Strategy and Policy Committee 12 March 2019
Report No. 19-29 Decision Required
LAKES MANAGEMENT UPDATE
1. PURPOSE 1.1. This paper provides Council with an update on Horizons non-regulatory work programme around lakes including an overview of the lakes monitoring and research programme and lake restoration work. This report summarises information analysed in preparation for Horizons State of Environment report and also overviews recent reports completed in 2018 for Horizons to inform restoration planning for lakes in the Region.
2. EXECUTIVE SUMMARY 2.1. In 2018, the data from the regional lakes programme was analysed to inform the 2019 State of Environment (SOE) report. The regional lakes monitoring programme was introduced in 2014 expanding the monitoring programme from one lake (Horowhenua) to monitoring four lakes. In 2015 the programme was further expanded to monitor a total of 15 lakes (7%) of the 226 that are more than a hectare in size within the region. At the time this programme was introduced, Lake Horowhenua was already being regularly monitored, with a comprehensive monitoring programme to inform restoration as a part of the Lake Horowhenua Accord, however no other lakes were being monitored for Sate of Environment water quality reporting purposes. 2.2. The regional lake monitoring programme has provided a significant step forward to providing information on lakes in the region. This information was analysed and compared to water quality targets of the One Plan and new requirements of regional councils introduced via the National Policy Statement for Freshwater Management (NPS-FM) in 2011 and its amendments in 2014 and 2017. The results of this analysis are overviewed in this paper below and it is noted that the analysis is limited in terms of the representation of the state of lakes in the region due to the small number of lakes monitored and the low frequency of sampling events (quarterly sampling, rather than monthly). A review of the lakes monitoring programme is being scoped for the next financial year. 2.3. The monitoring results show that a number of the region’s lakes are in poor condition. A key finding of the analysis is that all lakes currently monitored for water quality in the Horizons Region fail to meet the national bottom line for at least one of the specified water quality attributes in the NPS-FM. Further detail is provided in the body of the report. 2.4. To date, Horizons has undertaken a range of regulatory and non-regulatory work around lakes. The regulatory programme has, through the One Plan, set water quality targets for lakes and identified some lake catchments as priority areas for nutrient management rules. Additionally, the One Plan has established non-regulatory methods for the protection and enhancement of Lake Horowhenua and other coastal lakes, as well as a method for lake quality research, monitoring and reporting. It is noted that the development of the One Plan, which was notified in 2007 predated the NPS-FM 2011 and its subsequent amendments (2014 and 2017) and that there are differences in the requirements of these policy documents. 2.5. Alongside the development and implementation of policy around lake management, there has been a range of consent and compliance work including consenting for restoration work at Lake Horowhenua and the ongoing consent process for the discharge of stormwater by Whanganui Prison to Lakes Pauri and Wiritoa. Trigger levels for
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Strategy and Policy Committee 12 March 2019 groundwater abstraction in coastal sand country have also been introduced via consent processes where there is a risk of reduced flows to coastal dune lakes. 2.6. The non-regulatory programmes traditionally focussed on fencing and planting of lake margins and inflowing streams, as well as education around the potential for transfer of aquatic weeds through use of lakes for food gathering and recreation. Around 2010, the focus of these programmes shifted toward developing further understanding of lakes and how to restore them using a wider tool box for restoration options including both in-lake interventions and out of lake (catchment) interventions. Prioritisation of lakes for this science and restoration work has largely been based around the lakes that are used recreationally, the lakes that are in priority catchments for the nutrient management rules of the One Plan and more broadly, coastal dune lakes. Examples of this work are provided in the paper below including two lakes that have received significant regional investment by Council (Lake Horowhenua and Lake Waipu). In both cases Horizons, iwi/hapu, the respective local District Council’s (Horowhenua and Rangitīkei) and others, have invested as a part of a work programme receiving significant investment via Central Government. 2.7. A key part of the investment in lake restoration, including seeking external resourcing from central government, has been obtaining the monitoring and science information to develop restoration options. To assist with development of further restoration work for other lakes in the region, two Envirolink-funded reports were commissioned to review existing data for lakes and to identify knowledge gaps for restoration planning. The reports were split based on lake types using examples of a small number of deep lakes (including Lakes Pauri, Wiritoa and Dudding) and shallow lakes (including Lakes Waipu and William). It is noted that these reports do not provide detailed action plans for restoration of the lakes. Another level of planning and information is required for lake specific action plans to be developed. As such, these reports identify data and information necessary to undertake the further work of developing restoration options, and subsequent action plans. 2.8. The restoration planning reports and more recent information from the regional lakes monitoring programme shows that some of the lakes in the region are at risk of ‘flipping’. This is a process where the lake shifts from having aquatic plants to being in a state where the lake is dominated by algae, where cyanobacteria blooms can dominate. Monitoring data from both Lake Dudding and more recently Lake Wiritoa, have shown signs of the lakes progressing to flipping. This paper provides further detail and discussion around this issue for both lakes. Some further information is being gathered for these lakes prior to a meeting of lake experts to advise on the issue. An initial workshop with lake experts is to be held this financial year for Dudding Lake, with an aim to obtain recommendations around any further information that is needed, an assessment of potential intervention options, information on the degree of risk of flipping and level of urgency for action. This workshop is being developed in collaboration with Rangitīkei District Council. A similar workshop is intended for Lake Wiritoa following initial data collection. Workshop outcomes will be reported to Council. 2.9. The initial focus for the lakes programme has been around the characterisation of a small number of the region’s coastal lakes with a view to establishing their current state and initiating work around lake restoration for some lakes. The combination of the state of environment reporting and the recently completed restoration options reports has provided insights into the state of water quality in some of the regions lakes and the amount of information available to analyse this. With this information now available, the programme would benefit from a wider review to ensure that future work is aligned with both regional and national monitoring and reporting requirements, and that sufficient information is collected to inform interventions for restoration. A number of identified options for monitoring or further restoration work are identified in the reports however are outside the current capacity and resourcing of the existing programme. As a part of the work programme in the next financial year, a group of experts will be engaged to work with Horizons staff to review the lakes programme including establishing a range of options for upgrading the monitoring programme to improve overall reporting on lakes in relation to the
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Strategy and Policy Committee 12 March 2019 national and regional policies and to inform potential restoration work. This will include an option to reconfigure the use of current budget and options for increased investment. The outcomes of this work will be reported to Council for consideration.
