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A. HEALTH OF WALKER RIVER AND LAKE
This project will evaluate and establish a benchmark for the environmental and ecological health of Walker Lake and Walker River. Decision tools will be developed to analyze the efficacy of different water acquisitions for improving future ecological integrity of Walker Lake and Walker River.
Researchers:
From DRI: Don Sada (PI), Division of Hydrologic Sciences (DHS); Kumud Acharya (Co-PI), DHS; Chris Fritsen (Co-PI), Division of Earth and Ecosystem Sciences (DEES); Alan Heyvaert (Co-PI), DHS; Ron Hershey (Co-PI), DHS; Duane Moser (Co-PI), DHS; Saxon Sharpe (Co-PI), DEES; and Mark Stone (Co-PI), DHS
From UNR:Sudeep Chandra, (PI), Department of Natural Resources and Environmental Science (NRES); Peter Weisberg (Co-PI), NRES
Updates:
2007: May | June | July | August | September | October | November| December
Current Year: 2008
Field work for Walker Lake limnology and Walker River ecology proceeding as scheduled. Field crew participated in a barbecue with two locals from Walker Lake that shared their impressions of the area. Incredibly hospitable folk, it was nice for our science team to engage the community and hear why the people in the town of Walker Lake enjoy this area so much.
UNR and DRI coordinated to collect a spatial synoptic of water quality from Walker Lake. Samples were collected for nutrients, biochemical measurements, algal biomass, and zooplankton production from four locations. Additionally we sampled six to eight locations for water quality parameters (dissolved oxygen, light irradiance, temperature, and conductivity).
June 2007:
We processed samples collected from Walker River and continued to sample Walker Lake. Walker river invertebrate samples were sorted and the process for identification was initiated. We are using a target count of 300 for all of these samples. Baetis spp. from the Walker River were sampled to obtain head capsule width, total length, and dry mass data. These data will be used for length: mass regressions and instar size relationships. Invertebrates were also collected for chemical analysis to determine the food web structure on the river. Temperature loggers were also checked at each site.
We also sampled four stations on Walker Lake for water quality, physical conditions, algae, and zooplankton. Zooplankton were collected for stoichiometry, (carbon, nitrogen, and phosphorus), fatty acid, isotope analysis, and species enumeration. Bacterial sample collections yielded zero growth and were also successfully collected for DNA and sulfide analysis. These will be used to obtain a better understanding of the production of toxic constituents (e.g. hydrogen sulfide) in the deeper portions of the lake. Benthic invertebrates were successfully collected from eight locations in the lake for enumeration and isotope analysis.
A second electrical conductivity (EC) survey for groundwater input to the lake was conducted. The survey covered the large alluvial fan on the west side of the lake (area of town of Walker). Survey consisted of continuous measurements of EC from 1 meter and 2 meters depth (zig-zag pattern toward and away from shore). Samples for isotopic analysis were collected every five minutes. Five vertical profiles at areas of varying EC were also conducted. Isotopic samples were collected for these profiles. A groundwater sample from the town of Walker water supply well was also sampled for isotopic analysis.
Highlight of the month
Our Walker Lake sampling in May was coordinated with two local residents from the town of Walker Lake. Our science team learned quite a bit about the local area and it was very enjoyable to connect with a few members of the local community. They were extremely supportive of our sampling efforts. We look forward to working with them soon.
July 2007:
We processed samples collected from Walker River during our spring sampling. We are continuing to process these samples in the laboratory. Temperature loggers installed at river sample sites were checked. The final electrical conductance and stable isotopic survey for groundwater input on the west side of the lake was conducted early this month.
Water quality and plankton biomass were sampled at the Walker Lake index station.
The application of ecological models is underway to describe the linkages between physical, chemical, and biological processes in the Walker River and Walker Lake. The model will be based on monitoring activities underway within other tasks and it will provide insight to guide policy decisions. To date, our focus has been on the hydrodynamic component of the lake model, which describes lake mixing and stratification.
Highlight of the Month:
We appreciate cooperation from the Walker River Paiute Tribe for our Walker River sampling, and we look forward to their participation in our work.
August 2007:
On Aug. 6-10, the team sampled Benthic Macroinvertebrates (BMIs) from eight sampling sites on the Walker River. Samples for community analysis were taken from six square feet of substrate, preserved in ethanol, and returned to the DRI lab for analysis. Samples of numerically dominant BMIs from both riffle and woody debris communities were taken for stoichiometry studies, frozen, and sent to the DRI Las Vegas facility for analysis. Samples of common organisms from the same BMI communities were preserved in ethanol for stable isotope analysis by the University of Nevada lab. Water-quality sampling was also conducted for the eight river sites.
Sample processing of April’s community analysis samples from the six sites above the reservation were identified to lowest possible taxonomic resolution. Baetis tricaudatus were collected from several sites, for the measurement of length to mass and head capsule width to mass ratios; measurements were taken by the team’s graduate student, Dianne Henneberry. Temperature data loggers were retrieved from the spring deployments, data downloaded, and loggers re-deployed to obtain the late summer through fall data. Fishes were collected from all sites, when there were fish, and analyzed for diet, age and body condition.
The team also sampled six locations from Walker Lake for water quality on Aug. 20. Samples were collected at discrete depths determined before sampling. Surface samples were taken at three of the six sites near the inlet of the Walker River. The team sampled three locations for zooplankton on Aug. 20 at the same locations water quality samples were taken from discrete depths. At the same three sites, samples were taken for stable isotope analysis while at one index site, near the middle of the lake, fatty acid samples were also taken. At all three sites samples were taken for: 1) zooplankton enumeration; 2) stable isotope and fatty acid analysis and; 3) stoichiometry. Two samples of 50 to 100 individuals were picked out for copepods, copidites, and, cladacearens and stored for stable isotope and fatty acid analysis. Zooplankton pulls ranged from 30 meters in the middle of the lake to 18 meters in the northern end of the lake. Water-quality sampling for the lake is being conducted in the nearshore on Aug 28.
