Abstract
Abstract. Laguna Lake, the Philippines’ largest freshwater lake, has always been historically, economically, and ecologically significant to the people living near it. However, as it lies at the center of urban development in Metro Manila, it suffers from water quality degradation. Water quality sampling by current field methods is not enough to assess the spatial and temporal variations of water quality in the lake. Regular water quality monitoring is advised, and remote sensing addresses the need for a synchronized and frequent observation and provides an efficient way to obtain bio-optical water quality parameters. Optimization of bio-optical models is done as local parameters change regionally and seasonally, thus requiring calibration. Field spectral measurements and in-situ water quality data taken during simultaneous satellite overpass were used to calibrate the bio-optical modelling tool WASI-2D to get estimates of chlorophyll-a concentration from the corresponding Landsat-8 images. The initial output values for chlorophyll-a concentration, which ranges from 10–40 μg/L, has an RMSE of up to 10 μg/L when compared with in situ data. Further refinements in the initial and constant parameters of the model resulted in an improved chlorophyll-a concentration retrieval from the Landsat-8 images. The outputs provided a chlorophyll-a concentration range from 5–12 μg/L, well within the usual range of measured values in the lake, with an RMSE of 2.28 μg/L compared to in situ data.
Highlights
1.1 Laguna LakeLaguna de Bay is the largest freshwater lake in the Philippines and the third in South-East Asia with an area of approximately 900 km2
Laguna de Bay lies at the center of urban development in Metro Manila, and it suffers from water quality degradation due to intensified exploitation of the its resources along with decades of industrial, household, and toxic pollution (Delos Reyes and Martens, 1994; Tamayo-Zafaralla et al, 2010)
The chlorophyll-a concentration output of the best performing run is shown in Figure 8 below
Summary
1.1 Laguna LakeLaguna de Bay is the largest freshwater lake in the Philippines and the third in South-East Asia with an area of approximately 900 km. Laguna de Bay lies at the center of urban development in Metro Manila, and it suffers from water quality degradation due to intensified exploitation of the its resources along with decades of industrial, household, and toxic pollution (Delos Reyes and Martens, 1994; Tamayo-Zafaralla et al, 2010). The Laguna Lake Development Authority is a body mandated to address these problems and aim to improve the lake’s ecological state along with its 21 major tributary rivers. With the increasing conflict regarding water use, allocation, and preservation of the lake, LLDA is expected to have a comprehensive resource management and monitoring system (Nauta et al, 2003). Data acquired at various times in a day may result to inaccuracies in water quality assessment (Bresciani et al, 2011). In situ measurements can hardly capture the temporal and spatial variability of large-scale lake phenomena (Dörnhöfer and Oppelt, 2016)
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