Year	Mean ammonium in rivers (mg N/l)
2000	0.47
2001	0.38
2002	0.39
2003	0.52
2004	0.41
2005	0.39
2006	0.52
2007	0.4
2008	0.32
2009	0.31
2010	0.42
2011	0.52
2012	0.6
2013	0.44
2014	0.42
2015	0.42
2016	0.52
2017	0.65