3. RECOMMENDATION That the Committee recommends that Council: a. receives the information contained in Report No. 19-29. b. endorses the proposed approach in the paper.
4. FINANCIAL IMPACT 4.1. There are no current financial impacts associated with this item. This report reflects previously endorsed budgets approved as part of Council’s annual planning and long term planning processes, and identified work programmes delivered as part of the Science and Freshwater Operational Plan’s, including use of resources from other partners such as central government.
5. COMMUNITY ENGAGEMENT 5.1. This item is a public item. Further presentation of information around lake ecological condition and water quality will be made to the public as part of Horizons State of Environment reporting during 2019.
6. SIGNIFICANT BUSINESS RISK IMPACT 6.1. No significant business risk has been identified.
7. BACKGROUND 7.1. In the Horizons region there are 226 lakes greater than one hectare in size. These range from coastal dune lakes such as Lake Wiritoa and Lake Horowhenua, through to dammed water courses found throughout the hill country to the north of the region, and volcanic lakes such as Crater Lake at Mt. Ruapehu. 7.2. Our region’s lakes, and their associated wetlands, provide for a range of community values. In addition to ecological, cultural and spiritual values, a number of lakes in the region are also popular areas for water sports, fishing and hunting and gathering of kai. 7.3. Within the margins of some of the regions lakes, important habitat is provided for plants and animals specially adapted to living in such conditions. Brown mudfish (threat status declining, 2017) have been found in the margins of Lake Horowhenua, Herbert, Waiwiri, Omanuka Lagoon, and Knottingly Swamp. Conning & Holland (2003) noted that the abundance of dune lakes and associated wetlands, although discontinuous, collectively provide important habitat for a number of threatened and regionally significant birds and several species including Matuku - Australasian Bittern (threat status, nationally critical, 2016) have been observed at lakes within the Region. Horizons biodiversity programme has completed a range of work to complete ecological assessments of habitat around lakes and lakes are a part of the biodiversity programme for protection of priority habitats. This paper does not provide further detail on the terrestrial biodiversity aspect of lakes management, rather focusses on the water quality and aquatic health aspects of lake management.
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Strategy and Policy Committee 12 March 2019 7.4. Lakes are unique and incredibly diverse, making them complex systems to understand. They are also vulnerable to the pressures of land use, water use, recreation, aquatic pests and a changing climate. Over time these pressures have contributed to degraded water quality in some lakes. Interventions can be required to remediate these lakes and also to maintain lake health in the lakes that are in better states of lake health. 7.5. Monitoring and investigation of lakes within the Horizons region has been carried out over many decades. Early investigations were completed by the local Catchment Board. However, these were generally short-term monitoring programmes largely focused on water availability and some water quality monitoring. Biosecurity monitoring and education have been a focus for the programme from the 1990’s and this is still an active component of the programme in 2019. Through analysis for the 2005 state of Environment Report and development of the One Plan in 2007, Horizons focus shifted to understanding the current state of the health of some of the region’s lakes. Policy development through the One Plan and non-regulatory work have progressed with the support of a dedicated lakes research and monitoring programme that has grown from around 2010 to include further monitoring introduced in 2013, 2014 and 2015 as well as a focus on restoration work. New requirements have been introduced for lakes via the NPS-FM and its various amendments. This report provides an update on the lakes programme drawing on recent State of Environment reporting and restoration planning reports.
