Aquatic Ecosystems
Watersheds
All fresh water on Earth – whether it is surface water such as lakes, rivers, streams, and ocean, or underground water –
is part of a watershed. A watershed is an area of land that drains into a body of water. Watersheds are also called
drainage basins.
When water falls on land, whatever water does not evaporate either filters into water that is under the ground or flows
downhill. Water that does not filter into the ground or evaporate but instead flows across the earth’s surface is called
run-off.
The area of land within a watershed can be small or large. Within large watersheds, there are many smaller ones. For
example, every stream is a part of a large watershed. A stream may merge with other small streams and these streams
may join larger rivers and those large rivers merge into major waterways.
A watershed includes land as well as water. Each watershed has a variety of habitats. These range from the bodies of
water themselves to forests, meadows, and farms. Cities, towns and villages are also a part of watersheds. This means
that the activities that occur on land or in water can affect the land or water around us.
Whether you live in urban or a rural area, wastes from your watershed eventually feed into a body of water, and they
will be carried to a different location. This location might be a place nearby or far away.
Ground Water
Water that enters soil and is not absorbed by plant roots filters through spaces in the soils and subsurface material until
it reaches rock layers through which it cannot longer penetrate. What that fills the spaces is called ground water.
The porous layer that becomes saturated with ground water is called an aquifer. An aquifer is an underground layer of
gravel, sand, or permeable rock that holds ground water, which can be extracted by wells. May of the farming
operations that feed the world depend on aquifers for their water. There are three basic types of aquifers: unconfined,
semi confined and confined.
An unconfined aquifer usually occurs near the surface, where water enters the aquifers from the land above it. The top
layer saturated with water is called the water table. The lower boundary of the aquifer is a layer of clay or rock that does
onto let water pass through it. Unconfined aquifers are replenished (recharged) mainly by rain that falls on the ground
directly above the aquifer and filters through the layers below.
A confined aquifer is bounded on both the top and bottom by impermeable rock layers. If water can pass in and out of
the confining layers, the aquifer is referred to as semi confined. Both confined and semi confined aquifers are mainly
recharged by rain and surface water that may come from an area many kilometers from where the aquifer is tapped for
use. If the recharged area is higher than where the aquifer is tapped, water will flow up the pip until it reaches the same
elevation as the recharge area. Such wells are called artesian wells. If the recharge zone is above the elevation of the top
of the well pipe, it is called a flowing artesian well, because water will flow from the pipe.
Salt Water Biomes
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Global ocean – one single body of water, it has been divided into 4 large areas:
o Atlantic, Pacific, Artic and Indian
Organism in each ocean are determined by the salinity
Major types of organisms
o Plankton
 Phytoplankton – algae (primary producers for aquatic biomes) – make food using
photosynthesis
 Zooplankton – primary and secondary consumers
 Ultraplankton – small photosynthetic bacteria
o Nekton – strong swimming consumers
 Fish, whales, turtles
o Benthos – bottom dwellers
 Oysters, lobsters, crabs, clams, worms,
o Decomposers – mostly bacteria
Types and numbers of organism in each areas are affected by
o Temperature, food, oxygen, light,
Costal Zones
o Warm, rich with nutrients, shallow water
o Home to many aquatic species
coastal wetlands
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areas covered with water for all or most of the year
o include – river mouths, inlets, bays, salt marshes and mangrove forests
o Very productive due to the high amounts of nutrients and the constant cycling (tides, rivers, etc.)
coral reefs
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large center of diversity
in warm waters of the tropics or subtropics
many organisms live in symbiotic relationships (polyps and algae)
estuaries
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where rivers meet the ocean
Mixture of freshwater and saltwater, as well as nutrients, pollutants, etc.
Fresh Water Biomes
Lakes
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Large bodies of standing water
Many fill from – precipitation, mountain streams, glaciers, runoff and streams
Oligotrophic lakes – poorly nourished (deep and steep banks)
Eutrophic Lakes – well nourished (shallow and turbid water)
o Can have nutrients supplied by agricultural runoff called cultural eutrophication
Mesotrophic lakes – between the 2 extremes
Rivers
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Flow downhill to ocean
Streams
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Surface water that does not sink into the ground
A watershed (drainage basin) delivers runoff, sediment and dissolved particles to a stream
Streams merge to form rivers
Wetlands
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Covered with water for all of most of the time
Include:
o marshes (dominated by grasses and reeds, few trees)
o Swamps (dominated by trees)
o Prairie potholes (depression carved out by glaciers)
o Floodplains (water when there is heavy rains and floods)
Aquatic Life zones – start of water to the ocean
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Source Zone
o Glaciers, waterfalls, rapids
Transition Zone
o Tributary
o Floodplain
Floodplain Zone
o Oxbow lake
o Salt marshes
o Deltas
Water Resources and Water Pollution
Fish and Seafood are Major Sources of Protein
We currently harvest about 95 million tonnes of wild fish and seafood a year (seafood includes lobster, shrimp, crab,
clams, and scallops). Of this amount, we each about two thirds directly, the remaining third is used as feed in
aquaculture operations. Aquaculture is commonly called “fish farming”, and it is the breeding, raising and harvesting of
animals in specially designed aquatic environments.
