Contract Description:

This contracting period represents the first year of resuming a nutrient supplementation project on Dworshak Reservoir after a stoppage of approximately 20 months.  This project is a joint venture between the U.S. Army Corps of Engineers (USACE) and the Idaho Department of Fish and Game (IDFG).  The USACE will supplement the reservoir with nitrogen to promote an improved nitrogen to phosphorus  ratio and increased foodweb efficiency.  The IDFG will be responsible for collecting limnological samples, which will be used for in-season management of nutrient supplementation and for evaluating project effectiveness.  The USACE has contracted Advanced Eco-Solutions to provide the nutrient prescription, interpret the results of limnological sampling, and recommend in-season adjustments to the amount of fertilizer to be applied.  Fish monitoring will also be conducted by the IDFG and, combined with limnological data, will allow for an overall assessment of project effectiveness.

Legal authority to conduct the fertilizer applications for this project was initially covered by a Consent Order from the Idaho Department of Environmental Quality (IDEQ) due to uncertainties as to whether a National Pollutant Discharge Elimination System (NPDES) permit was appropriate. During the end of the fourth year (2010), an Orofino resident filed intent to sue claiming the project did not have the proper permits and was causing blue-green algae blooms.  At this point, the U. S. Environmental Protection Agency (EPA) decided that a NPDES permit was necessary for the project to continue.  In response to EPA's decision, the USACE halted the nutrient applications in late July of 2010 and resumed efforts to secure an NPDES permit.  The NPDES permit became effective on October 15, 2011, which precluded nutrient applications until the spring of 2012.  IDFG continued to monitor limnological conditions and the kokanee population within the reservoir.  Due to an abnormally high snowpack and resultant runoff during the spring of 2010, the reservoir was drawn down to near the lowest operational level (1450 feet above mean sea level) and underwent a high rate of flushing.  These events likely returned the reservoir to pre-supplementation conditions.  Therefore, monitoring results from 2011 will prove useful as an additional year of data to describe reservoir conditions in the absence of nutrient supplementation.  Furthermore, this scenario has unintentionally resulted in a unique opportunity to evaluate a nutrient supplementation project using an interrupted time series study design.  Since the effects of nutrient supplementation are believed to be cumulative, progressing up trophic levels as the project progresses, it will likely take another four years to see the full effects of the project again.

The first four years of nutrient supplementation produced promising results.  Nitrogen supplementation resulted in immediate increases of picoplankton densities. By the second year, we observed increases in the proportion of edible plankton concurrent with decreases in the proportion of inedible phytoplankton.  Furthermore, the percentage of the phytoplankton community that was composed of toxigenic cyanobacteria (blue-green algae) steadily declined as the project progressed, to the point that it was significantly less than pre-supplementation years by the fourth year of the project.  Zooplankton densities were also higher by the fourth year of the project than they had been in recent years.  Daphnia biomass and densities were higher in all supplementation years than in pre-supplementation years.  Daphnia were also larger in three out of four supplementation years than in pre-supplementation years.  Kokanee were larger by the fourth year of the project than in a pre-supplementation year of similar density and biomass was at least double that of recent years.  These results were achieved without violating water quality standards set forth in the Consent Order.

Both limnological and fish sampling during this contracting period will be similar to the last contracting period.  During the last contracting period, sampling of the hypolimnion was scaled down somewhat, while additional analyses from the epilimnion were required by the draft NPDES permit.  This sampling scheme has provided adequate data to address the goals of the project.  Limnological sampling will be continue to be evaluated to determine how much it can be scaled back as the project transitions from an experimental phase to an operational phase.  Future changes to the sampling scheme will focus on key parameters to be monitored and times of year which prove to be most useful in actively managing the nutrient applications.