Weed Management Plan for Hornwort in Lake Karāpiro 2016 to 2025
Prepared for LINZ on behalf of the Lake Karāpiro Aquatic Weed Management Group
September 2016
Prepared by : D E Hofstra M de Winton
For any information regarding this report please contact: Dr D E Hofstra Scientist Aquatic Plants +64-7-859 1812 [email protected]
National Institute of Water & Atmospheric Research Ltd PO Box 11115 Hamilton 3251
Phone +64 7 856 7026
NIWA CLIENT REPORT No: HAM2016-071 Report date: September 2016 NIWA Project: BML7201
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Contents
Executive summary ...... 5
1 Introduction ...... 7
2 Background on the weed issue ...... 8 2.1 Biology and ecology of hornwort ...... 8 2.2 Status, impacts and values at risk ...... 8
3 Feasible control methods ...... 10 Diquat ...... 10 Harvesting ...... 10 The future for weed control options...... 11
4 Key stakeholders ...... 13
5 Weed management strategy ...... 14 5.1 Goals ...... 14 5.2 Objectives ...... 14 5.3 Key milestones ...... 16
6 Site Prioritisation Framework (SPF) ...... 19
7 Record keeping, Annual planning and Review ...... 20
8 Risks to implementation ...... 22
9 Acknowledgements ...... 23
10 References ...... 23
Appendix A Designated activity zones and navigation features for Lake Karāpiro...... 25
Appendix B Reference Maps and Images ...... 29
Appendix C Summary of control methods ...... 35
Appendix D Framework for site evaluation and prioritisation ...... 36
Weed Management Plan for Hornwort in Lake Karāpiro
Tables Table 1: Key stakeholder roles, responsibilities and interests. 13
Figures
Figure 1: Goals and objectives for weed management in Lake Karāpiro. 6 Figure 2: Comparison of weed control tools - diquat and harvesting. 12
Weed Management Plan for Hornwort in Lake Karāpiro
Executive summary Lake Karāpiro is a multi-use lake with intrinsic, cultural, environmental, recreational, sporting and utility values (e.g., hydro-power generation and water takes). These values are threatened by the submerged aquatic weed hornwort ( Ceratophyllum demersum ). Previously, a feasibility report commissioned by Waikato Regional Council in 2015 has described the issues, identified the options and outlined high level goals for weed management over the long term. Development of a weed management plan (WMP) for the lake was identified as the next step that would then be used to inform annual weed control operations.
NIWA was engaged by LINZ, to develop a WMP for Lake Karāpiro on behalf of the Lake Karāpiro Aquatic Weed Management Group (Waikato Regional Council, Waipa District Council, Mana Whenua represented by Ngāti Koroki Kahukura, Land Information New Zealand and Mercury).
The WMP includes a strategy to deliver on the high level goals and objectives (see Figure 1) for long term management of aquatic weed at Lake Karāpiro. A site prioritisation framework (SPF) is presented to guide annual weed control operations. Risks or barriers to implementation of the WMP are considered along with risk mitigation measures.
The SPF is based on criteria for scoring and then ranking sites for control works. These criteria include: 1. External factors or pressures that influence what can be achieved (in terms of weed reduction) and when (e.g., public perception and events calendar). 2. Biosecurity, or the risk of weed transfer from Lake Karāpiro to other lakes. 3. The intrinsic, amenity and utility uses of the lake and the benefits derived from those uses. 4. Environmental dependencies, or the potential for habitat to influence the nature of the weed management outcome using current control methods.
The primary risks to implementation of weed management in Lake Karāpiro relate to the multiple uses of the lake, public perceptions and expectations, certainty of funding and although effective, the weed control tool set is small and has its own use constraints. Planning, clear communication, pre and post-treatment monitoring, record keeping and timely review of plans and progress with a longer term review of the WMP (5 years) can be used to mitigate negative impacts from most of these potential risks and barriers to successful weed management in Lake Karāpiro.
Weed Management Plan for Hornwort in Lake Karāpiro 5
Figure 1: Goals and objectives for weed management in Lake Karāpiro.
6 Weed Management Plan for Hornwort in Lake Karāpiro
1 Introduction Lake Karāpiro is a dammed riverine lake, the furthest downstream in a chain of lakes created along the Waikato River for hydro-generation purposes. The lake is large, of moderate depth and receives a very high nutrient load due to a rapid flow-through of relatively enriched water. Lake Karāpiro is a multi-use lake (Appendix A, designated activity zones), that is valued for its recreational, hydro- generation, cultural and environmental values. These values are threatened by the development of extensive and persistent hornwort ( Ceratophyllum demersum ) weed beds and the drifting weed that floats downstream.
A collaborative group of key stakeholders representing Land Information New Zealand (LINZ), Waikato Regional Council (WRC), Waipa District Council (WDC), Mana Whenua (represented by Ngāti Koroki Kahukura) and Mercury (formerly Mighty River Power) identified the need to explore the options for managing the invasive aquatic plant hornwort in Lake Karāpiro over the long term. To inform the key stakeholder group WRC commissioned NIWA to undertake a feasibility study (Hofstra et al. 2015) to describe the issues for weed management, the available options for weed control, and to outline high level goals for weed management in the lake.
The next step was to develop a weed management plan for hornwort in the lake, drawing on the feasibility study, which could be used to guide annual weed control operations. LINZ (with their biosecurity partner Boffa Miskell) have contracted NIWA to develop a weed management plan (WMP) for Lake Karāpiro.
This WMP seeks to provide a shared view of hornwort management over the next 10 years (2016 to 2025).
The WMP for Lake Karāpiro includes a:
° Summary of the weed issues and feasible control methods,
° Description of key stakeholder roles and responsibilities,
° Management strategy incorporating high level goals and objectives and key milestones to progress the goals,
° Site prioritisation framework (SPF) to inform annual control operations,
° Process for record keeping, and review of the WMP, and
° Risks to implementation are outlined.
Preparation of the WMP was undertaken in two phases. A draft or ‘strawman’ Site Prioritisation Framework (SPF) for weed control works was initially developed (Phase One) for discussion with key stakeholder representatives during a workshop (Phase Two, 25 th August 2016). The workshop provided a mechanism to document and incorporate stakeholder perspectives into the SPF and hence into the WMP.
Related to the WMP is the establishment of the Lake Karāpiro Weed Management Group, comprised of representatives from the key stakeholders, Land Information New Zealand (LINZ), Mana Whenua represented by Ngāti Koroki Kahukura, Waikato Regional Council, Waipa District Council, and Mercury, who are all signatories to a Memorandum of Understanding (MoU) for weed management in the lake (21 st October 2016).
Weed Management Plan for Hornwort in Lake Karāpiro 7
2 Background on the weed issue
2.1 Biology and ecology of hornwort Hornwort is an alien submerged freshwater plant that occurs as stems attached to the sediment or as floating mats or drifting fragments. It does not have roots but may be anchored in the sediment by the base of its stems, by means of special branches that bear finely divided foliage (Aston 1977). Propagation is via vegetative reproduction of brittle stem material. Hornwort is characterised by its extremely dense subsurface canopy and forms monospecific beds that displace and exclude native and non-native vegetation (Coffey and Clayton 1988). It is also common for rafts of buoyant, dislodged hornwort to be driven into bays or against shorelines by wind where it smothers and shades resident vegetation. This can have concomitant impacts on associated fauna with decline in habitat and water quality.
The plant performs well in disturbed habitats such as moderate water flow, as the effects of fragmentation, loss of apical tips and sediment burial have negligible effects for early regrowth of hornwort, with plants capable of forming many side-branches, making them highly buoyant in the water and allowing them to float out of the sediment where they could receive more light to grow (Cao and Wang 2012). Hornwort also has a tendency to anchor itself to the pre-existing submerged plant canopy, rather than anchoring in sediment (Santos et al. 2011). In some situations the establishment of hornwort can be aided by the presence of other (rooted) weeds, which can initially shelter hornwort from dislodgement by currents (Schwarz et al. 1999).
