Substantial role of check dams in sediment trapping and carbon sequestration on the Chinese Loess Plateau

The study addresses the unresolved fate of terrestrially eroded organic carbon (OC) during lateral transfer and deposition, a key uncertainty in the global carbon budget. While a substantial portion of eroded OC (approximately 34–82%) is deposited in terrestrial depositional systems, most research has focused on aqueous environments (reservoirs and lakes), which often act as net carbon sources due to strong emissions. Dry terrestrial depositional environments (e.g., alluvial fans, floodplains, and especially check dams) remain under-quantified despite their potentially higher sediment and OC storage. The Chinese Loess Plateau (CLP), characterized by severe erosion, arid to semi-arid climate, and dense check-dam networks, provides a natural setting to quantify sediment retention and OC burial in dry depositional systems. The research quantifies the magnitude of sediment and OC burial behind check dams, evaluates OC burial rates and efficiency, and explores the fate (preservation vs. decomposition) of buried OC to clarify whether these systems constitute a significant terrestrial carbon sink and how they influence riverine sediment and carbon fluxes to the ocean.

Prior work indicates that a large fraction of eroded OC is deposited in terrestrial depositional environments, with recent compilations predicting increased sediment and OC burial due to climate change and human activities. However, most studies have emphasized reservoirs and lakes, documenting high OC burial but also high greenhouse-gas emissions, generally making them net atmospheric carbon sources. Dry depositional systems (floodplains, colluvial/alluvial deposits, and check dams) are less studied, though evidence suggests substantial OC storage and differing OC properties that may favor preservation. On the CLP, human interventions (e.g., widespread construction of check dams since the 1970s) have drastically reduced Yellow River sediment loads (~90% decline from pre-1970 to post-2000). Existing studies have evaluated hydrological, ecological, and geomorphic roles of check dams and carbon dynamics in other depositional environments, but a systematic quantification of sediment retention, OC burial rates, and OC burial efficiency in check dams at regional scale has been lacking. This study builds on and extends these findings by providing high-resolution spatial mapping of check dams, large-scale field sampling, and isotope-based decomposition/source partitioning to assess OC burial and preservation in check-dam sediments.

Study area: The Chinese Loess Plateau (~640,000 km²) in the middle reaches of the Yellow River, with 200–600 mm mean annual precipitation (mostly June–September), arid to semi-arid climate, sparse vegetation (grassland), highly erodible loess, and widespread check dams for erosion control. Remote sensing and dam inventory: An object-oriented classification using multi-source high-resolution Google Earth imagery was applied to map the spatial distribution and silted areas of check dams across the CLP, identifying 50,226 existing check dams. Silted farmland area totaled ~93,100 hm², with individual silted areas ranging 0.01–625 hm². Sediment volume and mass estimation: Unmanned Aerial Vehicle (UAV) photogrammetry and virtual dam construction were used to derive an empirical area–volume relationship to estimate sediment volume behind each dam. Bulk density (BD) was measured on 60 samples from six deep profiles (max BD 1.68 g cm−3; depth to 11.3 m), showing a linear depth–BD relationship. BD at half of the estimated sediment depth was used to convert volumes to masses, assuming loess sediment homogeneity. Sediment depths per dam were inferred from the silted area–depth relationship. Field sampling (2017–2021): Surveys encompassed >400 dam-controlled catchments; 86 intact check dams were selected for detailed sampling. Source-area soils (315 samples) were taken as composites of ten 0–5 cm subsamples on a 5×5 m grid. Depositional sediments (2121 samples) were collected using manual drills, impact drills, well-drilling machines, excavators, and manual well digging, typically at the center of silted land. Vertical sampling intervals: every 25 cm from surface to 6 m and every 50 cm below 6 m to as deep as 30 m; sampling generally began at 50 cm to minimize cropland root influence. Laboratory analyses: Particle size distributions were measured by laser analyzer (Mastersizer 2000). Organic carbon (OC) and total nitrogen were measured by K2Cr2O7–H2SO4 oxidation and Kjeldahl methods, respectively, on 0.25 mm-sieved samples. Radiocarbon (Δ14C) was analyzed by AMS (Beta Analytic); stable carbon isotopes (δ13C) were measured using IRMS after H3PO4 pretreatment to remove carbonates. Spatial interpolation of OC: Kriging interpolation of measured OC contents from the 86 depositional profiles was performed over the hilly and gully region (highest dam density) to map spatial OC content, which was then combined with per-dam sediment mass to estimate total OC burial. Temporal sediment and OC burial rates: Historical proportions of sediment trapped by check dams were compiled from the Yellow River Water Resources Commission statistics. These proportions, combined with total estimated sediment retention and OC burial, yielded period-specific retention and burial rates (1970s–2010s). OC burial efficiency estimation: Burial depths of 3–30 m correspond to 7–60 years of burial time. For 86 representative cores, linear regressions of OC content versus burial depth (or time) were used to infer decomposition rate (slope S). OC burial efficiency (OC_b) was estimated as OC_b = 1 − (S × D) / OC_topsoil, where D is burial depth and OC_topsoil is OC content of the topsoil sample. Source partitioning of OC: A binary radiocarbon mixing model separated petrogenic OC (OC_petro; Fm_petro = 0) from biospheric OC (OC_bio), using relationships between Fm × %OC and %OC to derive %OC_petro (x-intercept) and mean Δ14C (Fm) of biospheric OC (slope). Complementary analyses examined relationships between OC and fine particle content, and comparisons of δ13C and C/N ratios between erosion sources and dam deposits to assess OC degradation. Data sources: SRTM 30 m DEM; Yellow River sediment load and tributary data from Yellow River Sediment Bulletin 2021; official statistics on sediment trapped by check dams; geographic and sampling information for the 86 catchments archived at Figshare (DOI provided).

