Transitional ecosystems, estuaries and the coastal seas, are distinctively affected by natural and anthropogenic factors. Organic matter (OM) originating from terrestrial sources is exported by rivers and forms a key component of the global biogeochemical cycles. Most previous studies focused on the bulk biochemical and anthropogenic aspects affecting these ecosystems. In the present study, we examined the sources and fate of OM entrained within suspended particulate matter (SPM) of the Zuari River and its estuary, west coast of India. Besides using amino acid (AA) enantiomers (L- and D-forms) as biomarkers, other bulk biochemical parameters viz. particulate organic carbon (POC), δ¹³C, particulate nitrogen (PN), δ¹⁵N and chlorophyll a were analyzed. Surprisingly no significant temporal variations were observed in the parameters analyzed; nonetheless, salinity, POC, δ¹³C, PN, δ¹⁵N, glutamic acid, serine, alanine, tyrosine, leucine and D-aspartic acid exhibited significant spatial variability suggesting source differentiation. The POC content displayed weak temporal variability with low values observed during the post-monsoon season attributed to inputs from mixed sources. Estuarine samples were less depleted than the riverine samples suggesting contributions from marine plankton in addition to contributions from river plankton and terrestrial C₃ plants detritus. Labile OM was observed during the monsoon and post-monsoon seasons in the estuarine region. More degraded OM was noticed during the pre-monsoon season. Principal component analysis was used to ascertain the sources and factors influencing OM. Principally five factors were extracted explaining 84.52% of the total variance. The first component accounted for 27.10% of the variance suggesting the dominance of tidal influence whereas, the second component accounted for heterotrophic bacteria and their remnants associated with the particulate matter, contributing primarily to the AA pool. Based on this study we ascertained the role of the estuarine turbidity maximum (ETM) controlling the sources of POM and its implications to small tropical rivers. Thus, changes in temporal and regional settings are more likely to affect the natural biogeochemical cycles of small tropical rivers.

中文翻译：

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热带小河（印度Zuari河）中颗粒有机物的来源及其影响

过渡性生态系统，河口和沿海海洋受到自然和人为因素的明显影响。源自陆地的有机物（OM）通过河流出口，并构成全球生物地球化学循环的关键组成部分。以前的大多数研究都集中在影响这些生态系统的大量生化和人为方面。在本研究中，我们检查了印度祖拉里河及其河口悬浮颗粒物（SPM）中夹带的OM的来源和去向。除了使用氨基酸（AA）对映异构体（L和D形式）作为生物标记物外，其他大量生化参数也适用。颗粒有机碳（POC），δ ¹³ C，颗粒氮（PN），δ ¹⁵ N和叶绿素一个被分析。令人惊讶的是，在所分析的参数中没有观察到明显的时间变化。尽管如此，盐度，POC，δ ¹³ C，PN，δ ¹⁵ N，谷氨酸，丝氨酸，丙氨酸，酪氨酸，亮氨酸和d天冬氨酸表现出显著空间变异表明源分化。POC含量显示出较弱的时间变异性，季风后季节观察到的低值归因于混合来源的输入。河口样品的消耗量少于河流样品，表明海洋浮游生物的贡献以及河流浮游生物和陆地C _3的贡献植物碎屑。在河口地区在季风和季风后的季节观察到不稳定的OM。在季风前季节，观测到更多的OM降解。主成分分析被用来确定影响OM的来源和因素。主要提取了五个因素，解释了总方差的84.52％。第一部分占潮汐影响的27.10％，表明潮汐影响占主导地位，而第二部分占异养细菌及其与颗粒物相关的残余物，主要是AA池。根据这项研究，我们确定了最大河口浊度（ETM）控制POM的来源及其对热带小河流的影响。从而，