Although hornwort is perennial and material can be found year round, height, cover and biomass tend to decrease in winter. Plants are often dirtier, accumulating epiphyton and fine sediments, during these times of lower growth. Growth in late spring can be rapid and biomass accumulation tends to peak in autumn. Relative growth rates for hornwort range from c. 0.02 to 0.08 day -1 based on proportional weight increase and up to 0.09 day -1 based on increased length (Larson 2007, Eller et al. 2015). Additionally, hornwort drift patterns have a seasonal component, but they are also influenced by weather (wind direction and intensity), and hydro-generation activities (Schwarz et al. 1999, Clayton et al. 2006). Greater weed efflux at the Karāpiro hydro-station screens results when south to south-east winds blow weed down the body of the lake (Wells et al. 2000).
2.2 Status, impacts and values at risk Hornwort is designated as an Unwanted Organism under the National Plant Pest Accord (NPPA) and is thus banned from sale and distribution under the Biosecurity Act (1993). It is also a National Interest Pest in the South Island, requiring an eradication response for any new incursions. Because it is widespread in the Waikato Region it is not declared as a pest managed under the Regional Pest Management Strategy apart from enforcing the NPPA ban on sale.
The introduction and establishment of hornwort has been the foremost driver of the weed issues in Lake Karāpiro. Hornwort is present at almost all shallow littoral areas of Lake Karāpiro (Appendix B) and is predominantly limited to <5 m depth. It is able to grow to c. 5 m in height indicating plants could grow to reach the surface over much of its depth range, although surface reaching beds are predominantly formed in backwaters where flows are low. Low operating levels for the lake also expose the canopy of near surface beds at times. Hornwort dominates the downstream regions of the lake, whilst egeria only dominates upstream of Little Waipa Domain (Appendix B) in the upper riverine section (McCarter et al. 1993, Schwarz et al. 1999, Clayton et al. 2006). Clayton et al. (2006) recorded an average weed bed width of 12 m at an estimated 40 km of shoreline, and identified
8 Weed Management Plan for Hornwort in Lake Karāpiro
additional larger (>1 ha) weed beds (e.g., Findlay Park, Horahora Domain) (excluding weed beds located up the long inlets) with an estimated area of 55-60 ha of nuisance weed beds that could be targeted for control. In March 2015 a re-assessment of nuisance weed beds in littoral areas identified ca. 45 ha up to Piarere ski club (Wells and de Winton 2015, Appendix B).
Problems caused by hornwort in Lake Karāpiro fall into two main categories; the impact of surface reaching weed on recreation use and access in specific areas, and drifting weed that interferes with recreational amenities and activities, or clogs hydro-electric water intakes.
Hornwort is well known at Lake Karāpiro for its impacts on water sports, and event organisers regularly ask Mighty River Domain management about weed bed conditions and the risk of interference to activities. Attractiveness of the venue as a training ground for elite (rowing and canoeing) athletes is also impacted by weed concerns. Large beds of canopy-forming weeds have been associated with depressed quantity and quality of boating, water skiing, swimming and nearshore recreation. Dense mats of weed provide good habitat for the snail hosts of parasites that cause ‘swimmer’s (duck) itch’ (Eiswerth et al. 2000). Entanglement and drownings have been linked to invasive weed beds (Getsinger et al. 2014), with a near drowning at Lake Maraetai in December 2014 being attributed to an uncontrolled weed bed.
Another national biosecurity consideration is the threat posed by transfer of hornwort to other waterbodies, particularly at South Island rowing venues. Uncontrolled hornwort around boat ramps, jetties and other infrastructure in Lake Karāpiro increases the risk of equipment contamination and transfer.
Weed Management Plan for Hornwort in Lake Karāpiro 9
3 Feasible control methods Budgetary constraints mean that cost-effective control works will achieve the best outcome and see the greatest degree of control achieved across the prioritised sites. To achieve the ‘best bang for buck’ it is important that control methods are matched appropriately to the site conditions and outcomes sought, whilst adopting an adaptive management approach. An adaptive approach can be achieved by documenting and reviewing what works best for each area of focus and amending tactics accordingly (Section 7). Control outcomes should be assessed and documented to inform changes in annual operations that may improve weed control outcomes and/or reduce costs.
Amongst the range of control methods evaluated in the feasibility study (summarised in Appendix C) only the herbicide diquat has a proven track record for reducing target weed beds within the short timeframes and on the spatial scale necessitated by the large number of events on, and multiple- uses of Lake Karāpiro. Harvesting (weed cutting and removal) could be used for small, localised areas of weed (Figure 2) at the north end of the lake (i.e., areas close to access points and a permitted weed dump site).
Diquat Diquat (technical name diquat dibromide) is the active ingredient (20% a.i.) in Reglone ®, a herbicide used as the primary method of large scale aquatic weed control in New Zealand lakes since 1960. Diquat is applied (at 1 ppm) to the water around the target weed bed by spraying on the water surface by heliocopter, via a boat trailing hoses, or subsurface using a submerged boom or diver injection. It is a selective herbicide that controls most unwanted target weed species in freshwaters (e.g., hornwort, Egeria densa, Lagarosiphon major and Elodea canadensis ), whilst important native plant species, such as Chara and Nitella species, are not affected by diquat (Clayton 2004, Clayton and Severne 2005, Netherland 2014). When diquat comes into contact with the green, photosynthesizing parts of nuisance aquatic weeds (leaves and stems) it is rapidly absorbed, desiccating plant tissue and disrupting cell membranes. Diquat can control weed beds at any time of the year, although efficacy is better in the warmer months (Netherland et al. 2000) and plant decay rates are slower in winter. Effective control is best when plants are clean (Clayton and Matheson 2010) and water movement is minimal (Clayton 2004, Clayton and Severne 2005, Netherland 2014).
Leading up to the 2010 World Rowing Championships in Lake Karāpiro, it was apparent that the scale of weed control had to be substantially increased to meet the demands of zero weed interference during the event. A range of options were considered and at that time diquat was assessed to be the only cost effective option available, considering the scale of control required (Clayton et al. 2006). Aerial helicopter treatment of 50-100 ha of targeted nuisance weed beds over a 1-2 day period was shown to provide effective weed control in the lake. Excellent results have been repeatedly demonstrated with favourable weather conditions and pre-inspection confirming suitable target weed cleanliness and density (Clayton 2004, Clayton et al. 2008).
Harvesting Mechanical harvesting refers to the cutting and collection of lake-weed. Typically, a boat-mounted sickle bar cuts the weed below the water surface and the weed is entrained onto a conveyor belt as the harvester moves forward. The collected lake weed may then be transported to shore directly for “out-of-lake” disposal. Alternatively the harvested weed may be shredded using a boat-mounted unit to reduce the bulk of harvested material thereby increasing the amount of weed that can be harvested prior to offload at the shore. A further option is for the shredded material to be
10 Weed Management Plan for Hornwort in Lake Karāpiro
discharged back into the water thereby eliminating the need for shore disposal (Sabol 1987, Madsen 2000).
Hornwort and other aquatic weeds that are found in Lake Karāpiro (e.g., egeria) are amenable to partial control by mechanical harvester and shredder. The water depth range typically occupied by these two species (<1 to c. 5-6 m) exceeds the reach of most mechanical harvester units, although weed that has collected along the weed boom is readily accessible. On Lake Karāpiro, a lake weed harvesting machine is operated by Karāpiro Rowing Incorporated, and used primarily to clear rowing structures such as buoys and lines, and the upstream chain that intercepts drift, and to clear some high use areas. A weed harvester owned by Mercury has also been utilised on Lake Karāpiro, when not required by Mercury on other lakes. Although harvesting is effective at reducing hornwort, the size and shape of Lake Karāpiro and the extensive areas over which weed reduction is required, within relatively short timeframes to coincide with downtimes between events, means that harvesting can be used to target small-scale areas only.
