Aquifers are permeable, underground rocks that hold water within their structure. This water flow underground to springs and rivers. Chalk is an example of a permeable rock that holds water. Permeable means that water can flow through the material. This water can be extracted for drinking water supply at pumping stations using wells.
Chalk streams or chalk rivers are a type of lowland river that occur on chalk geology, where > 75% of the flow of the water comes from the chalk aquifer (i.e. is groundwater). Chalk streams are characterised by clear water, rich in calcium and magnesium carbonate with a high biological diversity including aquatic plants, invertebrates and fish.
Organic matter is the term given to the great variety of different carbon-based compounds derived from plants, animals and microbes in the environment. Large organic matter includes leaves, twigs, animal remains which are visible to the naked eye, but organic matter also includes carbon-based compounds which have decomposed, and and are so small that they are no longer visible.