Jonathan J. Cole1, Nina F. Caraco1
1Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA
Tóm tắt
For a majority of aquatic ecosystems, respiration (R)
exceeds autochthonous gross primary production (GPP). These systems have
negative net ecosystem production
([NEP]=[GPP]–R) and
ratios of [GPP]/R of <1. This net
heterotrophy can be sustained only if aquatic respiration is subsidized by
organic inputs from the catchment. Such subsidies imply that organic materials
that escaped decomposition in the terrestrial environment must become
susceptible to decomposition in the linked aquatic environment.
Using a moderate-sized catchment in North America, the Hudson River (catchment
area 33500 km2), evidence is presented for the magnitude
of net heterotrophy. All approaches (CO2 gas flux;
O2 gas flux; budget and gradient of dissolved organic C;
and the summed components of primary production and respiration within the
ecosystem) indicate that system respiration exceeds gross primary production
by ~200 g C m-2 year-1. Highly
14C-depleted C of ancient terrestrial origin
(1000–5000 years old) may be an important source of labile organic
matter to this riverine system and support this excess respiration. The
mechanisms by which organic matter is preserved for centuries to millennia in
terrestrial soils and decomposed in a matter of weeks in a river connect
modern riverine metabolism to historical terrestrial conditions.
