Sensitivity of Freshwater Habitats
Oil spills occurring in freshwater bodies are less publicized than spills into the ocean even though freshwater oil spills are more frequent and often more destructive to the environment. Freshwater bodies are highly sensitive to oil spills and are important to human health and the environment. They are often used for drinking water and frequently serve as nesting grounds and food sources for various freshwater organisms. All types of freshwater organisms are susceptible to the deadly effects of spilled oil, including mammals, aquatic birds, fish, insects, microorganisms, and vegetation. In addition, the effects of spilled oil on freshwater microorganisms, invertebrates, and algae tend to move up the food chain and affect other species.
Freshwater is divided into two types: standing water (lakes, marshes, and swamps) and flowing water (rivers and streams). The effects of an oil spill on freshwater habitats varies according to the rate of water flow and the habitat's specific characteristics.
Standing water such as marshes or swamps with little water movement are likely to incur more severe impacts than flowing water because spilled oil tends to "pool" in the water and can remain there for long periods of time. In calm water conditions, the affected habitat may take years to restore. The variety of life in and around lakes has different sensitivities to oil spills.
- The bottoms of standing water bodies, which are often muddy, serve as homes to many worms, insects, and shellfish. Lake bottoms also serve has a breeding ground and food source for these organisms and higher animals. Oil in sediments may be very harmful because sediment traps the oil and affects the organisms that live in or feed off the sediments.
- In the open water, oil can be toxic to the frogs, reptiles, fish, waterfowl, and other animals that make the water their home. "Oiling" of plants and grasses that are rooted or float in the water also can occur, harming both the plants and the animals that depend on them for food and shelter. Fisheries located in freshwater also are subject to the toxic effects of oil.
- On the surface of the water, water bugs that skim the water surface and floating plants such as water lilies are threatened by oil slicks that spread across the surface.
- In the shoreline habitats of lakes and other bodies of standing water, cattails and other weeds and grasses provide many important functions for life in and around the water. They serve as food sources, nesting grounds for many types of animals, and shelter for small animals. Oil spills can coat these areas, affecting the plants and the organisms that depend on them.
- Marsh environments are among the most sensitive freshwater habitat to oil spills due to the minimal water flow. Oil spills have a widespread impact on a host of interconnected species. For example, lush marsh vegetation is used as nurseries for shellfish and fish, as a food source for many organisms, and a home for fish, birds, and mammals.
Oil spills impact flowing water less severely than standing water because the currents provide a natural cleaning mechanism. Although the effects of oil spills on river habitats may be less severe or last for a shorter amount of time than standing waters, the sensitivity of river and stream habitats is similar to that of standing water, with a few special features:
- Oil spilled into most rivers often collects along the banks, where the oil clings to plants and grasses. The animals that ingest these contaminated plants may also be affected.
- Rocks found in and around flowing water serve as homes for mosses, which are an important basic element in a freshwater habitat's food chain. Spilled oil can cover these rocks, killing the mosses and disrupting the local ecology.