Importance of Nitrate Attenuation In A Small Wetland Following Forest Harvest: 18O/16O, 15N/14N in nitrate and 15N/14N) in vegetation
Abstract
Forest harvest can result in elevated nitrate concentrations in streams and groundwater affecting forest regeneration and downstream aquatic ecosystems. Turkey Lakes Watershed, located near Sault Ste Marie, Ontario (TLW), exhibits relatively high nitrate export due to naturally high rates of nitrification. During a forest harvest experiment at the TLW, stable isotope techniques were used to investigate nitrate attenuation in an intermediate position natural wetland receiving high concentrations of nitrate following forest clear-cutting. Isotopic analysis of nitrate (18O/16O, 15N/14N) and vegetation (15N/14N) demonstrated that denitrification and plant uptake of nitrate resulted in significantly lower nitrate concentrations in wetland outflow compared to incoming stream water and groundwater. The 0.2-hectare forested swamp, too small to show up on standard topographic maps, retained 65 to 100 percent of upgradient nitrate inputs, elevated due to increased nitrification in soils. The 15N/14N enrichment factor associated with nitrate attenuation in wetland surface water was lower than observed during denitrification in groundwaters, suggesting that denitrification proceeded to completion in some areas of the wetland. Even small, shallow, carbon rich pockets of organic matter in topographic depressions can significantly affect biogeochemical fluxes of C, N, S and Ca. Future forest management practices designed to recognize and preserve small wetlands could significantly reduce the potentially detrimental effects of forest harvest on aquatic systems.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.H21D..02S
- Keywords:
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- 1040 Isotopic composition/chemistry;
- 1615 Biogeochemical processes (4805);
- 1871 Surface water quality;
- 1890 Wetlands