1. Reducing sediment & nutrient losses from intensive agriculture Restoring eutrophic shallow lakes
Pastoral agriculture is the dominant land use in New Zealand covering 38% of the country (Statistics NZ 2010). In recent years intensification of agriculture has occurred to meet the demands of New Zealand’s growing dairy industry at the expense of sheep, beef and deer farming. The number of dairy cattle has more than double since 1981 and increased by more than 175% in the last decade. At 30 June 2011: The number of dairy cattle was 6.2 million (Statistics NZ 2010). Waikato is our largest dairying region with more than 1.7 million dairy cattle, 30% of New Zealands dairy herd
Rebecca S Eivers
Postgraduate student
University of Waikato
Lake Kainui, February 2012

2. Introduction
Lakes and rivers under increasing pressure from elevated sediment and nutrient loads associated with intensification of agriculture in NZ
Eutrophication and toxic algal blooms common problem in shallow Waikato peat lakes within intensive agricultural catchments
Lake Kainui, May 2011

3. Streams and drains running through intensively farmed systems transport high concentrations of suspended sediment, total nitrogen (TN) and total phosphorus (TP)
Intro

4. Silt-trap/constructed wetland, Lake Kainui
To improve water quality end-of-drain treatment systems have been implemented to reduce sediment and nutrient loads to downstream waterways
Intro
Silt-trap/constructed wetland, Lake Kainui

5. Silt-trap/constructed wetland
Objectives
How well do end-of-drain treatment systems reduce sediment and nutrient loads?
Do floating wetlands improve sediment and nutrient reduction?
Silt-trap/constructed wetland
Infiltration filter

6. Silt-trap/constructed wetland
Silt-trap/infiltration filter, Lake Kainui
Winter Summer 2011

7. Methods
Up to 26 treatment systems were surveyed over 5 seasons within 5 peat lake catchments in the Waikato
Water samples collected & analysed for:
Morphological & physico-chemical parameters also measured
Total suspended solids (TSS)
Nitrite (NO2-N)
TN & TP
Ammonium (NH4-N)
Nitrate (NO3-N)
Phosphate (PO4-P)

8. Map
Horsham lakes within Kainui peat bog, Koromatua within Rukuhia, Serpentine edge of Moanatuatua.

9. Pollutant loads Results
Inflowing nutrient & suspended solids concentrations varied significantly seasonally, between lakes and soil types.
Results
Estimates of Components of Variation as obtained by multivariate PERMANOVA analyses from all sites across five seasons. The variability explained by each term is expressed as a proportion of the total variation .

10. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Environmental variables had significant associations with nutrient and suspended solids concentrations, particularly pH, dissolved oxygen, and temperature. *
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DISTLM results relating environmental variables to variation of total and individual nutrient species and suspended solid concentrations. * and ** denote P<0.05 and P<0.01 respectively.

11. Nutrient reduction Results
Highly variable seasonally and between types of treatment systems
Autumn Winter Spring 2011
Autumn Winter Spring 2011

12. In silt-trap wetlands TN and TP reduction was influenced by flow and temperature
Winter Autumn Winter Spring 2011
Winter Autumn Winter Spring 2011

13. Enhancing pollutant reduction
Floating Treatment Wetlands (FTW) trial to test for reduction of TN, TP and fine sediments
Installed within two existing systems on Lake Kaituna, KT1 & KT2
FTW Trial
Site KT2
Site KT1
Lake Kaituna

14. KT2 FTW, Lake Kaituna, May 2012

15. KT2 FTW, 17th October2012
FTW Trial
KT2 FTW, 6th January 2013

16. Enhancing pollutant reduction
FTWs sampled for TN, TP & TSS upstream & downstream in spring 2012 and summer 2013
FTW Trial
Measuring plant roots, Warrick Powrie, field technician

17. Preliminary Results FTW Trial
No TN reduction from KT1 and a minor TN reduction from KT2 when spring and summer results examined together (n=10).
Preliminary Results
FTW Trial
No TP reduction from either KT1 or KT2 when spring and summer results examined together (n=10).

18. Preliminary Results FTW Trial
Site KT2
TN reduced by 0.08 mg/L in spring (n=6), and 0.97 mg/L during summer (n=4).
Preliminary Results
FTW Trial
Spring Summer 2013
TP increase by 0.08 mg/L in spring (n=6), however reduced in summer by 0.09 mg/L (n=4).
Spring Summer 2013

19. End-of-drain treatment systems can reduce suspended sediment and nutrient loads to downstream waterways, however careful design considerations must be made;
Soil types, catchment sizes and seasonality should be incorporated into treatment system designs; and
FTWs may be appropriate for treatment of surface waters within intensive agricultural environments, however further analyses and monitoring is required.
Conclusions

20. Questions? Acknowledgements:
Supervision from Professor David Hamilton (University of Waikato) & Dr. John Quinn (NIWA, New Zealand)
Funding from:
Waikato Regional Council and the Department of Conservation
Questions?