Lake Ngatu MANAGEMENT PLAN CONTENTS

1. PURPOSE...... 3

2. INTRODUCTION...... 3

3. LAKE LOCATION MAP...... 5

4. LAKE OVERVIEW...... 6

5. SOCIAL AND CULTURAL DIMENSION...... 7

6. PHYSICAL CHARACTERISTICS...... 8

7. CHEMICAL CHARACTERISTICS...... 17

8. BIOLOGICAL CHARACTERISTICS...... 23

9. LAND USE...... 27

10. MONITORING PLAN...... 29

11. WORK IMPLEMENTATION PLAN...... 30

12. BIBLIOGRAPHY...... 31

13. APPENDIX 1. GLOSSARY...... 32

2 LAKE NGATU MANAGEMENT PLAN | Introduction

1. Purpose LAKE NGATU MANAGEMENT PLAN The purpose of the Outstanding Northland Dune Lakes Management Plans is to implement the recommendations of the Northland Lakes Strategy Part II (NIWA 2014)1. PURPOSE by producing Lakes Management formedPlans, between starting stabilised with sand the dunes 12 along ‘Outstanding’ the west coast, represent a large proportion of warm, lowland valueThe purposelakes ,of and the Outstanding by facilitating Northland actionsDune with mana whenua iwi, landowners and other lakes in New Zealand which still have relatively good stakeholdersLakes Management in thePlans lakeis to implement catchments the to deliver priority work which will protect water water quality and high ecological values. qualityrecommendations and mitigate of the Northland current Lakes pre Strategyssures. Part II (NIWA 2014) by producing Lakes Management

Plans, starting with the 12 ‘Outstanding’ value The outstanding dune lakes are grouped on the 2. Introduction lakes, and by facilitating actions with mana whenua Aupouri, including Sweetwater, Karikari and Pöuto iwi, landowners and other stakeholders in the lake Peninsulas and the Kai Iwi group North of Dargaville. Thecatchments following to deliver text priority is worktaken which directly will protect from the Northland Lakes Strategy. Northland dunewater lakesquality and and mitigate their current pressures.associated wetlandsThe lakes vary are in size, of with nationalthe majority beingand international significance. These lakes, most of whichbetween have 5 beenand 35 hectaresformed in areabetween and generally stabil less ised sand dunes2. INTRODUCTION along the west coast, represent athan large 15 metres proportion deep. Lake Taharoa of warm, of the Kailowland Iwi lakes in Group is one of the largest and deepest dune lakes in NewThe followingZealand text iswhich taken directly still from have the Northland relatively good water quality and high ecological the country, covering an area of 211.07 hectares and values.Lakes Strategy. Northland dune lakes and their being 38.81 metres deep. Lake Taharoa also has the associated wetlands are of national and international deepest recorded submerged vegetation of any lake Thesignificance. outstanding These lakes, dune most oflakes which haveare been grouped on the Aupouri, including Sweetwater, Karikari and Pōuto Peninsulas and the Kaiin the Iwi North group Island, North to 24 metres. of Dargaville.

The lakes vary in size, with the majority being between 5 and 35 hectares in area and generally less than 15 metres deep. Lake Taharoa of the Kai Iwi Group is one of the 3 largest and deepest dune lakes in the country, covering an area of 211.07 hectares and being 38.81 metres deep. Lake Taharoa also has the deepest recorded submerged vegetation of any lake in the North Island, to 24 metres.

The dune lakes generally have little or no continuous surface inflows or outflows, being primarily fed by rainfall directly onto their surfaces and surrounding wetlands. As a result, their levels fluctuate considerably with climatic patterns. As most of the lakes are relatively small and shallow, they have limited capacity to assimilate any contaminants. They are prone to nutrient enrichment from stock and fertiliser,

LAKE NGATU MANAGEMENT PLAN | Introduction

The dune lakes generally have little or no continuous Recreational and commercial activities on or around surface inflows or outflows, being primarily fed by some of the lakes can affect water quality, lake rainfall directly onto their surfaces and surrounding ecology and increases the risk of introduction of pest wetlands. As a result, their levels fluctuate considerably weeds and fish. with climatic patterns. As most of the lakes are relatively small and shallow, they have limited capacity The Northland Lakes Strategy (NIWA 2012) presents a to assimilate any contaminants. They are prone classification and ranking system for Northland lakes to nutrient enrichment from stock and fertiliser, including assessment of ecological values and lake particularly where lakeside vegetation has been grazed pressures and threats. The 12 highest ranked lakes or removed, and where there is direct stock access from north to south are: to the lake. Further effects on the lakes result from Outstanding (12) forestry fertilisation, sediment mobilisation during • Lakes - Wahakari, Morehurehu, Waihopo, harvest and water budget dynamics. Ngatu, Waiporohita, Waikare, Kai iwi, Taharoa, Humuhumu, Kanono, Rotokawau These lake and wetland ecosystems are important and Mokeno habitats for a wide variety of plant and animal species, some of which are regionally or nationally significant Northland Lakes Strategy (NIWA 2012, 2014) because of their rarity. These include birds such as recommends that individual lake management plans the pateke/brown teal, banded rail, New Zealand should be developed for each high value lake. This dabchick, marsh crake, fern bird and Australasian would include: bittern, the aquatic plants Hydatella inconspicua and • Descriptions of each lake and lake catchment Myriophyllum robustum and native freshwater fish • Outline of lake values and significance including the giant kokopu, banded kokopu, short (including ecological and social) jawed kokopu, inanga, dwarf inanga and dune lakes • List of agencies and individuals involved in galaxias. management

The most outstanding characteristic of these lakes is • Communications plan the limited impact of invasive species on their biota, • Monitoring plan which is unparalleled elsewhere on mainland New • Identification of gaps in knowledge/research Zealand. Despite these values, the status of these lakes plan is not secure and the overall trend has been gradual • Current threats and pressures deterioration. • Management actions to mitigate or ameliorate threats and pressures Northland Regional Council monitors water quality • Work implementation plan quarterly in 26 dune lakes and undertakes ecological monitoring, along with NIWA, for ~90 dune lakes on an annual rolling basis. Annual weed surveillance Key principals of lake management are: is undertaken at high value lakes with public access. • Balance between protection and utilization Threats and pressures include biosecurity (aquatic • Managing the environmental quality of the weeds, pest fish and the risk of invasion and spread), catchment, in particular water quality eutrophication from surrounding land use for farming • Integrated management of habitat and species and forestry, occurrence of algal blooms and water (including pests) level fluctuations, especially dropping lake levels. • Monitoring as a key environmental Natural events such as summer droughts and high management tool rainfall events place further pressure on these lakes.

4 LAKE NGATU MANAGEMENT PLAN | Lake Location Map

The plan takes the approach of presenting robust Further south within Northland, on the west coast information on all aspects of the lakes. This includes north of Dargaville, are the three Kai Iwi Lakes (Lake Kai social and cultural, physical, chemical and biological Iwi itself, and Lakes Taharoa and Waikare, sometimes summaries of information not generally available to referred to as Waikere). the public in a condensed format. This data is the best available at the time of writing and does not represent Finally, four outstanding lakes on the Pöuto Peninsula, peer-reviewed science in the sense that errors may be on the north head of the Kaipara Harbour, round out inherent in the raw data and presence and absence the final twelves lakes of covered in the Outstanding of species changes over time. Yet it offers trends for dune lake plans. These include the west Pöuto Lake further discussion among partners involved in protection Mokeno and the east Pöuto lakes Humuhumu, Kanono and restoration activities. The plan goes on to scope and Rotokawau (Pöuto). required work for the mitigation of threats and offers a communication strategy to implement this work. Most lake names come from te reo Mäori and, therefore, some names refer to several lakes around 2.1. Geographic Lake Groupings Northland. Rotokawau is a name given to several The outstanding dune lakes within these plans all sit lakes, with one in Pöuto, two in Karikari and one in within two broad ecological districts; Aupouri and Sweetwater. Additionally, the word “kawau” means Kaipara. Within these two districts there are further the waterbird shag or cormorant and two additional geographical associations of lakes, especially relevant to lakes are also called Shag Lake. To avoid confusion, biosecurity species spread. lakes sharing a name are further referred to with their sub-regional area following in parentheses. Within the Aupouri group, there are three lakes situated near Parengarenga and Houhora Harbours on the narrow LINZ topographic maps do not legally name every Aupouri Peninsula (Lakes Wahakari, Morehurehu and freshwater body. Therefore, for the purposes of the lake Waihopo). plans, additional common lake names are used which are the same as those used in the NIWA ecological At the base of the Aupouri peninsula, another cluster of surveys. These may not be the same as traditional lakes form the west coast Sweetwater group and Lake names used by iwi, which are yet to be known by the Ngatu is the only outstanding lake in this area. To the east, NRC. NRC will endeavour to consult with mana whenua on the Karikari Peninsula, Lake Waiporohita is found. iwi on their preferred traditional names for each lake. 3. LAKE LOCATION MAP

4. Lake Overview 5 Lake Ngatu (NRC Lake Number 120) has a shallow northern half and three deep basins to the south (6.26 m max and 2.67 mean depth) and is a 55.54 ha in area. Lake Ngatu is located at the corner of Sweetwater and West Coast Road in the lower Aupōuri Peninsula of Northland. The lake is classified as a Class 1 Perched dune lake (Timms, 1982), meaning it sits above ground water level and relies on rainfall and overland flows for recharge.

The catchment is largely influenced by high and low producing exotic grassland and freshwater sedgeland/rushland. Other influences, although at lower percentage covers, include short rotation cropland and orchard, other perennial crops and built- up settlement, all of which will be contributing to nutrient inputs to the lake. The NRC- defined catchment area, including the lake, is 177.9 hectares. The surface area of the lake is 55.54 ha.

Of significance is the influence of built up settlement area, orchard and other perennial crops and short-rotation cropland which drain into the lake. There is historic urban development overlooking the lake with possible effects from septic tanks, some of them being older systems, increased road runoff, a school nearby with an older septic system and DOC toilets close to the road on northern side, also with an older septic system. The reserves at either end are used regularly by freedom campers who also use the lake for bathing, and cleaning cooking equipment. The lake is popular for swimming and bathing over summer, with use of soap products. These cumulative effects add to the overall decline of water quality.

The shallow water is wind-mixed and does not thermally stratify, mixing excess nitrogen and phosphorus making them available to phytoplankton throughout the year. Algal blooms have occurred in 2009 and 2015. Chlorophyll-a levels are in National Policy Statement for Freshwater Management (NPS) States C and D and push well into State D during blooms. If this continues, the lake may “flip” to an algal dominated state causing blooms to shade submerged vegetation leading to dieback of bottom-rooted plants. Recent results from 2017 (available after this plan was written) are showing substantial improvements in water quality.

Nitrogen levels are trending upward and have remained well into a consistent State D since late 2012 and phosphorus has seen a long-term decline, currently in State B

LAKE NGATU MANAGEMENT PLAN | Lake Overview

4. LAKE OVERVIEW rooted plants. Recent results from 2017 (available Lake Ngatu (NRC Lake Number 120) has a shallow after this plan was written) are showing substantial northern half and three deep basins to the south improvements in water quality. (6.26 m max and 2.67 mean depth) and is a 55.54 ha in area. Lake Ngatu is located at the corner of Nitrogen levels are trending upward and have Sweetwater and West Coast Road in the lower remained well into a consistent State D since late Aupöuri Peninsula of Northland. The lake is classified 2012 and phosphorus has seen a long-term decline, as a Class 1 Perched dune lake (Timms, 1982), currently in State B with smaller event modes meaning it sits above ground water level and relies than in the past. Toxic ammonia levels peaked in on rainfall and overland flows for recharge. November 2015. The lake was mesotrophic (average water quality) for some time before degrading to The catchment is largely influenced by high and eutrophic (poor water quality) since 2015. There low producing exotic grassland and freshwater is an occasional oxygen depletion in water deeper sedgeland/rushland. Other influences, although than 4-4.5 meters between August and February. at lower percentage covers, include short rotation The pH has historically been neutral, but has risen cropland and orchard, other perennial crops and (more alkaline), most likely from phytoplankton built-up settlement, all of which will be contributing using up carbon dioxide. Lake levels are variable to nutrient inputs to the lake. The NRC-defined for this perched dune lake due to the influences of catchment area, including the lake, is 177.9 hectares. inter-annual rainfall and drought patterns as the The surface area of the lake is 55.54 ha. lake largely receives water from rainfall. The range in levels varies by 1.8 m. The overall trend is of slight Of significance is the influence of built up settlement increase in level, largely due to early historic low area, orchard and other perennial crops and short- levels. Water retention time is just over 18 months. rotation cropland which drain into the lake. There is historic urban development overlooking the lake One of the reasons that Lake Ngatu is among the top with possible effects from septic tanks, some of outstanding dune lakes in Northland is because of its them being older systems, increased road runoff, a diverse aquatic plant community. The lake supports school nearby with an older septic system and DOC 20 native plant species, including five rare natives. toilets close to the road on northern side, also with Lake Submerged Plant Index is high at 55%. There an older septic system. The reserves at either end are are five exotic species recorded, three of these being used regularly by freedom campers who also use the invasive, and including yellow flag iris (eradicated by lake for bathing, and cleaning cooking equipment. the NRC in 2007), alligator weed and Lagarosiphon, The lake is popular for swimming and bathing over which was first recorded in 1988. Lagarosiphon is summer, with use of soap products. These cumulative highly invasive and is capable of occupying the entire effects add to the overall decline of water quality. lake bed. The Invasive Impact Index is high at 47%.

The shallow water is wind-mixed and does not Gambusia, goldfish, rudd, perch and even introduced thermally stratify, mixing excess nitrogen and trout, in the past, suggest there has been a range of phosphorus making them available to phytoplankton vectors for pest fish entry. Common bully and inanga throughout the year. Algal blooms have occurred in are still present as native fish, but their survival will be 2009 and 2015. Chlorophyll-a levels are in National under sustained pressure given the deterioration of Policy Statement for Freshwater Management (NPS) water quality. States C and D and push well into State D during blooms. If this continues, the lake may “flip” to The lake has a moderate level of non-game bird an algal dominated state causing blooms to shade native bird diversity at four species. Of interest is the submerged vegetation leading to dieback of bottom- sole occurrence of the Caspian tern in the area.

6 LAKE NGATU MANAGEMENT PLAN | Social and Cultural Dimension

5. SOCIAL AND CULTURAL DIMENSION 5.1. Mana whenua South and Rotokawau (Sweetwater) by way of cultural redress. The lake is largely managed by Ngäi Takoto. Three iwi/hapu have rohe whenua Area of Interest in the area of Lake Ngatu; Ngäi Takoto (green), Te The rohe whenua of each iwi is displayed in the Aupöuri (pink) and Te Rarawa (yellow). All three iwi/ diagram below and was sourced from Te Puni Kökiri’s hapu have reached Deed of Settlement with the Te Kahui Mangai web pages (www.tpk.govt.nz). Crown and Ngäi Takoto has been given ownership of Lake Ngatu, along with lakes Ngakapua North and

The yellow line on the following map shows Ngāi Takoto ownership of the four lakebeds. The light green areas are wetland. The yellow line on the following map shows Ngäi Takoto ownership of the four lakebeds. The light Thegreen yellowareas are line wetland. on the following map shows Ngāi Takoto ownership of the four lakebeds. The light green areas are wetland.

