Experimental instrumentation
Runoff from each of the 12 experimental plots passed into a gravel filled trench located at the bottom edge of each plot. An impermeable membrane was installed at a depth of approximately 0.5 m below the ground on the bottom and opposite side of the trench to the plot to capture both surface and sub-surface lateral flowing water exiting the experimental plots. A V-shape base of the trench ensured that all water exited the trench at the same point, where it was channelled into a V-notch weir fitted with a baffle plate to smooth out changes in the height of the water. The height of the water within the weir was monitored via an ADCON LEV1 level sensor (0 – 1 m range) positioned within a stilling well. Data were recorded every minute via a Delta T GP1 data logger as millivolt values and converted to discharge using a regression equation established under laboratory calibration conditions. To allow for the areal difference between the control plots (340 m2) and the buffer treatment plots (340 m2 + 120m2 = 460 m2), the runoff volumes were adjusted by multiplying them by a correction factor calculated using the formula: