Aquatic Ecology II

Thermal Stratification

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.– This equalizes the temperature at all

depths.– 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 Wetlands

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.

Figure 6-18

Freshwater Inland Wetlands: Vital Sponges

Filter and degrade pollutants. Reduce flooding and erosion by

absorbing slowly releasing overflows. Help replenish stream flows during dry

periods. Help recharge ground aquifers. Provide economic resources and

recreation.

Marshes

• An area of temporarily flooded, often silty land beside a river or lake. Only green herbacious plants.

Swamps

• A lowland region permanently covered with water. Have woody plants (Trees)

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.• Flood Control along rivers

Liquidity: The Value of Wetlands

• https://youtu.be/zLymJKYOWzQ

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.

Question of the Day

• Defining characteristics of a wetland involve which of the following.

(I. Hydrology, II. Soil type, III. Species composition)• I only• II only• I and II only• II and III only• I, II, and III only

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.

Water & The 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).

Two categories of aquifers• Confined or artesian = water-bearing,

porous rocks are trapped between layers of less permeable substrate (i.e., clay) – Is under a lot of pressure

• Unconfined aquifer = no upper layer to confine it– Readily recharged by surface water

• Groundwater becomes surface water through springs or human-drilled wells

• Groundwater may be ancient: the average age is 1,400 years

A typical aquifer

Groundwater Problems

• These include pollution, salt, and draining too much.

Other Effects of Groundwater Overpumping

• Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater.

Figure 14-10

Groundwater Depletion: A Growing Problem

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

Areas of greatest aquifer depletion from groundwater overdraft in the continental U.S.

Figure 14-8

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.

Water Use & Water Managment

Water Usage

• Irrigation – watering crops• Industry – coolant (power plant)• Domestic and Municipal – drinking,

sewage, bathwater, dishwater & laundry

Water supplies houses, agriculture, and industry

• Proportions of these three types of use vary dramatically among nations– Arid countries use water for agriculture– Developed countries use water for

industry

Different types of water use

• Consumptive use = water is removed from an aquifer or surface water body, and is not returned

• Non-consumptive use = does not remove, or only temporarily removes, water from an aquifer or surface water– Electricity generation at hydroelectric dams

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.

Fig. 14-13b, p. 317

Powerlines

Reservoir

Dam

PowerhouseIntake

Turbine

Benefits and drawbacks of dams

• Benefits:– Power generation– Emission reduction– Crop irrigation– Drinking water– Flood control– Shipping– New recreational

opportunities

• Drawbacks:– Habitat alteration– Fisheries declines– Population

displacement– Sediment capture– Disruption of

flooding– Risk of failure– Lost recreational

opportunities

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.– The dam will be 2 kilometers long.– The electric output will be that of 18 large coal-burning

or nuclear power plants.– It will facilitate ship travel reducing transportation

costs.– Dam will displace 1.2 million people.– 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.– 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.

– The Federal Energy Regulatory Commission has approved the removal of nearly 500 dams.

– 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

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).

Case Study: The Colorado Basin – an Overtapped

Resource• Lake Powell, is

the second largest reservoir in the U.S.

• It hosts one of the hydroelectric plants located on the Colorado River.

Figure 14-15

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.– About 85% of the wetlands have been

eliminated and roughly 50% of the local bird and mammal species have disappeared.

– 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.

Modern Marvels: Dams

https://www.youtube.com/watch?v=eoTKcsgUEj0&feature=share&list=PL7WxmjMiAYikNGKPUWeZxBNOhKsd8LxSo

Impact of Human Actions on Water

Question of the Day

• Negative environmental impacts associated with large scale hydroelectric projects has been demonstrated in which areas?

• James Bay, Quebec• Three Mile Island, Pennsylvania• Kissimmee River, Florida• Aral Seas, Former USSR

Question of the Day

Too Little Water

Examples

• 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).1964 1997

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.

