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Leyte Sab-A Basin peatland (LSBP) is the second largest peatland in the Philippines and comprises 3,088 ha (31 km²). The study estimated the C storage and carbon sequestration capacity of the peatland's four (4) ecotypes, namely, swamp forest (SF), marshland (ML), agroforestry (AF), and agricultural land (AL) using allometric equations. SF rendered the highest downed wood C-stocks followed by AL and AF. For the litter C-stocks, AF rendered the highest, followed by SF, ML, and AL. SF rendered the highest root C-stocks and CO2 sequestered, followed by AL and AF. C% is highest in ML with values ranging from 32-43 C% across the soil peat depth, while SF ranges from 29-34 C%, and AL and AF both with 19-37 C%. The LSBP stores 36.6 Tg of C and 134.5 Tg of CO2 sequestered. This C storage amount can represent 0.04% of tropical peat carbon. [ABSTRACT FROM AUTHOR]

Laguna de Bay, the largest and nationally significant freshwater lake ecosystem in the Philippines, has been increasingly subjected to anthropogenic pressures over the years. Domestic, agricultural, and industrial activities in the surrounding areas have contributed directly and indirectly to the deterioration of the lake's overall ecological health and integrity. This study assessed the chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), lead (Pb), and cadmium (Cd) contamination in Asiatic clam, Corbicula fluminea, using quadrupole inductively coupled plasma–mass spectrometry. Estimated daily consumption of Asiatic clam was determined through a social survey. The data from analytical analysis and social surveys were utilized to calculate the target hazard quotient (THQ) to determine the potential health risks of consuming heavy metal–enriched clams to fishing households. Results from the Knowledge, Attitude, and Practices (KAP) survey indicated that the majority of the respondents have an acceptable level of knowledge on the hazards posed by the intake of contaminated clams but disapproved the banning of its collection and consumption. Sampled households with high consumption rates in all municipalities except Victoria were also found to be exposed to imminent health risk due to the high toxicity level of As based on their THQ values. Overall, one-third of the fishing households exposed to elevated health risk based on their total target hazard quotient (TTHQ) values already warrant a concern. The potential human health risks validate the worsening condition of Laguna de Bay. Integrative and holistic management of the lake through collaborative efforts of various stakeholders and institutions is necessary, to restore the health of the ecosystem and safeguard the health of the public. [ABSTRACT FROM AUTHOR]

The impacts of land use/land cover (LULC) change and the relationship between landscape pattern and hydrologic processes in the ungauged Calumpang watershed, Batangas, Philippines were studied. LULC change from 2003 to 2008 included an increase in built-up areas (69%) and a reduction of mixed vegetation including riparian vegetation (−10%), which have significant effects on hydrology. Using the Soil and Water Assessment Tool (SWAT), significant increases in surface runoff (5%) and sediment yield (6%) and a reduction in baseflow (−11%) were shown. Spatial and temporal variations of the impacts were observed: degraded sub-basins experienced increased streamflow (up to 31%) during stormy months and reduced baseflow (up to −26%) during dry months. In contrast, improved sub-basins decreased stormflow (up to −4%), and increased baseflow (up to 5%) during dry months. Nine landscape metrics known to affect hydrology were quantified using Fragstats and were correlated with surface runoff, baseflow and sediment yield using partial least square (PLS) regression. The results indicated that increasing patch density and largest patch index of agricultural and forested landscapes, respectively, leads to a decrease in surface runoff and sediment yield while increasing baseflow. In contrast, increasing cohesion and aggregation index of agricultural and forested landscapes, respectively, results to an increase in surface runoff and sediment yield as baseflow decreases. Although more observed data is needed for validation, the relationship model produced in this study can be applied to new data or used for scenario analysis. When coupled with economic, social and political assessments, the model serves as a useful tool in formulating comprehensive watershed management and land use policies. [ABSTRACT FROM AUTHOR]

Abstract: In the first half of January 2009, the southern Philippine island of Mindanao was overwhelmed by numerous natural disasters caused by the passage of the tail-end of the cold front. This otherwise ordinary weather condition was accompanied by unusually heavy precipitation sustained over a period of several days. This triggered numerous landslides and caused many drainage systems to swell, flooding huge tracts of low lying areas that have not experienced similar events in the recent past. Many communities were caught unprepared for the calamity. The amount and extent of damage reflect both the magnitude of the natural disaster itself and the community''s nominal level of disaster-preparedness. In view of the increasing atmospheric moisture levels and the likelihood that global warming will affect the weather patterns, there is a possibility that similar weather disturbances can become more frequent. Therefore, there is an urgent need for disaster risk management programs to be developed or enhanced at the local community level especially in areas most vulnerable to weather-related natural hazards, in light of changing global climatic patterns. [Copyright &y& Elsevier]

