RIVER

• They contain only about 0.0001% of the total amount of water in the world at any given time, rivers are vital carriers of water and nutrients to areas all around the

earth.

• They are critical components of the hydrological cycle, acting as drainage channels for surface water – the world's rivers drain nearly 75% of the earth's land surface.

• They provide habitat, nourishment and means of transport to countless organisms.

• They provide travel means for exploration, commerce and recreation.

• They leave valuable deposits of sediments, such as sand and gravel.

• Their power provides much of the electrical energy we use in our everyday lives.

WHERE DOES THE WATER COME FROM?

THERE ARE 3 MAIN SOURCES FOR THIS WATER:

1) PRECIPITATION – RAIN OR SNOW

2) GROUND WATER – PRECIPITATION THAT HAS BEEN STRORED DOWN FOR A LONG TIME

3) MELTING GLACIERS

EXISTENCE OF RIVER DEPENDS ON:• THE AVAILABILITY OF SURFACE WATER

• A CHANNEL IN THE GROUND

• AN INCLINED SURFACE

MAJOR RIVERS

LOCTIC SYSTEMS

Rivers and streams are characterized by flowing waters and are called lotic systems (as opposed to lentic systems, such as lakes)

• Lotic environments have been described as having four dimensions:

• a longitudinal dimension with a pronounced zonation of chemical, physical and biological factors (comparable to the vertical stratification in lakes)

• a lateral dimension involving exchanges of organic matter, nutrients and biota between the stream channel and the adjacent floodplain

• a vertical dimension consisting of a hydraulic connection linking the river channel with groundwater.

• and a fourth dimension of time which pertains to the velocity of the water flow.

VARIATION IN SPACE AND TIME

The shape, size and content of a river are constantly changing, forming a close and mutual interdependence between the river and the land it traverses.

STRUCTURE

RIVER ZONATION

IT DIVIDES RIVERS INTO THREE PRIMARY ZONES:

• (a) The crenon is the uppermost zone at the source of the river. It is further divided into the eucrenon (spring or boil zone) and the hypocrenon (brook or headstream zone). These areas are characterized by low temperatures, reduced oxygen content and slow moving water.

• (b) The rhithron is the upstream portion of the river that follows the crenon. It is characterized by relatively cool temperatures, high oxygen levels, and fast, turbulent flow.

• (c) The potamon is the remaining downstream stretch of river. It is characterized by warmer temperatures, lower oxygen levels, slow flow and sandier bottoms.

PHYSICAL CONDITIONS

LIGHT• REDUCED CLARITY OF RIVERS RESULTS FROM 2 MAIN

FACTORS:

1) RIVERS ARE IN INTIMATE CONTACT WITH THE SURROUNDING LANDSCAPE, AND INORGANIC AND ORGANIC MATERIALS CONTINUOUSLY WASH, FALL, OR BLOW INTO RIVERS.

2) RIVER TURBULENCE ERODES BOTTOM SEDIMENTS AND KEEPS THEM IN SUSPENSION, PARTICULARLY DURING FLOODS.

THE EXTENT OF SHADING DECREASES PROGRESSIVELY DOWNSTREAM AS STREAM WIDTH INCREASES.

FOREST STREAM DESERT STREAM

TEMPERATURE

THE COLDEST RIVER TEMPERATURES, THOSE OF HIGH ALTITUDES AND HIGH LATITUDES, MAY DROP TO A MINIMUM OF O .

THE WARMEST RIVERS ARE THOSE FLOWING THROUGH DESERTS, BUT EVEN DESERT RIVERS SELDOM EXCEED 30 .

THE OUTFLOWS OF HOT SPRINGS CAN BE BOILING IN THEIR UPPER REACHES, BUT POPULATIONS OF THERMOPHILIC BACTERIA LIVE IN EVEN THE HOTTEST OF THESE.

WATER MOVEMENTS

CURRENTS IN QUIET POOLS MAY FLOW AT ONLY A FEW MILLIMETERS PER SECOND, WHILE WATER IN THE RAPIDS OF SWIFT RIVERS IN A FLOOD STAGE MAY FLOW AT 6m PER SECOND.

THE AMOUNT OF WATER CARRIED BY RIVERS, WHICH IS CALLED RIVER DISCHARGED, DIFFERS A LOT FROM ONE CLIMATIC REGIME TO ANOTHER.

RIVER FLOWS ARE OFTEN UNPREDICTABLE AND “FLASHY” IN ARID AND SEMIARID REGIONS, WHERE EXTENDED DROUGHTS MAY BE FOLLOWED BY TORRENTIAL RAINS..

MANY TROPICAL RIVERS, WHICH FLOW VERY LITTLE DURING THE DRY SEASON, BECOME TORRENTS

DURING THE WET SEASON.

SOME OF THE MOST CONSTANT FLOWS ARE FOUND IN FORESTED TEMPERATE REGIONS, WHERE PRECIPITATION IS OFTEN FAIRLY EVENLY DISTRIBUTED

THROUGHOUT THE YEAR.

HISTORICAL PATTERNS OF FLODDING HAVE PATICULARLY IMPORTANT INFLUENCES ON RIVER ECOSYSTEM PROCESSES, ESPECIALLY ON THE EXCHANGE OF NUTRIENTS AND

ENERGY BETWEEN THE RIVER CHANNEL AND THE FLOODPLAIN AND ASSOCIATED WETLANDS.

CHEMICAL CONDITIONS

SALINITY• THE AMOUNT OF SALT DISSOLVED IN RIVER WATER REFLECTS THE HISTORY OF

LEACHING THAT HAS GONE ON ITS BASIN.

