Rotorua Lakes Symposium 2015

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https://researchcommons.waikato.ac.nz/handle/10289/15108

Lake Weed and Wallabies: Their Role and Control in the Ecology of the Rotorua Lakes

12 – 13 March 2015

Sir Howard Morrison Performing Arts Centre (Rotorua Convention Centre)

1170 Fenton Street, Rotorua, 3010

EDITOR’S NOTE

Programme

SESSION SEVEN: SCENE SETTING

SESSION TWO: THE ISSUES

SESSION THREE: THE TOOLBOX

SESSION FOUR: LAKE WEEDS - THE WAY FORWARD

SESSION FIVE: ECOLOGICAL HEALTH OF THE CATCHMENTS

SESSION SIX: CONTROL OF ANIMAL PESTS

SESSION SEVEN: RESPONSIBILITIES AND FUNDING

CLOSING COMMENTS

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Session 4 Discussion: Rototrua Lakes Symposium 2015
(Conference Contribution, LakesWater Quality Society, 2015)
Session 4 Discussion: Rototrua Lakes Symposium 2015
Closing comments: Rotorua Lakes Symposium 2015
(Conference Contribution, LakesWater Quality Society, 2015) Green, John
Closing comments: Rotorua Lakes Symposium 2015
Session 7 Discussion: Rototrua Lakes Symposium 2015
(Conference Contribution, LakesWater Quality Society, 2015)
Session 7 Discussion: Rototrua Lakes Symposium 2015
Responsibilities and funding – consenting pathways and options
(Conference Contribution, LakesWater Quality Society, 2015) McKenzie, Angus
This presentation will outline the regulatory framework for biosecurity programmes within the Rotorua Lakes and explore a range of potential options for tackling the framework, drawing on my experiences with collaborative comprehensive consenting and national policy tools. Examples to be discussed will include: · National aquatic weed consent. A multi-agency reassessment that has expanded the aquatic weed toolkit under HSNO and provided efficiencies through reducing administration costs. · Comprehensive consenting in the Waikato region. Programme level consents for the Waikato Regional Council, their effectiveness, outcomes and relevance to the Rotorua Lakes context. These examples showcase a range of alternative responses to regulatory requirements that have resulted in positive outcomes for the agencies involved and could provide a framework for the Rotorua Lakes programmes.
The role of a weed management Agency – a smart approach to delivering innovative biosecurity services
(Conference Contribution, LakesWater Quality Society, 2015) Mole, David
Over the past year, Land Information New Zealand (LINZ) has taken a new approach to biosecurity as a result of significant external factors and a new, organisation-wide 10 year vision. We have reviewed our biosecurity aims and goals, and re-examined the tools and processes that determine our ability to fulfil these overarching outcomes and objectives. Our new thinking about biosecurity has been informed by what we call SMART procurement, and this approach has encouraged innovation, ensured a better focus on outcomes, and laid the foundations for a truly strategic partnership with our suppliers. This presentation will outline our SMART philosophy, and offer some thoughts on its benefits over traditional models of biosecurity management, focusing in particular on our aquatic weed control work.
Statutory responsibilities and barriers to action
(Conference Contribution, LakesWater Quality Society, 2015) Salmon, Guy
Looking at the context of current policies and institutions, this presentation will explore possibilities for enhancing the effectiveness of control actions for lake weed and wallabies.
Watching for invasive species: public engagement
(Conference Contribution, LakesWater Quality Society, 2015) Burton, Tracey
Invasive species continue to be one of the greatest threats to the Rotorua lakes and include not only water weeds and wallabies, but other organisms too. Invasive molluscs such as zebra and quagga mussels have the potential to cause wide spread devastation to our freshwater ecosystems and are just one example of other invasive aquatic species not yet found in our New Zealand lakes. The management of invasive species is a shared problem that requires the cooperation and support of a diverse range of stakeholders, interest groups and members of the general public. The early detection of an invasive species is critical and may make the difference in being able to appropriately manage, control or eradiate a species before it has a chance to spread. Anyone can help prevent the incursion and spread of invasive species into our lakes. In New Zealand, we can learn from the success of programmes in other countries where they are recruiting citizen scientists to look for anything new or unusual. Citizen science, broadly defined as the involvement of volunteers in research, provides a means of combining research activities with environmental education and public engagement in science. Volunteers are able to increase their knowledge and understanding of the environment, learn more about local issues of importance, and contribute to science based recommendations. In addition, observations collected by citizen scientists can provide valuable records and knowledge that otherwise wouldn’t have been available.
