Background report on Lake Ngaroto

Transcription

1 Background report on Lake Ngaroto by Melinda Dresser and Nardene Berry November 2011 Lake Ngaroto from the air. Photo: John Greenwood Produced with funds from the Ministry for the Environment s Community Environment Fund. 1

2 Contents 1 Introduction Lake Ngaroto: the current situation Ngarotoiti Recreational Use of the Lake Peat lake formation and ecology Pre European History Threats and Pressures to Lake Ngaroto Drainage and cultivation Nutrients Aquatic pests Restoring Lake Ngaroto Council role; Rules and regulations listed peat lakes and drainage rules NZ Landcare Trust and shallow lake restoration Lake Ngaroto Landowner survey Scientific Research and Monitoring Monitoring buoy Managing pest fish Where to from here? Bibliography Websites

3 1 Introduction Lake Ngaroto is situated in the Waipa district of the Waikato Region, 19km south of Hamilton. It is the largest of the remaining 34 peat lakes in the region. Peat lakes are water bodies that are either entirely surrounded by peat or sandwiched between the edge of a peat bog and low hills or ridges. Their unique character is due to a combination of the low fertility peat surrounding them and the fact that they traditionally had few, if any, surface water inflows. Most water flowing into these lakes passed through the surrounding peat, being stripped of nutrients and becoming mildly acidic and tea or peat coloured as a result. The loss of peat around these lakes and the change to surface water inflows are the two biggest factors in their decline. (M. Peters, 2008) Globally, peat lakes are a rare phenomenon and as such are of national significance. Peat itself takes thousands of years to form. The occurrence of so many peat lakes in a small area as is found in the Waipa is rare and therefore they add to the local diversity of landforms as well as having significant cultural values. Lake Ngaroto itself is an important valuable landscape and recreational resource. It is also important habitat for wildfowl, as it acts as a staging and dispersal area (Boubée 1977). Ngaroto in context of other peat lakes in the Waikato and Waipa Districts. Image courtesy of Waikato Regional Council. 3

4 2 Lake Ngaroto: the current situation Lake Ngaroto is a shallow lake with a maximum depth of four metres and an average depth less than two metres. The catchment area covers 1846 ha and has 31 farms greater than 20 ha. The land use of the catchment is 1416 ha dairy pasture, 270 ha drystock pasture and 60 ha non-agricultural use (Environment Waikato, 2006). The lake is a recreation reserve which includes an open water area of around 89 ha, a considerable wetland margin of 60 ha, giving a total area of 149 ha. The Waipa District Council is responsible for day to day administration and management of the reserve. Water quality in the lake has been impacted greatly by land use in the catchment resulting in a Trophic Level Index (TLI) classification of hypertrophic (Hamill & Lew 2006). Hypertrophic lakes are fertile and have extremely high levels of phosphorus and nitrogen. They are rarely suitable for recreation and habitat for desirable aquatic species is limited 1. The TLI calculation is based on Total Nitrogen, Total Phosphorous and chlorophyll a concentrations, and Secchi depth, the water clarity variable. Due to the shallow nature of Lake Ngaroto and absence of macrophytes (aquatic vegetation), concentrations of suspended solids are high, which contributes to poor water clarity. Lake Ngaroto has recurrent algal blooms which are dominated by the cyanobacterial (blue-green algae) species Microcystis spp. (Paul et al., 2008). This has detrimental effects on the recreational use of the lake as it is toxic and therefore no contact with the water is permitted during a bloom. Lake Ngaroto and Jetty during an algal bloom. Photos: Paul Champion No submerged aquatic vegetation was recorded in the last vegetation survey in 2003 by the National Institute of Water and Atmospheric Research (NIWA) (Edwards et al., 2007). There has been no significant change in water quality in recent years (Environment Waikato 2008)

5 Ngaroto has large populations of invasive fish which include bullhead catfish, rudd, gambusia, goldfish and koi carp. Native fish in the lake include common bullies, shortfinned eels and common smelt. The drainage outlet flows from the lake at the northwestern end and eventually joins the Waipa River nine kilometres downstream via the Mangaotama Stream. During drought conditions, outflows can fall to zero when evaporation exceeds inflows (Hicks 2001). 2.1 Ngarotoiti Adjacent to Ngaroto lies Lake Ngarotoiti, a Department of Conservation administered Wildlife Management Reserve. Despite its small surface area (3.42 ha), Ngarotoiti has a sizeable catchment of 504 ha incorporating the township of Ohaupo. Water from Ohaupo, and drains alongside the North Island trunk railway line running to the west of the township, discharge to the lake. A constructed, main drain discharges water from Lake Ngarotoiti to Lake Ngaroto. Waipa District Council have plans to divert the outflow from Ngarotoiti away from Ngaroto which will benefit Ngaroto as the amount of nutrients entering Ngaroto will reduce (personal communication, Tony Roxburgh, 2011). 5

