Concepts in Stream Ecology

• Streams are ecosystems

• Communities of organisms and their physical, chemical, and biological environments

Ecosystems

Major Abiotic Factors

• Flow

• Light

• Temperature

• Chemistry

• Substrate

Flow

• Water flow is the key factor in lotic systems

• Strength and speed of water flow can vary between systems and within a system- based upon variability of friction with bottom

or sides, obstructions, and incline- Input can affect flow rate

• Erosion creates a variety of habitats:- Riffles and pools

Particular longitudinal and transversal shape

Highly variable parameters of the ecosystem

• Velocity and weight of water create momentum and shear stress at the sediment water interface

• High variability- Velocity, momentum and shear stress- Transport of bedload - Turbidity and particulate matter- Nutrient and oxygen concentrations

Stream Ecosystems

• Mostly downstream fluxes of energy and matter

• Lateral and vertical the riparian and hyporheic zones

The riffle

• Elevation dropHigher velocityHigher shear stressMore resuspension of fine sedimentsOnly bigger particles stayRiffle contain gravel size stones at their

surfaces

The riffle

• Relatively Shallow

• Smaller cross section area

• Obstacles relatively bigger

• Woody debris go agroud

• Leaf pack can develop

How do all organisms find their requirements for life in streams?

• Water?

• Source of nutrients?

• Source of energy?

• Source of electron donor (oxygen)?

Sources and sinks of oxygen in water

• Sources:- Photosynthesis from autotrophs- Reaeration at the interface between water

and atmosphere

Reaeration

• Partial pressure equilibrium between atmosphere and water

• dissolved gas mole fraction of any gas, xi, at equilibrium conditions

• PO2=0.2095

• The colder the water the

higher the potential for

oxygenated waters

Reaeration (Cont’d)

• DO values also depend on - The depth of the water- The velocity of the water- Water T°C

Where is water fast and shallow in streams?

- Oxygen concentration highest in riffles!!!

Can oxygen be a problem?

• Oxygen content in streams and sediment driven by the ratio between supply and demand.

• All organisms from bacteria to fish respire and consume oxygen

• In sediment oxygen can be all consumed: anoxia

• Oxygen: major driver of stream habitat and biogeochemical processes

Challenges when an autotroph in a stream

• Find a spot

• Find a point of anchorage

• Stay in place

• Find light

• Find nutrients

• Avoid being grazed

Autochthonous Vs. Allochthonous

• Autochtonous- Energy sources derived from within the lotic

systemoPhotosynthesis and decomposition of organisms

originating in the system

• Allochthonous- Energy sources derived from outside the lotic

systemoLeaves, twigs, fruitsoFeces and dead carcasses

Biofilms

Biofilms

Increased water exchange in Biofilms

Challenges for macrophytes in streams

• Withstand the currents

• Obtain nutrients from both sediment and water column

Macrophytes

Challenges when a fungus or Shredder

• Have something to shred upon- Leaf packs, dead algae macrophytes

Riparian plant community = stream organic dynamics

Wood Mass Estimates (Valette, et. Al.)

•Old Growth Streams = 8.33 kg/m²

•Second Growth Streams = 0.05 kg/m²

Challenges when a fungus or Shredder

• Have something to shred upon- Leaf packs, dead algae macrophytes

• Capture particulate matter

• Clogging

• Not getting washed away- Ability to hide

Challenges when a fungus or Shredder

• Have something to shred upon- Leaf packs, dead algae

macrophytes

• Capture particulate matter• Clogging• Not getting washed away• Ability to hide from current and

predators

Challenges for scrapers

• Be were the biofilms are

• Have oxygen

• Withstand current

• Hide or develop strategies

against predators

Challenges for filters and collectors

• Have enough oxygen

• Enough food

• Not too many fine particles

• Clogging

• Hide from predators

Challenges for invertebrate predators

• The food chain above must exist

• Have enough oxygen

• Live where the preys live

• Not get washed away

Ephemeroptera

Challenges for higher predators

• Have enough oxygen

• Find where the insects and fish are

• Locations to rest, feed and reproduce

• Depend on the entire food chain above

Take home points: Where does energy come from?

• Light for the autotrophs (autochtonous origin)

• For most organisms:- Dead organic matter- Crucial importance of Fine Particulate Organic

Matter (FPOM)

Why would anyone want to live in a riffle?

• Autotrophs- More light- More renewal of nutrients

• Heterotrophs- More oxygen in water and sediment- Smaller cross section area thus higher probability

of capturing food for the same volume scanned- Higher chance for obstacle for leaf packs

oWoody debris essential as physical barriers

Take home points: Why would anyone want to live in a pool?

• Autotrophs- Less shear stress- Soft sediment for roots and for nutrient supply

• Heterotrophs- Less shear stress (herbivores)- Soft sediment for habitat (Bivalva)- Fine particulates for detritivores

Take home points: Small obstacles: key to ecosystem health

Who lives in streams?

• Bacteria, virus

• Amoeba, rotifers

• Plants:- Algae: microscopic and macroscopic- Bryophytes (mosses) - Angiosperms (flowering plants)- Fungi

Who lives in streams?

