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Threats to Estuaries: Human Impact & Problems

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Estuaries are where rivers meet the sea. They are biologically important but are at risk from human influences and activities. In this lesson learn about how humans impact estuaries and some of the problems it causes.

What Are Estuaries?

Between where the land stops and the vast ocean waters begin is an important transitional area. This zone filters pollutants and sediments from land, provides a buffer from floods and storms like hurricanes and creates a home for fish, birds, turtles, and other types of wildlife.

Estuaries provide important habitat for birds, turtles, fish, and other types of wildlife.
Heron in an estuary

We call these places where rivers meet the sea estuaries. Estuaries can range widely in salinity, having freshwater at one end and salt water at the other. When people think of estuaries they typically think of places like salt marshes and mangrove forests. Even though estuaries come in all shapes and sizes, one thing they share is that they are all essential to our coastlines.

Estuaries and Development

One function that estuaries serve is as buffer zones. They stabilize shorelines and protect inland areas from storm surges, flooding, and erosion. Without estuaries, our shorelines would have no protection and would wash away with tides and waves. Estuaries also reduce the impact of floods and storms by acting like sponges that soak up excess water and keep it from reaching land.

Unfortunately, because people love living by the water, estuaries are at risk from human activities. As people develop the land in and around estuaries they remove estuarine land, change the natural water flow, increase the amount of nutrients and sediment reaching the estuary, increase erosion, and affect the number and distribution of plant and animal species.

People are drawn to the water. However, development along coastlines can cause numerous problems for estuaries.
Houses along a coastline

Estuaries are like any other system - they need the right balance of things in order to function properly. It might help to think about your own body. You need to take in the right amount of water, vitamins, minerals, proteins, fats, and carbohydrates. The balance of these things in your body is very important. Estuaries and the plants and animals that live in them need the right amount of water at the right time, the right balance of nutrients such as phosphorous and nitrogen, and the right amount of land to provide habitat for wildlife.

As we build houses, roads, channels, and marinas and dredge, drain, and dam coastal areas, we affect how water and nutrients reach and flow through estuaries. We also build directly on top of estuaries, as well as drain and clear them for agriculture. All of these activities significantly degrade and disrupt estuary habitats.

Estuaries and Pollution

When you think of pollution in marine environments you may think of toxic chemical waste or oil spills, but pollution can also be as simple as an overabundance of nutrients.

These types of pollution occur from land-use practices such as clearing land, human development, and agriculture. If you fertilize your lawn, you are adding nutrients to it to help the grass grow. However, not all of it gets absorbed by the grass and the excess nutrients can end up in estuaries. This excessive nutrient load causes eutrophication, or excessive plant and algae growth. Eutrophication can lead to algal blooms such as red tides, low or depleted oxygen conditions, and toxins in the water. These, in turn, affect fish, plant, and even human health.

Agricultural land use also leads to problems in estuaries. Pesticides, herbicides, and excess nutrients get picked up by rain water and carried to estuaries. Clearing land for agricultural use increases land erosion and sediment load into estuaries. The process of sediment build up in estuaries is called infilling, and it makes estuaries shallower and changes the hydrology. While estuaries naturally filter out pollutants and sediments, the overload from human land use puts too much stress on the estuary and it can no longer perform this function properly.

Estuaries and Climate Change

Clearly, our local activities can have global impacts, especially when it comes to sensitive areas like estuaries. Human-driven climate change is putting an enormous amount of stress on coastal and estuarine environments from all directions.

In addition to the impacts from human land use, warmer global temperatures directly affect estuaries. When Earth's temperatures are more extreme, the naturally occurring plants and animals within estuaries may not be able to survive.

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