This is the main component of limestone. Calcium
is an essential ingredient of the macro invertebrate exoskeleton. This
compound dissolves in weak acid, dissociating into Ca++
. In doing so, it makes calcium available to the life
forms of the stream, and at the same time changes the overall pH of
the environment to slightly basic in pH (typically 7.2-7.8). These are
the two reasons why limestone streams are so productive.