Quality of watercourses vis-à-vis nitrates in Brittany

Values extracted from the layer " Quality data of surface waters of Brittany" since 2014. Concerns nitrate concentrations (SANDRE 1340 parameter). The indicators calculated are as follows: maximums, averages, Q90 on the calendar year The number of results taken into account for the calculation is also provided. For the calculation of the Q90, which is a kind of percentile 90: number of analyses available (na) na less than 4: no calculation of Q90; na greater or equal to 4: *grading results in descending order; Rank of result to remember = rounded (0.9 x na + 0.5) __Origin__ data from the surface water quality layer __Partner organisations__ DREAL Bretagne [See this page on geo.data.gouv.fr](https://geo.data.gouv.fr/fr/datasets/7b1d54c9ccbee9f1a3591578266848a85b5c6730)