6 Map of the lake Ngaroto / Ngarotoiti catchment courtesy of Waikato Regional Council. 6

7 2.2 Recreational Use of the Lake Recreational use of the lake is varied. Yachting, windsurfing and rowing take place on the lake, with duck shooting on and around the margins. Duck hunters have a long standing arrangement with other users for exclusive use of the lake during May and June. The southern access is also popular for picnickers, walkers and as a place where local people can exercise their dogs (on leads). Current visitor numbers are estimated to be between per annum (personal communication, Tony Roxburgh 2011). 3 Peat lake formation and ecology Lake Ngaroto and the other Waikato and Waipa District peat lakes were formed around years ago as a result of the Waikato River changing course and carrying with it a flood of soil and sediments (alluvium). This alluvium was deposited downstream in the Waikato Basin and blocked off small streams, producing small lakes which eventually turned into peat lakes and bogs (McGraw 2002) (see also diagrams below). Diagrams courtesy of Dr. David Lowe (University of Waikato) Peat Lakes have unique physical, chemical and biological characteristics. Peat itself takes thousands of years to form. Peat is made up of the remains of wetland plants in wet environments. The high water table and acidic conditions prevents the rapid break-down of the dead plants by fungi and bacteria, causing the peat to grow upwards, in some cases forming broad domes. It grows very slowly on average around 1mm per year. The term peat generally applies when the organic content is 50 per cent or more. Peat land applies to all land having a peat substrate, regardless of degree of drainage. The peat lakes in the Waikato Region are generally shallow (c1-3m deep), with part, or all, of the lake margin surrounded by peat. Their main water source (historically) is from subsurface flow and rainfall, This meant that the lakes were higher in winter months due to rainfall and lower in summer months due to evaporation. Today lakes receive water due to the drainage systems put in place to enable the surrounding peat to be farmed. In their natural state peat lakes have low ph (acid), and very low nutrients have unmodified, primarily forested catchments, clear, but tannin stained water with carpets of aquatic vegetation. Wetland birdlife, such as the Australasian bittern (Botaurus poiciloptilus), or matuku as it is known to Maori and New Zealand fernbird (Bowdleria punctata) were once abundant. However, currently all peat lakes in the Waipa District are situated in highly modified catchments, mostly cleared for intensive dairy farming and cropping, with the lakes themselves often 7

8 dominated by undesirable algae. There are few lakes with aquatic plants, the majority of which are exotic and high populations of pest fish including koi carp and rudd. Lake Serpentine east, just a few kilometres from Lake Ngaroto still has a high degree of natural character including clear, tannin stained water and a margin of mainly native plants. Photo: Monica Peters The Waikato peat lakes are the remnants of once extensive peat bogs, with <1% of the pre European area of peat bog remaining in the Waipa District Map of current and historic extent of wetlands in the Waikato courtesy of Landcare Research 8

9 4 Pre European History In a report prepared for Waipa District Council by the Centre for Biodiversity and Ecology Research at the University of Waikato, Modelling of restoration scenarios for Lake Ngaroto, (Paul, Özkundakci & Hamilton, 2008) a history of Lake Ngaroto is given: Archaeological evidence from six pa sites around Lake Ngaroto indicates people lived here and they cultivated their own food as well as using the nearby forest and lake as a food source (Amess et al. 1978), and as a resource for building materials, medicine, and traditional rituals and ceremony. The first people to settle here were members of hapu or sub tribes of Ngati Apakura, who were originally guided to this land by Uenuku, the sacred patron and icon of the tribe. The area was also important in times of war and Lake Ngaroto was the scene of one of the largest battles to take place on New Zealand soil. The Battle of Hingakaka took place sometime between 1790 and 1803 on a ridge near Lake Ngaroto when an army of around Maori warriors from several tribes from the lower North Island, led by Pikauterangi, a Ngati Toa chief, attempted to settle a long-running grievance over land and food resources, by destroying a settlement of people, mostly Ngati Apakura hapu, who lived on the shores and on the man made island of Lake Ngaroto. The shoreline dwellers used great stealth as well as familiarity with their local wetland and lake environment to kill many of the invaders, some of whom were forced to swim for safety in the lake, only to drown or be dispatched as they attempted to return to shore. Around one century later, as the wetlands around the lake were drained and the lake water level decreased to support agricultural development, not only were the bones of many who drowned in the lake uncovered, but also a carving was discovered in which a stone was embedded. This stone is reputed to hold one of the traditional gods of Maori people, Uenuku, and was brought across the Pacific Ocean to New Zealand in a canoe by some of the first Maori settlers of the Tainui tribe. Uenuku had apparently been placed in Lake Ngaroto for safe-keeping during the battle of Hingakaka and is now housed in the Te Awamutu Museum (at the time of writing this report, he is now in Te Papa in Wellington for the next two and a half years). Uenuku. Photo courtesy of Te Awamutu Museum. One of the swamp pa sites at Lake Mangakaware outlined by a darkened trench. Photo courtesy of Waipa District Council and John Greenwood. 9

