B1: Pollution loads entering waters
Short Description
This indicator will track changes in selected contaminant loads entering rivers from water company sewage works and also in riverine loadings to tidal waters. The riverine loadings reflect inputs of nutrients and selected metals from point and diffuse sources across river catchments (where sources include agriculture, sewage treatment and metal mines). It will focus on selected contaminants that adversely affect the quality and uses of receiving waters. These also affect the wildlife and ecology of rivers, estuaries and coastal waters.
Readiness and links to data
This indicator is not available for reporting in 2023 in a finalised form. An interim indicator is presented here that shows (i) relative changes in measured riverine loads (inputs) of selected metals and nutrients into English tidal waters between 2008 and 2019, covering cadmium, copper, lead, mercury, zinc, nitrogen and ortho-phosphate and (ii) loads of ammonia, biochemical oxygen demand and phosphorus entering rivers from water company sewage treatment works. Some data for this interim indicator are published as part of the OSPAR assessments (Inputs of Mercury, Cadmium and Lead via Water and Air to the Greater North Sea) and via the Marine online assessment tool although for different time periods and so these data should be compared with caution. An additional data line has been added to the figure for B1a and B1b to include a representation of the variation of flow within rivers in England. This has been done to highlight the variation within the data that can be caused by higher and lower flows which can vary considerably year on year. This flow line is indicative of the total outflow of rivers in England, using data from the UK Centre for Ecology and Hydrology National River Flow Archive
Figure B1c is a new addition to the interim B1 metrics. It shows the loadings of selected pollutants entering rivers in England from water and sewerage company discharges of treated sewage effluent. The pollutants for which loads are assessed are ammonia, Biochemical Oxygen Demand (BOD, a measure of organic pollution) and total phosphorus. Annual loadings are assessed every 5 years at the end of each water industry asset management period. The data reported here are for the years 1995, 2000, 2010, 2015 and 2020. These data are reported periodically with the Environment Agency’s RPEG reports.
Further development is required to present statistical trends for the selected contaminants in an indicator. The data for B1a and B1b are taken from the existing OSPAR database. The Environment Agency reports a subset of these data to Defra on an annual basis known as the Riverine and Industrial Discharges (RIDS) dataset. Contact the Environment Agency’s National Customer Contact Centre enquiries@environment-agency.gov.uk for the OSPAR database extract used for the interim indicator.
Notes on indicator
Data collection for B1a and B1b was heavily impacted by adherence to the government’s COVID-19 restrictions during the pandemic. This severely restricted sample collection and analysis during 2020 and 2021, so the available results are not considered representative of the riverine inputs to tidal waters, so have not been reported.
Load (input) calculations (kilograms per day) are the product of the monitored concentration of substance and flow rate. The annual total loads (kilograms per year) for selected metals (total fraction), total nitrogen and ortho-phosphate are calculated using chemical concentration data reported in the Water quality data Archive and flow data reported in the Environment Agency’s core system of hydrometric and hydrological values (Water Information System by Kisters).
Figures B1a and B1b show each annual load relative to the 2008 monitored load (2008 is represented as a baseline index = 100). Observed fluctuations in the data could be influenced by a number of external factors affecting movement and loading within river systems. These factors include flow caused by high or low rainfall in a given year and local impacts of changing industry or land use over time. There appears to be a relationship between high flows and high loads, and it should also be noted that the baseline year of 2008 saw high flows, the variation in flows can now be identified via the flow line on B1a and B1b, also calculated relative to the 2008 baseline.
The pollutant loadings for B1c are primarily estimated from measured sewage effluent flow and concentration data for each pollutant at sewage treatment works (STWs) with numeric permits for the pollutants in question. For smaller STWs that do not have numeric conditions, modelled loads are estimated using default concentrations and measured or default flow figures. The total load per pollutant is the measured and modelled wastewater load discharged in that year in tonnes per annum. The totals are presented in Figure B1c as kilo tonnes (thousands of tonnes) per annum. The data reported are for STWs that discharge to rivers in England operated by those water and sewerage companies wholly or mainly operating in England. This means that works operated in England (River Wye and River Dee catchments) by Dwr Cymru Welsh Water are not part of the estimates.