There is currently only one permitted dump site for harvested weed near the dam, which is operated by Mercury. Mercury recognise that this current location is not culturally acceptable to all of the key stakeholders and are investigating alternative sites. In seeking appropriate sites to dispose of harvested weed, as well as access from the lake, consideration must also be given to the potential for site contamination based on the heavy metal content of the weed (Hofstra et al 2015). In comparison, in-lake disposal by shredding eliminates the need for transport of harvested weed to shore. Sabol (1987) reported that in-lake disposal of hydrilla reduced harvester down time by 50%, and for Lake Karāpiro in-lake disposal of shredded weed in small volumes is unlikely to be a concern for water quality (Matheson 2014).
The future for weed control options The key stakeholders have expressed a desire to consider new or alternative methods that may have a place in the weed control programme once they have been validated from an effectiveness, environmental and economic viewpoint. Improvements to existing weed control and methods that could be assessed further for Lake Karāpiro include;
° the permitting of a weed disposal site at another strategic location (near the dam) and a second weed boom upstream of Horahora domain to minimise downstream entrainment of drift weed (with an adjacent weed disposal site),
° mulching and deep-water disposal of small volumes of cut weed,
° the proof of concept for endothall use on weed beds in open water, and
° benthic barrier installation for small difficult to control weed beds (Hofstra et al. 2015).
In addition the potential benefit of using harvested weed for anaerobic digestion and biogas production, as a weed disposal subsidy, requires experimental verification to validate the science and economics (Hofstra et al. 2015).
Weed Management Plan for Hornwort in Lake Karāpiro 11
Figure 2: Comparison of weed control tools - diquat and harvesting. The changing scale of the weed-bed (green) indicates that weed cutting is only cost effective for small weedbeds, and as the scale of the weed-bed increases the most cost effective option (orange) is aerial application of diquat.
12 Weed Management Plan for Hornwort in Lake Karāpiro
4 Key stakeholders The key stakeholders have articulated their interest or support in working in a collaborative programme to provide a long-term management approach for hornwort control in the lake. The interests, roles and responsibilities of the key stakeholders in Table 1 have been summarised from the feasibility study (Hofstra et al. 2015) based on position statements that had been made previously.
Table 1: Key stakeholder roles, responsibilities and interests.
Land Information New Zealand (LINZ) LINZ has responsibility for the management of the bed of Lake Karāpiro, under delegation of the Commissioner of Crown Lands who represents the Crown as owner of the lakebed pursuant to the Land Act 1948. LINZ funded the 2010 works leading up to the 2010 World Rowing Championships and is interested in being party to a long-term management solution for hornwort control. Waipa District Council (WDC) Lake Karāpiro sits within Waipa District. WDC manages a number of lake side reserves including the Mighty River Domain but has no direct responsibility for lake weed management. The Council recognises Lake Karāpiro’s status as a strategic recreational asset and the use made of the Lake for regional, national and international sporting events. Karāpiro is also the ‘raw’ water source for Cambridge township and District. Council is required to meet statutory obligations around water supply and public health. Council is happy to participate in lake weed management at Karāpiro, and acknowledges the value in adopting a collaborative approach and advancing sustainable long term solutions. Waikato Regional Council (WRC) WRC has responsibilities under the Biosecurity Act for managing ‘pest plants’. Hornwort is not declared a ‘pest’ in the Regional Pest Management Plan, but Council contributes to a national collective for biological control, including investigating options for a range of aquatic weeds. WRC acknowledges that Lake Karāpiro is a regional amenity and is very supportive of pest management partnership opportunities. WRC also has obligations for navigation safety on lakes in the region and this includes signage, regular waterway patrols and removal of navigation hazards. WRC can add value to this project through its technical catchment management skills and expertise in aquatic management issues. WRC is a potential funding partner, along with some of the other parties identified. Mana Whenua represented by Ngāti Koroki Kahukura (NKK) This forum recognises the multiple layer of treaty settlements over the Waikato River. For the purposes of this working group NKK as kaitiaki and on behalf of all mana whenua is supportive of attempts to develop a collaborative long term management approach. Mercury (formerly Mighty River Power, MRP) Mercury is a renewable energy company with interests in controlling hornwort on other Waikato hydro lakes, which are also important and valued community assets. Mercury has participated in previous weed control efforts on Lake Karāpiro, and in both monitoring and management on the other seven hydro lakes on the Waikato River. If left untreated, there is some potential that the hornwort could affect both recreational activity and hydro operations. Mercury is interested in a collaborative partnership approach involving local stakeholders and relevant local and national agencies, as part of an inherent interest in the long-term health and well-being of the river .
Weed Management Plan for Hornwort in Lake Karāpiro 13
5 Weed management strategy The strategy for weed management in Lake Karāpiro over the next 10 years includes high level goals supported by objectives, with key milestones that will track progress towards the goals.
5.1 Goals The goals for weed management recognise that Lake Karāpiro is a multi-use lake with intrinsic, cultural, environmental, recreational, sporting and utility values. Stakeholders and interested parties contacted for the feasibility study (Hofstra et al. 2015) provided their perspectives on the weed issue, the value of the lake to them, and the effectiveness of previous weed control work undertaken on the lake. These perspectives were distilled into high level goals for Lake Karāpiro weed management. Subsequently, based on conversations with key stakeholders a fifth goal was added.
Goal 1 The mauri (health, wellness and cultural values) of the river is supported The health, wellness and cultural values of the river and its associated flora and fauna is supported over the longer term. This goal recognises that although the lake is highly impacted by the invasive weed hornwort, the lake has important intrinsic, spiritual, cultural and habitat values. Goal 2 Maintain and improve amenity, recreation and sporting values Weed beds and weed drift are reduced sufficiently to provide the recreation and amenity values of the lake for the community (e.g., safe swimming and boating zones, aesthetic shorelines) and for larger sporting events (e.g., an ‘even playing field’ for competition).
Goal 3 Support the continued utility values of the lake Weed beds and weed drift are reduced with methods that support the continued utility values of the lake (e.g., water takes, hydro-generation).
Goal 4 Ensure sustainable management of hornwort impacts The control programme is sustainable in the long-term, and effectiveness (cost, outcomes) is maximised over time. Management of hornwort has to be efficient and cost-effective to be viable in the longer-term. It also has to be acceptable to and supported by the community. The use of herbicides can be emotive and controversial. However, this control tool is essential to the programme at this time and any perceived risks posed by herbicide use can be mitigated by appropriate precautions on its application. Advances in the use of additional control tools, herbicide application and efficacy will seek to minimise the environmental load of herbicide over time, and incorporate other control methods with demonstrated efficacy.
Goal 5 Biosecurity awareness - minimise the risk of weed spread to other waterbodies Hornwort in Lake Karāpiro represents a threat to other, uninvaded waterbodies, especially in adjacent regions, but also South Island lakes sharing similar recreational or sporting events. Minimising this risk requires targeting the pathways of spread by increased public awareness and reduced recreational/sporting contact with hornwort beds.
