared with the flow-weighted mean concentration (FWMC) from high-resolution bank-side analysers at each site. Results from the passive samplers were variable and largely underestimated the FWMC derived from the bank-side analysers. Laboratory tests using ambient river samples indicated good replication of advective throughflow using pumped water, although this appeared not to be a good analogue of river conditions where flow divergence was possible. Laboratory tests also showed good nutrient retention but not elution and these issues appeared to combine to limit the utility in ambient river systems at the small catchment scale.