Chlorine.....

WHAT IS IT?

     The element chlorine, 17th in the periodic table, is very reactive. In water, it pulls electrons from other elements to become the anion chloride (Cl-).

WHY IS IT IMPORTANT?

     1. In living cells, chloride ions regulate osmotic pressure and maintain the integrity of cell membranes. Chloride ions essentially prevent cells from swelling and bursting or shriveling up.

     2. Elevated levels of chloride in water can make it difficult for aquatic insects and fish to regulate the water and ion balance in their cells. If the chloride concentration is very high in the water, organisms have a hard time preventing their cells from shriveling; if chloride is very low, cells would tend to swell.

WHAT INFLUENCES IT?

     1. Salt drainage from roads: Road crews sometimes use salt (NaCl) on roads to help melt snow and ice. Meltwater runs into local streams, carrying chloride from the salt.

     2. Evaporation of large areas of standing water: As water evaporates, it leaves behind natural salts and minerals which contain chlorine, and this increases the concentration. Mineral-laden streams flow into the Great Salt Lake in Utah, but none flow out. Since the only outlet for water is evaporation, salts levels continually increase in the lake.

     3. Water treatment plants and septic systems: Most cities have sewage treatment systems that use chloride to clean water after we use it. (Similarly, swimming pool managers use chlorine to keep pools bacteria-free.) When treated water is returned to a water system, it takes chloride with it.

     4. Geology and soil: As water flows over land, some of the chemicals, including chlorine, in the rocks and soils seep into the waterway. The longer a river flows over these rocks and soils, the more minerals the water accumulates. So, in general, chlorine increases as you go downstream.

WHAT HAPPENS AS WE TRAVEL DOWNSTREAM?

A kayaker splashes through the South Platte River as it flows through Waterton Canyon near South Platte, CO.