10 Several Swamp Pa, like the one on the shores of Lake Ngaroto and Lake Mangakaware (photo above) are now recognised as very important historical sites and regarded by archaeologists as being perhaps the best preserved open air neolithic settlements in the world (Gumbley, John and Law 2005). 5 Threats and Pressures to Lake Ngaroto (From Waikato Regional Council website 2 and Waipa District Peat Lakes and Wetlands booklet 3 ) The main threats to Lake Ngaroto and peat lakes in general are drainage and cultivation of the surrounding peatland and the introduction of aquatic pests. Since 1840, many of the peatlands in the region have been drained for farming. Outlet drains from the peat lakes were dug to drain the land, often significantly lowering water levels. For example, the Komakorau, Rukuhia and Moanatuatua peat bogs once covered over 40,000 hectares. However today, only the 80 ha Moanatuatua Scientific Reserve remains. Vegetation clearance in the past, and more recently, land management practices (such as drainage for agricultural development), have affected all peat lakes in the region by: reducing water quality lowering lake levels degrading native habitat reducing biodiversity fewer plants and animals present changing the natural character of the lake from a native vegetated environment to a grassed farmed environment. 5.1 Drainage and cultivation Drainage and cultivation of peat soils for pasture and cropping results in oxidation and shrinkage of peat soil that cannot be reversed. Growing any agricultural crop on peat soils requires drainage to aerate the soil. Although this allows for productive plant growth, aeration also results in oxidation which causes peat to decompose, dry and shrink. Cultivation accelerates this oxidation and shrinkage process. Landowners often need to deepen drainage systems to maintain production on shrinking peat soils. Deepening drains lowers the water table in surrounding farmland. However, the water level in nearby peat lakes becomes higher than the surrounding water table, causing water to spill out onto neighbouring land. Lake levels in the peat lakes are then lowered to prevent flooding. This cycle of land drainage and lake lowering can continue until all the peatland and associated lakes are drained. Today many of the peat lakes are much smaller and shallower than they were in the past and many lakes are perched due to on going peat shrinkage, caused by clearing the original forest and wetland plant cover and draining the peat for farming purposes. Shallower lakes tend to have less stable environments than deeper lakes because they have: increased turbidity from wind stirring up bottom sediments greater temperature extremes. Continued lowering of peat lake water levels threatens the survival of the lakes and their unique wildlife

11 In spite of the degraded state of most peat lakes some still do support unique plants and animals which have evolved to cope with the acidic conditions, for example mudfish. In good condition (or restored), peat lakes represent a nationally significant wildlife habitat type for common and rare native flora and fauna species. 5.2 Nutrients 4 Although nitrogen (N) and phosphorus (P) are critical for farm production, excess quantities entering lakes (through surface runoff, subsurface flows and via drains and streams) can be extremely damaging. Even small increases in N and P can cause weeds or undesirable species to proliferate producing algal blooms. Some algal blooms can have very serious consequences for recreational use, livestock and native animals if the resulting toxins are ingested. Nitrogen (N) N is supplied to the soil from fertiliser, stock urine, manure, effluent irrigated to land and nitrogen fixing bacteria living in the root nodules of clover. N is relatively mobile and easily lost from pasture once it has converted to the nitrate form. N requires careful management to ensure the right quantities are maintained in the soil, without excessive amounts being lost from the productive farming system. up to 30 % of N entering soils on intensive farms may end up leaching into ground water, eventually flowing into drains, waterways and lakes. Phosphorus (P) P is supplied to the soil from fertiliser, animal effluent, manure and natural weathering of rock and soil. P will not generally move far from the soil surface and is not easily leached except in peat and coarse textured soil with low P retention properties. serious losses of P occur through soil erosion. P enrichment of waterways occurs through poor fertiliser placement and the release of P from eroded soil particles. Soil particles/sediment may enter the lakes through drain clearing in the catchment, poorly designed raceways and unvegetated steep areas. Some farm nutrient and sediment hot spots can include the following: High animal traffic zones such as: the dairy shed and all raceways entering it stand off/feed pad operation raceway runoff into drains and waterways, especially those close to the shed. Other parts of the farm and farming operations: compaction with increased runoff due to overgrazing drain/waterway/lake margin erosion due to poor management stock access to drains/waterways/lakes fertiliser too close to drains/waterways/lakes effluent disposal area drainage clearing silage pits offal holes and farm dumps overuse of fertiliser