5.2. Land Tenure

5.2.1. Catchment landowners and Lake bed owners 5.2. Land Tenure

Thirty-eight landowners own 49 parcels within the lake catchment. The lake bed is 5.2.1. Catchment landowners and Lake bed owners 7 owned by Ngāi Takoto. There is a paper road which encircles the lake. Thirty -eight landowners own 49 parcels within the lake catchment. The lake bed is owned5.3. by Community Ngāi Takoto involvement. There is a paper road which encircles the lake.

Restoration5.3. Community activity involvementin this area has been undertaken by Bushland Trust and the local school and community. An active management group called Lake Ngatu Action RestorationGroup is in activityplace comprised in this area of has Ng beenāi Takoto undertaken, the Department by Bushland of Conservation,Trust and the local Far schoolNorth Districtand community Council,. NorthlandAn active management Regional Council, group Bushlandcalled Lake Trust Ngatu and Action local Grouplandowners is in place. comprised of Ngāi Takoto, the Department of Conservation, Far North District Council, Northland Regional Council, Bushland Trust and local landownersNgāi Takoto. have installed bollards at entry points to exclude power boats and the public using the lake to wash vehicles after coming off the beach. They have also Ngdiscouragedāi Takoto have the use installed of the bollards lake for at bathing entry point withs soapto exclude products power and boats have and erected the publicinformational using the sign lakeage to. washRiparian vehicles planting after has coming been off underway the beach. for They a number have alsoof years . discouraged the use of the lake for bathing with soap products and have erected informational signage. Riparian planting has been underway for a number of years. 9

LAKE NGATU MANAGEMENT PLAN | Physical Characteristics

5.2. Land Tenure with soap products and have erected informational 5.2.1 Catchment landowners and Lake signage. Riparian planting has been underway for a bed owners number of years. Thirty-eight landowners own 49 parcels within the lake catchment. The lake bed is owned by Ngäi 5.4. Public use Takoto. There is a paper road which encircles the lake. 5.4.1. Access Public access is easy via West Coast Road and 5.3. Community involvement Sweetwater Road. 5.4. Public use Restoration activity in this area has been undertaken 5.4.2. Boating by Bushland5.4.1. Trust Access and the local school and 5.4.2.1. Boat access Publiccommunity. access An is activeeasy viamanagement West Coast group Road called and LakeSweetwater Road. Boat access is easy to the northern and southern end Ngatu Action Group is in place comprised of Ngäi 5.4.2. Boating of the lake but is now limited mainly to waka ama. Takoto, the Department of Conservation, Far North Bollards stop access to trailer or power boats, although District Council,5.4.2.1. Northland Boat Regionalaccess Council, Bushland access through chained launch points for events Trust and local landowners. Boat access is easy to the northern and southern end of andthe managementlake but is now purposes limited is possible by permission mainly to waka ama. Bollards stop access to trailer or power boats, although access through Ngäi Takoto throughNgäi Takoto chained have launch installed points bollards for events at entry and points management to purposes is possible by permission through Ngāi Takoto exclude power boats and the public using the lake 5.4.3. Events to wash5.4.3. vehicles Events after coming off the beach. They Summer events are periodic including concerts and have also discouraged the use of the lake for bathing Summer events are periodic including concerts and WorldWorld Wetlands Wetlands Day Day celebrations. celebrations.

6. Physical Characteristics

6.6.1. PHYSICALCatchment CHARACTERISTICS Area a is a rationalised boundary created by NRC staff is on the right. By the end of 2018, a highly-accurate The6.1. following Catchment map shows Area the extent with of theMap lake catchment. On the left is the FENZ boundary and a is a rationalised boundary created by NRCLiDAR staff boundary is on the will right. be available.By The NRC-defined The following map shows the extent of the lake the end of 2018, a highly-accurate LiDAR boundary will becatchment available. area, The including NRC- the lake itself, is 177.9 definedcatchment. catchment On the area, left is inthecluding FENZ theboundary lake itself and, is 177.9 hectares. hectares.

6.2. Catchment Geology and soil types

The following map ((C) GNS Science 2016) of the Pōuto Peninsula and table below it 10 shows the geological history8 of the lake catchment. Mokeno has a geology comprised of Late Quaternary dunes (lQd). These ancient dunes are now poorly consolidated sand.

6.2. Catchment Geology andLAKE soil NGATUtypes MANAGEMENT PLAN | Physical Characteristics

The following map ((C) GNS Science 2016) of the Sweetwater area and the table uniform geology comprised solely of Early Quaternary below6.2. itCatchment shows the Geologygeology of and the soillake catchment. Lake Ngatu has a uniform geology comprisedtypes solely of Early Quaternary dunes dunes(eQd) (eQd) which which formed formed duringduring higher higher sea levelssea levelsThe following 12,000 map years ((C) GNS ago Science and 2016) earlier. of the These ancient12,000 years dunes ago andare earlier. now Theseweakly ancient cemented dunes are toSweetwater uncemented. area and the table below it shows the now weakly cemented to uncemented. geology of the lake catchment. Lake Ngatu has a

Plot Symbol eQd Plot Symbol Name eQd Early Quaternary dunes Name Early QuaternaryDescription dunes Weakly cemented and uncemented dune sand and associated facies. Clay-rich sandy soil. These Description Weakly cemented and uncemented dune sand and dunes arose during higher sea level 12,000 years associated facies. Clay-rich sandy soil. These ago and earler. dunes aroseGeologic during higher history sea level 12,000 yearsEarly Quaternary ago and earler.Simple name Zealandia Megasequence Terrestrial and Shallow Geologic history Early Quaternary Marine Sedimentary Rocks (Neogene) Absolute minimum age (millions of Simple name Zealandia Megasequence Terrestrial and Shallow 0.78 Marine Sedimentaryyears before Rocks present) (Neogene) Absolute maximum age (millions of Absolute minimum age (millions of 2.6 years before0.78 present) years before present) Supergroup equivalent stratigraphic Pakihi Supergroup Absolute maximum age (millions of name 2.6 years before present) Lithology Sand Supergroup equivalent stratigraphic Pakihi Supergroup name Soil types in the catchment are portrayed in the soil map and table below. The eastern shore of the lake is dominated by organic soils of the One Tree Point series Sand Lithology (OT) and the western shore is organic soils of the Ruakaka series (RK) with a northern area of the catchment with patches of yellow brown 11sands of the Houhora Soil types in the catchment are portrayed in the soilseries map (HO). and The table One below. Tree Point The peaty sands have deposited an iron pan which eastern shore of the lake is dominated by organiccreates soils of an the impermeable One Tree water Point-holding series layer . (OT) and the western shore is organic soils of the Ruakaka series (RK) with a Soil types in the catchment are portrayed in the soil northern area of the catchment with patches of yellow brown sands of the Houhora mapseries adjacent (HO). Theand tableOne below.Tree Point The easternpeaty sands shore ofhave deposited an iron pan which thecreates lake isan dominated impermeable by organic water -soilsholding of the layer One. Tree

Point series (OT) and the western shore is organic soils of the Ruakaka series (RK) with a northern area of the catchment with patches of yellow brown sands of the Houhora series (HO). The One Tree Point peaty sands have deposited an iron pan which creates an impermeable water-holding layer.

LAKE NGATU MANAGEMENT PLAN | Physical Characteristics

Soil Genetic soil Geological Suite Subgroup Series Soil name Description Symbol group origin OT Organic Ruakaka One Tree One Tree One Tree Point peaty sand (OT) is a ‘groundwater podzol’, soils Point Point its development has been similar in many ways to that of the peaty pakahi soils of Westland. It will have carried kauri forest at sand some stage in its development but not since human settlement in New Zealand. A typical profile has up to 75 mm of dark reddish brown slightly peaty loamy sand with weakly developed structure and containing bits of kauri gum, on 100 mm of very dark grey peaty sand also with little structure, over 100 mm of very dark grey peaty sand with increasing proportions of white silica sand grains. The boundaries between the layers are indistinct to this point but beneath this last layer is a distinct, iron-cemented layer which acts as a barrier to further root penetration and to the drainage of water on through the profile. Water drains horizontally along this pan. Wind erosion of dust and peat has been a problem during development of this land for urban and industrial use at One Tree Point., causing both onsite problems and difficulty of revegetation, and air quality off-site nuisance problems. RK Organic Ruakaka Ruakaka Ruakaka Ruakaka peaty sand loam (RK) is found throughout soils peaty Northland (except around the Kaipara where there is PZ) in sand what were swampy basins adjoining dunes, for example, in loam inter-dune swamps and the fringes of peaty sand plains. A representative profile of this low to very low fertility soil would have 150 mm of black fine sandy peaty loam, on 450 mm of black to reddish brown fine sandy peaty loam, on black loamy peat, which will contain wood fragments. There may well be ash layers where the swamp has been burnt and then peat has developed on top. HO Yellow- Sands of Pinaki Moderately Houhora Hourhora Houhora series – on older west coast dunes, more mature brown Upper to strongly sand than Pinaki series, having more soil development, more sands Quaternary leached organic matter and stronger structure. Can have iron dune series cementing but generally iron content is a much lower than Red Hill series. [Either developed on sand from a separate source – (Central North Island rhyolitic/feldspathic sand rather than Taranaki iron sands) or the iron had settled out before this sand reached the Aupouri Peninsula.] A typical profile of Houhora sand (HO & HOH) may include: 80 to 150 mm of very dark greyish brown to olive brown loamy sand, on 80 to 150 mm of yellowish brown to pale brown sand, on brownish yellow to strong brown loamy sand.

6.3. Catchment Hydrogeology 6.3. Catchment Hydrogeology sub-region having considerably shorter residence Although the the Aupöuri Aup sandsōuri sandsholds an holdsextensive an extensivetimes. groundwater The average particle aquifer, size of Ngatusurface rockis a in the perched lake unaffected by the water table. The lake sits to the southern edge of the groundwater aquifer, Ngatu is a perched lake catchment is 1.63 on a scale of 5, a value of 1 being Aupōuri aquifer range. sand (FENZ database). unaffected by the water table. The lake sits to the southern6.4. edge of Catchmentthe Aupöuri aquifer drainage range. and sedimentation rates 6.5. Geomorphology - Lake type

The6.4. NRCCatchment-defined catchment drainage andarea, includingand the lakeorigin, itself area,, is 177.9 depth, hectares volume and producessedimentation a mean rates annual flow, based on hydrologicalIn common with models, other dune of 715,552.5 lakes in the Sweetwater m³/year. The NRC-defined lake has ancatchment estimated area, includinglake residence the lake timearea, of Lake 1.565 Ngatu years, is a shallow meaning Class 1 perchedany water lake enteringitself, is 177.9 the hectares lake will and remainproduces afor mean over annual 18 monthsoriginating. This as residence an elevated deflationtime is similarhollow with to a nearbyflow, based Ngakapua on hydrological North models, (2.268 of 715,552.5 years) andm³/ Rotoroasealed organic (1.805 basin years) with humic with characteristics. other lakes The in thisyear. subThe lake-region has an having estimated considerabl lake residencey time shorter lakeresidence has a maximum times. depth The of average 6.26 m with particle a mean size of surface rock in the catchment is 1.63 on a scale of 5, a value of 1 being sand of 1.565 years, meaning any water entering the lake overall depth of 2.67 m. The surface area of the lake (FENZ database). is 55.54 hectares with a volume of 1,548,165.50 will remain for over 18 months. This residence time is similar6.5. to nearby NgakapuaGeomorphology North (2.268 - Lakeyears) andtype andm³ origin(NIWA ,bathymetric area, depth survey). and The volume NRC-defined Rotoroa (1.805 years) with other lakes in this catchment area, including the lake itself, is 177.9 In common with other dune lakes in the Sweetwaterhectares. area, Lake Ngatu is a shallow Class 1 perched lake originating as an elevated deflation hollow with a sealed organic basin with humic characteristics. The lake has a maximum depth of 6.26 m with a mean overall depth of 2.67 m. The surface area of the lake is 55.54 hectares 10

with a volume of 1,548,165.50 m³ (NIWA bathymetric survey). The NRC-defined catchment area, including the lake itself, is 177.9 hectares.

6.6. Bathymetry map

The bathymetric depth map below comes from a survey done by NIWA for the NRC. LAKE NGATUThe deepest MANAGEMENT point is within the PLAN southern | - mostPhysical basin Characteristicsfollowed by central and eastern basins. Please note that the scale of this map is in feet, not meters.

6.6. Bathymetry map The bathymetric depth map adjacent comes from a survey done by NIWA for the NRC. The deepest point is within the southern-most basin followed by central and eastern basins. Please note that the scale of this map is in feet, not meters.

6.7. Natural inlets and outlets Several drains enter the lake (please see section 10.2 Drains). There are no outlets.

6.7. Natural inlets and outlets 6.8. Wetland associations Several drains enter the lake (please see section 10.2 Drains). There are no outlets. A shallow water wetland surrounds the lake edges, 6.8. Wetland associations shown in the map below in light green. This is not A shallow water wetland surrounds the lake edges, shown in the map below in light agreen. “Top This 150” is not wetland a “Top 150” meaning wetland meaning that it thatis not it is rankednot ranked as one of the asregion’s one ofbest the wetland region’ss. The bestsubregion wetlands. contains Thea mosaic subregion of such wetlands and dune lakes. contains a mosaic of such wetlands and dune lakes.

6.9. Connectivity 6.9. Connectivity 14 The lake is not connected to any other waterbody

although there are smaller dune lakes nearby, including The lake is not connected to any other waterbody although there are smaller dune lakes nearby, including Lake Gem to the south,Lake Gem which to the has south, a whichwalking has atrack walking around track it from Lake Ngatu carpark and has been fencedaround and it from replanted. Lake Ngatu carpark and has been fenced and replanted.

