The large organic matter flow in tropical coastal areas is recognized as an important process in the global carbon (C) cycle. However, the nature of organic matter flow in semi-enclosed tropical estuaries remains unclear due to the various environmental processes (tidal change, river flow, waves from the sea, and internal circulation) and organic matter sources therein. Thus, sediment organic matter (SOM) sources, and their distribution pattern, are key to understanding ecosystem material flow. Our research in the Batan Bay Estuary, Philippines, a semi-enclosed estuary under large mangrove deforestation, was conducted to determine ecosystem properties through analysis of C and nitrogen stable isotope ratios and environmental factors. First, we determined that mangrove litter, microphytobenthos, and phytoplankton are the main SOM sources in the Batan Bay Estuary. Second, the estuary was classified into three ecological zones (the Bay zone, Back-barrier zone, and River zone). In addition, we estimated SOM source ratios using the Stable Isotope Analysis in R package and determined different organic matter sources in different zone. The high ratios of mangrove litter as SOM indicate that a large amount of terrestrial plant organic matter remains despite the heavy mangrove deforestation that has occurred since the 1980s, and that the Back-barrier zone consists of a different type of ecosystem that promotes accumulation of C from mangrove litter and microphytobenthos.

热带沿海地区的大量有机物流动被认为是全球碳（C）循环的重要过程。然而，由于各种环境过程（潮汐变化，河流流量，海浪和内部循环）和其中的有机物来源，半封闭热带河口中有机物流动的性质仍不清楚。因此，沉积物有机物（SOM）的来源及其分布模式是理解生态系统物质流的关键。我们在菲律宾的Batan湾河口（大红树林砍伐下的半封闭河口）进行了研究，目的是通过分析碳氮稳定同位素比和环境因素来确定生态系统特性。首先，我们确定了红树林凋落物，微型底栖动物，浮游植物和浮游植物是巴坦湾河口的主要SOM来源。其次，将河口分为三个生态区（海湾区，后屏障区和河区）。此外，我们使用R包中的稳定同位素分析估算了SOM的源比，并确定了不同区域中的不同有机物源。红树林枯枝落叶作为SOM的比例很高，尽管自1980年代以来发生了严重的红树林砍伐，但仍保留了大量陆生植物有机质，并且后垒带由促进C积累的不同类型的生态系统组成来自红树林垃圾和微底栖动物。我们使用R包中的稳定同位素分析估算了SOM源比，并确定了不同区域中的不同有机物源。红树林枯枝落叶作为SOM的比例很高，这表明尽管自1980年代以来发生了严重的红树林砍伐，但仍有大量陆生植物有机物存在，并且后垒带由不同类型的生态系统组成，可促进C的积累来自红树林垃圾和微底栖动物。我们使用R包中的稳定同位素分析估算了SOM源比，并确定了不同区域中的不同有机物源。红树林枯枝落叶作为SOM的比例很高，尽管自1980年代以来发生了严重的红树林砍伐，但仍保留了大量陆生植物有机质，并且后垒带由促进C积累的不同类型的生态系统组成来自红树林垃圾和微底栖动物。