In recent years, climate change has led to frequent eutrophication of lakes in cold-arid regions. To explore the potential release of P in sediments in cold-arid regions and its impact on eutrophication, we investigated P in Hulun Lake and Ulanor Wetland, lakes typical of cold-arid regions of China. Using continuous extraction of P and gradient diffusion film technology (DGT), the characteristics of P in the overlying water and sediments of Hulun Lake and Ulanor Wetland were analyzed. Bioavailability and the potential for release of P in sediments were evaluated. Mean concentrations of total P (TP) in the overlying water of Hulun Lake and Ulanor Wetland were 0.21 and 0.27 mg/L, respectively, mainly in particulate form. These concentrations fall into Class V for surface water, indicating inferior quality. The sediments of Hulun Lake and Ulanor Wetland mainly contain calcium-bound P and residual P, which together accounted for 68.7% and 67.0% of total P, respectively. The mean concentrations of bioavailable P (CDGT-P) in the sediments of Hulun Lake and Ulanor Lake were 0.04 and 0.01 mg/L, respectively, lower than those of Taihu Lake and Dianchi Lake, indicating low bioavailability of P in sediments. The concentration of inorganic P in the interstitial water of the surface sediments in Hulun Lake and Ulanor Wetland was higher than that in overlying water, indicating that there was a risk of P release from sediments. However, the recharge capacity of P from sediments was limited.

Sediment (SOM) and suspended particulate (SPOM) organic matters are two important organic matters in water. Their occurrence, migration and transformation, and stability have important effects on the environmental behaviors of carbon, nitrogen, phosphorus, and other pollutants in a water environment. The content, composition, fluorescence characteristics, source, and stability of SOM and SPOM in Hulun Lake, a typical lake in cold and arid region of China, were compared by sequential extraction, three-dimensional fluorescence spectroscopy, parallel factor technique, carbon-nitrogen ratio, and stable carbon isotope. SOM and SPOM in north and west were higher than those in east and south. The average content of SPOM (24.70 ± 4.63 g/kg) was slightly higher than that of SOM (23.04 ± 10.27 g/kg), but the difference was not significant. Humin was the dominant component in SOM and SPOM, accounting for 73.7% and 61.2%, respectively. Humus was the main fluorescence component of water-extractable organic matter in SOM and SPOM, accounting for 79.9% and 70.4%, respectively, of the total fluorescence intensity. SOM and SPOM were derived from terrestrial sources with relative contribution rate of about 70%. SPOM was more influenced by autochthonous sources and had significantly lower humification degree and stability than SOM. Effects of climate changes on migration, transformation, stability, and bioavailability of organic matters and endogenous pollutants closely related to organic matters in lakes of cold and arid regions should be paid attention in the future.

Lake organic matter is one of the important forms of terrestrial carbon, and its sedimentary evolution is affected by many factors such as climate and source. However, few studies have been conducted on the bidirectional feedback mechanism between the sedimentary evolution of organic matter and climate change in cold and arid lakes. Historical variations of the sediment organic matter (SOM) and source construction of Hulun Lake, a typical lake in the cold and arid region of China, were studied by multiple methods. The interactions and feedback mechanisms between the sedimentary evolution, climate change, and source construction change were also discussed. Overall, the characteristic indexes of the SOM showed obvious and uniform characteristics of periodical changes. The indexes were relatively stable before 1920, and uctuated from 1920 to 1979. Since the 1980s, the total organic carbon, carbon stable isotope, and uorescence intensity of the protein-like component in the water extractable organic matter in the SOM has increased, while the carbon to nitrogen ratio decreased. The absolute dominant contribution of terrestrial source to the SOM had changed, and the relative average contribution rate of autochthonous source increased from 17.6% before 1920 to 36.9% after 2000. The increase of temperature, strong evaporation concentration effect, and the source construction change are the important driving factors of the sedimentary evolution of organic matter in Hulun Lake.

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