Summary of recommendations
Recommendation 1: That the Rotorua Lakes Restoration and Protection Programme is written up as a brief document to explain how all of the elements, from Research and Monitoring to Regulations, are brought together to produce and implement the best management options through Lakes Action Plans.
Recommendation 2: That Environment Bay of Plenty (EBOP) considers developing supplementary lake quality indicators to focus on the factors that cause algal problems in the Rotorua lakes that will complement the trophic level index.
Recommendation 3: That as far as practicable, monitoring should be extended into the catchments and sub-catchments with the highest nutrient inputs to characterise any 'point' sources that may become a priority for management.
Recommendation 4: EBOP should work with the Western Australian Department of the Environment to investigate the use of its catchment monitoring system in the Lake Rotorua Catchments to measure the efficacy of catchment management measures.
Recommendation 5: EBOP should consider developing a simple catchment model that can be co-operatively used by landowners and community groups to see how nutrients move through their catchments as an aid to understanding how they can be managed.
Recommendation 6: EBOP should consider carrying out hydrogeological investigations to determine the chemistry of the younger deeper groundwater and use this and other information to develop a 'mid-level catchment model', to enable land managers to estimate how proposed land use changes and/or mitigation measures will modify nutrient concentrations in the deeper groundwater.
Recommendation 7: EBOP and Rotorua District Council (RDC) should carry out more detailed monitoring of storm-flows into Lake Rotorua, especially in the late spring, summer, autumn period to determine if these 'events' are initiating or prolonging blue-green blooms.
Recommendation 8: That EBOP approaches the Western Australian Department of the Environment to form a partnership to jointly trial and develop Phoslock for nutrient stripping in catchments and water bodies, separately and in conjunction with other nutrient management methods.
Recommendation 9: EBOP should investigate the use of Allaphanic soils and related clays for use in stripping phosphorus and as a substrate for preparation of Phoslock.
Recommendation 10: That EBOP urgently investigate options to strip phosphorus from streams that have high levels of phosphorus coming from springs and other sources, starting with the Waingaehe, Hamurana and Awahou streams.
Recommendation 11: That EBOP and RDC divert the flow from the Tikitere geothermal field to the Rotorua District Sewage Treatment Plant as a high priority.
Recommendation 12: That EBOP and RDC establish a zero target for nutrient inputs from the Rotorua Land Treatment Site to Lake Rotorua.
Recommendation 13: Repeat studies of the nutrient stripping processes and pathways at the Rotorua Land Treatment Site should be undertaken under the new spray regime to determine the nutrient stripping effectiveness.
Recommendation 14: Wetlands within and below the Rotorua Land Treatment Site should be modified if necessary to strip any residual nutrients 'leaking' from the spray irrigation areas.
Recommendation 15: The RDC should continue to monitor nutrient levels above and below the Rotorua Land Treatment Site to measure its efficiency at stripping nutrients as spray volumes are increased to cope with increasing population.
Recommendation 16: That EBOP identifies opportunities for constructed and enhanced natural wetlands to strip nutrients in the catchments and on the foreshores of Lake Rotorua and, as a high priority, construct or enhance such wetlands where there are opportunities to intercept high nutrient level base-flows.
Recommendation 17: EBOP and RDC could consider the use of certified and contractually managed Alternative Treatment Units with nutrient stripping capacity in nutrient sensitive areas where reticulated sewerage is too costly or too difficult.
Recommendation 18: That EBOP continues to support investigations that are aimed at clarifying the relationships between catchment and internal lake nutrient loads, lakes water quality and algal blooms.
Recommendation 19: That EBOP focuses in the short-term on investigations that will set clear targets for:
- an annual total catchment load for Lake Rotorua for phosphorus and nitrogen that builds in capacity for future development around the lake
- annual catchment phosphorus and nitrogen load targets for each of the main Lake Rotorua catchments
- internal lake phosphorus and nitrogen load targets for Lakes Rotorua and Rotoiti
- annual average stream phosphorus and nitrogen concentration targets for each of the nine Lake Rotorua catchments
- annual average lake water quality phosphorus and nitrogen concentration targets for Lakes Rotorua and Rotoiti.
