Gil Jacinto - Academia.edu (original) (raw)

Papers by Gil Jacinto

Geophysical Research Letters, Aug 1, 2010

Submarine groundwater discharge (SGD) is an important component of the hydrologic cycle connectin... more Submarine groundwater discharge (SGD) is an important component of the hydrologic cycle connecting terrestrial to marine environments. SGD in fringing reefs and its consequences on biogeochemistry and ecology remain mostly unexplored. The 222Rn activity and salinity of seawater indicate a substantial groundwater contribution throughout most of the 20 km2 studied tropical reef in Pangasinan, Philippines. Over 30 km of electrical resistivity profiles with a penetration depth of 12.5 m shows widespread zones within the reef that are much more resistive than porous reef rocks or sediment saturated with typical seawater. Some discrete resistive areas are located close to where seawater has 222Rn peaks and where geologic lineaments are likely located suggesting that these are preferential pathways for fresher groundwater discharging to the reef. SGD at the site could be a major ecological factor connecting the reef to the subsurface environment which in turn may lead to connections to land.

Thammasat International Journal of Science and Technology, 1997

This paper represents one of the few attempts to understand the behavior of trace metals in the s... more This paper represents one of the few attempts to understand the behavior of trace metals in the sediments of a tropical estuarine environment. The concentrations of Fe, Mn, Cu, Pb, Zn, Cd, Cr, and Ni in the porewaters of Bang Pakong River Estuary sediments were examined. Porewater Fe and Mn were found to increase with depth and may be due to the recycling of Fe and Mn between solid diagenetic mineral phase and pore solutions. Dissolved Cu, Pb, and Zn in the pore fluids are enriched near the sedimenVwater interface where they may be released from the reduction of Fe/Jvln oxides. The decrease of dissolved Cu and Pb in the oxidized zone may be due to reconsumption of Fe/JvIn oxides during recycling and/or sorption by organic materials at the top portions of the sedimentary cores. The results of the chemical partitioning of the sediments show that the reducible phase plays an important role in the transfer of Cu, Pb, and Zn between solid and aqueous phases. In contrast, dissolved Cr and Ni appear to increase with depths as a result of the recycling of Fe/I\4n oxides in the oxidized zone and the release ofthese elements during early diagenesis in the deeper portions ofthe Bang Pakong sedimentary cores.

Marine Chemistry, Oct 1, 2017

To further understand dissolved carbon dioxide (CO 2) dynamics and the link between surface produ... more To further understand dissolved carbon dioxide (CO 2) dynamics and the link between surface productivity and carbon content in the sediments of the Sulu Sea, seawater samples were obtained from high and low productivity areas during the northeast monsoon of December 2007/January 2008, which also corresponded to a period of weak La Niña. CO 2 concentrations in surface waters of the Sulu Sea are mostly governed by productivity, while sub-surface CO 2 concentrations are influenced by physical processes including vertical mixing and bottom-intensified flow southwest of Mindoro and Panay Straits (central Philippines), and upwelling off the west coast of Zamboanga in Mindanao (south Philippines). These physical processes are manifested in the downward sloping isolines of carbonate parameters near the straits and weak upwelling of waters saturated with respect to atmospheric CO 2. Deep waters ventilated from the Sulu Sea have lower dissolved inorganic carbon (DIC) and total alkalinity (TA), and higher pH T (pH in the total scale) and carbonate ion concentrations (CO 3 2-) than the deep waters of the South China Sea. Nevertheless, TA in the deep waters of the Sulu Sea increases below 2000 m at almost twice the rate as DIC, suggesting possible dissolution of sedimentary CaCO 3. A small positive "excess" alkalinity signal is observed in the South China Sea but negative values in the Sulu Sea may reflect the possible contribution of organic acids. This study suggests that the upwelling area within the Sulu Sea, albeit limited in size, could be a source of CO 2 to the atmosphere especially during the stronger northeast monsoon periods. Other processes such as dissolution of CaCO 3 in the sediments and possible organic acidity should be considered in understanding the Sulu Sea's CO 2 sink capacity for the coming years.