8. Legislative Overview 8.1. The Resource Management Act 1991 (RMA) is New Zealand’s principle piece of environmental legislation. The purpose of the RMA is to promote the sustainable management of natural and physical resources [RMA s5]. Lakes are one of the water bodies provided for in the RMA and under s35, regional councils are charged with giving effect to the RMA in their regions. This is primarily achieved through development and implementation of regional policy statements and regional plans. Regional councils are also charged with a duty to gather, monitor, and keep records in order to do its job effectively [RMA s35]. 8.2. A national framework for freshwater management to give effect to the RMA is set out in the National Policy Statement for Freshwater Management 2014 (NPS-FM). Ecosystem health and human health for recreation are compulsory national values. In terms of lakes, the NPS-FM establishes national attribute states and bottom lines for phytoplankton (measured as chlorophyll a), total nitrogen, total phosphorus, ammonia, E coli, and cyanobacteria (blue-green algae). Regional councils are responsible for giving effect to the NPS-FM and to monitor current state and progress towards achievement of freshwater objectives and values. 8.3. Freshwater management in the region is implemented through rules and non-regulatory methods in the One Plan. Management of the effects of activities affecting lakes is primarily implemented through identification of lakes, lagoons and their margins as threatened habitats in the indigenous biological diversity provisions (Schedule F). The majority of activities affecting threatened habitats are non-complying activities. The One Plan also provides for research, monitoring and reporting to assess the state and quality of the Region’s lakes and measure changes in water quality (Methods 5-6 and 5-7). 8.4. Management of lakes can be complex due to the diversity of the lakes and the pressures they face, while different interest groups may have different values that they hold for the lake. Lake interest groups may include: iwi/hapu, Horizons, the local Territorial Authority, Department of Conservation, public health, Fish and Game, recreational user groups (including swimmers, campers, boaties, anglers and hunters), local community groups, land owners, local residents, and others.
9. Biosecurity monitoring and education
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Strategy and Policy Committee 12 March 2019 9.1. Biosecurity issues have been a traditional focus of work in relation to lakes, with monitoring of the region’s lakes largely focusing on identifying the submerged plant species that were present. The key objective being to prevent the spread of introduced macrophytes (lake weeds) between lakes, primarily through public education. This work continues through regular efforts around public education, for example Horizons is updating signage at three of the regions well used lakes this summer (Dudding, Pauri, and Wiritoa) in the interests of reducing the potential for introduction of new macrophytes species to lakes where they are currently absent (Figure 1). Other signage is promotes not spreading weeds that are in the lake to other lakes, an example of this that is currently installed at Lake Wiritoa is also shown below (Figure 2).
Figure 1 Image of new educational and warning signage to be established at Lake Pauri, Wiritoa and Dudding that focuses on not introducing weeds that are currently absent from the lake.
Figure 2 Current educational signage at Lake Wiritoa around aquatic weeds that focuses on not moving weeds to other lakes.
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Strategy and Policy Committee 12 March 2019 Macrophyte monitoring using LakeSPI 9.2. Horizons has established a regular monitoring programme for macrophytes. This monitoring provides information on spread of introduced macrophytes and also provides a measure of ecological condition of the lakes monitored. The method used is known as LakeSPI (Lake Submerged Plant Indicators). This bio-assessment method that uses the degree of development by native submerged plants, and level of impact by non-native, invasive weeds to indicate an ecological condition. Lake SPI surveys are now undertaken every year at different lakes throughout the region. This monitoring was started in 2014 following new funding being made available for this this monitoring and a regional lake water quality monitoring programme via the annual plan process. 9.3. Increased sediment and nutrient loading from catchment activities, and displacement of native vegetation by invasive alien plant species are major influencers of lake ecology and condition. The submerged plant indicators used in LakeSPI provide an effective means of assessing these impacts and compliments traditional water quality monitoring, such as the Trophic Level Index method (see below). 9.4. To date 31 lakes have been surveyed using the LakeSPI method. The majority of these lakes have been recorded as having at least one introduced macrophyte species present. Results (Figure 3) show: - Five lakes in the region are in excellent condition, having a LakeSPI Index that exceeds 75%, and one lake is determined to be in high ecological condition, meaning they have little or no impact from invasive weed species. - Fourteen lakes are classified as ‘Moderate’, reflecting some degree of impact from invasive weeds and/or restricted development of native plant communities. - Seven lakes are categorised in poor condition, with all lakes being heavily impacted by hornwort (Ceratophyllum demersum) or egeria (Egeria densa). - Four lakes are non-vegetated. Poor water quality and prevalence of algal blooms were noted for most lakes, with the prolonged effects of these impacts likely to lead to further deterioration of submerged vegetation (NIWA, 2018). 9.5. The presence of introduced macrophytes in some of the regions lakes has changed internal lake processes and can be considered as a driver of some of the issues that we encounter with water quality. An example of this being Lake Horowhenua and the presence of Potamogeton crispus and its annual life cycle in Lake Horowhenua driving the release of phosphorus from the lake bed and the associated blue-green algal bloom that occurs. This is also likely to be a driver of blue-green algal blooms in other lakes in the region however, we currently lack the necessary information to establish how common this occurrence is. 9.6. Although invasive macrophyte species are not favourable in terms of overall lake condition, their presence in a lake is preferable to none, in that they can help mitigate many of the symptoms of eutrophication (e.g., lock-up nutrients, maintain water clarity, compete with phytoplankton). Plants reduce wind action on the lake, which in turn reduces the resuspension of bottom sediment and associated nutrients. This results in improvements in water clarity and the subsequent ability of plants to grow. Therefore, understanding the species of macrophytes present and their distribution within a lake is an important factor in understanding the drivers of lake processes and any potential management interventions.
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Figure 3 Map of LakeSPI results for 31 of the region’s lakes.
