ENVIRON 102 Chapter 12, Mod 1-9: Chapter 12 (textbook) Modules 1 – 6, 8 – 9
10 May 2018
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Chapter 12 Water (Modules 1 – 6, 8 – 9)
12.1 Water World
The Global Water Budget: Water falling onto land may evaporate, percolate into groundwater, or flow in
streams to the sea.
(ydrologists: scientists who study Earth’s waters
Water is the third most abundant molecule in the atmosphere but only .% of Earth’s water is
in atmosphere
Water falling on land has 3 fates:
o (1) Evaporate back into atmosphere from land and plant surfaces
▪ Little less than / of Earth’s water
▪ Evapotranspiration s
o (2) Flow over land in streams and rivers
o (3) Percolate through soil and rock into underground aquifers
▪ Groundwater
Majority of Earth’s water exists in ice
Components of water budget vary from place to place
Water balance coefficient: general index of the availability of water in a particular region
o Rainfall – potential evaporation = water balance coefficient
o Ex: deserts can around between -200 to -300 cm while rain forests can exceed 400 cm
Watersheds: Scientists study a river’s drainage basin to measure water flow and evaporation.
Watersheds (aka drainage basins): area of land from which rainfall drains into a river or lake
o Separated from one another by mountain ridges and other divides
o Ideal for understanding water flows and budgets and human activities
o Come in many sizes
To understand flow of water in a watershed
o Rain gauges
o Monitor flow of streams and groundwater
Open watersheds: drained by rivers that eventually make their way into the sea
o Ex: Nile, Mississippi, Congo, and Amazon
Closed watersheds: inland basin that do not drain to the sea, often to inland lakes or seas
o Great Salt Lake, Lake Chad, and the Dead Sea
Case study: Mississippi River
o Total volume of rain falling on its watershed = area of watershed x average rainfall
o Includes flows from surface runoff and groundwater
o Pumping from aquifers
o Evapotranspiration = rain volume + groundwater pumping – river discharge
Factors that influence the flow of water
o Impermeable surfaces, shed water, and increase runoff
Human Water Use: Humans use over half of the water flowing in Earth’s streams.
Nonconsumptive uses: activities that use water and then return it to streams or aquifers
o Ex: generation of hydroelectric power and the disposal of wastewater in septic systems
Consumptive uses: activities in which much of the water is evaporated into the atmosphere and
are not returned to streams or aquifers
Human activities: industry, agricultural, and domestic
12.2 Streams
Stream Flow: The volume and speed of flowing water determine a stream’s structure.
Stream: all natural bodies of flowing water
o Stream can be more specifically referred to as a rill, a brook, a creek, or a river
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o Less than .% of Earth’s water
Streams are classified by stream order
o Stream order: number of streams feeding into them
o First-order stream flows from a single headwater
o Two first-order streams converge to form a second-order stream and so on
Force of gravity pulls streams downhill
o Speed of stream determined by gradient (slope) of land
o The faster the water, the more sediment is carried and the more erosion of rocks and
sediments
Perennial streams: flow all year round
Intermittent streams: flow only at certain times, such as only when it rains
Stream’s channel: waterway through which it normally flows
Floodplain: next to the channel, land that experiences period flooding
o Described in terms of time
o Ex: 100-year floodplain – area that is flooded once every 100 years
o Streams with low gradients often have very broad floodplains
Streams channels in wide floodplains often are bordered by levees
o Levees: embankments that are formed from sediments deposited during floods
Streams on broad, gently sloping floodplains flow in wide loops called meanders
Streams and rivers are constantly reshaped by erosion and deposition
Gradient flattens out as streams enter lakes or oceans
Delta: complicated array of channels that fan out
o Ex: Nile delta – an extremely fertile region
Stream Ecosystems: Streams influence ecosystem biodiversity and processes.