AGU Fall Meeting Abstracts, Dec 1, 2013

Ocean Science Journal, Jun 1, 2015

A major source of nutrient load to periodically hypoxic Manila Bay is the urban nutrient waste wa... more A major source of nutrient load to periodically hypoxic Manila Bay is the urban nutrient waste water flow from humans and industries to surface water. In Manila alone, the population density is as high as 19,137 people/km2. A model based on a global point source model by Morée et al. (2013) was used to estimate the contribution of the population to nitrogen and phosphorus emissions which was then used in a water transport model to estimate the nitrogen (N) and phosphorus (P) loads to Manila Bay. Seven scenarios for 2050 were tested, with varying degrees and amounts for extent of sewage treatment, and population growth rates were also included. In scenario 1, the sewage connection and treatment remains the same as 2010; in scenario 2, sewage connection is improved but the treatment is the same; in scenario 3, the sewage connection as well as treatment is improved (70% tertiary); and in scenario 4, a more realistic situation of 70% primary treatment achieved with 100% connection to pipes is tested. Scenarios 5, 6, and 7 have the same parameters as 1, 2, and 3 respectively, but with the population growth rate per province reduced to half of what was used in 1, 2, and 3. In all scenarios, a significant increase in N and P loads was observed (varying from 27% to 469% relative to 2010 values). This was found even in scenario 3 where 70% of the waste water undergoes tertiary treatment which removes 80% N and 90% P. However, the lowest increase in N and P load into the bay was achieved in scenarios 5 to 7 where population growth rate is reduced to half of 2010 values. The results suggest that aside from improving sewage treatment, the continued increase of the human population in Manila at current growth rates will be an important determinant of N and P load into Manila Bay.

PeerJ, May 16, 2018

Microbes are central to the structuring and functioning of marine ecosystems. Given the remarkabl... more Microbes are central to the structuring and functioning of marine ecosystems. Given the remarkable diversity of the ocean microbiome, uncovering marine microbial taxa remains a fundamental challenge in microbial ecology. However, there has been little effort, thus far, to describe the diversity of marine microorganisms in the region of high marine biodiversity around the Philippines. Here, we present data on the taxonomic diversity of bacteria and archaea in Benham Rise, Philippines, Western Pacific Ocean, using 16S V4 rRNA gene sequencing. The major bacterial and archaeal phyla identified in the Benham Rise are Proteobacteria, Cyanobacteria, Actinobacteria, Bacteroidetes, Marinimicrobia, Thaumarchaeota and, Euryarchaeota. The upper mesopelagic layer exhibited greater microbial diversity and richness compared to surface waters. Vertical zonation of the microbial community is evident and may be attributed to physical stratification of the water column acting as a dispersal barrier. Canonical Correspondence Analysis (CCA) recapitulated previously known associations of taxa and physicochemical parameters in the environment, such as the association of oligotrophic clades with low nutrient surface water and deep water clades that have the capacity to oxidize ammonia or nitrite at the upper mesopelagic layer. These findings provide foundational information on the diversity of marine microbes in Philippine waters. Further studies are warranted to gain a more comprehensive picture of microbial diversity within the region.

AGU Fall Meeting Abstracts, Dec 1, 2018

Frontiers in Marine Science, 2022

Coral reefs are typified by their benthic components, and reef diversity and productivity are tra... more Coral reefs are typified by their benthic components, and reef diversity and productivity are traditionally ascribed to the symbiotic association between corals and zooxanthellae, and other macroalgal forms. Less understood is the role of plankton and adjacent pelagic areas in contributing to reef productivity. Half of the reef benthos are filter or particle feeders, while a significant proportion of reef fishes are planktivorous. These organisms can serve as bridges between adjacent oceanic areas to the reef proper, and the pelagic and benthic realm. Here, we investigate the plankton trophic dynamics in two reef systems in the West Philippine Sea. Physico-chemical data, phytoplankton and mesozooplankton samples were collected from stations spanning offshore to reef areas per site. These were subjected to microscopic and stable isotope analysis to determine variability in plankton distribution, phytoplankton and zooplankton interactions, and gain insights into the trophic dynamics a...