5.2 Objectives There are six objectives that identify specific intentions of the weed management plan.
Objective 1. No control zones for weed management are identified to maintain intrinsic values [supports Goal 1]
14 Weed Management Plan for Hornwort in Lake Karāpiro
The selection of sites that will be set aside as zones in which weed control is not undertaken provides certainty for the public that these areas of the lake will be free from diquat and the off- target impacts of weed harvesting. Candidate zones have been listed in the SPF (Appendix D). Objective 2. Sites/activity zones are prioritised for control works [supports Goals 2, 3, 4 and 5] For control works to benefit the majority of lake users, be sustainable and reduce the risk of weed transfer there needs to be site/activity zone prioritisation based on the predominant use areas, the level of impact by hornwort development, and the outcomes that can be achieved from weed control. An agreed prioritisation process will help ensure the control works budget can be used to maximum effect. Objective 3. Control the impact of weed beds (and drift) for amenity and utility use [supports Goals 2, 3 and 5] Community and recreational users should not have their enjoyment and activities on Lake Karāpiro hindered or safety compromised by hornwort. Sporting professionals should not have their training or competing on Lake Karāpiro severely curtailed by hornwort. Commercial gains are derived from a weed free Lake Karāpiro, and businesses that are reliant on the water or access to it seek to continue their uses unimpeded by weed. Furthermore, the reduction of nuisance weed beds will also reduce watercraft contact with, and transfer of hornwort (link to objective 6). Nuisance weed beds should be targeted for control, primarily with diquat and where feasible, by weed harvesting to reduce the weed in situ and to reduce the weed drift thereby supporting lake uses. Objective 4. Advance effectiveness and cost-efficiency of control works [supports all Goals] Increasing the effective outcomes from hornwort control and improving cost-efficiency is an important objective of this programme given the multi-use values and scale of weed issues in Lake Karāpiro. There is a need to adapt tactics and techniques as new knowledge becomes available, or efficiencies are identified through monitoring and record keeping. Objective 5. Engaging and communicating with lake-users [supports all Goals] Local community and lake-users have knowledge of the nature of impacts from hornwort on lake use and they also stand to gain the greatest benefit from an effective weed control programme. Incorporating lake-user views and aspirations into the management response will ensure relevant control targets, better engagement with the public in terms of the options (tools) available for weed control and to better convey the risks and impacts of hornwort spread to other waterbodies (link to objective 6). Objective 6. Minimise the risk of inter-lake weed spread [supports Goal 5] Align with, and reinforce the Check, Clean, Dry message co-ordinated by MPI to raise public awareness on freshwater pests. Initiatives at Lake Karāpiro should use this message and available resources to highlight the threat of hornwort transfer from the lake to other regions where hornwort is not present. Here it is recognised that while hornwort is established in the Waikato there are many other regions and lakes where it is actively managed, or unwanted. In addition, public initiatives should be sought wherever possible (e.g., boater self-check forms, education campaigns). An informed and engaged public are less likely to spread hornwort if they understand the risks posed by the weed (link to objective 5).
Weed Management Plan for Hornwort in Lake Karāpiro 15
5.3 Key milestones Milestones have been identified to address the objectives over the term of this weed management plan. Milestones are numbered 1 to 6, indicating the corresponding objective number (Section 5.2). These milestones provide the means for checking progress toward the weed management goals.
Objective 1. No control zones for weed management are identified to maintain intrinsic values Milestone 1. Exclusion zones are considered when operations are confirmed annually. Weed bed areas that are identified for intrinsic or high wildlife value are designated as exclusion zones, where weed control is not undertaken. These zones should be considered every year when annual operations are being decided, with a view to ensuring that the values are being met by excluding these zones, and whether or not there is benefit in altering the exclusion zones.
Objective 2. Sites/activity zones are prioritised for control works
Milestone 2A. The SPF is used to rank sites for annual weed control and the frequency at which these should be reassessed is agreed by spring 2017.
The SPF will be used for the first time in the spring/summer of 2016 to prioritise weed control operations in Lake Karāpiro. After its first year of use, is a prime opportunity to amend or update the SPF as required by the key stakeholder weed management group to ensure it is fit for purpose.
Milestone 2B. Agree on a process to identify annual weed control priorities and methodologies by 2017.
The key stakeholder agencies have followed an informal process when setting weed control operations, based primarily on lake-user issues and significant up-coming events. Closely linked to Milestone 2A is the agreed setting of a process for annual control priorities. This process should also be informed by previous weed control outcomes (Section 7, linked to Objective 4 Milestone 4A) and needs to consider trialling of new or improved control methodologies or tactics within annual priorities (Milestones 4B - 4D).
Milestone 2C. Future development and replacement of lakeside amenities includes consideration of hornwort impacts and risks (2016 to 2025)
Development of lake-side amenities should consider local weed development and contamination risks at the design stage with a view to minimising the impact by hornwort and risk of transfer. This would include considering shoreline gradient and exposure when locating reserves and their amenities, especially boat ramps, ski lane access points, jetties and pontoons.
Objective 3. Control the impact of weed beds and drift for amenity and utility use
Milestone 3. Weed control works carried out annually are effective and affordable.
Sites are prioritised for control works using established weed control methods (Section 3 and Appendix C) alongside the budget in the annual operations plan. This process should be completed by October each year, and again during the growing season as required based on weed re-growth and the events calendar. The distribution of budget effectively across
16 Weed Management Plan for Hornwort in Lake Karāpiro
priority sites will achieve the greatest control outcome. The milestone is closely aligned with the milestones in Objective 4 (record keeping and advances).
Objective 4. Advance effectiveness and cost-efficiency of control works
Milestone 4A. Clarify the lead agency(s), from within the key stakeholder weed management group, responsible for weed control works and formalise record keeping of weed control actions and outcomes. Proposed timeframe is before weed control operations are undertaken in spring-summer 2016/2017.
Adaptive management is an essential component of every waterbody management plan. This can only be achieved by documenting and reviewing what works best for each area of focus and amending tactics accordingly.
Milestone 4B. Additional weed removal methodologies or strategies are assessed for control of hornwort and adopted if appropriate by 2021.
Control methods additional to the ones currently used in Lake Karāpiro may provide future options to minimise or reduce the reliance on diquat, and solutions for weed (e.g., drift) that has proved difficult to control to date. Methods that could be assessed further for Lake Karāpiro include mulching and deep-water disposal of cut weed, the permitting of a weed disposal site at another strategic location (near the dam), a second weed boom upstream of Horahora domain (with an adjacent dump site) and validating the science and economics of anaerobic digestion of harvested weed (as a disposal subsidy).
Milestone 4C. New or alternative weed control tools that become operational in New Zealand for hornwort control are screened and adopted if appropriate by 2025.
The herbicide endothall which is registered for submerged aquatic use and effective on hornwort, requires evaluation for its use on weed beds in open water environments such as Lake Karāpiro. Additional herbicides that are in use in the US could have application here if they prove effective against target species under New Zealand conditions. Control options should be assessed for potential application to Lake Karāpiro as they become operational, and where supported by better environmental and economic data than diquat.
Milestone 4D. Opportunities for improved control outcomes are identified annually (2016- 2025) Based on feasible weed control options, any opportunity for further refinement to enhance control outcomes will be identified and assessed. This may require access to expert advice to help assess appropriateness.
Objective 5. Engaging and communicating with lake-users
Milestone 5A. A Memorandum of Understanding identifies roles, responsibilities and nature of engagement of the key stakeholder group for weed management in Lake Karāpiro by October 2016 The membership, roles, responsibilities and nature of engagement for the key stakeholder group is documented and agreed in a Memorandum of Understanding (MoU) which includes frequency and timing of meetings, information to be provided to the group, and the lines of responsibility for external communications.
Weed Management Plan for Hornwort in Lake Karāpiro 17
Milestone 5B. Develop a communications strategy for the weed management programme in Lake Karāpiro. Proposed timeframe is before weed control operations are undertaken in spring-summer 2016/2017. An agreed communications strategy should identify the lines of responsibility for communication with lake-users, external agencies and the media about the weed control programme on behalf of the key stakeholder weed management group.
Milestone 5C. Weed control outcomes are assessed and communicated to the key stakeholder group for feedback on an annual basis (2016- 2025). The degree that stakeholder and community aspirations are met by hornwort control outcomes is important to recognise. Further dialogue on control outcomes will help refine community priorities and expectations.
Objective 6. Minimise the risk of inter-lake weed spread
Milestone 6. A refreshed and ongoing campaign informs the public of the risks posed by freshwater pests and actions they can take to prevent weed spread. The timeframe is immediate and ongoing (2016 to 2025).
