Abstract
The Haihe River Basin, which is one of the most water-scarce and polluted river basins in China, has abnormally high nitrogen levels. In this study, total hydrolyzable amino acids (THAAs) were measured in surface sediment and sediment core samples in the Haihe River Basin to determine if amino acids were potential sources of ammonium, organic nitrogen, and organic carbon. The rivers were found to be in a state of hypoxia and contain abnormally high levels of ammonium and organic nitrogen. Additionally, NH3-N was the predominant form of inorganic nitrogen in the surface sediments, while organic nitrogen accounted for 92.53% of sedimentary nitrogen. THAAs-C accounted for 14.92% of the total organic carbon, while THAAs-N accounted for more than 49.59% of organic nitrogen and 45.68% of total nitrogen. The major fraction of THAAs were protein amino acids. Three sediment cores of the most heavily polluted rivers also showed high levels of THAAs. Evaluation of the degradation index (DI) of sedimentary organic matter in sediments evaluated based on the THAAs revealed that most positive DI values were found in the downstream portion of the Ziya River Watershed. Additionally, the DI of surface sediment was correlated with THAAs (r2 = 0.763, p < 0.001), as was the DI of sediment cores (r2 = 0.773, p < 0.001). Overall, amino acids in sediments were found to be an important potential source of ammonium, organic nitrogen, and organic carbon.
Highlights
IntroductionSedimentary organic matter plays an important role in sediment biogeochemical processes [1], and 30%–99% of organic matter deposited on the surface sediment is remineralized during early diagenesis [2]
Evaluation of the degradation index (DI) of sedimentary organic matter in sediments evaluated based on the total hydrolyzable amino acids (THAAs) revealed that most positive DI values were found in the downstream portion of the Ziya River Watershed
Sedimentary organic matter plays an important role in sediment biogeochemical processes [1], and 30%–99% of organic matter deposited on the surface sediment is remineralized during early diagenesis [2]
Summary
Sedimentary organic matter plays an important role in sediment biogeochemical processes [1], and 30%–99% of organic matter deposited on the surface sediment is remineralized during early diagenesis [2]. Factors such as sediment physicochemical properties, water column depth, and redox conditions, especially the compositions of organic matter, influence organic matter degradation [3]. The chlorin index, which is based on degradation products of chlorophyll, has been successfully applied to estimate organic matter freshness in marine sediments [4]. High total hydrolyzable amino acids concentrations have been shown to be correlated with a low chlorin index [5].
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