New Zealand Freshwater Sciences Society (NZFSS) Conference: The effectiveness of a natural wetland in removing nitrate loads


 The 2016 New Zealand Freshwater Sciences Society (NZFSS)  conference was held in Invercargill, Southland from 5 to 8th of December 2016. The conference was themed ‘Freshwater on the edge’ which reflects the push towards the edge of our scientific knowledge, including the scientific innovation to maintain and restore the health of some of our special freshwater resources.


I presented my latest work on modelling in the conference session “Wetlands” on:
“The effectiveness of a natural wetland in removing nitrate loads”

The performance of a small natural pastoral seepage wetland was studied in the headwaters of the Toenepi catchment, Kiwitahi, Waikato from 2011 to 2013. A simple dynamic model operating on an hourly time step was used to explore potential wetland nitrate removal performance. Hourly measurements of inflow, outflow, rainfall and Penman evapotranspiration estimates were used to calculate dynamic water balance for the wetland. In addition, nitrate concentration measurements at inflow and outflow and piezometers installed in the wetland were used as input data for the model. A dynamic nitrate-N mass balance was calculated by coupling influent concentrations to the dynamic water balance and applying a first order areal removal coefficient (k20) adjusted to the ambient temperature. Storm events above a certain threshold were assumed to always result in surface runoff or overland flow and were assigned higher nitrate based on surface run-off measurements.  Results showed a wide variation in N-removal depending on the flow regime, with performance better during low flow and poorer during high flow events.
Model outputs for 2012 showing modelled and measured in and out loads for nitrate-N
 

I would like to acknowledge my co-authors Chris Palliser, Andrew Hughes and Chris Tanner from NIWA.
Location: Invercargill, New Zealand

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