Sources and sinks of nutrients in a New Zealand hill pasture catchment II. Phosphorus

Abstract

The management of the riparian zone has been suggested as a technique for controlling the amounts of phosphorus (P) entering watercourses draining pasture catchments. A study was therefore made of P entering a stream from various sources (rainfall, surface and subsurface derived runoff, direct fallout from aerial topdressing), with the object of providing a rational basis for the design of effective riparian management schemes. P entrained in surface runoff could account for virtually all of the P entering the stream during storms. Approximately 20 per cent of the annual P export from the catchment could be accounted for by direct aerial input of P to the stream during autumn fertilizer topdressing. More than 85 per cent of the P was exported from the catchment as particulate P. Stream sediment had higher P sorption capacities, and were enriched with P relative to the soils from which they were derived. There was a pronounced seasonal variation in sediment enrichment which could be predicted (r2 = 0-92) by the logarithm of the rainfall since fertilizer topdressing (LNFERT) and flood intensity. The amount of P lost in streamflow during any flood event was predicted (3 = 0.94) by peak flow, seven day antecedent peak flow and LNFERT. Approximately 40 per cent of the 1.3 kg P ha-' exported during 1981 occurred in four storms with recurrence intervals of more than three months. From a P budget compiled from nine events it was hypothesized that the stream acted as a net sink for P at baseflow and low-medium intensity floods but was a source of P at higher flood intensities.It was concluded that P losses from hill pasture catchments could be reduced by avoidance of direct application of P fertilizer to the stream channel, and by fencing out stock from seasonally saturated areas during periods of saturation. The ultimate success of the latter technique would depend on whether buffer vegetation could retain accumulated P during extreme storm events.

Temporal variability in phosphorus transfers: classifying concentration–discharge event dynamics

“…Cooke, 1988;Haygarth and Jarvis, 1997;Hergert et al, 1981a;Hergert et al, 1981b;Pionke et al, 1993;Preedy et al, 2001;Sinaj et al, 2002;Stamm et al, 1998). Table 1 presents a summary of these.…”

“…All samples were collected, prepared and analysed for either reactive P that was filtered (<0.45 mm, RP <0.45 mm ) (Haygarth et al, 1995;Haygarth and Sharpley, 2000) or total P that was unfiltered (TP), using standard protocols (Eisenreich et al, 1975;Murphy and Riley, 1962;Rowland and Haygarth, 1997). A full description of all the sites used follows below (Table 2 summarises soil type, P status, P management and hydro-sampling methods):…”

Riparian pasture retirement effects on sediment, phosphorus, and nitrogen in channellised surface run‐off from pastures

“…A large fraction of the nitrogen andphosphorus is transported in surface run-off in particulate forms (Sharpley & Syers 1979;Cooke 1988;Cooke & Cooperl988) andclearly, any technique which substantially lowers these surface run-offloads will reduce diffuse source pollution. Riparian zone retirement is a frequently recommended technique (e.g., Williams & Brickell 1983) because a dense, vegetative ground cover filters sediments from run-off (e.g., Wilson 1967).…”

Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution

“…Johnson et al, 1976;Meyer and Likens, 1979;Rigler, 1979;Cooke, 1988;Jordan-Meille et al, 1998a). This may not be the case however, in populated lowland rivers.…”

“…These types of studies, however, are rare (but see Rigler, 1979;Cooke, 1988;Dorioz et al, 1989Dorioz et al, , 1998Svendsen and Kronvang, 1993;Jordan-Meille et al, 1998a). Generally the sampling frequency has not been high enough to quantify phosphorus exports during storm events (e.g.…”