Denitrification Capacity of Hill Country Wet and Dry Area Soils as Influenced by Dissolved Organic Carbon Concentration
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ECOSYSTEM SERVICES OF WETLANDS
Denitrification Capacity of Hill Country Wet and Dry Area Soils as Influenced by Dissolved Organic Carbon Concentration and Chemistry Grace Chibuike 1 Qinhua Shen 1
&
Lucy Burkitt 1 & Marta Camps-Arbestain 1 & Ranvir Singh 1 & Mike Bretherton 1 & Peter Bishop 1 &
Received: 1 June 2019 / Accepted: 12 September 2019 # Society of Wetland Scientists 2019
Abstract The quantification of the nitrate attenuation capacity of pastoral hill country wet areas, especially seepage wetlands, would aid in the proper management of hill country farms for improved water quality outcomes. This study investigated the denitrification capacity, dissolved organic carbon (DOC) concentration and chemistry of wet areas and adjacent dry areas soils in a hill country landscape in New Zealand. Soil samples were collected during spring (November 2017) from different soil depths down to 100 cm. The results showed that the mean DOC concentration in the surface 30 cm soil depth was in the order: seepage wetland (498 mg kg−1) > hillside seep (172 mg kg−1) > dry area (109 mg kg−1). The denitrification capacity of the seepage wetland within the 0–30 and 30–60 cm soil depths was 7 and 69 times greater (p ≤ 0.05), respectively, than that of the dry area. The high concentration of readily-decomposable (e.g. lower molecular weight) DOC in the seepage wetland soil could have contributed to its higher denitrification capacity. The contrasting nitrate attenuation capacities of the seepage wetland soil versus that of the dry area soil highlight the important contribution of seepage wetlands to water quality improvement in pastoral hill country landscapes. Keywords Seepage wetland . Hillside seep . Nitrate attenuation . Water quality . Pastoral agriculture . New Zealand
Introduction Pastoral hill country landscapes occupy more than 60% of New Zealand’s agricultural area (Hoogendoorn et al. 2011), and contribute substantially to the country’s export earnings (Morris 2013). Pastoral farming in hill country landscapes is not unique to New Zealand, as it is also practised in some European countries such as Scotland and Ireland (Morgan-Davies et al. 2012; Williams et al. 2012). Hill country landscapes contain important naturally occurring wet areas, which have the capacity to attenuate excess nitrate before it reaches receiving waters (Clarkson et al. 2013; Rutherford et al. 2018). These natural wet areas include Bseepage wetlands^, which are flat, boggy
* Grace Chibuike [email protected] 1
School of Agriculture and Environment, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
areas (approximately
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