Point and nonpoint source water pollution

• Point source water pollution = discrete locations of pollution– Factory or sewer pipes

• Nonpoint source water pollution = pollution from multiple cumulative inputs over a large area– Farms, cities, streets, neighborhoods

• The U.S. Clean Water Act– Addressed point sources – Targeted industrial discharge

• In the U.S., nonpoint sources have a greater impact on quality– Limit development on watershed land surrounding

reservoirs

Freshwater pollution sources

Indicators of water quality

• Scientists measure properties of water to characterize its quality– Biological indicators:

presence of fecal coliform bacteria and other disease-causing organisms

– Chemical indicators: pH, nutrient concentration, taste, odor, hardness, dissolved oxygen

– Physical indicators: turbidity, color, temperature

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.

Figure 6-16

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.– Oligotrophic (poorly nourished) lake:

Usually newly formed lake with small supply of plant nutrient input.

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

Effects of Plant Nutrients on Lakes:

Too Much of a Good Thing

• Cultural eutrophication:– 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.

Impacts of Human Activities on Freshwater Systems

• Dams, cities, farmlands, and filled-in wetlands alter and degrade freshwater habitats.– Dams, diversions and canals have

fragmented about 40% of the world’s 237 large rivers.

– Flood control levees and dikes alter and destroy aquatic habitats.

– Cities and farmlands add pollutants and excess plant nutrients to streams and rivers.

– Many inland wetlands have been drained or filled for agriculture or (sub)urban development.

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.

Inefficient irrigation wastes water• Today, 70% more water is withdrawn

for irrigation than in 1960– The amount of irrigated land has doubled– Crop yields can double

Most irrigation is highly inefficient

• Only 45% of water is absorbed by crops via “flood and furrow” irrigation

• Overirrigation leads to waterlogging, salinization, and lost farming income

• Most national governments subsidize irrigation

• Water mining = withdrawing water faster than it can be replenished

Your Yard Is Evil

• https://www.youtube.com/watch?v=-enGOMQgdvg&feature=share&list=PL7WxmjMiAYikNGKPUWeZxBNOhKsd8LxSo

Question of the Day

• All of the following are commonly used to deal with the side effects of eutrophication in lakes EXCEPT

– applying herbicides to kill nuisance plants– dredging out lakes to deepen them– pumping oxygen into the lowest layers of water– introducing insects that eat certain nuisance plants– adding nitrates

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?).

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.

Possible Solutions for Water Use

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.

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.– Distillation: heating saltwater until it evaporates,

leaves behind water in solid form.– Reverse osmosis: uses high pressure to force

saltwater through a membrane filter.

DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND

GIANT BAGGIES• Seeding clouds with tiny particles of

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

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.– It allows 80% of water to reach crop.– Has reduced depletion of Ogallala aquifer in

Texas High Plains by 30%.

Fig. 14-18, p. 325

Center pivot

Drip irrigation

Gravity flow(efficiency 60% and

80% with surge valves)

Above- or below-ground pipes or tubes deliver water to individual plant roots.

Water usually comes from an aqueduct system or a nearby river.

(efficiency 90–95%)

(efficiency 80%–95%)

Water usually pumped from underground and sprayed from mobile boom with sprinklers.

Legislative efforts reduce pollution

• Federal Water Pollution Control Act (1972)– Renamed the Clean Water Act in 1977– Illegal to discharge pollution without a permit– Standards for industrial wastewater– Funded sewage treatment plants

• Because of legislation, the situation is much better than it was

• Other nations have also reduced pollution

Water 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

Treating wastewater• Wastewater = water that has been used by

people in some way– Sewage, showers, sinks, manufacturing, storm

water runoff

• Septic systems = the most popular method of wastewater disposal in rural areas– Underground septic tanks separate solids and oils

from wastewater– The water drains into a drain field, where

microbes decompose the water– Solid waste needs to be periodically pumped and

landfilled

Dirty Jobs: The Honey Pot

• https://www.youtube.com/watch?v=NXgoUpbgo68&feature=share&list=PL7WxmjMiAYikNGKPUWeZxBNOhKsd8LxSo

Municipal sewer systems• In populated areas, sewer systems carry

wastewater – Physical, chemical, and biological water treatment

• Primary treatment = the physical removal of contaminants in settling tanks (clarifiers)

• Secondary treatment = water is stirred and aerated so aerobic bacteria degrade organic pollutants– Water treated with chlorine is piped into rivers or

the ocean– Some reclaimed water is used for irrigation,

lawns, or industry

A typical wastewater treatment facility

END