Water Quality – Lake Waikare Presentation to Waikato District Council 24 June 2014

Presentation outline Context - Lake Waikare and surrounding catchment Lake Waikare water quality challenge Existing governance arrangements Future

Lake Waikare Context One of many shallow lowland peat lakes in the Waikato delta Lower Waikato Flood Protection scheme Area of significance for Waikato-Tainui Whangamarino wetland Catchment land use and sedimentation Shallow lakes accord (Waikato-Tainui, WDC, DoC, WRC)

Lower Waikato Lakes 25 lakes in the Lower Waikato zone 35 Lower Waikato Lakes 28 21 25 lakes in the Lower Waikato zone 3 provisionally ranked in Top 10 Waipa/Waikato/ Hamilton lakes Lakes Rotokawau (3), Areare (9) and Waahi (10) 16 3 38 11 42 40 10 9 13

Lake Waikare Context A shallow lake, high sediment input Flood control scheme lake level storage and management Large sediment inflow from Matahuru catchment Downstream impacts of sediment through the wetland Current Waikare gate consent compliance review Other consents to discharge to Lake Waikare

Rangiriri Spillway & 1971 when in operation

Lower Waikato Flood Protection Scheme

Lower Waikato Zone

Bloom of the red-pigmented algae Monoraphidium in Lake Waikare, May 2014

Lake Waikare water quality Nitrogen, phosphorus – promote algal growth Sediment (reduced clarity impacts ecology and suitability for contact recreation) Wind and pest fish disturb bottom sediments

Red pigment “zeaxanthin” Monoraphidium sp. Red pigment “zeaxanthin” Sample of lakewater from Lake Waikare, May 2014

Water quality in some shallow lakes 2008-12 Total P (mg/m3) Total N Chlorophyll Secchi (m) Rotomanuka 20 1070 11 1.4 Serpentine 30 1350 13 1.3 Waikare 170 2640 110 0.2 Taupo 5 80 1 16 Compared to Lake Taupo, all the shallow lakes in the Waikato Region have elevated levels of the nutrients nitrogen and phosphorus, and thus support the growth of more of the microscopic plants called “algae” – shown here as the plant pigment “chlorophyll”. So while Taupo’s water appears clear and blue, that in the shallow lakes appears discoloured and murky – shown here as the low “Secchi depth” values (“how far can a submerged disc be seen through the water?”). But Lake Waikare has particularly high levels of nutrients and algae, and the water is especially murky. (It also appears red at present because the dominant species of algae contains an uncommon – but harmless – red pigment called “zeaxanthin”.)

Estimated phosphorus loads from lakes’ catchments Load of P (kg/ha/yr) Farming (%) Rotomanuka 1.0 94 Serpentine 93 Waikare 88 So, algal and nutrient concentrations in Lake Waikare are much higher than in some of the other shallow lakes in the region: why is this? This table shows the estimated catchment loads of phosphorus to the three shallow lakes. You’ll see that the loads are similar in all three cases. So why is the phosphorus concentration in Lake Waikare itself so much higher (as in the previous slide)? The explanation is that the marked shallowness of Waikare means that the bottom sediments are constantly being stirred up (by wind and fish), such that phosphorus that settles to the bottom of the lake is rapidly recycled to the overlying water. Rotomanuka and Serpentine are deeper, so phosphorus is less likely to be recycled in those cases. Why is there so much P in the bottom sediments of Waikare? We can speculate that some of it is “legacy” phosphorus that had been stored in the lake in the decades when lakeweeds stabilised the water column. These plants collapsed in the 1970s and no longer protect the lake bed from disturbance. Lowering the lake level as part of the flood control scheme has probably exacerbated recycling from the bottom sediments. In the long term, this legacy phosphorus should be washed out of the lake, so concentrations in the lake should fall to some degree. Indeed the records from the past 5-10 years do suggest this is happening – see next slide.

Lake Waikare, P concentrations 1996-2014 18-year record of total phosphorus at WRC’s routine water quality monitoring site at Lake Waikare. Although the concentrations are all very high, they have fallen over the past decade. (The overall water quality of the lake – nutrients, algae and clarity – has remained stable over this period.) Further information is available at the following WRC webpage (and its “sister” pages). http://www.waikatoregion.govt.nz/Environment/Environmental-information/Environmental-indicators/Freshwater/Lakes/lake4-keypoints/

Automated carp cage and thermophillic digester aimed at point source control of invasive fish into Lake Waikare. Approximately 30 tonnes of invasive fish have been removed and prevented from entering this lake in the last 2 years