Journal of Geophysical Research: Biogeosciences, 2017

The high precipitation around Southeast Asia results in abundant freshwater outflow, which transp... more The high precipitation around Southeast Asia results in abundant freshwater outflow, which transports terrestrial dissolved and particulate material to the world's largest marginal sea, namely, the South China Sea (SCS). To estimate the riverine carbon flux to the SCS, carbonate data from 42 rivers were collected. These results, combined with literature data for 13 rivers, indicate that the concentrations of dissolved inorganic carbon (DIC) are positively correlated with the cation exchange capacity and the bulk density, except for the Low Discharge category. The highest DIC concentration and flux are in the Low and Medium Discharge categories. Negative correlations exist between dissolved organic carbon (DOC) concentrations and the base saturation in the Low and High Discharge categories and between DOC and bulk density in the Low and Medium Discharge categories. However, the correlation between the DOC concentration and the organic carbon content in the soil is only significan...

Science (New York, N.Y.), Jan 5, 2018

Oxygen is fundamental to life. Not only is it essential for the survival of individual animals, b... more Oxygen is fundamental to life. Not only is it essential for the survival of individual animals, but it regulates global cycles of major nutrients and carbon. The oxygen content of the open ocean and coastal waters has been declining for at least the past half-century, largely because of human activities that have increased global temperatures and nutrients discharged to coastal waters. These changes have accelerated consumption of oxygen by microbial respiration, reduced solubility of oxygen in water, and reduced the rate of oxygen resupply from the atmosphere to the ocean interior, with a wide range of biological and ecological consequences. Further research is needed to understand and predict long-term, global- and regional-scale oxygen changes and their effects on marine and estuarine fisheries and ecosystems.

Asian Journal of Agriculture and Development

Geopolitical issues pose a challenge to the holistic management of fisheries and associated ecosy... more Geopolitical issues pose a challenge to the holistic management of fisheries and associated ecosystems in two Philippine fisheries management areas (FMAs 5&6) encompassing the West Philippine Sea. One way to allay these issues is through a common values approach based on heritage. This paper presents evidence of the heritage value of FMAs 5&6 that could be integrated into an ecosystem approach to fisheries management to manage conflicts. This presupposes a common understanding of their heritage value and the fundamental principle that sustaining this value is good—in fact, essential—for everyone and our planet. Heritage value is assessed as a composite and dynamic unity of human gains and investments in the ecological value, economic value, and value to society of ecosystem services, which create cultural significance and socioeconomic worth for communities and peoples. Ecological value is assessed by way of selected indications of the ecosystem services of the two FMAs; economic va...

