TRANSPORT OF DISSOLVED ORGANIC-MATTER THROUGH A SANDY FOREST SOIL

We assessed the transport of dissolved organic matter (DOM) through a sandy, Ultisol forest soil on the southeastern U.S. Coastal Plain, and contrasted the results with similar studies from other forest regions , to test the hypothesis that DOM transport is greater through sandy U ltisols than finer textured Ultisols and Spodosols. Within a small hea dwater catchment, concentrations of dissolved organic carbon (DOG), a measure of DOM, were measured in soil solution at three depths (10, 30 , and 90 cm) in sand A and E horizons of soil profiles, and in sand al ong the valley bottom at 198- to 264-cm depth in shallow groundwater. Water samples were collected after every rainfall event for 21 mo usin g zero-tension lysimeters, suction samplers, and piezometers. Mean con centration of DOC in soil water decreased from 25.5 mg C L-1 at 10-cm depth to 13.7 mg C L-1 at 30 cm, and to 1.8 mg C L-1 at 76 to 99 cm, b efore contacting clay-enriched horizons. All valley bottom stations co nsistently averaged between 0.3 and 2.1 mg C L-1. We did not find sign ificant seasonal patterns, nor a correlation between DOC concentration and magnitude of rainfall events. We estimate that the nux of DOC dec reased more sharply with soil depth than concentration due to attenuat ion of water transport through the soil profile. Compared with literat ure data from other forest regions, our results do not support the hyp othesis that there is greater DOM transport through sandy upland soils on the Coastal Plain. Our results suggest that this is due to strong DOM retention within deep sand E horizons of these soils. Thus, strong DOM retention in forest soils appears to occur across a broader range of soil types than those exhibiting podzolization or having high clay content.