Initiatives under the Check, Clean and Dry message should include signage at boat ramps and print resources, as well as advocacy from trained personnel at targeted venues during periods of high recreational use, and at water sport events. Other initiatives could include wash-down facilities, weed cordons (netted enclosures at boat ramps) if these were agreed by the key stakeholder group.
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6 Site Prioritisation Framework (SPF) The SPF has been developed (Appendix D) to provide a transparent and agreed process to select or prioritise sites where control works should be focussed based on the available budget (objective 2, Section 5.2).
The proposed sites for hornwort control were selected using the designated activity zones map (WDC 2011) and incorporate activity, amenity and utility zones as well as areas previously targeted for weed control from 2007. Sites were then ranked according to:
1. External factors or pressures that influence what can be achieved (in terms of weed reduction) and when (e.g., public perception, events calendar). Rankings were assigned by key stakeholder representatives during a workshop (25 th August 2016). There are 3 categories, with scores from 1 to 5 per category.
2. Biosecurity, or the risk of weed transfer from Lake Karāpiro to other lakes. Rankings were based on expert opinion. There is 1 category, with scores from 1 to 5.
3. The intrinsic, amenity and utility uses of the lake and the benefits derived from those uses. Rankings were agreed by key stakeholders and expert opinion. There are 3 categories, with scores from 1 to 5.
4. Environmental dependencies, or the potential for habitat to influence the nature of the weed management outcome using current control methods. Rankings were assigned based on expert opinion. There are 2 categories, with scores from 1 to 5.
The results of the current rankings for sites or activity zones are given in Appendix D. Additional sites may be removed or added to the SPF as agreed by key stakeholders as new needs or concerns are communicated by lake-users.
In development of the annual operational plan (Section 7) sites can be prioritised within the agreed framework (SPF) against the available budget, cost of control, and the level and duration of control that may be achieved (‘best bang for buck’). The SPF should be used in winter / early spring prior to the development of significant nuisance weed.
Weed Management Plan for Hornwort in Lake Karāpiro 19
7 Record keeping, Annual planning and Review
Record keeping Weed control works should be reported on annually, documenting the location, method and area treated at each target site (Figure 3). It will also be important to keep a record of outcomes from control works, including the degree and duration of weed reduction, where additional unplanned treatments of nuisance weed have been necessary, as well as any public complaints. Record keeping will build up a picture of where different site tactics or control methods may be beneficial, particularly in minimising the occurrence and extent of drift weed. Reporting these findings to the key stakeholder group on an (at least) annual basis will ensure a common view of progress and issues and a foundation for planning the subsequent control.
Annual planning An annual planning process should be followed to determine the control works in Lake Karāpiro (Figure 3). This enables annual operations to be adaptive, responding to any improvements in methods or their application that was made in the preceding year, and provides an opportunity to realign priorities and address any arising issues. Setting the annual control priorities can be viewed as a process that starts with reviewing records of the previous control outcomes, the state of weed bed development, budget setting and allocation across agreed site priorities (Section 6, Appendix D), leading to the development of an annual operational plan (Figure 3).
Operations should identify the most cost-effective method for each site based on detail in this WMP (Section 3, Appendix C and D) and the feasibility study (Hofstra et al. 2015) to achieve site specific priorities such as boat ramp hygiene, access for swimmers, access to other amenities (e.g., jetties) and general control for shoreline or ski lane access. Management actions can then also be matched with the best time of the year for works for likely weed bed development, and be responsive to the needs of known events (e.g., rowing competitions or waka ama) in the Lake Karāpiro events calendar.
Once the budget priorities are agreed experienced contractors that meet industry requirements can then be engaged. Initial tasks annually, also include consultation specific to the proposed operations (eg., with Council’s Water Services team or public health officials in relation to the treatment of the weed, depending on the type of treatment), and inspection of the sites for weed and site conditions that may modify the timing or control methods used.
Review While the WMP has been developed for a 10 year term, it should be considered a ‘living document’ and subject to review within this period. It is suggested that this plan will benefit from a formal review after five years. The purpose of such a review is to revisit the goals, objectives and milestones of the management programme, making amendments as necessary and documenting and assessing any science advances for weed control or weed disposal subsidies that may be of value in Lake Karāpiro. In the same way that the feasibility study incorporated views from a wider group of lake users (as well as the key stakeholders), the five year review process should also provide an opportunity for interest groups to make statements about the status of the weed management programme and achievements.
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Figure 3: Annual process of planning and review that sets the control works.
Weed Management Plan for Hornwort in Lake Karāpiro 21
8 Risks to implementation Potential risks and barriers to the progress on weed management objectives are considered below and possible mitigation measures are identified.
Some risks or barriers have been experienced during the management of hornwort in Lake Karāpiro in the past and this history highlights possible future challenges such as certainty of funding, public acceptance or endorsement of the feasible control options, and investment that is required for improved weed control methods.
Funding Currently the funding for weed control is primarily from local rate-based sources (WRC, WDC) with support from central government administered by LINZ, and from Mercury (e.g., through the use of their weed harvester). Arguably, reliance on rate-based sources means there is a need to ensure that the facilities are available to the general public who are paying for them. Contributions from specific clubs could provide a means for those groups to ensure the patch of the lake that they use is targeted for treatment in conjunction with wider operations for general public amenities.
While specific actions to widen the funding base is beyond the scope of this document it is recognised that a broader funding base would provide better security for the ongoing sustainable management of hornwort in Lake Karāpiro (Goal 4).
Public expectations and perceptions The nature of hornwort in Lake Karāpiro means that there are limitations to the extent of control that can be achieved on a spatial and temporal basis due both to feasibility (e.g., timing of treatment based on events) and budgetary constraints. Providing the public with information on hornwort and the aims and achievements of the management programme will be important in managing their expectations. It is also important to have a community voice in decisions on hornwort weed beds that will be targeted for annual operations.
Opposition from even small sectors of the community can result in a restriction on control tools (particularly herbicides) and adverse publicity for the programme. Proactive communication (objective 5) to inform and engage with the public is likely to moderate community support for extreme views.
Weather, lake and plant conditions Lake, plant and weather conditions have the potential to impact the feasibility and effectiveness of control methods. Amongst possible risks are local eutrophication (nutrient enrichment) with fouling on target plants that reduces their susceptibility to diquat herbicide. Periods of poor weather may constrain control works, limiting either the timing of application or effectiveness. Contingency to accommodate such events should include transfer of budget from one year to the next. It is important to retain flexibility in the programme to capitalise on favourable lake and weed condition within the constraints of the events calendar and scheduling treatment operations outside of weekends and public holiday periods.
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9 Acknowledgements This management plan has benefited from discussions with key stakeholders and the insight gained from the development of a site prioritisation model for Lake Wanaka by Drs John Clayton and Fleur Matheson from NIWA, LINZ (David Morgan and Matthew Fanning) and Enveco (Annabelle Giorgetti).
10 References Aston, H.I. (1977) Aquatic plants of Australia. A guide to the identification of aquatic ferns and flowering plants of Australia, both native and naturalised . National Herbarium of Victoria. Melbourne University Press.
Cao, Q., Wang, D. (2012) Fragment growth of rooted and rootless submerged aquatic macrophytes: Effects of burial modes and decapitation of shoot apex. Journal of Freshwater Ecology , 27(3): 315-324. doi:http://dx.doi.org/10.1080/02705060.2012.659452
Clayton, J., Matheson, F. (2010) Optimising diquat use for submerged aquatic weed management. Hydrobiologia , 656: 159–165.
Clayton, J., Matheson, F., Smith, J. (2009) Lake Karāpiro weed control from March to June 2009. NIWA Client Repor t HAM2009-133, prepared for Land Information New Zealand. (LMT08201): 23.
Clayton, J., Matheson, F., Smith, J., Franklyn, G. (2008) Lake Karāpiro weed control from 2007 to 2008. NIWA Client Report HAM2008-073, prepared for Land Information New Zealand, (LMT08201): 29.
