AHW20-10 日本地球惑星科学連合2018年大会
Stable Isotopes Reveal Anthropogenic Impacts on the Littoral Food
Webs of Laguna de Bay, Philippines
*Elfritzson Martin Peralta1,3, Cybill Bacinillo2, Jesusa Christine Balani2, Shairah Basmala2, Earl
John Serafin Calalin2, Maureen Althea Calleja2, Jennifer Bea Go2, Mariah Therese Gosiengfiao2,
Francesca Anna Valdecañas2, Julie-An Gregorio4, Norman Mendoza5, Takuya Ishida6, Francis
Magbanua4, Jonathan Carlo Briones1,2,3, Rey Donne Papa1,2,3, Noboru Okuda6
1. Research Center for the Natural and Applied Sciences, University of Santo Tomas (UST), Philippines, 2. Department
of Biological Sciences, UST, 3. The Graduate School, UST, 4. Institute of Biology, University of the Philippines,
Philippines, 5. Philippine Nuclear Research Institute, 6. Research Institute for Humanity and Nature, Japan
Freshwater ecosystems are currently threatened because of unsustainable urbanization. Human activities
in catchment alter lake and marine ecosystems through rivers. Especially in developing countries, lake
ecosystems in urban areas are heavily affected by industry, sewage, household wastes, and deforestation.
Driven by rapid population growth in the Philippines, Laguna de Bay (LDB) is highly suitable test
ecosystem to further understand how anthropogenic disturbances impact biological communities and
trophic relations in lakes. We aim to assess such impacts using land use data and human population
density (HPD) of each catchment surrounding the LDB. Moreover, we use carbon (δ13C) and nitrogen (δ
15
N) stable isotope analysis to examine how human activities in the catchment affect water quality, and in
turn, littoral food webs at 30 sites of the LDB. In all these sites, we measured total nitrogen and total
phosphorus as indicators for nutrient loadings from the catchment and total dissolved solids, dissolved
oxygen, conductivity, pH, salinity, temperature as physico-chemical environments. We collected biological
samples zoobenthos, phytoplankton, meio- and macrozooplankton, and Oreochromis niloticus. We also
collected epilithic organic matter (EOM) and particulate organic matter (POM) as basal resources of
littoral food webs. We measured δ13C and δ15N for these samples. With an 82% cumulative variance
from PC1 and PC2, principal component analysis successfully clustered sites according to its bays
(Central, West, East, and South). The results showed that the sites in the Central and West Bays are more
disturbed than the ones in the East and South Bays which is reflected in the water quality parameters and
community structures of mollusks and zooplankton around LDB. Ultimately, significant variation (Kruskal
Wallis H test, P < 0.01) among the trophic levels of benthic and pelagic primary consumers (mollusks and
zooplankton, respectively) and O. niloticus between sites was observed which may indicate heterogeneity
of water quality due to varying degrees of anthropogenic disturbances. Our isotope data on food webs
provide clarity and evidence on the link between human activities and food web properties in the lake
ecosystem.
Keywords: trophic position, stable isotope analysis, food web, human population density, eutrophic lake
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