tailieunhanh - Handbook of Water and Wastewater Treatment Plant Operations - Chapter 13

Điệp khúc đầu tiên của con ếch - những rhapsodies the thé peepers mùa xuân, những người "bình-o-rum" cuộc gọi của ễnh ương, những banjo-như hòa âm bass của con ếch màu xanh lá cây, những và nhịp điệu giọng cổ ếch da báo, họ hát một khúc dạo đầu cho bài hát tuyệt vời của các loài chim - bên cạnh một cách khác vẫn ao vào một buổi tối mùa xuân báo hiệu sớm của sự kiện ấn tượng thiên nhiên: các bộ phim truyền hình của biến thái. Biến thái này bắt đầu với khối lượng của trứng sớm nở thành mang, thở, ăn cỏ,. | 13 Water Quality Are We to Wait Until All Frogs Croak The earliest chorus of frogs those high-pitched rhapsodies of spring peepers those jug-o-rum calls of bullfrogs those banjo-like bass harmonies of green frogs those long and guttural cadences of leopard frogs their singing a prelude to the splendid song of birds beside an otherwise still pond on an early spring evening heralds one of nature s dramatic events the drama of metamorphosis. This metamorphosis begins with masses of eggs that soon hatch into gill-breathing herbivorous fishlike tadpole larvae. As they feed and grow warmed by the spring sun almost imperceptibly a remarkable transformation begins. Hind legs appear and gradually lengthen. Tails shorten. Larval teeth vanish and lungs replace gills. Eyes develop lids. Forelegs emerge. In a matter of weeks the aquatic vegetarian tadpole will should it escape the many perils of the pond complete its metamorphosis into an adult carnivorous frog. This springtime metamorphosis is special this anticipated event especially for the frog marks the end of winter the rebirth of life and a rekindling of hope especially for mankind . This yearly miracle of change sums up in a few months each spring what occurred over 300 million years ago when the frog evolved from its ancient predecessor. Today however something is different strange and wrong with this striking and miraculous event. In the first place where are all the frogs Where have they gone Why has their population decreased so dramatically in recent years The second problem That this natural metamorphosis process perhaps a reenactment of some Paleozoic drama whereby over countless generations the first amphibiantypes equipped themselves for life on land now demonstrates aberrations of the worst kind of monstrous proportions and dire results to frog populations in certain areas. For example reports have surfaced of deformed frogs in certain sections of the . specifically Minnesota. Moreover the . .