Effectiveness of eDNA for monitoring riverine macroinvertebrates.

Environmental DNA (eDNA) is a technique increasingly used for monitoring organisms in the natural environment including riverine macroinvertebrates. However, the effectiveness of eDNA for monitoring riverine macroinvertebrates compared with the more traditional method of sampling the organisms directly and identifying them via morphological analysis, has not been well established. Furthermore, the ability of the various gene markers and PCR primer sets to detect the full range of riverine invertebrate taxa has not been quantified. Here we conducted a meta-analysis of the available literature, to assess the effectiveness of eDNA sampling for detecting riverine macroinvertebrates compared with sampling for the organisms directly and applying morphological analysis. We found, on average, eDNA sampling, irrespective of the gene marker used, detected fewer riverine invertebrates than morphological sampling. The most effective PCR primer set for identifying taxa was mlCOIintF/jgHCO2198, (mlCOIintF- forward primer, jgHCO2198, - reverse primer). Regardless of the gene marker or primer sets used, however, many taxa were not detected by eDNA metabarcoding that were detected by sampling directly for these invertebrates, including over 100 members of Arthropoda. eDNA sampling failed to detect any species belonging to Nematoda, Platyhelminthes, Cnidaria or Nematomorpha and these markers applied for eDNA sampling in terrestrial systems also do not detect members of Nematoda. In addition to these issues, uncertainties relating to false positives from upstream DNA sources, the stability of DNA from different species, differences in the propensity for DNA release into the environment for different organisms, and lack of available sequence information for numerous taxa illustrates the use of eDNA is not yet applicable as a robust stand-alone method for the monitoring of riverine invertebrates. As a primary consideration, further methodological developments are needed to ensure eDNA captures some of the key freshwater taxa, notably taxa belonging to the phyla Arthropoda, Nematoda, Platyhelminthes, Cnidaria and Nematomorpha.

Assessment of the impacts of GABA and AChE targeting pesticides on freshwater invertebrate family richness in English Rivers.

Globally, riverine system biodiversity is threatened by a range of stressors, spanning pollution, sedimentation, alterations to water flow, and climate change. Pesticides have been associated with population level impacts on freshwater invertebrates for acute high-level exposures, but far less is known about the chronic impact of episodic exposure to specific classes of pesticides or their mixtures. Here we employed the use of the UK Environment Agency's monitoring datasets over 40 years (covering years 1980 to 2019) to assess the impacts of AChE (acetylcholinesterase) and GABA (gamma-aminobutyric acid) receptor targeting pesticides on invertebrate family richness at English river sites. Concentrations of AChE and GABA pesticides toxic to freshwater invertebrates occurred (measured) across 18 of the 66 river sites assessed. For one of the three river sites (all found in the Midlands region of England) where data recorded over the past 40 years were sufficient for robust modelling studies, both AChE and GABA pesticides associated with invertebrate family richness. Here, where AChE total pesticide concentrations were classified as high, 46 of 64 invertebrate families were absent, and where GABA total pesticide concentration were classified as high, 16 of 64 invertebrate families were absent. Using a combination of field evidence and laboratory toxicity thresholds for population relevant endpoints we identify families of invertebrates most at risk in the selected English rivers to AChE and GABA pesticides. We, furthermore, provide strong evidence that the absence of the invertebrate family Polycentropodidae (caddisfly) from one field site is due to exposure effects to AChE pesticides.

Pesticide pollution associations with riverine invertebrate communities in England.

Globally freshwater biodiversity has experienced major decline and chemical pollutants are believed to have played a significant role in this decline, but this has not been well quantified for most riverine invertebrate populations. Here we applied a biogeographically independent trait-based bioindicator, SPEARpesticides across sites across five regions (Northern, Midlands and Western, Anglian, Southeast, and Southwest) in England to investigate for associations specifically between pesticide use/pollution and riverine invertebrate communities over a 55-year period (1965-2019). Both spatially and temporally post-1990, the Anglian and Thames regions consistently showed the lowest SPEARpesticides scores, illustrating the presence of fewer pesticide sensitive species. The Anglian region had the highest pesticide use compared to all other regions from 1990 to 2018 and there were negative relationships between the level of pesticide/insecticide use and the regional SPEARpesticides score. Biochemical Oxygen Demand and ammonia, as measures of general water quality, were also negatively correlated with the SPEARpesticides scores across the regions, but these factors were not the driver for the lower SPEARpesticides scores seen in the Anglian region. Based on SPEARpesticides scores, riverine invertebrate communities in England have been most impacted in the Anglian region and we evidence chronic insecticide exposure is likely a significant factor in shaping the status of those invertebrate communities.