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Strategy and Policy Committee 12 March 2019 10. Lake Trophic Index (TLI) 10.1. The Trophic Level Index (TLI) for lakes is a common measure of ecological health or the trophic state in lakes. A national report in 2010 that ranked monitored lakes nationally identified Lake Horowhenua as the 105th worst lake in the country out of 112 lakes monitored nationally. The 2010 national report did not have a lot of other information on TLI for lakes in the region. The new monitoring programme enables TLI to be calculated from the parameters that Horizons collect as part of the monthly and quarterly water quality sampling. 10.2. Based on the TLI lakes can be classified in seven trophic categories ranging from <1 ultra- microtrophic (pristine) to >6 hypertrophic (Table 10). As the TLI score increases, the ecological condition of the lake declines. 10.3. Of the 15 lakes we currently monitor, only Lake Koitiata falls within the eutrophic category. Six lakes are classed as supertrophic and eight lakes are classified as hypertrophic (Figure 4).
Figure 4 Lakes in the Manawatū-Whanganui Region based on their TLI classification.
11. Bathymetric surveys 11.1. Lake bathymetric surveys provide information on how the depth of the lake varies within the lake area. Surveys of 15 coastal dune lakes are available from as early as 1982 although the results of these early surveys are overly simplified and of limited use. Currently lake bathymetric surveys are completed based on individual project demands with surveying including bed profile, weed biomass and substrate mapping (Figure 5, Figure 6). More recent data are available for seven lakes in the region, with a current target of undertaking three additional surveys per year.
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Figure 5 Lake depth contours and weed biomass profile for Lake Waipu, Horizons Region. Image courtesy of Biobase.
Figure 6 Lake depth and weed biomass information for Lake Dudding, Horizons Region. Image courtesy of Biobase.
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Strategy and Policy Committee 12 March 2019 12. State of Environment Water Quality Monitoring 12.1. Following the 2005 state of Environment Report and development of the One Plan in 2007, Horizons focus shifted to understanding the current state of the health of some of the region’s lakes. At that time the health of some of the region’s lakes was known to be poor however water quality data was limited. 12.2. In recent years Horizons has developed and implemented a dedicated lakes monitoring and research programme. Water quality in Lake Horowhenua has been monitored since 2003, with monitoring stopping in September 2009 and recommencing on a monthly basis in 2013. In 2014 Horizons commenced water quality monitoring at three of the regions deep coastal lakes on a quarterly basis and in 2015 another 11 lakes were incorporated into the programme on a quarterly basis. These coastal dune lakes were initially selected due to their potential vulnerability to land use change in the Whanganui, Manawatū and Rangitīkei coastal plains in recent years. This monitoring has helped to create baseline knowledge of lake water quality but is, for most lakes, too infrequent to assess water quality state against policy targets with the required statistical robustness, or to inform the development of restoration plans. Representativeness of the lakes being monitored 12.3. Overall, work to date has largely focussed on the region’s coastal dune lakes, of which there are 57. This focus was primarily driven by the need to understand the current state of the health of the lakes to inform implementation of the One Plan nutrient management rules for priority catchments and is noted that in the interests of cost efficiency the programme has focussed on areas of the region that are most accessible and cost- effective to monitor. The limitations of such an approach are acknowledged and highlight that the current water quality and ecological status of the remaining 169 lakes within the region is presently poorly understood and in many cases, unknown. A summary of the number of lakes monitored, compared to the number of lakes in each of the major categories of lakes in the region is provided in Figure 6. This shows that there are over 100 lakes in the Landslide/ Slump category, however none of these are included in the state of environment monitoring programme. 12.4. As it is currently designed, the programme is yet to fulfil NPS-FM policy CB1 which requires the monitoring programme to include representative sites for each Freshwater Management Unit (FMU), with three FMUs not currently covered at all (Figure 7). This includes the Manawatū Freshwater Management unit that has the highest number of lakes, however none are currently monitored as a part of the State of Environment network.
Figure 6 Bar chart showing the number of monitored and not monitored lakes in the Manawatū-Whanganui region by morphological lake type.
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Figure 7 Bar chart showing the number of monitored and not monitored lakes in the Manawatū-Whanganui region by Freshwater Management Unit (FMU).
Water Quality Sampling Frequency 12.5. Currently Horizons monitors 15 coastal lakes for a range of water quality indicators. All lakes, with the exception of Lake Horowhenua, are sampled on a quarterly basis (Lake Horowhenua is monitored on a monthly basis). In a 2016 report to the Ministry for the Environment, McBride recommends calculating the annual statistics based off at least monthly sampling (ideally weekly) and a rolling window of at least 5 years of data (http://www.mfe.govt.nz/sites/default/files/media/Fresh%20water/Final_attribute_stats_repo rt%208_September_2016_Graham_McBride.pdf. While quarterly sampling has provided us with an initial insight into the condition of 14 of the region’s lakes, the frequency of data collection does not currently allow for a statistically robust assessment against NPS-FM criteria, or One Plan targets such as can be determined for Lake Horowhenua.
Comparison with One Plan Targets 12.6. While additional data collection is necessary to provide a more robust and valid analysis, an interim analysis based on the available data has been completed. This suggests that One Plan targets for lake algae (measured as chlorophyll a) are generally not met at monitored sites, Lake Koitiata being the exception. All sites perform fail to meet the targets for total nitrogen (TN) and for total phosphorus (TP), only Lake Koitiata met the TP target. Most sites, with sufficient data for analysis, do meet the One Plan target for ammoniacal nitrogen, except for Lake Heaton (Table 1).