• MANY TROPICAL SOILS HAVE BEEN LEACHED OF MUCH OF THEIR SOLUBLE MATERIALS AND IT IS IN THE TROPICS THAT THE SALINITY OF RIVER WATER IS OFTEN VERY LOW.

• DESERT RIVERS GENERALLY HAVE THE HIGHEST SALINITIES.

OXYGEN• OXYGEN CONTENT OF RIVER WATER IS INVERSELY CORRELATED WITH

TEMPERATURE.

• OXYGEN SUPPLIES ARE GENERALLY RICHEST IN COLD, THOROUGHLY MIXED HEADWATER STREAMS AND LOWER IN THE WARM DOWNSTREAM SECTIONS OF RIVERS.

• HOWEVER, BECAUSE THE WATERS IN STREAMS AND RIVERS ARE CONTINUOUSLY MIXED, OXYGEN IS GENERALLY NOT LIMITING TO THE DISTRIBUTION OF RIVER ORGANISMS.

BIOLOGY

The temperature is cooler at the source than it is at the mouth. The water is also clearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs can be found

there. Towards the middle part of the stream/river, the width increases, as does species diversity — numerous aquatic green plants and algae can be found. Toward the mouth of the river/stream, the water becomes murky from all the sediments that it has picked up

upstream, decreasing the amount of light that can penetrate through the water. Since there is less light, there is less diversity of flora, and because of the lower oxygen levels, fish that

require less oxygen, such as catfish and carp, can be found.

THE RIVER CONTINUUM

A river begins at a source and flows following elevation gradients (i.e., by the force of gravity) down to its endpoint, called the mouth (which may be another river, a lake, or an ocean).

The source is the highest point in the watercourse and may be a spring, a lake or marshy area, or glacial melt waters in high mountain regions.

The river continuum is a concept based on the characteristic changes in a river as it progresses from the source to the mouth. It identifies a downstream gradient of physical and chemical factors moving from the headwaters to the lowland rivers, correlating this gradient with changes in the biological communities.

ADAPTATIONS IN FLOWING WATER

FAST WATER:

- STREAMLINED FORM, OFFERS LESS RESISTANCE TO WATER CURRENT.

REQUIRE HIGH, NEAR-SATURATION CONCENTRATIONS OF OXYGEN AND MOVING WATER TO KEEP THEIR ABSORBING AND RESPIRATORYSURFACES IN CONTINUOUS

CONTACT WITH OXYGENATED WATER.

dace

Brook trout

- FLATTENED BODIES AND BROAD, FLAT LIMBS THAT ALLOW THE CURRENT TO FLOW OVER THEM.

- LARVAL FORMS OF MANY SPECIES OF INSECTS CLING TO THE UNDERSURFACES OF STONES, WHERE THE CURRENT IS WEAK.

- SOME ATTACH THEMSELVES TO THE SUBSTRATE AND OBTAIN FOOD BY STRAINING PARTICLES CARRIED TO THEM BY THE CURRENT.

- STICKY UNDERSURFACES HELP SNAILS AND PLANARIANS CLING TIGHTLY AND MOVE ABOUT ON STONES AND RUBBLE IN THE CURRENT.

- WATER MOSS AND HEAVILY BRANCHED FILAMENTOUS ALGAE CLING TO ROCKS BY STRONG HOLDFASTS.

- OTHER ALGAE GROW IN CUSHIONLIKE COLONIES OR CLOSELY APPRESSED SHEETS THAT ARE COVERED WITH A SLIPPERY, GELETINOUS COATING AND

FOLLOW THE CONTOURS OF STONE AND ROCKS.

FOR SLOW-FLOWING STREAMS:

- THEY TRADE STRONG LATERAL MUSCLES NEEDED IN FAST CURRENT FOR COMPRESSED BODIES THAT ENABLES THEM TO MOVE THROUGH BEDS OF

AQUATIC VEGETATION.

Small mouth bass

shiners

darters

- PULMONATE SNAILS AND BURROWING MAYFLIES REPLACE RUBBLE-DWELLING INSECT LARVAE.

- CATFISH FEED ON LIFE IN THE SILTY BOTTOM, AND BACK SWIMMERS AND WATER STRIDERS INHABIT SLUGGISH STRETCHES AND STILL BACKWATERS.

4 MAJOR GROUPS OF INVERTEBRATES:1) SHREDDERS – MAKE UP ONE LARGE GROUP OF INSECT LARVAE.

- FEED ON CPOM - BREAK DOWN CPOM, FEEDING ON THE MATERIAL NOT

SO MUCH FOR THE ENERGY IT CONTAINS BUT FOR THEBACTERIA AND FUNGI GROWING ON IT.

2) FILTERING AND GATHERING COLLECTORS- FEED ON FPOM.

3) GRAZERS – FEED ON ALGAL COATING OF STONES AND RUBBLES.

4) GOUGERS – ASSOCIATED WITH WOODY DEBRIS. THESE ARE THE INVERTEBRATES THAT BURROW INTO WATER-LOGGED LIMBS AND TRUNKS OF FALLEN TREES.

FEEDING ON DETRITAL FEEDERS AND GRAZERS ARE:

FAMOUS RIVERS

RIO GRANDE, NEW MEXICO

EUPHRATES

YANGTZE RIVER, CHINA

AMAZON RIVER

MISSOURI RIVER AND MISSISSIPPI

RIVERS IN PHILIPPINES

PASIG RIVER

CAGAYAN

LOBOC RIVER

DAVAO

HUMAN INFLUENCES

- POLLUTION- ALIEN SPECIES- BUILDING OF RESERVOIRS (DAMS)- MINING / FACTORIES