Long‐term irreversible changes in a lake ecosystem affected by the I ndian O cean T sunami

This study focused on ecosystem responses to the environmental perturbations caused by the 2004 I ndian O cean T sunami in a small lake that was a freshwater body in 1996, prior to the tsunami. The physicochemical and biological characteristics of K okilamedu Lake ( KKM ) revealed drastic changes, compared with pretsunami conditions. Monthly average observations on water quality indicated the electrical conductivity of the water increased steeply to 17.41 mS cm −1 in 2009, from the lowest pretsunami value of 1.83 mS cm −1 (range of 1.83–5.25 mS cm −1 ). Simultaneously, the nitrate + nitrite (NO 3  + NO 2 ) values increased significantly from 0.49 μmol L −1 in 1996 to 74.47 μmol L −1 in 2006. Silicate (SiO 4 ‐Si) exhibited a dramatic increase in concentration, from an average of 64.87 μmol L −1 in the pretsunami period to 309.71 μmol L −1 the post‐tsunami period (2009–2010). Inorganic phosphate had increased to a maximum of 9.59 μmol L −1 from a pretsunami maximum of 1.09 μmol L −1 . The chlorophyll‐α concentrations did not respond to the increased nutrient stoichiometry of the lake. There was a decreased chlorophyll‐α concentration under post‐tsunami conditions. The recent infilling of the lake with sediment during the tsunami, associated with wind‐driven resuspension reduced the light penetration. There was a significant improvement in dissolved oxygen concentrations (2006–2010 average of 8.27 mg L −1 ) in the lake, however, compared with the pretsunami values (1994–1995 average of 5.94 mg L −1 ). The algal component is now dominated by blue‐green algae, while green algae had dominated in the pretsunami period. Pre‐ and post‐tsunami observations from a control site did not exhibit such dramatic shifts from the 1995 and 1996 conditions, whereas a shift was apparent in the case of KKM . Certain marine fishes have adapted to this altered ecosystem. These marine species encountered ( E lops machnata , C ociella punctata , S phyraena jello , P latycephalus indicus , G lossogobius giuris ) might have been recruited during the intrusion of the tsunami waves.