Lake Rotoma Action Plan ISSN: 1175 9372 (Print) ISSN: 1179 9471 (Online) Environmental Publication 2009/04 November 2009 (As amended April 2011) THE ROTORUA LAKES Protection and Restoration Action Programme A Bay of Plenty Regional Council, Rotorua District Council and Te Arawa Lakes Trust joint project Environment Bay of Plenty, Rotorua District Council, Te Arawa Lakes Trust i Contents Status of Action Plan ........................................................................................... i Chapter 1: Introduction ...................................................................................... 1 1.1 Lake Rotomā .................................................................................................. 1 1.2 What’s the problem? ....................................................................................... 2 1.3 What’s causing the problem? ......................................................................... 5 1.4 Why has this Action Plan been developed? ................................................... 6 1.5 Delivering the Action Plan .............................................................................. 7 Chapter 2: Reducing and preventing nutrient loading from point sources .............................................................................................................. 9 2.1 Nutrients from wastewater entering Lake Rotomā .......................................... 9 Chapter 3: Reducing and preventing nutrient loading from diffuse sources ............................................................................................................ 11 3.1 Nutrients leached to Lake Rotomā as a result of farming ............................. 11 3.2 New advances in technology ........................................................................ 12 3.3 Exploring wetland enhancement .................................................................. 13 3.4 Preventing nutrient release as result of land use .......................................... 14 Chapter 4: Improving knowledge of nutrient sources ........................... 15 4.1 Uncertainty regarding phosphorus entering Lake Rotomā in groundwater ... 15 Chapter 5: Reviewing regulatory interventions ....................................... 17 5.1 Statutory regulatory methods ....................................................................... 17 Chapter 6: Action Plan implementation timeline ..................................... 19 6.1 Implementation timeline ................................................................................ 19 Lake Rotomā Action Plan November 2009 ii Environment Bay of Plenty, Rotorua District Council, Te Arawa Lakes Trust Appendices .......................................................................................................... 21 Appendix 1 - Trophic Level Index (TLI) and other indicators ..................................... 23 Appendix 2 - Estimated nutrient loss from the catchment ......................................... 27 Appendix 3 - Calculation of Lake Rotomā’s nutrient reduction target ....................... 29 Appendix 4 - Regional Water and Land Plan Methods 41, 42, 47 and 52 (as applicable to Lake Rotomā) ................................................................. 31 Appendix 5 - Working Party ...................................................................................... 35 November 2009 Lake Rotomā Action Plan Environment Bay of Plenty, Rotorua District Council, Te Arawa Lakes Trust iii Status of Action Plan This Action Plan is a non-statutory document. This means that it does not contain rules and cannot require changes to other statutory documents. It provides guidance for the management of Lake Rotomā. It may or may not result in changes to planning documents. Some of the actions may require resource consent. Any such decision will be made at the discretion of individual agencies and will follow statutory process. The Action Plan is a live document and regular reviews will be undertaken to keep it up to date with science, technology and community expectations. Lake Rotomā Action Plan November 2009 1 Chapter 1: Introduction 1.1 Lake Rotomā 1.1.1 Overview This Action Plan encompasses Lakes Rotomā and its catchment (refer Figure 2). It sets out what interventions (or actions) should be undertaken to reduce nutrient (phosphorus and nitrogen) inputs to Lake Rotomā. The Action Plan is a community document as all parts of the community are working together to improve water quality in Lake Rotomā. This Action Plan outlines current known actions and sets out processes to identify future actions to improve water quality in Lake Rotomā. 