6.10. Air Temperature 6.9. Connectivity

Temperature6.10.The lake Air is not Temperature connected appears to any to other be reflectingwaterbody although a cyclic there arepattern smaller likedune based on El Nino/La Nina Temperaturelakes nearby, appearsincluding to Lake be reflectingGem to the asouth, cyclic which pattern has like a walking based on track El Nino/Laaround it Nina oscillations. Lake level drops oscillationsfrom Lake Ngatu. Lake carpark level and has drops been fenced follow and summer replanted. droughts due to evaporation. follow summer droughts due to evaporation. 6.10. Air Temperature

TemperatureKaitaia appears Observatory to be reflecting a cyclic Mean pattern Monthly like based on El Air Nino/La Nina Temperature (deg C) oscillations. Lake level drops follow summer droughts due to evaporation. 25 20 Kaitaia Observatory Mean Monthly Air Temperature (deg C) 15 10 25 20 5 15 0 10 5 0 Jan 2006 Jan 2007 Jan 2008 Jan 2009 Jan 2011 Jan 2013 Jan 2015 Jan 2016 Jan 2010 Jan 2012 Jan 2014 Sep 2006 2006 Sep 2007 Sep 2008 Sep 2009 Sep 2011 Sep 2013 Sep 2015 Sep 2016 Sep Jan 2006 Jan 2007 Jan 2008 Jan 2009 Jan 2011 Jan 2013 Jan 2015 Jan 2016 Sep 2010 2010 Sep 2012 Sep 2014 Sep Jan 2010 Jan 2012 Jan 2014 Sep 2006 2006 Sep 2007 Sep 2008 Sep 2009 Sep 2011 Sep 2013 Sep 2015 Sep 2016 Sep Sep 2010 2010 Sep 2012 Sep 2014 Sep May 2006 May 2007 May 2008 May 2009 May 2011 May 2013 May 2015 May 2016 May 2010 May 2012 May 2014 May 2006 May 2007 May 2008 May 2009 May 2011 May 2013 May 2015 May 2016 May 2010 May 2012 May 2014

6.11. Temperature and Thermal stratification

The6.11. graph belowTemperature shows temperature andat depth Thermal throughout stratification the water column. Each 11 coloured line represents one sample. Water temperatures throughout the year range from 12.6 degrees C to 27.67 degrees C. The graph below shows temperature at depth throughout the water column. Each colouredThe lake, being line very represents shallow at 2.67 one m mean sample. depth, doesWater not thermally temperatures stratify in throughout the year range summer and temperature is fairly uniform at all depths, year-round. In order for a lake fromto stratify, 12.6 water degrees depth must C exceedto 27.67 10 meters degrees. C.

The lake, being very shallow at 2.67 m mean depth, does 15not thermally stratify in summer and temperature is fairly uniform at all depths, year-round. In order for a lake to stratify, water depth must exceed 10 meters.

LAKE NGATU MANAGEMENT PLAN | Physical Characteristics

6.11. Thermal stratification The lake, being very shallow at 2.67 m mean depth, The graph below shows temperature at depth does not thermally stratify in summer and temperature throughout the water column. Each coloured is fairly uniform at all depths, year-round. In order for a line represents one sample. Water temperatures lake to stratify, water depth must exceed 10 meters. throughout the year range from 12.6 degrees C to 27.67 degrees C. Due to lack of stratification, nutrients are available throughout the water column throughout the year

Due to lack of stratification, nutrients aredue availableto wind mixing. throughout the water column Due to lack of stratification, nutrients are available throughout the water column throughout the year due to wind mixing. throughout the year due to wind mixing.

Ngatu Summer Temperature Depth Proﬁles 30 30 28 26 28 24 26 22 24 20 22 20

Temp c Temp 18

Temp c Temp 16 18 14 16 12 14 10 12 10 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 Depth m Depth m

08/12/05 29/01/08 01/02/11 08/12/05 29/01/08 01/02/11 07/02/11 20/02/12 10/02/14 07/02/11 20/02/12 10/02/14

Ngatu Autumn Temperature Depth Proﬁles 30 30 28 28 26 24 26 22 24 20 22 20 18 Temp C Temp 18 Temp C Temp 16 14 16 12 14 10 12 10 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 Depth m Depth m

15/03/06 22/05/06 09/03/09 25/05/09 15/03/06 22/05/06 09/03/09 25/05/09 17/05/10 23/05/11 14/05/12 13/05/13 17/05/10 23/05/11 14/05/12 13/05/13

16 16

LAKE NGATU MANAGEMENT PLAN | Physical Characteristics

Ngatu Winter Temperature Depth Proﬁles Ngatu Winter Temperature Depth Proﬁles 30 30 28 26 28 24 26 24 22 22 20 18 Temp C Temp 20 16 18 Temp C Temp 14 16 14 12 12 10 10 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 2 2.5 Depth 3 3.5 m 4 4.5 5 5.5 6 Depth m 07/08/06 06/08/07 30/06/08 17/08/09 07/08/06 06/08/07 30/06/08 17/08/09 16/08/10 06/08/12 13/08/13 16/08/10 06/08/12 13/08/13

Ngatu Spring Temperature Depth Proﬁles Ngatu Spring Temperature Depth Proﬁles 30 30 28 28 26 24 26 22 24 \ 20 22 20 18 18 16 Temp C Temp 14 16 12 14 10 12 10 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 Depth m 2 2.5 3 3.5 4 4.5 5 5.5 6 Depth m 10/11/04 30/10/06 05/11/07 10/09/08 10/11/04 30/10/06 05/11/07 10/09/08 17/11/10 22/11/11 05/11/12 17/11/10 22/11/11 05/11/12

6.12. Rainfall and drought 6.12. Rainfall and drought The graph below shows how many summers are experienced as drought. This will Theresult graph in a reductionbelow shows in lake how level many. Peak summers sustained are experiencedrainfall events as result drought. in an This influx will of newresult nutrients in a reduction from the in lakemany level inflow. Peak drains sustained. rainfall events result in an influx of new nutrients from the many inflow drains.

17 17

LAKE NGATU MANAGEMENT PLAN | Physical Characteristics

6.12. Rainfall and drought in lake level. Peak sustained rainfall events result in an The graph below shows how many summers are influx of new nutrients from the many inflow drains. experienced as drought. This will result in a reduction

6.13. Lake level The range in levels varies by 1.8 m. The overall trend is Lake levels are variable for this perched dune lake due of slight increase in level, largely due to the low levels to the influences of inter-annual rainfall and drought in 1995. patterns as the lake largely receives water from rainfall.

6.14. Sunshine 6.15. Wind speed Peak summer sun seasons likely increase the Although wind stirs up nutrient-loaded sediment and evaporation rates of the lake resulting in lake level mixes nutrients in the water column, Ngatu is more decrease. likely to be affected by influx of new nutrients during peak rain events.

14 Kaitaia Observatory monthly total sunshine hours SUMMER AUTUMN WINTER SPRING

350 300 LAKE MOREHUREHU MANAGEMENT PLAN | Physical Characteristics 250 200 150 Kaitaia Observatory monthly total sunshine hours SUMMER AUTUMN WINTER SPRING 100 350 50 300 0 250 200 150 Jan 2006 Jan 2007 Jan 2008 Jan 2009 Jan 2011 Jan 2013 Jan 2015 Jan 2016 Jan 2010 Jan 2012 Jan 2014 Sep 2006 2006 Sep 2007 Sep 2008 Sep 2009 Sep 2011 Sep 2013 Sep 2015 Sep 2016 Sep Sep 2010 2010 Sep 2012 Sep 2014 Sep May 2006 May 2007 May 2008 May 2009 May 2011 May 2013 May 2015 May 2016 May 2010 May 2012 May 2014 100 50 0 6.15. Wind speed

Jan 2006 Jan 2007 Jan 2008 Jan 2009 Jan 2011 Jan 2013 Jan 2015 Jan 2016 Jan 2010 Jan 2012 Jan 2014

Although wind 2006 Sep stirs 2007 Sep up nutrient 2008 Sep -loaded 2009 Sep sediment 2011 Sep and mixes nutrients 2013 Sep in the 2015 Sep water 2016 Sep Sep 2010 2010 Sep 2012 Sep 2014 Sep May 2006 May 2007 May 2008 May 2009 May 2011 May 2013 May 2015 May 2016 May 2010 May 2012 May 2014 column, Ngatu is more likely to be affected by influx of new nutrients during peak rain events. 6.15. Wind speed

AlthoughKaitaia wind Ews stirs up nutrient monthly -loaded mean sediment wind and mix speed (m/s) SUMMERes nutrients AUTUMN in WINTER the water SPRING column, Ngatu is more likely to be affected by influx of new nutrients during peak rain events.6 5 4 3 SUMMER AUTUMN WINTER SPRING 2 Kaitaia Ews monthly mean wind speed (m/s) 1 0 6 5 4 3 Jan 2006 Jan 2007 Jan 2008 Jan 2009 Jan 2011 Jan 2013 Jan 2015 Jan 2016 Jan 2010 Jan 2012 Jan 2014 Sep 2006 2006 Sep 2007 Sep 2008 Sep 2009 Sep 2011 Sep 2013 Sep 2015 Sep 2016 Sep Sep 2010 2010 Sep 2012 Sep 2014 Sep May 2006 May 2007 May 2008 May 2009 May 2011 May 2013 May 2015 May 2016 2 May 2010 May 2012 May 2014 1

0 6.16. Light incidence (Secchi, Total Suspended Solids, Chlorophyll-a)

Jan 2006 Jan 2007 Jan 2008 Jan 2009 Jan 2011 Jan 2013 Jan 2015 Jan 2016 Jan 2010 Jan 2012 Jan 2014 Sep 2006 2006 Sep 2007 Sep 2008 Sep 2009 Sep 2011 Sep 2013 Sep 2015 Sep 2016 Sep Three measures which are indicators of 2010 Sep water clarity 2012 Sep include chlorophyll 2014 Sep a (presence May 2006 May 2007 May 2008 May 2009 May 2011 May 2013 May 2015 May 2016 May 2010 May 2012 May 2014 of micro-algal growth in the water column, total suspended solids and the direct measure 6.16. Light of visibility incidence at depth (Secchi, by Totallowering a blackNovember and 2015. white This lakeSecchi has a disknumber until of external it is no longerSuspended6.16. visible. LightSolids, As seen incidence Chlorophyll-a) from the(Secchi, graph Total below, Suspendedinfluences the lake and experiences possibleSolids, nutrient Chlorophyll ainputs sporadic which-a) can pattern of algal blooms (green line), occurring in lateresult spring in algal and blooms. summer Without as better well information as in on aThreeutumnThree measures measures. A peak which bloomwhich are indicators occurredare indicators of water in clarityMay of 2015waterland at clarity use 37 practices, mg/m include ³it chlorophyllis difficult chlorophyll to point-a witha to (presence a singlea smallerofinclude micro chlorophyll bloom-algal growthfollow a (presenceing in theofin micro-algalNovember water column, growth 2015. total causeThis suspended of lake these has events. a solids number and of the external direct influencesmeasurein the water of column,and visibility possible total atsuspended depth nutrient solidsby loweringinputs and the which a black can andresult white in algal Secchi blooms. disk until Without it is no betterlongerdirect measure informationvisible. of Asvisibility seenon at land depth from use by the lowering practices, graph a black below, it isThe difficult the table lake below to experiences point the following to a single graph a sporadic shows cause the ofpattern theseofand algal white events. blooms Secchi disk (green until it isline), no longer occurring visible. As in lateNational spring Policy and Statement summer for Freshwateras well as Management in autumnseen from. Athe peak graph bloombelow, the occurred lake experiences in May a 2015states at for37 phytoplankton mg/m³ chlorophyll (chlorophyll-a).-a with A sharply a Thesmallersporadic table patternbloom below of follow algal the blooms followinging in (green November graph line), occurring shows 2015. the increasingThis National lake trend has inPolicy chlorophyll-a,a number Statement withof external recent for algal Freshwaterinfluencesin late spring andand Management summer possible as well nutrient statesas in autumn. inputsfor phytoplankton whichblooms can pushingresult (chlorophyll intoin algal State- a).D blooms. is relatedA sharply to Without increasing increasingbetterA peak information bloom trend occurred in on inchlorophyll May land 2015 use at -37practices,a, mg/with recent it isnitrogen algaldifficult levels.blooms to point pushing to a single into State cause D of is relatedthesem³ chlorophyll-a events. to increasing with a smaller nitrogen bloom followinglevels. in

The table below the following graph shows the National Policy Statement for Freshwater Management states for phytoplankton (chlorophyll-a). A sharply increasing trend in chlorophyll-a, with recent algal blooms pushing into State D is related to increasing nitrogen levels.

1519

LAKE NGATU MANAGEMENT PLAN | Physical Characteristics

40 Lake Ngatu Water Clarity 35 (NPS State colours apply to green line only)

30 Total Suspended Solids g/m3

25 Secchi Depth m Chlorophyll a (low level) mg/m3 20

0 4/8/2012 4/8/2006 8/8/2006 4/8/2007 8/8/2007 4/8/2008 8/8/2008 4/8/2009 8/8/2009 4/8/2010 8/8/2010 4/8/2011 8/8/2011 8/8/2012 4/8/2013 8/8/2013 4/8/2014 8/8/2014 4/8/2015 8/8/2015 4/8/2016 12/8/2005 12/8/2006 12/8/2007 12/8/2009 12/8/2010 12/8/2011 12/8/2012 12/8/2013 12/8/2014 12/8/2008 12/8/2015

Attribute Unit Lake Type State Annual Median Annual Maximum Narrative State Lake ecological communities are healthy and resilient, similar to natural Phytoplankton mg Chlorophyll-‐a/m³ All A ≤2 ≤10 reference conditions. Attribute Unit Lake Type State Annual Median Annual Maximum Narrative Lake State ecological communities are slightly impacted by additional algal and/or Lake ecological communities are healthy and resilient, similar to natural PhytoplanktonPhytoplankton mg mg Chlorophyll-‐a/m Chlorophyll-‐a/m³ ³ AllAll A B >2 ≤2 and ≤5 >10 ≤10 and ≤25 plant growth arising from nutrients levels that are elevated above natural reference reference conditions. conditions. Lake Lake ecological ecological communities communities are slightly are moderately impacted impacted by additional algal and/or by additional algal and Phytoplankton mg Chlorophyll-‐a/m³ All B >2 and ≤5 >10 and ≤25 plant plant growth growth arising arising from from nutrients nutrients levels levels that that are are elevated above natural elevated well above natural Phytoplankton mg Chlorophyll-‐a/m³ All C >5 and ≤12 >25 and ≤60 reference reference conditions. conditions. Reduced water clarity is likely to affect habitat available Lake for ecological native macrophytes. communities are moderately impacted by additional algal and plant growth arising from nutrients levels that are elevated well above natural Phytoplankton mg Chlorophyll-‐a/m³ All C >5 and ≤12 >25 and ≤60 Lake ecological communities are moderately impacted by additional algal and reference conditions. Reduced water clarity is likely to affect habitat available National plant growth arising from nutrients levels that are elevated well above natural Phytoplankton mg Chlorophyll-‐a/m³ All 12 60 for native macrophytes. Bottom Line reference conditions. Reduced water clarity is likely to affect habitat available Lake ecological communities are moderately impacted by additional algal and for native macrophytes. National plant growth arising from nutrients levels that are elevated well above natural Phytoplankton mg Chlorophyll-‐a/m³ All 12 60 Lake ecological communities have undergone or are at high risk of a regime Bottom Line reference conditions. Reduced water clarity is likely to affect habitat available shift to a persistent, degraded state (without native macrophyte/seagrass for native macrophytes. Phytoplankton mg Chlorophyll-‐a/m³ All D >12 >60 Lake cover), ecological due to communities impacts have of elevated undergone nutrients or are at leading high risk of a regime to excessive algal and/or shift plant to growth, a persistent, as well degraded as from state losing (without oxygen native macrophyte/seagrass in bottom waters of deep lakes. Phytoplankton mg Chlorophyll-‐a/m³ All D >12 >60 cover), due to impacts of elevated nutrients leading to excessive algal and/or plant growth, as well as from losing oxygen in bottom waters of deep lakes.

