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Federated Farmers Presentation (AGM 2013)

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Tom Stephens

on 23 September 2013

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Transcript of Federated Farmers Presentation (AGM 2013)

LAKE ROTORUA - Recent trends
Outcome: "Oturoa Agreement"
Lake Management:
Scientific principle:
Reduction in limiting nutrient (P+N) = reduction in algal biomass
Fundamentals of
Lake Science
Rapid 'ageing' through nutrient addition (10-100 yrs vs. 100-1,000 yrs in lakes)

Alters nutrient balance (greater N and P)

Negative effects
on water quality:
More algal blooms + lower biodiversity
Lower clarity
Lower amenity and cultural value
1. Tight coupling with landscape (catchment)...

2. Bottom of watershed (receiving water)

3. Water pooled for days-years (retention time)

4. Unique thermal and nutrient processes (sedimentation, stratification, internal loads)
Cultural Eutrophication
("nutrient enrichment")
Application to:
Lake Rotorua (EC Mediation)
Federated Farmers National Conference (4 July 2013)
Community "target" = Trophic Level Index < 4.2
Sustainable load (435 tN/yr = 42% drop, 10 years)

BUT "target" reached in 2012...

DairyNZ role to investigate:
1. If reducing TLI is part of a longer trend?
2. If reducing TLI affects limiting nutrients?
3. What does this mean to managers?

Less N-limitation
More co- and P-limitation
TP (-9% p.a.)
Clarity (+2.6% p.a.)
TN (-3.6% p.a.)
Chl-a (-7.0% p.a.)
Site 2
Economic principle:
Target bigger bang for $$$ (P>>N)

Water quality is IMPROVING:
Part of TREND (continuously since 2006), throughout lake...
Probable causes:
Alum dosing, climate
Retiring critical source areas, upgrading effluent systems, nutrient budgeting, riparian planting

RESULTS for Primary Producers Collective
Non-binding targets
224 tonne N reduction by 2022 (compared to 320 tonne N)
Regular review of targets - 10 yearly (hope to push P harder)
Less limiting nutrient = less algal growth
Full transcript