Fish and seafood are the main sources of animal protein for about 1.5billion people in developing countries. In
developing counties, people eat mainly locally caught fish. In developed countries, industrial–scale fishing provides most
fish and seafood.
Overfishing of Marine Fisheries
The United Nations estimates that 70% of the world’s marine fisheries are being overexploited or are in danger of being
overexploited. In marine ecosystems in which efforts were made to limit overfishing, they found improvement – a sign
that the efforts were made to limit overfishing, they found improvements.
Effects of Overexploitation on Sustainability
Because wild fish in the open ocean are a shared resource belonging to no single country, the competition to catch them
is high. Rising numbers of boats, along with more efficient technology, allow for the exploitation of a shrinking resource.
Boats as big as ocean liners travel thousands of kilometers, using global positioning equipment (GPS), sonar, spotter
planes, and other technology to locate and catch large numbers of fish and seafood. This helps meet the growing
demand of these sources of protein.
Different fishing methods
Longline fishing boats set up cables to 130km long
hooks every 2m to catch fish such as tuna, halibut,
swordfish. In the process, longlines catches
unintended animals such as sea birds, turtles, sharks,
dolphins. These unintended catches (called by-catch)
significant effects on local populations as well as
endanger species.
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Trawlers drag heavy nets across the ocean bottom to catch fish
and seafood, including cod, flounder, shrimp and scallops. As the
heavy net is drug across the ocean floor, it damages large areas of
habitat. Organisms that live on the ocean floor, such as corals,
sponges, and other fish, are killed. As well, clouds of sediment
stirred up from the enormous net remain in the water long after
the trawler is gone.
Pots and Traps are wire or wooden cages use to catch
as crabs, shrimp, and lobster, as well fish such as cod and
bass. Pots and traps are set out along the bottom of the
usually attached to a line with floating buoys at the
catch includes small-sized individuals of the target
Habitat damage can occur when pots or traps are
along the bottom when harvested. Traps that are
still trap fish and seafood and can lead to increased
a given area.
seafood such
Chilean sea
ocean –
surface. Byspecies.
dragged
abandoned
death rates in
Harvesting Fish and Seafood Sustainably
There are several methods to harvest wild-caught fish that have low rates of by-catch and minimal impact on the
environment. For example, fish that feed near the surface in school, including herring anchovies, and mackerel, are
caught in purse seines. A spotter plane spots the school of fish and then the fishing boat traps them in a large circular
net called a purse seine. By-catch rates are low, and since the nets do not touch the bottom, no damage occurs.
Sustainable Aquaculture
Aquaculture in land-based ponds or warehouses can reduce many of the problems associated with aquaculture pens in
marine and freshwater ecosystems. This is especially true when raising herbivorous fish, such as catfish, carp, or tilapia,
which consumes less feed than do carnivorous species.
One ecologically balanced system uses four carp species that feed at different levels of the food chain. The grass carp
feeds largely on vegetation, while the common carp is a bottom feeder. It feeds on decomposing material that settle on
the bottom. Silver carp and bighead carp are filter feeders that eat plankton from the water. Aquaculture wastes such as
manure, dead worms, and rice straw are used to fertilize ponds and encourage algal growth. This integrated Polyculture
system typically boosts fish yields by 50% or more per hectare compared to monoculture systems.
