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

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Water Sample and Instantaneous Water Quality Monitor Data Results

Water sample collection started on June 21 at site FCM1 and on June 28 at sites FCM2 and FCM3, and continued on a weekly basis until the final sample collection on September 11, 2006. Samples were collected on 11 dates at site FCM1 and 10 dates at sites FCM2 and FCM3. Concentrations of chlorophyll a and total nutrients trended upward through the summer from the lowest value on the first sampling date in June to the highest value on variable dates in August at each site (fig. 6). With the exception of total phosphorus, the concentrations of total nutrients and chlorophyll a were consistently lower at site FCM2 than at sites FCM1 and FCM3. Chlorophyll a ranged from a low of 3 µg/L at site FCM2 on June 28 to a high of 189 µg/L at site FCM3 on August 23 (table 1); total particulate nitrogen ranged from a low of 90 µg/L at site FCM1 on June 21 to a high of 2,890 µg/L at site FCM3 on August 9; total nitrogen ranged from a low of 1,000 µg/L at site FCM1 on June 21 to a high of 4,940 at site FCM3 on September 11; total particulate carbon ranged from a low of 500 µg/L at site FCM1 on June 21 to a high of 15,487 µg/L at site FCM3 on September 11; total phosphorus ranged from a low of 89 µg/L at site FCM1 on June 21 to a high of 530 µg/L at sites FCM2 and FCM3 on August 23 and August 9, respectively.

Dissolved nutrient concentrations were more variable in the timing and location of maximum and minimum values than chlorophyll a and total nutrient concentrations. Orthophosphate concentrations increased slightly over the course of the summer until early August and then decreased (fig. 7); during most of the summer the concentrations at site FCM2 were greater than at sites FCM1 and FCM3. Ammonia and nitrite-plus-nitrate concentrations were greater at site FCM2 than at sites FCM1 and FCM3 until early August for ammonia and late August for nitrite-plus-nitrate. DOC concentrations increased steadily at all sites from June 28 through September 11—when sample collection ended—and concentrations at site FCM2 were greater than sites FCM1 and FCM3 (table 1). Orthophosphate ranged from a low of 59 µg/L at site FCM1 on June 21 to a high of 354 µg/L at site FCM2 on August 9; ammonia ranged from a low of 6 µg/L at site FCM1 on July 12 to a high of 369 µg/L at site FCM2 on June 28; nitrite-plus-nitrate ranged from a low of 8 µg/L at sites FCM1 and FCM3 on August 16 to a high of 126 µg/L at site FCM2 on August 9; DOC ranged from a low of 9,500 µg/L at site FCM1 on June 21 to a high of 22,900 µg/L at site FCM2 on September 6.

For most sampling dates, dissolved oxygen concentrations and pH were lower and specific conductance concentrations were greater at site FCM2 than at sites FCM1 or FCM3 (fig. 8, table 1), and the overall trend in these three variables was increasing through the summer at all three sites. Dissolved oxygen conentrations ranged from a low of 2.90 mg/L at site FCM2 on June 28 and July 12 to a high of 13.21 mg/L at site FCM3 on September 6; pH ranged from a low of 7.07 at site FCM2 on July 17 to a high of 9.34 at site FCM1 on September 11; specific conductance values ranged from a low of 131 µS/cm at site FCM1 on June 21 to a high of 273 µS/cm at site FCM2 on September 6.

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