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Anthropogenic Disturbances
Anthropogenic disturbances to estuaries include coastal development, introduction of invasive species, pollution via runoff, over fishing, dredging and filling, dams and global climate change.
Anthropogenic means relating to or resulting from the influence of humans on the natural world. Because we are all connected to the nation’s coasts, our activities can create disturbances to estuaries. The following are human induced, or anthropogenic, disturbances to estuaries.
- Coastal development – Concrete structures like bulkheads “harden the shoreline”. This means that land near the coast that once made up wetlands and estuaries is changed to hard surface and can no longer absorb storm surge and provide shelter or food for the animals and plants that exist in coastal regions.
- Invasive species – Purple loosestrife, nutria, snakehead fish, green crabs, and zebra mussels are just a few invasive species wreaking havoc on estuaries. Many invasive species were introduced by humans though ballast water exchange or through dumping of aquaria containing non-native fish. Many exotic species compete for food and shelter, prey on native species or push native species out of their natural habitat.
- Polluted runoff – When water runs downstream from cities, farms and factories, this runoff can carry many things harmful to estuaries such as excess nutrients, raw sewage and manure and chemical waste.
- In an estuary, excess nutrients can cause eutrophication. Eutrophication can lead to large algae blooms. When the algae die off and decompose they use up all the dissolved oxygen, creating anoxic conditions that can kill fish. Excess nutrients can come from many sources, including runoff from crop land that carries excess fertilizer, or runoff from farms that carries animal waste.
- Raw sewage can carry disease-causing organisms that, when in estuaries, can kill fish and other organisms and can be harmful to humans who use the estuary.
- In an estuary, chemical waste can also kill or harm plants and animals. Chemical waste can come from many sources including motor oil discarded in storm drains, pesticides from crops and factory spills or waste.
- Over fishing – Over fishing reduces the number of commercially valuable estuarine organisms, not only impacting the diversity of the ecosystem, but also impacting local economies. Also, some types of fishing can have a negative effect on estuary bottoms and the organisms living in them (the benthic communities), on juvenile fish and on by-catch, altering the estuarine food web.
- Dredging and filling – Filling and draining of wetlands, and dredging deep navigation channels through estuaries and wetlands ultimately destroys and damages habitat. They also change water and sediment flow.
- Dams - Changing river water flow can restrict sediment deposits and nutrient availability downstream, fish migration, and can increase saltwater intrusion into underground water tables.
- Global climate change – Scientists are confident that the Earth’s climate has entered a period of more rapid change than experienced over the past 1,000 years. Climate change can result in changes in the amount and timing of freshwater inputs to estuarine ecosystems, changes in temperature of the air and water, increases in sea level, more frequent and intense tropical storms, and changes in coastal currents. All of these changes can cause stress to estuarine organisms, can change where estuarine species are found, can alter estuarine processes and the physical and chemical patterns and make-up of estuaries.
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Last Updated on: 06-23-2008
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