Spatiotemporal variability of hypoxia and eutrophication in Manila Bay, Philippines during the northeast and southwest monsoons (original) (raw)
Related papers
2017
Manila Bay is a major source of livelihood for the fishermen living around the area. The occurrence of hypoxia, a state where dissolved oxygen (DO) is not enough to support marine life, poses a serious threat to the bay and consequently to its fisheries sector. This study documents the variation of hypoxia throughout the bay for a sampling period of four years, from January 2012 to November 2015, with a monthly interval each survey. A total of 24 field surveys on 16 designated sampling stations, at varying depths, were conducted. Results show that hypoxia was present all year round but was more severe during the wet season (July, September, November) compared to the dry season. The averages of bay-wide DO concentration ranged from 3.42 to 7.63mg/l during the 4-year survey. Low DO concentrations were associated with high concentrations of nutrients, particularly nitrate. Nitrate spiked to a 44.6 µM concentration while bay-wide DO concentration dropped to as low as 0.01 mg/l in the we...
Hypoxia in Manila Bay, Philippines during the northeast monsoon
Marine Pollution Bulletin, 2011
Herein we present results from one of the first extensive bay-wide oceanographic surveys of Manila Bay, wherein 31 stations were sampled during the northeast monsoon (cold and dry season). A band of hypoxic bottom water (dissolved oxygen <2.8 mg/L) spanned the midsection of the bay from east to west. Bottom nitrate concentrations (5.7–16.8 μM; avg. 11.1 μM) and total organic carbon values in sediments (1.7–3.1%; avg. 2.4%) were high in the midsection, which coincided with the band of hypoxic bottom water. Physical processes and site-specific accumulation of organic material likely lead to hypoxic conditions in Manila Bay, even during the northeast monsoon period when the water column is relatively well mixed. The results of this study complement the previously reported widespread hypoxia that occurs during the rainy season. Thus, hypoxia may be pervasive in the bay throughout the year, although it varies in intensity and spatial extent.► Hypoxia in Manila Bay during the NE monsoon (dry season) is confined to the midsection of the bay. ► Physical features and stratification at deeper parts of the bay may promote occurrence of hypoxia. ► Organic material breakdown, nitrification, and sediment oxygen demand likely cause DO depletion. ► During the southwest monsoon (wet season), hypoxia is expected to be more widespread.
Eutrophication of Manila Region, Philippines
2014
In the Philippines about 37% of the total water pollution originates from agricultural practices, which include use of animal waste, fertilizer and pesticide runoff. As a consequence, eutrophication is observed in the Manila coastal region in connection with the major drainage region around Manila. The PasigMarikina-Laguna de Bay Basin as a water drain to Manila Bay is unique because it represents an interconnection between several water bodies and is partly controlled by the Manggahan Floodway and the Napindan Hydraulic Control Structure. The high nutrient emission from Manila and the catchment area around the Manila Bay results in eutrophication of the bay and its adjacent coastal waters. Chlorophyll estimates with satellite measurements show elevated levels and it seems that eutrophication of Manila Bay is present throughout the year but is decoupled from the monsoon seasons.
Environmental Monitoring and Assessment, 2018
The Laoyehai (lagoon) is located at the east coast of Hainan Island in the South China Sea and has been subject to perturbations from human activities, notably marine aquaculture, and has eutrophic surface and hypoxic near-bottom waters. A lack of knowledge of hydrodynamic and biogeochemical processes is a challenge to the sustainable management of lagoon at the ecosystem level in science. Five field campaigns, including three during the southwest monsoon and two in the northeast monsoon periods, were carried out at the Laoyehai in 2008-2011. The aim of this study is to investigate the impacts of dynamic processes of hydrography and human activities on nutrient geochemistry and their relationships to the system eutrophication and hypoxia in the lagoon. In this coastal system, high levels of ammonium relative to nitrate are found, elevated phosphate skews the DIN/DIP relative to the Redfield ratio, and the dissolved silicate concentration is high because of submarine groundwater discharge. The organic fraction in the Laoyehai accounts for a large proportion of the total nutrients associated with the release of wastes from marine aquaculture. The hypoxia of near-bottom waters in the Laoyehai is created and maintained by heterotrophic processes that are fueled by organic matter, which are exacerbated by poor water exchange as a consequence of the geomorphology and weak tidal circulation.
