Riparian zones attenuate nitrogen loss following bark beetle-induced lodgepole pine mortality

Nitrogen was lost below the major rooting zone to hillslope groundwater, where dissolved organic nitrogen (DON) increased by 3-10 times (mean 1.65 mg L⁻¹) and NO₃-N increased more than 100-fold (3.68 mg L⁻¹) compared to preinfestation concentrations. Most of this N was removed as hillslope groundwater drained through riparian soils, and NO₃ remained low in streams. DON entering the stream decreased 50% within 5 km downstream, to concentrations typical of unimpacted subalpine streams (~0.3 mg L⁻¹).

Although beetle outbreak caused hillslope N losses similar to other disturbances, up to 5.5 kg ha⁻¹y⁻¹, riparian and in-stream removal limited headwater catchment export to <1 kg ha⁻¹y⁻¹. These observations suggest riparian removal was the dominant mechanism preventing hillslope N loss from impacting streams.