Water Quality Comparison with NPS-FM Attributes 12.7. All lakes currently monitored for water quality in the Horizons Region fail to meet the NPS- FM national bottom line for at least one of the specified attributes. The majority of these lakes fail for both nutrient attributes total nitrogen (TN) and total phosphorus (TP), with Lakes Kohata and Koitiata being exceptions: both are graded a ‘C’ for phosphorus (Table 2). Lakes Heaton, Horowhenua and Wiritoa fail to meet the national bottom line for all parameters.
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Table 1 Water quality assessment against the One Plan targets for the 15 coastal lakes monitoring in the Horizons region.
One Plan One Plan One Plan One Plan Total One Plan Total Site Name Chlorophyll a Chlorophyll a Ammoniacal Nitrogen Phosphorous (average) (maximum) Nitrogen Lake Alice Fail Fail Fail Fail Pass Lake Dudding Fail Fail Fail Fail Pass Lake Heaton Fail Fail Fail Fail Fail Lake Herbert Fail Pass Fail Fail NA Lake Horowhenua Fail Fail Fail Fail Pass Lake Kohata Fail Fail Fail Fail Pass Lake Koitata Pass Pass Fail Pass NA Lake Koputara Fail Fail Fail Fail Pass Lake Pauri Fail Fail Fail Fail Pass Pukepuke Lagoon Fail Fail Fail Fail Pass Lake Waipu Fail Fail Fail Fail NA Lake Westmere Fail Fail Fail Fail Pass Lake William Fail Fail Fail Fail NA Lake Wiritoa Fail Fail Fail Fail Pass Omanuka Lagoon Fail Fail Fail Fail NA
Table 2 Water quality assessment against the Freshwater National Policy Statement attributes for the 15 coastal lakes monitoring in the Horizons region.
NOF: Lake NOF: Lake Phytoplankton NOF: Lake Total NOF: Lake Total Phytoplankton (Max) Nitrogen Phosphorous (Median) Lake Alice B D D D Lake Dudding C C D D Lake Heaton D D D D Lake Herbert C C D D Lake Horowhenua D D D D Lake Kohata C D D C Lake Koitata A A D C Lake Koputara D D D D Lake Pauri B C D D Lake Waipu B C D D Lake Westmere C C D D Lake William C D D D Lake Wiritoa D D D D Omanuka Lagoon C D D D Pukepuke Lagoon B C D D
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Strategy and Policy Committee 12 March 2019 13. Swim Spot Monitoring 13.1. Four lakes are monitored on a weekly basis from November through to April as part of the Swim Spot programme (Lakes Dudding, Wiritoa, Pauri and William). In addition to bacteria (measured as E. coli), these lakes are also monitored for the presence of cyanobacteria. Cyanobacteria are known to produce toxins which can be released into the water column and the cells themselves can also cause skin rashes, respiratory, and other health issues, when density is above a certain threshold. Guidance levels are set out in national guidelines published by the Ministry for Health and the Ministry for the Environment. Information from the swim spot monitoring is shared publically via Horizons website, the LAWA website (www.lawa.org.nz) and via some emails to interested parties. 13.2. Monitoring information is provided to Midcentral District Health Board’s Public Health Officers, who use the guidelines to decide on the alert level for the monitored lakes and to issue health warnings if required. An increase in the occurrence of exceedances of guideline values has been observed for Dudding Lake over recent swim spot seasons (Figure 8). Further data analysis would be required to see if similar patterns occurred in the other three lakes.
Figure 8 Swim spot monitoring data for Dudding Lake showing the biovolumne of cyanobacteria over time.
14. Current Lake Restoration Activity 14.1. Given the uniqueness of the lakes, their size, and morphological characteristics there is no one size fits all approach to restoration. Horizons, in conjunction with iwi, and other stakeholders has scoped a range of options and opportunities for the restoration of a small number of lakes within the region. Lakes Horowhenua, Pauri, Wiritoa, and Oporoa now have recommended actions outlined for their restoration and these are overviewed further below.
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Strategy and Policy Committee 12 March 2019 Lake Horowhenua 14.2. Horizons commissioned via Envirolink two reports on restoration options for Lake Horowhenua. The first of these reports reviewed the data for the lake and built on lake restoration activity and research around the country to provide a list of potential options for restoring the lake. The second report provided further detail for priority actions in consultation with some stakeholders. Subsequently, the Lake Horowhenua Accord was formed and the financial commitment to restoring the lake over the first 10 years of the lake accord is estimated to be in the order of $7 million. 14.3. Lake Horowhenua is the most intensively monitored lake within the Horizons region and includes continuous monitoring using equipment on a lake buoy. This significant investment in monitoring has allowed for lake specific management interventions to be developed and which are currently in the process of being implemented. 14.4. Working with the entity that represents the lake owners (the Lake Horowhenua Trust), the restoration of Lake Horowhenua has been significantly funded by Horizons ratepayers, with a range of funding partners including three central government funds administered through the Ministry for the Environment (Freshwater Clean Up Fund, Te Mana o Te Wai, and the Freshwater Improvement Fund), Horowhenua District Council, industry bodies (DairyNZ and Tararua Growers Association) and the Lake Horowhenua Trust. Significant interventions such as a fish pass and a large sediment trap have recently been completed as these will be providing some benefits to the lake health. These interventions have been a part of a package of restoration works over time and although the science is clear on the interventions, legal challenges have hampered the ability to implement some of the actions. Thus, despite considerable effort, we are yet to see any significant change in either water quality or the ecological health of the lake. In part this is due to the full range of proposed restoration actions not being able to be implemented. In particular the lake weed harvesting activity that seeks to break the internal cycle within the lake that leads to cyanobacteria blooms in the lake. A detailed report on Lake Horowhenua was provided to the Regional Council meeting in September 2018.
