Solving the P problem
Dr Steph Parkyn lowering a koura cage used to evaluate the effects of modified zeolite addition to Lake Okaro on koura health. (Photo: Chris Hickey, NIWA)
Restoration of lakewater quality is frequently constrained by ongoing ‘internal loading’ of phosphorus (P), which is released from lake sediment into the water under certain conditions.
One possible remedy is to add compounds to the lake which deactivate the phosphorus. NIWA’s research on P-inactivation agents began with a focus on alum, which was added to Lake Okaro in 2003 in the first whole-lake addition of its kind in New Zealand. Since then two other P-inactivation products, ‘Phosloc’ and ‘modified zeolite’, have been introduced, requiring expansion of the research to include comparisons of the physical and ecotoxicological effects of all three agents. Modified zeolite is a pre-commercial product developed by Scion by treating raw zeolite to enhance its uptake of anionic pollutants, such as phosphorus.
NIWA is part of a team comprising researchers from the University of Waikato, Scion and Environment Bay of Plenty, that has advised on several aspects of the lake-wide trial addition of modified zeolite to Lake Okaro. We conducted laboratory research that allayed concerns that the modified zeolite might reduce nitrogen removal by lake-bed microbial communities, and we are also contributing to monitoring the impacts and effectiveness of a modified zeolite treatment to Lake Okaro, carried out in late September 2007.