科研之友
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摘要
We examined intra-basin spatial variability of sedimentary geochemical and isotopic signals using a network of five sediment cores from a small lake in southern Costa Rica with a history of prehistoric maize agriculture in its watershed. All cores show a similar pattern of agricultural activity (2000-1000 cal yr BP), a transitional period of forest recovery (1000-675 cal yr BP), and a period after forest reestablishment (675-400 cal yr BP). During the agricultural period, bulk sediment stable carbon isotope ratios (delta C-13(TOC)) indicate significant forest clearance, percent total organic carbon (%TOC) is low due to accelerated erosion and dilution from mineral inputs to the lake, and carbon/nitrogen (C/N) ratios are consistent with increased productivity. At the conclusion of the agricultural period, delta C-13(TOC) and %TOC indicate rapid forest recovery and reduced mineral inputs and C/N ratios suggest lower lake productivity. There is little between-core variation in the magnitude of the agricultural signal for the four cores taken near the shore, but these cores indicate different timing for the end of widespread agriculture in the watershed. Three of these four cores indicate nearly all agriculture ended by 1000 cal yr BP, but in the fourth core agricultural indicators persist until 675 cal yr BP. The core from the center of the lake shows a gradual decline in proxies indicating agriculture from 950 to 650 cal yr BP, which suggests sediment-reworking processes are integrating material from the entire basin as it is transported to the deeper portions of the lake. Differences between the records from the cores recovered near the shore illustrate the potential of multiple core studies to create spatially explicit paleoenvironmental reconstructions, while the delayed and less abrupt changes in the core from the center of the lake highlight the importance of sediment reworking of paleoenvironmental indicators.
- 出版日期2015-12