12 These two images below graphically show the loss of Waikato s special peat lakes. The map on the left dates from the early 20 th century and highlights the significant reduction in lake size as well as the total loss of Round Lake compared with a recent aerial map on the right: Map and aerial photo courtesy of Waipa District Council 5.3 Aquatic pests Low nutrient ecosystems, such as bogs and swamps, often contain unique plant species specially adapted to extreme conditions. While these habitats are more resilient to generalist invasive species they may be destabilised by introduced specialist invasive species adapted to similar environments. Lake Ngaroto has been detrimentally affected by the introduction of invasive aquatic plants (Hicks 2001). The oxygen weeds Elodea and Egeria were present in 1977, and were documented as problematic for boating (Boubée 1977). Introduced aquatic plants such as oxygen weeds (Lagarosiphon and Egeria) and Hornwort can grow faster and taller than native aquatic plants. They take over and limit light and space available for native species (WDC Peat Lakes and Wetlands). Pest fish can play a major role in the disappearance of native aquatic plants from peat lakes also. For example, introduced koi carp and brown bullhead catfish affect water quality by stirring up the lake sediments and uprooting aquatic vegetation (Hicks 2001). Rudd also affect native plants by grazing them (See section on Pest fish for more information). The main plant pest surrounding peat lakes is grey willow (Salix cinerea). It is deciduous and has the ability to encroach into open water. It dominates most lake margins and replaces native woody vegetation, such as manuka, 12

13 and shades out native grasses and sedges. Royal fern can be a problem under willow or manuka also. Blackberry, Japanese honeysuckle, convolvulus and gorse are all problem weeds at Lake Ngaroto too. 6 Restoring Lake Ngaroto Much has been done around the riparian margins of Lake Ngaroto to try and slow the decline in water quality s A weir was installed in 1971 to control water level during the summer period for recreational purposes (Boubée 1977). By the early 1970 s the lake weed Egeria densa was deemed to be interfering with sailing and rowing activity and a consent was granted to use the herbicide diquat to control infestations. Two consents were granted to spray Lake Ngaroto with herbicide. The first was granted n 15 th January 1976 (expired 15 January 1981) and authorised the spraying of 5.6 litres of diquat, twice per annum, for five years. The second consent was granted on 10 th February 1982, and authorised the spraying of up to 50 litres of diquat (diluted to 1000). Records from Environment Waikato record that in both consents the area sprayed each year included the total area of the lake, including the littoral margins. Reports on water quality prepared by Waikato Catchment Authority when reviewing the resource consent to apply diquat, described the lake as highly eutrophic with nutrient and chlorophyll a concentrations very high and reduced water transparency. High algal production was evident in winter as well as summer, including the presence of blue green algae. Some parameters measured, namely phosphorous and nitrogen, were considerably higher than values measured in 1977, some ten years previously. This is likely the period when submerged plants began to collapse and algal communities began to dominate. In 1978 Waipa District Council funded a range of research initiatives aimed at documenting the water quality and biological attributes of the Waipa Peat Lakes. This work was overseen by M Chapman and J Boubee (Biological Sciences, School of Sciences, Waikato University). This was the first attempt to visit and record data on the peat lakes and it provided a very useful base line to compare change. A management plan for the lake was first approved by Waipa District Council in s Restoration planning was done in the early 1980 s and this was the basis for the work by the Preemployment Programme (PEP) gangs of the period. Much of the margin was fenced, albeit on a line inside the true legal boundary. In 1981, as part of a broader lakes survey, the quality of Lake Ngaroto waters was surveyed. The water was described as dark brown, with transparency affected by algal turbidity. Twenty two species of algae were recorded. It was recorded that on the bases of the high algal productivity, restricted light penetration and history of herbicide applications, Lake Ngaroto will likely remain algal dominated Waipa District Council Lake Ngaroto Plan by John Greenwood was put in motion. This was a very comprehensive plan which proposed and then implemented the following: The boundary of the lake to be recognised as the outside boundary of a legal road that encircles the Lake Ngaroto Recreation Reserve. The entire boundary of the lake to be fenced on the proposed new legal boundary. Water discharges to the lake to have some form of silt and nutrient filtration before final discharge into the lake in an attempt to limit the infilling and nutrification of the water. Silt traps were installed in 1999 and cleaned out for the first time in Grey willow to be totally removed from the lake reserve over a period of time, with other species of willow to be progressively controlled also. 13