Session 6 Discussion: Rototrua Lakes Symposium 2015
(Conference Contribution, LakesWater Quality Society, 2015)
Session Six Discussion: Rototrua Lakes Symposium 2015
Perspective of a consultant and contractor
(Conference Contribution, LakesWater Quality Society, 2015) Speedy, Cam
Pest management can be a very polarising issue. Every pest management operation is different, reflecting variations in terrain, accessibility, ecology, the types of pests present and the nature and scale of previous pest management. Most importantly, stakeholders often seek different outcomes based on very diverse drivers and beliefs. There is no 'onesize- fits-all' approach to pest management. From experience with a wide variety of pest management operations within diverse communities, a pest management regime specifically developed for the Okataina Scenic Reserves is described. One that will contribute positively to water quality, the sustainability of forest ecology and to community engagement.
Dama Wallabies: Their history of colonization and control at Okataina/Tarawera
(Conference Contribution, LakesWater Quality Society, 2015) Williams, Dale
Dama wallabies (Macropus eugenii) were liberated near the southern end of Lake Okareka in 1912. By the 1970s their numbers had built to high levels in the forests surrounding Okareka, Okataina and Tarawera and the damage they were causing to the forest understorey was marked. In 1984 the New Zealand Forest Service established a pair of ‘exclosure plots’ at Okataina designed to isolate the impacts of wallabies from those caused by deer. A decade later when the vegetation plots were remeasured, species diversity had increased by 142% where both deer and wallabies were excluded. Diversity had increased by 57% where wallabies were excluded and continued to decline by 7% where browsing was unrestricted. Between 1988 and 1999 three aerial poisoning operations and some ground based pest control, targeting wallabies and possums, were carried out around Okataina and the Makatiti Dome. Though these operations were highly successful at reducing wallaby numbers (93-95% reductions based on cleared-plot faecal pellet counts) remeasurement of permanent 20x20 metre vegetation plots showed no response in the forest understorey. To some extent this is not surprising as the control operations were effectively ‘one-offs’ in separate areas and only limited follow-up control took place.
Control of pests in Lake catchments – the Department of Conservation’s perspective
(Conference Contribution, LakesWater Quality Society, 2015) Fairweather, Alastair
A key part of the Department of Conservation’s (DOC) work is to ensure the diversity of New Zealand’s natural heritage is maintained and restored. However, is a huge task and DOC’s resources cannot stretch to do everything everywhere. DOC therefore has to make decisions about what work to do and not do, juggling limited resources while meeting both biodiversity and community needs. To help make these decisions, DOC has developed the Natural Heritage Management System (NHMS) Programme which identifies the highest priority sites (both terrestrial and freshwater) that need to be protected and where work needs to be done. For NHMS to correctly identify the priority sites and what work it needs to be done at the sites, it relies on good information. For the freshwater sites, the data came out of the Freshwater Ecosystems of New Zealand (FENZ) dataset. This data set describes the environmental and biological patterns in NZ’s freshwater ecosystems (rivers, lakes and wetlands). Once priority sites have been identified, it is important to understand what pressures the sites face and what activities, including pest control, need to be undertaken to reduce these pressures. In this presentation, the Rotorua lakes, with particular reference to Lake Okataina, will be placed in the context of this prioritisation process, the pressures they face and pest control activities DOC has identified as necessary to ensure the priority lakes are protected.
Session 5 Discussion: Rototrua Lakes Symposium 2015
(Conference Contribution, LakesWater Quality Society, 2015)
Session 5 Discussion: Rototrua Lakes Symposium 2015
The link between erosion, phosphorus and water quality
(Conference Contribution, LakesWater Quality Society, 2015) Gibbs, Max M.