1.1.2 Background information Formed by volcanic eruptions approximately 8,500 years ago, this eastern-most of the Rotorua Lakes has two distinct basins. The northern basin is the deepest at 83 metres, and the southern basin has a maximum depth of 73.5 metres. The lake surface area is about 1,112 hectares. The lake has a small outflow through porous pumice substrate to Lake Rotoehu, and has some outflow to groundwater. Lake Rotomā means clear water. Lake Rotomā is the cleanest of all the Rotorua Lakes, with around 11 metres water clarity. Figure 1 View from Matahi Bay – southern end of Lake Rotomā Lake Rotomā Action Plan November 2009 2 Environment Bay of Plenty, Rotorua District Council, Te Arawa Lakes Trust Table 1 Lake Rotomā at a glance Population Catchment area (km²) Lake area (km²) Max depth (m) Mean depth (m) 258 29 11 83 37 1.1.3 Tangata whenua “The relationships of tangata whenua with Lake Rotomā and its catchment are longstanding and endure. Recognition and provision for their active, ongoing involvement as kaitiaki is a matter of national importance.” – Ngati Awa and Te Arawa. 1.1.4 Community perspective Rotomā is valued by its community for its clean water, healthy ecosystems, recreational and cultural values. “It’s vital that the lake stays in good nick because so much business comes from people who are out here waterskiing and fishing and so on. Rotomā is in good shape but it's also deteriorating – far better to spend the money now to keep it clear than to clean it up down the track." – Keith Marx “Every landowner and leaseholder should be aware that if Lake Rotomā deteriorates to a stage where it is closed for algal blooms then their life style of water skiing fishing etc is no longer available plus the down value of their properties so its up to everybody to make an effort to save the lake not waiting for somebody else to do it or hoping the problem will go away.” - Rae Green 1.2 What’s the problem? The Rotorua Lakes are under pressure from development, land use and other activities that have resulted in a deterioration of lake quality. Twelve of the lakes are in a state of long term deterioration, primarily due to excess nutrient inputs. Lake water quality will continue to deteriorate for the foreseeable future unless the causes are permanently addressed. Although Lake Rotomā has the best lake water quality out of the 12 large Rotorua Lakes in the Bay of Plenty region there are some indicators that lake water quality is slowly getting worse.1 1.2.1 Dissolved oxygen Dissolved oxygen in the bottom waters of the lake has decreased significantly from 1993 to 20061. Although the oxygen levels are still high enough to support bottom- dwelling aquatic life, the decline indicates that water quality is deteriorating. When a lake becomes oxygen-depleted (anoxic) in its bottom waters (usually around a TLI of 3.1 – 3.5, like Lakes Tikitapu and Okareka)2, sediment-bound nutrients are released into the water column. This release of nutrients can change 1 During the 1992 – 2006 water quality analysis period that Environment Bay of Plenty has monitored Scholes, P., Bloxham, M. Rotorua Lakes Water Quality 2006 Report. Environment Bay of Plenty Environmental Publication 2007/12. 2 An explanation of TLI is given in section 1.2.5. November 2009 Lake Rotomā Action Plan Environment Bay of Plenty, Rotorua District Council, Te Arawa Lakes Trust 3 the nutrient status of the lake. As a lake becomes eutrophic (nutrient enriched), the nutrient cycling from lakebed sediments starts to dominate lake water quality. Figure 2 Lake Rotomā catchment Lake Rotomā Action Plan November 2009 4 Environment Bay of Plenty, Rotorua District Council, Te Arawa Lakes Trust 1.2.2 Phosphorus The estimated phosphorus load to Lake Rotomā is 736 kg/yr Total phosphorus concentrations in the lake have approximately doubled since 1992 in the bottom and surface waters3. Lake Rotomā tends to be phosphorus-limited, meaning that phosphorus is the limiting factor that controls the growth of algae. 1.2.3 Nitrogen The estimated nitrogen load on Lake Rotomā is 18,110 kg/yr. Total nitrogen concentrations in Lake Rotomā have stayed relatively constant since 1990, despite year-to-year fluctuations. However, since 1992 there has been an increase in ammonium-nitrogen and nitrate-nitrogen concentrations in the bottom waters which mixes throughout the lake in mid-winter each year. Nitrogen levels are increasing in the lake although this increase is not statistically significant at this stage. 1.2.4 The Balance between nitrogen and phosphorus Maintaining the balance between Nitrogen and Phosphorus is important to restore the lake to its former quality. In most of the Rotorua lakes, the lower the N:P ratio, the poorer the water quality. The nitrogen:phosphorus (N:P) ratio in Lake Rotomā has decreased from about 40 in 1994 to 25 in 2008 which is another indicator that