Clayton, J., Wells, R., Taumoepeau, A. (2006) Weed control in Lake Karāpiro. NIWA Client Report HAM2006-130, prepared for Land Information New Zealand: 25.
Coffey, B.T., Clayton, J.S. (1988) New Zealand waterplants. A guide to plants found in New Zealand Freshwaters . Ruakura Agricultural Centre.
Eiswerth, M.E., Donaldson, S.G., Johnson, W.S. (2000) Potential environmental impacts and economic damages of Eurasian watermilfoil ( Myriophyllum spicatum ) in western Nevada and Northeastern California. Weed Technology, 14: 511–518.
Eller, F., Alnoee, A.B., Boderskov, T., Guo, W., Kamp, A.T., Sorrell, B.K., Brix, H. (2015) Invasive submerged freshwater macrophytes are more plastic in their response to light intensity than to the availability of free CO2 in air-equilibrated water. Freshwater Biology , 60(5): 929-943.
Getsinger, K., Dibble, E., Rodgers, J.H., Spencer, D. (2014) Benefits of controlling nuisance aquatic plants and algae in the United States: 12. http://www.cast- science.org/download.cfm?PublicationID=282524&File=1030b3a54ebea7b19997c7d3a 20702ea2c5TR
Hofstra, D., de Winton, M., Clayton, J., Matheson, F., Wells, R., Craggs, R. (2015) A feasibility study for the control of hornwort in Lake Karāpiro. NIWA Client Report HAM2015-120, project EVW16201.
Weed Management Plan for Hornwort in Lake Karāpiro 23
Irwin, J., van Kampen, J. (1986) Lake Karāpiro bathymetric chart. Lake Series by the Division of Marine and Freshwater Science , DSIR.
Larson, D. (2007) Growth of three submerged plants below different densities of Nymphoides peltata (SG. Gmel.) Kuntze . Aquatic Botany , 86: 280–284.
Matheson, F. (2014) Reassessment of water quality effects of discharging shredded aquatic weed: first five year review for the Waikato hydro lakes. NIWA Report for Mighty River Power HAM2013-118: 61.
Matheson, F., Clayton, J., Smith, J. (2010) Lake Karāpiro weed control from April to June 2010. National Institute of Water and Atmospheric Research (NIWA) Client Report HAM2010-072, prepared for Boffa Miskell Ltd and Land Information New Zealand. Wellington, Land Information New Zealand: 23.
McCarter, N.H., de Winton, M., Clayton, J.S., Wells, R., Tanner, C. (1993) Grass carp in Lake Karapiro: options for plant management. NIWA Client Report.
Santos, M.J., Anderson, L.W., Ustin, S.L. (2011) Effects of invasive species on plant communities: an example using submersed aquatic plants at the regional scale. Biological Invasions : 13(2): 443–457.
Schwarz, A-M., Wells, R., Clayton, J. (1999) An overview of aquatic weeds in Lake Taupo and the Waikato River. NIWA Client Report CHC98/0A, ELE80520: 35.
WDC (2011) Karāpiro Lake Domain (Mighty River Domain) Reserve Management Plan 2011 . http://www.waipadc.govt.nz/our- council/Documentsandpublications/ReserveManagementPlans/Documents/Karapiro%2 0Reserve%20Management%20Plan%20(2011).pdf
Wells, R., Clayton, J., Schwarz, AM., Hawes, I., Davies-Colley, R. (2000) Mighty River Power aquatic weeds: issues and options. NIWA Client Report MRP00502.
Wells, R., de Winton, M. (2015) Lake Karāpiro March 2015 weed bed assessment. NIWA memo, prepared for Boffa Miskell Ltd.
24 Weed Management Plan for Hornwort in Lake Karāpiro
Appendix A Designated activity zones and navigation features for Lake Karāpiro. Sourced from WDC (2011), Karāpiro Lake Domain (Mighty River Domain) Reserve Management Plan.
Weed Management Plan for Hornwort in Lake Karāpiro 25
NB: Waipuke Park is marked on the map above simply as a reserve downstream of the pylons. The WDC website does not report a boat ramp at this location (Oct 2014).
26 Weed Management Plan for Hornwort in Lake Karāpiro
Weed Management Plan for Hornwort in Lake Karāpiro 27
28 Weed Management Plan for Hornwort in Lake Karāpiro
Appendix B Reference Maps and Images
Bathymetric map of Lake Karāpiro (from Irwin and van Kampen 1986). The lake area north of Little Waipa Domain (indicated by the large blue arrow) has been considered within the weed management plan. The areas of the lake in blue are greater than 20m deep.
Weed Management Plan for Hornwort in Lake Karāpiro 29
Location of nuisance weed beds . The assessment made in March 2015 shows weed beds (in magenta) including the submerged islands adjacent to Flynn Cove. Note weed bed width is not to scale but for display purposes (Source: Wells and de Winton 2015).
Location of the submerged weed covered islands. An aerial photograph showing the two islands immediately adjacent to the area of red dye (Source: J Clayton). Decimal GPS points for the islands are -37.9339820, 175.5456280 and -37.9353610, 175.548860 (Source: A Taumoepeau).
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Areas of Lake Karāpiro treated with diquat from 2007 to 2015 May 2007 – 50 ha (Clayton et al. 2008)
September 2007 – 50 ha (Clayton et al. 2008) 2007
Weed Management Plan for Hornwort in Lake Karāpiro 31
May 200 8 – 100 ha (Clayton et al. 2008)
Yellow is untreated areas for potential follow up
May 200 9 – 100 ha (Clayton et al. 2009)
32 Weed Management Plan for Hornwort in Lake Karāpiro
April 20 10 – 100 ha (Matheson et al. 2010)
September 2010 – 80 ha (Contractor notes)
Weed Management Plan for Hornwort in Lake Karāpiro 33
Nov 2014 & April 2015 – 13 ha (NIWA Memo 201 5)
Summer 2015 – 2016 (Map supplied by Boffa Miskell )
(Sprayed areas in dark blue)
34 Weed Management Plan for Hornwort in Lake Karāpiro
Appendix C Summary of control methods
Summary of the feasibility of control methods and weed disposal subsidies (Source: Hofstra et al. 2015). Control Methods Chemical control methods Diquat has a proven track record for the control of hornwort in Lake Karāpiro. Endothall is efficacious against hornwort, proof of concept for its use on weed beds in open water environments of Lake Karāpiro requires evaluation. Physical control methods Water level drawdown is not suitable for the control of hornwort in Lake Karāpiro. Benthic barriers may provide small-scale localised weed control as a minor part of an integrated weed management approach in Lake Karāpiro. Harvesting is effective at reducing hornwort. The size and shape of Lake Karāpiro and the extensive areas over which weed reduction is required, within relatively short timeframes to secure amenity values, means that harvesting could be used to target small-scale areas only. Biological control method Grass carp are the only biological control method for submerged aquatic weed control, and they consume hornwort. However grass carp are not suitable for Lake Karāpiro, primarily because they cannot be targeted to consume and reduce only the key nuisance weeds. They would be difficult to contain. Weed disposal subsidies The use of harvested macrophytes in composting, vermiculture, stockfood or for the generation of biogas to potentially offset harvesting costs and reduce landfill disposal was explored. Consideration must be given to the concentrations of potential contaminants (e.g., arsenic) within the plant material, and its safe use, as well as the likelihood of creating contaminated sites where weed is disposed of, or in temporary stockpiles. The potential benefit of using harvested hornwort as a feedstock for anaerobic digestion to produce biogas shows promise, but requires experimental verification. NB: Additional references for weed control operations in Lake Karāpiro are noted alongside the treatment maps in Appendix B.
