1. Freshwater Ecology
Freshwater ecosystems are divided into two categories
Lentic systems which include lakes, ponds, marshes, swamps and bogs
Lotic systems which include rivers and streams

2. Oxbow Lakes
These lakes are formed by meanders in rivers that flow over flood plains and low valleys.
These snake-like loops are cut off from the rest of the river and form a long, narrow, crescent or U shaped lake.

3. Aquatic Ecosystems - Lentic
Pond
Lake
Bog
Swamp
Marsh

4. Aquatic Definitions
Bogs are peat lands, they develop in poorly drained areas. They are characterized by evergreen trees, shrubs and often blanketed with a carpet of sphagnum moss.
A lakes is a body of water where depth of light penetration can vary from several inches to many feet in open water
A pond is defined as a body of water where light penetrates to the bottom.
Marshes are characterized by soft-stemmed herbaceous plants such as cattails and pickerelweed.
Swamps are dominated by woody plants such as Red Maple, gums, ashes, cedars, firs and spruces.

5. Texas Lakes
Oxbow lakes are commonly formed in the mature segments of Texas rivers.
In the lower Rio Grande Valley, these oxbows are called “Resaca's”.

6. Texas Reservoirs
Most of the major lakes in Texas are man-made lakes called “reservoirs”.
Other small lakes are remnants of quarry and mining operations, or agricultural stock ponds.
The closest thing to a “natural lake” in Texas is Caddo Lake.

7. Playa Lakes
These lakes are usually small depressions in the lower parts of a desert basin sometimes filled with water.
They are most often found in the western part of the state.

8. Succession Lakes and ponds go through a natural ageing process.
Marshes, swamps and bogs are generally the mature stages.

9. Succession Over time sediments begin to fill in ponds and lakes
As depth decreases the number of plants increase.
Emergent plants move out from the shoreline areas.
Eventually water tolerant shrubs, grasses, and other plants move into the area.
If left undisturbed, grasses and shrubs will be replaced by larger trees and forests.

10. Lentic Environments
The lentic environment has well defined boundaries;
the shoreline
The sides of the basin
The surface water and bottom sediments
It is divided into three major zones:
Littoral zone
Limnetic zone
Profundal zone

11. Lentic Zones
Profundal Zone

12. Littoral Zone – shallow vegetate areas

13. Littoral Zone
Characterized as shallow shoreline area inhabited by plants
Light penetrates to the bottom allowing for rooted plant growth
Coarse sediment such as rocks, cobbles, pebbles, gravel or sand
Inhabited by invertebrates and small fish
Aquatic plants

14. Types of Aquatic Plants
Emergent – rooted plants with lower portion submerged and growing near the shore
Example: cattails, bulrush, sedges
Floating – rooted plants (some free floating) with leaves floating on the surface
Example: water lilies, water hyacinth, duckweed
Submerged – rooted plants with nearly all leaves below the surface
Example: Chara, Naja, coontail, and Hydrilla

15. Emergent Plants Arrowhead Cattail Bulrush Spike Rush Pickerel Weed
Cattails
Arrowhead
Arrowhead
Cattail
Bulrush
Spike Rush
Pickerel Weed

16. Floating Plants Water Lily Salvinia Lotus Water Hyacinth Duckweed
Water Lettuce

17. Submerged Plants
Coontail
Hydrilla
Chara
Elodea
Naja
Watermilfoil

18. Limnetic Zone – open water area

19. Limnetic Zone Open water of a pond or lake
Characterized by the lack of rooted plants and limited light penetration
Area normally inhabited by plankton and fish
Photic zone – area of light penetration limited by color and amount of suspended solids and plankton in the water
Pond – light penetrates to the bottom
Lake – light penetration can vary from several inches to many feet in open water

20. Productivity
Productivity is related to the amount of plants, animals, and nutrients (PAN) in the water
Plant nutrients (nitrogen and phosphorus) in a lake are important in limiting growth of planktonic algae or other aquatic vegetation
There are three major categories of lakes based on productivity.
Oligotrophic
Mesotrophic
Eutrophic

21. Oligotrophic A body of water low in mineral nutrients
Supports little life
Low plant and plankton populations
Little organic material in the sediments
Low chlorophyll a levels

22. Mesotrophic Bodies of water with moderate amount of nutrients
A transition from oligotrophic to eutrophic

23. Eutrophic
Lakes, ponds, (streams and rivers) that are highly productive
Large populations of plants and animals
High levels of plant nutrients
Water color – green and turbid
High chlorophyll a levels

24. Ponds are shallower and smaller than lakes and have relativity uniform temperatures
Lakes are generally deeper and have a layering of temperature during the summer

25. Thermocline Found in the metalimnion zone
Area in which there is a rapid decrease in temperature – approximately 1 oC per each meter of depth
Also described as the “interface between warm and cold water”
Warm water is much lighter than cold water and cold water tends to sink to the bottom of the lake

26. Stratification
During summer months increased sunlight and warm winds heat the surface water trapping colder water on the bottom.
Differences in the densities of warm and cold water resist mixing by wind
Stratification creates three different zones:
Epilimnion
Metalimnion
Hypolimnion

27. Epilimnion The warmest water
Characterized by freely circulating surface water with variable temperatures.
Area where the majority of the organism’s is found
Area of greatest productivity and light penetration
Oxygen concentration is usually greatest in this zone.