In lakes, the solubility of phosphorus (P) in water, and therefore its availability to aquatic plants (macrophytes and algae) for growth, is controlled by oxygen and pH. The supply of dissolved reactive P (DRP) to the lake water column is mostly from sediment release from decomposing plant material and iron oxides during periods of low oxygen, although in Lake Rotorua and most of the other lakes on the central volcanic plateau, spring-fed streams carry relatively high concentrations of DRP into the lakes. The mechanism for releasing iron-bound DRP from the sediment focusses around the oxidation state iron (Fe) and manganese (Mn). In well oxygenated conditions iron exists in the oxidised state as ferric ions which form ferric oxides that are insoluble in water. These oxides sequester DRP as they precipitate and remove it from the water column. When the oxygen concentration falls to zero (anoxic conditions) iron exists in the reduced state as ferrous ions, which are soluble in water. As the ferric form reduces to the ferrous form it dissolves and the DRP bound to the iron is released into the water column where it is used by algae for growth. The algae eventually senesce and die, returning the P to the sediment as particulate P, where it can be recycled during the next period of anoxia. Apart from recycling of algal biomass, P also comes from the catchment, bound to the iron oxides in soil particles. The P content of the soil is greatest in the finest soil particles, which are the first to be eroded by rainfall and do not settle until they reach the calm waters of a lake. There they augment the P load from the senescing algal biomass, thereby increasing the amount of DRP that can be released during the next anoxic event. Because of the high background concentration of dissolved inorganic nitrogen in the lake water, the addition of any DRP will stimulate algal growth and thus result in a deterioration of lake water quality. Land management strategies to reduce soil erosion include changes to the way land is farmed and the interception and retention of fine sediment using detention bunds.
The changing face of Lake Okataina’s ‘phosphorus scape’: Who is the culprit?
(Conference Contribution, LakesWater Quality Society, 2015) Kpodonu, Theodore
Lake sediments contain a great wealth of data on biogeochemical and limnological processes of historical importance, which can be used to interpret natural ecosystem dynamics, and climatic and anthropogenic impacts. In this study, this information was used to understand the dynamics of phosphorus speciation in deep Lake Okataina, to assist with understanding how changes in the catchment influence lake productivity. A 49-cm sediment core was retrieved from Lake Okataina and its depositional history was dated using 210Pb and tephra chronology. Amongst New Zealand lakes, Okataina may be considered close to a ‘reference’ lake, with 89% native forest and without a significant change in its land use in the past c. 800 years. However, perturbations to the lake during this time may be due to expanding populations of invasive terrestrial mammals, earthquakes, volcanic eruptions and tree felling, which may alter the geochemistry of the soils in the catchment, composition of runoff and, ultimately, the composition of the bottom sediments of the lake. We hypothesised that changes in soil phosphorus geochemistry in the catchment will result in a changing phosphorus species in the lake sediments.
An ecological perspective on ‘undisturbed’ lake catchments in the Rotorua District
(Conference Contribution, LakesWater Quality Society, 2015) Shaw, William
There is currently concern about trends in water quality in some lakes in largely natural catchments. Various potential contributing causes are under consideration, including pest animals, such as wallabies, and pest plants. This presentation provides an overview of aspects of ecological history and processes at work in the catchments of selected lakes. By necessity, this is largely an historical analysis, but this provides important background for current trends, and also to understand landscape-level processes. The effects of potentially threatening influences, such as pest plants and animals, need to be evaluated within various contexts, including landscape history, ongoing geomorphological change, human disturbance, vegetation dynamics, and the relative contributions of natural and human-induced changes.
New Zealand’s indigenous forests – their status and drivers of change
(Conference Contribution, LakesWater Quality Society, 2015) Allen, Robert
New Zealand’s remaining indigenous forests and shrublands are of immense cultural, environmental, and economic significance. A representative plot-based sample of these forests and shrublands has recently allowed an unbiased depiction of their composition and structure. This is necessary for international reporting, performance assessment and management prioritisation. Their composition, structure, and function are driven by a diverse array of factors, many of which are complexly interrelated. The imprint of disturbances is pervasive and it is necessary to understand disturbances to interpret human-related impacts. For example, understanding impacts of exotic browsing mammals is only possible within a context of forest ecosystem development and tree demographic processes. There are now extensive areas of shrublands successional to forest, often composed of mixtures of indigenous and exotic species. These shrublands expand the pportunities for ecosystem services from, for example, carbon sequestration to water quality. An increasing area of indigenous forests and shrublands are managed for distinctive Māori aspirations that include sustainable use.
