| |
Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Biogeochemistry
STREAM-LAKE ECOTONE INFLUENCE ON THE FORMS AND AMOUNTS OF TRANSPORTED NITROGEN.
M.M. Bozeman and M.A. Baker. Department of Biology, Utah State University, Logan, Utah, 84322-5305
Ecotones, areas representing interfaces between ecosystems, have high biogeochemical activity and influence the amount and form of nitrogen in watersheds. While the hyporheic zone is a well-understood ecotone in the context of stream ecology, little is known about ecotones between streams and lakes, despite the fact that they are often hydrologically linked. To understand how stream-lake ecotones affect nitrogen amounts and forms, we collected biogeochemical data from two watersheds in the Sawtooth Mountains, Idaho. We hypothesized that deltas, created by streams flowing into lakes, are inorganic nitrogen (DIN) producers and should have the highest DIN content. In contrast, lakes are organic nitrogen (DON) producers, so lake outlets should have lowest DIN and highest DON content. Our results support this hypothesis in that delta nitrate (NO3–N) averaged 22.1±8.2 and was significantly higher (ANOVA p<0.05) than outlet NO3–N (2.2±0.4). However, lake DON (80.4±7.9), not outlet DON (52.3±5.0), was significantly higher (ANOVA p<0.05) than delta DON (43.8±7.3). The DON:DIN ratio traces the dominant N form and may indicate differing process mechanisms. Lake outlets had a DON:DIN ratio of 27, an order of magnitude higher than the ratio (3) of inflowing streams. Future study will address whether observed structural differences indicate different processing mechanisms.
|
|
