Sun is the primary source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR) . Photosynthetically active radiation , often abbreviated PAR , designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world. The energy of sunlight fixed in food production by green plants is passed through the ecosystem by food chains and webs from one trophic level to the next. In this way, energy flows through the ecosystem. The Trophic Structure of Ecosystems The organisation and pattern of feeding in an ecosystem is known as the trophic structure. => The levels through which food energy passes from one group of organism to the other...
Students, These are the notes for Assamese medium students of the Environmental Science subject. Download all the PDF files from the link given below.....
Environmental Impacts of Dams The environmental consequences of large dams are numerous and varied, and includes direct impacts to the biological, chemical and physical properties of rivers and riparian (or "stream-side") environments. 1. The dam wall itself blocks fish migrations, which in some cases and with some species completely separate spawning habitats from rearing habitats. 2. The dam also traps sediments, which are critical for maintaining physical processes and habitats downstream of the dam (include the maintenance of productive deltas, barrier islands, fertile floodplains and coastal wetlands). 3. Another significant and obvious impact is the transformation upstream of the dam from a free-flowing river ecosystem to an artificial slack-water reservoir habitat. Changes in temperature, chemical composition, dissolved oxygen levels and the physical properties of a reservoir are often not suit...
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