VOLUME 5 NUMBER 2 (July to December 2012)

by Mary Joyce L. Flores^1,* and Macrina T. Zafaralla²

¹ Sciences Cluster, University of the Philippines Cebu, Lahug, Cebu City, Philippines
² Institute of Biology, University of the Philippines Los Baños, College, Laguna, Philippines

The water quality of Mananga River was assessedbetween February and December 2006 usingselected physicochemical factors in combinationwith macroinvertebrate composition and diversityindices. Three sampling stations, each 100 mlong, were established. Alkalinity, total phosphates and nitratenitrogenwere similar in all sampling stations. The significantvariation in stream depth, width and stream bed profile resultedin diminishing velocity but increasing discharge downstream.These physical characteristics led to increased total suspendedsolids, water temperature, and biological oxygen demand, butdecreased pH and dissolved oxygen levels downstream. Thephysicochemical factors influenced the composition anddiversity of macroinvertebrates in Mananga River. A total of 37families representing 15 orders were recorded. Aquatic insects(Class Hexapoda) made up 58.6% of total abundance followedby the gastropods (Class Gastropoda) at 39.9%. The orderEphemeroptera of Hexapoda had the highest abundance (47.6%of total) and highest richness (6 families). Family Thiaridae wasthe most persistent and the most abundant macroinvertebratetaxa followed by Caenidae. Almost all taxa were represented inthe upper stations, except for Neritidae, Grapsidae andNereididae, which were limited to the downstream station.Macroinvertebrate richness and diversity were significantlyhigher in the upper stations, but there was an apparent lack ofseasonal variation. Signs of increasing water qualitydeterioration were evident in the results of the physicochemicalanalyses, and validated by the diversity index where the upperstations came out as moderately polluted, and the downstreamstation as moderately to highly polluted.