Variability of annual CO<sub>2</sub> exchange from Dutch grasslands
An intercomparison is made of the Net Ecosystem Exchange of CO<sub>2</sub>, <i>NEE</i>, for eight Dutch grassland sites: four natural grasslands, two production grasslands and two meteorological stations within a rotational grassland region. At all sites the <i>NEE</...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2007-10-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/4/803/2007/bg-4-803-2007.pdf |
| Summary: | An intercomparison is made of the Net Ecosystem Exchange of CO<sub>2</sub>, <i>NEE</i>, for eight Dutch grassland sites: four natural grasslands, two production grasslands and two meteorological stations within a rotational grassland region. At all sites the <i>NEE</i> was determined during at least 10 months per site, using the eddy-covariance (EC) technique, but in different years. The <i>NEE</i> does not include any import or export other than CO<sub>2</sub>. The photosynthesis-light response analysis technique is used along with the respiration-temperature response technique to partition <i>NEE</i> into Gross Primary Production (<i>GPP</i>) and Ecosystem Respiration (<i>R<sub>e</sub></i>) and to obtain the eco-physiological characteristics of the sites at the field scale. Annual sums of <i>NEE</i>, <i>GPP</i> and <i>R<sub>e</sub></i> are then estimated using the fitted response curves with observed radiation and air temperature from a meteorological site in the centre of The Netherlands as drivers. These calculations are carried out for four years (2002–2005). Land use and management histories are not considered. The estimated annual <i>R<sub>e</sub></i> for all individual sites is more or less constant per site and the average for all sites amounts to 1390±30 gC m<sup>−2</sup> a<sup>−1</sup>. The narrow uncertainty band (±2%) reflects the small differences in the mean annual air temperature. The mean annual <i>GPP</i> was estimated to be 1325 g C m<sup>−2</sup> a<sup>−1</sup>, and displays a much higher standard deviation, of ±110 gC m<sup>−2</sup> a<sup>−1</sup> (8%), which reflects the relatively large variation in annual solar radiation. The mean annual <i>NEE</i> amounts to –65±85 gC m<sup>−2</sup> a<sup>−1</sup>. From two sites, four-year records of CO<sub>2</sub> flux were available and analyzed (2002–2005). Using the weather record of 2005 with optimizations from the other years, the standard deviation of annual <i>GPP</i> was estimated to be 171–206 gC m<sup>−2</sup> a<sup>−1</sup> (8–14%), of annual <i>R<sub>e</sub></i> 227–247 gC m<sup>−2</sup> a<sup>−1</sup> (14–16%) and of annual <i>NEE</i> 176–276 gC m<sup>−2</sup> a<sup>−1</sup>. The inter-site standard deviation was higher for <i>GPP</i> and <i>R<sub>e</sub></i>, 534 gC m<sup>−2</sup> a<sup>−1</sup> (37.3%) and 486 gC m<sup>−2</sup> a<sup>−1</sup> (34.8%), respectively. However, the inter-site standard deviation of <i>NEE</i> was similar to the interannual one, amounting to 207 gC m<sup>−2</sup> a<sup>−1</sup>. Large differences occur due to soil type. The grasslands on organic (peat) soils show a mean net release of CO<sub>2</sub> of 220±90 g C m<sup>−2</sup> a<sup>−1</sup> while the grasslands on mineral (clay and sand) soils show a mean net uptake of CO<sub>2</sub> of 90±90 g C m<sup>−2</sup> a<sup>−1</sup>. If a weighing with the fraction of grassland on organic (20%) and mineral soils (80%) is applied, an average <i>NEE</i> of 28 ±90 g C m<sup>−2</sup> a<sup>−1</sup> is found. The results from the analysis illustrate the need for regionally specific and spatially explicit CO<sub>2</sub> emission estimates from grassland. |
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| ISSN: | 1726-4170 1726-4189 |