Ontogeny of Lakes. Successional Development of Lake Ecosystems

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1 Ontogeny of Lakes Successional Development of Lake Ecosystems

2 Factors That Determine Rates of Ontogeny Filling rates Inorganic material Basin morphometry Drainage basin characteristics Climatic factors Organic material Autochthonous production Allochthonous inputs Decomposition rates

3 Ontogeny In late stages of ontogeny, autochthonous productivity shifts from planktonic dominance to littoral dominance Rates of ontogeny are greater in shallow basins

4 Oligotrophic to Eutrophic Transition from unproductive to productive has been conceptualized as the transition from oligotrophic to eutrophic

5 Oligotrophic to Eutrophic "Trophy" refers to the input of organic matter per unit time Eutrophe is German for "nutrient rich" Oligotrophy and eutrophy were first addressed in 1919 by Naumann and 1925 by Thienemann Trophy is generally restricted in definition to pelagic zones

6 Oligotrophic Lakes Oligotrophic lakes are generally characterized by low rates of nutrient input

7 Oligotrophic Lakes Large deep lakes usually remain oligotrophic longer because of the greater dilution and volume for biological activity and also because of slower filling rates Large, deep lakes do not develop anaerobic hypolimnia as quickly and complexation and formation of insoluble compounds is more common in well-oxygenated water

8 Oligotrophic Lakes Sedimentation of nutrients reduce the nutrient availability for biological activity Loading rates of nutrients are extremely critical determinants of rates of eutrophication

9 Oligotrophic Lakes Precipitation reactions remove nutrients and reduce autochthonous production in hard water lakes and subsequently maintain low concentrations of dissolved organic matter Hard water lakes tend to resist eutrophication and factors (such as acid rain in small quantities) that reduce the buffering capacity increase the rate of eutrophication

10 Dystrophic Lakes Dystrophy refers to high loading rates of allochthonous organic matter Bogs are fequently dystrophic but all dystrophic lakes are not bogs and do not contain bog flora Allotrophy refers to the rate of input from allochthonous sources

11 Highly stained lakes with large inputs of allochthonous organic matter have low rates of phytoplankton production

12 Abundance of refractory humic substances and the low ph generally cause low rates of microbial activity Divalent cations are low in concentration because of cation exchange and low inputs from the drainage basin Low ph and low nutrient availability restrict phytoplankton production

13 Successional Development in Shallow Lakes Moss Bog Macrophytes Vegetation Systems And Associated Reed Swamps Marshes Microflora and Fens Terrestrial Vegetation All lakes do not become bogs before becoming terrestrial

14 Bogs, Swamps, Marshes Development of bogs requires abundant precipitation and high humidity throughout the year As the basin fills, littoral vegetation advances toward the center of the lake

15 Bogs, Swamps, Marshes Swamp conditions are present when standing water occurs among the vegetation throughout the basin Marsh conditions exist when there is no standing water and sediments are saturated throughout the year

16 Bogs, Swamps, Marshes Mosses can grow on the saturated sediments and raise the elevation of water in the mat above the original lake level - a "raised bog" The moat-like ring of water that surrounds the central mat of moss and vegetation is called the lagg zone

17 Bogs, Swamps, Marshes Quaking bogs form when rapid growth of Sphagnum grows over an open water area resulting in a floating mat

18 Think About It

19 Goodbye and Good Luck