湖沼学Chapter 3 Physical factors2.ppt

Chapter 2 PHYSICAL FACTORS - Light, Heat, Temperature , Water movements Waves and Currents Physical environment of lakes The sun provides the energy which drives the worlds wind patterns. Wind energy generates waves which lead to the vertical mixing of water in lakes. The light energy transmitted directly to the aquatic environment through solar radiation also influences the distribution of organisms and water temperature, as well as powering plant photosynthesis. Physical structural components of lakes include their shape, distribution of light, distribution of heat, and movement of water. Distribution of Light: The Photic Environment  The elements of lake structure that involve light distribution are often used to describe conditions within the influence of the shore or lake bottom. Primary production in large, deep lakes is entirely dependent on light transmitted through the water to enable photosynthesis. Lake Zonation (Source: Biodiversity Institute of Ontario) The following depth zones are recognized in lakes: a) littoral zone extends from the shore just above the influence of waves and spray to a depth where light is barely sufficient for rooted plants to grow. b) photic (or euphotic) zone is the lighted and usually well-mixed portion that extends from the lake surface down to where the light level is 1% of that at the surface. c) aphotic zone is positioned below the littoral and photic zones to bottom of the lake where light levels are too low for photosynthesis. Respiration occurs at all depths so the aphotic zone is a region of oxygen consumption. This deep, unlit region is also known as the profundal zone. d) compensation depth is the depth at which rates of photosynthesis and respiration are equal. e) sublittoral zone, which is the deepest area of plant growth, is a transition between the littoral and profundal zones. f) pelagic zone (or limnetic zone) is the surface water layer in offshore areas beyond the influence of the shoreline. Boundarie