Watersheds & WetlandsLesson 1.3

Stream Biology Factors That Affect Freshwater Ecosystems

Chapter 1

PA Academic Standards for Environment & Ecology

Standard 4.1.10.C Describe the physical characteristics of a stream

and determine the types of organisms found in aquatic environments.

Learning Objectives• Describe and explain the physical factors that affect a stream

and the organisms living there.• Identify terrestrial and aquatic organisms that live in a

watershed.• Categorize aquatic organisms found in a watershed continuum

from headwater to mouth (e.g., shredder, predator, decomposer).

• Identify the types of organisms that would live in a stream based on the stream’s physical characteristics.

• Explain the habitat needs of specific aquatic organisms.

Stream Biology

• Streams and rivers are home to, or relied upon by many organisms.

• Dominant groups of organisms Algae Animal-like protists Invertebrates Vertebrates

Algae• Algae are plant-like protists that make their own food.• Algae are known as autotrophs or producers, forming the

base of most aquatic food chains.• Freshwater algae use energy from the sun and dissolved

nutrients in a stream and river to make their own food.

Animal-like Protists• Some protists have many of the same characteristics as

animals.• Common protists include amoebas, ciliates and

paramecia that eat sediments that contain bacteria and algae.

• Some protists are saprotrophs and feed on decayed organic matter.

• Some protists eat other protists and are classified as raptors.

Invertebrates

• Common Freshwater Invertebrates

Insects Mollusks Worms

Caddisflies

True flies Beetles

Damselflies & Dragonflies

Mayflies

Stoneflies

Common Stream Insects

Freshwater Mollusks

Aquatic Worms

Vertebrates• Common Freshwater Vertebrates

Salamanders Frogs Fish Reptiles

Factors That Affect Freshwater Ecosystems

• Two types of factors can be found in any ecosystem

Biotic factors – the living components of an ecosystem

Abiotic factors – the non-living components of an

ecosystem

Interactions among the biotic and abiotic factors determine the numbers and kinds of organisms in any environment.

Biotic and Abiotic Factors – a Simple Diagram

Abiotic

Biotic

Abiotic

Within any ecosystem the living organisms play specific roles as they interact with one another.

Producers – Autotrophs, make their own food

Consumers – Heterotrophs, Feed on other

organisms

Eg. Herbivores – eat plants

Carnivores - eat meat

Omnivores – eat both

Detritivores – consume or filter

decaying organic matter

Decomposers – break down organic matter

Predators – kill for food

Prey – killed by predators

Abiotic Factors That Affect Freshwater Ecosystems

• Stream Order• Temperature• Current and Velocity• Substrate• Sunlight• Turbidity

• Dissolved Gases• Oxygen• Carbon Dioxide• Organic Matter• pH

Stream Order

• Rivers form over time as smaller streams join to form larger streams.

• The smallest (headwater) streams are called first-order streams.

• Two first-order streams eventually join forming a second-order stream.

• Two second-order streams eventually join forming a third-order stream.

• Two third-order streams eventually join forming a fourth-order stream.

• Almost 80% of streams in Pennsylvania are either first-order or second-order streams.

• The stream order directly relates to the organisms that inhabit the ecosystem.– Example: First-order streams tend to have higher

populations of insects, while third-order streams and above tend to contain larger populations of plants and game fish.

Stream Orders

RIVER

CONTINUUM

Temperature

• Several factors cause differences in a stream’s temperature– Velocity of the water in the channel– Depth of water in the channel– Water Circulation within the channel– Vegetation along the stream bank– Season Variations

• Several factors cause changes in temperature in a waterway, but what affect does this change in temperature have or populations within the channel?– Some species have a lower tolerance for changes in temperature.

Thus, areas which typically exhibit fluctuations in temperature often have carp and catfish, for example, which tolerate a wide range of temperatures.

Temperature

( or any other abiotic factor)

Current and Velocity• Currents

• Currents are unidirectional, meaning they flow in one direction and carry nutrients which must be used quickly by living organisms.

• Organisms must adapt to this flowing environment. • Examples: The streamlined body of a fish, a mollusk’s muscular

foot, tiny hooked feet of macroinvertebrates.

• Velocity• The velocity within a channel changes with the course and

depth of the channel.• Examples: decrease in slope = decreased velocity

Smooth bed = increased velocity

(Velocity is most rapid in the middle of the water column due to less resistance)

Substrate• Definition: The material that organisms live in, on, or around.

Types of substrate• Organic

• Example: algae

• Inorganic• Example: rocks, pebbles, silt, sand & mud

How do organisms use substrates in freshwater ecosystems?

Some organisms live on a substrate.• Example: freshwater sponges

Some organisms live in a substrate.• Example: dragon fly larva

Some organisms use plants as alternative substrate• Example: midges

Sunlight

• The amount of light a stream or river receives also affects an ecosystems’ biodiversity.

• Plants rely on sunlight to make their own food via photosynthesis.

• Thus, segments of streams which receives little or no sunlight tend to have fewer organisms than places which receive adequate sunlight which penetrates to the bottom of the channel.

Turbidity• Definition: The amount of suspended matter in water.

The “cloudiness” of the water.

The suspended matter may include …

• Silt• Clay• Small organisms• Organic debris• Nonliving materials

• Factors that affect turbidity

Stream erosion• Example: poor streamside buffers or agricultural

practices Heavy rains or large snowmelts Temperature

• Example: warmer months promote the growth of plankton in the water column, reducing the overall clarity of the water

Dissolved Solids

• Dissolved solids (dissolved load) enter the waterway in two ways

(1) as groundwater recharges a stream or river

(2) as water flows over the riverbed

• Common elements found in freshwaterCalcium Nitrogen

Magnesium Phosphorus

Iron Sulfur

Sodium Potassium

Excess amounts of nutrients like N & P can stimulate plant and algae growth.

Algae blooms are large masses of algae that, when they die, are eaten by oxygen-using bacteria. The result: organisms that need oxygen to survive often die.

Dissolved Gases

• Rivers and streams contain dissolved gases.• Common dissolved gases

Oxygen

Carbon Dioxide

Oxygen• Oxygen levels in the water (dissolved oxygen) depend

on several factors:

– Temperature of the water• Example: the cooler the water, the more oxygen the water can

dissolve– Amount of photosynthesis

• Example: photosynthesis adds oxygen to the water– Amount of respiration

• Example: respiration removes oxygen from the water– Current

• Example: as the current decreases, the oxygen levels also decrease

– Decomposition• Example: oxygen is consumed during decomposition

Carbon Dioxide

• Most of the carbon dioxide that enters the stream or river comes from two main sources– Earth’s atmosphere– Groundwater systems

• Some additional carbon dioxide enters waterways from respiration and decomposition.

Organic Matter

• Most organic matter is freshwater systems is used as food.

• Examples include: algae, plankton, bits of leaves & wood, and decaying organisms.

Too many nutrients can result in a decrease in the amount of oxygen in the waterway. Too little and the organisms may move or die.

“Biological Oxygen Demand”: a test to determine the amount of biodegradable waste in a water sample

pH• A measure of the amount

of hydrogen ions present in a sample.

• pH fluctuations can alter the amount and kinds of organisms found in a freshwater system.

• Many streams in Pennsylvania are subject to acidification because of acidic rainfall, underlying rock structure, and coal mining.

• However, many streams in Pennsylvania can buffer and prevent large fluctuations in pH. (limestone)