7. Chemical Characteristics 7. Chemical Characteristics 7.1. Water Quality 7.1. Water Quality 7.1.1. Nutrients 7.1.1. Nutrients 7.1.1.1. Limiting nutrient assay 7.1.1.1. Limiting nutrient assay Max Gibbs (pers. comm.) from NIWA conducted limiting nutrient assays on several Maxlakes Gibbs including (pers. Ngatu comm.). Significant from NIWA results conducted are highlighted. limiting nutrient For the assays years on and several seasons lakesassayed,, including both phosphorusMorehurehu .and Significant nitrogen results plus phosphorus are highlighted. are Forthe limitingthe years nutrient and seasonscombination assayed, in summer phosphorus with no is limitingthe limiting nutrients nutrient in inautumn. summer. The Lack summer of this 2015nutrient regulatessample contained the ability peak of plants chlorophyll to optimally a (from grow. algal bloom).

AutumnAutumn 2014 2014 Summer Summer 2015 2015 Autumn Autumn 2014 2014 Summer Summer 2015 2015 AutumnAutumn 2014 2014 SummerSummer 2015 2015 Lake Initial Chla Initial Chla Change in Change in Proportional change over control Proportional change over control Lake Initial -3Chla Initial-3 Chla Change in Change in Proportional change over control Proportional change over control ( mg m )-3 ( mg m ) -3 Control Control +N +P +N+P NP-‐P +N +P +N+P ( mg m ) ( mg m ) Control Control +N +P +N+P NP-‐P +N +P +N+P Morehureru 1.5 2.6 0.81 0.92 1.01 1.08 0.98 -‐0.11 1.00 1.25 1.25 Ngatu 1.25 13.7 1.06 1.01 0.96 0.91 0.87 -‐0.04 1.03 1.10 1.17

7.1.1.2.7.1.1.2. Ammoniacal Ammoniacal Nitrogen Nitrogen (Toxicity) (Toxicity)

Ammoniacal nitrogen (NH -N), also often called ‘ammonium’, covers two forms of 16 Ammoniacal nitrogen (NH4 -N), also often called ‘ammonium’, covers two forms of nitrogen; ammonia (NH ) and4 ammonium (NH ). It enters waterways primarily nitrogen; ammonia (NH3 ) and ammonium (NH4 ). It enters waterways primarily through point source discharges,3 such as raw sewage4 or livestock effluent. It is toxic to aquatic life at high concentrations.

20 The table following the graph shows the National Policy Statement Freshwater

Management limits for lake state. Morehurehu has remained in State A or low ammonia toxicity levels, but with an increasing trend.

40 Lake Ngatu Water Clarity 35 (NPS State colours apply to green line only)

30 Total Suspended Solids g/m3

25 Secchi Depth m Chlorophyll a (low level) mg/m3 20

0 4/8/2006 8/8/2006 4/8/2007 8/8/2007 4/8/2008 8/8/2008 4/8/2009 8/8/2009 4/8/2010 8/8/2010 4/8/2011 8/8/2011 4/8/2012 8/8/2012 4/8/2013 8/8/2013 4/8/2014 8/8/2014 4/8/2015 8/8/2015 4/8/2016 12/8/2005 12/8/2006 12/8/2007 12/8/2008 12/8/2009 12/8/2010 12/8/2011 12/8/2012 12/8/2013 12/8/2014 12/8/2015

Attribute Unit Lake Type State Annual Median Annual Maximum Narrative State Lake ecological communities are healthy and resilient, similar to natural Phytoplankton mg Chlorophyll-‐a/m³ All A ≤2 ≤10 reference conditions. Lake ecological communities are slightly impacted by additional algal and/or Phytoplankton mg Chlorophyll-‐a/m³ All B >2 and ≤5 >10 and ≤25 plant growth arising from nutrients levels that are elevated above natural reference conditions. Lake ecological communities are moderately impacted by additional algal and plant growth arising from nutrients levels that are elevated well above natural Phytoplankton mg Chlorophyll-‐a/m³ All C >5 and ≤12 >25 and ≤60 reference conditions. Reduced water clarity is likely to affect habitat available for native macrophytes. Lake ecological communities are moderately impacted by additional algal and National plant growth arising from nutrients levels that are elevated well above natural Phytoplankton mg Chlorophyll-‐a/m³ All 12 60 Bottom Line reference conditions. Reduced water clarity is likely to affect habitat available LAKE NGATU MANAGEMENTfor native macrophytes. PLAN | Chemical Characteristics Lake ecological communities have undergone or are at high risk of a regime shift to a persistent, degraded state (without native macrophyte/seagrass Phytoplankton mg Chlorophyll-‐a/m³ All D >12 >60 cover), due to impacts of elevated nutrients leading to excessive algal and/or 7. CHEMICAL CHARACTERISTICS 7.1.1.2.plant Ammoniacal growth, as well Nitrogen as from losing (Toxicity) oxygen in bottom waters of deep lakes. Ammoniacal nitrogen (NH4-N), also often called 7.1. Water Quality ‘ammonium’, covers two forms of nitrogen; ammonia 7. Chemical Characteristics 7.1.1. Nutrients (NH3) and ammonium (NH4). It enters waterways

primarily through point source discharges, such as raw 7.1.1.1.7.1. Limiting Water nutrient Quality assay sewage or livestock effluent. It is toxic to aquatic life at

Max Gibbs (pers. comm.) from NIWA conducted high concentrations. 7.1.1. Nutrients limiting nutrient assays on several lakes including

Ngatu. Significant results are highlighted. For the years The table, following the graph below, shows the 7.1.1.1. Limiting nutrient assay and seasons assayed, both phosphorus and nitrogen National Policy Statement Freshwater Management plus phosphorus are the limiting nutrient combination limits for lake state. Ngatu has an increasing trend Max Gibbs (pers. comm.) from NIWA conducted limiting nutrient assays on several in summer with no limiting nutrients in autumn. The and has recently seen a marked increase in ammonia lakes including Ngatu. Significant results are highlighted. For the years and seasons summer 2015 sample contained peak chlorophyll a spiking into State D in November 2015. Earlier on assayed, both phosphorus and nitrogen plus phosphorus are the limiting nutrient (from algal bloom). it moved from State A into State B. If this trend combination in summer with no limiting nutrients in autumn. The summer 2015 continues, acute impacts on native aquatic fauna are sample contained peak chlorophyll a (from algal bloom). likely.

Autumn 2014 Summer 2015 Autumn 2014 Summer 2015 Autumn 2014 Summer 2015 Lake Initial Chla Initial Chla Change in Change in Proportional change over control Proportional change over control ( mg m-3) ( mg m-3) Control Control +N +P +N+P NP-‐P +N +P +N+P Ngatu 1.25 13.7 1.06 1.01 0.96 0.91 0.87 -‐0.04 1.03 1.10 1.17

7.1.1.2. Ammoniacal Nitrogen (Toxicity)

Ammoniacal nitrogen (NH4-N), also often called ‘ammonium’, covers two forms of nitrogen; ammonia (NH3) and ammonium (NH4). It enters waterways primarily

Attribute Unit Lake Type State Annual Median Annual Maximum Narrative State Ammonia mg NH4-N/L (mg ammoniacal- 99% species protection level: No observed effect on any All A ≤0.03 ≤0.05 (Toxicity) nitrogen per litre) species tested Ammonia mg NH4-N/L (mg ammoniacal- 95% species protection level: Starts impacting occasionally All B >0.03 and ≤0.24 >0.05 and ≤0.40 (Toxicity) nitrogen per litre) on the 5% most sensitive species 80% species protection level: Starts impacting regularly on Ammonia mg NH4-N/L (mg ammoniacal- All C >0.24 and ≤1.30 >0.40 and ≤2.20 the 20% most sensitive species (reduced survival of most (Toxicity) nitrogen per litre) sensitive species) 80% species protection level: Starts impacting regularly on Ammonia mg NH4-N/L (mg ammoniacal- National All 1.3 2.2 the 20% most sensitive species (reduced survival of most (Toxicity) nitrogen per litre) Bottom Line sensitive species) Ammonia mg NH4-N/L (mg ammoniacal- Starts approaching acute impact level (ie risk of death) for All D >1.30 >2.20 (Toxicity) nitrogen per litre) sensitive species

17 LAKE NGATU MANAGEMENT PLAN | Chemical Characteristics

7.1.1.3. Nitrogen The table, following the chart below, shows the The following graph shows a total nitrogen timeline National Policy Statement for Freshwater Management for the lake from 2005-2016. The trendline shows limits for lake state. Ngatu has an increasing trend a gradual rise, which is mainly due to peaks in well into State D after an earlier history between November 2012 and May 2014. This is most likely a States C and D. The trend shows a regime shift from sign of intensified land use in the catchment. macrophytes to phytoplankton.

Lake Ngatu Total Nitrogen (TN) g/m3-‐N

1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1/12/2005 1/05/2006 1/10/2006 1/03/2007 1/08/2007 1/01/2008 1/06/2008 1/11/2008 1/04/2009 1/09/2009 1/02/2010 1/07/2010 1/12/2010 1/05/2011 1/10/2011 1/03/2012 1/08/2012 1/01/2013 1/06/2013 1/11/2013 1/04/2014 1/09/2014 1/02/2015 1/07/2015 1/12/2015 1/05/2016

AttributeAttribute UnitUnit Lake Lake Type Type StateState Annual Annual Median Median NarrativeNarrative State State Total Total Nitrogen Nitrogen LakeLake ecological ecological communities communities are healthy are and resilient, healthy similar and to resilient, natural reference similar to natural reference g/m3g/m3PolymicticPolymicticA A ≤.3≤.3 (Trophic (Trophic state) state) conditions. Lake ecological communities are slightly impacted by additional algal and/or plant Total Nitrogen Lake ecological communities are slightly impacted by additional algal and/or plant Total Nitrogen g/m3 Polymictic B >.3 and ≤.5 growth arising from nutrients levels that are elevated above natural reference (Trophic state)g/m3 Polymictic B >.3 and ≤.5 growth arising from nutrients levels that are elevated above natural reference (Trophic state) conditions. conditions. Lake ecological communities are moderately impacted by additional algal and plant Total Nitrogen Lake ecological communities are moderately impacted by additional algal and plant Total Nitrogen g/m3 Polymictic C >.5 and ≤.8 growth arising from nutrients levels that are elevated well above natural reference (Trophic state)g/m3 Polymictic C >.5 and ≤.8 growth arising from nutrients levels that are elevated well above natural reference (Trophic state) conditions. conditions. Lake ecological communities are moderately impacted by additional algal and plant Total Nitrogen National Lake ecological communities are moderately impacted by additional algal and plant Total Nitrogen g/m3 Polymictic National 0.8 growth arising from nutrients levels that are elevated well above natural reference (Trophic state)g/m3 Polymictic Bottom Line 0.8 growth arising from nutrients levels that are elevated well above natural reference (Trophic state) Bottom Line conditions Lakeconditions ecological communities have undergone or are at high risk of a regime shift to a persistent,Lake ecological degraded state communities (without native have macrophyte/seagrass undergone or cover), are due at to impacts high risk of a regime shift to Total Nitrogen g/m3 Polymictic D >.8 ofpersistent, elevated nutrients degraded leading state to excessive (without algal and/or native plant growth, macrophyte/seagrass as well as from cover), due to impacts Total (Trophic Nitrogen state) g/m3 Polymictic D >.8 losingof elevated oxygen in bottom nutrients waters leading of deep lakes. to excessive algal and/or plant growth, as well from (Trophic state) losing oxygen in bottom waters of deep lakes.

7.1.1.4. Phosphorus

Total phosphorus levels are showing long term decline with periodic modes still occurring7.1.1.4. Phosphorus as late as 2015. As phosphorus isThe a limitingtable, following nutrient, the chart this below, is a shows hopeful the trend. Total phosphorus levels are showing long term decline National Policy Statement for Freshwater Management Thewith table periodic, following modes still occurringthe chart as late below, as 2015. shows limitsthe forNational lake state. Policy More recently, Statement phosphorus for ranged Freshwater Management limits for lake state. More recently, phosphorus ranged As phosphorus is a limiting nutrient, this is a hopeful between States A and B, with an earlier history of between States A and B, with an earlier history of peaks into State C. trend. peaks into State C.

Lake Ngatu Total Phosphorus (TP) g/m3-‐P

0.07 0.06 18 0.05 0.04 0.03 0.02 0.01 0 1/12/2005 1/05/2006 1/10/2006 1/03/2007 1/08/2007 1/01/2008 1/06/2008 1/11/2008 1/04/2009 1/09/2009 1/02/2010 1/07/2010 1/12/2010 1/05/2011 1/10/2011 1/03/2012 1/08/2012 1/01/2013 1/06/2013 1/11/2013 1/04/2014 1/09/2014 1/02/2015 1/07/2015 1/12/2015 1/05/2016

Lake Ngatu Total Nitrogen (TN) g/m3-‐N

Attribute Unit Lake Type State Annual Median Narrative State Total Nitrogen Lake ecological communities are healthy and resilient, similar to natural reference g/m3 Polymictic A ≤.3 (Trophic state) conditions. Lake ecological communities are slightly impacted by additional algal and/or plant Total Nitrogen g/m3 Polymictic B >.3 and ≤.5 growth arising from nutrients levels that are elevated above natural reference (Trophic state) conditions. Lake ecological communities are moderately impacted by additional algal and plant Total Nitrogen g/m3 Polymictic C >.5 and ≤.8 growth arising from nutrients levels that are elevated well above natural reference (Trophic state) conditions. Lake ecological communities are moderately impacted by additional algal and plant Total Nitrogen National g/m3 Polymictic 0.8 growth arising from nutrients levels that are elevated well above natural reference (Trophic state) Bottom Line conditions Lake ecological communities have undergone or are at high risk of a regime shift to persistent, degraded state (without native macrophyte/seagrass cover), due to impacts Total Nitrogen g/m3 Polymictic D >.8 of elevated nutrients leading to excessive algal and/or plant growth, as well from (Trophic state) losing oxygen in bottom waters of deep lakes.

