Aquatic Ecology Notes

Chapter Overview Questions What are the basic types of aquatic life zones and what factors influence the

kinds of life they contain? What are the major types of freshwater life zones, and how do human activities

affect them? What do we know about aquatic biodiversity, and what is its economic and

ecological importance? How are human activities affecting aquatic biodiversity? How can we manage and sustain the world’s marine fisheries? How can we protect, sustain, and restore wetlands? How can we protect, sustain, and restore lakes, rivers, and freshwater fisheries? Why is water so important, how much freshwater is available to us, and how

much of it are we using? What causes freshwater shortages, and what can be done about this problem? What are the advantages and disadvantages of withdrawing groundwater? What are the advantages and disadvantages of using dams and reservoirs to

supply more water? What are the advantages and disadvantages of transferring large amounts of

water from one place to another? Can removing salt from seawater solve our water supply problems? How can we waste less water? How can we use the earth’s water more sustainably? What causes flooding, and what can we do about it?

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Water keeps us alive, moderates climate, sculpts the land, removes and dilutes

wastes and pollutants, and moves continually through the hydrologic cycle. Only about 0.02% of the earth’s water supply is available to us as liquid

freshwater. Comparison of population sizes and shares of the world’s freshwater among the

continents.

Some precipitation infiltrates the ground and is stored in soil and rock (groundwater).

Water that does not sink into the ground or evaporate into the air runs off (surface runoff) into bodies of water.

The land from which the surface water drains into a body of water is called its watershed or drainage basin.

We currently use more than half of the world’s reliable runoff of surface water and could be using 70-90% by 2025.

About 70% of the water we withdraw from rivers, lakes, and aquifers is not returned to these sources.

Irrigation is the biggest user of water (70%), followed by industries (20%) and cities and residences (10%).

Salinity The saltiness.

Niches: What Kinds of Organisms Live in Aquatic Life Zones? Aquatic systems contain floating, drifting, swimming, bottom-dwelling, and

decomposer organisms.o Plankton: important group of weakly swimming, free-floating biota.

Phytoplankton (plant), Zooplankton (animal), Ultraplankton (photosynthetic bacteria)

o Necton: fish, turtles, whales.o Benthos: bottom dwellers (barnacles, oysters).o Decomposers: breakdown organic compounds (mostly bacteria).

Phytoplankton Description – small drifting plants Niche – they are producers that support most aquatic food chains Example – cyanobacteria & many types of algae

Zooplankton Description – herbivores that feed on phytoplankton or other zooplankton Niche – food stock for larger consumers Example – krill; small crustaceans

Nekton Description – larger, strong-swimming consumers Niche – top consumers in the aquatic ecosystem Example – fish, turtles, and whales

Benthos Description – bottom-dwelling creatures Niche – primary consumers, decomposers Example – barnacles, oysters, and lobsters

Freshwater Ecosystems: FRESHWATER LIFE ZONES

Freshwater life zones include:o Standing (lentic) water such as lakes, ponds, and inland wetlands.o Flowing (lotic) systems such as streams and rivers.

Flowing Water Ecosystems Because of different environmental conditions in each zone, a river is a system of

different ecosystems.

Freshwater Streams and Rivers: From the Mountains to the Oceans Water flowing from mountains to the sea creates different aquatic conditions and

habitats.Headwater Stream Characteristics

A narrow zone of cold, clear water that rushes over waterfalls and rapids. Large amounts of oxygen are present. Fish are also present. Ex. trout.

Downstream Characteristics Slower-moving water, less oxygen, warmer temperatures, and lots of algae and

cyanobacteria.

Energy Source Gravity

Standing Water Ecosystems Lakes, ponds, etc.

Life in Layers Life in most aquatic systems is found in surface, middle, and bottom layers. Temperature, access to sunlight for photosynthesis, dissolved oxygen content,

nutrient availability changes with depth. Euphotic zone (upper layer in deep water habitats): sunlight can penetrate.

