This record is for Approval for Access product AfA162.2 'Historic GQA Headline Indicators of Water Courses - Chemistry (Wales). The General Quality Assessment (GQA) Headline Indicator scheme or GQAHI (previously known as GQA) was the Environment Agency's national indicator for water quality in rivers and canals. It was designed to provide an accurate and consistent assessment of the state of water quality and how it changed over time as a national picture. These assessments were made for Biological, Chemical and Nutrients and undertaken for discrete river stretches.
The Chemistry GQAHI scheme had over 3000 sampling sites which provided information for approximately 22500 km of watercourses. In Wales we maintained the full GQA network until 2010 based on 800 sampling sites which provided information for approximately 4700km. Chemistry GQAHI/GQA sites were sampled twelve times a year, the samples being taken at the same spot on each sampling occasion to ensure consistency. In England each chemical sample was measured for ammonia and dissolved oxygen. In Wales each chemical sample was measured for biochemical oxygen demand (BOD), ammonia and dissolved oxygen (the most common types of organic pollution from sewage treatment works, agriculture and industry). A category was assigned using three years worth of samples for each sampled chemical and assigned a category assessed against chemical standards expressed as percentiles The data collected over three years were used to determine average nutrient concentrations. So the classification for the year 2008 includes the results for 2006 and 2007. Subsequently a category was assigned to each length of river according to the lowest standard achieved by any of the two or three measurements.
The Chemistry GQA used in Wales described quality in terms of three chemical measurements that detect the most common types of organic pollution from sewage treatment works, agriculture and industry. The chemistry GQAHI scheme used in England used the same methods however the biochemical oxygen demand (BOD) component of the assessment had been removed.Grades of river quality for the chemical GQA. Chemical grade, Likely uses and characteristics*
A: Very good, All abstractions, Very good Salmonid fisheries, Cyprinid fisheries, Natural ecosystems.
B: Good, All abstractions, Salmonid fisheries, Cyprinid fisheries, Ecosystems at or close to natural.
C: Fairly good, Potable supply after advanced treatment, Other abstractions, Good Cyprinid fisheries, Natural ecosystems, or those corresponding to good Cyprinid fisheries.
D:Fair Potable supply after advanced treatment, Other abstractions, Fair Cyprinid fisheries, Impacted ecosystems.
E: Poor Low grade abstraction for industry, Fish absent or sporadically present, vulnerable to pollution, Impoverished ecosystems
F: Bad Very polluted rivers which may cause nuisance, Severely restricted ecosystems.
Provided other standards are met.
*Where the grade is caused by discharges of organic pollution.
2009 is the final year of the scheme.
In 2007 the England GQA river network was reduced to the GQAHI river network. The assessment was changed to be based on total ammonia and dissolved oxygen only. Biochemical oxygen demand (BOD) was removed from the assessment and all past grades re-calculated. The data described have been amended to be consistent and comparable for all years. Attribution statement: © Environment Agency copyright and/or database right 2014. All rights reserved.