9.2 Lake Ecosystem

1. 9.2 Lake Ecosystem • Can be formed from many natural forces • Tectonic activity, volcanic activity, glaciers, flowing water, meteorites, and human activity • Largest and deepest are formed by tectonic activity or major glacial processes • Lake Zonation • 3 main zones : littoral, limnetic, profundal

3. Littoral Zone • The shallow margin of the lake • Has rooted vegetation in specific locations • Emergent plants – extend above water (cattails) • Floating plants – on the surface, may have roots on the bottom • Submergent plants – completely underwater • High level of photosynthesis, sunlight reaches • Has plankton – phytoplankton and zooplankton • Limnetic Zone • Open water beyond the littoral zone • Down to where sunlight reaches • Compensation zone – photosynthesis = respiration • Has lost of phytoplakton, mainly algae

4. Profundal Zone • Beneath the limnetic zone to the bottom • Very little sunlight • In very cold climates, where the warmest water is during winters, has coldest water in summer • Large numbers of bacteria and fungi in deepest depths • Decompose organic matter; releases N and P • Thermal Stratification • Winter • Ice forms on surface • Temperatures increase as depth increases • Temperatures remain stable throughout winter

6. Spring • Ice begins to melt and surface water warms • Wind agitates the water and mixes dissolved oxygen and nutrients from surface to bottom (spring overturn) • Surface water warms and results thermal stratification • Summer • The warm upper layer is the epilimnion • Usually has the highest O2 concentration • Beneath the epilimnion is the thermocline – more rapid fall in temperature • Bottom layer is called hypolimnion • Becomes depleted of oxygen because of BOD of bacteria, no potosynthesis and minimal mixing

8. Autumn • Surface water cools again and lake becomes same temperature from top to bottom • Wind stirs the water causing fall overturn

9. 9.3 Stream Ecosystems • Origin and Classification • Ephemeral streams – flow only during one part of the year • Perennial Streams – flow year round • Tributary – a stream that flows into a larger stream • Watershed – the area that drains into a stream • Stream order – a classification system based on the position of a stream within the network of tributaries

12. Physical Features • Channel Shape – the cross-sectional shape of a section of stream channel depends on the water discharge, sediment load, and the composition of the bed and bank materials • Dense vegetation and silt or clay bed streams are narrower • Most streams are trapezoidal in shape • Rivers get wider faster than they get deeper • Channel Pattern – 3 different patterns: meandering, straight, or braided • Position in watershed influence channel pattern • Meandering Pattern is the most common

13. Pools and Riffles • Deeper areas = pools • Shallow areas = riffles • Floodplains and Terraces • Floodplains are areas of fine sediment extending outward from the banks • Have rich plant life • Overflow of stream or river- bankfull discharge • Terraces – areas that have eroded from overflow and are now above floodplain

14. Biological Communities and Energy Flow • Producers, consumers, and decomposers • Producers - aquatic plants, diatoms, algae, macrophytes • Consumers – invertebrates and fish • Herbivores, predators • Stream food webs receive large amount of material from land • Upstream receives larger proportion of energy from land, downstream receives most of energy from up stream

15. Roots from riparian vegetation stabilize stream banks and create undercut banks • Composition of biological community is determined by channel characteristics and energy sources • Pg 224 7, 9-16