Towards integrated management of a shallow tropical lake: assessment of water quality, sediment geochemistry, and phytoplankton diversity in Lake Palakpakin, Philippines.

The limited carrying capacities of shallow tropical lakes render them more vulnerable to ecological problems like eutrophication. Unregulated human activities such as unsustainable aquaculture and urbanization can alter ecosystem dynamics rapidly, and this warrants more comprehensive researches than what has been previously conducted. Here, we presented an integrated assessment of the nutrient dynamics, phytoplankton diversity, and sediment geochemistry in Lake Palakpakin, a shallow tropical lake of volcanic origin, to understand its deteriorating ecological state. Water, phytoplankton, and sediment samples were collected, and in situ water quality measurements were done during wet and dry seasons in four critical areas in the lake, namely, the inlet, center, sanctuary, and outlet. Results revealed that high light extinction coefficient (1.13 m-1), high turbidity (28 NTU), high phosphate concentration (> 2.0.5 mg/L), and the abundance of Microcystis aeruginosa, Anabaena helicoidea, and Lyngbya sp. indicate that from a relatively healthy lake in 2008, Lake Palakpakin has become a eutrophic to hypereutrophic freshwater body. High concentrations of available nutrients such as N and P were detected in the center and sanctuary sediments, which drive the internal nutrient loading in the lake. We recommend that management efforts be directed towards a whole-ecosystem approach in addressing the problem of eutrophication, especially in shallow tropical lakes.