Impact of runoff on nutrient patterns in northern Port Phillip Bay, Victoria

As part of the Port Phillip Bay Environmental Study, bay-wide nutrient (ammonium, nitrate, nitrite, phosphate, silicate) and chlorophyll a distributions were measured at monthly intervals for two years. Reported here are nutrient distribution and variation in northern Port Phillip Bay during periods of high runoff (September 1993) and low runoff (January 1995). Nutrient data were collected by a continuous profiling technique, whereby nutrients were measured in a continuously flowing stream of seawater pumped into a mobile laboratory aboard ship, filtered, and measured by flow-segmented colorimetric analysis, using flow-through cells. Measurements were made every 10 s and, after accounting for mixing in the apparatus, allowed nutrient features to be resolved (at ship speed of 10 kn) over scales of about 200 m. Hydrographic and chlorophyll a data were collected simultaneously with the nutrient data. Surveys of the whole of Port Phillip Bay (approximately 2000 km2) could be completed in 3 days. Ammonium concentration varied between