RESUMEN
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 were 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.
Asunto(s)
Fósforo , Contaminantes Químicos del Agua , Carbono/análisis , China , Monitoreo del Ambiente , Eutrofización , Sedimentos Geológicos , Lagos , Nitrógeno/análisis , Fósforo/análisis , Contaminantes Químicos del Agua/análisisRESUMEN
Channelization significantly affects soil erosion in river floodplains. The object of this study was to use 137Cs as a tracer to determine the 137Cs inventory and derived soil erosion rates under various land use types in a catchment on channelized river floodplain in the lower reaches of Yangtze River, China. Sampling was carried out to establish a137Cs reference inventory in a 70-year old paddy field located on the shoulder-slope of a local hill. The mean reference inventory of 137Cs was 1275 Bq m-2, whereas the 137Cs inventory within the catchment ranged from 284 to 1150 Bq m-2 and the soil erosion rates from -33.3 to -2.4â¯tâ¯ha-1 yr-1, respectively. The dominated land use of paddy in cultivated soils contributed relative low soil erosion. Bamboo and castanea mollissima were preferential for local land uses in uncultivated soils in comparison with woodland and Pinnus massoniana. The rates of soil erosion rates in old tea garden were higher than that in new tea garden. Overall, severe soil erosion and no deposition in the entire catchment occurred in the entire catchment due to the human-induced channelization in the 1970s. Our results suggest that restricting farmland being returned to tea plantations, thereby maintaining the current land use types would reduce soil erosion in river floodplain in the future.