Coastal Processes, Hazards, and Society

Earth Complexity in Action: Estuaries


Earth Complexity in Action: Estuaries

The complexity of natural systems and the complexity of the interaction between the various spheres of the Earth is extremely evident when considering coasts and coastal systems.

Consider the potential for the complexity of salinity and circulation within an estuarine system, a partially enclosed coastal body of brackish water that has freshwater input by rivers and saltwater input by marine processes. The circulation of an estuary can vary substantially across a range of time scales such as daily, seasonally, or annually. Changes in freshwater input during periods of heavy rain, fluctuations in tides, or changes in the direction that the wind is blowing can all contribute toward how water moves around within the estuarine system. During periods of heavy rainfall, freshwater input may result in a much-lowered salinity in the estuary, whereas during periods of drought and strong onshore winds, salty water can be pushed into the estuary by waves and the salinity of the estuary increases. Complexity in an estuarine system exists because of the numerous interacting physical processes of the hydrosphere and atmosphere that act on the system.

Now, consider how this complexity may affect the anthrosphere or the part of the environment that is made or altered by humans for human activities or habitat. Suppose you were making a viable living, fishing oysters for commercial resale. Most oysters are relatively environmentally restricted, and too much freshwater can kill them, as can too much saltwater. Perhaps, one year, you are able to very successfully oyster fish an area of the estuary because the freshwater and saltwater input has been perfectly balanced to create optimal conditions for oysters very close to your home. The following year, there is so much freshwater runoff into the estuary that all of the oysters near to your home die or do not grow to the adequate size. As a result, you would have to travel to new locations in the estuary to find the optimal oyster growing conditions, something that might mean longer boat travel time for you and more fuel to get onsite, thereby reducing your net profit. So, the complexity of natural processes interacting with each other generates complexity for how society deals with these changes.