Site: Hubbard Brook LTER
The v-notch weir is used to quantify the hydrologic and biogeochemical mass-balance of small watersheds and responses to whole-ecosystem experimental manipulations.
Hubbard Brook website

The northeastern United States has been blessed with beautiful and bountiful forests that provide human society with a variety of valuable ecosystem goods and services including forest products, recreational opportunities, diverse wildlife, stable water flow, pure water quality, and sequestration of carbon. Pioneering research at Hubbard Brook, designed to elaborate ecological theory on the biological control of element cycling, demonstrated the overarching role played by healthy forests in regulating the water and chemical element cycles of coupled land-water systems.

Deforestation resulted in a tremendous flush of nutrients into surface waters resulting from elimination of tree root uptake and consequent disruption of normal soil microbiological activity and soil chemical reactions. However, these negative consequences of forest harvest could be greatly reduced by employing best management practices such as buffer strips along stream channels, practices that have become standard in forest management operations.

More subtle effects of forest composition and dynamics on ecosystem services have been demonstrated by continuing, long-term studies at Hubbard Brook. Young forests growing back on cut-over land apparently use considerably more water, and thereby reduce water yield of streams by as much as 20% compared with adjacent mature forests. Natural disturbance events, such as severe ice storms and wind storms, result in significant though less severe impacts on surface water quality than large-scale deforestation. Quantification of these more subtle effects was only possible because of careful, detailed monitoring of the forest ecosystem allowed us to take advantage of natural disturbance events as “natural experiments.”

The future provision of valuable ecosystem services by our forested landscapes is threatened by continuing human-accelerated environmental changes: air pollution, climate change, invasive species, land-use change, etc. Long-term studies of the Hubbard Brook forest allow us to better understand and predict the effects of these changes and their complex interconnections. For example, over the past two decades the Hubbard Brook forest has switched from being a significant carbon sink to a carbon-neutral landscape, owing largely to the decline of key tree species caused in part by pollution deposition and exotic pest organisms. Reliable assessments of environmental policies to mitigate these changes depends upon accurate evaluations derived from Hubbard Brook and other LTER sites of the potential benefits to society from the maintenance and recovery of the many ecosystem services provided by our forest resources.

Graph for
A classic experiment at HBR involved the deforestation (shaded) of watershed 2 (dashed line) which resulted in striking increases in the flux of key nutrients in comparison with the reference watershed 6.
Bormann et al. 1968 (see above).