Phosphorus (P) plays a crucial role in both agricultural productivity and water quality. There has been growing recognition of the importance of 'legacy' P (that which has accumulated in watersheds over time), for understanding contemporary water quality outcomes; however, little is known about how different watersheds respond to cumulative P pressures. The "buffering capacity" concept describes the ability of watersheds to attenuate P loading to surface waters by retaining cumulative P inputs over time. To explore the role of various watershed characteristics in buffering capacity, we compared Net Anthropogenic P Input (NAPI) estimates to riverine total P flux across a thirty-year time span (1981-2011) in 16 large watersheds in southern Quebec, Canada. We used this historic P data to calculate indices describing long-and short-term buffering for these watersheds. We then examined the correlation between this buffering capacity and a set of key geochemical, hydrological, landscape, and socio-ecological variables that were hypothesized to influence P buffering dynamics. Both long-and short-term buffering metrics were most strongly correlated with hydrologic characteristics, indicating that watershed hydrology may be the most prominent characteristic in P buffering within watersheds. However, we found that considering estimates of long-term P accumulation along with biophysical characteristics of the watershed (including hydrology) predicts water quality better (R 2 =0.69) than either factor would alone (R 2 =0.35). Our findings provide a step towards improving models of watersheds' unique relationships to P pressure and can help guide management of historically agricultural landscapes with considerable amounts of legacy P. Manuscript Highlights Watershed buffering is a concept used to explore how watersheds respond to legacy P pressure Hydrology and landscape features play major role in watershed buffering 40 Combining P data and watershed characteristics gives a comprehensive picture of watershed buffering