Rural water strategy rationale vindicated by water quality results

Water quality plays a vital role in determining the physical health of waterways, but it is not the only factor, according to Otago Regional Council (ORC) director environmental information and science John Threlfall.

Dr Threlfall was a presenter at the ORC's 2010 Good Water, Good Farming forum in Cromwell last week.

He told the forum the integrity of a river or stream's physical habitat, the availability and quality of fish food, and the density and condition of the fish themselves, were also major factors in the health of a waterway.

The ORC has launched an effects-based strategy which aims to control the level of contaminants in discharges from rural land, by providing users with innovative tools which allow for agricultural uses, but also provides flexibility in achieving discharge standards.

Dr Threlfall said several places in Central Otago enjoyed excellent water quality: Lakes Wakatipu, Dunstan, Wanaka, and Hawea; and the upper catchments of the larger rivers: the Taieri at Stonehenge, the Manuherikia at Blackstone Hill, and the Pomahaka at Glenken.

Conversely, several sites-mainly the smaller streams of agriculturally intensive catchments-were experiencing degradation of their water quality.

Pomahaka River tributaries, particularly those at Washpool, Wairuna Stream, Heriot Burn, and Crookston Burn were among the worst sites.

ORC started a 12-month water quality sampling programme in 2008, with the aim of getting a better understanding of the effects of land use on water quality in the Pomahaka catchment.

This mainly involved monitoring the effects on water quality of tile drains located in both intensive and non-intensive land use units within the catchment, and on ecology.

The study pulled together the results of the monitoring work. It found that tiles draining dairy farms typically exceed recommended guidelines for nutrients, and have substantially higher concentrations of contaminants than tiles draining sheep farms.

Dr Threlfall said high nutrient and bacteria levels were the major threats to river health, but could be controlled by good land management, which the ORC strategy promotes.

The ORC uses a Water Quality Index (WQI) to compare water quality at sites throughout Otago, based on the median values of six variables. It classifies each sites into one of four categories ranging from very good to poor.

The WQI results for 2000-2006 found 36 sites were very good, 19 were good, 17 were fair, and five were poor.

South and south-west Otago, as well as Dunedin urban streams were the poorest areas, where water quality suffered because of high nutrient and bacteria levels.

Dr Threlfall said the monitoring results underlined the rationale behind the ORC's rural water quality strategy, which promotes collaboration between the council, farmers, and other rural land users.