Weed Management Plan for Hornwort in Lake Karāpiro 35
Appendix D Framework for site evaluation and prioritisation
The SPF is organised by Criteria (left) and Sites (right). Note that there is a separate section at the end of the appendix with more detailed Site Descriptions, and additional points in Considerations and Notes. The SPF summary is presented first, followed by the tables from which the summary was derived. Scores were assigned for the four criteria at the key stakeholder workshop (25 th August 2016) and based on expert opinion. Higher total scores indicate higher priority sites.
SPF Summary
Site
LB Z7 Camps Watertake Boat ramps Swimming Z3 Swimming Z7 Swimming The Boatshed The Submerged Isl Submerged RB Z3-4, LB Z5 MR domain Z4 MR domain Rowing course Weedboom Z7 Weedboom RB Z5-6, LB RB Z6
com. Watertake Karāpiro ski club ski Karāpiro Brooklyn ski club Brooklyn ski No No control zones Piarere, barefoot Piarere, Horahora domain Rowing workshop RB Z7,Landing Bobs Mercury weedboom Mercury Criteria LB, Waipa to Little RB External influences 3 10 15 15 0 15 15 0 3 0 13 13 0 8 0 10 10 15 4 4 4 4 4 Biosecurity 1 0 0 3 0 5 2 1 2 1 5 5 1 2 0 2 2 2 1 1 1 1 1 Assurance of use 10 15 15 13 15 15 12 11 7 7 12 13 7 10 7 9 9 9 8 8 8 8 9 Environmental dependencies 0 5 5 5 4 5 3 1 5 3 5 5 5 5 0 5 5 5 5 5 5 5 5 Total Scores (max value of 40) 14 30 35 36 19 40 32 13 17 11 35 36 13 25 7 26 26 31 18 18 18 18 19 40 40 35 36 35 36 32 30 31 30 25 26 26 19 18 18 18 18 19 20 17 14 13 13 11 10 7
Ranking from all criteria 0 Sites
36 Weed Management Plan for Hornwort in Lake Karāpiro
External influences : External factors or pressures (eg., public perception, events calendar) that influence what can be achieved (in terms of weed reduction) and when. The Objective is to minimise negative impacts on the wider LB Z7 LB Z7 community from implementation of (or failure to carry out) Camps Watertake Boat ramps Boat ramps Swimming Z3 Swimming Z7 Swimming The Baotshed The Submerged Isl Submerged RB Z3-4, LB Z5 RB Z5-6, LB Z6 MR domain Z4 Z4 MR domain Rowing course Rowing course weed management. Z7 Weedboom Watertake com. Watertake Karāpiro ski club ski Karāpiro Brooklyn ski club Brooklyn ski No control zones No control zones Piarere, barefoot barefoot Piarere, Horahora domain Horahora domain Rowing workshop Rowing workshop RB Z7,Landing Bobs Mercury weedboom Mercury LB, RB to Little Waipa LB, Waipa to Little RB Indicator: Key stakeholders' perception Definition: Stakeholder requirement to maximise positive gains (e.g., addressing priority areas identified in management plans) while minimising exposure to criticism and/or adverse publicity. 0 5 5 5 0 5 5 0 0 0 5 5 0 3 0 3 3 5 2 2 2 2 2 Scores: Inadequate progress towards clearing weed at visible locations = 0; Moderate progress towards goals = 3; Meeting all expectations of stakeholder requirements in visible location = 5. Identifier: Key stakeholders. Indicator: General public perception of need Definition: General public perception on the need for and progress of weed control within different regions/zones/sites in the lake. 3 5 5 5 0 5 5 0 0 0 5 5 0 3 0 5 5 5 2 2 2 2 2 Scores: Little or no public support for weed control at the site = 0; moderate =3; High public support for weed control at the site = 5. Identifier: Key stakeholders. Indicator: Events calendar Definition: Need values that relate to how booked-up the zones are within the year, and hence the timeframes within which (excluding weekends and public holidays) weed control activities can be undertaken. Scores: Not booked = 0 0 5 5 0 5 5 0 3 0 3 3 0 2 0 2 2 5 0 0 0 0 0 0; weeks within which control can be undertaken at that site =3; Few opportunities to control weeds in the lead up to events, days at a time = 5. Identifier: Events manager/MRD Site Manager. Total Score (max. value of 15) 3 10 15 15 0 15 15 0 3 0 13 13 0 8 0 10 10 15 4 4 4 4 4
Weed Management Plan for Hornwort in Lake Karāpiro 37
Biosecurity: Recognition that Karāpiro is an aquatic weed hub, and as such there is a risk of transfer to other lakes. LB Z7
Objective is to minimise risk of inter-lake spread of weed - Camps Watertake Boat ramps
boat ramps and haul out areas are High Priority. Z3 Swimming Z7 Swimming
Baotshed The Submerged Isl Submerged RB Z3-4, LB Z5 RB Z5-6, LB Z6 MR domain Z4 MR domain Rowing course Weedboom Z7 Weedboom Watertake com. Watertake Karāpiro ski club ski Karāpiro Brooklyn ski club Brooklyn ski No control zones No control zones Piarere, barefoot Piarere, Horahora domain Rowing workshop RB Z7,Landing Bobs Mercury weedboom Mercury LB, Waipa to Little RB Indicator: Risk of inter-lake spread Definition: Boat ramps and some shorelines allow boats & trailers to pick up weeds and transport to other waterbodies. The only significant vector of spread is human related. Scores: Nature of weed beds (e.g., surface reaching) and proximity to human activities (e.g., launching sites, fishing 1 0 0 3 0 5 2 1 2 1 5 5 1 2 0 2 2 2 1 1 1 1 1 etc.,) influences the level of risk. Minimal risk = 0; High risk = 5 . [NB: no weed contact e.g., watertake 0; weed present and potentially people/boats 1; people/boats/weed e.g., ski clubs, boatshed access 2; 3-4 popularity of boat ramp, public boat ramp 5] Identifier: Expert opinion. Total Score (max. value of 5) 1 0 0 3 0 5 2 1 2 1 5 5 1 2 0 2 2 2 1 1 1 1 1
38 Weed Management Plan for Hornwort in Lake Karāpiro
Assurance of intrinsic, amenity and utility values :
Recognises the threat that hornwort poses to the intrinsic, recreation, amenity and utility values of the lake. Recognises the LB Z7
significant commercial revenue that is gained from management Camps Watertake Boat ramps
of weed in the lake. Objective is maximum weed control for Z3 Swimming Z7 Swimming The Baotshed The Submerged Isl Submerged RB Z3-4, LB Z5 RB Z5-6, LB Z6 MR domain Z4 MR domain Rowing course Weedboom Z7 Weedboom Watertake com. Watertake Karāpiro ski club ski Karāpiro Brooklyn ski club Brooklyn ski No No control zones Piarere, barefoot Piarere, Horahora domain Rowing workshop
minimum costs to provide for multiple uses. RB Z7,Landing Bobs Mercury weedboom Mercury LB, Waipa to Little RB Indicator: Intrinsic values (no control areas) Definition: Although Karāpiro is a modified (dammed) lake that is highly impacted by submerged weed, intrinsic values are still derived from the lake and wildlife is supported by the 0 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 macrophytes. These values are supported in particular by leaving some areas in which the weed is not managed. Scores: 0= set aside as unmanaged; 5 = managed . Identifier: Key stakeholders, and Expert opinion. Indicator: Benefits how many Definition: This value addresses how many people are likely to derive benefit from managing the weed at a site. Scores: no one = 0 e.g., Mercury, nursery watertake; select or private groups e.g., 5 5 5 4 5 5 3 3 1 0 4 5 0 1 0 1 1 1 1 1 1 1 1 ski clubs =1; larger groups = 2; Domain venue=3; general public i.e., access or use is open to all, e.g., boat ramp =4; e.g., safe weed free public swimming beach =5 . Identifier: Key stakeholders. Indicator: Benefits whom Definition: This value addresses who is likely to derive benefit from managing the weed at the different sites. Scores: private/commercial interests =0 e.g., Mercury, nursery watertake; sites reserved for club or local events =1; regional 5 5 5 4 5 5 4 3 1 2 2 2 0 4 0 1 1 1 2 2 2 2 3 events =2; national events =3; sites used for training for International events =4; general public =5 e.g., public swimming beaches, hosting large/International events that bring revenue to the region. Of consideration is the scale/relative contribution to the weed issue as a whole. Identifier: Key stakeholders. Total Score (max. value of 15) 10 15 15 13 15 15 12 11 7 7 12 13 7 10 7 9 9 9 8 8 8 8 9 NB: highest priority, threshold sites for treatments are those Values reflect likely contribution of large above 10 (10=backwater unmanaged score). weed beds to drift
Weed Management Plan for Hornwort in Lake Karāpiro 39
Environmental dependencies: Recognition that habitat
influences the nature of the weed management outcome.
