Alongside samples collected for chemical analysis in the UK, three additional biological river water sample replicates (100 mL) were filtered via 50 mL syringes through sterilized filter holder units containing 0.2 μm cellulose filter papers (Whatman, UK). Filter papers were kept in the housing unit and transported back to the lab. DNA was then extracted directly from the filter paper using FastDNA SPIN Kit for Soil (MP Bio, UK). The amount of extracted DNA was determined using a Qubit 4 Fluorometer (Thermo Scientific, UK). DNA was kept at -20 °C before further analysis.