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 2024 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 Convention for the Protection of the Marine Environment of the North-East Atlantic (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 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 Regulating for People, the Environment and Growth (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 were not considered representative of the riverine inputs to tidal waters and were not reported. Data has not been reported for 2022 and 2023 due to ongoing resource pressures resulting in the frequency of sampling and number of sites sampled being spatially and temporally skewed. It is not yet clear how this data will be integrated into the time series.

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 with numeric permits for the pollutants in question. For smaller sewage treatment works 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 sewage treatment works 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

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 3 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. In comparison the loads for BOD and phosphorus have dropped by 55% and 68%.

Assessment of change

A decrease (or improvement) was observed across all 3 of the loads of pollutants discharged to rivers from water company sewage treatment works in England across the long term trend, this period covers all 6 datapoints from 1995 to 2020.

Further information on this assessment, along with details on the methodology, is provided in the Assessment background. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results.

Table B1c: Assessment of change

Component Subcomponent Period Date range Percentage change Smoothing function Assessment of change
B1c Ammonia Short term N/A N/A N/A Not assessed
B1c Ammonia Medium term N/A N/A N/A Not assessed
B1c Ammonia Long term 1995 to 2020 -79.88 Unsmoothed Improvement
B1c BOD Short term N/A N/A N/A Not assessed
B1c BOD Medium term N/A N/A N/A Not assessed
B1c BOD Long term 1995 to 2020 -54.82 Unsmoothed Improvement
B1c Phosphorus Short term N/A N/A N/A Not assessed
B1c Phosphorus Medium term N/A N/A N/A Not assessed
B1c Phosphorus Long term 1995 to 2020 -68.47 Unsmoothed Improvement

The B1c metric ‘Loads discharged to rivers from water company sewage treatment works in England’ reports one data point for each 5-year period included within the indicator, unlike the majority of other indicators that report annually. Therefore, it is only possible to assess long-term trends as there are insufficient data points to establish trends over shorter time periods.

Indicator Metadata