A tall-tower study of CO2, water vapor, and energy exchange from developed land use in the U.S. Upper Midwest

A new tall-tower site has been established to study CO2, water vapor, and energy exchange from developed land use in the U.S. Upper Midwest. The main objectives of the study are:

1. To quantify the components of the net ecosystem exchange of CO2 in developed land and their variation over diurnal, synoptic, seasonal, and interannual time scales. The net ecosystem exchange of CO2, as measured from a tall tower in developed land, comprises a number of source and sink terms, including biological component fluxes (net land-atmosphere exchange of CO2 due to vegetation and soils) and fossil-fuel component fluxes from mobile and stationary sources. The study focuses on the biological components of net ecosystem exchange in developed land because their magnitude and controlling mechanisms are poorly understood relative to those of the fossil-fuel components. Component fluxes are quantified by dividing the flux data into time periods when we know that one or more component fluxes equal zero and by making additional measurements that include only specific component fluxes.

2. To determine the specific ecosystem controls on net exchange of CO2, water vapor, and energy by analyzing the relationships between the fluxes and a suite of biophysical properties measured within the footprint of the flux tower.

3. To evaluate the relationship of the MODIS vegetation index, land surface temperature, and snow cover products to temporal dynamics of net ecosystem exchange of CO2 and water vapor at a range scales from the flux tower to the metropolitan area.

Measurements are made from a 170-m antenna tower located in a first-tier suburban neighborhood (45.0°N, 93.2°W, 300 m a.s.l.) in the Minneapolis-Saint Paul metropolitan area. The study site is primarily residential, with most homes built between 40-60 years ago. Eddy covariance flux measurements are made at two levels on the tower, at approximately 60 m and 140 m a.g.l. The whole-ecosystem flux observations are complemented by component flux measurements from soils, herbaceous vegetation (lawns and gardens), and trees in the tower footprint. Ecosystem carbon stocks are measured using ground plots that are co-located with the flux measurement points. The design, implementation, and first results of the site will be presented. The long-term goal of this research is to understand how developed land use affects regional- to continental-scale carbon dynamics, how these effects may change with increased development, and ultimately, how they could be managed to mitigate carbon sources and maximize sinks.