Analyzing the Temporal and Spatial Trends of Water Quality and Eutrophication in Laguna de Bay, Philippines, 2000-2012

Abstract

Pollution levels may vary greatly in large waterbodies over long periods of time. Hence, classifying pollution must be inclusive of crucial locations and temporal variabilities. This study applied various statistical techniques to look into the spatial and temporal trends of nine physicochemical parameters within the lake: Biochemical Oxygen Demand (BOD, mg L-1), Ammonia (NH3, mg L-1), Chloride (Cl, mg L-1), Nitrate (NO3, mg L-1), Inorganic Phosphate (PO4, mg L-1), Total Nitrogen (TN, mg L-1), Total Phosphorus (TP, mg L-1), Turbidity (Turb, NTU), and Chlorophyll a (Chl a, μg L-1). Trends were analyzed using data from 2000 to 2012 in five selected stations spread out across the lake. The Trophic State Index (TSI) values of the stations within the study period were also derived from TP, TN, Chl a, and the average of the three parameters. In terms of temporal analysis, general trends, relative monthly values (MV), percent annual changes (PAC) of the nine parameters and their derived TSI values were assessed and analyzed. Spatial trends were assessed by calculating the relative station values (RV) and their standard deviations (SV), principal component analysis (PCA), and hierarchical agglomerated cluster analysis (HACA). BOD and Chl-a have shown statistical growth over the period of 12 years while Cl revealed a consistent decrease in concentration. Moreover, results also showed that Stations 1 and V located at West Bay is the most polluted of all five stations studied, most likely because of its proximity with the highly urbanized and densely populated National Capital Region. This was further supported by HACA results, wherein the two have overwhelmingly similar trends in terms of nutrient and pollutant loadings. Lastly, PCA results revealed that the lake’s current condition can be attributed to BOD, TP, and Chl-a. The generated results comprehensively describe the significant changes in pollution levels within the 13-year period and the relationships between the pollution status of stations located at the lake.