Currently there are two feasible control tools, diquat (herbicide) and weed cutting (harvesting). The objective is to take account of environmental factors that may influence weed management LB Z7 methods, timing and outcomes. [*Some factors e.g., plant Camps Watertake Boat ramps Swimming Z3 Swimming Z7 Swimming The Baotshed The RB Z5-6, LB Z6 Submerged Isl Submerged RB Z3-4, LB Z5 MR domain Z4 MR domain Rowing course Weedboom Z7 Weedboom Watertake com. Watertake condition, height of weed-bed, can only be evaluated at pre- club ski Karāpiro Brooklyn ski club Brooklyn ski No No control zones Piarere, barefoot Piarere, Horahora domain Rowing workshop RB Z7,Landing Bobs Mercury weedboom Mercury treatment assessments]. This is about ‘ease of control’ i.e., scale LB, Waipa to Little RB of sites, timeframes and relative costs. Indicator: Diquat Definition: Identifying sites where diquat can be used, assuming external and habitat factors* are appropriate. The scale refers to the amount of area that can be treated in short timeframes (to fit within the events/weather calendars) providing confidence in lake amenity and utility use. Easier control means more sites cleared 0 5 5 5 0 5 2 1 5 2 5 5 1 5 0 5 5 5 5 5 5 5 5 for the cost. Scores: appropriate use by watertakes = 0; compressed weed =1; potential for off target herbicide movement =2, (more predictable outcome based on likely diquat contact time=3, =4); target weed reduction possible in one spray event = 5. Identifier: Expert opinion. Indicator: Weed cutting Definition: Identifying sites where weed cutting can be undertaken, assuming external factors and habitat factors* are appropriate. The scale refers to the amount of area that can be cut in short timeframes (to fit within the events/weather calendars) providing confidence in lake amenity and utility use. Easier control means more sites cleared for the cost. Scores: 0 4 1 0 4 4 3 1 3 3 0 0 5 2 0 4 2 0 3 2 0 0 0 Remote sites, large distances for a weed cutter/harvester to travel from its access point = 0; relative to distance from access and permitted dump site = 1, 2, 3; rapid improvement at small localised sites = 4; target weed reduction possible in one cutting event (e.g., compressed weed on the booms) = 5. NB: assumes cut weed is taken to a permitted dump site, so all scores revert to zero with distance from the dump. Identifier: Expert opinion. Score (max. value of 5) 0 5 5 5 4 5 3 1 5 3 5 5 5 5 0 5 5 5 5 5 5 5 5 Demonstrating there is a method with a high certainty of outcome
40 Weed Management Plan for Hornwort in Lake Karāpiro
NB: the category “Source of drift” has been removed because there is little certainty as to which beds contribute how much to the drift and when. It is recognised that the more weed beds are reduced overall the less drift material will be present. It is also recognised that the large weed beds upstream and along bank margins do have a role in weed drift and their scores under the criteria “assurance” have been increased to reflect this.
Weed Management Plan for Hornwort in Lake Karāpiro 41
Site Descriptors . The abbreviation Z refers to the Zone numbers within Lake Karāpiro as indicated in Appendix A No control zones Intrinsic value, no control sites - where weed is not managed i.e., Zone 2; backwaters fed by Hauoira, Waione, Mangahanene Strms; embayment immediately south of zone 8. Swimming Z3 Swimming zone on northeastern shore Z3. Swimming Z7 Waipuke Park swimming beach Z7. Camps Finlay Park and Epworth Camps shoreline Z12. Watertake Water treatment intake, public Z3. MR domain Boat ramp, Cambridge Rowing Club, Mighty River Domain, Rowing tower; Cambridge Yacht Club (whole of LB). Rowing course Rowing course Z4, Z5, Z6 LB. Weedboom Z7 Weed boom Z7. Rowing workshop Flynn Cove with Karāpiro Rowing workshop. Submerged Isl Submerged islands located between Flynn Cove and the rowing course, Z5. Boat ramps Keeley Reserve Z7, Moana Roa Reserve Z7, Little Waipa Domain Z12. Horahora domain Horahora Domain and boat ramp Z9. Mercury weed boom Weed boom for Karāpiro hydro station Z3. Boatshed access The Boatshed, Right Bank access Z6. Watertake com. Becks Nursery watertake Z7. Karāpiro ski club Karāpiro Waterski Club slalom course Z1, club Z3. Brooklyn ski club Brooklyn Waterski Club Z5, slalom Z6. Piarere, bare foot Bare foot ski jump course Z8; Piarere Waterski Club Z9, jump and slalom Z9. RB Z3-4, LB Z5 Right Bank Z3-4, Left Bank Z5. RB Z5-6, LB Z6 Right Bank Z5 and Z6, Left Bank Z6. LB Z7 Left Bank (up to ca Stokes Rd in 2015) Z7. RB Z7, Bobs Landing Right Bank (especially Moana Roa to Horahora bridge) Z7, Bobs Landing Z7. LB, RB to Little Waipa Left Bank, Right Bank upstream to Little Waipa Domain Z10, Z11, Z12.
42 Weed Management Plan for Hornwort in Lake Karāpiro
Considerations and Notes Considerations: Environmental dependencies for annual operations, informed by monitoring Indicator: Plant Condition Factor (*assessment required). Definition: Condition of weed, how 'clean' it is makes a difference to diquat efficacy. Plant condition at target treatment sites must be considered in a pre-treatment assessment to inform whether or not spray can go ahead and/or if weed cutting can be used at a smaller number of sites (with dependencies). Identifier: Expert opinion. Indicator: Plant Accessibility Factor (*assessment required) Definition: Surface reaching weed, water depth (willingness of Mercury to manipulate water level). Whether or not the weed is surface reaching makes a difference to how much could be cut (blade depth) and spray efficacy (penetration through canopy layer, vs thermal boundary layer). Pre-treatment assessment of weed at target sites should be used to inform whether or not spray can go ahead and/or if weed cutting can be used at a smaller number of sites (with dependencies). Identifier: Expert opinion. Indicator: Recovery Rate (*assessment required) Definition: This is best expressed in terms of plant growth rate/doubling times, which can vary for different times of the year and sites. It is a measure of how long the target outcome endures before further control work is necessary. SLOW recovery is BEST since this reduces control effort and associated costs. Scores: 0 = rapid recovery with biomass doubling in <6 months; 5 = Very slow regrowth rate with little change after 1 year. Scores are based on past results. Identifier: Expert opinion Notes: (1). Zone (Z) numbers refer to locations in the 'designated activity zones and navigation features for Lake Karāpiro' (WDC 2011). (2). Areas identified incorporate activity, amenity and utility zones and areas previously targeted for weed control from 2007. (3). Sites have been bundled for like activities/characteristics as control targets. Intrinsic values (light blue); swimming beaches (mid blue); camps (purple); public boat ramps (yellow, not MR Domain); private clubs (peach); MR Domain and rowing course zones (light green); watertakes public (light purple); commercial interests (dark grey); left and right banks (mid green).
Weed Management Plan for Hornwort in Lake Karāpiro 43