Rufus Woods Lake – Columbia River Reservoir Morphometrics, Initial Food Web and Rainbow Trout Fishery Studies 31 October 2011 Submitted to: Ed Shallenberger Colville Confederated Tribes Fish and Wildlife Department P. O. Box 150 Nespelem, WA 99155 Prepared by: David C. Richards, Ph.D. J.E. Jack Rensel, Ph.D. Zach Siegrist, M.Sc. Senior Research Ecologist Frank J. O’Brien, M.A. EcoAnalysts, Inc., Dale Kiefer, Ph.D. Wenatchee, WA 98801 System Science Applications, Inc. Los Angeles, CA Executive Summary This study was conducted to provide a baseline and preliminary understanding of the food web and physical habitat of Rufus Woods Lake (RWL), a run-of-the-river hydropower reservoir located downstream of Grand Coulee Dam, so that the rainbow trout fishery can be more efficiently managed or enhanced. A laudable goal for RWL is to create a sustainable fishery. However, a myriad of information is needed to fully understand a complex and rapidly changing reservoir such as Rufus Woods Lake. Commercial net pens are used in RWL within Colville Confederated Tribal jurisdiction to rear and in some cases intentionally release sterile rainbow trout (RBT). Determination of possible net pen effects was not the primary goal of this study, although positioning of sampling locations was performed throughout the reservoir with consideration to net pen location. Generally conditions for rearing RBT in net pens are good in RWL. However, high river flow years and operating practices of Grand Coulee Dam have resulted in supersaturated dissolved gas, gas bubble disease of aquatic organisms and severe mortality of the pen fish used for enhancing the fishery and for commercial fish farm production. As most of the fish caught in the RWL fishery are from net pen origin, the net pens are considered an important tool for managing the RBT fishery. Presently, relatively large size RBT released by the CCT into RWL are purchased from net pen growers operating in the reservoir. RBT are released at different intervals throughout the year for fishing by CCT members and non-treaty anglers. The fish are very heavy relative to length, and little was known about their diet after release, longevity in the reservoir, the supporting food web and the distribution of different types of habitat in the system. Our study incorporates information from companion studies conducted by the CCT Fish and Wildlife Department that involved collection of fish stomachs for analyses of contents by our team. CCT also conducted an acoustic tagging study with a separate contractor that is being completed at the time of this report production. We surveyed the reservoir extensively to create a digital bathymetric map so that the morphometrics of the reservoir could be documented in relation to habitat features, focusing on the biologically-active littoral (nearshore) zone. Food web studies included benthic sampling using suction dredging, cobble basket deployments, periphyton (attached benthic algae) studies using tile samplers and cobble scrapes were conducted at a number of locations and times throughout RWL beginning in August 2010 and extending through the summer of 2011. To place our results within the context of changing interannual conditions, we reviewed basic water quality conditions in the Grand Coulee Dam tailrace from the past decade and contrasted those results to conditions in 2010 and 2011 during this study. Several experienced observers of RWL had noted that in 2010 and 2011, macrophytes (rooted plants) were covered with epiphytic growth and many had a slime-like coating. Morphology of RWL The bathymetric map and subsequent geographic information study (GIS) study indicated that the reservoir can indeed be considered as having three regions as first proposed by Dr. Quentin Stober in 1977: 1) a relatively shallow, narrow and very fast flowing tailrace that is retained with a large amount of revetment on the right bank (looking downstream); 2) a generally wider and moderate depth fast flowing mid river section from Seaton’s Grove many miles downstream to an area where river width increases with depth forming; and 3) a shorter Chief Joseph Pool area with greater depths and apparent reduced water flow velocities (Erickson et al. 1977). RWL is unique among mid and lower Columbia River reservoirs due to its very narrow, relatively deep morphology that limits the amount of backwater fisheries and wildlife riparian habitat. Rufus Woods Lake: Morphometrics, Initial Food Web and Rainbow Trout Fishery Studies ii The digital map was analyzed to construct tables of littoral habitat and other features that indicated: RWL is 11% shallow littoral by surface area and 2% by volume Upper reservoir is 23% littoral by surface area and 6% by volume Middle reservoir is 11% littoral by surface area and 2% by volume Lower reservoir is 7% littoral by surface area and 1% by volume Upper reservoir has highest, lower reservoir the lowest percent of shallow littoral-zone habitat Mixtures of fines, gravel and cobble are most dominant habitat class Hard bottom habitat is dominant in upper reservoir Macrophytes and filamentous algae are