Pomahaka study adds weight to rural water quality push

The Otago Regional Council's launch of a rural water quality strategy for the region has been given added momentum by the findings of a major ORC study of the Pomahaka River catchment.

The report, which was considered this week by the ORC's environmental science committee, highlights that water quality in the lower Pomahaka catchment has been degrading for a number of years, while land use has rapidly intensified.

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

ORC director environmental information and science John Threlfall said these nutrient-enriched discharges were often the result of inappropriate use of dairy shed effluent when the soil was saturated, or when the application rate of effluent was too high for the soils to absorb.

E.coli bacteria were found in streams in excess of health guidelines after wet weather: coming from both dairy and sheep/beef farms. However, tile drains from dairy farms were also found to flow during dry weather, entering the streams when recreational activities such as swimming were most likely to occur, Dr Threlfall said.

The study underlined that sediment control was critical, as it could smother habitat, degrading river ecology, and be a source of phosphorus, which potentially increases algal growth in waterways.

The study found that issues such as poor effluent control management and stock access to streams continued to adversely affect ecological values, but that these issues were manageable through good farming practices.

ORC environmental science committee chairwoman, Cr Gretchen Robertson, said the degradation of water quality resulting from dairy farm conversions had been evident for several years.

In 2005, regional and central government, along with the dairy industry, established a voluntary accord known as the Clean Streams Accord Regional Action Plan (RAP).

The RAP did not deal with the serious issue of dairying on tile and mole drained land, Cr Robertson said.

A Memorandum of Understanding (MoU) between ORC and Fonterra was agreed at the same time as the RAP to work cooperatively to address the water quality impacts of dairy farming on tile and mole-drained land.

"The ORC had a comprehensive programme and has been working closely with local farmers and river catchment groups to promote best management practices," Cr Robertson said.

However, she said the continued degradation of the water quality in the Pomahaka catchment clearly showed that the RAP, MoU and other attempts by ORC to educate land users were proving to be insufficient.

"Further intensification is only putting further pressure on the environment," Cr Robertson said.

"This continuing problem has been the major incentive for the ORC to launch the new Rural Water Quality Strategy, which focuses on the effects of land use on water quality," Cr Robertson said.

Explanatory note: The Pomahaka catchment is located in south-west Otago and has a catchment area of roughly 2,060 km2. It flows from its headwaters in the Umbrella Range in a south-west direction to its junction with the Clutha River/Mata-Au near Clydevale. Much of the upper half of the catchment is located in steep mountainous areas dominated by tussock, while the lower catchment lies primarily in pastoral rolling hill country.