Tukituki PC6 and RWSS Kate McArthur (EDS) Effects of excessive - - PowerPoint PPT Presentation

Summary evidence presentation: Tukituki PC6 and RWSS

Kate McArthur (EDS)

Effects of excessive periphyton

• No. and quality of ‘swimming days’ reduced by slime
• No. and quality of ‘angling days’ reduced
• River closure due to Phormidium sp. blooms
• Passive use affected by reduced aesthetic appeal

and/or odour

• Dissolved oxygen reduction at night affects life-

supporting capacity, extremes cause fish mortality

• Few high quality macroinvertebrates (EPT taxa) –

snails, worms and midge larvae instead

• Lower growth and reproduction in fish

Pollution sensitive taxa: the “good guys”

Pollution tolerant taxa: the “bad guys”

Reducing periphyton effects

• Effects on values reduced by decreasing

duration and frequency of nuisance growth (i.e. more swimming and angling days, better ecological health through more stable dissolved oxygen and higher life-supporting capacity)

• Meeting nutrient limits more often reduces

frequency and duration of nuisance growth

80 mg/m2 chlorophyll a: 20% cover

120 mg/m2 chlorophyll a: 30% cover

160 mg/m2 chlorophyll a: 40% cover

300 mg/m2 chlorophyll a: 55% cover

900 mg/m2 chlorophyll a: 70% cover

90% cover by green filamentous periphyton

• Effects on recreational and ecological

values

Risk management of nutrients

• Reducing and controlling P is important to

reduce the frequency and duration of excessive periphyton in the Tukituki catchment

• Reducing and controlling N is also important
• N concentrations contribute (with P) to the

frequency and duration of periphyton blooms

Risk management of nutrients

• Reliance on a single limiting-nutrient approach

is less effective at reducing excessive periphyton

• Reductions of P and N will further reduce the

duration and frequency of nuisance periphyton growths across the catchment

• Other effects and risks are also reduced

through dual nutrient management

Potential effects of single nutrient management

• Increased Phormidium sp. dominance of

periphyton communities

• Leads to increased probability of high-impact

effects on safe contact recreation and amenity values e.g. river closure, dog deaths, public health

• Ecological and aesthetic effects: reduction in

macroinvertebrate health and odour issues

Periphyton is a multi-species assemblage

85% cover of benthic cyanobacteria (Phormidium sp.)

• Effects on ecological values
• River closed to recreational use

Potential effects of single nutrient management - estuary

• Increased estuarine enrichment from N:

nuisance macroalgae, anoxic sediment, loss of in-fauna

• Mortality of estuarine in-fauna is an effect of

low probability but high impact

• Resulting effects on aesthetic and recreational

values in the estuary are more likely e.g.

• dour issues

Risks…

• Failure to effectively manage P: greater

impacts if P management is slow, incomplete

• r fails in the presence of uncontrolled or

elevated N

• Failure to successfully reduce P from point

sources is common. Catchment-wide reductions in diffuse P inputs are uncertain - increasing risk of ‘surprise’ ecological effects and implementation lags (Jarvie et al. 2013)

• Combined risks and potential effects require a

cautious approach to nutrient management

• Level of risk supports the requirement for an

DIN limit/target in PC6 (Zones 1, 2, 3 and 5) to reduce the duration and frequency of nuisance periphyton

• Contaminants directly related to aquatic

health and safe contact recreational objectives (i.e. deposited sediment, MCI & water clarity) require control through PC6 as limits/targets

Outcomes

• Remaining P neutral and allowing increased N

is unlikely to achieve OBJ TT1(a), (b) or (c)

• Positive periphyton outcomes are more likely

through dual nutrient and contaminant management

• Periphyton cover limits in 5.9.1B should utilise

PeriWCC

• Linking sediment, MCI and water clarity to

OBJTT1(a) & (b) through limits/targets is preferable to provide certainty of outcomes

Water quantity and allocation

• Combined adverse effects from increased allocation ,

continuation of takes below minimum flow (deep & stream depleting groundwater and takes for permanent root stock and spray contracting)

• Increases in allocation (ground or surface water)

require increases in minimum flow to compensate adverse effects on ecology

• Increases in allocation or reduction in minimum

flows are unlikely to meet OBJ TT1(a)

RWSS effects

• Makaroro catchment: healthiest measured native

fish & macroinvertebrate communities in TT

• Permanent loss of aquatic habitat upstream of dam,

including threatened species e.g. Northern dwarf galaxid, torrentfish, longfin eel, bluegill and redfin bullies

• Significant adverse effects from altered flows 11km

between dam & Waipawa confluence, flow alteration effects in upper Waipawa also

• Catchment-wide adverse effects from intensification
• f land use within and downstream of irrigation

command area

RWSS effects

• Increases in nitrogen in combination with

phosphorus neutral conditions unlikely to achieve OBJTT1(a), (b) or (c)

• Mitigation of periphyton growth uncertain and only

affects Waipawa and Tukituki mainstems – even if fully effective, flushing flows will not mitigate full area of effects

• Diffuse P neutrality cannot be ‘offset’ by reduced

WWTP discharges – ecological outcomes of upgrades uncertain, any benefits only apply to Waipawa and Tukituki mainstems downstream of SH2

• Consent requirements are an existing benefit

Photo acknowledgements

• Slide 3: (Top to bottom) stonefly, caddis fly and mayfly larvae

(EPT macroinvertebrates), the late Stephen Moore, courtesy

• f Landcare Research
• Slide 4: (Top to bottom) Snail, oligocheate worm and

chironomid midge larva, Stephen Moore, Landcare Research

• Slides 6-10: Periphyton growth (biomass and %cover) Waipara

River, courtesy of Barry Biggs (reproduced from the NZ Periphyton Guidelines)

• Slide 11: Rangitikei River at Mangaweka 2009, Kate McArthur
• Slide 12: Rangitikei River at Mangaweka 2008, Kate McArthur
• Slide 16: Mangaone Stream, tributary of the Manawatu River

at Palmerston North 2005, Kate McArthur

• Slide 17: Manawatu at Hopelands, 2008, Kate McArthur