Freshwater Ecology Freshwater ecosystems are divided into two categories Lentic systems which include lakes, ponds, marshes, swamps and bogs Lotic systems which include rivers and streams

Oxbow Lakes These lakes are formed by meanders in rivers that flow over flood plains and low valleys. These snake-like loops are cut off from the rest of the river and form a long, narrow, crescent or U shaped lake.

Aquatic Ecosystems - Lentic Pond Lake Bog Swamp Marsh

Aquatic Definitions Bogs are peat lands, they develop in poorly drained areas. They are characterized by evergreen trees, shrubs and often blanketed with a carpet of sphagnum moss. A lakes is a body of water where depth of light penetration can vary from several inches to many feet in open water A pond is defined as a body of water where light penetrates to the bottom. Marshes are characterized by soft-stemmed herbaceous plants such as cattails and pickerelweed. Swamps are dominated by woody plants such as Red Maple, gums, ashes, cedars, firs and spruces.

Texas Lakes Oxbow lakes are commonly formed in the mature segments of Texas rivers. In the lower Rio Grande Valley, these oxbows are called “Resaca's”.

Texas Reservoirs Most of the major lakes in Texas are man-made lakes called “reservoirs”. Other small lakes are remnants of quarry and mining operations, or agricultural stock ponds. The closest thing to a “natural lake” in Texas is Caddo Lake.

Playa Lakes These lakes are usually small depressions in the lower parts of a desert basin sometimes filled with water. They are most often found in the western part of the state.

Succession Lakes and ponds go through a natural ageing process. Marshes, swamps and bogs are generally the mature stages.

Succession Over time sediments begin to fill in ponds and lakes As depth decreases the number of plants increase. Emergent plants move out from the shoreline areas. Eventually water tolerant shrubs, grasses, and other plants move into the area. If left undisturbed, grasses and shrubs will be replaced by larger trees and forests.

Lentic Environments The lentic environment has well defined boundaries; the shoreline The sides of the basin The surface water and bottom sediments It is divided into three major zones: Littoral zone Limnetic zone Profundal zone

Lentic Zones Profundal Zone

Littoral Zone – shallow vegetate areas

Littoral Zone Characterized as shallow shoreline area inhabited by plants Light penetrates to the bottom allowing for rooted plant growth Coarse sediment such as rocks, cobbles, pebbles, gravel or sand Inhabited by invertebrates and small fish Aquatic plants

Types of Aquatic Plants Emergent – rooted plants with lower portion submerged and growing near the shore Example: cattails, bulrush, sedges Floating – rooted plants (some free floating) with leaves floating on the surface Example: water lilies, water hyacinth, duckweed Submerged – rooted plants with nearly all leaves below the surface Example: Chara, Naja, coontail, and Hydrilla

Emergent Plants Arrowhead Cattail Bulrush Spike Rush Pickerel Weed Cattails Arrowhead Arrowhead Cattail Bulrush Spike Rush Pickerel Weed

Floating Plants Water Lily Salvinia Lotus Water Hyacinth Duckweed Water Lettuce

Submerged Plants Coontail Hydrilla Chara Elodea Naja Watermilfoil

Limnetic Zone – open water area

Limnetic Zone Open water of a pond or lake Characterized by the lack of rooted plants and limited light penetration Area normally inhabited by plankton and fish Photic zone – area of light penetration limited by color and amount of suspended solids and plankton in the water Pond – light penetrates to the bottom Lake – light penetration can vary from several inches to many feet in open water

Productivity Productivity is related to the amount of plants, animals, and nutrients (PAN) in the water Plant nutrients (nitrogen and phosphorus) in a lake are important in limiting growth of planktonic algae or other aquatic vegetation There are three major categories of lakes based on productivity. Oligotrophic Mesotrophic Eutrophic

Oligotrophic A body of water low in mineral nutrients Supports little life Low plant and plankton populations Little organic material in the sediments Low chlorophyll a levels

Mesotrophic Bodies of water with moderate amount of nutrients A transition from oligotrophic to eutrophic

Eutrophic Lakes, ponds, (streams and rivers) that are highly productive Large populations of plants and animals High levels of plant nutrients Water color – green and turbid High chlorophyll a levels

Ponds are shallower and smaller than lakes and have relativity uniform temperatures Lakes are generally deeper and have a layering of temperature during the summer

Thermocline Found in the metalimnion zone Area in which there is a rapid decrease in temperature – approximately 1 oC per each meter of depth Also described as the “interface between warm and cold water” Warm water is much lighter than cold water and cold water tends to sink to the bottom of the lake

Stratification During summer months increased sunlight and warm winds heat the surface water trapping colder water on the bottom. Differences in the densities of warm and cold water resist mixing by wind Stratification creates three different zones: Epilimnion Metalimnion Hypolimnion

Epilimnion The warmest water Characterized by freely circulating surface water with variable temperatures. Area where the majority of the organism’s is found Area of greatest productivity and light penetration Oxygen concentration is usually greatest in this zone.

