1. Freshwater Systems
Lotic Systems

2. Freshwater Ecosystems
What are the characteristics of freshwater ecosystems?
A freshwater ecosystem is defined as the living organisms (biotic) and the non-living (abiotic) environment they inhabit.
The type of freshwater ecosystem —whether it be a pond, lake, stream, or river— is determined by the watershed (drainage basin) in which it exists.
Remember that a watershed is a complex system of components that affect water bodies in a given drainage basin.
Each watershed includes a variety of fac­tors that interact with the water in the sys­tem, including climate, amount of rainfall, geology and geography of an area (rocks, soil, hills, lowlands, forests), and human activities (urban and industrial devel­opment, agriculture).

3. What are the characteristics of a freshwater ecosystem?
Drainage basins and watersheds that drain into the body of freshwater
Drainage basin is an area of land where surface water from rain and melting snow or ice converges to a single point at a lower elevation, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean
Including the geology (rocks and soil), geography and topography (landforms), and human activities (urban and industrial development and agriculture) of the area

4. The red lines describe the watersheds for the drainage basins of first order streams. The yellow lines define the watersheds for two drainage basins from locations further upstream. Note that the first order basins are components of these much large drainage basins. (Source: PhysicalGeography.net)

5. Figure 2: Common drainage pattern types. (Source: PhysicalGeography
Figure 2: Common drainage pattern types. (Source: PhysicalGeography.net)

6. Contribution of watersheds to freshwater ecosystems
Components of the watershed affects the bodies of water, or habitats, that they flow into.
Contributing factors include:
geology (rocks and soil)
geography and topography (landforms)
human activities (urban and industrial development and agriculture)

7. TYPES OF FRESHWATER SYSTEMS
There are generally three types of freshwater ecosystems: Lotic Systems, lentic systems, and freshwater wetlands.
Lotic systems include flowing water, such as rivers, streams, creeks, etc.
Lentic systems include standing bodies of water, such as lakes and ponds.
We will discuss freshwater wetlands at another time.

8. General Differences Between Streams and Lakes Streams (Lotic System)
Characteristic
Streams (Lotic System)
Lakes (Lentic System)
Water flow
One direction of flow, upstream to downstream
Various flows, no particular direction
Oxygen content
Normally oxygen rich because of the constant mixing
Oxygen depletion exists at times in deeper water or older lakes
General Depth
Shallower on average
Deeper than average
Size Description
Narrower and longer
Wider and shorter
Riparian Zone Description (the riparian zone is the land area along the banks of the body of water)
Various effects from different terrestrial environments along the stream’s course. The shoreline has more potential to affect water quality because a larger portion of the water body is near shore.
Terrestrial environment similar all around the lake shore. A smaller portion of the water is in close proximity to the shore.
Changes in shape / depth over time
Stream continually cuts into the channel, making it longer, wider, and deeper
Lakes become shallower over time from depositing sediments
Age progression
Age progression of a stream goes from young stream, narrow and shallow, to mature stream, wider and deeper
Age progression of a lake or pond goes from lake to marsh or swamp to land
Water retention time (how long it holds water)
Shorter retention time for water (b/c it’s always flowing)
Longer retention time for water (because it stores water)
Temperature characteristics
Top and bottom waters generally have the same temperature (b/c of the constant mixing)
May have different temperatures from the top to bottom (b/c it has layers based on density)

9. LOTIC SYSTEM A. What are lotic systems?
Lotic environments include streams and rivers.
Flowing waters are very diverse, not only in size but in characteristics.
Streams and rivers are defined by things like surrounding land use (urban, agricultural, natural), size of the watershed, stream order, geology, soils, topography, flow, and vegetation.

10. Characteristics of a Lotic System
Flow in one direction (downhill)

11. Characteristics of a Lotic System
Usually high in dissolved oxygen
Shallower than lakes
Narrower and longer than lakes

12. Characteristics of a Lotic System
Flowing water continually cuts into the channel, making it deeper and wider as it ages

13. Characteristics of a Lotic System
Water temperature from top to bottom is usually the same
Water doesn’t stay put for very long

14. What are the sources of running water systems?
The places where streams begin are called headwaters.
a)Many begin in mountain areas from snowmelt.
b)Some begin or are fed by water seeping up from the water table. (Remember that these are called gaining streams)
c)Some begin or are fed by other streams flowing into them. These are called tributaries

15. What defines a stream?
Lotic systems consist of flowing bodies of water
Rivers and streams are more diverse than lakes for many reasons:
Surrounding land use
Size of the watershed
Stream order
Geology and soil type
Topography
Rate of stream flow
Vegetations type

16. What are stream orders?
Stream orders are numbered based on their role in feeding into another body of water.
Stream Types
Streams and rivers are primarily characterized by the length of time that they flow.
There are three main types of streams:
Perennial streams
Intermittent streams
Ephemeral streams

17. Three types of streams 1. Perennial streams
Have a constant flow of water, flow year round.
The amount of water can, and will, vary with the different seasons, however.

18. Three types of streams 2. Intermittent streams
May run dry now and then, but have regular periods of water flow.
Over 76 percent of the streams in Texas fall into the intermittent category.
These usually occur in arid or semi-arid areas or in areas that are experiencing especially dry conditions. During times of extreme drought, even perennial streams can become intermittent.
Although shallow sections of intermittent streams and rivers can dry up, perennial pools are often maintained in the deeper sections of a stream channel. Large pools can often sustain aquatic life through the hot summer months.

19. Three types of streams
3. Ephemeral streams
Only rarely have water in them, usually after rainfall in desert areas
are intermittent streams that regularly exist for a short period of time.
Ephemeral streams are best illustrated by the dry stream beds in west Texas that flow only following rainfall and cease to flow soon after.