14 Restoration plantings around the lake margins have been primary native and now cover the majority of the lake edge The Waipa Peat Lake and Wetland Accord was signed (on World Wetlands Day, 1 st February). The signatories were Environment Waikato, Waipa District Council, Department of Conservation, Auckland/Waikato Fish and Game Council and Ngā Iwi Tōpu O Waipa. The purpose of the Accord is to align the activities of management agencies when working with landowners, Tangata Whenua and interested parties, towards the restoration and enhancement of lakes and wetlands in the Waipa District. Supporting the overriding purpose of the Accord is a series of objectives. These objectives relate to ways in which the Accord agencies can work collaboratively towards the restoration and enhancement of lakes and wetlands in the Waipa District. The objectives are to: Promote the sustainable use and conservation of lake and wetland resources by developing and implementing relevant local management projects, regional and national policies and action plans, and international conventions. Encourage restoration of degraded lakes, wetlands and associated species that are in an unfavourable conservation status, through the application of sound environmental management and research. Maintain an overview of the status of lake and wetland resources by developing, promoting and coordinating assessment and monitoring programmes and disseminating the results. Develop a regional network of experts for the transfer of know how, research and information through effective partnerships with like-minded organisations. Raise awareness of the functions and values of lakes and wetlands through education, information and awareness programmes Waipa District Council and Environment Waikato agree on a five year programme to protect priority peat lakes from intensive agriculture land use in the lake catchment. The five priority lakes included Ngaroto. 6.1 Council role; Rules and regulations listed peat lakes and drainage rules Rules exist under the Waikato Regional Plan which limit and control land drainage in areas adjacent to identified wetlands and wetlands bigger than one hectare. The wetlands which are covered by these rules are listed in the regional plan and include some peat lakes 5. The creation of any new drains, or deepening of drain invert levels in areas adjacent to and within 200 metres of the edge of identified wetlands (including Lake Ngaroto) are discretionary activities and require resource consents. These rules aim to avoid further degradation and size reduction of these specified wetland areas. Waipa District Councils Rural Zone rules relating to Peat Lakes are below: RULE - Protection of Peat Lakes and their Margins 1. For the purpose of this Rule the Waipa peat lakes as shown on the Planning Maps are: 5 Identified wetlands can be found here: Plan/3-Water-Module/37-Wetlands/377-Table-of-Wetlands-in-the-Waikato-Region-for-Rule-3746/ 14

15 Cameron, Maratoto, Rotopatak, Koromatua, Ngarotoiti, Ruatuna, Mangahia, Ngaroto, Serpentine, Mangakaware, Rotomanuka. 2. No activity shall be allowed which: a) modifies the natural indigenous vegetation composition within 50 metres of the edge of any peat lake measured at its maximum annual water level; or b) involves any land drainage which will alter the hydrological regime of any peat lake; provided that this Rule shall not apply to conservation measures undertaken by the Council, the Waikato Regional Council or any conservation organisation approved by the District Council. Any activity which does not comply with Rule shall require a resource consent for a Discretionary Activity and shall be considered in accordance with Rule (Refer to Policies RU18-RU21, RU33-RU35,RU37, RU38, RU , RU ,RU , RS69, RS73, Rule 2.7.2) 6 Waikato Regional Council has developed resources for landowners farming on peat soils: For Peat s Sake. Good management practices for Waikato peat farmers by Environment Waikato 7 Farmers can help by: Keep drains shallow and take care not to deepen drains during maintenance Fence drains that flow into peat lakes Maintain pasture water tables over summer which reduces peat shrinkage Avoid cultivating close to peat lakes. Continuous cultivation can double the rate of peat shrinkage EA8B677F5/79513/WRALTrackChangeWaipaRuralv1.pdf

