Associated Press: The world’s oldest, deepest and biggest freshwater lake is growing warmer, dirtier and more crowded. Lyubov Izmestieva is charting these insidious changes. Marina Rikhvanova is fighting them. And the fate of one of the world’s rarest ecosystems, a turquoise jewel set in the vast Siberian taiga, hangs in the balance. For centuries Lake Baikal has inspired wonder and, more recently, impassioned defenders. With more fresh water than America’s Great Lakes combined, and home to …