Current state and historical changes of nutrient loading and ecological status of large lakes Peipsi and VõrtsjärvNõges, Tiina; Järvet, Arvo; Laugaste, Reet; Loigu, Enn; Tõnno, Ilmar; Nõges, PeeterProceedings of 4th International Lake Ladoga Symposium 20022003 / p. 199-203