Variation in the reactive phosphorus concentrations in rivers of northwest Europe with respect to their potential to cause eutrophication

By 2002, there had been a variable implementation of phosphorus (P) removal at waste water treatment works in a set of countries in northwest Europe; ranging from close to 100% of the urban populations in Austria, Denmark, Finland, Germany, the Netherlands and Sweden to between 2% and 56% of the inland urban populations in Belgium, France, Ireland and the UK. This variable application has resulted in a proportional lowering of reactive phosphorus (RP) concentrations in rivers. Thus, although the inland urban population density of Germany exceeds that of the UK (207 vs. 148 persons km⁻²), mean RP in 2004 was lower in German rivers (75 vs. 265 μg P L⁻¹). By adjusting urban populations downwards by the P equivalent populations removed through tertiary treatment, the resulting effective urban population density was strongly and positively correlated with mean river RP concentration (r = 0.99) and the percentage of rivers with average RP >100 μg P L⁻¹ (r = 0.98). Two agricultural variables, the agricultural area as a percentage of total area and the application of P in manures and fertilizers to the national land area were uncorrelated with either mean or median RP concentrations but were negatively correlated with the proportion of rivers with low mean concentrations of RP (