• 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 worlds rivers drain nearly 75% of the earths 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 SNOW2) GROUND WATER – PRECIPITATION THAT HAS BEEN STRORED DOWN FOR A LONG TIME3) MELTING GLACIERS
EXISTENCE OF RIVER DEPENDS ON:• THE AVAILABILITY OF SURFACE WATER• A CHANNEL IN THE GROUND• AN INCLINED SURFACE
LOCTIC SYSTEMSRivers and streams are characterized byflowing waters and are called loticsystems (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 riverare constantly changing, forming a closeand mutual interdependence betweenthe river and the land it traverses.
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.
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 THEMIN SUSPENSION, PARTICULARLY DURING FLOODS.
THE EXTENT OF SHADING DECREASES PROGRESSIVELY DOWNSTREAM AS STREAM WIDTH INCREASES.FOREST STREAM DESERT STREAM
THE OUTFLOWS OF HOTSPRINGS CAN BE BOILING INTHEIR UPPER REACHES, BUTPOPULATIONS OFTHERMOPHILIC BACTERIALIVE IN EVEN THE HOTTESTOF THESE.
CURRENTS IN QUIET POOLS MAY FLOW AT ONLY A FEW MILLIMETERS PERSECOND, WHILE WATER IN THE RAPIDS OF SWIFT RIVERS IN A FLOOD STAGE MAY FLOWAT 6m PER SECOND.THE AMOUNT OF WATER CARRIED BY RIVERS, WHICH IS CALLED RIVERDISCHARGED, DIFFERS A LOT FROM ONE CLIMATIC REGIME TO ANOTHER.RIVER FLOWS ARE OFTEN UNPREDICTABLE AND ―FLASHY‖ IN ARID AND SEMIARIDREGIONS, WHERE EXTENDED DROUGHTS MAY BE FOLLOWED BY TORRENTIALRAINS..
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 ONRIVER ECOSYSTEM PROCESSES, ESPECIALLY ON THE EXCHANGE OF NUTRIENTS AND ENERGY BETWEEN THE RIVER CHANNEL AND THE FLOODPLAIN AND ASSOCIATED WETLANDS.
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.
The temperature is cooler at the source than it is at the mouth. The water is alsoclearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs canbe 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 haspicked 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 followingelevation gradients (i.e., by the force of gravity)down to its endpoint, called the mouth (whichmay be another river, a lake, or an ocean).The source is the highest point in thewatercourse and may be a spring, a lakeor marshy area, or glacial melt waters inhigh mountain regions.The river continuum is a concept based on thecharacteristic changes in a river as it progressesfrom the source to the mouth. It identifies adownstream gradient of physical and chemicalfactors moving from the headwaters tothe lowland rivers, correlating this gradient withchanges in the biological communities.
ADAPTATIONS IN FLOWING WATER
FAST WATER: REQUIRE HIGH, NEAR-SATURATION CONCENTRATIONS OF OXYGEN AND MOVING WATER TO KEEP THEIR ABSORBING AND RESPIRATORYSURFACES IN CONTINUOUS CONTACT WITH OXYGENATED WATER. - STREAMLINED FORM, OFFERS LESS RESISTANCE TO WATER CURRENT. Brook trout dace
- LARVAL FORMS OF MANY SPECIES OF INSECTS CLING TO THE UNDERSURFACES OF STONES, WHERE THE CURRENT IS WEAK.- FLATTENED BODIES AND BROAD, FLAT LIMBS THAT ALLOW THE CURRENT TO FLOW OVER THEM.
- 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: shiners Small mouth bassdarters - THEY TRADE STRONG LATERAL MUSCLES NEEDED IN FAST CURRENT FOR COMPRESSED BODIES THAT ENABLES THEM TO MOVE THROUGH BEDS OF AQUATIC VEGETATION.
- 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 THE BACTERIA 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:
RIO GRANDE, NEW MEXICOEUPHRATES
YANGTZE RIVER, CHINA
MISSOURI RIVER AND MISSISSIPPI
RIVERS IN PHILIPPINES
- POLLUTION- ALIEN SPECIES- BUILDING OF RESERVOIRS (DAMS)- MINING / FACTORIES