Elucidating phosphorus removal dynamics in a denitrifying woodchip bioreactor.

Denitrifying woodchip bioreactors (DBRs) are an established nitrate mitigation technology, but uncertainty remains on their viability for phosphorus (P) removal due to inconsistent source-sink behaviour in field trials. We investigated whether iron (Fe) redox cycling could be the missing link needed to explain P dynamics in these systems. A pilot-scale DBR (Aotearoa New Zealand) was monitored for the first two drainage seasons (2017-2018), with supplemental in-field measurements of reduced solutes (Fe, HS/HS) and their conjugate oxidised species (Fe/SO) made in 2021 to constrain within-reactor redox gradients.

Flow analysis and hydraulic performance of denitrifying bioreactors under different carbon dosing treatments.

Denitrifying bioreactors are an effective approach for removing nitrate from a variety of non-point wastewater sources, including agricultural tile drainage. However, compared to alternate mitigation approaches such as constructed wetlands, nitrate removal in bioreactors may decline with time and low temperature, resulting in poor long-term nitrate removal rates. To address the low nitrate removal rates in bioreactors, the addition of an external carbon source has been found to be an effective method for enhancing and maintaining nitrate removal rates.

High-frequency, in situ sampling of field woodchip bioreactors reveals sources of sampling error and hydraulic inefficiencies.

Woodchip bioreactors are a practical, low-cost technology for reducing nitrate (NO) loads discharged from agriculture. Traditional methods of quantifying their performance in the field mostly rely on low-frequency, time-based (weekly to monthly sampling interval) or flow-weighted sample collection at the inlet and outlet, creating uncertainty in their performance and design by providing incomplete information on flow and water chemistry. To address this uncertainty, two field bioreactors were monitored in the US and New Zealand using high-frequency, multipoint sampling for in situ monitoring of NO-N concentrations.

Assessing changes in nitrogen contamination in groundwater using water aging: Waikato River, New Zealand.

Groundwater and surface water contamination by nitrogen can produce serious health issues particularly regarding the contraction of methemoglobinemia in infants; prevention of this disorder is a main reason for regulating drinking water quality in New Zealand. To assist the management of water quality in the Upper Waikato Catchment in the light of growing intensification of nitrogen producing land uses, a regional groundwater flow and contamination transport model was developed to assess probable future nitrogen concentrations. Calibration of the steady state model was achieved with a root mean square error of 4.

The effects of denitrification parameterization and potential benefits of spatially targeted regulation for the reduction of N-discharges from agriculture.

Diffuse nitrate leaching from agricultural areas is a major environmental problem in many parts of the world. Understanding where in a catchment nitrate is removed is key for designing effective land use management strategies that protect water quality, while minimizing the impact on economic development. In this study we assess the effects of spatially targeted nitrate leaching regulation in a basin with limited knowledge of the complexity of chemical heterogeneity.