Effects of precipitation and air temperature on phosphorus fluxes from Rhode River watersheds

We studied fluxes of total P, total phosphate, and total organic P from sev en contiguous small watersheds on the Atlantic Coastal Plain in Maryland fo r up to 25 yr. These watersheds have perched aquifers so all groundwater di scharges as well as surface runoff were measured at V-notch weirs equipped with volume-integrating, flow-proportional samplers. Interannnal variations in annual and seasonal precipitation during this study spanned approximate ly the range of 160-yr weather records in the region. Annual total-P area y ields from the overall watershed varied 28-fold, correlations of all P-spec ies fluxes with precipitation were highly significant, and power function r egressions of precipitation vs. P-flux explained from 42 to 55% of the vari ance in the latter. Phosphorus fluxes from a cropland watershed mere much h igher and more variable with volume of precipitation, while fluxes from a f orested watershed were much lower and primarily composed of organic P. Corr elations of P fluxes with precipitation were higher in the spring. Annual a nd seasonal P concentrations also often increased significantly with precip itation. Variations in seasonal mean air temperature sometimes explained si gnificant amounts of variance in P fluxes, especially phosphate from cropla nd. A regression model was used to construct graphical and tabular summarie s.