Abstract Title: Daily Stream Carbon Concentration as a Proxy for Whole Wetland Carbon Exchange in Fens

Abstract Submitted to: ATMOSPHERIC SCIENCES

Abstract Text:

Wetland net carbon exchange is difficult to directly measure, but important for global carbon cycle assessment. Among existing techniques, the eddy covariance technique (EC) is arguably the most accurate way to directly analyze the exchange of CO2 and water vapor from entire ecosystems. Other methods such as upscaling chamber measurements and downscaling satellite imagery provide less spatial and temporal information than EC. However, expensive instrumentation, complex set-up, and the need for expert analysis among other issues limit the implementation of EC flux towers and consequentially, our understanding of small-scale atmospheric fluxes. Fortunately, many wetlands, such as fens, are hydrologically connected, so we asked: can the emergence of inexpensive, continuous measurement of stream CO2 concentration serve as an inexpensive proxy for high temporal resolution estimates of whole ecosystem wetland carbon exchange? To test this question, we conducted a comparison of stream concentration of CO2 from an earlier and ongoing USGS study and half-hourly EC net ecosystem exchange of CO2 (NEE) fluxes at a Northern Wisconsin fen (US-ALQ) during three growing seasons. The comparison revealed close linkages in the daily cycle of CO2 among the measurements. These findings show there is also potential for the daily pattern of stream concentration to inform environmental controls of wetland C cycling and also have good potential for upscaling. We attempted to develop a potential model for ecosystem CO2 fluxes in fens based on stream data. To do so, we calibrated a multiple linear regression model of hourly mean stream concentration and other factors such as air temperature, wind speed, and time of day against EC NEE, and compared our calibrated model to out of sample EC NEE to assess model performance. Utilizing stream concentration to estimate total ecosystem fluxes of CO2 could create a more accessible method of understanding land-atmosphere fluxes or their environmental drivers in fens or other hydrologically connected wetlands.
Plain language summary:
A common way that scientists measure how much CO2 is absorbed into or emitted from different ecosystems is by using the eddy covariance technique. It is essential to forecasting and understanding natural processes. Other ways of measuring CO2 exchange involve chamber measurements or satellite imagery and provide less data. However, eddy covariance requires expensive instrumentation, complex set-up, and the need for expert analysis. As a result, data collected using this technique is limited. The daily cycle of stream CO2 concentration and half-hourly eddy covariance measurements from a fen in Northern Wisconsin have similarities. We analyze how factors such as air temperature, wind speed, and time of day influence stream CO2 concentration to see if we can estimate the more expensive eddy covariance carbon exchange measurement. Using stream data to estimate ecosystem CO2 could be a simpler and more inexpensive way to understand CO2 exchange from many fens.