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 4μM 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.

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Despite being a major component in the mangrove carbon (blue carbon) budget, "outwelling" flux (or export to the sea) has gained little attention relative to other biogeochemical fluxes and reservoir carbon stock estimations. This study aims to estimate lateral exchange fluxes of dissolved and particulate organic carbon (DOC, POC) and dissolved inorganic carbon (DIC) from the watershed through a microtidal mangrove-dominated estuary to the coastal sea in Panay Island, Philippines. Along the estuarine transect, consistent addition of DOC, DIC, and POC at higher salinities were attributed to mangrove organic matter input. Upstream groundwater input (carbonate weathering) and downstream mangrove organic matter decomposition (possibly sulfate reduction) were the main controls on DIC. DOC corresponded to relatively pure mangrove sources in creek water, while POC was a mixture of detrital and algal organic matter. The mangrove system acted as net exporter of carbon to the sea in both dry and wet seasons. From short-term observations, outwelling fluxes of mangrovederived DOC, DIC, and POC contributed 27-53%, 8-31%, and 42%, respectively, to their estuarine outflow. Unlike other studies, such low percentage for DIC might result from other external nonmangrove input (e.g., watershed carbonate weathering). Overall estuarine carbon flux was dominated by DIC (90-95%) with only minor contribution from DOC. The approach utilized in this study to estimate lateral carbon flux specific to a small mangrove setting can be useful in delineating blue carbon budgets that avoid geographical and methodological biases.

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.

Abstract. The recycling of scarce nutrient resources in the sunlit open ocean is crucial to ecosystem function. Nitrification directs ammonium (NH4+) derived from organic matter decomposition towards the regeneration of nitrate (NO3-), an important resource for photosynthetic primary producers. However, the technical challenge of making nitrification rate measurements in oligotrophic conditions combined with the remote nature of these environments means that data availability, and the understanding that provides, is limited. This study reports nitrite (NO2-) regeneration rate (RNO2 – the first product of nitrification derived from NH4+ oxidation) over a 13 000 km transect within the photic zone of the Atlantic Ocean. These measurements, at relatively high resolution (order 300 km), permit the examination of interactions between RNO2 and environmental conditions that may warrant explicit development in model descriptions. At all locations we report measurable RNO2 with significant variability between and within Atlantic provinces. Statistical analysis indicated significant correlative structure between RNO2 and ecosystem variables, explaining ∼65 % of the data variability. Differences between sampling depths were of the same magnitude as or greater than horizontally resolved differences, identifying distinct biogeochemical niches between depth horizons. The best overall match between RNO2 and environmental variables combined chlorophyll-a concentration, light-phase duration, and silicate concentration (representing a short-term tracer of water column physical instability). On this basis we hypothesize that RNO2 is related to the short-term autotrophic production and heterotrophic decomposition of dissolved organic nitrogen (DON), which regenerates NH4+ and supports NH4+ oxidation. However, this did not explain the observation that RNO2 in the deep euphotic zone was significantly greater in the Southern Hemisphere compared to the Northern Hemisphere. We present the complimentary hypothesis that observations reflect the difference in DON concentration supplied by lateral transport into the gyre interior from the Atlantic's eastern boundary upwelling ecosystems.