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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.
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 is consistent around the clock due to an increase in wind action creating waves. Lake Georgetown
Zones of a Lake Benthic Zone Littoral ZoneLimnetic 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, free- floating 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.