e-Digest Statistics about: Coastal and marine waters
Coastal and marine waters
Riverine and Direct inputs
Annual estimates of inputs from the United Kingdom of selected contaminants are submitted to the Oslo and Paris Commissions (OSPAR). Table 8 shows OSPAR information for direct riverine and total inputs from the UK to marine waters in 2004. The information is derived from annual surveys. The aim of each survey is to monitor 90 per cent of the riverine and direct inputs of each pollutant. All main river systems are sampled approximately monthly at a sampling point close to but upstream of the tidal limit. All major direct discharges of industrial or sewage effluent entering estuaries downstream of the riverine sampling point are also sampled, as are major coastal discharges. Since some samples contain quantities of substances below the detection limits, two sets of load estimates (lower and upper) are given. The lower load estimates assume that the true concentrations in such samples are zero. The upper load estimates assume that the true concentrations are at the limit of detection.
Table 11 shows longer term changes in direct and riverine inputs from the United Kingdom to marine and estuarine waters around the United Kingdom. Overall, for the period 1990 to 2004 there has been a substantial reduction in metal inputs, particularly mercury and cadmium. For nutrients there are no clear trends. Year on year changes should be treated with caution as the data can vary considerably due to natural variations such as rainfall (the United Kingdom riverine flow rate was 265,000 Ml/day in 2000, for example, compared with a long-term average of 280,000 Ml/day) [3]. The year 2000 was an extremely wet year which was reflected in increases in some riverine inputs, for example nitrogen, lead and zinc.
Information on direct plus riverine inputs for other substances (Annex 1A) not included in the OSPAR returns, are given in Table 12 for the period 1991-1999. These estimates are those reported to the fifth North Sea Conference and are based on data provided by the Environment Agency (for England and Wales) and by the Scottish Environment Protection Agency (for Scotland). The estimates are calculated in the same way as the OSPAR inputs, but the geographical coverage is not as extensive, with monitoring effort being directed at those rivers and direct discharges where the individual substances are more likely to be found. It should be noted that for some substances (mainly pesticides) most concentrations were below the level of detection. Consequently, the input estimates are at, or near, zero. This means that no reliable trends could be established. For other substances, there is a general pattern of reductions in inputs. However, some do show an increase in 1998 and 1999. This probably reflects the variations in riverine flow over the period (see table 11 for the flow rates).
Riverine and Direct inputs of metals from the UK to marine waters around the UK: 1990-2004
Over the last decade there have been substantial reductions in most inputs of metals via rivers and direct discharges to estuaries and coastal waters. The apparent increase in inputs of some metals in more recent years compared to the previous years' trend is due to higher levels of riverine inputs from 1998 to 2002 that result from elevated riverine flows over this period. This highlights the importance of looking at the patterns of change in inputs and riverine flow together, preferably over a long period, rather than at year on year changes which can be misleading.
Riverine inputs are the loads conveyed by rivers based on sampling points just upstream of the zone of tidal influence. They reflect all point sources and diffuse losses upstream of these points.
Direct inputs are those reaching the marine environment via discharges downstream of the riverine monitoring points. Typically, inputs are estimated from 12 samples taken each year. Some samples are taken that contain substances below the limits of detection and where this occurs two estimates are made: an upper and a lower. The upper estimate assumes that the substance is present at the level of detection and the lower assumes that concentrations are zero. Upper (worst case) estimates are used.
Further Information:
- Data Tables:
- Riverine and Direct inputs of metals from the UK to marine waters around the UK: 1990-2004 XLS
- 8 Annual estimates of total UK inputs (direct and riverine) from the UK to coastal waters around the UK: 2004 XLS
- 11 Annual estimates of total United Kingdom inputs (direct and riverine) to coastal waters around the United Kingdom: 1990-2004 XLS
- 12 Annual estimates of total United Kingdom inputs (direct and riverine) of metals, pesticides and organic substances from Great Britain to coastal waters around the United Kingdom: 1991-1999 XLS
- Internet Links:
- Commission for the Protection of the Marine Environment of the North East Atlantic (OSPAR)
- Environment Agency: Discharges to the sea
- References, further reading and links to other resources:
- [3] The Oslo and Paris Commissions (OSPAR) RID 2000 inputs survey, results from the UK
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Page last modified: 28 September 2006
Page published: 28 September 2006