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