In the starting years of the Hubbard Brook experimental forest, the scientists mainly researched the ecosystem processes, water cycling, water yield, water flow, and biogeochemical cycles.
About 3160 hectares of land area covered by the Hubbard Brook. Its elevation ranges from approximately 220 m to 1015 m.
The watersheds are surrounded by glaciers. It is rich in the flora and fauna. It is the home to various species of trees like beech, sugar maple, and birds, and animals like the black bear, moose, and other species.
The watershed of Hubbard Brooks serves as the ecosystem with underlaid impermeable rocks that make the quantification of the inputs and outputs of the study simple and easier. Although determining the gaseous inflow and outflow is a little difficult, it is not impossible. The entry and exit of animals are not controlled and they are free to enter or leave which makes a net flux zero. This makes the quantification of the inputs and outputs of the whole ecosystem easily determinable.
Six of the watersheds are similar in size and are south facing, they possess similar characteristics like soil, geology, vegetation. The similarity in the surroundings helps in easily deducing the results.
Experimental analysis of the entire watershed has been the focus of the researchers at Hubbard Brook. By setting up two reference watersheds and comparing the long term and short-term responses of it with four experimental watersheds, they were able to collect quantitative information regarding the environmental issues, ecosystem patterns, and other information concerning the environmental changes.
The research at the experimental forest widened with the entry of scientists and research students to study the ecosystem and hydrology of the forestland. This formed the basis of the Hubbard Brook ecosystem study (HBES).
To expand the scientific research the nutrient cycling research was taken to the next level. Calcium was trailed using the watershed experiment.
The Watershed experiment:
Watershed 1-The entire ecosystem was tracked for calcium and aimed to determine its role in the ecosystem. With the funding received from the National Science Foundation (NSF), the estimated amount of (about 56 tons of calcium) that was strayed off by the leaching process by acid rain was burdened on watershed I. To achieve this, the rocks of calcium silicate were broken down into smaller pieces and were spread by the helicopter onto watershed I. This treatment added base saturation of soil from about 10% to 19%. The added element has a distinctive ratio of the molecules of calcium and strontium and the strontium isotope ratio allows the scientists to trace the compound.
Watershed 2- This watershed aimed to find the response of the ecosystem to deforestation. Using herbicides like bromicil, the vegetation in that area was destroyed and no plants were allowed to grow for about three years. The observations of this experiment were- an increase in annual streamflow during de-vegetation, an increase in nitrate content in the stream, the occurrence of snowmelt discharge earlier than usual.
Watershed 3– It is a reference watershed for studying the change in hydrology.
Watershed 4- Strip cutting of vegetation was done progressively. The water yield and nutrient concentration in the streamwater increased after strip cutting was done.
Watershed 5-The whole of trees including the stem were harvested and the biomass portions removed completely from the site. The observations of this treatment were – rise in the moisture content of the soil, temperature increase in the stream, increase in the rate of nitrification. It was followed by further research in examining the changes in the yield of water.
Watershed 6- It is also a reference watershed, but used for surveillance of the biogeochemical cycling.
Watershed 7- No treatment was done on this watershed.
Watershed 8- No treatment was done.
Watershed 9- No treatment was ever done. In these non-treated watersheds, the streamflow was assessed on daily basis, the chemistry of the stream water was studied, and the deposition of the sediment was estimated.
Watershed 101- It was aimed to analyze the consequences of block cutting of trees on the hydrology of the watershed, nutrient cycling, and its flux. Blocks of vegetation were cut, leaving the branches on the site. The observations were as follows- initial increase in the streamflow later followed by its decline, an increase in the level of concentration of ions after two years.
