Partitioning of catchment water budget and its implications for ecosystem carbon exchange

• Main Authors: D. Lee, J. Kim, K.-S. Lee, S. Kim
• Format: Article
• Language: English
• Published: Copernicus Publications 2010-06-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/7/1903/2010/bg-7-1903-2010.pdf

Spatially averaged annual carbon budget is one of the key information needed to understand ecosystem response and feedback to climate change. Water availability is a primary constraint of carbon uptake in many ecosystems and therefore the estimation of ecosystem water use may serve as an alternative to quantify Gross Primary Productivity (<i>GPP</i>). To examine this concept, we estimated a long-term steady state water budget for the Han River basin (~26 000 km<sup>2</sup>) in Korea and examined its application for catchment scale carbon exchange. For this, the catchment scale evapotranspiration (<i>ET</i>) was derived from the long term precipitation (<i>P</i>) and discharge (<i>Q</i>) data. Then, using stable isotope data of <i>P</i> and <i>Q</i> along with other hydrometeorological information, <i>ET</i> was partitioned into evaporation from soil and water surfaces (<i>E<sub>S</sub></i>), evaporation from intercepted rainfall (<i>E<sub>I</sub></i>, and transpiration (<i>T</i>). <i>E<sub>S</sub></i> was identified as a minor component of <i>ET</i> in the study areas regardless of the catchment scales. The annual <i>T</i>, estimated from <i>ET</i> after accounting for <i>E<sub>I</sub></i> and <i>E<sub>S</sub></i> for the Han River basin from 1966 to 2007, was 22~31% of annual <i>P</i> and the proportion decreased with increasing <i>P</i>. Assuming that <i>T</i> further constrains the catchment scale <i>GPP</i> in terms of water use efficiency (<i>WUE</i>), we examined the possibility of using <i>T</i> as a relative measure for the strength and temporal changes of carbon uptake capacity. The proposed relationship would provide a simple and practical way to assess the spatial distribution of ecosystem <i>GPP</i>, provided the <i>WUE</i> estimates in terms of <i>GPP/T</i> at ecosystem scale could be obtained. For carbon and water tracking toward a sustainable Asia, ascertaining such a spatiotemporally representative <i>WUE</i> and their variability is a requisite facing the flux measurement and modeling communities.