Understanding the redistribution of soil organic carbon (OC) driven by erosion contributes to the global carbon budget and watershed management. Quantifying the sources of eroded OC in sediments provides new insights to addressing this issue. However, limited quantitative information on the factors influencing OC sources has constrained the behavior of regulating the OC exported from the watershed. Here, we explored the sources of OC in lake sediments over the last 100 years and quantified the effects of climate change and human activities on OC sources. Results from the stable isotope fingerprinting and MixSIAR model indicated that phragmites (30.34%) and croplands (21.48%) were consistently the main OC sources. Therefore, efforts should be concentrated on controlling soil erosion from cropland and managing the endogenous environment. In addition, the partial least squares pathways (PLS-PM) and random forests revealed that human activities (Path coefficients (r∂): 0.45 to 0.61) have controlled the OC sources over the last hundred years. Agricultural activities, urbanization, and land use change altered the quality of OC sources by affecting the vegetation productivity in source areas. The quantity of OC sources was also influenced by underlying surface and surface connectivity changes. The effects of climate change (temperature (r∂): −0.41 to 0.1; precipitation (r∂): 0.1 to 0.29) on OC sources have not been significant, but their long-term effects cannot be ignored. These findings provide a better insight into the origin and behavior of OC in lake sediments under global change, which is crucial for basin management and lake governance. 

Human activities control the source of eroded organic carbon in lake sediments over the last 100 years: Evidence from stable isotope fingerprinting

Intertidal wetlands are important carbon reservoirs that play a significant role in climate change mitigation. However, the lack of large-scale quantification and source identification of sediment organic carbon (SOC) in different discharge estuaries hampers the assessment of the carbon storage potential in these systems. In this study, based on the elemental ratios and stable carbon isotopes of the core sediment from the intertidal wetlands along the east coast of China, we quantified the contribution of organic carbon (OC) derived from terrestrial/estuarine particulate organic matter (POM), marine phytoplankton, and local plants, such as mangrove and salt marsh plants in the study area. We explored the hydrological and plant drivers controlling the variation in the contribution of OC sources among different coastal environmental settings. We found that SOC in high discharge estuaries (river runoff more than 50 billion m3/a) originated predominantly from terrestrial/estuarine POM (45 ± 6%), whereas the primary source for low discharge estuaries was marine phytoplankton OC (51 ± 14%). Moreover, our estimates revealed a sharp increase in the contribution of OC from mangroves to deep sediments compared with surface sediments, owing to the infiltration of mangrove roots at greater depths and the slow degradation of roots contributing to the substantial refractory OC buried in the deep sediments. These findings indicate that carbon storage in the intertidal wetlands varies among contrasting coastal environmental conditions, which provides implications for intertidal wetlands as a critical carbon sink in the global carbon budget. 

Source Identification and Estimation of Organic Carbon in the Intertidal Wetlands of the Eastern Coast of China

Identifying organic carbon (OC) sources in lake sediment is essential for elucidating biogeochemical cycling processes and effectively supporting watershed management. However, the complexity of sources as well as environments in the land–river–lake continuum makes it challenging to accurately identify OC sources. Accordingly, the current study utilized a systematic approach to identify and validate OC sources in a typical land–river–lake continuum. Two tracer groups (group 1: δ13C and δ15N; group 2: fluorescence index and biotic index, respectively (where C is carbon and N is nitrogen)) and one model (MixSIAR) were eventually selected from five tracer groups and two models to identify the OC sources in a land–river–lake continuum according to a consistency evaluation and virtual mixing test. The results showed that the distribution of OC sources in lake sediment was spatially heterogeneous. Closer to the lake center (from sampling site S1 to S3), the autochthonous contributions increased while the allochthonous contributions decreased. Downstream of the inlet river (site S1) was dominated by allochthonous contributions (78.6%), especially cropland (28.7% ± 0.5%, where ± indicates a standard deviation range) and urban land (30.5% ± 2.5%). From site S1 to S2, the allochthonous contribution decreased 11.4%. Autochthonous OC gradually became the major source closer to the lake center (site S3: phragmites: 48% ± 4.5%). This distribution of OC sources in the land–river–lake system was attributed to the mixing effect of the autochthonous sources, selective transport of sediment, and human activities. The current findings may aid in validating the ability of different tracers and models to identify OC sources in complex ecosystems and also provide a theoretical basis for watershed management. 

Quantification of sedimentary organic carbon sources in a land–river–lake continuum combined with multi-fingerprint and un-mixing models

Intertidal wetlands are important carbon reservoirs that play a significant role in climate change mitigation. However, the lack of large‐scale quantification and source identification of sediment organic carbon (SOC) in different discharge estuaries hampers the assessment of the carbon storage potential in these systems. In this study, based on the elemental ratios and stable carbon isotopes of the core sediment from the intertidal wetlands along the east coast of China, we quantified the contribution of organic carbon (OC) derived from terrestrial/estuarine particulate organic matter (POM), marine phytoplankton, and local plants, such as mangrove and salt marsh plants in the study area. We explored the hydrological and plant drivers controlling the variation in the contribution of OC sources among different coastal environmental settings. We found that SOC in high discharge estuaries (river runoff more than 50 billion m3/a) originated predominantly from terrestrial/estuarine POM (45 ± 6%), whereas the primary source for low discharge estuaries was marine phytoplankton OC (51 ± 14%). Moreover, our estimates revealed a sharp increase in the contribution of OC from mangroves to deep sediments compared with surface sediments, owing to the infiltration of mangrove roots at greater depths and the slow degradation of roots contributing to the substantial refractory OC buried in the deep sediments. These findings indicate that carbon storage in the intertidal wetlands varies among contrasting coastal environmental conditions, which provides implications for intertidal wetlands as a critical carbon sink in the global carbon budget.

Optimal Mapping of Soil Erodibility in a Plateau Lake Watershed: Empirical Models Empowered by Machine Learning

The applicability of commonly-used tracers in identifying eroded organic matter sources

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The applicability of commonly-used tracers in identifying eroded organic matter sources