Excessive Phosphorus Loading to Dal Lake, India: Implications for Managing Shallow Eutrophic Lakes in Urbanized Watersheds

Extensive watershed development has resulted in excessive total phosphorus (TP) loads to Dal Lake, a high altitude Himalayan lake known for its tourism and economic potential. External and internal TP loads of 5 and ∼1 g m –2 yr –1 , respectively, were estimated for the lake. These loading rates are high in relation to the lake's critical tolerance range of 0.1–0.2 g m –2 yr –1 , and, over time, have resulted in severe eutrophication in view of extremely high macrophyte biomass (average = 3.2 kg m –2 ‐fresh weight) and bottom sediment enrichment (79 tons of TP reserves which contribute 88% of the annual TP budget). This study emphasizes the importance of external TP load reduction as a primary management objective to counteract internal TP loading and P storage within bottom sediments resulting from historic anthropogenic loads. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)