Losses of nitrogen in surface runoff from a plantation horticulture farm in coastal Queensland, Australia
Peter R. Stork A , David J. Lyons B and Michael J. Bell CA Department of Primary Industries and Fisheries, 49 Ashfield Road, Bundaberg, Qld 4070, Australia. Present address: Nha Trang University, 2 Nguyen Dinh Chieu, Nha Trang, Khanh Hoa, Vietnam.
B Department of Natural Resources and Water, 50 Meiers Road, Indooroopilly, Qld 4078, Australia.
C Corresponding author. Department of Primary Industries and Fisheries, PO Box 23, Kingaroy, Qld 4610, Australia. Email: mike.bell@deedi.qld.gov.au
Australian Journal of Soil Research 47(6) 565-573 https://doi.org/10.1071/SR08238
Submitted: 24 October 2008 Accepted: 12 June 2009 Published: 30 September 2009
Abstract
Surface losses of nitrogen from horticulture farms in coastal Queensland, Australia, may have the potential to eutrophy sensitive coastal marine habitats nearby. A case-study of the potential extent of such losses was investigated in a coastal macadamia plantation. Nitrogen losses were quantified in 5 consecutive runoff events during the 13-month study.
Irrigation did not contribute to surface flows. Runoff was generated by storms at combined intensities and durations that were 20–40 mm/h for >9 min. These intensities and durations were within expected short-term (1 year) and long-term (up to 20 years) frequencies of rainfall in the study area. Surface flow volumes were 5.3 ± 1.1% of the episodic rainfall generated by such storms. Therefore, the largest part of each rainfall event was attributed to infiltration and drainage in this farm soil (Kandosol). The estimated annual loss of total nitrogen in runoff was 0.26 kg N/ha.year, representing a minimal loading of nitrogen in surface runoff when compared to other studies.
The weighted average concentrations of total sediment nitrogen (TSN) and total dissolved nitrogen (TDN) generated in the farm runoff were 2.81 ± 0.77% N and 1.11 ± 0.27 mg N/L, respectively. These concentrations were considerably greater than ambient levels in an adjoining catchment waterway. Concentrations of TSN and TDN in the waterway were 0.11 ± 0.02% N and 0.50 ± 0.09 mg N/L, respectively. The steep concentration gradient of TSN and TDN between the farm runoff and the waterway demonstrated the occurrence of nutrient loading from the farming landscapes to the waterway. The TDN levels in the stream exceeded the current specified threshold of 0.2–0.3 mg N/L for eutrophication of such a waterway. Therefore, while the estimate of annual loading of N from runoff losses was comparatively low, it was evident that the stream catchment and associated agricultural land uses were already characterised by significant nitrogen loadings that pose eutrophication risks. The reported levels of nitrogen and the proximity of such waterways (8 km) to the coastline may have also have implications for the nearshore (oligotrophic) marine environment during periods of turbulent flow.
Additional keywords: nitrate, ammonium, eutrophication, macadamia.
Acknowledgments
This research was funded by the Australian Federal Government and the Queensland State Government via the Queensland Department of Primary Industries and Fisheries (DPI&F), under the Agriculture State Investments Program (AGSIP) of the National Action Plan for Salinity and Water Quality. The technical support of Dr Fred Bennett, Ralf Bebernitz, Ron Pedder and Joel LeLagadec (DPI&F) is gratefully acknowledged.
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