The importance of restoring the Rotorua Lakes
(Conference Contribution, LakesWater Quality Society, 2015) Chadwick, Hon Steve
In November last year the Rotorua District Council resolved to change our trading name to Rotorua Lakes Council. This was passed at Council and caused a stir; everything I do seems to cause a stir because we did not consult the wider community. In retrospect I still believe it was the best decision to keep at the Council table.
Wrap up summary of the day
(Conference Contribution, LakesWater Quality Society, 2015) Madsen, John
Summary of Day 1 2015 LakesWater Quality Society conference.
Biosecurity management overview
(Conference Contribution, LakesWater Quality Society, 2015) Champion, Paul
Today’s symposium topic is the issue of water weeds in the Rotorua Lakes and their management. I will discuss how and where these weeds came from and how they got into New Zealand. The weeds discussed are only a small sample of potential weeds that could have additional or even greater impacts on Rotorua and New Zealand as a whole. I will discuss our legislation and how management at the border protects us from future weeds yet to enter this country. Unfortunately, it appears that our legislation has been too effective at keeping out new plants, with no new aquatic plants legally introduced since the mid 1990’s but over 25% of aquatic plants in the aquarium/pond plant trade appear to have got here illegally. Several prosecutions have resulted from interception of smuggled plants. Once inside our border, there are several biosecurity measures initiated that have kept a number of our worst weeds at bay. These include banning the propagation, sale and distribution of 30 aquatic weed species, national and regionally run eradication programmes for high-risk weeds, with the successful eradication of five species and great progress towards the eradication of around twelve other weeds. However, some of these plants, such as water hyacinth, are still illegally kept by some individuals and several new infestations have originated from such sources. Despite this, the programmes have successfully kept the volume of deliberate spread for a wide number of aquatic weeds to a trickle. As previous speakers will have discussed, humans are the major cause of spread of aquatic weeds, with contaminated watercraft and trailers, fishing nets, diggers etc. all contributing to this spread. Bay of Plenty Regional Council have been proactively managing their lakes, identifying which lakes are threatened by which weeds, and then carrying out surveillance in order to detect and manage any new weed incursions. To assist with surveillance, they have designed and constructed weed cordons that effectively net off access points such as boat ramps (the main sites of new weed introduction) and have successfully detected and prevented establishment of new incursions of the weeds hornwort and egeria in Lake Rotoma. Each summer holidays an awareness programme run under the national ‘Check, Clean, Dry’ banner promotes inspection for weeds at boat ramps around the region. Additionally, surveillance of ornamental ponds near to high-value lakes has led to the detection of a number of potential weeds.
Success studies and the way forward
(Conference Contribution, LakesWater Quality Society, 2015) Wells, Rohan
This paper will cover what successful aquatic weed management looks like. It follows a range of historical management actions with numerous examples of ‘success’. Successes include preventing weed problems arriving, detecting them early and, in some cases, eradicating them. There is no single best option for weed control; none of them are without potential environmental impacts. For each situation and in each location it is up to managers and the community to weigh up the option(s) and decide on an approach that best suits each weed issue and their desired outcomes within economic, political, cultural and environmental constraints particular to that situation. As history has shown, the way forward is to keep adapting and refining existing management tools, testing and, if deemed effective, adopting new control options. In all cases, the scientific rigour behind weed management options and evaluation of environmental impacts must be provided to the public, and authorities remain open to a rational consideration of the options available that could benefit the health of our lakes.

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