Intensive farming affects water quality — not exactly a news flash. However, this issue is one tough nut to crack and one that is creating plenty of anxiety for both central and local government, land users, resource managers and groups like Fish and Game New Zealand. 

Around the country, the approach to managing this issue is variable. Some like the Manawatu-Wanganui region have decided to take the matter head on with tight rules linking land use with water quality. Some regions are considering catchment specific approaches; others are looking at dedicated discharge plans. Hawke’s Bay does not escape this problem. 

While we don’t have the intensive land use that some regions do, we do have areas where the impacts are evident. One such area is the upper Mohaka River in the Taharua valley.  This small area of the region contains a third of the region’s total dairy herd, some 9,000 dairy cows. The Mohaka River is also the only river in the Hawke’s Bay region that has a Water Conservation Order over it to protect, among other things, the nationally outstanding trout fishery. And without a doubt, putting a third of the region’s dairy herd into a small valley containing a unique and outstanding trout fishery is chancing fate. 

The Taharua River flows through a small pumice in-filled valley at the very headwaters of the Mohaka River. The soils in the valley are light and free draining. In the late 90’s large areas of the valley were converted from light pastoral farming and forestry to intensive dairy platforms. Since the conversion of land to dairy farming, the quality of water flowing down the Taharua River has declined, with increasing levels of nutrient (mainly nitrogen) in the water. The initial evidence suggests that this is not a coincidence and the changes are related.

The issue came to a head recently when the dairy farm owners sought consents to discharge dairy shed effluent (FDE) to land. This is the only on-farm activity that the Hawke’s Bay Regional Council has chosen to exert any control over.  Through the consent process it quickly became evident that discharging properly managed FDE to land was not going to have a significant effect on water quality in the nearby Taharua River. 

Instead, the increases in nutrient is almost certainly the result of concentrated urine patches from 9,000 dairy cows leaching nutrient into the groundwater and then appearing in the surface waters of the nearby Taharua River. Despite the seemingly clear link to land use and water quality changes in this catchment, the Regional Council was powerless to control the wider activity of farming and its insidious affects. This is simply because the current Regional Resource Management Plan (RRMP) has no specific mechanisms in it to deal with situations where land is being used beyond its sustainable capability.

In fairness to the Regional Council, at the time the RRMP was being written, managing land use sustainably was not an issue that was obvious. Like much of the rest of the country, the subsequent intensification of land use has overrun the planning instruments intended to control it.

During this time, anglers have been complaining that the trout in the upper Mohaka River are becoming smaller and there are less of them. Their claim is supported by figures F&G has obtained through assessments such as drift diving. This is naturally of concern to us given the significance of the fishery and the fact that it is protected by a Water Conservation Order.

The evidence on trout size and abundance was not definitive, however, and more intensive monitoring is now underway to determine exactly what is happening to the upper Mohaka trout fishery. A substantial study is looking at the available food supply for trout and how the changes in water quality are impacting on the food and subsequent trout growth. While still in the early stages, initial evidence suggests that trout in the sections of river affected by increased nutrient are showing lower growth performance compared to the unaffected sections.

To some the issue is difficult to comprehend.  A decline in water quality is something that is hard to put adequate words around to give it credence. To try and give people an appreciation of the significance of the changes that have occurred we recently dived the Mohaka River. We videoed the river as we swam from an area of unmodified catchment above the confluence of the Taharua River and then well downstream in the Mohaka again. We did this all on the same day and after a long period of settled flows in the peak of summer. This video is available on the online version as of this story on www.baybuzz.co.nz

The intention is to give those who struggle with the concept of the need to manage land use some appreciation of an unmanaged situation. The impacts are real and undisputable.  The real challenge is now to develop some tools to manage this and for this we will work hard with our elected Regional Councillors to help achieve the vision they sit under – ”Our vision is for a region that develops and prospers within a clean and healthy environment.”

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