most common in lower reservoir, least common in upper reservoir Medium littoral zone slopes are most common in RWL; steep slopes are least common Steep and medium backshore slopes are most common; low slopes are less common The habitat types can eventually be related to food web production contribution, but that was not attempted in this preliminary project Water Quality We provide water quality data analysis to illustrate that water entering RWL in the two study years of 2010 and particularly 2011 exhibited increased concentrations of total phosphorus and dissolved inorganic phosphorus (orthophosphate) after a multi-decade period of declines to the 2000-2009 period that qualified the reservoir as nutrient poor (oligotrophic). Several other water quality variables showed major departures from the norm especially in 2011 including: elevated ammonia-nitrogen, water column chlorophyll a (an indicator of phytoplankton standing stock), fecal coliform, turbidity. Concurrent reduced dissolved oxygen concentrations were measured. The specific causes of the water quality change entering the reservoir appears to be related to higher than normal, midsummer river discharge in 2010 and much higher-than-normal river discharge in most of 2011. High flows in regulated rivers may result in shoreline flooding and erosion and resuspension of bed load (river bottom) which mobilizes nutrients and fecal coliforms from riparian and tributary runoff. High flows in 2011, combined with the use of spill through “diffuser ports” in the face of the dam instead of spillway (over the top) discharge and the loss of turbine generation through poorly-timed maintenance work, all resulted in excessively high total dissolved gasses in RWL for weeks. Wild fish (including ESA-listed fish downstream) and invertebrates were adversely affected by this unfortunate event and millions of dollars of fish loss occurred at the net pens in RWL. Such events have happened previously, but the cumulative effects on the food web for our study are not fully known and no mitigation has been attempted for waters within Rufus Woods Lake. Macrophytes, Periphyton and Blue Green Algae Given the above, our study occurred at the most inopportune time if we were interested in documenting “normal conditions”, but we were able to seize the opportunity to understand the system in its perturbed state by increasing our emphasis on algal communities that appeared to be altered and worked cooperatively with other users and managers of RWL. We found noxious forms of filamentous periphyton and benthic diatoms on macrophytes throughout the lake where macrophytes occurred, often varying highly in density over scales of a few meters distance that was related to difference in exposure to water currents. Areas of high flows had macrophytes that were mostly free of periphyton, but macrophytes in calm areas were much more Rufus Woods Lake: Morphometrics, Initial Food Web and Rainbow Trout Fishery Studies iii commonly covered with periphyton including dominance by the noxious species Spirogyra sp. and Cladophora sp. The former has been a problem in upstream reaches and tributaries of the Columbia River and the latter was a major problem in the pre-1990 era when thousands of kilograms per day of phosphorus were being discharged into Lake Roosevelt from a fertilizer plant in Canada. At that time, Cladophora sp. formed large floating mats in Lake Roosevelt that led to the call for phosphorus discharge abatement. An additional problem occurred in 2011 with the appearance of floating mats of algae in RWL that tested positive for anatoxin-a, a biotoxin associated with blue green (cyanobacteria) algae. The reservoir was posted by the US Army Corps of Engineers to warn user groups. Sampling by USACE and consultants for Pacific Seafoods showed the presence of small densities of Oscillatoria sp., a potentially toxic blue green organism. Professor Wayne Carmichael was hired by Pacific Seafoods to advise and conduct taxonomic analysis of samples along with a consultant hired by the USACE. A 1999-2000 study downstream of downstream Rocky Reach Reservoir indicated blue green algae had peak biovolume occurrences in February, June, and August and were principally represented by Oscillatoria spp. and Aphanizomenon flos-aquae. These species were found in subsamples in RWL in 2011 mostly within floating mats accumulating just above Chief Joseph Dam along the boomstick used to catch debris (although the latter species is often misidentified). While conducting bathymetric surveys, we navigated the entire shoreline area in depth of < 5 m on both banks to make observations about the presence or absence of filamentous periphyton growth on macrophytes. We observed and sampled floating mats from upstream in RWL near Buckley Bar for algal species composition and abundance and found variable concentrations throughout the lake, suggesting the possibility of an upstream source. However, limited observations in Banks Lake and lower areas of Lake Roosevelt did not detect any of the floating mats, thus the actual source distribution of the mats remains undetermined.