Useful Physical Parameters of Water Qualities - Page 2

Consequently, their metabolism increases as the water warms and decreases as it cools. Each species of aquatic organism has its own optimum (best) water temperature. If the water temperature shifts too far from the optimum, the organism suffers. Cold-blooded animals can't survive temperatures below 0 C (32 F), and only rough fish like carp can tolerate temperatures much warmer than about 36 oC (97 F). Fish can regulate their environment somewhat by swimming in the water where temperatures are close to their requirements. Fish usually are attracted to warm water during the fall, winter, and spring and to cool water in the summer.

Did you ever notice how fish swim down to the cooler parts of the lake to escape the heat of the noonday sun? Fish can sense very slight temperature differences. When temperatures exceed what they prefer by 1-3 C, they move elsewhere! Fish migration often is linked to water temperature.

In early spring, rising water temperatures may cue fish to migrate to a new location or to begin their spawning runs. The autumn drop in temperature spurs baby marine fish and shrimp to move from their nursery grounds in the estuaries out into the ocean, or into rivers, as the case may be.

As you can see, all sorts of physiological changes take place in aquatic organisms when water temperatures change. The American Public Health Association (APHA) defines turbidity as "the optical property of a water sample that causes light to be scattered and absorbed rather than transmitted in straight lines through the sample." In simple terms, turbidity answers the question, "How cloudy is the water?" Light's ability to pass through water depends on how much-suspended material is present.

Turbidity may be caused when light is blocked by large amounts of silt, microorganisms, plant fibers, sawdust, wood ashes, chemicals, and coal dust. Any substance that makes the water cloudy will cause turbidity. The most frequent causes of turbidity in lakes and rivers are plankton and soil erosion from logging, mining, and dredging operations.