The team also sampled eight locations for benthic invertebrates on Aug. 20. Of the eight locations sampled, three were in conjunction with the water quality locations. The remaining six locations were on the west and east shorelines ranging in depth from 3.5 meters at the northern end of the lake to 30 meters in the middle of the lake. The team identified three orders of invertebrates from benthic sampling: Diptera: tanypodinae 731 (532 found in June); Ostracoda: 37; Odonta: coenagrion/emallagena 2.
Stoichiometric (C, N and P) analysis of all zooplankton samples from the Walker Lake and benthic macro-invertebrate samples from the Walker River collected in March and May 2007 have been now completed. New sets of zooplankton and invertebrate samples were collected in August ’07 from both Walker River and Lake.
Highlight of the month
Highlights of this month included sampling BMIs for summer index period, finishing taxonomy of BMIs from the April sampling, being given sampling access permission by the Schurz tribe, and obtaining thermal data for the spring through mid-summer period.
September 2007:
Field work for Walker Lake limnology and Walker River ecology proceeding as scheduled.
Highlight of the month
During the week of September 17th thru 21st, we sampled Benthic Macroinvertebrates (BMIs), fish, and water chemistry from 8 sampling sites on the Walker River project, for the “baseflow” autumnal sampling event. Identifying and enumerating BMI samples, and analyzing water chemistry continued on schedule.
October 2007:
Our team has reached the point where we are both processing samples from the laboratory and collecting important information from the river and lake as it transitions into fall. Most of our group has spent October processing samples collected in September and at the beginning of the month. Our microbial ecologist had a particularly interesting month since he utilized a new direct pumping system to acquire cultures of microbes from different depths in the lake. A method enabling the accurate determination of hydrogen sulfide concentrations in the saline, high pH waters of Walker Lake was also developed. Cultivation-based studies, aimed at both enumerating and isolating specific microbial groups which control oxygen consumption and the production of noxious sulfur compounds during the summer are also underway. Go microbes!
A collection of alkali-tolerant microorganisms from the low-oxygen deep portions of Walker Lake has been established and is currently under characterization.
We coordinated with the Nevada Department of Wildlife and the U.S. Fish and Wildlife service to obtain fish samples from the lake. These samples will be used to determine the current food web structure and energetics of the lake.
November 2007:
During microbial ecology studies, nucleic acids extracted from the October depth profile of the lake were used as templates for PCR amplification and subsequent T-RFLP (terminal restriction fragment length polymorphisms) analyses. Three different T-RFLP profiles were generated for each of the seven collected depths. Direct cells counts were made from each depth using preserved samples stained with a nucleic acid dye and visualized with epifluorescent microscopy.
Contact with the organizations and individuals working on Walker Lake has continued to ensure that existing lake monitoring data are the most current available. Some data has been obtained to date, but most is still being checked for quality control, appropriateness, and errors or omissions. A draft database structure was reviewed by Jim Thomas, Alan Heyvaert, and Saxon Sharpe at the end of October. Based on comments to the draft version, a beta version was developed at the end of November and was presented at the general meeting on November 30. Comments made during the meeting were noted and will be incorporated into version 1.0 of the database, which is currently being developed.
T-RFLP analyses indicated that different communities of microorganisms were present in the hypolimnion during lake stratification. Additionally, despite the relatively high pH of Walker Lake, the water contained average concentrations of microbial biomass for a freshwater lake (~106 cells/ml).
In the past month, the researcher team assessing theWalker River continued to process macroinvertebrate, periphyton, and fish stomach samples collected in August and September.
December 2007:
Sampling of Walker Lake occurred early in the month (Dec. 4 and Dec. 5). Vertical profiles of temperature showed the water column as having a very slight stratification with temperatures in the upper 5 meters measured at 9.35°C with warming during the day up to 9.7°C. Temperatures at 20 to 25 were more constant throughout the day and remained at 9.2 to 9.3°C. This slight temperature stratification and diurnal warming and cooling is indicative of complete vertical winter mixing with brief periods of weak stratification. Sampling was coordinated among the UNR and DRI programs and led to collections for determining the suite of water quality constituents, zooplankton and phytoplankton community structure, bacterial abundances and distributions as well as diurnal oxygen dynamics. These data are contributing to the long term monitoring datasets as well as the more intensive time series of information gained from this year's interagency efforts. All data will contribute to our overall ability to capture the lake's dynamics through modeling efforts.
Since the lake is fully mixed during the winter and should thus be sulfide-free, the microbial team focused on completing analysis of archived samples collected earlier in 2007. Microbial community analysis (molecular and cultivation-based) is underway for the sample sets collected in May and October 2007. One set of new samples from December 2007 was obtained and is being analyzed to establish baseline microbial community data for the interpretation of samples to be collected after summer stratification and into the future.
Permission was granted by the Hawthorne Army Depot for access to the Mount Grant watershed. Two water samples were collected in early December for stable isotopic analyses. These analyses will provide baseline data to compare with isotope values from lake water collected near the town of Walker Lake. In contrast to the mostly homogenous microbial community that was present across the depth profile during the fall overturn, Terminal Restriction Fragment length polymorphism (T-RFLP)analyses of the May sample set indicates a very different community in shallow vs. deep samples, corresponding with the onset of summer stratification.