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Dworshak Reservoir limnological data
||limnology, temperature, dissolved oxygen, nutrients, Secchi, compensation depth, chlorophyll, pico-plankton, phytoplankton, zooplankton
|Dates of Data
||2003 TO 2016
|Data Set Status
|Data Set Update Schedule
|Date Data Set Published on StreamNet Data Store
|Project Name & Number
|Purpose of Data Set
||The goal of this project is to improve resident fisheries in Dworshak Reservoir as partial mitigation for losses from the construction of Dworshak Dam and continuing impacts from ongoing dam operations. Dworshak Dam was built in 1971 by the U.S. Army Corps of Engineers (USACE). This 218.8 m (718 ft) high dam irrevocably blocked the North Fork of the Clearwater River for access to hundreds of miles of tributaries for anadromous fish production and flooded 86.9 km (54 mi) of riverine habitat for resident fishes. The resident fisheries that were developed in the reservoir were intended to mitigate for some of these losses; however, they were only partial mitigation for the historic losses. Current fish mitigation is inadequate for the reservoir operations that continue to severely impact native and non-native resident fish in Dworshak Reservoir and the North Fork Clearwater ecosystem. In addition, the productivity of this ecosystem has been significantly reduced due to the loss of ‘marine derived nutrients’ from anadromous salmonids that no longer access the drainage.
Kokanee are the best-adapted species for this fluctuating reservoir since they occupy the pelagic zone and spawn in tributary streams. Kokanee densities have exceeded 100 adults per hectare, and angler harvest has exceeded 200,000 fish in some years. In addition, kokanee function similarly to historical anadromous fish runs by providing an important prey source for other resident fish, including threatened bull trout. They also contribute to the productivity of the reservoir and its tributaries.
Although kokanee may serve as a surrogate for anadromous fishes in the ecosystem, bull trout and other resident fish may still be limited by reductions in available forage, aquatic macroinvertebrate biomass and taxonomic richness, and reduced growth rates due to loss of anadromous fish production and the nutrients that large anadromous carcasses provided (Clearwater Subbasin Plan, section 8.3.1, pg. 342). A limited food supply, due to declining reservoir productivity and nutrient levels, has been suggested as a critical limiting factor to stable fish populations in Dworshak Reservoir.
The IDFG fish management objective for kokanee in Dworshak Reservoir is to maintain densities of 30 to 50 adult kokanee per hectare on an annual basis and catch rates of at least 0.7 fish/hr, at an average length of at least 25 cm. This project addresses this objective through supplementing the reservoir with nutrients in an effort to increase the efficiency of the food web. This will result in more desirable phytoplankton community (i.e. edible taxa) and increased zooplankton abundance, which should, in turn, provide more forage for kokanee. While kokanee will be the primary species benefiting from this project, it will also benefit other resident fish throughout the entire ecosystem. An improved kokanee population provides forage for the reservoir’s bull trout and smallmouth bass. Also, having 300,000+ adult kokanee migrate up tributary streams and die each fall will add nutrients to these stream systems, thereby enhancing fluvial fish populations above the reservoir.
This project will be conducted jointly with the USACE. The USACE Walla Walla District recently contracted Dr. John Stockner to evaluate the current state of the reservoir and develop a prescription for a 5-year nutrient enhancement experiment. The USACE will be purchasing the needed fertilizer and equipment and performing the nutrient applications, while IDFG project staff will work cooperatively with both Dr. Stockner and the U.S. Army Corps of Engineers to assess the effectiveness of nutrient additions to increase reservoir productivity and enhance kokanee size or abundance.
In order to assess the effects of the nutrient supplementation, IDFG will monitor reservoir limnology at eight limnological stations; seven throughout Dworshak Reservoir and a single station in the North Fork Clearwater River below Dworshak Dam (NFC). Nutrient treatments will occur in the main reservoir and the North Fork Clearwater Arm, therefore stations in these areas will represent the treatment area. Since the Elk Creek Arm and Little North Fork Arm will not receive any nutrient supplementation, EC-6 and LNF-3 will serve as controls. A detailed description of the monitoring efforts and study area can be found in the QAPP attached to this project in Pisces.
Figure 1. Map of Dworshak Reservoir, major tributaries, reservoir sections, and limnological sampling stations.
|Summary / Abstract
||This data set contains physical, chemical and biological measurements of the limnological characteristics of Dworshak Reservoir.
|Broad Biological Groups
|NPCC Subbasins (2001 Subbasins)
||Provincial (Mountain Snake/Clearwater)
||Clearwater Fish Hatchery
Dworshak National Fish Hatchery
||limnology, temperature, dissolved oxygen, Secchi. compensation depth, chlorophyll, pico-plankton, phytoplankton, zooplankton
|Lead Person and Organization That Created the Data Set
Idaho Department of Fish and Game (IDFG)
|Other Participating Organizations
||Funding provided by Bonneville Power Administration
|Contact Person for Questions About the Data
||Name: Sean Wilson
Position: Sr. Fisheries Research Biologist
Organization: Idaho Department of Fish & Game
Address: 3316 16th St
|Broad Category of Methods
|Data Collection Methods
||We conducted limnological sampling at seven stations on the reservoir and one station on the North Fork Clearwater River (NFC) below Dworshak Dam (Figure 1). Five stations on the main reservoir were designated as RK-2, RK-31, RK-56, RK-66, and RK-72, corresponding with the approximate river kilometer (RKM). Two additional stations were located in untreated areas of the reservoir, RKM six of the Elk Creek arm (EC-6) and RKM three of the Little North Fork arm (LNF-3). Sampling at RK-66 was discontinued in 2012.