• Animals:- Protozoa:

o Sponges (Bryozoa)

- Macroinvertebrateso Acoelomate worms

– Planaria or flatworm (Turbellaria)

– Nematode or Threadworm, Horsehair worm (Nematoda)

o Mollusca– Clams (Bivalva)

– Snails (Gasteropoda)

o Annelida– Leeches (Hirudinea or Achaeta)

– Tubifex worm (Oligochaeta)

– Bristle worms (Polychaeta)

Who lives in streams?

• Animals:- Macroinvertebrates (Cont’d)

o Arthropods:– Spiders (Arachnida)– Crayfish, Water flea (Crustacea)– Stonefly, Mayflies, Caddisfly (Insects)

- Vertebrates:o Vertebrates

– Lamprey (Agnatha)– Fish (Osteichthyes)– Frogs (Amphibians)– Water snakes and turtles (Reptiles)– Kingfisher, Dipper (Birds) – Otter, beaver (Mammals)

Algae: What do they look like?

• Microscopic and macroscopic algae- Diatoms commonly

comprise the dominate algal group in river biofilms in terms of species number and biomass.

Aquatic mosses (Bryophytes)

Christmas Moss (Vesicularia montagnei)

Zipper Moss – (Fissidens zippelianus)

Aquatic flowering plantsMyriophyllum spp – Watermilfoils

Water lilies – Nuphar spp

Glyceria Fluitans

Aquatic sponges

• Freshwater sponges are aquatic animals that grow in lakes, rivers, bogs, and streams attached to submerged rocks, sticks, logs, or aquatic vegetation. These sedentary animals feed by filtering small particles from the water, and so are thought to be sensitive indicators of pollution.

• The sponges may be colored green by algae that live inside their cells or they may be beige to brown or pinkish in color.

• Sponges can be delicate to very firm feeling but are not slimy or filmy. Some sponges prefer the underside of logs and sticks; these are usually not green in color.

Acoelomate worms

• Turbellarians or planarians (Turbellaria) possess a pharynx tube that extends to feed on whole small animals or suck tissues from dead or wounded prey.

http://trc.ucdavis.edu/biosci10v/bis10v/media/ch16/blood_fluke.html

Nematods

• Nematodes exhibit a wide range of feeding habits: carnivorous, herbivorous and parasitic

Horsehair worms

• Horsehair eggs are laid in the water in long strings where the adults live.  After hatching, the larvae penetrate some aquatic insect;

• they escape in some unknown way from this host and find their way into a second host; usually a beetle, cricket, or grasshopper;

• in the body cavity of the second host the larvae continue their development eventually passing out into the water where they become mature. 

• Since the adults live only in water, those that survive probably emerge from terrestrial (flying) insects, which constitute their second hosts, that chance to  drown in watering troughs and small ponds.

Leeches

• Leeches suck the blood of fishes, amphibians, birds, and mammals. They also eat snails, insect larvae, and worms

Clams

• Freshwater mussels feed by filtering algae and small particles from the water.

• Most species have a larval stage that is parasitic on fish.

• Larvae are released by the female mussel and must locate a certain fish species or die.

• They usually attach to the host fish's gills or fins where they remain for a few weeks or months.

• Larval mussels rarely harm infected fish under natural conditions.

• If essential fish species are removed from the habitat, mussels will not be able to reproduce.

• Support muskrats, otters, wading birds and game fish

Aquatic snails

• Aquatic snails are a crucial host to the flatworm parasite

• Herbivores

Tubifex worms

• Tubifex tubifex, also called the sludge worm, is a species of tubificid segmented worm that inhabits the sediments of lakes and rivers on several continents.

• These worms ingest sediments and gain nutrition by selectively digesting bacteria and absorbing molecules through the body wall.

• The worms can survive without oxygen for months, and can survive in areas so heavily polluted with organic matter that almost no other species can endure.

• By forming a protective cyst and lowering its metabolic rate, T. tubifex can survive drought and food shortage.

• Encystment may also function in dispersal of the worm.

• Ecologically, it is important as a source of food for leeches, crustaceans, insects, and fishes.

Bristle worm

• Mostly in seawater

Aquatic Spiders

• Water spiders breathe air. They use their silk to make a spherical container under the water, attaching the silk to water plants.

• When this is done they collect air from the surface and place it in the silk container.

• They even lay their eggs in this trapped air bubble

Crustaceans

Sawbug

Crayfish

Daphnia

Copepods

Mostly herbivores

Insects

• Ephemeroptera – mayflies• Plecoptera – stoneflies• Trichoptera – caddisflies• Odonata – damsel and dragonflies• Coleoptera – beetles• Megaloptera – Dobson and Alderflies• Diptera – True flies

EPT

Biological indicators of good health

Mayfly (Ephemeroptera)

Stonefly

(Plecoptera) Caddisfly

(Trichoptera)

EPT

In-Stream habitat

• Macrohabitats: riffles and pools

• Microhabitats: bankroots, leaf packs, large woody debris, hyporheos, other vegetation

Great diversity of habitat in streams

Can search for nutrient, energy, oxygen be altered?

• Eutrophication

• Turbidity of water, erosion and increased bedload

• No woody debris

• No habitat for the whole food chain

Human Impact

• Pollution- Hard to control due to many sources over a wide area- Clean Water Act

• Flow Modification- Dams alter the flow, temperature, and sediment

regime

• Invasive Species- Compete for resources - Harmful diseases and parasites