Another system integrates agriculture and aquaculture more closely. In china, certain species of fish are raised in rice
paddies. These fish help fight rice pests (like the golden snail by consuming them). This system of rice-fish farming
increases the yields of rice and provides extra income to farmers when they sell the fish
Aquaculture
Freshwater
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Irreplaceable resource that is not well managed
Most is not available – in ice form
Groundwater
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Valuable source of water
Located in the water table or lower down – aquifers
Replenishes by precipitation or by stream and rivers
Surface water
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From precipitation and snowmelt
Moves to lakes, streams, rivers, wetlands and finally to the ocean
Increase Water Supplies
Withdrawing Groundwater
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Advantages
o Can be used
o Available year round
o Renewable if not over pumped or contaminated
o No evaporation loss
Disadvantages
o Aquifer depletion
o Sinking of land due to over pumping
o Reduced water flows into surface water
o Increase cost and contamination from deeper wells
o Reduce unnecessary waste of water
Building Dams
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Stores water to be released later
Advantages
o Provides irrigation water
o Provides water for drinking
o Used for recreation and fishing
o Can produce electricity
o Reduces flooding
Disadvantages
o Destroys forests and cropland
o Loss of water due to evaporation
o Loss of sediment downstream – nutrients
o Could fail and cause devastating flooding
o Disrupts migrant and spawning of some fish
Converting salt water to fresh water
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Desalination – removes salt and minerals from ocean water via reverse osmosis (high pressure to force salt
water through a membrane filter small enough to remove salt)
Problems
o High cost
o Pumping of water and the sterilization of the water with chemicals kills algae and therefore kills marine
life
o Produces salty wastewater which is dumped into coastal water increasing the salinity of the water and
damages ecosystems and threatened aquatic life
Using Water More Sustainably
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Reducing water waste
Higher water costs to encourage water conservation
Redesign manufacturing process to use less water
Recycle water
Landscape yards with plants that require little water
Use drip irrigation
Fix water leaks
Use water meters
Use composting toilets
Use water saving – toilets, water heads, front loading washers
Collect and reused household water to irrigate lawns
Cut water waste in irrigation
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Line canals bringing water to irrigation ditches
Irrigate at night to reduce evaporation
Monitor soil moisture and add water only when needed
Grow several crops – polyculture
Encourage organic farming
Irrigate with treated urban waste water
Use different irrigation system
o Gravity flow
o Drip irrigation
o Center Pivot
Reduce the Threat of Flooding
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Floodplain – streams overflow their natural channel and spill into adjacent areas. They are usually wetlands that
provide natural flood and erosion control and to recharge groundwater. However people have populated and
taken over floodplains by cultivating them, living in them, over grazing and deforestation. Causing flooding to
occur and water quality to decrease.
Prevention
o Preserve forests and wetlands
o Restore wetlands
o Tax development on flood plains
o Only allow floodplains to be used for recharging aquifers, sustainable agriculture and forestry
Control
o Straighten and deepen streams
o Build levees or floodwalls along streams
o Build dams
Water Pollution
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Water pollution – is any change in water quality that harms humans or other living things
Point Sources
o Leakage of pollutions from a specific source through pipes, ditches or sewer lines into water
o Easy to find and regulate
Nonpoint Sources
o Broad, diffuse areas
o Runoff from crop land, livestock
Natural Cleansing
o Bacteria naturally clean and remove low amounts of pollution – but not when it is overloaded
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Oxygen Sag curve
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Lakes and Reservoirs
o They are at high risk for water pollution – lack of flowing water
o Cultural Eutrophication – accelerated eutrophication by human means
o Prevention or Reduction
 Treat water before it enters lakes
 Ban the use of phosphates from household detergents and other cleaning agents
Groundwater
o at risk of pollution due to the lack of flowing water
o Prevention
 Find substitutes for Toxic chemicals
 Install monitoring systems near landfills and underground tanks
 Ban hazardous waste disposal in landfills
o Cleanup
 Pump to surface, clean and return to aquifers
 Inject microorganisms to clean up contamination
 Pump nanoparticles of inorganic compounds to remove pollutants
Ocean pollution o Prevention
 Reduce input of toxic pollutants
 Separate sewage and storm lines
 Ban dumping of wastes of ships in coastal waters
 Regulate coastal development, oil drilling and oil shipping
 Require double hulls of oil tankers
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Cleanup
 Improve oil spill cleanup technology
 Use nanoparticles on sewage an oil spills
 Require secondary treatment of coastal sewage
 Use wetlands, and other wetlands to treat sewage
Sewage Treatment
o Primary sewer treatment – physical process using screens and tanks to remove large floating objects a
others to settle out
o Secondary Sewer Treatment – biological process to remove organic wastes
o Before released it undergoes bleaching – to kill disease carrying bacteria and some viruses
o Alternatives
 Businesses and industries to remove hazardous wastes from water
 Composting toilets
Reducing water pollution
o Fertilize with organic fertilizer instead of inorganic
o Minimize the use of chemicals – pesticides
o Prevent yard waste from entering storm drains
o Don’t use water fresheners in toilets
o Do not flush unwanted medicines down the toilet
o Do not pour pesticides, paints, solvents, oils, antifreeze, or other products down the drain or on the
ground