Lake Pauri and Wiritoa 14.5. In 2013, through Envirolink funding, Horizons commissioned a restoration plan and gap analysis for Lakes Pauri and Wiritoa to enable works to reduce the extent and frequency of algal blooms that result in the closure of the lakes to contact recreation. 14.6. The report made a number of recommendations in terms of monitoring and its frequency as well as implementation actions that would aid in improving the health of the lakes. Some of the actions identified in the plan had already began to be implemented and others are a work in progress although progress has not been as fast as some would like mostly due to the ability to fund the interventions or a willingness of other parties to implement actions that were identified within the plan. 14.7. One of the key recommendations from the report was the removal of the stormwater discharge from the Whanganui Prison to the connecting stream between Lake Pauri and Wiritoa. Horizons has recently notified a consent application from Corrections to seeking the continued discharge of stormwater to the Lakes.
Lake Oporoa 14.8. As part of the Ngā Puna Rau o Rangitīkei project (the Rangitīkei Te Mana o Te Wai project) an intensive period of monitoring was undertaken to help inform the development of a restoration plan for Lake Oporoa. Lake Oporoa is near Utiki and close to the confluence of the Rangitīkei and Hautapu Rivers. The lake has significant cultural importance and was frequently used (and still is on some occasions) for the harvest of
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Strategy and Policy Committee 12 March 2019 tuna. Due to the recent blue-green algal blooms the frequency of tuna harvesting has decreased. 14.9. The monitoring on the lake involved the deployment of a continuous buoy for five months, monthly water quality sampling over this period, collection of sediment samples and the completion of LakeSPI monitoring. All this information was provided to Cawthron to enable the development of a restoration plan. 14.10. This restoration plan identified five main areas in which actions needed to be undertaken to restore the health of the lake. These five areas being: Riparian management (removal of deciduous trees around the lake margin and replacement with native vegetation); Lake aeration; Legacy sediment; Cyanobacterial bloom control; and Aquatic plant re-establishment. 14.11. Further details and options from each of the above headings were included within the report; a copy of the report can be made available on request. The Ngā Puna Rua o Rangitīkei project is currently in the process of having the poplars removed from the hillside, and native vegetation is being replanted.
Lake Waipu 14.12. Lake Waipu is also receiving significant investment through the Freshwater Improvement Fund (FIF) administered through the Ministry for the Environment, with co-funding from Rangitīkei District Council and Horizons Regional Council. A number of other partners are also involved in the delivery of this five-year project, which is overseen by a working group that includes members from the local iwi, hapu and the community of Rātana. 14.13. The majority of this funding ($1.75 million) is to be dedicated to the removal of the Rātana Wastewater discharge to Lake Waipu and to apply the wastewater to land. This sub-project is led by Rangitīkei District Council and partners. The remaining resourcing is dedicated to a five-year monitoring programme, led by Horizons, to inform the development of a restoration plan. This restoration plan will include potential in-lake and catchment-wide interventions. The discharge of wastewater to the lake has created a legacy load of nutrients that will likely require intervention in some form.
15. Lake Restoration Planning Reports 15.1. To aid in the development of further lake restoration action plans, Horizons recently commissioned two Envirolink projects to undertake a gap analysis on the information that Horizons holds to enable further restoration plans for the regions lakes to be developed. The reports looked at both deep and shallow coastal lakes as lake processes as slightly different in each. These reports were received at the end of 2018 and provide important guidance on the types of information that needs to be collected. 15.2. The reports identified that the information that Horizons currently holds is limited. Investment in the collection of this data and science is required to enable further restoration plans to be developed. Given the uniqueness of lakes, it is likely that these plans will need to be developed on an individual, lake by lake, basis. Stakeholder engagement is also an important component of restoration plan development for lakes. 15.3. An important thing to remember for this gap analysis is that although information gaps have been identified, this does not mean that no restoration works can be undertaken until these gaps are filled. There are general principles in lake restoration that are known to aid in restoration i.e. removal of nutrient and sediment inputs into these systems such as the
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Strategy and Policy Committee 12 March 2019 removal of the Rātana Wastewater discharge to Lake Waipu or the sediment trap for Lake Horowhenua. However, caution needs to be taken when contemplating some restoration activity in the absence of good information as implementation of the wrong solution for a lake has the potential to result in limited change or potentially further degradation (including potential for irreversible change). 15.4. The reports provide a range of recommendations for monitoring including: . Increasing lake water quality monitoring to a monthly time-scale to support state and trend analysis; . Increasing the number of lakes in monitoring programme to be more representative of the lake types found within the region; . Undertaking the collection continuous data to establish stratification events, residence times and groundwater inputs (monitoring to include lake level and water quality parameters – for example temperature and dissolved oxygen); . Implementing pest fish surveys to assess pest fish impact on internal nutrient cycling within the lakes; and . Undertaking heterocyte counts on quarterly cyanobacteria analysis over a year of monitoring as an indication for N-fixation potential in monitored lakes. 15.5. Additionally the reports recommended one-off research that could also inform the development of restoration plans, including: . One-off investigations of sediment geochemistry to determine the likely extent of internal nutrient loading from sediments during anoxic or high-pH events (collection of sediment cores); . Introducing surface and groundwater monitoring to enable mass balance modelling of nutrient loads and water balances of the regions lakes. Note, in most cases this will installation of piezometer’s and monitoring bores, as insufficient surface water monitoring of inflows and outflows exist; . Further bathymetric surveys of study lakes; . One-off seasonal nutrient limitation investigations of a selection of priority lakes, including nutrient ratios and nutrient bioassays; . Continuation of one-off seasonal macrophyte biovolume surveys (LakeSPI); . Waterbird counts to quantify nutrient loading by birds; and . Paleolimnological investigations of a few priority lakes to evaluate reference conditions for dune lake types in the region and paleo-history of water quality. 15.6. These recommendations are helpful to inform future work for Council however are outside of the current resourcing for the programme. As a part of the work programme in the next financial year, a group of experts will be engaged to work with Horizons staff to review the lakes programme including establishing a range of options for upgrading the monitoring programme to improve overall reporting on lakes in relation to the national and regional policies and to inform potential restoration work. This will include an option to reconfigure the use of current budget and options for increased investment. The outcomes of this work will be reported to Council for consideration.