28. Metalimnion Middle layer or transition zone
Temperature layer where the “thermocline” is found

29. Hypolimhion A deep cold layer with little temperature change
Low oxygen content due to little or no photosynthetic production by plants
Water does not come in contact with air
Oxygen quantity decrease with depth
Oxygen is depleted by bottom dwelling organism and bacteria feeding on organic matter
Little or no light penetration

30. Lake Overturns
In the fall months, the cooler air temperature also cool the surface waters of a lake
The densities of the upper and lower waters become similar and the wind mixes the layers of water together.
The temperature of the lake becomes uniform, this is known as “fall overturn”
Oxygen levels are replenished in deep water
In Texas, there is generally one turnover per year
One fall overturn – monomictic
Two fall overturn - dimictic

35. Profundal Zone – Bottom zone found in deep water bodies
Characterized by the lack of light penetration
Lack of rooted aquatic plants and the absence of photosynthesis
Sediments are generally silt/clay mixed with organic matter
Oxygen levels in this zone are extremely low
Organisms resting or borrowing on the bottom and tolerant of little or no oxygen are common

36. Aquatic Organisms Aquatic organisms are classified by their habits
Neuston – organisms resting near the surface
Nekton – free swimming organisms
Periphyton – organisms that cling to rocks, logs, and other debris
Benthos – organisms living on and in the bottom sediments
Plankton – microscopic plants and animals that are suspended in the water column

37. Aquatic Food Webs

38. Food Chains and Webs
Primary producers – aquatic plants, algae, and phytoplankton
Primary consumers – zooplankton, some aquatic invertebrates and fish
Herbivores – plant eaters
Secondary consumers – some aquatic invertebrates, fish, snakes and turtles
Carnivores – flesh eaters
Omnivores – eats both plants and animals
Scavengers – vultures, crabs and other animals
Detritivores – bacteria and fungi that feed on organic material

39. Lotic Systems (Running Water)
Characterized by flowing water and currents
Lotic erosional – characterized by fast running water and riffles
Lotic depositional – characterized by pools and areas with slower velocities

40. Hydrology As water moves towards streams and rivers it:
Is absorbed by plants
Filters through the soil profile and can end up as groundwater
It can evaporate
It can enter the stream as runoff

41. Hydrology and Soil
Water capture is a process where water is stored in soil
Water can infiltrate the soil surface and percolate throughout the soil profile
Percolate is the downward movement of water through the soil profile
Infiltration and percolation is affected by soil type, topography and climate

42. Hydrology and Water Storage
Water is captured in soil
It is stored in pores (air spaces) between soil particles
More water is stored in sandy soils than clay soils
Vegetation can also affect the amount of water stored

43. Water Release
Water moves through the soil profile to seeps and springs or across the land as runoff and evidentially into streams and rivers
Vegetation along stream banks slows release of water into streams
During heavy rains it can help prevent erosion, reduce sediment and maintain water quality

44. Riparian Zones Riparian means “of the river”
It is the non-cultivated, vegetated land that touches and surround a stream
It often includes wetlands
It helps stabilize shorelines, filters pollutants
Helps maintain water temperature and provides cooler water for fish
Provides habitat for wildlife

45. Steam Velocity
Erosional Zone
Depositional zone

46. Erosional Zone
Outer bank of a stream where flow velocities are at a maximum and bank erosion is high.
Riffle areas – important habitats for many aquatic insects which require flowing water for feeding and high oxygen levels.
Few plants grow in the fast moving water of a stream, but some are adapted for living in a current

48. Depositional Zone
Refers to the inner bank of a stream where velocity is at a minimum
Slower velocities allow for deposition of sediments which form bars
Bars often support emergent aquatic vegetation
Pool areas support fish, aquatic invertebrates and aquatic plants
Sediments are composed of sand/silt/clay and organic matter

49. Depositional zone

50. Slower moving water supports organisms similar to lakes and ponds
Larger rivers with slower velocities can support plankton populations
Most of the rivers in the southeastern portion of Texas are slow-moving with large amounts of organic sediments support a large number of aquatic insects

51. FloodPlains
Floodplains are the areas of land surrounding a body of water that is subject to periodic flooding
Floodplains hold excess water during heavy rains
Allows water to be slowly released into river systems or seep into groundwater aquifers
Help filter out sediment
Not a great place to build on!

52. Aquatic Insects
Streams support those organisms adapted to life in fast moving waters.
Algae, plants and invertebrates that can anchor themselves to rocks, logs and other stream debris
Some fish prefer the fastest part of stream
Sediments are usually coarse
Many fish spawn in riffles of streams

53. Aquatic Insects
Primary producers – algae is dominant in slow moving rivers and streams. In faster moving streams aquatic plants are found but no phytoplankton or zooplankton
Primary consumers – snails, invertebrates and some fish are dominant
Secondary consumers –predatory invertebrates, fish, turtles