GQA Headline Indicators of Water Courses - Nutrients - phosphate GQA grades 2009 (England)'. The General Quality Assessment Headline Indicator scheme (GQAHI) was the Environment Agency's national method for creating a water quality indicator based on rivers and canals in England. This was a reduced network compared to the original GQA network used in England from 1990 to 2006. The Nutrients GQAHI scheme had over 3000 sampling sites which provide 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.
The GQAHI/GQA scheme was designed to provide an accurate and consistent assessment of the state of water quality and how it changes over time. The Nutrients GQA described quality in terms of two nutrients: nitrates (mg NO3 /l) and phosphates (mg P/l) and graded from 1 to 6. Grades were allocated for both phosphate and nitrate; they were not combined into a single nutrients grade. There were no set 'good' or 'bad' concentrations for nutrients in rivers in the way that we describe chemical and biological quality. Rivers in different parts of the country have naturally different concentrations of nutrients. ‘Very low’ nutrient concentrations, for example, are not necessarily good or bad; the classifications merely stated that concentrations in this river were very low relative to other rivers.
Classification for phosphate: Grade limit (mgP/l) Average Description
<0.02 Very low
0.02 to 0.06 Low
0.06 to 0.1 Moderate
0.1 to 0.2 High
0.2 to 1.0 Very high
1.0 Excessively high
Classification for nitrate
Grade limit (mg NO3/l) Average Description
<5 Very low
5 to 10 Low
10 to 20 Moderately low
20 to30 Moderate
30 to 40 High
40 Very high
2009 is the final year of the scheme. Attribution statement: © Environment Agency copyright and/or database right 2019. All rights reserved