Lakes: Water-Filled Depressions Lakes are large natural bodies of standing freshwater formed from precipitation,

runoff, and groundwater seepage consisting of:o Littoral zone (near shore, shallow, with rooted plants).o Limnetic zone (open, offshore area, sunlit).o Profundal zone (deep, open water, too dark for photosynthesis).o Benthic zone (bottom of lake, nourished by dead matter).

Littoral Zone A shallow area near the shore, to the depth at which rooted plants stop growing.

Ex. frogs, snails, insects, fish, cattails, and water lilies.

Limnetic Zone Open, sunlit water that extends to the depth penetrated by sunlight.

Profundal Zone Deep, open water where it is too dark

for photosynthesis.

Thermal Stratification Lakes: Water-Filled Depressions

Definition The temperature difference in deep lakes

where there are warm summers and cold winters.Lakes: Water-Filled Depressions

During summer and winter in deep temperate zone lakes the become stratified into temperature layers and will overturn.

o This equalizes the temperature at all depths.o Oxygen is brought from the surface to the lake bottom and nutrients from

the bottom are brought to the top.Causes

During the summer, lakes become stratified into different temperature layers that resist mixing because summer sunlight warms surface waters, making them less dense.

Thermocline The middle layer that acts as a

barrier to the transfer of nutrients and dissolved oxygen.

Fall Turnover As the temperatures begin to

drop, the surface layer becomes more dense, and it sinks to the bottom. This mixing brings nutrients from the bottom up to the surface and sends oxygen to the bottom.

Spring Turnover As top water warms and ice melts, it sinks through and below the cooler, less

dense water, sending oxygen down and nutrients up.

Freshwater Inland Wetlands: Vital Sponges Inland wetlands act like natural sponges that absorb and store excess water from

storms and provide a variety of wildlife habitats.

Marshes An area of temporarily flooded, often silty land beside a river or lake.

Swamps A lowland region permanently covered with water.

Hardwood Bottomland Forest An area down by a river or stream where lots of hardwoods, like oaks, grow.

Prairie Potholes These are depressions that hold water out on the prairie, especially up north in

Canada. It is a very good duck habitat.

Peat Moss Bog A wet area that over time fills in (the last stage of succession is peat moss). It

can be very deep. In Ireland, they burn this for wood.

Importance of freshwater wetlands They filter & purify water. Habitat for many animals and plants.

Historical Aspects Developers and farmers want Congress to revise the definition of wetlands. This

would make 60-75% of all wetlands unavailable for protection. The Audubon Society estimates that wetlands provide water quality protection worth $1.6 billion per year, and they say if that wetlands are destroyed, the U.S. would spend $7.7 billion to $31 billion per year in additional flood-control costs.

Estuaries

Definition A partially enclosed area of coastal water where sea water mixes with

freshwater.

Salt Marshes The ground here is saturated with water and there is little oxygen, so decay takes

place slowly. It has a surface inlet and outlet, and contains many invertebrates. It is also the breeding ground for many ocean animals. Ex. crabs and shellfish.

Mangrove Forests These are along warm, tropical coasts where there is too much silt for coral reefs

to grow. It is dominated by salt-tolerant trees called mangroves (55 different species exist). It also helps to protect the coastline from erosion and provides a breeding nursery for some 2000 species of fish, invertebrates, and plants.

Importance of Estuaries Just one acre of estuary provides $75,000 worth of free waste treatment, and has

a value of about $83,000 when recreation and fish for food are included.

Prime Kansas farmland has a top value of $1,200 and an annual production value of $600.

The Everglades Southern Florida to the Keys

Case Study: Restoring the Florida Everglades The world’s largest ecological restoration project involves trying to undo some of

the damage inflicted on the Everglades by human activities.o 90% of park’s wading birds have vanished.o Other vertebrate populations down 75-95%.o Large volumes of water that once flowed through the park have been

diverted for crops and cities.o Runoff has caused noxious algal blooms.

