TerraGraphics Environmental Engineering

Dworshak Nutrient Restoration
North Central Idaho

TerraGraphics was contracted to assemble data to enable assessment of the current trophic status of Dworshak Reservoir, examine the Nitrogen:Phosphorus (N:P) ratio, and determine where and when imbalances occur. TerraGraphics then worked with Dr. John Stockner, principal of Eco-Logic, Ltd. based out of Vancouver, B.C., to prepare a prescription of nutrient supplementation to restore a proper N and P balance through the growing season so Carbon flows are restored to Kokanee Salmon.

To accomplish these objectives TerraGraphics completed the following tasks:

Reviewed existing limnological information on Dworshak Reservoir and commented on the state of the ecosystem and quality of the database.
Examined relevant nutrient data and summarized balance or imbalance in NO3:TDP ratio on production of edible/inedible phytoplankton as forage base and its impact on the productive (trophic) state of the reservoir and its fisheries.
Calculated the annual areal total phosphorus (TP) loads - TP/m2, using existing limnological and hydrological data, and compared with historic loads.
Wrote the prescription for the proper addition of N and P at appropriate frequencies to restore a balanced N:P ratio to selected regions of the reservoir to promote a higher level of primary and secondary (forage) production.
Listed anticipated water quality changes with nutrient supplementation.
Recommended appropriate suppliers of high quality liquid fertilizer of correct N:P formulations and listed equipment required for application.
Developed a cost-effective state of the art limnological monitoring program that is based on assessment of key variables (i.e., those considered to be the most sensitive for the detection of major shifts in the reservoir’s physio-chemical and biological systems).

Dworshak Nutrient Restoration North Central Idaho

Dworshak Nutrient Restoration
North Central Idaho