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The Freshwater Biome - mixing As a consequence...

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The Freshwater Biome The freshwater biome is subdivided into two zones: running waters and standing waters. Larger bodies of freshwater are less prone to stratification (where oxygen decreases with depth). The upper layers have abundant oxygen, the lowermost layers are oxygen-poor. Mixing between upper and lower layers in a pond or lake occurs during seasonal changes known as spring and fall overturn. Lakes are larger than ponds, and are stratified in summer and winter, as shown in Figure 16. The epilimnion is the upper surface layer. It is warm in summer. The hypolimnion is the cold lower layer. A sudden drop in temperature occurs at the middle of the thermocline. Layering prevents mixing between the lower hypolimnion (rich in nutrients) and the upper epilimnion (which has oxygen absorbed from its surface). The epilimnion warms in spring and cools in fall, causing a temporary
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Unformatted text preview: mixing. As a consequence, phytoplankton become more abundant due to the increased amounts of nutrients. Sublittoral zone harbors seaweed that becomes sparse where deeper; most dependent on slow rain of plankton and detritus from sunlit water above. Bathyal zone continues with thinning of sublittoral organisms. Abyssal zone is mainly animals at soil-water interface of dark abyssal plain; in spite of high pressure, darkness and coldness, many invertebrates thrive here among sea urchins and tubeworms. Thermal vents along oceanic ridges form a very unique community. Molten magma heats seawater to 350 o C, reacting with sulfate to form hydrogen sulfide (H 2 S). Chemosynthetic bacteria obtain energy by oxidizing hydrogen sulfide. The resulting food chain supports a community of tubeworms and clams....
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