DOM commonly found in aquatic environments is an important component of offshore, estuarine (Das, 2018), regulating the behavior, transformation and fate of nutrients and pollutants (Alongi, 2014; Chu et al., 2020; Dittmar and Lara, 2001; Kristensen et al., 2008; Tait et al., 2017). OM in the mangrove forest mainly comes from plant and animal residue decomposition products, microorganisms and their metabolites, plant root secretions, etc. (Zsolnay, 2003). All the forms of OM above continually decompose due to microbial activities to form DOM, which enters the oceans through surface runoff and tidal action(Alongi, 2014; Wu et al., 2012), influencing the carbon and nutrient cycle (Chen et al., 2013; Cory and Mcknight, 2005; Dalmagro et al., 2017; Derrien et al., 2019; Stedmon et al., 2011) and providing bait source for aquaculture near mangrove forests (Lee, 1995; Odum, 1968). Oyster can feed on DOM as a food preference through tidal action, and bait residual, excreta, biological and other organic residues are decomposed into DOM during the breeding process conversely(A et al., 2010; Tang et al., 2022; Wu et al., 2014), resulting in a significantly higher concentration of DOM in the aquaculture sea area than in the surrounding seawaters (Yan, 2019; Yang, 2018). On the other hand, OM can also settle with suspended particle, organic flocs, accumulate in sediments and achieve mineralization and nutrient transformation under the action of extracellular enzymes secreted by microorganisms. It is known that the insoluble compounds in mangroves (e.g., lignin, cellulose) are more difficult to degrade than readily soluble compounds (e.g., algae or OM from municipal domestic wastewater) (Fontaine et al., 2003; Guenet et al., 2010) .For example, lignin consists mainly of p-hydroxyphenyl, guaiacol (or vanillin) and eugenyl units (Pasquini et al., 2005) and the naturally hard-to-degrade polymer lignin is degraded to DOM by the action of peroxidase to provide a reaction substrate for hydrolase (Pasquini et al., 2005; Stursova and Sinsabaugh, 2008). It was pointed out that OM concentration in mangrove sediment is significantly correlated with the hydrolase activity (Jk et al., 2021)d input might affect microbial diversity and enzyme activity in the soil (Guenet et al., 2010). Oyster farm release large amounts of nutrient-rich substances (especially contain N and P) that contribute to water and soil pollution in mangrove forests (Loiola et al., 2022), and changes in the ratio of N to P in mangrove sediment affect the production of related enzymes by microorganisms to achieve a balance between enzyme types, activities, and OM (Luo et al., 2017). For example, phosphatases circulate P in soils by hydrolyzing phosphate monoesters and phosphate diesters into microbially assimilable inorganic phosphorus (Doran et al., 1994; Hou et al., 2015; Huang et al., 2011; Luo et al., 2017), while excessive N input reduces the phosphatase activity (Kang and Lee, 2005; Saiya-Cork et al., 2002; Wang et al., 2014). As a product of enzymatic activity, the type of DOM in the sediments likewise change under the influence of the N/P and enzyme activity. At present, many studies have been conducted on the source, humification characteristics, molecular structure and size, and persistent pollutant-binding characteristics of DOM in mangroves(Burdige et al., 2004; Duan et al., 2020; Yan et al., 2021), but relationships between DOM and N/P concentration and enzyme activity in sediments has not been fully developed(Verhoeven et al., 2015). In this study, we first collected profile sediments from oyster farms near the Zhanjiang mangrove forests in China for TN/TP concentration investigation and then explored the effects of TN/TP concentration on the activities of different enzymes by measuring the activities of Nep, Lip and PPO. Then, we analyzed the UV-Vis spectrum of the DOM in the mangrove sediments and oyster farms. Finally, the influence of relevant enzymes on the UV-Vis spectral characteristics of the DOM under the influence of natural TN/TP in the mangrove forest and oyster farm sediments was obtained.