HR: 11:30h
AN: H22B-05 INVITED [Abstracts]
TI: The Role of In-stream Processes in Regulating Stream Outputs of N and P From Forested Catchments:
Evidence From Studies in Walker Branch Watershed
AU: * Mulholland, P J
EM: mulhollandpj@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division, ORNL, Bldg 1505, MS 6036, PO Box 2008,
Oak Ridge, TN 37831-6036
AU: Roberts, B J
EM: robertsbj@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division, ORNL, Bldg 1505, MS 6036, PO Box 2008,
Oak Ridge, TN 37831-6036
AB:
In many early studies of catchment biogeochemistry, processes occurring in soils (plant and microbial uptake) and groundwater
(weathering, ion-exchange) were thought to control catchment outputs and little consideration was given to processes
occurring in streams. In recent years, a number of studies have pointed to the importance of in-stream processes in
regulating nutrient concentrations and outputs. We have used a combination of short-term and long-term studies of catchment
hydrology and biogeochemistry and nutrient tracer experiments in the stream to identify the potential role of in-stream
processes in controlling N and P outputs in Walker Branch Watershed, a 1st-order catchment in eastern Tennessee. These
studies have shown that consistent seasonal minima in N and P concentrations are the result of high rates of in-stream
nutrient uptake associated with algal blooms (early spring) and leaf decomposition (autumn). In winter and summer, nutrient
concentrations and outputs are primarily controlled by a combination of hydrologic flowpath and biogeochemical processes in
the catchment. In Walker Branch in-stream processes retain about 20-30% of the annual inorganic N and P load to the stream
from the surrounding catchment. We hypothesize that the effect of in-stream processes on catchment nutrient retention is
likely to be greatest in small streams such as Walker Branch and diminish with increasing stream size due to reductions in
surface to volume ratios and inputs of organic material that create ideal conditions for biological activity.
DE: 1806 Chemistry of fresh water
SC: Hydrology [H]
MN: Fall Meeting 2005