Water quality in New Zealand rivers: current state and trends

Abstract

ABSTRACT River water quality, particularly in lowland catchments, is a matter of concern to the New Zealand public. We assessed river water quality and biological state and trends using data from more than 900 monitoring sites. Parallel state and trend analyses were carried out using all sites and a subset of lowland river sites. Median water‐quality state in urban and pastoral land‐cover classes was poorer than in exotic forest and natural land‐cover classes, and lowland sites in the urban and pastoral classes had the poorest water quality. Nutrient and Escherichia coli concentrations increased and visual clarity and Macroinvertebrate Community Index scores decreased as proportions of catchments in high‐intensity agricultural and urban land cover increased. Ten‐year trends (2004–2013) indicated recent improvements in ammoniacal nitrogen, dissolved reactive phosphorus and total phosphorus in the pastoral and urban classes, possibly reflecting improved land management. In contrast, trends in nitrate‐nitrogen in the exotic forest and cool‐dry/pastoral classes indicated worsening conditions.