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3.10 Lake Taupo Catchment

Area covered by Chapter 3.10 – Lake Taupo Catchment
This chapter applies to land within the Lake Taupo catchment. The map at 3.10. shows the general catchment boundary. The Waikato Regional Plan Lake Taupo Catchments Maps are available electronically or for viewing at Waikato Regional Council or Taupo District Council offices on request.

Background and Explanation
Lake Taupo is the largest lake in New Zealand. It is known for its dramatic vistas, deep clear near pristine waters, superb trout and volcanic heritage.

Ngati Tuwharetoa is the iwi with mana whenua in the Lake Taupo catchment*. Generations of Ngati Tuwharetoa have lived within the Taupo rohe, and as a result, have developed tikanga and kawa that reflect a special and unique relationship with the environment. Taupo nui-a-Tia, ‘the great cloak of Tia,’ is their taonga. Ngati Tuwharetoa are Treaty partners with the Crown and hold legal title to the bed of the Lake and its tributaries. Accordingly, Ngati Tuwharetoa are the kaitiaki of the Lake.

A 1998 community survey identified 14 values about the Lake that are most important to the Taupo community. Tuwharetoa Maori Trust Board, Waikato Regional Council, Taupo District Council and other agencies and organisations are working together to protect these values for the future as part of the 2020 Taupo-nui-a-Tia action plan1. The Variation to The Proposed Waikato Regional Plan focuses on protecting a subset of those values – most importantly, clear water in the Lake, high water quality feeding into the Lake and good trout fishing. All of these values are of local, regional and national significance. Central Government has identified the water quality of Lake Taupo as a national sustainable development issue in its Sustainable Development Action Programme.

Scientific evidence2 gathered over the past 30 years shows that the water quality of the Lake is declining. Lake Taupo’s excellent water quality is reflected by extremely low levels of plant nutrients and phytoplankton. Unlike many other lakes, nitrogen availability rather than phosphorus, limits phytoplankton growth in Lake Taupo. Development and intensification of the surrounding rural and urban land has increased the amount of nitrogen entering the Lake through ground water and rivers. This has promoted algal and phytoplankton growth in the Lake.

More specifically, there has been an increase in chlorophyll a (an indicator of the amount of tiny, free-floating algae) in the Lake’s surface waters between 1994 and 2003. There have also been increases in the amount of nitrate nitrogen in the bottom waters of the Lake just before winter when the Lake’s bottom waters mix with its surface.

Nutrients such as nitrogen and phosphorus are a staple food for plant life, promoting healthy, vigorous growth. Nitrogen is of particular concern because the increasing amounts of nitrogen in the Lake are feeding the growth of tiny free-floating algae in the water. Some algae are able to make their own nitrogen and their growth is controlled by the amount of phosphorus entering the Lake.

More algae in the water reduces the water’s clarity. There are also more nutrient dependent weeds and slimes growing in sheltered waters near lakeshore settlements. Potentially toxic algae have, for the first time in 2001, and then again in Autumn 2003, bloomed unexpectedly in the Lake, resulting in health warnings being issued for Whakaipo Bay and Omori. All these factors are unmistakable signs that the Lake’s water quality is slowly deteriorating. Because Lake Taupo is a complex and sensitive ecosystem, the changes being seen now are cause for serious concern. Overseas experience shows that in similar deep, low nutrient lakes, an increasing load of nutrients almost always results in increased algal growth and reduced water clarity. If left unchecked Lake Taupo will no longer be a clear blue lake with exceptional water quality.

Table 3-10 summarises the current water quality characteristics.

Table 3-10 Mean and standard deviation for four water quality variables measured at Lake Taupo deep water monitoring site

Water Quality Characteristic Mean Standard Deviation
Total Nitrogen (mg/m3) 70.3 19.1
Total Phosphorus (mg/m3) 5.57 1.4
Chlorophyll a (mg/m3) 1.18 0.6
Secchi depth (m) 14.6 2.7

Note: Statistics based on Lake Taupo data set, January 1999 to December 2003 inclusive.

