Spatial and temporal variability of stream phosphorus in a New Zealand high‐country agricultural catchment

Abstract

Spatial and temporal variability of stream total phosphorus (TP) concentrations and loadings was evaluated over a year in a high‐country agricultural catchment. One storm event was also sampled at the inflow to a lake. An upland tributary had the highest median concentration (0.064 mg 1^‐1), but the maximum (0.614 mg 1^‐1) occurred at the inflow during the storm. Values near the lake surface were low but increased with depth in summer. There was a large difference between two streams, and values exceeded water quality guidelines in several locations. Seasonality in concentrations was not evident. Mean and median loadings at the inflow were approximately 7000 and 680 g day^‐1, respectively, and the maximum was 81 540 g day^‐1during the storm. TP loadings to the lake during a synoptic survey were 470 g day^‐1 or 13 g km^‐2day^‐1. The lower half of the catchment contributed 72% of the loading to the lake. Baseflow, snowmelt, and one storm accounted for 47%, 30%, and 23%, respectively, of the total annual loading. Fertiliser, livestock waste, and trampling of stream banks by livestock contribute to the problem and can be minimised though use of best management practices in areas identified in this study.

Keywords:

• Lake Hayes
• phosphorus
• water quality
• nonpoint source pollution
• eutrophication