Trends in nutrients and metals in Norwegian rivers and point sources 1990–2009

This assessment of nine river catchments in Norway covers 20 years (1990–2009) of water quality data on total phosphorus (TP), orthophosphate, total nitrogen (TN), ammonium, nitrate, copper, zinc, cadmium, lead and nickel. The nine catchments are located from the south to the north of the country and are included in the Riverine Inputs and Direct Discharges (RID) programme of the OSPAR Commission for Protection of the Marine Environment of the North-East Atlantic. The partial Mann–Kendall test was used to evaluate long-term monotonic trends. For both TP and TN, decreasing trends (p < 5%) were found in three out of nine rivers under study. Downward trends in riverine metal loads were found in 23 of 45 tests. Only one significant increasing trend in nutrient loads was found, and there were no upwards trends in metal loads. To some extent, the trends in riverine loads could be explained by trends in discharges from point sources. Even after taking potential sources of error into consideration, these results indicate that mitigation measures implemented since 1990 to reduce pressures from point sources have had an impact on water quality in Norwegian rivers.