A pilot study to determine where sediment deposited in the Jacobs River Estuary comes from has just been completed by NIWA and funded by DairyNZ.
Four sites in the estuary, as well as sites along the Aparima River and Pourakino River, were sampled and the sediment was analysed for unique fingerprints to identify their origin, based on the plant fatty acids found in the sediment.
The study found that the majority of sediment originated from coastal sources brought into the estuary by incoming tides. Marine sediment comprised up to 75 percent of the total sediment across the four sites.
Of the remaining 25 percent of sediment, most came from bank erosion (50 percent) and sheep pasture (30 percent). Dairy farming, deer farming and drain clearance made relatively small contributions to sediment levels, at approximately five percent each.
Waituna Lagoon sediment
AgResearch recently completed a study funded by Environment Southland into sediment sources in Waituna Lagoon.
The study used a technique which analyses rare earth and heavy metals to identify sediment sources. They found up to 95 percent of sediment in Waituna Creek came from stream banks, with bank collapse and drain cleaning pointed to as the major offenders.
The remaining five percent of sediment was attributed to topsoil losses. At some sites, the loss of topsoil was relatively high, most likely associated with winter forage cropping.
Regional research vital
DairyNZ invests levy funding in these studies to ensure robust, science-based evidence feeds into regional policy processes that aim to control sources of sediment, nutrients and faecal contaminants. With this knowledge, problem areas can also be targeted more cost effectively.
Planting reduces sediment
Increasing bank stability through riparian planting is a key action to reducing sediment in waterways. To support farmers with riparian planting, DairyNZ has developed a guide specific to each region. Guides for Southland, Waikato and Manawatu-Whanganui are now available at dairynz.co.nz/riparian.
New techniques used in 'sediment fingerprinting'
Two new science techniques have been used in the sediment fingerprinting research to identify where sources of sediment come from.
Jacobs River Estuary research
The latest forensic technique, pioneered by NIWA, is the 'Compound-Specific Stable Isotope (CSSI) technique' which uses stable isotopes found within plant fatty acids to identify sediment sources.
The research was led by NIWA senior scientist, Max Gibbs, (the Gil Grisham of New Zealand sediment fingerprinting), an internationally recognised expert in this technique.
Waituna Lagoon research
This study used a technique of sediment fingerprinting which analyses rare earth and heavy metals to identify sediment sources.