Recalcitrant Problems in Environmental Instrumentation

Abstract

Frontiers in any science are generally defined by measurement limitations, and that is especially true in environmental biophysics. Among the more persistent issues are surface–atmosphere exchange, soil water and solute fluxes, plant water status, and plant/soil nutrient status. Measurement of surface–atmosphere exchange is particularly critical to global climate change research. Despite advances in instrumentation, accuracy of flux measurements, particularly eddy covariance, remains unacceptable, partly because the underlying assumptions of stationarity and surface homogeneity are so restrictive. Even when these assumptions are valid, the method appears to systematically underestimate for reasons that are not yet well understood. Similarly, soil water and solute fluxes cannot yet be measured accurately and routinely, hampering water quality research. Recent advances in tension lysimetry offer hope for improvement, but most field experiments still rely on modeling of water and solute flow, supported by indirect measurements of ancillary variables, e.g., soil water content, soil water potential, and solute concentration, at discrete points in time and space. A third area of ongoing concern is that of plant water status. The major uncertainty here concerns which property should be measured. Nearly all of the effort over the past 30 yr has been directed at measuring water potential, but water potential measurements are equilibrium measurements, and plants operate in dynamic environments. Furthermore, many physiological processes appear to be more related to relative water content than to water potential. Finally, more accurate and more timely (e.g., in situ) measurements of plant/soil nutrient status are sorely needed to take advantage of the promise of precision agriculture.