Metalimnion Middle layer or transition zone Temperature layer where the “thermocline” is found

Hypolimhion A deep cold layer with little temperature change Low oxygen content due to little or no photosynthetic production by plants Water does not come in contact with air Oxygen quantity decrease with depth Oxygen is depleted by bottom dwelling organism and bacteria feeding on organic matter Little or no light penetration

Lake Overturns In the fall months, the cooler air temperature also cool the surface waters of a lake The densities of the upper and lower waters become similar and the wind mixes the layers of water together. The temperature of the lake becomes uniform, this is known as “fall overturn” Oxygen levels are replenished in deep water In Texas, there is generally one turnover per year One fall overturn – monomictic Two fall overturn - dimictic

Profundal Zone – Bottom zone found in deep water bodies Characterized by the lack of light penetration Lack of rooted aquatic plants and the absence of photosynthesis Sediments are generally silt/clay mixed with organic matter Oxygen levels in this zone are extremely low Organisms resting or borrowing on the bottom and tolerant of little or no oxygen are common

Aquatic Organisms Aquatic organisms are classified by their habits Neuston – organisms resting near the surface Nekton – free swimming organisms Periphyton – organisms that cling to rocks, logs, and other debris Benthos – organisms living on and in the bottom sediments Plankton – microscopic plants and animals that are suspended in the water column

Aquatic Food Webs

Food Chains and Webs Primary producers – aquatic plants, algae, and phytoplankton Primary consumers – zooplankton, some aquatic invertebrates and fish Herbivores – plant eaters Secondary consumers – some aquatic invertebrates, fish, snakes and turtles Carnivores – flesh eaters Omnivores – eats both plants and animals Scavengers – vultures, crabs and other animals Detritivores – bacteria and fungi that feed on organic material

Lotic Systems (Running Water) Characterized by flowing water and currents Lotic erosional – characterized by fast running water and riffles Lotic depositional – characterized by pools and areas with slower velocities

Hydrology As water moves towards streams and rivers it: Is absorbed by plants Filters through the soil profile and can end up as groundwater It can evaporate It can enter the stream as runoff

Hydrology and Soil Water capture is a process where water is stored in soil Water can infiltrate the soil surface and percolate throughout the soil profile Percolate is the downward movement of water through the soil profile Infiltration and percolation is affected by soil type, topography and climate

Hydrology and Water Storage Water is captured in soil It is stored in pores (air spaces) between soil particles More water is stored in sandy soils than clay soils Vegetation can also affect the amount of water stored

Water Release Water moves through the soil profile to seeps and springs or across the land as runoff and evidentially into streams and rivers Vegetation along stream banks slows release of water into streams During heavy rains it can help prevent erosion, reduce sediment and maintain water quality

Riparian Zones Riparian means “of the river” It is the non-cultivated, vegetated land that touches and surround a stream It often includes wetlands It helps stabilize shorelines, filters pollutants Helps maintain water temperature and provides cooler water for fish Provides habitat for wildlife

Steam Velocity Erosional Zone Depositional zone

Erosional Zone Outer bank of a stream where flow velocities are at a maximum and bank erosion is high. Riffle areas – important habitats for many aquatic insects which require flowing water for feeding and high oxygen levels. Few plants grow in the fast moving water of a stream, but some are adapted for living in a current

Depositional Zone Refers to the inner bank of a stream where velocity is at a minimum Slower velocities allow for deposition of sediments which form bars Bars often support emergent aquatic vegetation Pool areas support fish, aquatic invertebrates and aquatic plants Sediments are composed of sand/silt/clay and organic matter

Depositional zone

Slower moving water supports organisms similar to lakes and ponds Larger rivers with slower velocities can support plankton populations Most of the rivers in the southeastern portion of Texas are slow-moving with large amounts of organic sediments support a large number of aquatic insects

FloodPlains Floodplains are the areas of land surrounding a body of water that is subject to periodic flooding Floodplains hold excess water during heavy rains Allows water to be slowly released into river systems or seep into groundwater aquifers Help filter out sediment Not a great place to build on!

Aquatic Insects Streams support those organisms adapted to life in fast moving waters. Algae, plants and invertebrates that can anchor themselves to rocks, logs and other stream debris Some fish prefer the fastest part of stream Sediments are usually coarse Many fish spawn in riffles of streams

Aquatic Insects Primary producers – algae is dominant in slow moving rivers and streams. In faster moving streams aquatic plants are found but no phytoplankton or zooplankton Primary consumers – snails, invertebrates and some fish are dominant Secondary consumers –predatory invertebrates, fish, turtles