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

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Comparison of Water Quality in the Flooded Caledonia Marsh and Upper Klamath Lake

During the months when water samples were collected at sites FCM1, FCM2, and FCM3 in flooded Caledonia Marsh, water samples also were collected from Howard Bay (HDB) and from five sites around Upper Klamath Lake (sites MDN, WMR, RPT, MDT, and EPT; fig. 1). Hereafter, the five sites around Upper Klamath Lake are referred to as “lakewide” sites. A median concentration for the lakewide sites was determined for each of the following constituents—chlorophyll a, total phosphorus, and total nitrogen (fig. 10). Howard Bay is adjacent to flooded Caledonia Marsh and was the source of the water that flooded Caledonia Marsh when the levee breached. Chlorophyll a concentrations were much higher at site HDB, but were similar among sites FCM1 and FCM3 and the median lakewide concentrations. In contrast, total phosphorus concentrations at site HDB were more similar to those at the flooded Caledonia Marsh sites, and the median lakewide concentrations were lower by comparison. Total nitrogen concentrations were higher at site HDB and more variable at all locations, except for the distribution observed in the median lakewide sites concentrations, which was more consistent.

The difference in total phosphorus concentrations between the flooded Caledonia Marsh sites and the median lakewide sites was indicative of the release of orthophosphate from peat soils in the marsh. Between June 5 and July 3, the median orthophosphate concentration at site HDB was 11 µg/L, as compared to the median orthophosphate concentration between June 21 and June 28 at sites FCM1, FCM2, and FCM3, which was 79 µg/L. The flux of orthophosphate from drained wetland soils that are subsequently flooded is expected to be greater than the flux from wetlands that were never drained. This difference is because the total phosphorus pool is greater, largely due to the greater bulk density of the drained soils, which results from compaction caused by the long-term drainage (Graham and others, 2005), and because more of the phosphorus is in labile form after long-term degradation of peat soils (Snyder and Morace, 1997). Although sampling did not start at all sites until June 28 (16 days after the levee breach) and orthophosphate flux may have been greater before sampling inception—especially within the first 48 hours (Aldous and others, 2007)—the daily orthophosphate flux from FCM sites was comparable with that in other studies. From June 28 to July 26, orthophosphate fluxes calculated from water samples collected at sites FCM1, FCM2, and FCM3 were 11.13, 7.51, and 10.71 (mg/m²)/d, respectively. These estimates of orthophosphate flux were calculated by dividing the difference in orthophosphate concentrations from June 28 to July 26 by the number of days and multiplying by the average depth at each site. Because some of the orthophosphate is taken up by algae for growth, the actual flux is greater and these values should be considered a lower bound. These values are at the lower end of the range in orthophosphate flux measured from cores collected from previously drained wetlands around Upper Klamath Lake and analyzed in a laboratory (between 8.56 and 55.52 (mg/m²)/d; Aldous and others, 2005).

As lake water levels lowered by approximately 1 m over the summer, water from the flooded Caledonia Marsh drained into Howard Bay, possibly transporting higher orthophosphate concentrations into the lake. Total phosphorus concentrations at site HDB and the lakewide sites were significantly higher in 2006 than in 2005, but a corresponding increase in chlorophyll a between the 2 years was not observed (fig. 11, table 3).

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