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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2009–5025

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Comparison of Water Quality Data Among Sites in Flooded Caledonia Marsh

Comparison of Water Sample Data

Water sample results generally were more similar between the two sites closest to the breach, sites FCM1 and FCM3 than site FCM2. The site farthest from the breach, site FCM2, was more influenced by the restored marshes in the southeastern corner of the flooded Caledonia Marsh. Total particulate nitrogen, total nitrogen, total particulate carbon, and total phosphorus tended to follow the week-to-week trends in chlorophyll a concentrations at sites FCM1 and FCM3 (fig. 6). At these two sites, total nutrient concentrations slowly increased over June, July, and the first week in August, after which there was more fluctuation in the concentrations, but no indication of a decrease before the end of the sampling period on September 11. The similarity between total particulate nitrogen, total nitrogen, and chlorophyll a indicates that most of the nitrogen is incorporated in algal biomass, for which chlorophyll a is a surrogate measurement. The same can be said of carbon and phosphorus, as indicated by the similar trends in total particulate carbon, total phosphorus, and chlorophyll a.

Consistent with the lower chlorophyll a concentrations at site FCM2, total particulate nitrogen and total particulate carbon concentrations also were lower at site FCM2 than at sites FCM1 and FCM3 (fig. 6). Total phosphorus concentrations at site FCM2, in contrast, were similar in magnitude to concentrations at sites FCM1 and FCM3. Total nitrogen concentrations at site FCM2 also were similar to those at sites FCM1 and FCM3 at least during the beginning of the sampling period. An ANOVA confirmed that the distributions of total phosphorus and nitrogen were not distinguishable statistically (p>0.05) among all three sites (table 2), whereas chlorophyll a concentrations were significantly less at site FCM2 than at sites FCM1 or FCM3.

Orthophosphate concentrations were significantly different at site FCM2 relative to those at sites FCM1 and FCM3, as detected by the ANOVA test (table 2), and consistent with the fact that orthophosphate concentrations at site FCM2 were greater than at sites FCM1 and FCM3 until the last three sampling dates (fig. 7). Ammonia concentrations were not different significantly among the sites, although concentrations at site FCM2 were greater than at sites FCM1 and FCM3 until August 8. Similar to orthophosphate concentrations at site FCM2, ammonia concentrations decreased toward the end of the sampling period, when chlorophyll a concentrations increased at site FCM2, which indicates the uptake of bioavailable nutrients by algae. Nitrite-plus-nitrate concentrations decreased from June 21 to July 16, then peaked at site FCM2 in early to mid-August, whereas concentrations at sites FCM1 and FCM3 varied minimally. The peak in nitrite-plus-nitrate concentrations at site FCM2 might have been the result of a nitrification process converting a small fraction of ammonia to nitrite.

DOC concentrations were slightly greater at site FCM2 than at sites FCM1 and FCM3 (fig. 7), although there was no significant difference among the sites (table 2). Among all sites, DOC ranged from 9,500 to 22,900 µg/L, with median values of 16,700 µg/L at site FCM1, 21,100 µg/L at site FCM2, and 18,266 µg/L at site FCM3. These median DOC concentrations measured in the flooded Caledonia Marsh are at the high end of the range of values in wetlands and eutrophic lakes, typically 10,000–15,000 µg/L (Thurman, 1985). These values also are higher than concentrations measured in Upper Klamath Lake, which ranged from 4,800 to 8,900 µg/L (Kuwabara and others, 2007). Over the course of the summer, a steady increase in DOC was measured at all three flooded sites and in the lake.

Decomposition of plants and woody debris creates tannic compounds that color the water in shades of brown. Field crews reported that the color of the water column at site FCM2 was darker than at the other sites, perhaps indicating more tannic compounds in the water column. The location of site FCM2, however, was very close to an internal levee where weedy vegetation exists during the growing season. The DOC concentrations at site FCM2 might have resulted from plant decomposition at the site or in the restored wetlands in the southeast corner of flooded Caledonia Marsh, which were hydraulically connected to the marsh near site FCM2.

Comparison of Instantaneous Water Quality Monitor Data

Dissolved oxygen concentrations and pH increased over the sampling period at all three sites, but both remained lower at site FCM2 than at the other two sites during the entire sampling period (fig. 8). These differences in dissolved oxygen concentration and pH among the three sites were similar to the differences in algal growth as indicated by chlorophyll a, in that dissolved oxygen concentrations, pH, and chlorophyll a were lower at site FCM2 than at sites FCM1 and FCM3 (figs. 6 and 8). Because the byproduct of photosynthesis is the production of dissolved oxygen and consumption of carbon dioxide, algal growth is often accompanied by an increase in dissolved oxygen and pH during the photosynthetic period. Dissolved oxygen concentrations and pH were lower at site FCM2 because algal growth (as measured by chlorophyll a concentrations) was lower at site FCM2 than sites FCM1 and FCM3.

Specific conductance ranged from 131 to 273 µS/ cm among all flooded Caledonia Marsh sites (fig. 8), and increased steadily throughout the sampling period at all three sites. As observed in the DOC concentrations, measured values were greater at site FCM2 than at sites FCM1 and FCM 3 (fig. 9). The similarity between the patterns of DOC and specific conductance among the three sites suggests that the same factors influenced the concentrations, whether different soils and land use at FCM2, or less mixing with water from Upper Klamath Lake. Specific conductance values measured in Upper Klamath Lake (100–140 µS/cm; Hoilman and others, 2008) were less than those measured in the flooded Caledonia Marsh and other wetlands around the lake. Concentrations in the Wood River Wetland, for example, were similar to those in flooded Caledonia Marsh (Kurt Carpenter, U.S. Geological Survey, oral commun., 2007). Specific conductance values in Wood River Wetland were correlated positively with chloride concentrations (Kurt Carpenter, U.S. Geological Survey, oral commun., 2007), but chloride was not measured in this study.

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