Effects of Nitrogen on Temporal and Spatial Patterns of Nitrate in Streams and Soil Solution of a Central Hardwood Forest

Abstract

This study examined changes in stream and soil water and their relationship to temporal and spatial patterns of in soil solution of watersheds at the Fernow Experimental Forest, West Virginia. Following tenfold increases in stream concentrations over a 13-year period (1969–1981) on untreated WS4, concentrations have declined through 2006. Following fourfold increases in stream on treatment WS3 from pretreatment levels to a 1998 maximum, concentrations have declined through 2006, despite additions of N. Concentrations of soil water were consistently lower for WS4 compared to WS3. Data for soil water on WS3 versus WS4 followed patterns of net mineralization and nitrification for these watersheds. Nitrogen additions to WS3 decreased spatial heterogeneity of N processing, which was largest in the pretreatment year and decreased significantly to a minimum by 2000-2001. Concurrently, soil water increased on WS3 from 1.3 mg -N L −1 in pretreatment 1989 to a maximum of 6.4 mg -N L −1 in 2001. Spatial heterogeneity in soil water on WS4 remained high during this period. Data suggest that temporal patterns of stream may be influenced by spatial heterogeneity of watershed processes which vary over time in response to N availability.