Browsing by Author "Duncan, MJ"

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    Managing pollutant inputs from pastoral dairy farming to maintain water quality of a lake in a high-rainfall catchment
    (CSIRO Publishing, 2013-05-03) Wilcock, RJ; Monaghan, RM; McDowell, RW; Verburg, P; Horrox, J; Chagué-Goff, C; Duncan, MJ; Rutherford, A; Zemansky, G; Scarsbrook, MR; Wright-Stow, AE; Howard-Williams, C; Cotton, S
    A study (2004–11) of a dairy catchment stream entering an oligotrophic lake in an area of very high rainfall (~5 m year–1) yielded median concentrations of total nitrogen (TN), total phosphorus (TP), suspended sediment (SS) and Escherichia coli (E. coli) of 0.584, 0.074 and 3.7 g m–3, and 405/100 mL (most probable number method), respectively. Trend analysis indicated significant (P < 0.01) decreases for TN (–0.08 ± 0.02 g m–3 year–1), TP (–0.01 ± 0.005 g m–3 year–1) and SS (–0.45 ± 0.14 g m–3 year–1) and were partly attributable to improved exclusion of cattle from the stream. Water balance calculations indicated that approximately one-half the rainfall left as deep drainage that by-passed catchment outlet flow recorders. Estimates of catchment yields for TN were improved by taking into account groundwater hydrology and concentrations from well samples. Storm-flow monitoring inflows exceeding the 97.5th percentile contributed ~40% of total loads leaving the catchment so that specific yields for SS, TN and TP augmented by groundwater inputs and storm flows were ~960, 45 and 7 kg ha–1 year–1, respectively. These compared well with modelled results for losses from dairy farms in the catchment of 40–60 kg N ha–1 year–1 and 5–6 kg P ha–1 year–1 and indicated that attenuation losses were relatively small. © CSIRO, 2013. Open Access.
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    Wetland development nutrient accumulation and runoff in New Zealand dairy pastures with very high annual rainfall
    (Aarhus University, 2012-06-17) Chagué-Goff, C; Sorrell, BK; Duncan, MJ; Cotton, S
    Agricultural activity in regions with high annual rainfall raises particular challenges for managing nutrient runoff. Here we report on a four-year study of patterns of nutrient accumulation and loss in dairy pastures from a catchment of the West Coast of the South Island of New Zealand, receiving up to 3500 mm annual rainfall. Due to poor drainage in the gley soils, farming practice involves contouring the pasture in broad corrugations, termed ‘humps and hollows’, to improve drainage; grazing is restricted to the humps, whilst wetland vegetation (predominantly a marsh of Juncus and Carex species) naturally colonizes the wetter drainage hollows. We aimed to quantify nutrient accumulation and runoff at this site, paying particular attention to the function of the wetland hollows in nutrient cycling. Subsurface flow was found to be negligible in the poorly draining soil, with water loss and nutrient yields restricted to surface flows. No fertiliser was applied the first year at one site. Specific nitrogen and phosphorus yields ranged from 11-56 kg N ha-1 yr-1 and 2.0-13.4 kg P ha-1 yr-1. The highest P yield (mostly in particulate form) was recorded even when no P fertiliser was applied. Wetland vegetation and soils showed prolonged accumulation of both N and P throughout their development, but failed to intercept peak events that occurred when cattle were allowed to graze the pastures following heavy rainfall events. Potential soil denitrification, measured from denitrification enzyme activity experiments, was very low, with median values < 50 ng N g-1 h-1 throughout the study, predominantly due to low nitrate concentrations. We conclude that (i) significant nutrient discharge is a feature of this system; (ii) the natural wetland formation in drainage hollows is an important nutrient sink that mitigates discharge; and (iii) much of the remaining discharge could be ameliorated by improved farming practices. © University, DCE – Danish Centre for Environment and Energy