7.1.1.4. Phosphorus

Total phosphorus levels are showing long term decline with periodic modes still occurring as late as 2015. As phosphorus is a limiting nutrient, this is a hopeful trend.

The table, following the chart below, shows the National Policy Statement for Freshwater Management limits for lake state. More recently, phosphorus ranged between States A and B, with an earlierLAKE NGATUhistory MANAGEMENT of peaks into PLAN State | Chemical C. Characteristics

Lake Ngatu Total Phosphorus (TP) g/m3-‐P

0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 1/12/2005 1/05/2006 1/10/2006 1/03/2007 1/08/2007 1/01/2008 1/06/2008 1/11/2008 1/04/2009 1/09/2009 1/02/2010 1/07/2010 1/12/2010 1/05/2011 1/10/2011 1/03/2012 1/08/2012 1/01/2013 1/06/2013 1/11/2013 1/04/2014 1/09/2014 1/02/2015 1/07/2015 1/12/2015 1/05/2016

7.1.2. Trophic Level Index the health of submerged native plant communities. The trophic level index (TLI) is used in New Zealand as The 2005-2016 TLI trend, shown below, indicates a measure of the nutrient status of lakes. The index a decline since 2015 with the lake moving from a combines four variables; phosphorus, nitrogen, visual mesotrophic to a eutrophic state, although 2017 clarity (Secchi disk depth) and algal biomass, each data (not shown) is showing improvement. The lake weighted equally. had been low level eutrophic before in 2009-2010. Anecdotal reports and old photographs suggest that A low TLI score indicates a healthy lake with clear the lake was historically a clear water lake. Visibility water and little algal bloom occurrence. A high TLI was described during an ecological survey in 2001 as shows an overly nutrient-rich lake prone to algal 4-5m with meadows of vegetation across the entire blooms and poor light incidence, this shading affecting lake bed.

19 LAKE NGATU MANAGEMENT PLAN | Chemical Characteristics

Lake Ngatu Trophic Level Index Score

Water Trophic TLI 5 Quality Level Score Very Good Microtrophic <2 4 Good Oligotrophic 2-3 Average Mesotrophic 3-4 3 Poor Eutrophic 4-5 Very Poor Supertrophic >5 2 No Data No data 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 available

Water TLI Trophic Level Quality Score Very Good Microtrophic <2 Good Oligotrophic 2-‐3 Average Mesotrophic 3-‐4 Poor Eutrophic 4-‐5 Very Poor Supertrophic >5 No data No Data available

7.1.3. Dissolved Oxygen g/m³ 24 Although the lake does not thermally stratify due to its shallowness, there is an occasional oxygen depletion in water deeper than 4 - 4.5 meters between August and February. 20

The table below shows the dissolved oxygen (at 15 degrees C) limits for New Zealand freshwater fish from https://www.niwa.co.nz/freshwater-and- estuaries/research-projects/dissolved-oxygen-criteria-for-fish. These guidelines help interpret the depth profiles as to the depth of the water column usable by fish species during the different seasons displayed in the graphs.

LAKE NAGTU MANAGEMENT PLAN | Chemical Characteristics

7.1.3. Dissolved Oxygen g/m³ from https://www.niwa.co.nz/freshwater-and- Although the lake does not thermally stratify due to its estuaries/research-projects/dissolved-oxygen- shallowness, there is an occasional oxygen depletion in criteria-for-fish. These guidelines help interpret the water deeper than 4 - 4.5 meters between August and depth profiles as to the depth of the water column February. usable by fish species during the different seasons displayed in the graphs. The table below shows the dissolved oxygen (at 15 degrees C) limits for New Zealand freshwater fish

Mokeno Summer DO Depth Proﬁles

14 Ngatu Summer DO Depth Proﬁles 12 10 10 8 8

DO 6 6 DO 4 4 2 2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 Depth 1.5 m 2 2.5 3 3.5 4 4.5 5 5.5 6 Depth m 14/12/05 28/02/06 19/02/08 27/02/12 08/12/05 29/01/08 01/02/11

07/02/11 20/02/12 10/02/14

LAKE NGATU MANAGEMENT PLAN | Chemical Characteristics Ngatu Autumn DO Depth Proﬁles Ngatu Autumn DO Depth Proﬁles 12 10 12 10 8 6 DO 6 8 DO 4 6 DO 4 2 4 0 2 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 Depth m 2 2.5 3 3.5 4 4.5 5 5.5 6 Depth m 15/03/06 22/05/06 09/03/09 17/05/10 15/03/06 22/05/06 09/03/09 17/05/10 23/05/11 14/05/12 13/05/13 23/05/11 14/05/12 13/05/13

Ngatu Winter DO Septh Proﬁles Ngatu Winter DO Septh Proﬁles 12 12 10 10 8 6 DO 8 6 DO 4 6 DO 4 2 4 0 2 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 2 2.5 Depth 3 3.5 m 4 4.5 5 5.5 6 Depth m 07/08/06 06/08/07 30/06/08 17/08/09 07/08/06 06/08/07 30/06/08 17/08/09 16/08/10 06/08/12 13/08/13 16/08/10 06/08/12 13/08/13

Ngatu Spring DO Depth Proﬁles Ngatu Spring DO Depth Proﬁles 12 10 12 10 8 6 DO 6 8 DO 4 6 DO 4 2 4 0 2 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.5 1 1.5 2 2.5 Depth 3 3.5 m 4 4.5 5 5.5 6 Depth m 10/11/04 30/10/06 05/11/07 10/09/08 10/11/04 30/10/06 05/11/07 10/09/08 17/11/10 22/11/11 05/11/12 17/11/10 22/11/11 05/11/12

22 27 27

LAKE NGATU MANAGEMENT PLAN | Biological Characteristics

7.1.4. pH 7.2. Lake and catchment water and The lake has a very slightly increasing trend to higher pH nutrient dynamic drivers (increased alkalinity conditions). This is most likely a result 7.2.1. Influence of nutrient loading of algal bloom activity using up dissolved carbon dioxide In general, the persistence of new nitrogen from the which would otherwise make the lake water relatively many culverts and drains entering the lake do not offer more acidic. As the lake has inanga present, this is a a chance for natural recovery unless these sources are positive indicator as these fish are basophilic (preferring mitigated. An NRC Freshwater Improvement Fund alkaline over acidic water). project will assist with sediment and nutrient detention structures to mitigate this.

8. BIOLOGICAL CHARACTERISTICS Native bladderwort (Utricularia australis), listed in 8.1. Lake Biodiversity and Biosecurity the highest threat category as Nationally Critical, species has not been recorded in Lake Ngatu since 2004. Its decline is most likely related to competition with the 8.1.1. Plants introduced yellow bladderwort (Utricularia gibba) and One of the reasons that Lake Ngatu is among the to increasing pH (alkalinity) as a result of algal blooms top outstanding dune lakes in Northland is due to its consuming dissolved carbon. diverse aquatic plant community. The lake supports 20 native plant species, including five rare natives, The table is organised as a depth gradient, from shown in the table below. emergent plants to those which are submerged, for each of the invasives and natives. Of note is the large population of the Nationally Endangered Trithuria inconspicua, a tiny rush-like In addition to the natives, there are five exotic species submerged plant which has become extinct in a most recorded, three of these being invasive, three being of the Northland lakes where it was found previously. invasive and including yellow flag iris (eradicated by the NRC in 2007), alligator weed and Lagarosiphon.

23 LAKE NGATU MANAGEMENT PLAN | Biological Characteristics

The latter is highly invasive and is capable of eradicated both plants (Heather appears green to covering the entire lake floor and overgrowing the signify that grass carp have now eaten all species, lake. There is also a patch of planted water lilies but natives will regrow once the fish are removed). which do not appear to have spread and are being These pest-weed species are still present in three eradicated by NRC. other lakes in the region, however.

The table presents plant communities in nearby dune Lake Ngakapua South was treated with herbicide lakes as a comparison and indication of biosecurity for Lagarosiphon and is due to be signed off species of concern which should be contained as a successful eradication (Ngakapua South wherever possible. Data is derived from annual Lagarosiphon is in purple in the table to indicate its NIWA ecological surveys. former presence). An NRC Freshwater Improvement Fund project is seeking to work with the community Nearby Lake Heather was a risk to Ngatu and to control or eradicate these species from lakes other lakes because it was infested with Egeria and Ngatu, Mini/Split, Rotoroa and Waimimiha North. hornwort, but the introduction of grass carp has

Depth and Plant Type Zone Biogeography Common Name Species Forest Lake/Dean's Swamp West Coast Rd Carrot/Ngakapua West Heather Gem Little Ngakapua Ngatu Rotokawau (SW) Rotoroa Mini/Split North Waimimiha South Waimimiha Frequency Erect emergent Invasive exotic yellow flag iris Iris pseudacorus x 1 Erect emergent Non-‐invasive exotic bulbous rush Juncus bulbosus x x 2 Sprawling emergent Invasive exotic alligator weed Alternanthera philoxeroides x x x x 4 Sprawling emergent Invasive exotic glyceria, swamp grass, water meadow grass Glyceria maxima x 1 Sprawling emergent Non-‐invasive exotic water purslane Ludwigia palustris x 1 Free floating Non-‐invasive exotic bladderwort, yellow bladderwort Utricularia gibba X x x x x x x X x x 10 Submerged tall pondweed Invasive exotic hornwort, coontail Ceratophyllum demersum x x x 3 Submerged tall pondweed Invasive exotic lakeweed, egeria Egeria densa x X x 3 Submerged tall pondweed Invasive exotic lagarosiphon, lakeweed, oxygen weed Lagarosiphon major x 1 Erect emergent Native oioi, jointed wire rush Apodasmia similis x x 2 Erect emergent Native sharp spike sedge Eleocharis acuta x x 2 Erect emergent Native bamboo spike sedge, tall spike sedge Eleocharis sphacelata x x x x x x x x x x x x 12 Erect emergent Native manuka, tea tree, kahikatoa Leptospermum scoparium x 1 Machaerina arthrophylla (syn. x x x Erect emergent Native sedge Baumea arthrophylla) 3 Machaerina articulata (syn. Baumea x x x x x x x x Erect emergent Native jointed baumea, jointed twig rush articulata) 8 Machaerina juncea (syn. Baumea x x Erect emergent Native sedge, tussock swamp twig rush juncea) 2 Erect emergent Native flax, harakeke, korari Phormium tenax x 1

x x x x Erect emergent Native softstem bulrush, grey club-‐rush, great bulrush Schoenoplectus tabernaemontani 4 Erect emergent Native burr-‐reed, maru Sparganium subglobosum x x 2 Erect emergent Native raupo Typha orientalis x x x x x x x 7 Erect emergent Rare native none known Cyclosorus interuptus x 1 Erect emergent Rare native Marsh fern, swamp fern Thelypteris confluens x 1 Sprawling emergent Native pennywort Hydrocotyle pterocarpa x 1 Sprawling emergent Native swamp millet Isachne globosa x 1 Sprawling emergent Native swamp willow weed Persicaria decipiens x 1 Low growing turf Native gratiola Gratiola sexdentata x x 2 Low growing turf Native none known (sedge) Isolepis prolifera x x x x 4 Low growing turf Native Zelandiae chain sword Lilaeopsis novae-‐zelandiae x x 2 Low growing turf Native mudwort Limosella lineata x 1 Low growing turf Native arrow grass Triglochin striata x x x 3 Trithuria inconspicua (syn Hydatella x x Low growing turf Rare native hydatella inconspicua) 2 Floating leaved Native red pondweed Potamogeton cheesemanii x x x x x x 6 Submerged milfoil Native common water milfoil Myriophyllum propinquum x x x x x 5 Submerged milfoil Rare native small water milfoil Myriophyllum votschii x 1 Submerged tall pondweed Native blunt pondweed Potamogeton ochreatus x x 2 Submerged tall pondweed Rare native bladderwort, yellow bladderwort Utricularia australis x x x x x x 6 Submerged charophyte Native stonewort Chara australis x x x x x x x x x 9 Submerged charophyte Native stonewort Chara fibrosa x x 2 Submerged charophyte Native stonewort Nitella leonhardii x x 2 Submerged charophyte Native stonewort Nitella pseudoflabellata x 1 Submerged charophyte Native stonewort Nitella sp. aff. cristata x x x x x 5 Total Plant Diversity 7 6 9 17 14 11 25 13 9 11 3 3 Exotic Plant diversity 111512513411 Native Plant Diversity 6 5 8 12 13 9 20 12 6 7 2 2

8.1.1.1.1. Lake Submerged Plant Index (LakeSPI), Native Condition Index and Invasive Impact Index 24 Three indices are valuable for considering the health of a lake’s plant community; Lake Submerged Plant Index, Native condition Index and Invasive Plant Index. From the 2004-2016 timeline below, the lake’s Native Condition Index and Submerged Plant Index are increasing and the Invasive Impact Index is decreasing. In short, this means that desirable native plants are improving while invasive plants, which were becoming dominant, are now declining.

