Hydrological Cycle

Streams Stream = water flowing downhill in a defined

channel. (River = large stream; Creek & Brook = small streams)

Lotic system = flowing (fresh)water system;

Riparian system = of/around river/stream;

Fluvial = river/stream ; Rheos/Rrheic = stream

Gradient = meters of drop per kilometer of streamHigh gradient = fast

Low gradient = slow

Discharge = the amount of water carried by a stream (often varies seasonally and with

precipitation) Usually measured as m3 per second at a given point of the stream.

Quantifying Stream Flow

Streams Basin/Drainage/Catchment = area drained

by a stream. Headwaters = small source streams that

originate from springs (groundwater) or runoff from the basin.

Mouth = terminus of a stream at another body of water.

Floodplain = level area along a stream that is “frequently” flooded.

Riparian Zone = area where vegetation is influenced by the stream.

Mississippi Basin

“Typical” Stream

“Typical” Stream Profileheadwaters / source

mouth

highlands stream-high gradient-low discharge-low turbidity

lowlands stream-low gradient-high discharge-high turbidity

Stream Order often streams begin at a

spring (ground-water becomes surface water).

Stream Order = pattern of stream branching.1st Order Stream = headwater streams. 2nd Order Stream = streams formed by uniting of 1st order streams.Etc.

Usually lower order = high gradient, cool, low turbidity, few species, small discharge, more variable flows over time.

Stream Order

“Typical” Stream Section Flood Plain = area around a higher order

stream covered by water during floods. Channel = area where a stream usually flows. Main Channel (thalweg?) = deepest part. Levee = raised area on either side of a

stream channel.

Channel

Main Channel

Streams, Runoff, & Groundwater More surface runoff → greater discharge Stream at groundwater level → more

continuous discharge (won’t “go dry”; if channel above groundwater, then may “go dry”)

If stream higher than groundwater and channel, then may “re-charge” groundwater (especially if lower flow).

groundwater

Channel & Flow Water flows faster further away from the

substrate which causes turbulence. More irregular channels slow flow more

than regular channels. Straighter channel sustains higher flow.

Meanders/Bends Channel composition determines erosion

Channels of evenly erodable material...still form regular meanders/bends.

deposition

Cutbanks & Bars

erosion

deposition

Meandering Channel

Meanders/Bends

Oxbow Lakes Oxbow lake = Portion of a bend cut

off from the main flow of the stream.

Braided Channels Braided Channel = multiple

channels in a large (high order) stream separated by islands/bars.

Pools, Riffles, & Runs

Pool = relatively deep portion with slower water flow (lower dO2)

Riffle = relatively shallow portion with faster water flow where the water ripples or breaks on the substrate (higher dO2)

Run = relatively deep portion with faster water flow.

Pools & Riffles

Substrate & Cover Substrate usually composed of larger

elements the lower the order. Cover = the percent of the sky above

the stream that is shielded by vegetation. % cover usually higher the lower the order.

Drift (Stream) Drift = normally benthic organisms

in the water column moving downstream.

Allows re-positioning and/or benthic predator avoidance (but makes vulnerable to large predators). - Always one way.

Drought and Floods Effects usually most dramatic on low and

mid- order streams. Drought – problem = too little water;

surface flow may be very low or absent drought refugia - isolated pools often connected by subsurface flow or connected higher order stream

Floods – problem = scouring flow; surface flow in channel very rapid flood refugia – inundated floodplain or water behind large structure (i.e., boulders) or connected higher order stream

In-Stream Primary Production Very high flow, intermittent stream flow, and

high turbidity reduce (or eliminate) in-stream photosynthesis.

In clear streams, periphyton (microphytes) & macrophytes may be able to undergo in-stream photosynthesis).

Phytoplankton (& zooplankton) only rarely present in very high order streams (consistent low flow but… high turbidity).

Marginal emergent vegetation and riparian zone vegetation can undergo significant production, especially in higher order streams.

Allochthonous Inputs In most streams most nutrients come from

surrounding terrestrial environments (dead parts of organisms, such as leaves, or dissolved molecules)

Allochthonous material = organic matter from a different habitat; CPOM – coarse particulate organic matter FPOM – fine particulate organic matter DOM – dissolved organic matter

Detritivores (animals that eat detritus) and decomposers (bacteria & fungi that decompose dead

organisms) are very important in most streams. Flow washes detritus downstream, more FPOM

and less CPOM in higher order streams.

Low Order Stream Food Web

periphyton

grazinginsects &

crustaceans

grazingfishes

bacteria& fungi

fine particulate organic matter (FPOM)

collectinginsects, crust.,nematodes, &

annelids

leaf litter

predatoryinsects &

crustaceans

dissolved organiccompounds (DOC)

runoff orgroundwater entry

coarse particulate organic matter (CPOM)

bacteria& fungi

conditioning(microbial colonization)

shreddinginsects &

crustaceans

“predatory”fishes

N. Amer. Stream Insect Shredderscrane fly larva

caddis flylarvae

N. Amer. Stream Insect Collectors

caddisflynet

chironomid, midge larva

blackflylarva

baetid, mayfly larva

N. Amer. Stream Insect Grazersstone fly

larva

heptageniid, mayfly larva

glossosomatid, caddis fly larva

N. Amer. Stream Insect PredatorsHellgrammite,

Dobson fly larva

damselflylarva

rhyacophilid, caddis fly larva(non-case building)

N. Amer. Decapod Crustaceans When crayfishes, crabs, and/or shrimps are

present, they often have significant ecological effects as feeding generalists (acting as shredders, collectors, grazers, AND predators).

Low Order Stream Fishes

High Order Stream Fishes

Colorado River Fishes

Differences in Tropical Streams Bacterial and fungal decomposition of

allochthonous material is more rapid. Allochthonous inputs are often (but not

always) less seasonal. Fewer aquatic insects. Fishes (and in some

places decapod crustaceans) serve as the major shredders, collectors, and grazers.

Human Impacts: Runoff/Erosion Increased nutrient inputs via agricultural

fertilizers – favors algal periphyton and bacteria (can result in anoxia)

Increased turbidity due to erosion – less in-stream photosynthesis

Human Impacts: Channelization Channelization and elimination of flood plains

– reduces groundwater recharge, increases water velocity in flood and severity of floods when levees breached

Human Impacts: Impoundments Formation of Lakes via damming of rivers.

Greatly changes conditions, especially downstream. (e.g., hypolimnetic release)