16. Lake Processes 16.1. One of the findings of the reports and more recent monitoring information is the risk of some lakes potentially ‘flipping’. Lake Dudding and more recently Lake Wiritoa have been identified as having this potential risk. This section discusses the specific of the two lakes, after a brief description of the lake processes involved. 16.2. Lakes are likely to be most stable and in the best ecological condition if their catchments are predominantly in indigenous vegetation (or at least forested), connected to large wetland systems, surrounded by extensive beds of emergent vegetation, and when diverse native aquatic vegetation is present.
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Strategy and Policy Committee 12 March 2019 16.3. Many of the regions lakes have no permanent outflow effectively meaning that any material that enters them such as nutrients, sediment etc. is trapped unless it is able to exit via groundwater. In these systems it effectively means that they are susceptible to nutrient inputs as the nutrients build up over time and even those soluble nutrients that may become bound to sediment particles can be released through internal lake processes such as high pH and/or low dissolved oxygen. A process known as internal nutrient cycling, with this particularly being seen with phosphorus in some lakes in the region. 16.4. Many lakes undergo thermal and/or chemical stratification, a process that results in three distinctive layers within the lake. Temperature driven shifts in water density lead to cooler, denser water sinking to the bottom of the lake forming the hypolimnion. The surface layer with warmer less dense water is called the epilimnion. The metalimnion or thermocline separates these two layers. When swimming, people may observe the surface water in a lake being warm and then the lower layer (around their feet) being colder. Often the stratification is strong enough that no mixing occurs between these layers and the hypolimnion (deeper water) is cut off from oxygen supply. Oxygen-dependent nutrient cycling processes continue until oxygen is used up eventually turning the hypolimnion into an anoxic environment. 16.5. While this process occurs naturally, it can be impacted by increased nutrient in the lake. Increased nutrient can result in further macrophyte growth. The macrophytes eventually die and sink to the bottom into the hypolimnion. The nutrients from these organic materials are then processed through anaerobic reactions which favour the accumulation of sulphide, phosphate and ammonia. The latter two are also released from the sediment under anoxic conditions which further increases their concentration in the hypolimnion. This process is called internal loading. The higher the nutrient load into the lake (internal and external loading) the stronger these effects can be. This can result in ‘dead zones’ in lakes that oxygen-dependent organisms will have to avoid in order to not suffocate. 16.6. Within changing weather and seasons the surface lake water will cool and water layers will mix again. This process is called “lake turning” and can be accelerated through wind. When the lake turns, phosphate and ammonia from the former hypolimnion will become available to macrophytes and phytoplankton species (including toxin producing cyanobacteria) and can contribute to toxic algal blooms and excessive macrophyte growth when daylight hours become longer and water surface temperatures become warmer again, thus completing the cycle. 16.7. While these effective recycling systems in lakes secure the survival of many organisms under natural conditions, once a certain threshold of cumulative nutrient input is reached, the internal loading of the lake alone will be sufficient to support toxic algal blooms and the formation of dead zones. At this stage, restoration of these lakes can become extremely time and resource intensive. 16.8. If no action is taken and internal and external nutrient loads remain high, dead zones in lakes can extend extensively and the conditions in the lake shift to a stage where macrophytes cannot survive. Phytoplankton becomes dominated by cyanobacteria (some of which can produce toxins) which are the only organisms capable to thrive under such conditions. The shift from this macrophyte-dominated to cyanobacteria-dominated state in a lake is called “lake flipping” (Figure 9). Although this process can be cyclic, such as in Lake Horowhenua, which is driven as a result of the macrophyte species present, in many cases a lake will remain algal dominated unless intervention action is taken to reverse the change. The reversal of a lake that has flipped will be costly exercise as it requires a significant reduction in the algae present within the lake to allow sunlight to reach the lakebed. It will also require the re-establishment of macrophytes which, depending on the seed source remaining in the lake bed, may require the importing of macrophytes from other lakes within the region. All of these interventions are required in-lake while also ensuring that the conditions that first resulted in the lake flipping in the first place are not repeated i.e. a plan developed and implemented for in-lake and catchment interventions.