Lotic: ecosystems dominated by flowing fresh water – includes organisms that live in streams,
living on lands next to and beneath the stream
Food chains in streams
o Primary production stems from detritus
▪ Detritus: organism matter such as dead leaves and nutrient-rich soil that is washed
in from adjacent terrestrial ecosystems
o Planktonic algae is scarce in fast-flowing streams
o Planktonic algae is abundant where water is slower or halted by natural/human-built
barriers or where there is runoff containing nitrogen and phosphorus
▪ Can lead to eutrophication
o Three main ways for feeding for primary producers
▪ (1) Scrapers use rasping mouthparts to feed on algae attached to rocks
▪ (2) Shredders feed directly on leaves, small twigs, and other detritus
▪ (3) Filter feeders use gills or netlike structures to collect detritus
o Stream herbivores and detritus feeders are sensitive to changes in water chemistry and
sediment load
▪ Numbers used to evaluate stream pollution (high pollution – low numbers, vice
versa)
Riparian zone: region of transition between a stream and the surrounding terrestrial ecosystems
o Plants growing on the edge of stream must endure frequent flooding, saturated soils, and
low levels of soil oxygen
o The farther from the stream, the less flooding
▪ Water is drawn from shallow aquifers for plants
o Riparian vegetation and soils filter the runoff and groundwater coming into rivers
▪ Absorb excess nutrients from agricultural runoff
▪ Alleviate effects of flooding
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The hyporheic zone: region of saturated sediment next to a stream and immediately beneath it
o Shelters a variety of microorganisms and invertebrate animals
o Constant flow of stream water filters out organic matter and sediment – facilitates nutrient
cycles
o Organisms returns dissolved nutrients to the water
Human Use and Impacts: Humans have modified streams in order to minimize the risks of both floods and
water shortages.
River floodplains provide fertile agricultural lands, energy, transportation for commerce, and
water for industrial and residential use
Human management of floods and periods of low flow; pollution
Dams and diversions
o Dams control floods, store water, and generate electricity
o Store water for irrigation or for use during dry seasons
o Create lakes with little or no water movement accumulation of sediment reduce
capacity of lake to store water
o Streams leaving dams do not carry enough sediment to replace the sediments
o Fragment stream ecosystems
▪ )nterferes with organisms’ movements
o Increase total storage of water within watersheds and reduce flow downstream
▪ Affect ecosystems downstream
o Ex: Colorado River – much water is lost to seepage and evaporation in reservoirs
Channelization and artificial levees
o Built to control flow of water, prevent flooding, and make floodplains available for
agricultural and urban development
▪ May protect the lands adjacent to a particular part of a river
▪ Also increased the speed of the water flowing through the modified channel
o Artificial levees elevate stream banks to confine water to stream channels
o Channelization: river is dredged and straightened, usually involves removal of most
riparian vegetation
Pollution
o Point-source pollution: comes from a specific location such as an industrial facility or
municipal sewage treatment plant
o Non-point-source pollution: comes from a variety of activities occurring at different places
across landscapes
o Negative impact on biodiversity
▪ Filter-feeding animals are sensitive to pollutants, especially sediments that clog up
their gills
o US EPA encouraged state water managers to develop bioassessment criteria for streams
▪ Bioassessment: consists of surveys of aquatic diversity (vegetation and animals)
that are known to be sensitive to overall water quality
▪ Successful in all 50 states in the US
12.3 Lakes and Pools
Characteristics of Lakes and Ponds: In geologic time, most lakes have a short life span.
Lentic: ecosystems associated with lakes and ponds
Lakes: bodies of water that are fed by a stream ad have sa greater than 12.5 acres
Ponds: smaller (less then 12.5 acres) bodies of water
Formation of lakes
o (1) Movement of tectonic plates create basins that collect water
o (2) Result of erosion and deposition by glaciers
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 12 water (modules 1 6, 8 9) The global water budget: water falling onto land may evaporate, percolate into groundwater, or flow in streams to the sea. Water is the third most abundant molecule in the atmosphere but only (cid:882). (cid:882)(cid:882)(cid:883)% of earth"s water is: little less than (cid:884)/(cid:885) of earth"s water, (1) evaporate back into atmosphere from land and plant surfaces. Water falling on land has 3 fates: evapotranspiration s in atmosphere, (2) flow over land in streams and rivers, (3) percolate through soil and rock into underground aquifers, groundwater. Majority of earth"s water exists in ice. Components of water budget vary from place to place. Water balance coefficient: general index of the availability of water in a particular region: rainfall potential evaporation = water balance coefficient. Watersheds: scientists study a river"s drainage basin to measure water flow and evaporation: ex: deserts can around between -200 to -300 cm while rain forests can exceed 400 cm.
