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Understanding the characteristics of riparian zones in low relief, sandy catchments that affect their nutrient removal potential

O’Toole, P., Chambers, J.M. and Bell, R.W.ORCID: 0000-0002-7756-3755 (2018) Understanding the characteristics of riparian zones in low relief, sandy catchments that affect their nutrient removal potential. Agriculture, Ecosystems & Environment, 258 . pp. 182-196.

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Riparian zones are considered to improve stream condition by providing a buffer between waterways and agricultural land that can intercept nutrients, but is their efficacy universal? This paper develops a conceptual model comparing the interactions of slope, soil, hydrology, vegetation and nutrient dynamics between 1) the riparian zone of an intermittent stream in a low-relief (1.6%) catchment with deep sands of low reactivity (Bingham Creek) and 2) a perennial stream in a sloped (10%) catchment with reactive soils over an impermeable layer (Lennard Brook), with a view to compare and contrast their riparian functionality. This study compared the attributes of groundwater (three rows of nested piezometers) (0.5 m,1.5 m and 2.5 m depth), stream, soil and vegetation across a transect from the stream, through the riparian zone to agricultural paddocks. In the low-relief catchment, water did not flow through the riparian zone as in a sloped catchment. Porous soils, together with a lack of slope or a confining layer meant water oscillated vertically through the soil profile over the season, with minimal horizontal movement and limited interaction with the active root zone of riparian vegetation; the intermittent stream discharged P-rich water into the riparian zone during the first flush of winter rains. The highly unreactive sands resulted in trivial P or C uptake resulting in high dissolved concentrations in adjacent streams (0.6–0.9 vs 0.001–0.002 mg/L TP, 58 vs 3 mg/L DOC for flat vs sloped catchments respectively). The high DOC in slow-moving groundwater resulted in highly reducing conditions, promoting P solubility and potentially denitrification. Litterfall from vegetation marginally improved riparian soils with better P retention relative to the adjacent paddock (3620–268 kg TP/ha storage) and reduced FRP in the groundwater relative to the stream (27 vs 80%). The conceptual model developed highlights an alternative functionality of riparian zones for low-relief catchments that challenges the assumption of riparian efficacy.

Item Type: Journal Article
Murdoch Affiliation: School of Veterinary and Life Sciences
Publisher: Elsevier B.V.
Copyright: © 2018 Elsevier B.V.
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