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Figure 9 Image showing that lake flipping occurs when nutrients in lakes drive the lake from a macrophyte dominated trophic state to an algal-dominated trophic state. Image courtesy of NIWA. Lakes showing signs of flipping - Lakes Wiritoa and Dudding 16.9. Recent sampling has identified some potential risks for Lake Dudding and more recently Lake Wiritoa. The results for Lake Dudding were presented to Council late last year. 16.10. Further information is being gathered for these lakes prior to a workshop with lake experts to assess any additional information that is needed, an assessment of potential intervention options, information on the degree of risk of flipping and level of urgency for action. A workshop with lake experts for Lake Dudding is currently being developed in collaboration with Rangitīkei District Council and is planned to occur in this financial year. A similar workshop is intended next financial year for Lake Wiritoa following further data collection. Workshop outcomes will be reported to Council.
17. Lake science
Lake Catchment Modelling 17.1. Assessments of interaction between groundwater and surface water have traditionally focussed on Lake Horowhenua (Phretos, 2050 and GNS, 2010). In 2014 PDP and NIWA completed a water balance and lake health assessment for Lake Horowhenua. These reports encompass both an assessment of the water balance and the effects that abstraction of groundwater has on lake health. While attempts have been made in the past to quantify a water balance for the catchment, this report provides quantification of the uncertainties of the water balance and relates water abstraction with water quality effects in the lake itself. This has informed both the immediate management of water allocation and provided direction for acquiring key information that will improve long-term management of water in this area. The Lake Horowhenua Freshwater Improvement Fund project, led by
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Strategy and Policy Committee 12 March 2019 the Lake Horowhenua Trust, will see the collection of some of this key information to further inform the long-term management of the Lake. This sub-project is being led by Horizons Regional Council. 17.2. Further to this, work has focussed on generating groundwater capture zones for the 26 coastal lakes identified in One Plan evidence to enable understanding of all contributors to lake water quality. This work was initially completed by PDP in August 2017 and then refined by Jacobs for Pukepuke Lagoon in October 2017 to include a catchment water balance assessment. In June 2018, Jacobs was contracted to complete a water balance for Lake Koitiata. Enhancing the health and resilience of New Zealand’s lakes 17.3. Horizons has partnered with the University of Waikato, NIWA, Cawthron, GNS, and the University of Otago, along with other partners, to explore a range of opportunities to enhance the health and resilience of New Zealand’s lakes. The MBIE-funded programme began in 2016, concludes in September 2019, and aims to provide underpinning research that supports the implementation of effective and targeted restoration of New Zealand lakes. 17.4. The project addresses declining water quality and biodiversity in lakes at catchment, regional and national scales. Case studies linked to the Horizons Region include the development of a geospatial platform to support mana whenua in the restoration of lakes, and sediment and water quality monitoring to understand legacy sediment and nutrient cycling in Lake Horowhenua. Lakes 380 – Unlocking the history of our lakes 17.5. In order to tailor successful restoration programmes, we need to know what drivers are behind the historical and current environmental conditions of each lake. Lake sediments are natural archives that can provide information on current and historical aquatic communities, water quality and changes in the landscape. 17.6. A national programme run by GNS Science and the Cawthron Institute in partnership with iwi and regional councils, is now seeking to unravel the history of our nation’s lakes. The Lakes 380 project aims to characterise the health of New Zealand lakes by analysing sediment cores from 380 locations nationwide, including 18 locations in the Horizons Region. Using a range of techniques, the team will explore how New Zealand lakes have changed over the past 1000 years. 17.7. The lakes to be sampled in the Horizons region range from our coastal dune lakes such as Lake Waiwiri, through to our back country lakes such as Lake Kokopunui (Lake Colenso) and our hill country landslide lakes such as Lake Pounamu. This programme is to be completed over the next few years with planning already underway.
18. Next Steps 18.1. An initial workshop with lake experts is to be held this financial year for Dudding Lake, with an aim to obtain recommendations around any further information that is needed, an assessment of potential intervention options, information on the degree of risk of flipping and level of urgency for action. This workshop is being developed in collaboration with Rangitīkei District Council. A similar workshop is intended for Lake Wiritoa following initial data collection. Workshop outcomes will be reported to Council. 18.2. As a part of the work programme in the next financial year, a group of experts will be engaged to work with Horizons staff to review the lakes programme including establishing a range of options for upgrading the monitoring programme to improve overall reporting on lakes in relation to the national and regional policies and to inform potential restoration work. This will include an option to reconfigure the use of current budget and options for
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Strategy and Policy Committee 12 March 2019 increased investment. The outcomes of this work will be reported to Council for consideration.
19. SIGNIFICANCE 19.1. This is not a significant decision according to the Council’s Policy on Significance and Engagement.
Janine Kamke SCIENTIST – WATER QUALITY Lizzie Daly SCIENTIST – ECOLOGY Barry Gilliland SENIOR POLICY ANALYST Abby Matthews SCIENCE AND INNOVATION MANAGER Logan Brown FRESHWATER AND PARTNERSHIPS MANAGER Jon Roygard GROUP MANAGER NATURAL RESOURCES & PARTNERSHIPS
ANNEXES There are no attachments for this report.
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