Comparison of nitrogen solute concentrations within alder (Alnus incana ssp. rugosa) and non‐alder dominated wetlands

Abstract

Abstract:This study examined differences in nitrogen solutes and groundwater flow patterns between a riparian wetland dominated by the N 2 -fixing shrub, Alnus incana ssp. rugosa, and an upstream coniferous forested riparian wetland along a stream of the Adirondack Mountains, where some surface waters are susceptible to nitrogen excess. Channel water NO 3 was up to 16 µmol l 1 greater in the alder reach, with peaks following maxima in groundwater dissolved inorganic nitrogen (DIN). NO 3 at 25 cm depth was 30 µmol greater in the alder than in the conifer reach in April, and 24 µmol l 1 greater than channel water and 30 µmol l 1 greater than that of 125 cm groundwater in June. Dissolved organic nitrogen and NH 4 C concentrations increased between 25 and 75 cm depths in both wetlands during the growing season. Inorganic nitrogen increased between the hillslope and stream in both wetlands, with the greatest increases in the alder reach during the dormant season. Greatest subsurface DIN (120 µmol l 1 ) occurred at 75 cm in the alder reach, within 1 m of the stream, between November (120 µmol l 1 NH 4 C ) and a January thaw (60 µmol l 1 each of NH 4 C and NO 3 ). Concentrations of deeper groundwater at 125 cm during this period were lower (10-30 µmol l 1 ). Lateral flow from the stream channel occurred in the alder reach during the dormant season, and channel water contribution to groundwater was correlated strongly to NO 3 at 25 cm. These results indicate that nitrification is stimulated in the presence of alders and oxidized exchange flow, producing NO 3 that may contribute to elevated channel water NO 3 during periods of peak flow.

Feedback in the Plant-Soil System

“…Forests in which N-fixing alders (Alnus spp.) are present provide a well-documented example (204,205). Invasions of N-fixing species into communities lacking such species also clearly demonstrate feedback.…”

The influence of watershed characteristics on nitrogen export to and marine fate in Hood Canal, Washington, USA

“…Red alder (Alnus rubra), a prevalent deciduous tree in the Pacific northwest region of North America, can fix 100-200 kg N ha -1 year -1 (Binkley et al 1994). Since alders often grow in riparian areas adjacent to surface and subsurface flow paths, high soil and litterfall N concentrations can lead to increased stream water N concentrations (Hurd et al 2001;Compton et al 2003;Hurd and Raynal 2004). Increased stream water N yields due to alders have been noted in the coastal range of Oregon (Compton et al 2003), the Olympic Peninsula in Washington (Bechtold et al 2003), the Adirondack Mountains in New York (Hurd et al 2001;Hurd and Raynal 2004), forests of Wisconsin (Younger and Kapustka 1983), and fens in Germany (Busse and Gunkel 2002).…”

Alder cover drives nitrogen availability in Kenai lowland headwater streams, Alaska

“…Alder receives its N from a symbiotic relationship with bacteria of the genus Frankia that convert atmospheric N 2 to NH 3 for uptake by the plant. Alder has been shown to increase both ammonium (Stottlemyer and Toczydlowski 1999) and nitrate soil concentrations (Van Miegroet and Cole 1984;Rhoades et al 2001;Hurd and Raynal 2004;Mitchell and Ruess 2009a) and also plant nitrogen concentrations directly beneath its canopy (Rhoades et al 2001). Alder-fixed N (AFN) may be transported to the stream by litterfall directly to the stream, soluble nutrients from riparian zones, or leaching and lateral transport by surface and groundwater from upland alder stands (Compton et al 2003;Stieglitz et al 2003;Cairns and Lajtha 2005).…”