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Nitrous Oxide Emission and Denitrification in Chronically Nitrate-Loaded Riparian Buffer Zones

Mariet M. Hefting^*, Roland Bobbink and Hannie de Caluwe

Section of Landscape Ecology, Dep. of Geobiology, Faculty of Biology, Utrecht Univ., P.O. Box 80084, 3508TB Utrecht, the Netherlands

View larger version (20K): [in a new window]   Fig. 1. Water table levels relative to the soil surface in strips parallel to the stream in the forested and grassland riparian buffer zones. Water table level was recorded from 11 Jan. 2000 to 13 Nov. 2000. Values are means; n = 5.

View larger version (26K): [in a new window]   Fig. 2. Nitrate concentrations in the shallow ground water in three strips parallel to the stream in the forested and grassland riparian buffer zones. Values are means with standard errors; n = 5.

View larger version (22K): [in a new window]   Fig. 3. Denitrification in strips parallel to the stream in the forested and grassland riparian buffer zones, and N2O emission in zones parallel to the stream in the forested and grassland riparian buffer zones. Values are means with standard errors; n = 3. Note differences in scale between the denitrification and N2O emission graphs.

View larger version (28K): [in a new window]   Fig. 4. Net nitrification in strips parallel to the stream in the forested and grassland riparian buffer zones. Values are means with standard errors; n = 3.

View larger version (16K): [in a new window]   Fig. 5. (A) Correlation bi-plot from the standardized principal component analysis (PCA) on soil variables. Components are given in Table 3. Correlations of the soil variables with the main axes are given by arrows. The term NO-3 is the nitrate concentration in soil water, OM is the organic matter content, MOIST is the moisture content, and exNO-3 and exNH+4 are the amounts of extractable nitrate and ammonium in the soil. Correlations with soil processes are given by dotted arrows and underlined abbreviations. The term LnDNT stands for denitrification, LnN2O is N2O emission, and NIT is the nitrification. (B) Correlation bi-plot from the standardized PCA with cluster centroids for the strips parallel to the stream in each of the two riparian buffers. The term F indicates the forest buffer zone, and G indicates the grassland buffer zone. Subscripts indicate the strip.

View larger version (22K): [in a new window]   Fig. 6. (A) Denitrification and N2O emission versus soil moisture content in the two riparian buffer zones. (B) Net nitrification versus soil moisture content in the two riparian buffer zones.