20. Comparing Erosional and Depositional Habitats of a Stream

21. Stream Habitat Types
There are two types of basic stream habitats, based on how quickly the water flows:
Those that have fast-running water (erosional)
Erosion = take away
Those that have slow-moving water (depositional)
Deposition = Deposit = to place

23. Erosional vs. Depositional Habitats
Erosional Habitats
Are usually shallower than depositional
Consist of varying parts:
Riffles – fast-moving, turbulent water
Run – fast-moving, non-turbulent water
Glide – slow-moving water

24. Riffles, pools, and cascades
Riffles and pools alternate in somewhat predictable patterns
Many other local irregularities in the profile of the channel have been described. Riffles are shallow regions paved by stones and gravel where the current moves more quickly and with more turbulence. They often alternate with pools, which are slower, calmer and deeper areas with fine- grained bottom deposits. Cascades are steep areas where flow occurs over a sequence of emergent boulders, with each drop known as a step. Such formations are constantly being created and destroyed as a result of the powerful dynamics of a flowing river.

25. Erosional Sediments Sediments are coarse (or larger in size)
Consist of cobble, pebbles, and gravel

26. Aquatic Plants and Animals
Rooted in the coarse sediment
Are able to withstand the force of the flowing water
Ex. pondweed
Animals
Require high O2 levels
Need flowing water to feed (filter feeders)
Strong swimmers or cling to rocks in riffle areas

27. Erosional Zones
Usually towards the outer bank (erosion of bank is high)
Figure 1.21

28. Depositional Habitats
Usually deep and wide
Slower moving water as compared to riffles, runs, and glides

29. Depositional Sediments
Sediments tend to build in pools and backwater areas
Sediment is finer (smaller particles)
Usually sand and/or silt

30. Aquatic Plants and Animals
Submergent vegetation (live completely underwater)
Able to grow in sand or silt
Animals
Many organisms use deeper water for cover or protection
Easier to find and eat food

31. Stream Erosion and Deposition
Streams are constantly changing as water flows through them.
The actions of the water move sand and rock from one place, and deposit it at another. The two driving forces are erosion and deposition.
Erosional zones usually occur in the fast-running water areas, and may cause high amounts of erosion along the outer banks of the stream.
Depositional zones are found in the slower moving water area, where sediments are able to settle to the bottom.
Materials such as gravel, pebbles, and sand slowly build, and may eventually form a bar. Bars often support aquatic plants.

32. Rivers and streams flow downhill seeking a path of least resistance.
Changing terrain alters the course of a river or stream creating bends called meanders.
These meanders move over time through the processes of erosion and deposition.

33. Meandering Rivers
Rivers and streams flow with gravity (uphill to downhill), seeking the path of least resistance
Changing landforms and terrain alters the course of a river, creating bends, or meanders
Meander means to wander
Sacromento River, California

34. Meandering Rivers
Meandering rivers change course over time as sediments build through deposition, and as banks erode.

36. Meandering rivers
A meander becomes more pronounced as the streamline shifts between the river banks.
Formation of an oxbow lake
The complex dynamics occurring as the river moves back and forth within the channel walls creates a range of habitats for the river biota. Sometimes a meander will curve so much that it almost becomes a complete loop. In this case the river will often create a new channel between the beginning and end of the loop, cutting off the meander core and resulting in the formation of an oxbow lake

37. Effect of the water table
Rain and snow melt soak into the ground, becoming part of the water table
When the water table is close to the ground, springs can form above ground

38. Effect of the water table
Gaining streams
Springs above ground that are recharged by underground sources
These springs are perennial

39. Effect of the water table
Losing streams
Streams that lose water to replace the water table as the level of water drops (water from the stream is lost to the water table)
These streams are intermittent

40. Riparian Zone
The riparian zone is a vegetated buffer on the banks of the stream (between nearby lands and the water itself.)
These areas are important in controlling the introduction of sediment and nutrients into a river or stream channel.
The riparian zone includes the stream bank and portions of the floodplain that are periodically covered by flood waters.
Interaction between the riparian zone and a stream is vital for the health of the stream.

41. Riparian Zone “Buffer” comprised of various plant species
Located between the stream and nearby land
Includes the bank and flood plain areas

42. Functions of Riparian Zones
Many important functions:
Controls the amount of sediments and nutrients that run-off into the stream
Protects streams from surrounding land uses
Helps provide flood control

43. E. Stream Habitats and Aquatic Organisms
In-stream habitats include pools, riffles, root mats, aquatic plants, undercut banks, submerged rocks and logs, overhanging vegetation, and leaf litter.
A combination of these, along with the depth and flow of the water, are key factors in determining the type of aquatic organisms found in a stream.
Under natural conditions, a wider variety of habitats equals greater aquatic life diversity.

44. Stream Habitats and Aquatic Organisms
Low diversity of aquatic life is often caused by poor quality of in-stream habitats rather than by poor water quality. In the past, stream quality was determined by the factors of the water itself. Now, however, scientist focus just as much as what is living in the stream.
We will look at what lives here after we look at lentic systems.

45. Importance of In-Stream Habitats
What determines the type of habitat? Habitats in the stream can be found anywhere:
Pools
Riffle
Under or in plant masses and overhanging vegetation
Submerged rocks and logs
Leaf litter on the bottom

46. In-Stream Habitats
The location of the habitat, combined with the depth of the water and the rate it is flowing are key factors in determining what type of organism lives in the stream.

47. Habitats and Diversity
The greater the number and types of habitats, the more diversity there will be
Poor stream quality = low diversity

48. Determining the Health of a Stream
The health and quality of a stream is determined by:
Water chemistry and physical aspects
How much dissolved O2, turbidity, pH, temp. etc.)
More recently, we also look at the communities of organisms living there