Recommendation 20: That EBOP focuses as a priority in the short-term on studies and investigations leading to management measures that reduce lake total nitrogen and lake total phosphorus concentrations and produce a high N:P ratio of 20-22:1 or greater in Lakes Rotorua and Rotoiti, especially during the late spring, summer and autumn period.
Recommendation 21: That EBOP focuses in the short-term on monitoring of the stratification and destratification, and sediment resuspension events over the most common meteorological conditions in Lake Rotorua, including concurrent monitoring of the Ohau Channel to provide critical data for management.
Recommendation 22: That EBOP uses the data collected from implementation of Recommendation 21 to interactively carry out hydrodynamic modelling to quantify the quantities and timing of nutrients and phytoplankton transport through the Ohau Channel into Lake Rotoiti.
Recommendation 23: That EBOP initiates studies to characterise the geothermal inputs to Lake Rotoiti, especially to determine if they contribute nutrients and how they interact with other hydrodynamic processes to cause algal blooms.
Recommendation 24: EBOP should work with NIWA and Professor David Hamilton to establish a more frequent monitoring regime for Lakes Rotorua and Rotoiti to gain a better understanding of the processes that cause algal blooms, especially blue-green blooms, as a basis for management measures that will best eliminate or reduce them.
Recommendation 25: That EBOP continues to pursue as a high priority further monitoring and hydrodynamic modelling of the flow of the Ohau Channel into Lake Rotoiti as the basis for short-term management decisions on manipulation of this flow to improve the health of the lake and reduce or eliminate blue-green blooms.
Recommendation 26: That EBOP and RDC initiate engineering design and construction of temporary groynes on either side of the entrance of the Ohau Channel to minimise transportation of suspended material into Lake Rotoiti. Permanent structures can be constructed when the best configuration to minimise transport of suspended material is determined.
Recommendation 27: That EBOP and RDC begin engineering investigations and designs for trial structures to divert the Ohau Channel to the Kaituna and/or Okawa Bay as soon as possible, and interactively with the monitoring and modelling work that has been recommended in Recommendations 24 and 25, so that work on trial structures can begin as soon as resource consent approvals have been obtained.
Recommendation 28: That EBOP builds temporary structures to test the favoured options for diversion of the Ohau Channel to the Kaituna River and/or Okawa Bay when resource consent approvals have been obtained, and monitor the trials to further refine the hydrodynamic models for the channel flows and the western end of Lake Rotoiti before building any more permanent diversion structures.
Recommendation 29: That EBOP continues trials with nutrient stripping materials such as Alum and Phoslock and begins trials with direct oxygenation separately and in combination, to determine the best methods of using these methods to reduce nitrogen and phosphorus in the lakes and manipulate the N:P ratio.
Recommendation 30: That the use of oxygenation and nutrient stripping materials be built into the modelling proposed in Recommendation 27 so as to inform any trials and help predict the best options for using these management methods individually and together in Lakes Rotorua and Rotoiti.
Recommendation 31: That EBOP and RDC investigate the use of oil pollution booms to contain and concentrate the worst algal blooms, and the use of 'suction trucks' to remove the worst of the accumulations.
Recommendation 32: That EBOP and the RDC, in liaison with the appropriate authorities, investigate the potential use of herbicides to control blue-green algal blooms.
Recommendation 33: That EBOP considers working with NIWA to develop an algal bloom risk prediction capacity for both longer periods (three months) and shorter periods (10 days or less).
Recommendation 34: That EBOP continues to work with Environment Waikato, and other organisations carrying out lake investigations, to share information and contribute to joint studies and management trials where appropriate.
Recommendation 35: That EBOP considers ways of better co-ordinating and focusing the scientific investigations that will underpin the preferred short- and longer-term management measures.
Recommendation 36: That EBOP continues to work with Fish and Game New Zealand and the University of Waikato to support investigations into the impact of the decline of Lakes Rotorua and Rotoiti on the trout fishery.
Recommendation 37: That EBOP works with other organisations, such as the Department of Conservation and the Ministry for the Environment, to develop readily measurable lake ecosystem health indicators as an aid to measure the success of short- and longer-term management measures.