The study analyzed the raindrop size distribution (DSD) measured by an optical Parsivel disdrometer in Southern Luzon, Philippines and utilized it to generate dual-pol relations for the nearby Tagaytay radar. The relations were generated using two methods (Method 1 - gamma-based and Method 2 - linear fitting), four time-integration steps (1-, 2-, 5-, and 10-minute) and datasets from two periods (wet season and single event). The resulting quantitative precipitation estimates (QPEs) calculated from the generated R(Z) relations were compared to rain gauge stations near the disdrometer and were evaluated for the Tropical Storm Yagi Monsoon event of August 10 (2200 UTC) to August 11 (0400 UTC), 2018 using six statistics: Pearson's correlation; mean error, percent bias, Nash-Sutcliffe Efficiency, mean absolute error, and root-mean-square error. Results show that the area's DSD demonstrates relatively larger average raindrop diameters than some of its Asian counterparts, albeit a smaller number in the total number of raindrops when compared with the same areas. In terms of QPE evaluation, results showed a consistent pattern observed wherein the R(Z) relations using finer time steps (1-min and 2-min) generally performed better than the longer ones. Moreover, Method 1 dominated Method 2 in terms of error statistics. As expected, Method 2 outperformed Method 1 in terms of r (as Method 2 itself is derived through linear fit). The best derived R(Z) relations were able to outperform other relations in terms of r, NSE, and RMSE. On the other hand, R(KDP) was able to perform the best in terms of ME, MAE, and pBIAS, reducing the bias of current standard method by up to 74%. [ABSTRACT FROM AUTHOR]

This paper presents the first field, geochemical and geophysical information on the recently recognized Early Cretaceous Balud Ophiolitic Complex (BOC) in the island of Masbate in the Central Philippines. Mapping of the western limb of the island revealed that only the upper crustal section of the BOC is exposed in this area. Geochemically, the pillow basalts are characterized by transitional mid-oceanic ridge basalt-island arc tholeiitic compositions. Gravity surveys yielded low Bouguer anomaly values that are consistent with the highly dismembered nature of the BOC. Short wavelength, high amplitude magnetic anomalies registered across the study area are attributed to shallow magnetic sources. This is taken to support the model that the ophiolitic complex occurs as thin crustal slivers that are not deeply-rooted in the mantle. Comparing BOC with other ophiolites in the Central Philippines, such as those in the islands of Sibuyan, Leyte and Bohol, suggests the possibility of a common or contiguous source for similarly-aged and geochemically composed crust-mantle sequences in the region. [ABSTRACT FROM AUTHOR]

Samar island in the eastern part of Central Philippines is underlain by a complete ophiolite suite, the Samar Ophiolite. We present the first geochronological and paleomagnetic data for the Samar Ophiolite. Whole rock K–Ar dating of two basalt samples yielded an age of 100.2 ± 2.7 Ma and 97.9 ± 2.8 Ma. Thirteen sites in four localities yielded characteristic remanent magnetization with in situ direction of D = 340°, I = − 24°, k = 15, α95 = 11° and tilt-corrected direction of D = 342°, I = − 27°, k = 15, α95 = 11°. These values suggest that the ophiolitic basement rocks of Samar formed in the Late Cretaceous at a paleolatitude of 14°S ± 6°. The paleolatitude is several degrees south of the sub-equatorial positions calculated for the three other Mesozoic ophiolites of the Philippine Mobile Belt (PMB) whose paleomagnetism had been previously studied. The PMB ophiolites in eastern and central Philippines share a common age, geochemistry and paleolatitude with the Halmahera Ophiolite, suggesting that they originated from a Mesozoic supra-subduction zone that spanned a few degrees north of the equator to around 15°S. [ABSTRACT FROM AUTHOR]

Offshore and ground gravity data were utilized to estimate crustal thickness across the Central Philippines where a transition from continental to island arc terrane occurs. Significant differences in gravity anomalies were observed between the Palawan Microcontinental Block (PCB) and the Philippine Mobile Belt (PMB), two major terranes that came together through arc-continent collision. Islands of the PCB (Mindoro, Tablas, Romblon, Sibuyan and western Panay), made up of an assortment of continent-derived sedimentary and igneous rocks and slivers of ophiolitic bodies, register lower Bouguer anomalies compared to that displayed by Masbate Island in the PMB. The calculated crustal thickness of this region exhibits a complex Moho topography of non-uniform depth across the collision zone with the thickest parts (∼32 km) corresponding with ophiolitic units emplaced consequent to arc-continent collision. On the other hand, relatively thinner crust (∼21 km) within the collision zone coincides with areas surmised to have undergone attenuation following intra-arc rifting. The same characteristics are observed offshore of western Mindoro and within the Marinduque Basin, areas known to have experienced crustal thinning following regional tectonic rearrangements that triggered riftings and intra-basin openings. [ABSTRACT FROM AUTHOR]

