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Water 2018, 10(3), 287;

Effectiveness of a Natural Headwater Wetland for Reducing Agricultural Nitrogen Loads

Department of Geography, University of Tartu, 51014 Tartu, Estonia
National Institute ofWater and Atmospheric Research Limited, P.O. Box 11 115, Hamilton 3251, New Zealand
Author to whom correspondence should be addressed.
Received: 10 February 2018 / Revised: 2 March 2018 / Accepted: 2 March 2018 / Published: 8 March 2018
(This article belongs to the Special Issue Wetlands for the Treatment of Agricultural Drainage Water)
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Natural wetlands can play a key role in controlling non-point source pollution, but quantifying their capacity to reduce contaminant loads is often challenging due to diffuse and variable inflows. The nitrogen removal performance of a small natural headwater wetland in a pastoral agricultural catchment in Waikato, New Zealand was assessed over a two-year period (2011–2013). Flow and water quality samples were collected at the wetland upper and lower locations, and piezometers sampled inside and outside the wetland. A simple dynamic model operating on an hourly time step was used to assess wetland removal performance for key N species. Hourly measurements of inflow, outflow, rainfall and Penman-Monteith evapotranspiration estimates were used to calculate dynamic water balance for the wetland. A dynamic N mass balance was calculated for each N component by coupling influent concentrations to the dynamic water balance and applying a first order areal removal coefficient (k20) adjusted to the ambient temperature. Flow and water quality monitoring showed that wetland was mainly groundwater fed. The concentrations of oxidised nitrogen (NOx-N, Total Organic Nitrogen (TON) and Total-N (TN) were lower at the outlet of the wetland regardless of flow conditions or seasonality, even during winter storms. The model estimation showed that the wetland could reduce net NOx-N, NH4-N, TON and TN loads by 76%, 73%, 26% and 57%, respectively. View Full-Text
Keywords: wetland attenuation; nitrogen; nutrient removal; denitrification; modelling; agricultural pollution wetland attenuation; nitrogen; nutrient removal; denitrification; modelling; agricultural pollution

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Uuemaa, E.; Palliser, C.C.; Hughes, A.O.; Tanner, C.C. Effectiveness of a Natural Headwater Wetland for Reducing Agricultural Nitrogen Loads. Water 2018, 10, 287.

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