- Inventory and sediment retention: 50,226 active check dams were mapped on the CLP, creating ~93,100 hm² of silted land. Estimated cumulative sediment intercepted during 1970–2020 is 10.2 ± 0.6 Pg, equivalent to ~46% of Yellow River sediment load to the Bohai Sea over the same period. In eight main tributaries, dense check dams reduced sediment loads by 11–53%. - Organic carbon burial magnitude and rates: Based on 2121 samples from 86 deep cores, mean OC content of dam sediments is 0.22 ± 0.21%. Total OC buried is 21.6 ± 9.9 Tg over ~50 years, with an absolute burial rate of 0.43 ± 0.19 Tg C yr−1. Area-normalized OC burial rate is 468 ± 204 g C m−2 yr−1, about an order of magnitude higher than global lake/reservoir averages (~24 and ~169 g C m−2 yr−1, respectively). - Burial efficiency and OC characteristics: Estimated OC burial efficiency in check dams is ~80% (n=86), significantly higher than reservoirs (~44%), lakes (~43%), colluvial/alluvial (~18%), and marine sediments (~24%). Radiocarbon data show old buried OC (mean 5509 ± 2679 yr BP; n=40), with petrogenic OC content 0.07 ± 0.02% comprising ~29.9% of buried OC. Biospheric OC exhibits mean Δ14C activity corresponding to ~2205 yr BP. OC content correlates positively with fine particles (r=0.72, P<0.01, n=540), indicating strong mineral association. δ13C and C/N ratios do not differ significantly between erosion sources and dam deposits, suggesting low decomposition over decades. - Comparative significance: Although absolute burial rates are lower than the national totals for Chinese lakes and reservoirs, per-area burial rates and preservation efficiencies in check dams are substantially higher. The dry, compact, and relatively anoxic depositional conditions, combined with recalcitrant, mineral-associated OC, promote efficient long-term carbon storage. - System-level impacts: Check dams likely reduce Yellow River OC export by 35–39% and avoid additional OC decomposition during fluvial transport (~0.21 Tg C yr−1) given regional decomposition ratios. Planned construction of an additional 56,161 check dams by 2030 is poised to further alter regional sediment and carbon dynamics.

The findings demonstrate that check dams on the Chinese Loess Plateau are major sediment traps and efficient OC burial sites, directly addressing uncertainties in the fate of eroded terrestrial OC. The high burial efficiency (~80%) and elevated area-normalized burial rates indicate that these dry depositional environments function as strong terrestrial carbon sinks, contrasting with many aquatic systems where emissions can offset burial. The old and partly petrogenic nature of the buried OC, its strong association with fine minerals, and the dry, low-oxygen depositional setting help explain the limited decomposition and enhanced preservation. Regionally, the widespread network of check dams has contributed substantially to the dramatic reduction in Yellow River sediment loads (and associated OC fluxes) to the ocean, modifying the downstream carbon cycle. By intercepting both biospheric and petrogenic OC near sources, check dams reduce in-river oxidation and emissions during transport. These results underscore the importance of incorporating dry depositional systems, especially check dams, into regional and global carbon budget assessments and point to practical co-benefits for erosion control and agricultural land creation.

This study provides a comprehensive, region-wide quantification of sediment retention and organic carbon burial by 50,226 check dams on the Chinese Loess Plateau, showing interception of 10.2 ± 0.6 Pg sediment since 1970 and burial of 21.6 ± 9.9 Tg OC with high per-area burial rates (468 ± 204 g C m−2 yr−1) and high burial efficiency (~80%). The results establish check dams as significant terrestrial carbon sinks and key drivers of reduced sediment and OC export in the Yellow River system. Policy and management implications include recognizing check dams in national and global carbon accounting, leveraging their triple benefits (erosion control, carbon sequestration, and agricultural land creation), and carefully planning future dam construction (e.g., the additional 56,161 planned by 2030) with environmental assessments. Future research should refine temporal dynamics of burial and preservation, quantify potential greenhouse-gas emissions from dry depositional systems, improve upscaling across other arid and semi-arid regions globally, and integrate these sinks into Earth system and carbon budget models.

- Spatial interpolation and representativeness: Kriging of OC content was limited to the hilly and gully region with the highest dam density; extrapolation beyond sampled areas introduces uncertainty. Only 86 intact dams were cored among >50,000, which may not capture all spatial variability. - Sediment mass estimation: Sediment volumes were inferred from an empirical area–volume relationship derived via UAV photogrammetry and virtual dam construction, and converted to mass using a depth-based bulk density model (BD at half-depth). These assumptions may not hold uniformly across all dams. - Temporal rates: Period-specific sediment retention and OC burial rates were estimated using proportions from official statistics combined with total retention/burial; the authors note these as rough estimates. - Burial efficiency method: OC burial efficiency was approximated from linear regressions of OC vs. depth (or burial time), a simplified approach that may not capture non-linear diagenetic processes. - Isotopic and compositional constraints: Radiocarbon constraints are based on a subset of samples (n=40), and petrogenic vs. biospheric partitioning uses a binary mixing model assuming Fm_petro = 0; deviations could affect source apportionment. - Land-use influence: Sampling generally began at 50 cm to reduce crop-root influence in cropland overburden; residual bioturbation or root effects cannot be completely ruled out.