Indicator components
Figure B1a: Riverine inputs of selected metals into English tidal waters, 2008 to 2019
Table B1a: Riverine inputs of selected metals into English tidal waters, 2008 to 2019
| Year | Cadmium | Copper | Lead | Mercury | Zinc | Flow |
|---|---|---|---|---|---|---|
| 2008 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
| 2009 | 108.90 | 85.90 | 167.35 | 66.39 | 103.39 | 78.31 |
| 2010 | 60.01 | 61.00 | 67.14 | 67.43 | 63.30 | 65.43 |
| 2011 | 59.33 | 50.78 | 81.54 | 51.55 | 65.91 | 62.71 |
| 2012 | 96.94 | 94.93 | 211.07 | 91.92 | 108.48 | 108.12 |
| 2013 | 64.65 | 64.27 | 91.94 | 82.55 | 70.95 | 81.36 |
| 2014 | 86.22 | 94.32 | 107.75 | 84.56 | 99.74 | 99.45 |
| 2015 | 48.00 | 49.28 | 58.47 | 47.83 | 54.14 | 82.67 |
| 2016 | 49.09 | 61.37 | 56.64 | 63.68 | 60.90 | 79.19 |
| 2017 | 63.84 | 66.26 | 105.80 | 63.28 | 67.01 | 65.64 |
| 2018 | 41.98 | 53.89 | 55.87 | 45.71 | 81.15 | 73.22 |
| 2019 | 51.49 | 58.71 | 78.89 | 54.72 | 68.34 | 90.11 |
Trend description for B1a
Riverine inputs of cadmium, copper, lead, mercury and zinc into English tidal waters have fluctuated considerably between 2008 and 2019 and using indexed data, overall, they have all fallen. Measured loads of cadmium, mercury, copper, zinc and lead were 49%, 45%, 41% 32% and 21% respectively less in 2019 than they were in 2008.
Assessment of change
No assessment of change was undertaken for this indicator as further development is required to present statistical trends for the selected contaminants in an indicator.
Figure B1b: Riverine inputs of selected nutrients into English tidal waters, 2008 to 2019
Table B1b: Riverine inputs of selected nutrients into English tidal waters, 2008 to 2019
| Year | Ortho-Phosphate | Total Nitrogen | Flow |
|---|---|---|---|
| 2008 | 100.00 | 100.00 | 100.00 |
| 2009 | 65.18 | 69.70 | 78.31 |
| 2010 | 59.07 | 57.26 | 65.43 |
| 2011 | 60.85 | 52.15 | 62.71 |
| 2012 | 81.06 | 79.80 | 108.12 |
| 2013 | 59.58 | 70.33 | 81.36 |
| 2014 | 63.64 | 82.38 | 99.45 |
| 2015 | 53.06 | 63.63 | 82.67 |
| 2016 | 53.67 | 76.99 | 79.19 |
| 2017 | 48.81 | 60.12 | 65.64 |
| 2018 | 48.99 | 80.66 | 73.22 |
| 2019 | 51.43 | 59.30 | 90.11 |
Trend description for B1b
B1b) Riverine inputs of selected nutrients Riverine inputs of total nitrogen and ortho-phosphate have also fluctuated considerably between 2008 and 2019, but overall, both have fallen, and both have remained below their baseline value with measured loads in 2019 being 41% and 49% respectively less than those measured in 2008
Assessment of change
No assessment of change was undertaken for this indicator as further development is required to present statistical trends for the selected contaminants in an indicator.
Figure B1c: Loads discharged to rivers from water company sewage treatment works in England, 1995 to 2020
Table B1c: Loads discharged to rivers from water company sewage treatment works in England, 1995 to 2020
| Year | Ammonia | BOD | Phosphorus |
|---|---|---|---|
| 1995 | 16.15 | 36.74 | 21.41 |
| 2000 | 8.17 | 27.11 | 16.68 |
| 2005 | 7.66 | 25.21 | 12.84 |
| 2010 | 5.42 | 22.40 | 10.61 |
| 2015 | 3.60 | 19.20 | 8.60 |
| 2020 | 3.25 | 16.60 | 6.75 |
Trend description for B1c
The loads of all three pollutants have dropped significantly since the recording began in 1995. Ammonia has reduced by the greatest degree to approximately 20% of loads (80% reduction) in 2020 compared to loadings in 1995. While the loads for BOD and phosphorus have dropped by 55% and 68%.
Assessment of change
No assessment of change was undertaken for this indicator as further development is required to present statistical trends for the selected contaminants in an indicator.