LAKE NGATU MANAGEMENT PLAN | Biological Characteristics

8.1.1.1.1. Lake Submerged Plant Index (LakeSPI), lake’s Native Condition Index and Submerged Plant Native Condition Index and Invasive Impact Index are increasing and the Invasive Impact Index is Index decreasing. In short, this means that desirable native Three indices are valuable for considering the health plants are improving while invasive plants, which of a lake’s plant community; Lake Submerged Plant were becoming dominant, are now declining. Index, Native condition Index and Invasive Plant Index. From70 the 2004-2016 timeline below, the 60 Lake Ngatu 70 50 Lake Submerged Plant 60 40 LakeIndex Ngatu % 50 30 Lake Na[ve Submerged Condi[on Plant Index % 40 20 Index % 30 10 Na[ve Invasive Condi[on Impact Index % Index % 20 0 10 Invasive Ecological Health Impact Submerged Index % Plant Index Score Excellent 75-100% 0 High 50-75% 1/1/2005 1/1/2007 1/1/2008 1/1/2009 1/1/2011 1/1/2015 1/1/2004 1/1/2006 1/1/2010 1/1/2012 1/1/2013 1/1/2014 1/1/2016 Moderate 20-50% Poor 1-20% 1/1/2005 1/1/2007 1/1/2008 1/1/2009 1/1/2011 1/1/2015 1/1/2004 1/1/2006 1/1/2010 1/1/2012 1/1/2013 1/1/2014 1/1/2016 Non-Vegetated 0% Ecological Submerged Plant Health Index Score

EcologicalExcellent Submerged75 Plant-‐100% 8.1.2.Health Fish Index Score fish diversity, yet has among the highest diversity High 50-‐75% The table below displays the fish of the Sweetwater of pest fish of all Northland lakes, largely due to its ExcellentModerate 75-‐100%20 -‐50% area of the Aupöuri Peninsula. Pest fish are shown in accessibility and history of multiple recreational uses. High 50-‐75%1-‐ 20% green andPoor conservation species in pink. Lake Ngatu Data has been derived from annual NIWA ecological ModerateappearsNon in yellow. -‐Vegetated The lake has20 -‐a50% low level0% of native surveys. Poor No Data 1-‐20% Non-‐Vegetated 0% 8.1.2. Fish No Data

The table below displays the fish of the Sweetwater area of the Aupōuri Peninsula. Pest8.1.2. fish Fish are shown in green and conservation species in pink. Lake Ngatu appears in yellow. The lake has a low level of native fish diversity, yet has among the highest The tablediversity below of displays pest fish the of allfish Northland of the Sweetwater lakes, largely area due of the to itsAup accessibilityōuri Peninsula. and history Pest fishof multiple are shown recreational in green anduses conservation. DataConservation has been species Degreederived in pink. from Lake annual Ngatu NIWA appears ecological in yellow.common nameThe lake has aspecies low level of nativestatus fish diversity,of loss yet has among the highest surveys. Forest Lake/Dean's Swamp West Coast Rd Carrot/Ngakapua West Heather Little Gem Ngakapua Ngatu Rotokawau (SW) Rotoroa Mini/Split frequency diversitygrass carp of pestCtenopharyngodon fish of all Northland idella lakes, largely due to its accessibilityx and history 1 ofrainbow multipleGambusia trout recreational, Oncorhynchus goldfish, uses rudd, mykiss. Data perch has andbeen, perhaps derived, fromeven annual introduced NIWA trout ecological in thex past, 1 surveys.goldfishsuggest thereCarassius has auratus been a history of illegal introductions via a range of xvectors x both 2 GambusiaaccidentalGambusia and intentional affinis . x x x x x x 6 perch Perca fluviatilis ? 1 Gambusia , goldfish, rudd, perch and, perhaps, even introduced trout in the past, suggestrudd there hasScardinius been erythrophthalmus a history of illegal introductions via a range of vectors bothx 1 shortfinnedCommon eel Anguillabully and australis inanga are still present, but will be under sustainedx pressure tox 2 accidentalsurvive and. intentional. longfinned eel Anguilla dieffenbachii at risk declining x 1 inanga Galaxias maculatus at risk declining x x x x 4 CommonA full bull fishy and survey inanga was are last still undertaken present, butby DOCwill be in under 2014 sustainedand should pressure be repeated. to x x x x x x x 7 survivecommon . bully Gobiomorphus cotidianus smelt Retropinna retropinna x 1 A full fish survey was lastdiversity undertaken pest fish by DOC in 2014 and 0should 1 0be 0repeated. 1 2 4 1 1 0 diversity native 1 0 1 2 1 1 2 2 4 1

8.1.3. Waterbirds 25 The table below displays the waterbirds of the Sweetwater area of the Aupōuri Peninsula. Game birds are shown in green and non-game bird native species in pink. Lake Ngatu appears in yellow. Canada goose is an exception, having been taken31 off the game bird list but able to be hunted year-round and posing a nutrient risk to lake when numbers swell. The lake has a moderate level of bird diversity and the area is 31 popular with duck-hunters. Caspian tern are probably feeding on schools of fish in the lake and account for their sole occurrence in the general area. Data has been derived from annual NIWA ecological surveys.

Conservation Criteria / status (DOC: Conservation status Degree of common name species , 2016) loss of NZ birds Forest Lake/Dean's Swamp West Coast Rd West Carrot/Ngakapua Heather Little Gem Ngakapua Ngatu Rotokawau (SW) Rotoroa Mini/Split Waimimiha North Waimimiha South frequency Cygnus atratus (resident native (not introduced) on x x x black swan game bird list) Not threatened 3 Tardorna variegata (resident native (not introduced) x x x paradise shelduck on game bird list) Not threatened 3 Branta canadensis (Introduced & naturalised, not Introduced & x x Canada goose protected, able to be hunted at any time) naturalised 2 New Zealand scaup Aythya novazeelandiae not threatened x x 2 nationally x x x x x x x x x Australasian bittern Botaurus poiciloptilus threatened critical 9 North Island fernbird Bowdleria punctata vealeae at risk declining x x x 3 nationally x Caspian tern Hydroprogne caspia threatened vulnerable 1 New Zealand dabchick Poliocephalus rufopectus at risk recovering x x x x x x x x x 9 spotless crake Porzana t. tabuensis at risk declining x x x 3 Australasian little grebe Tachybaptus n. novaehollandiae coloniser x x x x x x 6 diversity resident native (not introduced) on game bird list 0 0 0 1 0 2 0 0 2 1 0 0 diversity introduced & naturalised 0 0 0 1 0 0 0 0 0 1 0 0 diversity native 1 3 3 2 2 3 4 4 4 2 2 3

8.1.4. Invertebrates

Invertebrates are of interest in lake systems as indicators of lake health. They are generally very sensitive to poor water quality. In the case of Lake Ngatu, the presence of the Tanytarsini midge, which cannot tolerate more than moderate

Conservation Degree common name species status of loss Forest Lake/Dean's Swamp West Coast Rd Carrot/Ngakapua West Heather Little Gem Ngakapua Ngatu Rotokawau (SW) Rotoroa Mini/Split frequency grass carp Ctenopharyngodon idella x 1 rainbow trout Oncorhynchus mykiss x 1 goldfish Carassius auratus x x 2 Gambusia Gambusia affinis x x x x x x 6 perch Perca fluviatilis ? 1 rudd Scardinius erythrophthalmus x 1 shortfinned eel Anguilla australis x x 2 longfinned eel Anguilla dieffenbachii at risk declining x 1 inanga Galaxias maculatus at risk declining x x x x 4 x x x x x x x 7 common bully Gobiomorphus cotidianus smelt Retropinna retropinna x 1 diversity pest fish 0 1 0 0 1 2 4 1 1 0 diversity native 1 0 1 2 1 1 2 2 4 1

8.1.3. Waterbirds LAKE NGATU MANAGEMENT PLAN | Biological Characteristics

The8.1.3. table Waterbirds below displays the waterbirds of theand Sweetwater posing a nutrient area risk toof lake the when Aup numbersōuri Peninsula.The table below Game displays birds the waterbirds are shown of the in green andswell. non The -lakegame has abird moderate native level species of bird diversityin pink. LakeSweetwater Ngatu area appears of the Aupöuri in yellow. Peninsula. Canada Game gooseand is the an area exception, is popular with having duck-hunters. been taken Caspian off thebirds game are shown bird in listgreen but and able non-game to be bird hunted native yeartern-round are probably and posing feeding a on nutrient schools of risk fish to in lakethe when numbers swell. The lake has a moderate level of bird diversity and the area is species in pink. Lake Ngatu appears in yellow. lake and account for their sole occurrence in the popular with duck-hunters. Caspian tern are probably feeding on schools of fish in general area. Data has been derived from annual theCanada lake goose and is accountan exception, for having their beensole takenoccurrence off in the general area. Data has been derivedthe game birdfrom list annual but able NIWAto be hunted ecological year-round surveys. NIWA ecological surveys.

8.1.4. Invertebrates 8.1.4. Invertebrates cannot tolerate more than moderate pollution is InvertebratesInvertebrates are of are interest of interest in lake systems in lake as systemsencouraging, as indicators but otherof lake sensitive health. species They are absent. are generallyindicators of verylake health. sensitive They are to generally poor water very quality.Freshwater In the casecrayfish of (koura/kewai) Lake Ngatu, are theabsent. Data is presencepollution is of enc theouraging Tanytarsini, but midge, other sensitive which cannot species tolerate are absent. more than Freshwater moderate crayfish sensitive(koura/kewai) to poor water are quality.absent. In the Data case is of aLake compilation a compilation of NIWA of NIWAand Northtecand Northtec surveys. surveys. The The lake Ngatu,lake has the presencetwo species of the Tanytarsini of non-native midge, whichsnails. has two species of non-native snails. 32

Pollution minimum tolerance -‐ Clean Water (>5.99) Mild Pollution (5.00-‐5.90) Moderate Pollution (4.00-‐4.99) Order or phylum and common name Family or species Severe Pollution (<4.00) Forest Lake/Dean's Swamp West Coast Rd Carrot/Ngakapua West Heather Little Gem NorthNgakapua basin South basin Ngakapua Ngatu (SW) Rotokawau Rotoroa Mini/Split Waimimiha North Waimimiha South frequency Hydrozoa, freshwater jellyfish medusae Craspedacusta sowerbyi x 1 Mollusc, ramshorn snail Planorbarius corneus x x x 3 Mollusc, snail Physa (Physella) acuta 0.1 x x x x 4 Mollusc, snail Planorbella scalaris x x x 3 Mollusc, snail Pseudosuccinea x x x x 4 Acarna, mite Oribatida 5.2 x 1 Coleoptera, dytiscid diving beetle Onychohydrus hookeri x x x x x 5 Coleoptera, whirigig beetle Gyrinus x 1 Crustacea, Cladocera sp 0.7 x 1 Crustacea, Copepoda sp 2.4 x 1 Crustacea, Ostracoda, koura Paranephrops planifrons 8.4 0 Crusteacea, Ostracoda Herpetocypris 1.9 x 1 Diptera, midge, non-‐biting, Chironomid Tanytarsini 4.5 x x 2 Diptera, midge, non-‐biting, Chironomid Chironomas sp 3.4 x x x x x x x 7 Diptera, midge, non-‐biting, Chironomid Orthocladiinae 3.2 x x x 3 Hemiptera, bug sp x 1 Hemiptera, bug, backswimmer Anisops 2.2 x 1 Hemiptera, bug, backswimmer Sigara arguta 2.4 x x x 263 Hemiptera, bug, waterboatman Corixidae sp x x x x x 5 Hirudinea, leech Alboglossiphonia x 1 Hirudinea, leech Richardsonianus mauianus x 1 Lepidoptera, aquatic moth Hygraula nitens 1.3 x x 2 Mollusca, freshwater mussel Hyridella menziesi 6.7 x x 2 Mollusca, pea mussel Musculium novazelandiae x 1 Mollusca, pea mussel Sphaerium novaezelandiae x 1 Mollusca, snail Planorbella sp x 1 Mollusca, snail, native Glyptophysa variabilis 0.3 x 1 Mollusca, snail, native Potamopyrgus antipodarum 2.1 x 1 Nemertea, proboscis worm sp 1.8 x 1 Odonata, damselfly Ischnura 3.1 x 1 Odonata, damselfly Xanthocnemis sp 1.2 x x x x 4 Odonata, dragonfly Hemicordulia australiae 0.4 x x x x 4 Odonata, dragonfly sp x x 2 Odonata, dragonfly Tramea loewii x 1 Oligocheate worm Oligochaeta sp 3.8 x 1 Oligocheate worm Tubificidae x 1 Ostracod crusteacean Ilyodromus x 1 Porifera, freshwater sponge sp x 1 Trichoptera, caddisfly Oecetis unicolor 6.8 x 1 Trichoptera, caddisfly Paroxyethira hendersoni 3.7 x x 2 diversity invasive 0212121222000 15 diversity native 0 5 13 9 1 12 4 5 4 10 0 0 0

8.1.5. Catchment weeds

A range of exotic tree species should be removed from the catchment. Efforts should be focused first on nitrogen-fixing weeds such as brush wattle, wattle, oxylobium and gorse.

9. Land Use

9.1. Catchment land cover (ha) and map

33 pollution is encouraging, but other sensitive species are absent. Freshwater crayfish (koura/kewai) are absent. Data is a compilation of NIWA and Northtec surveys. The lake has two species of non-native snails.

Pollution minimum tolerance -‐ Clean Water (>5.99) Mild Pollution (5.00-‐5.90) Moderate Pollution (4.00-‐4.99) Order or phylum and common name Family or species Severe Pollution (<4.00) Forest Lake/Dean's Swamp West Coast Rd Carrot/Ngakapua West Heather Little Gem NorthNgakapua basin South basin Ngakapua Ngatu (SW) Rotokawau Rotoroa Mini/Split Waimimiha North Waimimiha South frequency Hydrozoa, freshwater jellyfish medusae Craspedacusta sowerbyi x 1 Mollusc, ramshorn snail Planorbarius corneus x x x 3 Mollusc, snail Physa (Physella) acuta 0.1 x x x x 4 Mollusc, snail Planorbella scalaris x x x 3 Mollusc, snail Pseudosuccinea x x x x 4 Acarna, mite Oribatida 5.2 x 1 Coleoptera, dytiscid diving beetle Onychohydrus hookeri x x x x x 5 Coleoptera, whirigig beetle Gyrinus x 1 Crustacea, Cladocera sp 0.7 x 1 Crustacea, Copepoda sp 2.4 x 1 Crustacea, Ostracoda, koura Paranephrops planifrons 8.4 0 Crusteacea, Ostracoda Herpetocypris 1.9 x 1 Diptera, midge, non-‐biting, Chironomid Tanytarsini 4.5 x x 2 Diptera, midge, non-‐biting, Chironomid Chironomas sp LAKE NGATU MANAGEMENT3.4 x PLAN x x | Biological x x x xCharacteristics7 Diptera, midge, non-‐biting, Chironomid Orthocladiinae 3.2 x x x 3 Hemiptera, bug sp x 1 Hemiptera, bug, backswimmer Anisops 2.2 x 1 Hemiptera, bug, backswimmer Sigara arguta 2.4 x x x 3 Hemiptera, bug, waterboatman Corixidae sp x x x x x 5 Hirudinea, leech Alboglossiphonia x 1 Hirudinea, leech Richardsonianus mauianus x 1 Lepidoptera, aquatic moth Hygraula nitens 1.3 x x 2 Mollusca, freshwater mussel Hyridella menziesi 6.7 x x 2 Mollusca, pea mussel Musculium novazelandiae x 1 Mollusca, pea mussel Sphaerium novaezelandiae x 1 Mollusca, snail Planorbella sp x 1 Mollusca, snail, native Glyptophysa variabilis 0.3 x 1 Mollusca, snail, native Potamopyrgus antipodarum 2.1 x 1 Nemertea, proboscis worm sp 1.8 x 1 Odonata, damselfly Ischnura 3.1 x 1 Odonata, damselfly Xanthocnemis sp 1.2 x x x x 4 Odonata, dragonfly Hemicordulia australiae 0.4 x x x x 4 Odonata, dragonfly sp x x 2 Odonata, dragonfly Tramea loewii x 1 Oligocheate worm Oligochaeta sp 3.8 x 1 Oligocheate worm Tubificidae x 1 Ostracod crusteacean Ilyodromus x 1 Porifera, freshwater sponge sp x 1 Trichoptera, caddisfly Oecetis unicolor 6.8 x 1 Trichoptera, caddisfly Paroxyethira hendersoni 3.7 x x 2 diversity invasive 0212121222000 15 diversity native 0 5 13 9 1 12 4 5 4 10 0 0 0

8.1.5. Catchment weeds 8.1.5. Catchment weeds

A rangerange of exoticof exotic tree species tree species should be shouldremoved be removed from the catchment. Efforts should frombe focused the catchment. first onEfforts nitrogen should be-fixing focused weeds first on such as brush wattle, wattle, oxylobium and nitrogen-fixinggorse. weeds such as brush wattle, wattle, oxylobium and gorse. 9. Land Use

9.1. Catchment land cover (ha) and map

9.The LAND catchment USE is largely influenced by high percentageand low producingcovers, include exotic short rotation grassland cropland and and freshwater sedgeland/rushland. Other influences,orchard, although other perennial at lower crops and percentage built-up settlement, 9.1.covers, Catchment include short land rotation cover tablecropland and and orchard, other perennial crops and built- all of which will be contributing to nutrient inputs mapup settlement, all of which will be contributing to nutrient inputs to the lake. There is to the lake. There is little native vegetation in the The catchment is largely influenced by high and low catchment, though most of this is on the lake margins 33 producing exotic grassland and freshwater sedgeland/ with replanted areas to the east and west. little native vegetation in the catchment, though most of this is on the lake margins rushland.with replanted Other influences, areas to thealthough east andat lower west.