16 7 NZ Landcare Trust and shallow lake restoration In 2009, the NZ Landcare Trust embarked on a three year, SMF funded project focusing on the Waikato Shallow Lakes. Work during that time centred on bringing together a wide range of community members, agencies and industry partners with a shared objective; to improve the health of nationally significant shallow lakes and wetlands through catchment focused sustainable land management initiatives. Supported by the Ministry for the Environment s Sustainable Management Fund (SMF #2246), the project targeted the farming community and used a 'bottom up' participatory approach to develop information sharing forums, such as workshops and resources on sustainable land management. The project was closely linked to an exciting range of community and agency-led initiatives which assisted landowners and farmers to reduce their environmental footprint as well as enhance regional biodiversity. PROJECT ACHIEVEMENTS Publications: Best Management Practices booklet for enhancing water quality in the Waikato, with farmer case studies Best Management Practice Fact sheet on silt trap and drainage Guidelines for Landowners in Peat Lake Catchments 8 provides information on history, ecology and key pressures facing lakes as well as recognised management approaches to improving the environmental footprint of farming, by the NZ Landcare Trust: Twice yearly newsletters Practical research: Survey with major landowners adjacent to Lake Ngaroto (see 7.1 for details) Surveys with landowners in priority shallow lake catchments Workshops and tours: Peat Lake Powwow held at Lake Ngaroto Practical Farm planning workshop at Lake Tunawhakaheke/E, Horhsam Downs Resource Managers Tour of Waikato Shallow Lakes Catchment water quality field day in Te Pahu (in conjunction with Te Pahu landcare and farm discussion groups) Silt trap and drainage management workshop, Lake Kaituna(B), Horhsam Downs Lake information day at Lake Serpentine (Waipa) bringing community together, liaison with scientists and landowners. Farm and catchment plans: Catchment Action Plan for Lake Tunawhakaheke/E - working in partnership with DOC, Waikato Regional Council, Waikato DC, landowners and the local Fish and Game community Whole Farm Plans for the two farms in the Lake Tunawhakaheke/E catchment

17 Nardene and Melinda facilitating a Practical Farm Planning Workshop at Horsham Downs. Photo: Abby Davidson 7.1 Lake Ngaroto Landowner survey Monica Peters from the NZ Landcare Trust carried out interviews with seven landowners, one sharemilker and three farm managers around Lake Ngaroto over a period from November February This equated to eight properties in total, all of which are major landholdings within the lakes catchment. The survey covered a wide range of topics including: Farm information Groups, networks and learning Best management practices The survey found that with the majority of landowners being long term inhabitants of the catchment, views expressed provide an insight into how the lake and surrounding catchment has changed over time particularly in relation to land use, riparian zones and water quality. With the exception of one farm, all are intensive dairy the predominant land use in most of the Waikato peat lake catchments. Stocking rates vary between farms with several farmers lowering their stocking rate to achieve lower input costs though not necessarily at the expense of lowering production. Most of the farmers had a Nutrient Management Plan but only a few have Nutrient Budgets, none have Whole Farm Plans. The topography of the catchment and the resulting range soil types clearly provides challenges low lying peat areas being the most difficult to manage. However, shrinkage of the peat resource was not widely regarded as a significant issue. The level of the lake established by a weir plays a strong influence on both lake catchments with flooding taking place regularly during wet periods. Drainage emerged as the most mentioned management challenge overall, hence the desire by landowners to find out about the setting of new lake levels. The following suggestions of a way forward for the lake were made based on the interviews with farmers in the Ngaroto and other shallow lake catchments in the area: Subsidised Whole Farm Plans for landowners. Catchment plan for Lakes Ngaroto and Ngarotoiti. Opportunities for farm visits to other farms, both within and outside the catchment, with a lake management focus. Further dialogues with landowners there is value in face to face communication. 17

