20 Element Budgets in Catchments
Anna Avila, Juan Bellot and Josep Pinol
20.1 Introduction
The element budget concept for the study of forest ecosystems was first developed by an interdisciplinary group of scientists at the Hubbard Brook Experimental Forest (New Hampshire, USA) in the early 1960s. The reasoning
behind the element budget concept was that "in humid regions, the chemical
flux and cycling is intimately linked to the hydrologic cycle" as quoted in
their seminal book Biogeochemistry of a Forested Ecosystem (Likens et al.
1977). In this way, terrestrial ecologists could take advantage of the broad experience in using small catchments for hydrological studies (e.g. the Coweeta
watersheds in the USA) in order to test hypotheses regarding the nutrient
circulation in small catchments. Input-output budgets were used to provide
information on the processes operating in catchments at different time scales
and to understand the effects of natural or anthropogenic perturbations on
biogeochemical cycles at the ecosystem level.
Two requirements for nutrient balance studies are the same as for hydrological balances: (1) the catchments have to be underlain by water-tight rock
so that water losses through deep drainage are negligible, and (2) a hydrological year has to be defined so that interannual changes in the amount of
water stored in the catchment (as snow or soil water) are minimized. A third
requirement for nutrient balances is that the biological inputs and outputs of
nutrients (by animals or plant debris) should be in balance so that there is
not a net flux into or out of the system, a condition that is usually met when
catchments are part of larger homogeneous landscape units. If these requirements are satisfied, the major element input to the ecosystem is the
deposition from the atmosphere and the most important output is usually
through the streamwater draining the catchment. Under these conditions, by
measuring the element inputs from the atmosphere and the element exports
in the streamwater, chemical budgets can be established. These fluxes constitute the external cycle of elements and are usually complemented with
detailed studies of the intrasystem circulation within the ecosystem (see
Ecological Studies, Vol. 137
Ferran Rodii et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Anna Avila, Juan Bellot and Josep Pinol
20.1 Introduction
The element budget concept for the study of forest ecosystems was first developed by an interdisciplinary group of scientists at the Hubbard Brook Experimental Forest (New Hampshire, USA) in the early 1960s. The reasoning
behind the element budget concept was that "in humid regions, the chemical
flux and cycling is intimately linked to the hydrologic cycle" as quoted in
their seminal book Biogeochemistry of a Forested Ecosystem (Likens et al.
1977). In this way, terrestrial ecologists could take advantage of the broad experience in using small catchments for hydrological studies (e.g. the Coweeta
watersheds in the USA) in order to test hypotheses regarding the nutrient
circulation in small catchments. Input-output budgets were used to provide
information on the processes operating in catchments at different time scales
and to understand the effects of natural or anthropogenic perturbations on
biogeochemical cycles at the ecosystem level.
Two requirements for nutrient balance studies are the same as for hydrological balances: (1) the catchments have to be underlain by water-tight rock
so that water losses through deep drainage are negligible, and (2) a hydrological year has to be defined so that interannual changes in the amount of
water stored in the catchment (as snow or soil water) are minimized. A third
requirement for nutrient balances is that the biological inputs and outputs of
nutrients (by animals or plant debris) should be in balance so that there is
not a net flux into or out of the system, a condition that is usually met when
catchments are part of larger homogeneous landscape units. If these requirements are satisfied, the major element input to the ecosystem is the
deposition from the atmosphere and the most important output is usually
through the streamwater draining the catchment. Under these conditions, by
measuring the element inputs from the atmosphere and the element exports
in the streamwater, chemical budgets can be established. These fluxes constitute the external cycle of elements and are usually complemented with
detailed studies of the intrasystem circulation within the ecosystem (see
Ecological Studies, Vol. 137
Ferran Rodii et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999