Scientific Investigations Report 2006–5209
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5209
Three datasets that were collected by the USGS as part of the fish-tracking study have been used in preparing this report. The first is continuous dissolved oxygen, pH, specific conductance, and water temperature collected from a network of continuous water-quality monitors, the second is meteorological data (wind, temperature, relative humidity) collected at two locations in the study area, and the third is chlorophyll a and nutrient data collected on a weekly basis at a subset of the sites in the study area. An additional dataset of light-meter readings, collected just under the water surface and at 0.5-m depth intervals at several sites around the lake as part of the ongoing monitoring effort in 2005, was used to generate estimates of the depth of the photic zone.
In 2002, the water-quality monitoring network consisted of 11 sites in the study area (fig. 1A). At nine of these sites, the monitor was located in a fixed position at 1 m off the bottom. At two of these sites, the monitor was installed on a profiling buoy, which was programmed to make a profile of the water column on an hourly basis. Starting in 2003, the network was modified on the basis of 2002 results. Most of the sites were slightly relocated, and three were added (fig. 1B). In 2004, one of the profiling buoys was relocated to a position outside of the immediate study area, in the middle of the deep trench running along the western shoreline of the lake (site UKL16 in fig. 1B).
The water-quality monitors were cleaned and field measurements were collected during weekly site visits. Deployments generally lasted 3 weeks; at the end of this time, the monitor at the site was replaced with a freshly calibrated unit. Quality of the data was assured by collecting field information at weekly site visits and processing the time series according to the procedures in Wagner and others (2000). The maintenance procedure for the monitors at the profiling buoys was the same as for those at fixed positions, except that deployments generally lasted only 2 weeks.
Data collected from the profiling buoys provided information on the variability in water-quality constituents over the water column at a single geographic location. The vertical resolution of the profiles changed over the 3 years of the study as the understanding of the system and the objectives of the profiling data evolved. Profiling was based on a user-supplied uppermost depth and a sampling interval; therefore, as the lake was drawn down over the summer, the programming needed to be adjusted to compensate for the decreasing overall depth. This resulted in some imprecision in the location of the sampling depths relative to the bottom, but the buoys were consistently programmed to collect data as closely as could be achieved to 1 m from the surface and 1 m from the bottom, in addition to other points in the profile. In 2002, the profiles were completed at 0.5-m intervals; in 2003 and 2004, a single midwater column position completed the profile. The profiling mechanism and proprietary computer on the profiling buoys proved difficult to maintain in working order over the three field seasons of the study, which resulted in numerous gaps in the profiling data. When possible, a fixed-position monitor was placed at 1 m off the bottom at the site of a nonfunctioning profiling buoy; as a result, the 1-m off-bottom dataset at each of the buoy sites is more complete than the dataset of water column profiles. The more complete 1-m off-bottom dataset was used in computations where the data were combined with data from the rest of the network.
Both profiling buoys were equipped with a wind compass and anemometer. One was additionally equipped with air temperature and relative humidity sensors. Because the locations of the profiling buoys changed from year to year, wind speed and direction was collected at site UKL07 in all 3 years, and at site UKL08 in 2002, site UKL13 in 2003, and at site UKL16 in 2004. Air temperature and relative humidity were collected at site UKL08 in 2002, site UKL07 in 2003, and at site UKL16 in 2004. Quality assurance of wind speed and relative humidity relied on factory calibrations of the equipment; air temperature was checked with a National Institute of Standards and Technology thermometer in the field. Wind direction was checked at the site using a handheld compass.
The same equipment problems that hindered the collection of complete water-quality profile data affected the collection of the meteorological data as well, so there were numerous data gaps, particularly in 2002 (68 and 24 percent of days were missing at sites UKL07 and UKL08, respectively, between June 15 and October 15). Fortunately, the locations of the buoys in 2002 were such that the wind data collected at sites UKL07 and UKL08 were highly correlated, and could be used interchangeably for most purposes. Data collected at sites UKL07 and UKL13 in 2003 were slightly less correlated and the data collected at sites UKL07 and UKL16 in 2004 were only moderately correlated, but the wind datasets were more complete in those years (10 percent of days were missing at site UKL07 between June 15 and October 15 in 2003, and 15 percent in 2004).
Water samples were collected for the analysis of dissolved nutrients (ammonia, orthophosphate, and nitrate/nitrite), total phosphorus and chlorophyll a on a weekly basis. In 2002, samples were collected at sites UKL05, UKL06, UKL07, and UKL08. In 2003, samples were collected at sites UKL05, UKL07, and UKL08, but not at site UKL06. In 2004, a fourth site was added at UKL02 (fig. 1).