18 8 Scientific Research and Monitoring Lake Ngaroto has become hypertrophic due to the high nutrient loading from the surrounding catchment, of which the predominate land use is dairy farming. Isotopic analyses of phytoplankton and lake sediments in 1982 and 1983 suggested that the lake had recently undergone an increase in productivity. This was inferred from the more negative d 13 C values of the sediments compared to the phytoplankton, which was attributed to forest clearance and current farming practices of the time (McCabe 1985; p172 and p ). Summer ph ranged from 6.6 to 8.7, and Secchi depth was m. Chlorophyll a concentration was mg m -3, and the water was described as weakly to moderately coloured (Vant and Devies-Colley 1988). Its appearance in was rated as poor (Vant and Davies-Colley 1988). A report prepared for Waipa District Council by the Centre for Biodiversity and Ecology Research at the University of Waikato (Paul, Özkundakci & Hamilton, 2008) looked at a variety of different restoration scenarios in an attempt to decide which would be the most successful in improving the lake water quality. Data were gathered on flow, nutrient concentrations, temperatures, dissolved oxygen, suspended sediments, meteorological variables and the lake morphology for the lake and its catchment. This data was calibrated as a means of comparison for modelled data and a number of scenarios were carried out to simulate outcomes of lake restoration measures. The lake water quality restoration scenarios simulated included: Diverting the major inflow (Lake Ngarotoiti) into the outflow Increasing and decreasing the lake water level by 0.4 metres Reducing the external nutrient load by 33% and 55% Reducing the wind speed by 50% Removal of the upper 20 cm of sediment from the lake bottom Most of these scenarios produced predictable results, with reduction of external nutrient load through change of land use had the most beneficial water quality impact measured by reduction of nutrients and chlorophyll a. Reduction of internal nutrient load through sediment removal also produced a marked improvement. Therefore it is important to emphasis that the external load and internal nutrient loads can negate any immediate effect from reduction of external loading. Thus controls of both external and internal nutrient loads should be addressed in an integrated management plan for the lake. 8.1 Monitoring buoy A buoy is located in Lake Ngaroto that takes readings every 15 minutes of water temperature, dissolved oxygen, chlorophyll a and phycocyanin (i.e., algae and blue-green algae, respectively) as well as meteorological variables (wind speed and direction, rainfall, air temperature, humidity). The data is collected by the Centre for Biodiversity and Ecology Research Department of Biological Sciences (CBER) at the University of Waikato and provided to Waipa District Council as part of their ongoing monitoring of the lake. 8.2 Managing pest fish Lake Ngaroto has a diverse fauna of native and introduced fish. In 1977, fish present in the lake were carp (probably Carassius auratus), common bullies, (Gobiomorphus cotidianus), and catfish (Ameiurus nebulosus). Eels and grey mullet were speculated to be present; though eels almost certainly were present, grey mullet were probably not present. (Hicks 2001). In 2001, a total of 4317 fish were caught in nets at seven sites around the lake. The most numerous species were brown bullhead catfish, rudd (Scardinius erythropthalmus), and shortfinned eels (Anguilla australis). Goldfish, koi 18

19 and gambusia were in low densities. In fish were caught via electrofishing and this time low numbers of catfish and higher numbers of goldfish, koi and gambusia were found. These differences can largely be attributed to differences in sampling methods. Fyke nets are biased towards catfish and eels whereas boat electrofishing is biased towards koi and goldfish. Interestingly all the introduced fish species found in Lake Ngaroto in 2001 were still present in Comparisons between densities of introduced fish species in 2001 and 2009 cannot be made as different sampling methods were utilised. The high productivity of Lake Ngaroto may be reflected by the presence of introduced fish species such as goldfish, koi car, koi/goldfish hybrid and catfish which all prefer highly productive habitats, and are very tolerant to poor water quality. The excretion and bioturbation of koi carp during feeding in bottom sediments has been shown to increase rates of nutrient cycling. (Zambrano et al. 2001). Species such as gold fish and catfish have a similar feeding mechanism to koi carp and thus could also be contributing to nutrient cycling. (Hicks 2009). Approximately 60% of the total biomass in the 2009 study was found to be koi carp. Biomass is a more accurate reflection of the potential ecological impact of koi carp than their density, and koi carp would have a deleterious impact on the aquatic habitat of the lake (Roberts & Ebner 1997). The total benthivorous fish biomass (60 90 kg ha -1 ) is between 50 and 150 kg ha -1, suggesting a moderate prospect for water quality improvement if these fish are removed (Hicks 2009). 9 Where to from here? Recommendations All scientific research on Lake Ngaroto and other peat lakes in the region generally recommend that change of land use in the catchment will aid the reduction of external nutrient load to lakes and will have the most beneficial water quality impact. Therefore focusing on land management issues within the catchment would be the logical place to start when trying to improve the water quality of the lake. This was also highlighted by farmers in the catchment whom felt Whole Farm Plans would be a beneficial way of bringing about changes of farming practices with no or very little impact on farm productivity. Therefore the Community Catchment Action Plan for Lake Ngaroto is a timely project and has the potential to make a significant difference to the state of the lake over the long term. The long standing Integrated Catchment Management (ICM) project in the Motueka River 9 concedes that people are at the heart of Integrated Catchment Management, and when people work collaboratively, much can be achieved. In the Waikato Region, many agencies and organisations already work in partnership with each other as already outlined in other areas of this report. The Waikato Regional Council (WRC) have a number of ICM projects underway and some of the lessons learned from these can be applied to the Lake Ngaroto project. For example some of the initial trends WRC have observed farmers who are involved in ICM projects are: increasing their effluent area reducing use of fertiliser nitrogen in the winter having less reliance on supplementary feeding having greater strategic use of fertiliser nitrogen having greater awareness around the importance of storage for dairy shed effluent 9 more info here: 19

