Freshwater ecosystems
Kinds
Characteristics
Threats
Aquatic ecosystems
Key distinction: salinity = salt content of the water
Measured in parts per thousand (ppt) 1 gm of salt in 1000 gms water = 1 ppt FRESH usually < 0.5 ppt OCEANS average 35 ppt 0.5 to 17 ppt is called BRACKISH
Kinds of freshwater habitats
Rivers, streams– Flowing freshwater– Source: where it starts– Mouth: where it ends
Lakes, ponds
Wetlands
All freshwater ecosystems
Just a fraction of the Earth’s water– .01% = one one-hundredth of one percent
Occupy less than 1 percent of the Earth’s surface
Rivers and streamsMore than 3.5 million miles of rivers and streams
(including intermittent streams)
– Just the U.S.! More than 140 times around the Earth.
www.noaa.gov/str-plan/images/river.gif
Rivers from start to finish
Source = Headwaters Can be:
– Snowmelt– Spring– Even a lake
Water is colder, clearer, more highly oxygenated
Organisms include trout, mayflies
Mouth: where the river ends
Usually the ocean or another river, or lake
River widens and slows, getting warmer, siltier.
Middle is most diverse, lots of plants
Near mouth, increased sediment limits light and plants, water is warmest
What are some of the differences?
Trout stream, NW NJ Mississippi R. Greenville, MS
Mouth
Mississippi River
delta
Lakes and ponds
What’s the difference?– Ponds typically smaller– May be seasonal—that is, dry up part of the year– Lakes exist hundreds or thousands of years
But, even lakes can fill in or dry up
Parts of a lake
Parts of a lake
Littoral zone: near shore– Nutrient rich, lots of plant and animal life– Warm
Limnetic zone: near surface, open water– Lots of light– Lots of plankton
Profundal zone: deeper, little light Benthic zone: the bottom, little light, low oxygen
Eutrophication
If nutrients increase too much in a lake, pond, or ocean, excessive plant growth results
Phosphorus Nitrogen NOT GOOD: why?
– As plants decay, decomposing bacteria use oxygen dissolved in the lake to do their jobs.
– Dissolved oxygen goes down
Wetlands
CA OR AK
Wetlands: what are they?
For regulatory purposes under the Clean Water Act, the term wetlands means "those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas."
Wetlands
May be fresh or brackish Freshwater types include:
– Marsh– Swamp– Bog– Fen
Marsh
Most common freshwater wetland in U.S.
Occur along streams or in depressions
Characterized by organic, wet soils and non-woody (i.e., no trees) vegetation.
Swamp
Wetland dominated by woody plants
Common in SE U.S.
New Jersey wetlands
About 916,000 acres, or 19% of New Jersey, is wetlands, which seems like a lot; but the bad news is that about 40% of the original 1,500,000 acres has been lost to dredging and filling, dams, farming, development and highways.
1. NJ wetlands
What good are wetlands?
Reduce flooding by acting like sponges
What good are wetlands?
Help clean water by acting like a filter– The plants and slow water flow in a wetland help
remove pollutants, leaving water cleaner downstream in a lake or river.
– Too much pollution can leave a wetland toxic to visiting animals, such as many birds.
What good are wetlands?
Protect shorelines from erosion
Erosion in this case came from grazing animals
Top Related