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A STABLE ISOTOPE SIMULATOR THAT CAN BE COUPLED TO EXISTING MASS BALANCE MODELS
Author(s) -
Rastetter Edward B.,
Kwiatkowski Bonnie L.,
McKane Robert B.
Publication year - 2005
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/04-0643
Subject(s) - stable isotope ratio , isotope analysis , environmental science , ecosystem , flux (metallurgy) , computer science , ecosystem model , nitrogen balance , isotope , nitrogen cycle , software , simulation , ecology , biological system , nitrogen , chemistry , biology , physics , organic chemistry , quantum mechanics , programming language
To facilitate the simulation of isotope dynamics in ecosystems, we developed software to model changes in the isotopic signatures of the stocks of an element using the output from any parent model that specifies the stocks and flux rates of that element based on a mass balance approach. The software alleviates the need to recode the parent model to incorporate isotopes. This parent model can be a simple mass balance spreadsheet of the system. The isotopic simulations use a linear, donor‐controlled approximation of the fluxes in the parent model, which are updated for each time step. These approximations are based on the output of the parent model, so no modifications to the parent model are required. However, all fluxes provided to the simulator must be gross fluxes, and the user must provide the initial isotopic signature for all stocks, the fractionation associated with each flux, and the isotopic signature of any flux originating from outside the system. We illustrate the use of the simulator with two examples. The first is based on a model of the carbon and nitrogen mass balance in an eight‐species food web. We examine the consequences of using the steady‐state assumption implicit in multi‐source mixing models often used to map food webs based on 13 C and 15 N. We also use the simulator to analyze a pulse chase 15 N‐labeling experiment based on a spreadsheet model of the nitrogen cycle at the Harvard Forest Long Term Ecological Research site. We examine the constraints on net vs. gross N mineralization that are necessary to match the observed changes in the isotopic signatures of the forest N stocks.