Abstract：
Dissolved organic matter (DOM), a pivotal component in the global carbon cycle, plays a crucial role in maintaining the productivity and functionality of aquatic ecosystems. However, the driving factors of variations in the properties of riverine DOM in tropical islands still remain unclear. In this study, the spatiotemporal response of the optical characteristics of riverine DOM to seasonality and land use on Hainan Island in southern China was investigated. Our results revealed that DOM in the rivers of Hainan Island exhibited a relatively high proportion of fulvic acid and demonstrated strong terrestrial sources. The optical properties of DOM exhibited significant variations both seasonally and spatially. Land use exerted a dominant influence on riverine DOM. Specifically, during the wet season, riverine DOM exhibited larger molecular weight, increased chromophoric DOM (CDOM) abundance, and higher Fmax compared to the dry season. Furthermore, riverine DOM influenced by grassland and farmland showed higher CDOM abundance, Fmax, and humification degree in contrast to those impacted by forest and urban. Random forest and correlation analysis results indicated that grassland and farmland enhanced the Fmax of DOM by increasing levels of TP, NO3--N, Chl a, and NH4+-N in the dry season. However, during the wet season, the increased Fmax of DOM induced by grassland and farmland relied on the increments of Chl a and TP concentrations. This study improves our understanding of the spatiotemporal fluctuations of DOM in the rivers of Hainan Island, highlighting the effects of season and land use on DOM. It offers valuable support for improving water quality and contributes to enhancing human comprehension of the global carbon cycle.
摘要：
溶解有机物(DOM)全球碳循环的关键组成部分，在维持水生生态系统的生产力和功能方面起着至关重要的作用。然而,热带岛屿河流DOM性质变化的驱动因素仍不清楚。在这项研究中,研究了中国南方海南岛河流DOM光学特征对季节性和土地利用的时空响应。我们的结果表明，海南岛河流中的DOM显示出相对较高的富里酸比例，并显示出强大的陆源。DOM的光学特性在季节和空间上都表现出明显的变化。土地利用对河流DOM产生了主要影响。具体来说,在雨季，河流DOM表现出较大的分子量，增加发色DOM(CDOM)丰度，与旱季相比，Fmax更高。此外，受草地和农田影响的河流DOM显示出较高的CDOM丰度，Fmax,与受森林和城市影响的程度形成鲜明对比。随机森林和相关分析结果表明，草地和农田通过增加TP水平来提高DOM的Fmax，NO3--N,Chla,和NH4+-N在旱季。然而,在雨季，草地和农田引起的DOMFmax增加依赖于Chla和TP浓度的增加。这项研究提高了我们对海南岛河流DOM时空波动的认识，强调季节和土地利用对DOM的影响。它为改善水质提供了宝贵的支持，并有助于增强人类对全球碳循环的理解。
