Ellison, Micaela. 2004. Particulate phosphorus bioavailability as a function of stream flow and land cover. M.S.
Using total phosphorus (TP) concentrations to estimate eutrophication risk is problematic for management purposes, as only some forms of phosphorus (P) are biologically available for phytoplankton growth. This study measured the bioavailability of one form of P, particulate phosphorus (PP), in forested, urban, agricultural and mixed land cover streams. Sixteen stream sites were sampled during base and storm flow conditions and the following parameters were determined: total suspended solids, TP, total dissolved P (TDP), PP, percent bioavailable particulate phosphorus (% BAPP) and particle size distribution. Algal assays with Pseudokirchneriella subcapitata were used to measure % BAPP. A two-factor ANOVA indicated that land cover type, flow state (base or storm flow) and the interaction between these factors all significantly influenced % BAPP. The results showed that % BAPP varied less between the different land types during storms and was lower during storms in the forested, mixed land cover and urban streams. Percent BAPP increased with increasing urbanization during baseflow only from an average of 20% in the forested streams to 73% in the urban streams. In the agricultural stream, % BAPP was similar between the two flow conditions and the highest of all the storm samples with a % BAPP average of 26%. The particle size distributions, which were measured as the volume of particles per size increment, did not correlate with % BAPP in these samples but a greater percentage of large particles was associated with the storm samples. This result indicates that the differences in % BAPP between the various land cover types cannot be explained in terms of suspended sediment sizes.