A limnological survey of Lake Duminagat, Mt. Malindang Natural Park, Misamis Occidental, Philippines

Abstract

Lake Duminagat is a crater lake located in Mt. Malindang Natural Park, one of the protected areas in the Philippines. Two communities are adjacent to it - Brgy. Duminagat, of which it is a part, and Brgy. Gandawan. Both barangays are part of the municipality of Don Victoriano, province of Misamis Occidental. The municipality of Don Victoriano is entirely circumscribed by the Park which represents the flora and fauna of the Zamboanga biogeographic zone. This paper focuses on the objective of characterizing the limnology of Lake Duminagat - its morphology, its physico-chemical components and its biota. The area of study consists of valleys and mountains. Brgy. Gandawan, Brgy. Lake Duminagat, and the lake basin are considered as crater valleys, surrounded by variably tall mountains. Being at a high elevation (~1,240 to 1,560 masl), the climate in the Lake Duminagat area is cooler compared to the lowlands. The area belongs to the region classified as Intermediate B type with no very pronounced maximum rain period and no dry season. Annual rainfall is 2099 mm. Lake Duminagat is a small lake, with an area of 8.04 ha, maximum depth of 20.95 m, water volume of 933,000 m3, mean depth of 11.6 m, shoreline length of 1,060 m, and shoreline development of 1.054. It is a thermally stratified lake, though whether it undergoes periodic mixing was not determined. The water is low in alkalinity and is very soft. The water at the middle of the lake is potable enough for drinking at various times of measurement. Its various morphometric and physico-chemical characteristics such as a low surface area to volume ratio, low lake area to watershed area ratio, low alkalinity, and low amount of dissolved solids all contribute to its low productivity. Its macrophytes (representing one component of primary productivity) and zooplankton (representing secondary productivity) populations are thus low in numbers, aside from being limited in number of species. Consequently, the fish population, which is at the top of the aquatic food chain, is also low in kind, numbers, and biomass. Nonetheless, the lake supports a high diversity of indigenous shoreline fauna and flora. Considering the lake s characteristics and that of its surrounding community, one potential for the Lake Duminagat area is its use for ecotourism with the local people being the hosts-entrepreneurs. The project, of which this paper is a part, was one of the projects in the Philippines-Netherlands Biodiversity Research Programme for Development: Focus on Mt. Malindang and Environs (shortened as BRP). The project used participatory approaches and involved the community as local researchers or partners. It is hoped that their involvement in this research gave the local communities an awareness of the natural and social factors that determine/affect the Lake Duminagat ecosystem. It is also hoped that results of this research would be used and would empower the local communities to come up with a strategy for conserving and sustainably utilizing the lake s biodiversity and resources, and improve livelihood and cultural opportunities.