Matahuru Catchment

Matahuru Catchment Soil stability Soil Conservation 65% of catchment unstable evidence of past erosion on hill slopes Erosion mainly landslides, gully erosion and stream bank erosion Soil Conservation Present on 4337 ha (42%) of catchment Absent and required on 1340 ha (13%) Upgrades to conservation required on 1445 ha (14%)

Matahuru Catchment

Matahuru Catchment

This photo taken on same day shows a new sediment ‘front’ moving into the lake via the Matahuru from the rainfall. The reddish colouration of the lake prior to this event and still visible in the foreground was caused by a the non toxic pigment ‘zeaxanthin’ produced by a dominant algal species of Monoraphidium. In this case the reddish colour enhanced the contrast between the existing sediment and algal laden lake water and newly arriving material from the rainfall event.

Existing Governance Arrangements

Land administered by DOC, WRC & Waikato –Tainui in the vicinity of Lake Waikare & Whangamarino Wetland

Land Ownership Lake bed owners – Waikato-Tainui Mixed ownership of lake margins (Fish and Game, DoC, local Iwi, WRC, WDC, private) Remainder of catchment upstream (mainly private) Remainder of catchment downstream (DoC, Fish and Game, private)

Governance Arrangements Waikato District Council Land use planning Consent to discharge (Te Kauwhata waste water) Waikato Regional Council RMA - Effects of land use, Healthy Rivers – Wai Ora, Water allocation V6 Lower Waikato Liaison subcommittee Lower Waikato Flood Protection Scheme and associated consents Project Watershed – Integrated catchment management Co-management (JMAs and co-managed lands)

Governance Arrangements Joint management Co-management Waikato District Lakes Memorandum of Agreement Waikato Tainui Co-governors and owners of lake bed Co-managed lands / Sites of significance DoC Wetland and Biodiversity management Fish and Game Wetland and game bird management

Future Management of upper catchment (soil conservation and water quality) Scale of issues major impediment to in-lake restoration Habitat enhancement of margins – ephemeral wetlands Management of lake depth – WQ/sediment re-suspension, irrigation Plant pest management (yellow flag, alligator weed)

Future Management of the flood protection scheme Challenge: Local -1500 ha surrounding lake Regional – 17,000 ha protected land National infrastructure – SH1 protection Lake Waikare an important part of the scheme Challenge: Maintaining viable flood protection scheme Improving lake water quality Protecting biodiversity Managing future demands for water All parties to act effectively towards a common goal

WRC Future Actions Consent review Lower Waikato Flood Control Scheme Lake Waikare discharge Impacts on Whangamarino wetland Long Term Plan 2015-25 Detailed assessment of high risk/opportunity sites in the zone Project management for inter-agency catchment plan Additional catchment management staff and incentives

Matahuru sediment

Minimal-no riparian protection of river corridors combined with cropping and intensive land-use in this catchment is primarily responsible for nutrient and sediment inputs to lake Waikare. This photo is taken at the junction of the Matahuru (left side of photo and carrying more sediment) with an unnamed and normally clear but tannin stained tributary (right side of photo).

A range of ‘products’ from the low energy invasive fish digestion process. Photo on the left shows trees grown in raw ‘carpaccino’ being planted at the fish removal demonstration site following nursery planting trials with this ‘fish recycled’ energy source. This thinking forms part of WRC’s innovative approach to explore the potential for creating a positive environmental outcome from a negative unwanted group of aquatic organisms. On the right, liquid ‘OJ’ condensate, corf lute pest ‘chew cards’ impregnated with a digested carp mix, moulded digested invasive fish baits for terrestrial pest use and raw digested ‘carpaccino’. Cards and baits in the centre of the picture were created by Connovations following supply of ‘raw’ product and are currently under further development and testing.

Sample of lakewater from Lake Waikare, May 2014

This photo was taken C. 36hrs after the peak flows from the latest high rainfall event in June 2014 – note proximity of cropping to Matahuru river margins and if you look closely on right hand side and you will see that this area would have been inundated and flowing during the peak. One of many sediment sources

Matahuru Catchment 10,327 ha Vegetation 158 km water ways Pasture 91 %, native 5 %, other 4% 158 km water ways Erodible greywacke and tephra 89 % LuC class 6 44% The Matahuru catchment is 10,327 ha in area, 91% pasture and 155 km waterways. The predominant Land Use Capability is class 6 (44% of catchment). The geology is predominantly sedimentary greywacke, mudstone, siltstone and sandstone with volcanic ash in places.

Matahuru Catchment Suspended sediment monitoring Annual specific sediment yield -193 t/km2/yr third highest specific sediment yield of all regional monitoring sites Annual sediment load -16 t/yr. No trend.

Matahuru Catchment