Thermodynamic constraints on effective energy and mass transfer and catchment function

摘要

Understanding how water, energy and carbon are partitioned to primaryproduction and effective precipitation is central to quantifying the limitson critical zone evolution. Recent work suggests quantifying energetictransfers to the critical zone in the form of effective precipitation andprimary production provides a first order approximation of critical zoneprocess and structural organization. However, explicit linkage of thiseffective energy and mass transfer (EEMT; W m?2) to critical zone statevariables and well defined physical limits remains to be developed. Theobjective of this work was to place EEMT in the context of thermodynamic statevariables of temperature and vapor pressure deficit, with explicitdefinition of EEMT physical limits using a global climate dataset. The relationof EEMT to empirical measures of catchment function was also examined using asubset of the Model Parameter Estimation Experiment (MOPEX) catchments. Thedata demonstrated three physical limits for EEMT: (i) an absolute vapor pressuredeficit threshold of 1200 Pa above which EEMT is zero; (ii) a temperaturedependent vapor pressure deficit limit following the saturated vaporpressure function up to a temperature of 292 K; and (iii) a minimumprecipitation threshold required from EEMT production at temperatures greaterthan 292 K. Within these limits, EEMT scales directly with precipitation, withincreasing conversion of the precipitation to EEMT with increasing temperature.The state-space framework derived here presents a simplified framework withwell-defined physical limits that has the potential for directly integratingregional to pedon scale heterogeneity in effective energy and mass transferrelative to critical zone structure and function within a commonthermodynamic framework.