Final answer:
Saltwater intrusion occurs when saltwater enters areas typically occupied by fresh water, often due to groundwater over-extraction and sea level rise from climate change. It impacts ecosystems by altering salinity in estuaries, reducing biodiversity, and affecting aquatic life cycles.
Step-by-step explanation:
Saltwater intrusion refers to the process by which saltwater enters into areas that are typically fresh water, such as groundwater aquifers, rivers, or soil. This phenomenon is primarily caused by over-extraction of groundwater, which reduces the pressure in freshwater aquifers and allows seawater to move inland.
Other contributing factors include sea level rise, which can be a result of global climate change, and reduced inflow of freshwater into estuaries due to droughts or large-scale water diversion projects.
The effects of saltwater intrusion can be detrimental to local ecosystems. It can lead to the degradation of salt marshes and estuaries, which are critical habitats for the young offspring of many aquatic species like crustaceans, mollusks, and fish.
Estuaries often experience brackish water conditions that are vital for the life cycles of certain species. Furthermore, the alteration of salinity can lead to reduced biodiversity and affect the reproductive cycles of organisms dependent on estuarine environments.