In 2004, we conducted limnological sampling once per month from May through November. In 2005, we sampled once per month from April through November. In 2006, we increased the sampling frequency to twice per month beginning in May. From 2007 through 2015, we sampled twice monthly from April through September and once monthly during March, October, and November. When all reservoir stations and the river station could not be sampled in one day, samples were collected over a two-day period.
Physical parameters measured included water depth, water clarity, water temperature, dissolved oxygen (DO), and photosynthetically active radiation (PAR). Chemical parameters included pH, total phosphorus (TP), total dissolved phosphorus (TDP), total nitrogen (TN), nitrate plus nitrite nitrogen (N+N), total ammonia (TA), total dissolved solids (TDS), and dissolved organic carbon (DOC). Biological parameters included chlorophyll a (Chl a), picoplankton, phytoplankton, and zooplankton. Sampling for TN, TA (beginning in 2011) and DOC (beginning in 2007) was only conducted during the first event each month. Turbidity, measured using a Hach 2100Q Turbidimeter, along with all previously mentioned chemical parameters, was analyzed for NFC.
Water depth was measured using a Garmin™ Model GSD22 depth sounder in conjunction with a GPS MAP 4212 chart plotter. Water clarity was measured using a 20 cm Secchi disc, which was lowered from the shaded side of the boat until no longer visible, then raised until it reappeared. Water temperature and dissolved oxygen (DO) measurements were taken concurrently with a Yellow Springs Instruments® (YSI) model 58 or ProPlus meter with a 60 m cable and probe assembly with a high sensitivity membrane. The probe was calibrated at each site following the manufacturer’s instructions. After recording air temperature, both water temperature and DO measurements were recorded at the surface, 1 m, 2 m, and every 2 m thereafter to 60 m or the reservoir bottom. The depth of the thermocline, defined as a one-degree change in temperature over a one-meter change in depth, was recorded.
The level of PAR was measured using a LI-COR® model LI-250A light meter and a 400-700 µm quantum sensor (model LI-192SA). The sensor was mounted on a frame and weighted with a lead weight. A 15-second average PAR reading was taken at the water surface and at one meter intervals to 15 m or a reading of zero. A second meter and dry sensor were used to take air readings concurrently with the wet readings.
Water samples were collected from the epilimnion (EPI) and hypolimnion (HYPO) at each station using a 2.2-L Kemmerer bottle. EPI samples consisted of a composite of water from 1, 3, 5, and 7 m, regardless of the presence or depth of a thermocline. One liter of water from each depth was mixed in a splitter bucket. HYPO samples were collected at every station during each sampling event through 2008. In 2009, HYPO samples were collected from each station once per month, and from 2011 on, HYPO samples were collected only once per month and at RK-2. They consisted of a single ‘grab’ from 25 m, or 3 m above the bottom if the depth was <28 m. Two 250-mL polyethylene sample bottles were filled from each sample depth (EPI and HYPO). One bottle (unfiltered sample) was pretreated with sulfuric acid (H2SO4) by the contracting lab as a preservative. The other bottle (filtered sample) was filled with water filtered through a 47-mm filtering manifold and a 0.45-µm cellulose acetate filter. A vacuum of up to 38 cm of mercury (Hg) was applied using a hand operated pump. The DOC samples were collected by filling a 40-mL glass vial, leaving no headspace, with the EPI composite water. All bottles were labeled with station, date, time, depth (EPI or HYPO), and filtered or unfiltered. Sample bottles were stored on ice while in the field and transferred to a refrigerator until shipping. Samples were shipped via overnight carrier to the contracting lab within two days of collection. Chemical analyses were performed by AM Test Labs of Kirkland, Washington. Analytical methods used for each parameter can be found in Wilson et al. (2010). While collecting the EPI sample at each station, a ‘grab’ was collected from 1 m and the pH was measured using a pH10A meter from YSI.
A Chl a sample was collected by filtering 250 mL of the EPI composite water through a 0.45-µm glass fiber filter using a similar filtering manifold and hand pump, also taking care not to exceed a vacuum of 38 cm Hg. The filter was removed from the manifold and folded in half on a 15-cm2 piece of aluminum foil. The foil was folded around the filter, placed in a Ziploc™ bag, and kept on ice until returning to the field office. After returning to the field office, Chl a samples were placed in a freezer until shipping.
Picoplankton samples were collected by filling a 60-mL amber polyethylene bottle with the EPI composite water and preserved with six drops of 50% glutaraldehyde. Phytoplankton samples were collected by filling a 125-mL amber polyethylene bottle with sample water and preserved with 15 drops of Lugol’s solution. All sample bottles were labeled with station, date, time, and depth (EPI or HYPO).
Zooplankton were collected using a 50-cm diameter, 80-µm mesh Wisconsin style net fitted with an OceanTest Equipment flow meter. One vertical tow was performed at each station from 10 m to the surface. Tows were completed by lowering the net to depth and retrieving at a rate of 0.5 m/s. The number of revolutions on the flow meter was recorded on the datasheet and plankton were rinsed from the net into the collection bucket, then rinsed into a collection jar and preserved in 70% ethanol. Collection jars were labeled with station, date, and depth of tow. Prior to the field season, several tows were performed with no net and the number of revolutions recorded to serve as a reference point. All plankton and Chl a samples were sent to Advanced Eco-Solutions of Newman Lake, Washington for analysis. Analytical methods used for each parameter can be found in Wilson et al. (2010).
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