20 increasing interest in low rate effluent irrigation moving away from high stocking rates swinging towards a greater focus on per cow production. Over the last few years, Fonterra has taken a stronger role in environmental issues with its every farm every year programme. DairyNZ has held a number of effluent field days and most farmers in the WRC ICM catchment have used DairyNZ s Enviro Walk 10 material. For the Lake Ngaroto project, the NZ Landcare Trust has set up a steering group involving representatives from Waikato Regional Council, Fonterra and DairyNZ, along with Waipa District Council, the University of Waikato, Ngā Iwi Toopu O Waipa, Headlands Consultants, local farmers and the Sailing Club. The steering group is aware the project will face many challenges in the years ahead. External influences such as the economic recession will potentially make it difficult for some farmers to make infrastructure changes. We have set realistic goals throughout the first year of the project and will continue to do so in the remaining two years. A catchment approach of the type NZLCT is carrying out at Lake Ngaroto will be able to be transferred to other regions in New Zealand and will be used as an example of what can be achieved over time. It will be able to be scaled up or down depending on the lake catchment, as already demonstrated in the Lake Tunawhakaheke/E catchment. The NZ Landcare Trust has Regional Coordinators around the country that can run workshops and use their extensive regional networks to promote the use of this catchment approach to improving lake water quality over the long term. The NZ Landcare Trust has a proven track record of national projects and lessons learnt from catchment work in other parts of the country will assist with this Community Catchment Action Plan for Lake Ngaroto. 10 More info here: 20

21 10 Bibliography Beaton, R., D. Hamilton, M. Brokbartold, C.Brakel and D. Özkundakci, Nutrient budget and water balance for Lake Ngaroto. CBER Contract Report No. 54. Centre for Biodiversity and Ecology Research, Department of Biological Sciences, School of Science and Engineering, The University of Waikato, Hamilton. Chapman, M.A The fauna of peaty lakes in the Waikato Valley. Biological Sciences, Waikato University. Duggan, I.C The distribution and dynamics of planktonic rotifers in the North Island, New Zealand. Unpublished PhD thesis, University of Waikato. Environment Waikato, NZ Landcare Trust, Waikato District Council, Waipa District Council Guidelines for landowners in peat lake catchments. Environment Waikato Farmers guide to permitted activities. Guide 2. Environment Waikato For Peat s Sake. Environment Waikato Peat and Lower Waikato River Lakes. Water factsheet 7. Environment Waikato Lake Ngaroto and Peat Lakes in the Waikato Region. Powerpoint presentation. Fenemor, A., Neilan, D., Allen, W. and Russell, S. Improving Water Governance in New Zealand Policy Quarterly, Volume 7, Issue 4. Hicks, B.J., Reynolds, G.B., Jamieson, P.M. & Laboyrie, J.L Fish populations of Lake Ngaroto, Waikato, and fish passage at the outlet weir. CBER Contract Report 14, prepared for the Waipa District Council. Hamilton, New Zealand: Centre for Biodiversity and Ecology Research, Department of Biological Sciences, University of Waikato. Hicks, B.J. and J. Brijs Boat electrofishing survey of Lake Ngaroto. Client Report prepared for Waipa District Council. CBER Contract Report No Centre for Biodiversity and Ecology Research, Department of Biological Sciences, School of Science and Engineering, University of Waikato, Hamilton. Greenwood, J Lake Ngaroto Restoration and Development Plan prepared for Waipa District Council. Greenwood, J Lake Ngaroto Restoration: A Case Study prepared for Ministry for the Environment. NIWA Waikato River Independent Scoping Study report commissioned by the Ministry for the Environment. Paul, W. Özkundakci, D. Hamilton, H Modelling for Restoration Scenarios for Lake Ngaroto, CBER Report 85. Prepared for Waipa District Council. Centre for Biodiversity and Ecology Research, Department of Biological Sciences, School of Science and Engineering, University of Waikato, Hamilton. Peters, M Monitoring and Management Plan. Recreated Restiad Wetlands, NZ Landcare Trust. Peters, M NZ Landcare Trust Lake Ngaroto Survey Thompson, K Policies and the management of shallow lakes in the Waikato. Presented at the Waikato Shallow Lakes Workshop, December

22 Waipa District Council, Environment Waikato, Department of Conservation, Fish and Game, Nga Iwi Toopu o Waipa. date unknown. Waipa District Peat Lakes and Wetlands. Waipa District Council A plan for the management of peat lakes and associated reserves administered by the Waipa District Council. DRAFT. Waipa District Council Lake Ngaroto Recreation Reserve. Reserve Management Plan Websites The Ministry for the Environment does not necessarily endorse or support the content of the publication in any way. This work is copyright. The copying, adaptation, or issuing of this work to the public on a non-profit basis is welcomed. No other use of this work is permitted without the prior consent of the copyright holder(s). 22