34 little native vegetation in the catchment, though most of this is on the lake margins with replanted areas to the east and west.

Total FENZ Total Hand-‐ Lake Cover Type (ha) drawn (ha) Lake Ngatu Built-‐up Area (settlement) 2.14 2.14 Lake Ngatu Deciduous Hardwoods 0.86 0.79 Lake Ngatu Exotic Forest 5.85 6.04 Lake Ngatu Herbaceous Freshwater Vegetation 10.40 10.16 Lake Ngatu High Producing Exotic Grassland 75.31 75.52 Lake Ngatu Lake or Pond 54.93 55.77 Total FENZ Total LiDAR Lake Ngatu Low Producing Grassland Lake 11.89 14.73Cover Type (ha) (ha) Lake Ngatu Manuka and/or Kanuka Lake Mokeno3.46 5.18Broadleaved Indigenous Hardwoods 64.09 0.00 Lake Mokeno Exotic Forest 1267.85 617.65 Lake Ngatu Orchard, Vineyard or Other Perennial Crop Lake Mokeno7.22 7.56Forest -‐ Harvested 370.62 139.87 LAKE NGATU MANAGEMENT PLAN | Land Use Lake Ngatu Total Lake 172.07 Mokeno 177.89Herbaceous Freshwater Vegetation 10.40 5.66 Lake Mokeno Lake or Pond 170.83 169.94 Lake Mokeno Low Producing Grassland 56.51 1.23 Lake Mokeno Manuka and/or Kanuka 253.23 141.57 Lake Mokeno Total 2193.53 1075.91

9.2. Road drains 9.5. Fire- The drains, culverts, septic systems and land-use fighting affecting this lake have been mapped, overleaf. It is yet The lake is a potential unclear what level of nutrients any of these structures source of water for forest and uses have contributed, but they may collectively fire-fighting. NRC and form the key issue for nutrient management in the forestry industry are 9.2. Fire-fighting mitigations this lake which suffers from over-nitrification. A working towards mitigation of lake-bed disturbance systematic assessment of each input is required and and biosecurity pathways by identifying the most unique mitigations put in place. The NRC Freshwater suitable sources of water for this purpose. 31 Improvement Fund will address this study and its mitigations. From the map overleaf, Lake Ngatu is identified as a high-risk water source due to the presence of 9.3. Pastoral farming Lagarosiphon oxygen weed, a highly invasive water Pastoral farming affects the northern, western and weed and a range of pest fish species not present in 34 southern areas of the lake. These paddocks are all waterbodies in the area. Therefore, if a helicopter fenced, however. Some of the fence-lines on the hurricane bucket or other firefighting equipment were western side of the lake are on the boundary of the to move between lakes for sourcing water, there is an paper road which surrounds the lake. These could be unacceptable risk of transfer of these species. Depth set back further and replanted to provide more of a cut-off for lake bed disturbance is 4 m and Lake Ngatu buffer between lake and farmland. is 6.26 m deep in the deepest basin, so that feature does not apply to this risk ranking. Lake Heather 9.4. Forestry (green square) is a preferred source due to the removal Forestry is not a major impact on the catchment. of weed species by grass carp in this lake.

28 hurricane bucket or other firefighting equipment were to move between lakes for sourcing water, there is an unacceptable risk of transfer of these species. Depth cut- off for lake bed disturbance is 4 m and Lake Ngatu is 6.26 m deep in the deepest basin, so that feature does not apply to this risk ranking. Lake Heather (green square) is a preferred source due to the removal of weed species by grass carp in Monitoring Plan LAKEthis NGATU lake. MANAGEMENT PLAN |

Road drains Fire-fighting 9.3. Pastoral farming 10. Monitoring Plan Pastoral farming affects the northern, western and southern areas of the lake. These paddocks10. MONITORINGare fenced, however. PLANSome of the fence-lines on the western side of the lake are on the boundary of the paper road which surrounds theThe lake. mapThese belowcould be shows the five transect lines surveyed during ecological setThe back adjacent further map and showsreplanted the to five provide transect more lines of a buffer between lake and farmland.surveyed during ecological assessments. The dark assessments. The dark triangle is the access point for the NRC vessel for water quality sampling. The pink point in the south of the lake is the water quality sampling triangle9.4. Forestry is the access point for the NRC vessel for water point, corresponding to the deepest point in the lake. quality sampling. The pink point in the south of the Forestry is not a major impact on the catchment. lake is the water quality sampling point, corresponding 9.5. Fire-fighting to the deepest point in the lake. The lake is a potential source of water for forest fire-fighting. NRC and the forestry industry are working towards mitigation of lake-bed disturbance and biosecurity pathways by identifying the most suitable sources of water for this purpose. 10.1. NIWA ecological monitoring From the map below, Lake Ngatu is identified as a high-risk water source due to the presenceThe lake ofis scheduledLagarosipho ton beoxygen fully weed,ecologically a highly monitored invasive water weed and a range of pestevery fish five species years not with present a weed in allsurvey waterbodies annually. in theThere area. Therefore, if a helicopter have been eight full surveys since 1984 with weed 36 surveillance recommended every 1-2 years and has been undertaken most years since 2007. The value class of the lake has held at Outstanding. The next full survey is likely to be done in 2021 with continuation of 1-2 yearly weed surveillance.

10.1. NIWA ecological monitoring 37

The lake is scheduled to be fully29 ecologically monitored every five years with a weed survey annually. There have been eight full surveys since 1984 with weed surveillance recommended every 1-2 years and has been undertaken most years since 2007. The value class of the lake has held at Outstanding. The next full survey is likely to be done in 2021 with continuation of 1-2 yearly weed surveillance.

KEY O = Outstanding H = High M = Medium L= Low Ecological Survey Reconnaissance or Visit Weed Surveillance Grass Carp Assessment Endothall Assessment SPI = Submerged Plant Index Surveillance

Eco Weed Survey survey Lake (yr) (yr) 1984 1985 1986 1987 1988 1989 1990 1991 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Carrot/Ngakapua West 1 M M Forest Lake/Dean's Swamp L M Heather 5 1 H H carp carp carp carp carp Little Gem 5 O M-‐H Mini/Split L Ngakapua 5 1 M-‐H M-‐H O2 weed Endoth Endoth Ngatu 5 1 O O O O Rotokawau (A) 5 M-‐H H M-‐H Rotoroa 5 H Waimimiha North L Waimimiha South L West Coast Rd 5 HH L

10.2. NRC Ecological monitoring 10.2.1. Water quality and quantity monitoring

Water quality sampling occurs quarterly in February, May, August and November. Samples taken by year are shown below.

Row Labels 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Grand Total Ngatu lower 1443344444451 45 Ngatu surface 1 1 1 1 1443444444451 50

11. Work implementation plan

10.1. NIWA ecological monitoring

The lake is scheduled to be fully ecologically monitored every five years with a weed

survey annually. There have been eight full surveys since 1984 with weed 10.1. NIWA ecological monitoring surveillance recommended every 1-2 years and has been undertaken most years

since 2007. The value class of the lake has held at Outstanding. The next full survey The lake is scheduled to be fully ecologically monitored every five years with a weed is likely to be done in 2021 with continuation of 1-2 yearly weed surveillance. survey annually. There have been eight full surveys since 1984 with weed

surveKEY illance recommended every 1-2 years and has been undertaken most years O = Outstanding sinceH = High 2007. The value class of the lake has held at Outstanding. The next full survey M = Medium isL= Low likely to be done in 2021 with continuation of 1-2 yearly weed surveillance. Ecological Survey Reconnaissance or Visit KEY Weed Surveillance O = Outstanding Grass Carp Assessment H = High Endothall Assessment M = Medium LAKE NGATU MANAGEMENT PLAN | Work Implementation Plan SPI = Submerged Plant Index L= Low Surveillance Ecological Survey Reconnaissance or Visit Weed Surveillance Eco Weed Grass Carp Assessment Survey survey EndothallLake Assessment (yr) (yr) 1984 1985 1986 1987 1988 1989 1990 1991 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 SPICarrot/Ngakapua = Submerged West Plant Index 1 M M SurveillanceForest Lake/Dean's Swamp L M Heather 5 1 H H carp carp carp carp carp Little Gem 5 O M-‐H Mini/Split Eco Weed L Ngakapua Survey5 survey 1 M-‐H M-‐H O2 weed Endoth Endoth Lake (yr) (yr) 1984 1985 1986 1987 1988 1989 1990 1991 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Ngatu 5 1 O O O O Carrot/Ngakapua West 1 M M Rotokawau (A) 5 M-‐H H M-‐H Forest Lake/Dean's Swamp L M Rotoroa 5 H Heather 5 1 H H carp carp carp carp carp Waimimiha North L Little Gem 5 O M-‐H Waimimiha South L Mini/Split L West Coast Rd 5 HH L Ngakapua 5 1 M-‐H M-‐H O2 weed Endoth Endoth Ngatu 5 1 O O O O KEY 10.2.Rotokawau (A) NRC Ecological5 monitoring M-‐H H M-‐H Rotoroa 10.2. 5 NRC Ecological monitoring H O = Outstanding Waimimiha North L H = High 10.2.1.Waimimiha South Water10.2.1. quality Water and quality quantity and quantity monitoringL monitoringWest Coast Rd 5 HH L M = Medium L= Low Water quality sampling occurs quarterly in February, May, August andEcological November. Survey Water10.2. quality samplingNRC occurs Ecological quarterly in mo February,nitoring Samples taken by year are shown below. Reconnaissance or Visit May, August10.2.1. and November. Water quality and quantity monitoring Weed Surveillance Samples Row Labels taken by year1989 are 1990 1991shown 1992 1993 below. 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011Grass 2012 2013 Carp 2014 Assessment 2015 2016 2017 Grand Total Ngatu lower 1443344444451Endothall Assessment 45 WaterNgatu surface quality sampling1 occurs quarterly1 1 in February,1 1443444444451 May, August and November. 50 SPI = Submerged Plant Index Samples taken by year are shown below. Surveillance 11. Work implementation plan Row Labels 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Grand Total Ngatu lower 1443344444451 45 Ngatu surface 1 1 1 1 1443444444451 50

11. Work implementation plan 38

11. WORK IMPLEMENTATION PLAN a consultation with the local community. • Goldfish are found in both Lake Ngatu and The NRC’s Freshwater Improvement Fund (FIF) Dune 38 neighbouring Lake Little Gem. Ngatu also Lakes project includes several work-streams at Lake contains rudd and likely perch. Eradication of Ngatu, including: the species will require sustained netting. The FIF • Set-back fencing the slopes of pasture to the work seeks to address these species. south-east. This fence would run 295 m at a cost of ~$2655. Further mitigation work to consider includes: • Lake Ngatu has been selected for a more detailed • The elevated wetland to the north has been modelling benefit-cost analysis for nutrient historically disturbed by kauri stump removal. Any mitigation. This process involves walking the proposals for future swamp kauri extractions in catchment and its sub-catchments, documenting the catchment need to be considered carefully to required works. The model, based on monitoring reduce any risk of effects on Lake Ngatu. of nutrient loads in each drain will estimate the • A range of exotic tree species, targeting nitrogen- nutrient load mitigated by works such as sediment fixing weeds such as oxylobium, gorse, brush detention structures and compare it to the cost of wattle and wattle, should be removed from the the work. The FIF work commits to investigating catchment. and mitigating eight drains to a total of $30,000. • A Check Clean Dry campaign for waka ama users Further voluntary reductions of fertiliser use by • Installation of an electronic continuous water level landowners in the catchment will further mitigate recorder loads. • Set back of fencing and planting along the paper • Eradicating Lagarosiphon with Aquathol K road boundary Endothall, budgeted at $96,576. This will require

30 LAKE NGATU MANAGEMENT PLAN | Appendix 1

• A field audit of sewage leachate from the public Champion, P. (2014) Northland Lakes Strategy Part toilets II update and implementation strategy. NIWA Client • Kuta (tall spike sedge or Eleocharis sphacelata) Report No: HAM2014-038, prepared for Northland restoration for harvesting for cultural material Regional Council: 35. • Eradication of water lily, alligator weed, mile-a- minute and Christmas berry. NIWA for the Northland Regional Council, 2015. de • Notify the rural fire service to avoid water take Winton, M., Taumoepeau, A. and Macdonald, A. from the lake due to pest species present. Lake (2015). Northland Lakes hydro-acoustic survey and Heather is a nearby alternative. bathymetric resources, NIWA CLIENT REPORT No: • The last full fish survey of native and exotic HAM2015-116, Prepared for Northland Regional species was undertaken in 2014 and should be Council. 56 pp. repeated • Trialled control of Gambusia by Gee minnow NIWA for the Northland Regional Council, 2014. trapping Rowe, D., 2014. Biosecurity status of non-native • Planting of the FIF fenced area through the Million freshwater fish species in Northland. Metres project NIWA for the Northland Regional Council, 2014. Wells, R., and P. Champion, 2014. Northland Lakes 12. BIBLIOGRAPHY Ecological Status 2014.

Department of Conservation, Freshwater Ecosystems of NIWA for the Northland Regional Council, 2014. New Zealand (FENZ) database, www.doc.govt.nz/our- Wells, R., P. Champion and T. Edwards, 2014. work/freshwater-ecosystems-of-new-zealand. Northland Lakes – Annual Report 2014.

LWP for Northland Regional Council, 2016. Lake NIWA for the Northland Regional Council, 2015. FMUs for Northland, Recommendations for Policy Wells, R. and P. Champion, 2015. Northland Lakes – development. Annual Report 2015.

Nicol, E. R., 1997. Common Names of Plants in New NIWA for the Northland Regional Council, 2016. Zealand, Press, Lincoln, Canterbury, New Zealand, Wells, R. and P. Champion, 2016. Northland Lakes – Manaki Whenua press. Annual Report 2016.

