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

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

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

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

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

Silt-trap/constructed wetland Silt-trap/infiltration filter, Lake Kainui Winter 2010 Summer 2011

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)

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

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 .

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Environmental variables had significant associations with nutrient and suspended solids concentrations, particularly pH, dissolved oxygen, and temperature. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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.

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

In silt-trap wetlands TN and TP reduction was influenced by flow and temperature Winter 2010 Autumn 2011 Winter 2011 Spring 2011 Winter 2010 Autumn 2011 Winter 2011 Spring 2011

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

KT2 FTW, Lake Kaituna, May 2012

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

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

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).

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 2012 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 2012 Summer 2013

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

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? bex.eivers@gmail.com