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 N O 3 − and their relationship to temporal and spatial patterns of N O 3 − in soil solution of watersheds at the Fernow Experimental Forest, West Virginia. Following tenfold increases in stream N O 3 − concentrations over a 13-year period (1969–1981) on untreated WS4, concentrations have declined through 2006. Following fourfold increases in stream N O 3 − on treatment WS3 from pretreatment levels to a 1998 maximum, concentrations have declined through 2006, despite additions of N. Concentrations of soil water N O 3 − were consistently lower for WS4 compared to WS3. Data for soil water N O 3 − 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 N O 3 − increased on WS3 from 1.3 mg N O 3 − -N L −1 in pretreatment 1989 to a maximum of 6.4 mg N O 3 − -N L −1 in 2001. Spatial heterogeneity in soil water N O 3 − on WS4 remained high during this period. Data suggest that temporal patterns of stream N O 3 − may be influenced by spatial heterogeneity of watershed processes which vary over time in response to N availability.