Discriminating the potential sources contributing to lacustrine sediment is helpful for decision-making for catchment soils and lake management strategies within lake-catchment systems. Using a sediment fingerprinting approach from the multivariate mixing model, the spatiotemporal sources of geology and land use were identified in a small agricultural catchment in southwest China. Results showed that sediment accumulation rates (SARs) were estimated to range from 0.002 to 0.065 g cm−2 a−1 (mean 0.015 ± 0.016 g cm−2 a−1), which has a positive correlation with instrumental Indian Summer Monsoon (ISM) precipitation. Time-integrated sources were divided into four zones in combination with the changes in SARs, which were qualitatively and quantitively interpreted by particle size, and precipitation, and historical land use polies over the past ~160 years. Spatially, Quaternary granite (QG) in geology and channel bank (CB) in land use were the dominant contributors to the lakeshore sediment, respectively. Two relatively higher contributions of abandoned land (AL) to lakeshore sediment were found during the periods of 1930s–1950s and post-1990s, which originated from the dual impacts of topographical factors of slope gradient and elevation, and socioeconomic factors of the gap of farmer’s expenditure to income. The results illustrate that restricting the farmland to be abandoned would be useful for reducing the soil erosion within the lake-catchment system.
The long-term accumulation, burial and release of nutrients, such as carbon (C), nitrogen (N) and phosphorus (P) in lacustrine sediments are responsible for the global lake eutrophication. Interpretation of the spatiotemporal sedimentary record of nutrients (C, N and P) in contrasting trophic level of lakes is helpful for understanding the evolutionary process of water eutrophication. Based on the radiochronology of 210Pbex and 137Cs, a comparative study of spatial and temporal concentrations, burial of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP), the sources of organic matter were conducted using sediment cores from two plateau lakes Dianchi (DC) and Fuxian (FX) of SW China. Results showed that concentrations and burial of C, N and P in sediments of DC, a shallow hypertrophic lake with the maximum depth of 5.8 m, were both higher than those in FX, an oligotrophic deep lake with the maximum depth of 155.0 m. For both lakes the molar ratio of TOC/TN increased in the sediments moving from north to south. The values of TOC/TN molar ratios increased over time in DC and was higher than in FX. The extremely high values of TOC/TN appeared in the central and southern parts of FX, indicating the impacts of accumulation effect and sediment focusing in the deeper region and indirect supplement from the Lake Xingyun (XY), an adjoining lake connected with FX via the Gehe River. Time-integrated sources identification in DC indicated the contribution of allochthonous sources was dominant over the past few decades, which contributed to the increased trophic level of the lake. The comparison of relationships of carbon accumulation rates (CAR), nitrogen accumulation rates (NAR) and phosphorous accumulation rates (PAR), the ratios of N/P and the utilizations of N and P fertilizer between DC and FX implied that both of N and P inputs should be limited for reducing the trophic level, but N control was predominant in comparison with P for both lakes. The results indicated that caution is required in plateau lakes to limit transition from oligotrophic to eutrophic in these lakes.
<p>Evaluation of the spatial and temporal composition of floodplain sediments and soils is critical in the creation of advanced soil management strategies for riverine catchments. The fertile catchment of the River Avon (Southwest, England) has natural and anthropogenic impacts that require enhanced definition aiding the development of a catchment management plan. The catchment was compartmentalized into its main functional units namely, cultivated land, pasture, woodland, wet moorland, and channel bank. Sediment samples were collected in each unit as surface soils and four cores were obtained along the floodplain. The samples were analyzed for particle size, fallout radionuclides and elemental concentrations. Sediment particle sizes and sediment accumulation rates (SARs) were affected by the construction of a reservoir, whereby the distributions of silt and clay in the floodplain were most affected over the past 60 years. Fertilizer components, Cr and P, were correlated in the mid-catchment, which unraveled downstream due to elevated concentrations of Cr from a geological source. Copper, As, Pb and Sn had variable down-core distributions, with pulses in concentrations due to mining inputs. The contributions of the end-member sources of particulate elements were evaluated, quantitatively, using a Bayesian Mixing Model. The statistics showed that cultivated land made a significant contribution to the sediment mixtures, independent of space and time. The results contribute to improvements in soil quality and soil conservation measures for the Avon which maybe applicable to other small catchments in the UK and elsewhere.</p>
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