The Cause of the Problem
Historically, the Lake had extremely low levels of nitrogen and other nutrients, which has limited the growth of nuisance plants in its waters. Before land around the Lake was developed, only very low concentrations of nitrogen entered the Lake from rain falling on the Lake and groundwater draining areas of indigenous vegetation. Today, groundwater draining from under pine forests, and water diverted into the Lake from the Tongariro Power Development (TPD) contains low concentrations of nutrient similar to indigenous vegetation. These levels cannot be reduced further.

Major land development in the catchment occurred in the middle of last century. The change to more intensive land uses around the Lake has increased the amount of nutrient and sediment entering the Lake. Much has been done by landowners over the years to protect the Lake from sediment, through extensive stream fencing, tree planting and land retirement under the Taupo Catchment Control Scheme. Landowners planted forestry in the eastern catchment and lakeshore reserves were created. All of these actions can be expected to aid management of phosphorus additions to the Lake, although recent data is showing slight increases in Lake water phosphorus concentrations. As yet phosphorus does not pose the same risk to Lake water quality as nitrogen. The role of phosphorus in this context will continue to be examined. Unfortunately, past landowner and agency efforts haven’t been enough to counter increases in nitrogen leaching* from rural land and wastewater systems.

The Lake responds very slowly to the many biophysical processes that control the movement of nitrogen from the land to the Lake. Nitrogen moves down into the soil and into groundwater, which in turn moves very slowly into streams and then into the Lake. This means that land use changes that occurred decades ago will continue to increase nitrogen inputs into the Lake via groundwater. Because of this time lag between what happens on the land and its effect on the Lake, it is only in recent years that the impact of the land conversion started in the 1930s has been seen in the Lake.

Although domestic wastewater discharges represent a relatively small proportion of the nitrogen entering the Lake, a number of studies have shown that discharges from community wastewater treatment plants and concentrations of on-site wastewater systems near the lakeshore, can have disproportionate effects in shallow near-shore waters3. Such discharges can increase the risk of weed and algae growth in shallow waters, as well as create a health risk from wastewater pathogens.

Nitrogen naturally enters the Lake from sources such as the atmosphere and decaying plant matter. Human activities have increased the amount of nitrogen entering the Lake. Scientific measurement and modelling indicate that pastoral farm land contributes most (93 percent) of the nitrogen leaching to the Lake which has been generated from human activities (manageable nitrogen), with urban stormwater and wastewater being a smaller localised nitrogen source (7 percent)4. Nitrogen concentrations in streams draining pastoral sub-catchments have increased by between 50 percent to 300 percent in all measured streams since the 1970s5.

Community Consultation
Given the scientific information that levels of nitrogen in the Lake were increasing and were likely to affect Lake water quality into the future, Waikato Regional Council was faced with two key options in October 2000:

  • Do nothing and accept the deterioration of Lake water quality into the future
  • Take action to reduce nitrogen entering the Lake to protect water quality.

The paper Issues and Options for Managing Water Quality In Lake Taupo6was prepared and circulated amongst stakeholders and the general public, seeking feedback on four different options for Lake water quality:

  1. Better water quality than now, with much less intensive land use in the catchment
  2. Maintain current water quality by reducing nitrogen output from existing land uses and preventing further land use intensification.
  3. Slightly lower water quality than now, with existing land use remaining the same but no further intensification.
  4. Lower water quality. Do nothing to change land use in the catchment.

Based on feedback received at earlier public meetings, Waikato Regional Council identified that Option 4 of doing nothing or Option 1 of trying to improve water quality substantially were not favoured by the community. For this reason, the options paper focused on Options 2 and 3.

During 2001 the Waikato Regional Council decided to pursue Option 2 – maintain current water quality in Lake Taupo by reducing nitrogen output from existing land uses and preventing further intensification. This decision was based on two factors:

  • community expectation for a clean Lake7
  • a legislative mandate under the Resource Management Act to sustainably manage land in order to protect water quality, further reinforced by objectives and policies in the Waikato Regional Policy Statement.

Nitrogen Loads and Catchment Modelling
The actual amount of nitrogen discharges from the land within the catchment is not known as it has not been measured. Waikato Regional Council has developed a nutrient budget for the Lake, which estimates that nitrogen loads entering the Lake (from natural and human-generated sources) are about 1360 tonnes per year. This load compares with a pre-development or natural nitrogen load entering the Lake of about 650 tonnes per year. Therefore about 710 tonnes per year of nitrogen can be attributed to human-generated sources.

