Chapter 9
Lakes and Ponds
Chapter 9
Lakes and Ponds
I. General Facts
A. Freshwater lakes and ponds are classified
as lentic water, meaning they do not flow.
B. Most are the results of building dams
across streams and rivers. The largest
ones in Texas are called reservoirs.
C.Size ranges from less than an acre to over
millions of acres.
D.Sunlight and water depth determine a pond
or a lake.
E. Purpose
1. Human usage for drinking, electrical power
plants and flood reduction.
2. Agriculturally for watering crops and
livestock.
3. Recreationally for fishing and boating.
F. A large log jam on the Red River hundreds
of years ago resulted in the only naturally
formed lake in Texas……..Caddo Lake.
Caddo Lake
II. Pond or Lake
A. Ponds
1. Shallow bodies of water allowing
sunlight to reach the bottom of the pond
promoting plant growth.
2. Rooted plants hold soil together creating
clearer water, which inturn causes plants
to grow deeper.
3. Consistent water temperatures based on
air temperature changes.
4. Dissolved oxygen in a pond is based
on the combination of surface air and
water mixing and photosynthesis from
aquatic plants and phytoplankton.
5. Animals and aerobic decomposition of
detritus consistently consume the DO
causing the levels
to drop at night.
6. Cold, freshwater
holds more DO.
B. Lakes
1. Larger and deeper than ponds.
2. Usually created by dams.
3. Divided into zones based upon the
amount of sunlight they receive.
4. Dissolved oxygen
Lake
is consistent around Georgetown
the clock due to an
increase in wind
action creating
waves.
Littoral Zone
Zones of a Lake
Limnetic Zone
Benthic Zone
5. Zones of a Lake-are defined by light and
temperature differences.
a.
Littoral zone-the part of a lake that is
shallow enough to support rooted aquatic
plants, such as shoreline and islands.
b. Limnetic zone-the part of a lake that is too
deep to support rooted aquatic plants.
(Open-water zone)
c. Photic zone-the upper part of a lake
where enough light penetrates the water
to allow photosynthesis to occur.
i. Species of large and open water fish
spend much of their time in this zone
ii. Also called the euphotic zone.
d. Aphotic zone-the deep part of a lake
which doesn’t receive enough light to
support photosynthesis.
e. Benthic zone-the bottom substrate of
aquatic ecosystems, where bacteria and
other decomposers such as some worms
and larval stages of some insects feed on
dead organic matter.
f. Thermocline-the part of a lake’s water
column where water temperature
changes rapidly from warm to cold; the
layer of water in between a lake’s
epilimnion and hypolimnion.
(Remember: epi-above and hypo-below)
III. Ecosystems
A. In any aquatic environment
underwater plants and plankton
make up most of the food base
for entire ecosystems.
1. Starting with phytoplankton, the
photosynthesizing aquatic
organisms found in a lake’s
sunlit open-water photic
zone; the producers.
2. Zooplankton are tiny, freefloating animals like protozoa;
the primary consumers.
3. Plankton have a high
nutritional content and make up most of
the living stuff in a pond.
4. Like in all food webs, the secondary
consumers are next in line, this includes the
invertebrates and small fish. Some
organisms filter plankton from the water by
using specialized mouthparts and
adaptations to gills are called filter
feeders.
5. The top aquatic predators in lakes and
ponds are the various species of fish there,
even the ones humans catch.
B. The role of aquatic plants in an ecosystem
1. Aquatic plants spread out in beds or
clumps and attract a
variety of animal life.
2. Plants living entirely
underwater are called
submergent plants,
while emergent plants
have some of their parts
sticking out of the water.
3. Like terrestrial plants, aquatic plants
survival needs includes water, carbon
dioxide, sunlight, and nutrients such as
phosphorous and nitrogen.
4. Special adaptations help
plants thrive in their
underwater environment.
a. Waxy or slimy coatings
protect them from
drying out when water
levels are low.
b. Porous stems or leaves let them absorb
minerals directly from the water.
c. Some have leaves that float on the
surface
d. Some plants float entirely on the surface.
5. The greatest biodiversity of life in a lake
ecosystem is in the narrow band of aquatic
plants reaching out into the water from the
shoreline and islands, providing a habitat
for many species of fish.
6. Plants play an important role by helping to
maintain or improve water quality.
7. Plants can become a problem if overgrowth
occurs in their habitat.
C. Other organisms in the Food Web
1. Insect larva
a. Scrapers-grazers have special
mouthparts that act like a sharp scraper
blade used to remove algae growth on
the surface of plants and solid objects.
b. Collectors gather small bits of loose
and decaying materials using mouth
parts or by brushing up the bits using
fine hairs on their head or legs.
c. Shredders’ mouthparts are designed to
nibble off and grind up pieces of live
plants in the water or plant materials
that fall into the water.
d. Omnivorous insects eat both plant and
animal materials.
e. Predator insects catch and feed on live
animals.
f. Some aquatic insects are fast and large
enough to catch and feed on small fish
and tadpoles.
2. The final members in the food web are
fish and insect-eating land animals, in
particular birds, seeking out the insects
in the littoral zone.
IV. Pond Succession
A. The definition of pond succession is the
natural process by which sediment and
organic material gradually replace the
water volume of a pond ultimately resulting
in the area becoming dry land.
B. The basics are as water moves downhill
through a watershed, erosion occurs
depositing sediment into ponds.
C. Phases of succession
1. Phase One-as ponds age sediment and
organic matter is deposited on the pond
bottom.
2. Phase Two-ponds become smaller and
shallower over time. Submergent plant
growth is present.
3. Phase Three-as the pond bottom becomes
shallower, emergent plants fill the bottom
creating a wetland, later giving rise to a wet
meadow.
4. Phase Four-growth of grasses followed by
shrubs. Over time tree growth occurs.
D. Eutrophication
1. Surface water can also carry pollution into
the pond. Soil and plant nutrients such as
fertilizer are examples of pollutants.
2. Excessive nutrient input in a body of water
causes excessive plant and algae growth.
3. If excessive amounts of plants or algae die
all at once, it creates an unnaturally high
level of anaerobic decomposition using up
all the dissolved oxygen in the water.
4. If the process is extreme, some fish in the
pond may die from lack of oxygen.
5. It is important to maintain a healthy
watershed and protect our water. Using
plants as a buffer around a pond can filter
out pollutants and sediment before they
reach the pond. A plant buffer can improve
the health of a pond or lake, and extend its
life.
V. Lake tourism and fishing are good for Texas
A. Texas lakes provide water for fishing,
boating, swimming, skiing, windsurfing,
paddling, sailing, kiteboarding, and many
other fun activities.
B. Lake-related recreation is important to the
economies where lakes are located. Gasoline,
groceries, bait and many other items are
purchased from local businesses.