Freshwater Ecosystems

This section will define and describe freshwater ecosystems. Specifically, you will learn:

What is a Freshwater Ecosystem?
What bodies of water are included in a freshwater ecosystem? What are the components of a lake's watershed?

Freshwater lacks the "salty" nature of saltwater. Streams, rivers, ponds and lakes are the most common freshwater environments. Like oceans, bodies of freshwater are products of the surrounding land and the tributaries that feed into them. Lakes, the largest of the freshwater bodies, often incorporates the products of freshwater springs as well as streams and rivers. Sometimes many streams will flow into a larger stream or a river, and rivers can flow together into larger rivers.

Because lakes are often the ultimate destination of flowing freshwater habitats, let's look at what makes up the ecosystem of a lake:

  • Springs that originate from rocks or from the soil
  • Streams and rivers, as well as their banks
  • The bank of the lake, or the beach around the lake
  • The lake basin
  • Freshwater fish and plants


The Lake Watershed

The watershed incorporates all of the land and water areas that ultimately drain into a river, stream or lake. The watershed areas can have their own subwatersheds; for example, the Haw River, which flows into Jordan Lake, has its own watershed. Watersheds that drain directly into rivers are often called river basins (NC DENR). The section on watersheds will give you more information on what watersheds are, how they influence the main body of water and how human actions can affect them.

Lake Chemistry
Lakes are the largest final destination of freshwater ecosystems. The water chemistry of a lake is important to maintain life and drinking safety. This section will tell you what the chemical balance of a lake must be and what endangers that balance.

Lakes contain a balance of positive and negative ions. Each lake has three major negative ions that balance four major positive ions when their amounts are summed together:

  • Negative ions (anions) Positive ions (cations)
  • Bicarbonate (HCO3-) Calcium (Ca+2)
  • Sulfate (SO4-2) Magnesium (Mg+2)
  • Chlorine (Cl-) Sodium (Na+)
  • Potassium (K+)


Other compounds make up less than 1% of the ion balance for freshwater lakes:

  • phosphate
  • nitrate (NO3-)
  • ammonium


All of these ions and compounds must balance each other out for the lake to be considered "healthy."

Problems occur when one or more nutrients exceeds their natural levels. Nutrient loading usually occurs when people disturb one of the elements in the watershed. Lakes are subject to two dangers that increase nutrient loading:

  • Soil erosion caused by disturbing the landscape (i.e., filling in a stream or river)
  • Nonpoint source pollution


Of all of these compounds, phosphates are the most critical ones to keep in balance because the element phosphorus controls the amount of algae in the water, and as a result, the amount of oxygen available for fish to survive.

Why We Need Freshwater Ecosystems
What do lakes and rivers provide us with on an everyday basis?

Besides providing a source of recreation, including swimming, boating and fishing, some rivers and lakes also feed into a city's water system for drinking water. Of course, water from lakes goes through an extensive purification process before it flows through anyone's faucet, but a seriously imbalanced lake can have toxins that will pass through a water purifier. In addition, some of the local fish in the western and central parts of North Carolina (such as trout and catfish) come from freshwater environments.