The presence of adakites has been used as an indicator for the occurrence of gold mineralization in many mineral prospecting works. Traditionally, the unique geodynamic controls to adakite formation, particularly the high temperature gradient and other slab-melting requirements, have been taken as key elements that must be present during their formation. However, several studies have suggested alternative mechanisms. This paper presents fractional crystallization as the most viable mechanism for the generation of adakitic rocks in the Masara gold-silver mine in Eastern Mindanao, Philippines. Furthermore, this paper also argues that the occurrence of adakitic rocks does not necessarily indicate the presence of mineralization. Depending on the scale, their occurrence may be an exploration marker at a regional or district level, but at the mine-level, other more localized parameters will have to be considered. [ABSTRACT FROM AUTHOR]

The Zambales Ophiolite Complex (ZOC) on the island of Luzon, Philippines is one of the most well-studied crust-mantle sequences in the region. Several massifs comprise the ZOC, one of which is the Coto Block overlain by clastic sedimentary units previously dated as Eocene. Geochronologic studies from diabase, granodiorites and other late-stage magmatic products similarly yielded the same age. Succeeding tectonic models have therefore all been grounded on the assumption that the entire ZOC is Eocene. Recent investigations, however, revealed the presence of chert blocks within the Early to Middle Miocene clastic formation overlying the Acoje Block in the northern part of the ophiolite complex. Radiolarians extracted from the cherts yielded a stratigraphic range that suggests a Late Jurassic to Early Cretaceous age. The recognition of a much older age than previously reported of the ZOC warrants a re-examination of its actual distribution and genesis. Correlating with other similarly-aged ophiolites, we suggest defining a western Mesozoic ophiolite belt, largely extending from the west-central portion of the archipelago to the northeastern tip of Luzon island. Tentatively, we attribute the Mesozoic ophiolitic and associated rocks in western Luzon to an arc-continent collision involving the Philippine Mobile Belt and the Palawan Microcontinental Block. In addition, differences in the clastic compositions of the Cenozoic sedimentary formations provide material not only for deciphering the ZOC’s unroofing history but also for constraining the timing of province linkage. The intermittent appearance of lithic fragments and detrital minerals from the ophiolite in the units of the Middle Miocene Candelaria Limestone and the Late Miocene to Early Pliocene Sta. Cruz Formation indicates significant but geographically variable contributions from the ophiolite complex. In the northern Zambales Range, the Sta. Cruz Formation caps the Coto Block and the Acoje Block of the ZOC, providing a minimum age for their amalgamation. [ABSTRACT FROM AUTHOR]

Northwest Panay consists of two terranes that form part of the Central Philippine collision zone: Buruanga Peninsula and Antique Range. The Buruanga Peninsula consists of a Jurassic chert-clastic-limestone sequence, typical of oceanic plate stratigraphy of the Palawan Micro-continental Block. The Antique Range is characterized by Antique Ophiolite Complex peridotites and Miocene volcanic and clastic rocks, representing obducted oceanic crust that serves as the oceanic leading edge of the collision with the Philippine Mobile Belt. The Nabas Fault is identified as the boundary between the two terranes. This study employed the gravity method to characterize the Northwest Panay subsurface structure. Results indicate higher Bouguer anomaly values for Buruanga Peninsula than those for Antique Range, separated by a sudden decrease in gravity values toward the east-southeast (ESE) direction. Forward gravity data modeling indicates the presence of an underlying basaltic subducted slab in the Buruanga Peninsula. Furthermore, the Nabas Fault is characterized as an east-dipping thrust structure formed by Buruanga Peninsula basement leading edge subduction beneath Antique Range. Additional geophysical constraints were provided by shallow seismic refraction and electrical resistivity surveys. Results from both methods delineated the shallow subsurface signature of the Nabas Fault buried beneath alluvium deposits. The gravity, seismic refraction and electrical resistivity methods were consistent in identifying the Nabas Fault as the terrane boundary between the Buruanga Peninsula and the Antique Range. The three geophysical methods helped constrain the subsurface configuration in Northwest Panay. [ABSTRACT FROM AUTHOR]

Abstract: The Antique Ophiolite Complex exposed along the western side of Panay Island, central Philippines was derived from the Jurassic to Cretaceous proto-South China Sea oceanic leading edge of the Palawan microcontinental block. The subduction and ultimate closure of this ocean basin resulted in the emplacement and exposure of this lithospheric fragment along the collisional boundary of the microcontinental block and the oceanic- to island arc-affiliated Philippine mobile belt. The ophiolite complex has volcanic rocks having normal- to transitional mid-ocean ridge basalt (MORB) to island arc tholeiitic (IAT) geochemistry consistent with the transitional MORB–IAT characteristics of its peridotites. The chromitites manifest subduction signature suggestive of the involvement of water in its generation. All of these would be consistent with generation in a supra-subduction zone environment, specifically in a subduction-related marginal ocean basin. The collision of the Palawan microcontinental block with the Philippine mobile belt along western Panay resulted, aside from ophiolite emplacement, into arc curvature, island rotation, serpentinite diapirism and thrusting along the forearc side. The offshore bathymetric expression of the microcontinental block along the collision zone shows the leading edge of this oceanic bathymetric high to have spread laterally. This is indicative of its being buoyant resulting to non-subduction as supported by available earthquake hypocenter data. [Copyright &y& Elsevier]