A study of the hydrological and sedimentological characteristics of two catchments of contrasting land use : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Soil Science at Massey University

Abstract

The hydrological and sedimentological characteristics of two catchments of contrasting land use were studied for a period of one year. Both catchments were situated in the Northern Tararua Ranges, near the Manawatu Gorge, some 27 km from Palmerston North, New Zealand. The 10 ha Ballance Catchment has native forest vegetation, whereas the 180 ha Tuapaka Catchment is part of a mixed sheep and cattle farm. The water balance estimated for the catchments indicated that a small amount of deep percolation occurred in both. Streamflow and rainfall were recorded at both catchments. During the study year approximately 26% and 14% of total rainfall was discharged as streamflow from the Tuapaka and Ballance Catchments, respectively. Throughfall and stemflow were also recorded at Ballance. The average monthly throughfall was 54% of total rainfall; the equivalent stemflow, was 16% of total rainfall. An attempt was made to identify and quantify the inputs of phosphorus (P) and nitrogen (N) forms to the two catchments. Phosphate fertilizer application, N - fixation by clovers, and rainfall, were considered as the inputs of P and N forms in the Tuapaka Catchment. In the Ballance Catchment, rainfall was assumed to be the only input of P and N forms. The output of suspended sediment, dissolved material, and P and N forms, was measured during the study year. The output of sediment was 1.4 x 10³kg/ha and 1.6 x 10² kg/ha from the Tuapaka and Ballance Catchments, respectively. The output of dissolved material from the Tuapaka Catchment was only 13% of the sediment output. Significant quantities of P and N output were associated with suspended sediment. Of the annual loss of total P (1.6 kg/ha) from the Tuapaka Catchment, 76% was in the particulate form. At Ballance, 52% of the annual loss of total P (0.2 kg/ha) was in particulate form. Within the bounds of error, the Ballance Catchment appeared to be slightly conservative of P and strongly conservative of N. At the Tuapuka Catchment, however, inputs of P and N balanced outputs, within the bounds of error. It is difficult, if not impossible, to determine whether a particular catchment is conservative for P and N unless adequate attention is paid to the errors involved. The differences obtained for the output of sediment and P and N forms, from the two catchments, are interpreted in terms of the effects of agricultural activities, particularly vegetation differences, on the inputs of particulate and dissolved phases to the streams.