Problems As Miami develops, it encroaches on everglades. Plus, it prompts people vs.

wildlife. It is freshwater and local areas are draining it.

Restoring the Florida Everglades The project has been attempting to restore the Everglades and Florida water

supplies.

Restoration Build huge aqueduct, or find other sources of fresh water an protect it federally

under endangered species act, etc.

The Water Resource:

Importance Leonardo da Vinci said that “Water is the driver of nature.” Without water, the

other nutrient cycles would not exist in their present forms, and current forms of life on earth could not exist.

Hydrogen Bonds: Attraction Between Molecules The strong forces of attraction between molecules of water.

Heat Capacity Water changes temp very slowly because it can store heat. This protects living

organisms from the shock of abrupt temperature changes.

Heat of Vaporization The temperature at which water turns to vapor.

Universal Solvent

Water can dissolve a wide variety of compounds. This means it can easily become polluted by water-soluble wastes.

Expansion When Frozen Ice has a lower density than liquid water. Thus, ice floats on water.

Hydrologic Cycle: Surface Water Examples – streams, rivers, and lakes Source – precipitation Watershed – Ex. small streams larger streams rivers sea

Groundwater Aquifers–porous rock w/ water flowing through Water Table – the level of earth’s land crust to which the aquifer is filled Renewability – the circulation rate of groundwater is slow (300 to 4,600 years).

Water Usage Irrigation – watering crops Industry – coolant (power plant) Domestic and Municipal – drinking, sewage, bathwater, dishwater & laundry

Problems

Too Much Water Problems include flooding, pollution of water supply, and sewage seeping into

the ground. Heavy rainfall, rapid snowmelt, removal of vegetation, and destruction of

wetlands cause flooding. Floodplains, which usually include highly productive wetlands, help provide

natural flood and erosion control, maintain high water quality, and recharge groundwater.

To minimize floods, rivers have been narrowed with levees and walls, and dammed to store water.

Comparison of St. Louis, Missouri under normal conditions (1988) and after severe flooding (1993).

Human activities have contributed to flood deaths and damages.

Examples

Too Little Water: Examples include drought and expanding deserts.

Overdrawing Surface Water Lake levels drop, recreation use drops, fisheries drop, and salinization occurs.

Ex. Soviet Union (Aral Sea); the inland sea drained the river that fed into it. Now it’s a huge disaster (read pg. 322 in text).

Case Study: The Aral Sea Disaster Diverting water from the Aral Sea and its two feeder rivers mostly for irrigation

has created a major ecological, economic, and health disaster.o About 85% of the wetlands have been eliminated and roughly 50% of the

local bird and mammal species have disappeared.o Since 1961, the sea’s salinity has tripled and the water has dropped by 22

meters most likely causing 20 of the 24 native fish species to go extinct.

Aquifer Depletion This harms endangered species, and salt water can seep in.

Salinization of Irrigated Soil Water is poured onto soil and evaporates. Over time, as this is repeated, nothing

will grow there anymore.

U.S. Water Problems Surface Water Problems The polluted Mississippi River (non-source point pollution) has too much

phosphorus. In the Eerie Canal, which connects the ocean to the Great Lakes, lampreys

came in and depleted the fish. The zebra mollusk is also a problem in the Great Lakes.

Effects of Plant Nutrients on Lakes: Too Much of a Good Thing Plant nutrients from a lake’s environment affect the types and numbers of

organisms it can support. Plant nutrients from a lake’s environment affect the types and numbers of

organisms it can support.

o Oligotrophic (poorly nourished) lake: Usually newly formed lake with small supply of plant nutrient input.

o Eutrophic (well nourished) lake: Over time, sediment, organic material, and inorganic nutrients wash into lakes causing excessive plant growth.

Cultural eutrophication:o Human inputs of nutrients from the atmosphere and urban and agricultural

areas can accelerate the eutrophication process.

Mono Lake (like the Dead Sea) This has a huge salt concentration due to man’s draining.

