Hydrologic regimes of forested, mountainous, headwater basins in New Hampshire, North Carolina, Oregon, and Puerto Rico

Abstract

This study characterized the hydrologic regimes at four forested, mountainous long-term ecological research (LTER) sites: H.J. Andrews (Oregon), Coweeta (North Carolina), Hubbard Brook (New Hampshire), and Luquillo (Puerto Rico). Over 600 basin-years of daily streamflow records were examined from 18 basins that have not experienced human disturbances since at least the 1930s and in some cases much longer periods. This study used statistical methods to systematically evaluate the relationship between precipitation and streamflow at a range of spatial and temporal scales, and draw inferences from these relationships about the hydrologic behavior of the basins. Basins in this study had fundamentally different abilities to store and release moisture at a range of time and space scales. These different hydrologic regimes are the result of different types of forest canopies, snow, and soils in the study basins. Through their influences on interception and transpiration, forest canopies appear to play a very important role in the hydrologic regimes at Andrews and Luquillo, but at Coweeta and Hubbard Brook, the current deciduous forest plays a more limited although seasonally important role. Because of the timing of melt and its interaction with soils, seasonal snowpacks at Hubbard Brook and Andrews have quite different effects upon streamflow and vegetation water use. A variety of water flowpath types in soil, from macropore flow to long flowpaths in deep soils or fractured bedrock, appear to operate at the four sites. Hydrologic regimes may help predict the temporal scales of biogeochemical cycling and stream ecological processes, as well as the magnitude and timing of hydrologic response to disturbance and climate change in headwater basins.