Overall, 27 percent of the dissolved nutrient samples and 30 percent of the total phosphorus samples collected were for quality-assurance purposes, and included equipment blanks (first sample collected every week), splits and method replicates (each type every other week), spikes (from one to three times per season), and a few sequential blanks that were designed to test particular procedures during the course of the season. Equipment and sequential blanks are samples of inorganic blank water collected in the field using the same methods and equipment as environmental samples. Sequential blanks are a series of blank samples that pass through distinct parts of the collection process. Blank samples determine if the processes of collection, handling, transport and analysis provide measurable contamination. Split samples are environmental water samples collected once and divided into two. Replicate samples are environmental samples collected twice in rapid succession at the same site. Split samples determine the variability of sample processing and preservation, whereas replicate samples determine both the variability of the system and the variability of processing and preservation. The results of the quality-assurance sampling indicated that precision and accuracy generally were acceptable and the variability in sampling and processing is lower than seasonal variability (Appendix A, tables A1-A4, fig. A1). The only area of concern was ammonia in equipment blanks, which showed many instances of detectable concentration, in some cases quite high in 2003 and 2004 (table A1). This problem did not occur in 2002, when the samples for dissolved nutrients were collected into evacuated bottles, even though a VanDorn sampler was used to collect the water from depth as in the other years. The difference in the sampling process between years suggests that the samples were contaminated by air deposition. A series of sequential blanks targeted at finding the cause of the problem was analyzed in those years, but the source of the contamination was never satisfactorily pinpointed, although a small amount of contamination seemed to come from the filters. The results of equipment blanks may overestimate the amount of contamination present in an environmental sample because the equipment is flushed with native water before an environmental sample is collected, thereby rinsing any contaminants. Nonetheless, it should be assumed that contamination of the ammonia samples on the order of 10 µg/L is possible. Although the lowest ammonia concentrations may not be as reliable in 2003 and 2004 as in 2002, the highest ammonia concentrations are reliable and important because ammonia at these concentrations has implications for fish health. In 2005, capsule filters were used to collect the samples to be analyzed for ammonia. The use of these filters does not eliminate all contact between the sample and sample bottle and the atmosphere, but it does limit this contact. Results indicate that the problem was not eliminated entirely but was much reduced by the use of these filters.
Field processing and equipment cleaning protocols were designed to procure samples in which concentrations at a parts per billion level of concentration could be detected (U.S. Geological Survey, variously dated; Horowitz and others, 1994). Samples collected for dissolved nutrients were collected with a VanDorn sampler at two locations in the water column—in the middle of the upper one-half of the water column (one-quarter of the water column depth), and in the middle of the lower one-half of the water column (three-quarters of the water column depth) and passed through a 0.45-µm filter. Samples were chilled and shipped within 24 hours to the National Water Quality Laboratory (NWQL) in Denver, Colorado. In 2002 only, samples for dissolved nutrients were collected into an evacuated container to minimize any loss of ammonia from a high pH sample (C.J. Patterson, U.S. Geological Survey, written commun., 2002). In 2002 and 2003, samples for total phosphorus and chlorophyll a were integrated over the water column by collecting water in a large-diameter flexible hose from the surface to 0.5 m from the bottom. In 2004, the flexible hose was replaced with a cage sampler that was lowered with sample collection bottles at a constant rate to 0.5 m from the bottom. This cage sampler proved easier to use, and the quality-assurance data did not indicate a significant change in the median difference between replicate samples of total phosphorus from 2003 to 2004 [although the median difference between replicates in chlorophyll a increased from 2003 to 2004, but remained within acceptable limits (table A3)]. In all years multiple subsamples as needed from either the VanDorn sampler or the hose/cage sampler were composited with a churn splitter, from which splits for different analyses were drawn. Total phosphorus samples were acidified, chilled, and shipped within 24 hours to the NWQL. Finalized data are stored in the USGS National Water Information System (NWIS) database (accessible through NWISWeb, http://waterdata.usgs.gov/or/nwis/qw).
Samples for the analysis of chlorophyll a were sent to Aquatic Analysts in White Salmon, Washington. The chlorophyll a sampling program was designed to measure this surrogate for algal biomass in a cost-effective way, with good precision, and allow a reliable assessment of relative changes in algal biomass. The results of quality-assurance sampling and other more qualitative assessments of the dataset indicate that the chlorophyll a dataset is well-suited to this purpose. Over the 3 years of the study, 20 method replicates were collected (7 percent of the total samples) and the median percentage of the difference between the replicates was 4, 11, and 11 percent in 2002, 2003, and 2004, respectively; 26 split samples were collected (10 percent of the total samples) and the median percentage of the difference between the splits was 3, 7, and 10 percent in 2002, 2003, and 2004, respectively. The difference between replicate and split samples is low and shows that the variability due to collection and analysis methods is small compared to the overall temporal variability of the data (Appendix A, fig. A1). Chlorophyll a was determined fluorometrically for this study. The quantitative comparability between this method and the high performance liquid chromatography method used by the NWQL to determine chlorophyll a in samples prior to October 1, 2005, has not been established, and the chlorophyll a data collected during this study are not stored in the USGS NWIS database. Chlorophyll a data collected by the Klamath Tribes in their biweekly sampling program were analyzed by a spectrophotometric method; therefore the chlorophyll a data collected during this study should not be assumed to be quantitatively comparable to that dataset either.
Nonparametric statistics were used in this report in order to accommodate data that are not normally distributed. When correlations between datasets were calculated, Spearman rather than Pearson correlations were used. When analysis of variance (ANOVA) was used, the test used was the Tukey studentized range test for differences in the means, performed on the rank-transformed data. All statistical tests were run using SAS System for Windows™, Release 8.02, SAS Institute Inc., Cary, North Carolina.
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Department of the Interior | U.S. Geological
Survey
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