Hydrological conditions in Clear Lake, Texas, 1958-66.

Temperature and salinity data were collected in 1958-66, and dissolved oxygen, dissoved organic nitrogen, and total phosphorus analyses were made on samples collected in 1964-66 in Clear Lake, a small estuary that flows into upper Galveston Bay. Seasonal trends in bottom water temperature were similar in the different years and were related closely to trends in air temperature. Average water temperatures were lowest (about 13 C) in January and February and highest (about 31 C) in July. The rate of warming and cooling was directly related to the magnitude of the annual temperature difference between the warm and cool months. Salinity ranged from 0.1 to 23.7 ppt and was related inversely to stream flow and precipitation. Variations in rainfall resulted in fluctuations in stream flow and these, in turn, were reflected by variations in salinity. Dissolved organic nitrogen ranged from 23.5 to 171.5 ug.at./l. (microgram atoms per liter) and averaged 66.4 up.at./l. Total phosphorus ranged from 1.7 to 26.3 up.at./l. and averaged 8.2 ug.at./l. Phosphorus values increased markedly in July 1966. No correlation existed between nitrogen or phosphorus and stream flow or rainfall. Dissolved oxygen ranged from 3.8 to 19.3 ppm.