NIWA for the Ministry for the Environment, 2002. Northland Regional Council, 2013. Cathcart, B., Champion, P., J. Clayton and D. Rowe, 2002. Lake 2013. Soils of Northland. Manager’s Handbook, Alien Invaders.

Northtec for Northland Regional Council, 2009. Ball, NIWA for the Ministry for the Environment, 2002. O. J.-P., S. R. Pohe and M. J. Winterbourn, 2009. The Rowe, D. and E. Graynoth, 2002. Lake Manager’s littoral macroinvertebrate fauna of 17 dune lakes of Handbook, Fish in New Zealand Lakes. the Aupöuri Peninsula, Northland.

NIWA for the Northland Regional Council, 2012. Te Puni Kokiri, Te Kähui Mängai (Directory of Iwi and Champion, P. and de Winton, M. (2012). Northland Mäori Organisations) http://www.tkm.govt.nz Lakes Strategy, NIWA Project: ELF12213, NIWA Client Report No: HAM2012-121, prepared for Northland Timms, B. V., 1982. Coastal dune waterbodies of Regional Council: 42. north-eastern New South Wales. Australian Journal of Marine and Freshwater Research 33: 203-222. NIWA for the Northland Regional Council, 2014.

31 LAKE NGATU MANAGEMENT PLAN | Appendix 1

13. APPENDIX 1. GLOSSARY Deoxygenation – Also called hypoxia. Air is 20.9% oxygen, whereas water contains around 1% oxygen Largely adapted from https://www.lawa.org.nz/Learn and this fluctuates depending on the presence Aquatic - Refers to anything that is related to water. of photosynthetic organisms (higher submerged For example, aquatic organisms are plants or animals plants and microalgae) and the distance to the that live in or near water. surface, as air diffuses oxygen into surface waters. Hypoxia can occur throughout the water column Algal or phytoplankton bloom - A rapid increase in as well as near sediments on the bottom. It usually the population of algae in an aquatic system. Blooms extends throughout 20-50% of the water column, can reduce the amount of light and oxygen available to but depending on the water depth, it can occur in other aquatic life. 10-80% of the water column. For example, in a 10-meter water column, it can reach up to 2 meters Bathymetry – The measurement of depth of water. below the surface. In a 20-meter water column, it can extend up to 8 meters below the surface. Oxygen Biodiversity - The variety of lifeforms at a given time in depletion can result from a number of natural a given place. factors, but is most often a concern as a consequence of pollution and eutrophication in which plant Biosecurity - The precautions taken to protect against nutrients enter a lake, and phytoplankton blooms the spread harmful organisms and diseases. are encouraged. While phytoplankton, through photosynthesis, will raise Dissolved Oxygen (DO) Catchment (area) - The total area of land draining into saturation during daylight hours, the dense a lake, expressed in hectares (ha). population of a bloom reduces DO saturation during the night by respiration. When phytoplankton Chlorophyll a – Chlorophyll a is a green pigment in cells die, they sink towards the bottom and are all plants, including algal phytoplankton, that is used decomposed by bacteria, a process that further for photosynthesis and is a good indicator of the reduces DO in the water column. If oxygen depletion total quantity of algae present. It can be measured in progresses to hypoxia, fish kills can occur and micrograms per litre (ug/l) or reflective florescence units invertebrates like freshwater mussels on the bottom (RFU). Large amounts of algae in a lake can decrease may be killed as well. the clarity of the water, make the water green, form surface scum, reduce dissolved oxygen and alter the pH Dissolved oxygen (DO) - The oxygen content of of the water. water. Dissolved oxygen is important for fish and other aquatic life to breathe. For example, water Clarity (of water) - Refers to light transmission quality guidelines recommend that water should be through water and has two important aspects: visual more than 80 percent saturated with DO for aquatic clarity and light penetration. Visual clarity indicates plants and animals to be able to live in it. how much sediment or runoff is in the water. Light penetration is also important as it controls light availability for growth of aquatic plants.

Classification of dune lakes (Timms, 1982) Dune lake class (Timms, 1982) Description 1. Perched lakes in deflation hollows Perched in leached dunes, in deflation hollows in elevated leached dunes where organic material has sealed the basin floor and provided humic (tea-stained) water. 2. Swamp-associated perched lakes Similar to Class 1 but close to the sea, associated with extensive swamps. 3. Window lakes Water table window lakes in a drowned valley or interdune basin, fed by springs with clear water character. 4. Dune contact lakes Waterbodies where at least one shore is in contact with a coastal dune, often but not exclusively humic. 5. Marine contact lakes Freshwater lakes with marine contact, where there may be intermittent connection with the sea. 6. Ponds in frontal sand dunes Ponds where wind erodes sand to form deflation hollows.

32 LAKE NGATU MANAGEMENT PLAN | Appendix 1

Eutrophic – A trophic level referring to a lake having the amount of native and invasive plants growing in an abundant accumulation of nutrients that support them. Higher Lake SPI scores are associated with the a dense growth of algae and other organisms, the better ecological health. decay of which may deplete the shallow waters of oxygen in summer resulting in potential death of Limiting nutrient assay – An analytic procedure animal life. In the Trophic Level Index (TLI), a trophic to determine what nutrient is limiting algal growth level of 4-5, meaning the water quality is poor. in a lake. If the limiting nutrient becomes available, increased growth of algal phytoplankton will occur. Exotic species (also called introduced, alien, non- indigenous or non-native) - A species living outside Macrophyte - Large water plants and algae that its native distributional range, which has arrived live in freshwater and are visible to the naked by human activity, either deliberate or accidental. eye, as opposed to the microscopic periphyton Exotic species can have various effects on the local and phytoplankton. Macrophytes can be either ecosystem. Exotic species that become established submerged, floating or emergent. Most macrophytes and spread beyond the place of introduction are in Northland are rooted to the bottom. called invasive species. Mana whenua – Te reo Mäori for territorial rights, Hapü - Te reo Mäori for a sub-tribe or a clan. Each power from the land, authority over land or territory, iwi can have a number of hapü. For example, the jurisdiction over land or territory - power associated Ngäti Whätua iwi has hapü including Te Uri-o-Hau, with possession and occupation of tribal land. The Te Roroa, Te Taou, and Ngäti Whätua ki öräkei. tribe’s history and legends are based in the lands they have occupied over generations and the land Humic - Of, relating to, or derived from humus, provides the sustenance for the people and to which is a dark brown or black mass of partially provide hospitality for guests. decomposed organic matter in the soil. Humic acids are present in peats. Humic acids are produced by Mesotrophic - A trophic level of 3-4 meaning the the bacterial decomposition of dead plant residues water quality is average. The lake has moderate levels and by the prolonged action of atmospheric oxygen of nutrients and algae. or water on organic matter. Run-off from land of this soil type can stain lake-water a dark brown (known Native Condition Index - The percentage of native as humic or tanin staining), limiting light for plant vegetation within a lake. A high native condition is growth. Forestry harvest has been shown to disturb desirable. It is one of the measures used to determine this soil type, leading to lake water quality decline. the Lake Submerged Plant Index.

Invasive exotic plant – An exotic species that Native species (also indigenous species) - A becomes established and spreads beyond the place species found naturally in an ecosystem, including of introduction, posing a risk to native ecology. naturally-arriving migrant species which may be found in other countries as well. Endemic natives are Invasive Impact Index - The percentage of invasive found only in one place or country. weeds within a lake. A high Invasive Impact is undesirable. Non-invasive exotic plant - Exotic species of plants that become established and do not readily spread Invertebrate - An animal that has no backbone or beyond the place of introduction, posing little threat spinal column, such as insects, worms, snails and to native species. freshwater mussels. Oligotrophic - A trophic level of 2-3 meaning the Lake Submerged Plant Index (SPI) - A method of water quality is good. The lake has low levels of characterizing the ecological health of lakes based on nutrients and algae, high oxygen levels due to a lack

33 LAKE NGATU MANAGEMENT PLAN | Appendix 1 or decaying organic material. The lake is clear and worldwide glaciations caused sea level to drop, as much blue, with very low levels of nutrients and algae. water was bound up in ice and snow. During warmer interglacial periods, the ice melted and sea level rose. pH - The degree of acidity or alkalinity as measured The effect of these oscillating sea levels is clearly seen in on a scale of 0 to 14 where 7 is neutral, less than 7 uplifted coastal terraces, each flat surface marking the is more acidic, and greater than 7 is more alkaline. position of an earlier high sea level. Periods of low sea Most natural waters fall within the range between pH level and cold climate created expanses of bare earth 6.5 to 8.0 and in the absence of contaminants most and sand with little vegetation. Winds blew the coastal waters maintain a pH value that varies only a few sand into dunes. In the North Island, there was little tenths of a pH unit. active glaciation except in the very highest mountain areas. The build-up of sand dunes was a result of low Phytoplankton - Microscopic algae and sea levels and cold climate. cyanobacteria that drift or float in the water column and are able to produce oxygen through Rare native plant - A rare plant is one that is not photosynthesis. When overgrowth or algal bloom commonly found in the wild. It may be naturally rare or occurs, it is an indication that excess nutrients are sparse or may have a restricted range. Rare plants may a problem. Algal blooms can shade light from or may not be of conservation concern. A threatened reaching submerged plants and if a bloom collapses, plant is a rare plant which is at risk of extinction in the deoxygenation of the water may occur. wild. An endangered plant is a category of threatened plant. It is a technical term for describing the degree of Quaternary dunes – We are currently still living risk of extinction a plant is under. Some technical terms, in the Quaternary period of geological time. The such as endangered, are commonly and inaccurately Quaternary period is subdivided into the Pleistocene used to refer to all threatened plants. epoch (2.6 million years ago to 11,700 years ago), the Holocene epoch (11,700 years ago to 1950) Residence time (also retention time, water age or and the Anthropocene epoch (1950-present or the flushing rate) – A calculated quantity expressing the period when the Industrial Revolution began to alter mean time that water spends in a particular lake. climate). When we refer to dune sand types, they are informally divided into Early/Lower Quaternary (dunes Riparian zone - A strip of land, usually of varying formed 2.6 million-78,000 years ago) and Late/Upper width, that is directly adjacent to a waterway and which Quaternary (dunes formed 12,000 years ago to the contributes to maintaining and enhancing the natural present, basically during the Holocene epoch). functioning, quality, and character of the waterbody. This area is commonly planted in native species to The material in present-day river valleys and beaches reduce sediment and nutrient inflows. has been mainly deposited since the last glacial stage ended, about 14 000 years ago. From then, until about Sp. aff. or aff. (short for “species affinis”) indicates 6000 years ago, there was a substantial warming of a potentially new and undescribed species has an climate which caused a rise in sea level; some dune affinity to, but is not identical to, the named species. deposits are recognised as having formed at the time ... spp.; short for “species”) indicates potentially new that sea level rise ended. species without remarking on its possible affinity.

Sea level has dropped again slightly since that time. Secchi disk - Lake clarity is measured using a Secchi Lakes are collecting mud and sand and will eventually disc attached to a measured line. The disc is lowered fill. Sand dunes naturally advance, blown by the wind into the water until it disappears and this depth is until stabilised by vegetation. noted. The disc is lowered a little further and then slowly raised until it reappears, this depth is noted. The Periods of cold climate occurred throughout the average of the two readings is the final Secchi depth Quaternary, not only in New Zealand but globally. The visibility depth.

34 LAKE NGATU MANAGEMENT PLAN | Appendix 1

Supertrophic - A trophic level greater than 5 meaning the water quality is very poor. The lake is fertile and saturated in phosphorus and nitrogen, often associated Acknowledgements with poor water clarity. Sincere thanks to those who have generously provided Thermal stratification - Refers to a change in the their time to the twelve outstanding dune lake plans lake water temperature at different depths in the project, including: lake, and is due to the change in water’s density with • Lisa Forester for the guidance, support, knowledge temperature. Cold water is denser than warm water and editing. and the epilimnion, or shallower waters, generally consists of water that is not as dense as the water in • Andrew Macdonald for countless analyses, data the hypolimnion, or deeper waters. When stratification presentation and editing. occurs, the two water masses are not mixing, leading • Bruce Howse for guidance and support along the to nutrients and lower oxygen levels being captured in way. deeper, colder water. This generally occurs in warmer months. When the upper water cools in colder months, • Katrina Hansen and Bruce Griffin in Biodiversity for mixing will occur, providing nutrients throughout the their editing. lake, which can lead to algal bloom conditions. • Ngä Kaitiaki o ngä roto tähuna – Each iwi/hapu/ Total Phosphorus (TP) - Total phosphorus is a whanau and marae who have engaged in this measure of all forms of phosphorus that are found in process and in the korero and mahi to come. a sample, including dissolved and particulate, organic • The NRC teams: Biodiversity, GIS, Biosecurity, and inorganic. High levels of total phosphorus in water Hydrology, State of the Environment, Area can come from either wastewater or run-off from Offices in Dargaville and Kaitaia, Land agricultural land. Too much phosphorus can encourage Management, Consents, IS&T, Planning and Policy, the growth of nuisance plants such as algal blooms. Communications, Finance and our Kaiarahi who all made valuable contributions of time, information Total Nitrogen (TN) - Total Nitrogen is a measure of all and thought. organic and inorganic forms of nitrogen that are found in a sample. High total nitrogen, like total phosphorus • The Northland Regional Council councillors and our can be a cause of eutrophication in lakes, estuaries and CEO Malcolm Nicolson who are passionate about coastal waters and can cause algal blooms. our region and our lakes.

• Paul Champion and the team at NIWA for data Total Suspended Solids (TSS) - Solids in water that provision and insight. can be trapped by a filter for measurement. TSS can include a wide variety of material, such as silt, decaying • Kevin Matthews of the Bushland Trust for local plant and animal matter, industrial wastes, and sewage. knowledge of the Aupouri and Karikari Peninsulas High concentrations of suspended solids can adversely ecology. affect aquatic life. • Graeme Doole at the Ministry for the Environment Trophic Level Index (TLI) - Used in New Zealand as a and Chris Tanner at the Cawthron Institute for the measure of nutrient status of lakes. The TLI is calculated modelling approach to nutrient mitigation presented from data from 4 parameters: water clarity (Secchi), in the Humuhumu and Kanono plans. chlorophyll a content, total phosphorus and total • Our friends at DOC, Taharoa Domain Committee nitrogen. at Kaipara District Council and Lake Ngatu Action Group for collaborations. Volumetric flow rate (as a mean annual total) - The amount of water entering a lake in a year, expressed in • The Catchment Groups, especially Pöuto and m3/s or cubic meters per second. Doubtless Bay, for their lakes-related planning.

35 LAKE NGATU MANAGEMENT PLAN | Appendix 1

• The forestry industry for their open engagement and the farmers who are taking steps to protect these lakes.

• The Ministry for the Environment and ratepayers of Northland for the Dune Lakes Freshwater Improvement Fund project which will address many of the actions in these plans over the next five years.