Estuarine, Coastal and Shelf Science

Abstract The vertical distribution of phytoplankton in the open ocean shows an increase in biomas... more Abstract The vertical distribution of phytoplankton in the open ocean shows an increase in biomass at a depth referred to as the Subsurface Chlorophyll Maximum (SCM) that contributes significantly to the primary production of the water column. Hence, it is important to understand the dynamics that lead its formation and maintenance. This study examines the SCM in the Philippine Sea off the northeast coast of Luzon, utilizing bio-optical and empirical phytoplankton data from two oceanographic cruises conducted northeast of the island of Luzon in May/June 2011 and April/May 2012. Chlorophyll (Chl) profiles were converted to smoothed chlorophyll functions by using a b-spline basis. In 2011, the mean SCM depth was 97.24 m ± 22.33 m with mean SCM concentration of 0.43 μg/L ± 0.09 μg/L while in 2012, mean SCM was deeper at 115.45 m ± 24.25 m and mean SCM concentration of 0.31 ± 0.09 μg/L. Functional principal component analysis showed that the first principal component (PC) explained variability in the SCM depth, the second PC showed variability in the magnitude of the SCM concentration while the third PC accounted for the presence of multiple peaks. K-means clustering using the principal components resulted in three clusters which represented the offshore stations with the deepest SCM, stations within an observed cyclonic eddy with intermediate SCM and stations with coastal and shelf waters showing shallow SCM. Correlation analyses between Chl and physico-chemical and bio-optical parameters showed that Chl was positively correlated to beam attenuation, a bio-optical property that has been used as an alternative proxy for phytoplankton. This suggests that the observed SCMs represent actual increase in phytoplankton biomass. When the influence of the Kuroshio recirculation gyre was dominant in 2011, cooler temperature in surface waters was seen to significantly increase surface Chl. In 2012, highly saline waters from the tropical North Equatorial Current (NEC) waters appeared to lower the Chl distribution, particularly at the SCM. Phytoplankton abundance was recorded to be higher at the SCM than the surface in both years. In 2011, different species of diatoms dominated all clusters, except at the SCM of the coastal and shelf cluster wherein the dinoflagellate Gyrodinium grossestriatum was dominant. Most dominant species from 2011 were conspicuously absent in 2012 and there was a shift to the diatoms Fragilariopsis (surface), Thalassiosira and Rhizosolenia spp. in all clusters. These provide new insights on the phytoplankton community in relation to the changes in the oceanic circulation from subtropical North Pacific water in 2011 to tropical NEC water in 2012.

SCIENCE DILIMAN is published semi-annually (June and December) by the University of the Philippin... more SCIENCE DILIMAN is published semi-annually (June and December) by the University of the Philippines Diliman through the Off ice of the Vice-Chancellor for Research and Development. The journal features articles of pure and applied sciences.

SCIENCE DILIMAN is published semi-annually (June and December) by the University of the Philippin... more SCIENCE DILIMAN is published semi-annually (June and December) by the University of the Philippines Diliman through the Office of the Vice Chancellor for Research and Development. The journal features articles of pure and applied sciences.

Sustainability, Jun 4, 2018

The sequestration of anthropogenic carbon dioxide in the form of organic carbon and its eventual ... more The sequestration of anthropogenic carbon dioxide in the form of organic carbon and its eventual deposition in the sediments is an important component of the marine carbon cycle. In the Sulu Sea, Philippines, organic carbon contents in the sediments have been relatively well studied, but the processes that describe the organic carbon distributions in the water column have not been elucidated. Dissolved and particulate organic carbon (DOC, POC) concentrations were measured at several stations in the Sulu Sea during the northeast monsoon of 2007/2008 to understand the dynamics of organic carbon in this unique internal sea. Analyses of primary productivity estimates, beam attenuation coefficient (at 660 nm) profiles, and correlation coefficients among DOC, POC and other parameters (e.g., apparent oxygen utilization) at different layers of the water column indicate that surface primary productivity, upwelling, bottom intensified flows across sills, and ventilation from shallow sills, which may contain semi-labile DOC that is estimated to largely contribute to microbial respiration in the bathypelagic layer, are the major processes that affect the DOC and POC distributions in the Sulu Sea. The variability of these processes should be taken into consideration when assessing the sustainability of internal and marginal seas as carbon sinks.

Journal of Environmental Science and Management, 2013

Coastal water quality conditions in the months prior to and during the 2010 fish kill of farmed m... more Coastal water quality conditions in the months prior to and during the 2010 fish kill of farmed milkfish (Chanos chanos) in Bolinao and Anda, Pangasinan were determined to have high total dissolved inorganic nitrogen (0.31 – 24.2 μM) and dissolved phosphate (0.09 – 4.47 μM) along the Guiguiwanen and Caquiputan channels. Low N:P ratios (0.18 – 11.7) coincided with the phytoplankton blooms of Alexandrium spp. and Skeletonema costatum in May and June 2010, respectively. The dense bloom of these two phytoplankton species for two consecutive months coupled with their die-off and decomposition depleted dissolved oxygen ( Key words: Eutrophication, fish kill