PARENT SESSION
Contributed Oral Session 133: Biogeochemistry of Streams and Wetlands
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal
Forest age, woody debris, and nutrient dynamics in headwater streams of the White Mountains, NH.
Warren, Dana*,1, Bernhardt, Emily2, Hall, Robert 3, Likens, Gene4, 1 Cornell University, Ithaca, NY2 Duke University, Durham, NC3 University of Wyoming, Laramie, WY4 Institute of Ecosystem Studies, Millbrook, NY
ABSTRACT- Instream processing can substantially alter nutrient export from forested watersheds. We evaluate the relationship between instream nutrient uptake and two related factors: forest age and woody debris volume. Using nutrient releases, we measured the uptake velocities of phosphate, nitrate, and ammonium for five streams within the Hubbard Brook Experimental Forest (HBEF), NH. The 1998 annual nutrient flux was also calculated for each watershed. We surveyed woody debris and debris dams in all five streams to quantify their volume and abundance in each stream. Relationships between nutrient uptake velocity and nutrient flux from each watershed were assessed relative to forest age and woody debris characteristics using linear regression. Contrary to expectations, nutrient fluxes were not related to forest age. Phosphate uptake velocity was strongly positively correlated with both forest age and woody debris volume (r2=0.99; p<0.001 in both cases); however, nitrate and ammonium were not related to either factor. We attribute the positive relationship between phosphate uptake velocity and forest age/large woody debris volume to increased abiotic adsorption of phosphate by the inorganic sediments retained by woody debris. Nitrogen uptake in these streams is primarily biological and is not predictably related to structural channel features. We expect woody debris abundance to increase in HBEF streams as the forest matures, with a subsequent increase in phosphate uptake in the drainage streams.
Key words: nutrient uptake, LWD, debris dam, Hubbard Brook