Colorado River Basin These are dams & reservoirs that feed from the Colorado River all the way to

San Diego, LA, Palm Springs, Phoenix & Mexico. So far has worked because they haven’t withdrawn their full allocations. See pg306.

The area drained by this basin is equal to more than one-twelfth of the land area of the lower 48 states.

Case Study: The Colorado Basin – an Overtapped Resource The Colorado River has so many dams and withdrawals that it often does not

reach the ocean. 14 major dams and reservoirs, and canals. Water is mostly used in desert area of the U.S. Provides electricity from hydroelectric plants for 30 million people (1/10th of the

U.S. population). Lake Powell, is the second largest reservoir in the U.S. It hosts one of the hydroelectric plants located on the Colorado River.

Groundwater Problems These include pollution, salt, and draining too much. Other Effects of Groundwater Over-pumping Sinkholes form when the roof of an underground cavern collapses after being

drained of groundwater.Groundwater Depletion: A Growing Problem

The Ogallala, the world’s largest aquifer, is most of the red area in the center (Midwest).

Ogallala Aquifer This is the world’s largest known aquifer, and fuels agricultural regions in the

U.S. It extends from South Dakota to Texas. It’s essentially a non-renewable aquifer from the last ice age with an extremely slow recharge rate. In some cases, water is pumped out 8 to 10 times faster than it is renewed. Northern states will still have ample supplies, but for the south it’s getting thinner. It is estimated that ¼ of the aquifer will be depleted by 2020.

Impacts of Human Activities on Freshwater Systems Dams, cities, farmlands, and filled-in wetlands alter and degrade freshwater

habitats.o Dams, diversions and canals have fragmented about 40% of the world’s

237 large rivers.o Flood control levees and dikes alter and destroy aquatic habitats.o Cities and farmlands add pollutants and excess plant nutrients to streams

and rivers.o Many inland wetlands have been drained or filled for agriculture or

(sub)urban development.

Core Case Study: A Biological Roller Coaster Ride in Lake Victoria Lake Victoria has lost their endemic fish species to large introduced predatory

fish. Reasons for Lake Victoria’s loss of biodiversity:

o Introduction of Nile perch.o Lake experienced algal blooms from nutrient runoff.o Invasion of water hyacinth has blocked sunlight and deprived oxygen.o Nile perch is in decline because it has eaten its own food supply.

Stable Runoff As water runs off from rain, it’s supposed to get into rivers, and finally off to the

sea. But when we dam rivers, less goes to the ocean, meaning the brackish water (where the river hits the ocean) becomes more salty. This is the breeding ground for many fish and invertebrates. This harms the ecology of the area.

Drinking Water Problems

Coliform Bacteria The W.H.O. recommends there be zero colonies of bacteria per 100ml of

drinking water and 200 colonies per 100ml of swimming water. The average human excretes 2 billion organisms per day (see how easily untreated sewage can contaminate water?).

Oxygen Demanding Wastes These are organic wastes that can be decomposed by aerobic bacteria (causes

lack of oxygen). Fish die as a result of a lack of oxygen.

Water-Soluble Inorganic Chemicals These include acids, salts, mercury, and lead. They make water unfit to drink.

Organic Material These include oil, gas, plastics, pesticides, and detergents.

Population Growth Problems include over-drawing fresh water, pollution, and over-building so that

water can’t seep into the ground.

Sharing Water Resources There are water wars out west. California bought the water from the Colorado

River, but Arizona wants it. Who owns it? The same thing is happening in Texas. More water rights are sold than the actual amount of water. How do you share water? This is a problem all over the world.

Dams and Reservoirs Description: A dammed stream that can capture & store water from rain &

melted snow. Benefits: Hydroelectric power; provides water to towns; recreation; controls

floods downstream Problems: Reduces downstream flow; prevents water from reaching the sea

(Colorado River) devastates fish life; reduces biodiversity.

