Sediment Phosphorus Chemistry and Microbial Biomass along a Lowland New Zealand Stream

An evaluation of the distribution of P concentrations in streamflow, P fractions and the microbial biomass P pool was made of bed and bank sediments along a lowland stream in New Zealand. Agricultural intensification increased downstream. However, most P fractions decreased downstream (total P decreased from c. 400 to 250 mg kg(-1)) in bed sediments, while P in streamflow remained relatively constant (generally < 0.005 mg l(-1)) and sediment microbial P increased from 2 to 8 mg kg(-1). An investigation of P release from dried and rewetted sediments showed that solution P (CaCl2-P) increased, on average > 300%, and proportional to the size of the microbial biomass P pool before drying, except in sediments with much organic carbon (OC). When supplied with a P source (1 mg l(-1)) and then simultaneously with a C source (glucose, 100 mg l(-1)), all sediment behaved similarly and biotic sorption accounted for, on average, 27 and 34% of the total sediment uptake, respectively (maximum of 58%). The quantity of P taken up was related to the initial size of the microbial biomass P pool, and the availability of P as influenced by organic P complexes and OC. The sediment microbial biomass represents a transient, but small store of P could be useful to indicate bioavailable P inputs.