Wisconsin's Role in Great Lakes Restoration - American Water ...

10. Desorption of Phosphorus from Stream Sediments and the Impact on Stream
Concentrations
** Amy A .Timm, UW-Stevens Point, Stevens Point, WI, atimm569@uwsp.edu
Paul McGinley, UW-Stevens Point, Stevens Point, WI, pmcginle@uwsp.edu
The interaction between sediment phosphorus and stream phosphorus concentrations can be
important to meeting nutrient standards in streams. Stream sediments may be a reservoir of
phosphorus that slows the reduction of stream concentrations after reductions in nonpoint and
point sources. This study examined the potential for phosphorus release throughout Mill
Creek in central Wisconsin. This stream has decreasing phosphorus concentrations ranging
from 0.5 to 0.1 mg/L across 70 km. Both point and nonpoint sources contribute to the
phosphorus load. Public treatment plants in the watershed serve a population of 20,000. The
watershed also contains approximately 11,000 cows with about 50% of the land in dairy crop
rotation. The stream is currently on the 303(d) list of impaired waters due to low dissolved
oxygen from high biological productivity.
We measured phosphorus stream concentrations, sorption/desorption to sediments, and
pore-water profiles to evaluate phosphorus-sediment interactions. The results were used to
develop a stream model that incorporated external loads and flow with internal sediment
phosphorus cycling. The model projects the sensitivity of stream phosphorus concentration on
the sediment phosphorus reservoir as a result of sorption/desorption in the sediment. These
results will be useful to assist restoration efforts in Mill Creek and elsewhere when stream
phosphorus concentrations must be reduced to meet water quality standards.
**Graduate student presentation
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