USING DAMS AND RESERVOIRS TO SUPPLY MORE WATER Large dams and reservoirs can produce cheap electricity, reduce downstream

flooding, and provide year-round water for irrigating cropland, but they also displace people and disrupt aquatic systems.

Case Study: China’s Three Gorges Dam There is a debate over whether the advantages of the world’s largest dam and

reservoir will outweigh its disadvantages.o The dam will be 2 kilometers long.o The electric output will be that of 18 large coal-burning or nuclear power

plants.o It will facilitate ship travel reducing transportation costs.o Dam will displace 1.2 million people.o Dam is built over seismatic fault and already has small cracks.

Dam Removal Some dams are being removed for ecological reasons and because they have

outlived their usefulness.o In 1998 the U.S. Army Corps of Engineers announced that it would no

longer build large dams and diversion projects in the U.S.o The Federal Energy Regulatory Commission has approved the removal of

nearly 500 dams.o Removing dams can reestablish ecosystems, but can also re-release

toxicants into the environment.

Water Diversion Description: Damming a river to control where the water flows Benefits: Keeps water where we want it- cities!

Problems: Drains wetlands, destroys land

Desalinization Description: Removing salt from salt water Benefits: Freshwater Problems: Uses lots of energy; costs 3-5X’s more money; what do we do with the

salt?

DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIES

Removing salt from seawater by current methods is expensive and produces large amounts of salty wastewater that must be disposed of safely.

o Distillation: heating saltwater until it evaporates, leaves behind water in solid form.

o Reverse osmosis: uses high pressure to force saltwater through a membrane filter.

Seeding clouds with tiny particles of chemicals to increase rainfall towing icebergs or huge bags filled with freshwater to dry coastal areas have all been proposed but are unlikely to provide significant amounts of freshwater.

Harvesting Icebergs Description: Towing massive icebergs to arid coastal areas (S. California; Saudi

Arabia) Benefits: freshwater Problems: Technology not available; costs too high; raise temperatures around

the earth.

INCREASING WATER SUPPLIES BY WASTING LESS WATER Sixty percent of the world’s irrigation water is currently wasted, but improved

irrigation techniques could cut this waste to 5-20%. Center-pivot, low pressure sprinklers sprays water directly onto crop.

o It allows 80% of water to reach crop.o Has reduced depletion of Ogallala aquifer in Texas High Plains by 30%.

Conservation Description: Saving the water we have Methods: recycling; conserving at home; xeriscaping; fix leaks Benefits: Saves money; Saves Wildlife Problems: bothersome to people; lack of caring; laziness

Fishing Problems & Techniques The major decline in the worldwide catch of fish since 1990 is because of over-

fishing. By-catch- fish or animals that were not meant to be caught.

Overfishing and Extinction: Gone Fishing, Fish Gone

About 75% of the world’s commercially valuable marine fish species are over fished or fished near their sustainable limits.

o Big fish are becoming scarce.o Smaller fish are next.o We throw away 30% of the fish we catch.o We needlessly kill sea mammals and birds.

Purse Seines A large purse-like net is put into the ocean and is then closed like a drawstring

purse to trap the fish. Tuna is a fish typically caught in purse seines Dolphins are a by-catch of purse seines

Long-line fishing Lines are put out that can be up to 80 miles long w/ thousands of baited hooks on

them. These are left out free-floating for days and then the boat comes back and picks them up.

Pilot whales, dolphins, sea turtles, and birds are by-catch of this technique.

Drift-net fishing Each net hangs as much as 50 feet below the surface and up to 34 miles long. Anything that comes into contact w/ these nearly invisible nets are entangled. This leads to overfishing Many unwanted fish and marine mammals, turtles and seabirds are caught.

HUMAN IMPACTS ON AQUATIC BIODIVERSITY Area of ocean before and after a trawler net, acting like a giant plow, scraped it.

Population Growth and Pollution Each year plastic items dumped from ships and left as litter on beaches threaten

marine life.