Page 663 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 19 ecosystem essentials 627
Open water
Increase in floating and submerged plants
Swampy, waterlogged central area
Accumulating sediments
Crevasses
Lake basin filled
Grasses and shrubs
(a) A lake gradually fills with organic and inorganic sediments, shrinking the area of open water. A bog forms, then a marsh, and finally a meadow, the last of the successional stages.
(d) Peat bog with acidic soils, Richmond Nature Park, near Vancouver, British Columbia.
▲Figure 19.20 Idealized lake–bog–meadow succession in temperate conditions, with real–world examples. [Bobbé Christopherson.]
becomes concentrated near the surface. Energy flow shifts from production to respiration in the eutrophic stage, with oxygen demand exceeding oxygen availability.
Nutrient levels also vary spatially within a lake: Oligotrophic conditions occur in deep water, whereas eutrophic conditions occur along the shore, in shal- low bays, or where sewage, fertilizer, or other nutrient
inputs occur. Even large bodies of water may have eu- trophic areas along the shore. As humans dump sewage, agricultural runoff, and pollution into waterways, the nutrient load is enhanced beyond the cleansing ability of natural biological processes. This human-caused eu- trophication, known as cultural eutrophication, hastens succession in aquatic systems.
(b) Spring Mill Lake, Indiana
(c) Organic content increases as succession progresses in a mountain lake.
Georeport 19.3 another Take on lake–Bog succession
in areas that have been recently deglaciated, scientists have uncovered a pattern that seems the opposite of lake–bog succession, underscoring the poor understanding of successional processes in aquatic ecosystems. evidence from lakes
in the arctic and antarctic suggests that these water bodies became more dilute, acidic, and unproductive—in other words, less eutrophic—over the past 10 000 years. Successional changes in the surrounding vegetation and soils seem to be linked to these changes in the aquatic ecosystem. The studies suggest that in various cool, moist, temperate rainforest climates with landscapes created by glacial retreat, different processes are at work in lakes than the ones described as typical in this chapter.