Pollution study in Manila Bay: Eutrophication and its impact on plankton community
… Research in Asia, 2009
Eutrophication and chemical pollution due to human activities have seriously affected coastal ecosystems during the last three decades. Manila Bay is one typical example suffering from such pollution problems. In the present study, the distribution of plankton community was investigated in June 2008 in relation to abiotic environmental parameters (salinity, temperature and dissolved oxygen concentration) and pollution factors particularly nutrient concentrations. The dissolved oxygen concentrations near bottom were lower than 3 mg l -1 inside of the bay. Average concentrations and standard deviations of dissolved inorganic nitrogen, nitrate, nitrite and ammonium in near surface were 0.90 ± 0.53, 0.10 ± 0.16 and 8.00 ± 1.35 µM, respectively. Northeastern area near Metro Manila showed higher concentrations of nitrogen. Phosphate and silica showed higher concentrations near northern shore with average concentrations of 0.92 ± 0.34 and 28.87 ± 9.53 µM, respectively, over the bay. From the results, Manila Bay is thought to be highly eutrophicated with high nitrogen concentration particularly ammonium. Among phytoplankton, the centric diatom, Stephanopyxis spp. were dominant, and they occupied 44% of total phytoplankton biomass. The small Cyclopoida Oithona spp. occupied 42% of total mesozooplankton abundance. Consequently, the plankton community of Manila Bay showed a structure composed of higher microbial activity and primary production but lower secondary production, particularly with lower mesozooplankton abundances.
Groundwater discharge as an important land-sea pathway into Manila Bay, Philippines
2010
TANIGUCHI, M.; BURNETT, W.C.; DULAIOVA, H.; SIRINGAN, F.; FORONDA, J.; WATTAYAKORN, G.; RUNG-SUPA, S.; KONTAR, E.A., and ISHITOBI, T., 2008. Groundwater discharge as an important land-sea pathway into Manila Bay, Philippines. Journal of Coastal Research, 24(1A), 15-24. West Palm Beach (Florida), ISSN 0749-0208.
Marine Pollution Bulletin, 2016
The dynamics of nitrogen (N) and phosphorus (P) was studied in mariculture areas around Bolinao and Anda, Philippines to examine its possible link to recurring algal blooms, hypoxia and fish kills. They occur despite regulation on number of fish farm structures in Bolinao to improve water quality after 2002, following a massive fish kill in the area. Based on spatiotemporal surveys, coastal waters remained eutrophic a decade after imposing regulation, primarily due to decomposition of uneaten and undigested feeds, and fish excretions. Relative to Redfield ratio (16), these materials are enriched in P, resulting in low N/P ratios (~6.6) of regenerated nutrients. Dissolved inorganic P (DIP) in the water reached 4 μM during the dry season, likely exacerbated by increase in fish farm structures in Anda. DIP enrichment created an N-limited condition that is highly susceptible to sporadic algal blooms whenever N is supplied from freshwater during the wet season.
Nutrient cycling in tropical and temperate coastal waters: Is latitude making a difference?
Estuarine, Coastal and Shelf Science, 2021
Tropical coastal waters are highly dynamic and amongst the most biogeochemically active zones in the ocean. This review compares nitrogen (N) and phosphorus (P) cycles in temperate and tropical coastal waters. We review the literature to identify major similarities and differences between these two regions, specifically with regards to the impact of environmental factors (temperature, sunlight), riverine inputs, groundwater, lateral fluxes, atmospheric deposition, nitrogen fixation, organic nutrient cycling, primary production, respiration, sedimentary burial, denitrification and anammox. Overall, there are some similarities but also key differences in nutrient cycling, with differences relating mainly to temperature, sunlight, and precipitation amounts and patterns. We conclude that due to the differences in biogeochemical processes, we cannot directly apply cause and effect relationships and models from temperate systems in tropical coastal waters. Our review also highlights the considerable gaps in knowledge of the biogeochemical processes of tropical coastal waters compared with temperate systems. Given the ecological and societal importance of tropical coastal waters, we hope that highlighting the differences and similarities to temperate systems as well as the existing gaps, will inspire further studies on their biogeochemical processes. Such knowledge will be essential to better understand and forecast impacts on tropical coastal nutrient cycling at local, regional, and global scales.