1. Freshwater Ecosystems

2. Standing Water Life Zones
1. Also called lentic (Latin : lentus which means sluggish)
2. Form when precipitation, runoff, streams, rivers, & groundwater seepage fill depressions in Earth’s surface
3. Vary in size, depth, & nutrient content

3. Zones of a Lake

4. Littoral Zone 1. Top zone near the shore
2. Consists of shallow, sunlit waters to depth at which rooted plants stop growing
3. High biodiversity because of ample sunlight & nutrient input from surrounding land
4. Organisms consists of: rooted plants, turtles, frogs, crayfish, bass, perch, and carp

5. Limnetic Zone 1. Open, sunlit surface layer away from the shore
2. Extends to depth penetrated by sunlight
3. Main photosynthetic zone; produces food and O2 that support the consumers
4. Most abundant organisms are phytoplankton & zooplankton
5. Large species of fish live here

6. Profundal Zone
1. Layer of deep, open water where it is too dark for photosynthesis
2. Cell Respiration occurs in all layers; this is a layer of oxygen consumption; O2 levels low
3. Fish are adapted to cooler, darker water

7. Benthic Zone 1. Bottom layer
2. Decomposers, detritus feeders & some benthos fish live here
3. Nutrients come from dead organic matter from littoral & limnetic zones & sediments washed into lake

8. Oligotrophic Lakes
1. "Oligo" means very little; have very little nutrients (N & P)
2. Deep and has steep banks
3. Glaciers & mountain streams supply water
4. Not much sediment brought into lake
5. Clear water; not much algae
6. Rocky or sandy bottom
7. Fish include small mouth bass and trout
8. Little photosynthesis so low primary productivity

9. Eutrophic Lake 1. Truly nutrient rich (N & P)
2. Shallow and have murky water and mucky, soft bottoms.
3. Also have a lot of plants and algae
4. Nutrients support high densities of algae, fish and other aquatic organisms
5. With all of the biomass, there is a lot of decomposition occurring at the bottom which uses up O2
6. decomposition uses up O2 causing the bottom of the lake to become anoxic (depleted of O2 ) causing fish kills

10. Mesotrophic Lake
1. Meso means middle; medium amount of nutrients (N & P)
2. Algae carry out photosynthesis; supply O2 for fish
3. Fish include sport fish such as walleye, perch, and smallmouth bass

11. Lake Turnover Water is densest at 4° C
Winter: coldest H2O lies just below surface ice; water progressively warmer at deeper levels, resulting in thermal stratification
Spring:
Ice melts, & surface water warms to 4°C & sinks, eliminating temperature differences. Winds mix water, brings O2 to bottom & nutrients to top.
Summer:
Lake regains thermal stratification, with warm surface H2O separated from cold bottom water by narrow zone of rapid temp change (thermocline)
Autumn:
Surface water cools & sinks below underlying layers, remixes the water until the surface begins to freeze & winter temperature profile is re-established

12. Ecosystem Services of Standing Water Ecosystems
1. Climate moderation
2. Nutrient cycling
3. Waste treatment
4. Flood control
5. Groundwater recharge
6. Habitats for many species
7. Genetic resources & biodiversity
8. Scientific information

13. Zones of a Stream

14. Source Zone 1. Headwaters or highland streams
2. Shallow, cold, clear, & swiftly flowing
3. Water tumbles downward over rocks, waterfalls, rapids & picks up O2 from air
4. Not much photosynthesis; low primary productivity
5. Nutrients come from organic matter (leaves, branches, & bodies of living and dead insects)
6. Fish: cold water such as trout that need a lot of dissolved O2

15. Transition Zone
1. Streams merge and form wider, deeper, and warmer streams
2. Flow down gentler slopes with fewer obstacles
3. Can be more turbid from sediment, slower flowing, and have less DO than headwaters

16. Floodplain Zone
1. Streams join into wider and deeper rivers that flow across broad, flat valleys.
2. Water is warmer and has less DO than source and transitional zones
3. Water tends to be very turbid with suspended sediment
4. San Jacinto River in the Humble / Atascocita area is in the floodplain zone

17. Some of the Ecosystem Services Provided by Freshwater Ecosystems

18. Riparian Zone
1. Areas that surround water bodies in the watershed, composed of moist to saturated soils, water-loving plant species & their associated ecosystems.
2. Transition areas that connect the water with the land
3. Complex interactions among the water, soil, microorganisms, plants and animals
4. Corridors for wildlife to travel between ecosystems

19. Ecosystem Services of Riparian Zones
1. Healthy riparian zones filter and purify water for drinking, irrigation and recreation
2. Vegetation and soils in riparian zones soak up and store water during high rainfall events
3. Stream corridor vegetation gives stability to stream banks and prevent erosion
4. Help to regulate greenhouse gases by producing large volumes of trees that remove CO2 from atmosphere
5. Complex interrelationships between microorganisms, plants and nutrients in riparian areas help to break down contaminants that we discharge into the environment