Brine rejection that drains from the newly formed ice is replaced by a weak flow of relatively fresh water, from the liquid region below it. The new water partially freezes within the pores of the ice, increasing the solidity of the ice. As sea ice ages and thickens, the initial salinity of the ice decreases due to the rejection of brine over time [Fig. 2]. While the sea ice ages, desalinization occurs to such a degree that some multiyear ice has a salinity of less than 1 PSU. This occurs in three different ways: Brine rejection occurs in the sea ice packs
Fresh water without some treatment. Fresh water can easily become polluted by human activities or due to naturally occurring processes, such as erosion. Water is critical to the survival of all living organisms. Some organisms can thrive on salt water, but the great majority of higher plants and most mammals need fresh water to live. Fresh water can be defined as water with less than 500 parts per million (ppm) of dissolved salts. Other sources give higher upper salinity limits for fresh water, e.g. 1000 ppm or 3000 ppm. Fresh water habitats are classified as either lentic systems, which are the still-waters