Effects of nitrogen on temporal and spatial patterns of nitrate in streams and soil solution of a central hardwood forest

This study examined changes in stream and soil water NO₃⁻ and their relationship to temporal and spatial patterns of NO₃⁻ in soil solution of watersheds at the Fernow Experimental Forest, West Virginia. Following tenfold increases in stream NO₃⁻ concentrations over a 13-year period (1969–1981) on untreated WS4, concentrations have declined through 2006. Following fourfold increases in stream NO₃⁻ on treatment WS3 from pretreatment levels to a 1998 maximum, concentrations have declined through 2006, despite additions of N. Concentrations of soil water NO₃⁻ were consistently lower for WS4 compared to WS3. Data for soil water NO₃⁻ 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 NO₃⁻ increased on WS3 from 1.3mg NO₃⁻-N L⁻¹ in pretreatment 1989 to a maximum of 6.4mg NO₃⁻-N L⁻¹ in 2001. Spatial heterogeneity in soil water NO₃⁻ on WS4 remained high during this period. Data suggest that temporal patterns of stream NO₃⁻ may be influenced by spatial heterogeneity of watershed processes which vary over time in response to N availability.Journal ArticleFinal article publishe