Chapter 1.3Stream Biology

There are 3 dominant groups of organisms in most stream communities.Algae and Animal like protists InvertebratesVertebrates

• Algae

•Are plantlike protists that make their own food (autotrophs)

•Since they are autotrophs it forms the base of most aquatic food chains. •Freshwater Alage use sunlight and dissolved nutrients in a stream to make their food.

•Animal-like protists•Has many characteristics as animals

•Are aquatic organisms that eat:

•Bacteria

•Sediments that contain bacteria

•Algae

•Ex. Ameoba, Euglena

Amoeba Are protists that engulf food by flowing around and over it

Raptors Protists that eat other protist

Saprotrophs Protists that feed on decayed organic material

Invertebrates Do not have an internal skeleton made of bone

Examples of freshwater invertebrates Insects, worms, mollusks Shredders & striders

Mollusk

Mollusk

strider

VertebratesHas an internal skeleton made of bone

Examples of freshwater Vertebrates amphibians (frogs, salamanders) fish

Factors that affect Freshwater ecosystemsStream order

Smaller streams ( 1st order) flow into larger streams (2nd order) and continue on. Two streams of the same

order must come together for a stream to move up

in order.The size or order of the stream relates directly on

the organisms that are in the ecosystem. 1st order streams are home to large insect populations,

few if any fish. Plants and game fish dominate 3rd & 4th order. Larger the stream the more diverse populations of

algae, fish, and other aquatic organisms.

Factors that affect Freshwater ecosystems

TemperatureChange in temp affects the kinds and #’s of species

in a stream. Some species can live in a wide range of temps (catfish

and carp), while others species can survive only in certain temps (algae, protists and trout).

Examples of factors that causes difference in stream temp Velocity Depth Seasonal change Riparian coverage

Factors that affect Freshwater ecosystemsCurrent

UnidirectionalCauses different forces on organisms in the stream

VelocityChange in distance over time.Fish are unaffected by velocity, while insects are

generally limited to calmer water.Waters moves the fastest in the middle of the stream

below the surface.

Substrate Is the material that organisms live in, on, or around.

EX. of Organic substrate – algae, plants, mosses EX. of Inorganic substrate – rocks, sand, silt and mud

Factors that affect Freshwater ecosystems

Sunlight (plants rely on it to make food thru photosynthesis)Less sunlight = less organisms

Turbidity (clarity) Reflects the amount of suspended matter in water

Facts that affect turbidity Increase in stream erosion Increase in water volume

Heavy rain/melting snow

Factors that affect Freshwater ecosystems

Dissolved GasesOxygen and Carbon dioxide

OxygenEnters the water from the airConcentration depends mainly on temp

As temp increases, D.O. decreases

Photosynthesis also adds oxygen to the waterCurrent

As current decreases, so does D.O.

Factors that affect Freshwater ecosystems

Organic MatterMostly used for foodAlgae and detritus (particulate organic matter)Too few nutrients = loss of organismsToo many can cause mass algal blooms and then loss of

other organisms

pHScale ranges 0-14, 7 neutral, below 7 acidic, above 7

basicRainwater tends to be slightly acidicMine drainage is a major contributor to stream

acidification