Total organic carbon and its environmental significance for the surface sediments in groundwater recharged lakes from the Badain Jaran Desert, northwest China

Abstract

Total organic carbon (ToC) content in lake sediments is typically used for the reconstruction of paleoenvironments. it remains uncertain, however, whether these sediment variables in lakes supplied by groundwater in the hinterland of the Badain Jaran Desert are applicable. Moreover, it is still uncertain whether the ToC content in these lakes can be used as a proxy to identify past climatic change and environmental evolution studies. in this study, the spatial distributions of the ToC contents and C/n ratios were analyzed for 109 surface sediment samples collected from five lakes without runoff recharge. The results revealed that the ToC content of the lake surface sediments was extremely low (0.03% -1.01%) and consisted of both allochthonous organic matter carried by wind, as well as autochthonous organic matter generated in the lakes. Within a lake, spatial differences in the amount of ToC found in surface sediments may be caused by several processes including bathymetry topography and wind-induced wave activity. in addition, wind-induced wave activity produces a higher ToC content, which is more pronounced in larger lakes (>0.21 km 2 ) with longer fetches. By contrast, in smaller lakes, organic matter accumulates in the deeper waters, but can be affected by many factors. it is therefore necessary to consider lake area when applying the ToC content of lake sediments for the reconstruction of a paleolake evolution. Furthermore, because the ToC content of lake sediments in hyper-arid regions is extremely low, and the organic matter may have multiple and varied sources, a single proxy (ToC) cannot be used to reconstruct lake evolution.

Environmental Significance of the Chemical Composition of Sediments in Groundwater‐Recharged Lakes of the Badain Jaran Desert, NW China

“…The data of the proportions of the various grain‐size fractions and mean grain‐size data are from Z. Li et al (). The data of TOC and C/N are from Dong et al (). REE = rare earth element; TOC = total organic carbon.…”

“…Mean monthly temperature in this desert varies from −10.3 °C in January to 26.2 °C in July (Q. Chen et al, ; Ma et al, ). The desert is strongly continental, and the annual average precipitation in the hinterland is only ~100 mm, most of which falls in summer (i.e., from June to August) because of the influence of the Asian monsoon in the southeastern part of the desert (Dong et al, ; Ma et al, ). However, mean annual surface water evaporation is more than 1,000 mm (Z. Li, Pan, et al, ; Yang et al, ).…”

“…However, mean annual surface water evaporation is more than 1,000 mm (Z. Li, Pan, et al, ; Yang et al, ). The high ratio of the evaporation to precipitation results in there being no surface runoff (Dong et al, ; Ma et al, ).…”

“…For lakes in the hinterlands of hyperarid desert regions, which are not recharged by river runoff, sediment is transported only by wind (Dong et al, ; Z. Li et al, ). Thus, the sediment transport and deposition processes in such water bodies differ from those in lakes with surface runoff; it remains uncertain whether the sediment chemistry of such desert lakes is affected by multiple processes, such as the sediment source, eolian transport, weathering, and the physical and chemical characteristics of the lake itself.…”

“…Thus, the sediment transport and deposition processes in such water bodies differ from those in lakes with surface runoff; it remains uncertain whether the sediment chemistry of such desert lakes is affected by multiple processes, such as the sediment source, eolian transport, weathering, and the physical and chemical characteristics of the lake itself. Previous studies discussed the paleoenvironmental significance of the spatial distributions of grain size and total organic carbon (Dong et al, ; Z. Li et al, ). Compared to lakes with surface runoff, the mechanisms controlling the spatial variability of sediment chemistry in closed‐basin desert lakes remain unclear.…”