Due to the time lag between the land and the Lake, current nitrogen leaching on the land and nitrogen loads entering the Lake are not in equilibrium. Therefore, if the only action taken was to hold nitrogen discharges on the land at current levels, this would not maintain current water quality.

The amount of nitrogen yet to come before equilibrium is reached with current land use has been estimated at between 30% and 41% of the annual manageable load attributed to human-generated. No one can say for certain how much nitrogen is in transit in the groundwater on its way to the Lake.

Previous studies concluded that there would need to be at least a 20 percent reduction to ensure Lake water quality would eventually stabilise at current levels.8 Therefore, a target nitrogen reduction of 20 percent of the manageable (human-generated) load, was considered a scientifically defensible target to maintain the current water quality of the Lake. It is estimated that it will be 2080 before equilibrium between nitrogen loads from the land and loads entering the Lake will be achieved.

The research and science involved with the issue of water quality decline in Lake Taupo does not provide absolute certainty. Estimates have been made with the best knowledge of the day but these may be refined as continued monitoring and modelling is carried out.

Social and Economic Costs Associated with Nitrogen Management
In August 2001, Waikato Regional Council formally agreed to liaise with Taupo District Council and Central Government on implementing land use change, including investigating funding options. This followed a July agreement from the Minister for the Environment to enlist Governmental support for the project with the view of developing a "whole of government" approach.

After considering a range of options to achieve the 20 percent reduction of nitrogen, Waikato Regional Council proposed a strategy that comprised regulation supported primarily by changes on Government land. The Government considered and revised this proposal in July 2003, proposing that the Government consider contributing to a joint public fund to assist the transition to more sustainable land use in the catchment.9

The funding partners (Central Government, Waikato Regional Council and Taupo District Council) agreed that the project costs should be shared 45 percent by Government, 33 percent by the Regional community, and 22 percent by the District community. In December 2003, the Minister for the Environment announced that Government would commit $36.7 million towards the joint fund.

The contributions from Regional and District communities were outlined when Waikato Regional Council and Taupo District Council released their draft Long-Term Council Community Plan (LTCCP) documents in early 2004. Both Councils’ judgement was that although landowners contribute significantly to the need for action, regulation alone is not likely to be successful because it is inherently unfair for most of the cost to fall on rural landowners. The effects currently seen in the Lake relate to Central and Local Government and landowner actions and practices since the middle of last century. Landowners have developed their properties in good faith, as until recently, there has been no community or regulatory requirement to manage non point source discharges of nutrient from rural land. If regulation alone was proposed, the rural community and infrastructure would decline as farmers exit the industry.

In their decisions on their respective LTCCP’s in June 2004, Waikato Regional Council and Taupo District Council made an overall judgement that funding was needed to achieve community change that leads to catchment land being used for productive uses that can sustain the local community (including pastoral landowners) as well as protect the Lake. Both Councils recognised that social, cultural, economic and environmental well-being is important for the local community. As a result, the nitrogen reduction using financial assistance approach proposed, is more likely to be successful than a rules only approach.

The joint public fund is intended to permanently remove 20 percent of the manageable nitrogen in the catchment through securing permanent change on individual properties to a lower nitrogen leaching land use.

No Precedent Effect
The Objective, Policies and implementation methods contained in Chapter 3.10 have been developed to address the decline in Lake Taupo water quality in the context of the unique set of circumstances which apply in the Lake Taupo catchment. In doing so the Waikato Regional Council does not intend to create a precedent, either direct or indirect, for any other catchments or water bodies and does not consider that any precedent is created.

Issues of water quality decline in other catchments or water bodies in the Waikato Region will be investigated by the Waikato Regional Council as the need arises. If necessary, regional plan provisions and implementation methods will be developed that are appropriate for the specific circumstances of those catchments or water bodies, following appropriate community consultation and the consideration of efficiency, effectiveness, costs and benefits as required under section 32 of the Resource Management Act.

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