DOI: 10.5061/dryad.00000008b
title: Data from: The combined effects of treated sewage discharge and land use on rivers

description: Freshwater ecosystems are increasingly threatened by multiple
 anthropogenic stressors. Release of treated sewage effluent and pollution
 from agricultural or urban sources can independently reduce water quality
 with implications for ecological communities. However, our knowledge of
 the combined effects of these stressors is limited. We performed a field
 study to quantify the combined effect of treated sewage discharge and land
 use on nutrient concentrations, sewage fungus presence, and communities of
 macroinvertebrates and benthic algae. Over three seasons in four rivers we
 found that a model which included an interaction between sewage pollution
 and time of the year (i.e., months) was the best predictor of nutrient
 concentrations and the abundance of algae and sewage fungus. Both
 macroinvertebrate and algae communities shifted downstream of sewage
 input. Specifically, more tolerant groups, such as cyanobacteria and
 Oligochaetes, were more abundant. The EPT (Ephemeroptera, Plecoptera, and
 Tricoptera) water quality score was best explained by an interaction
 between month and agriculture in the surrounding landscape. Overall, our
 results show that sewage discharge has a significant impact on water
 quality and benthic riverine communities, regardless of the surrounding
 land uses. Agricultural inputs, however, could be more important than
 treated sewage discharge in reducing the abundance of sensitive
 invertebrate taxa. We need both improvements to wastewater treatment
 processes and reductions in agricultural pollution to reduce threats to
 vulnerable freshwater communities.
description: The study was conducted during three sampling campaigns in 2021
 at four rivers in the UK. Two areas were sampled at each river: 5-10
 meters upstream (controls) and 5-10 meters downstream (impacts) of sewage
 discharge points. Nutrient analysis and sewage fungus estimation were
 performed on collected water samples. Benthic algae biomass was quantified
 using BenthoTorch. Macroinvertebrates were collected using Surber samples
 and identified in the lab. Land cover classification used Sentinel-2
 satellite data through Google Earth Engine, distinguishing
 "agriculture" and "urbanisation" types.
 Water samples from upstream and downstream areas were collected
 on each occasion to collect sewage fungus. Nutrient concentrations
 (nitrate, phosphate, chloride, sulfate) were analysed, and sewage fungus
 abundance was enumerated using preserved samples using a FlowCam
 machine. Benthic algae biomass was measured using
 BenthoTorch on rocks collected from streams. Macroinvertebrates were
 collected using Surber samples, preserved, identified, and counted in the
 lab. The EPT score indicating sensitive macroinvertebrate groups was
 calculated. Google Earth Engine and Sentinel-2 data
 were used to classify land cover. A region encompassing upstream areas was
 selected, and a supervised classification was conducted based on NDVI
 bands, defining "agriculture" and "urbanisation"
 categories. Percentages of these categories were determined for each
 area.
description: R studio was used to perform all the statistical analysis and to
 create the graphs.