Investigating Anthropogenic Impacts on the Utah Lake-Jordan River Transition Zone Using a Multi-proxy Approach

Sediment cores were collected (GPS coordinates taken) at three transects, one at the north end of Utah Lake and two within a kilometer of the Lake on the Jordan River. The cores were sub-sampled at 5 cm resolution for sediment grain size, C and N stable isotope and C/N ratio, and lead-210 analyses. All sampling was standardized. Sampling data is one time data (summer field collection). Carbon and nitrogen stable isotope compositions show a 4 per mil and a 2 per mil positive shift, respectively, as a depth of 55cm. C/N ratios show large variations (9-18) at depths shallower that 55cm, but are more stable (11-14) with greater depth. These results indicate a shift in organic matter sources to Utah Lake at a depth of 55cm, which likely represents the boundary between pre- and post-pioneer settlement in the valley around 1847. At depths greater than 55cm, the major contribution of soil organic matter was likely terrestrial C3 and autochthonous native C4 plants, whereas at depths shallower than 55cm terrestrial vegetation, manure/sewage-derived matter, and lake algae were the major lake organic matter sources. From this information, we approximate the post-settlement sedimentation rate in the lake to be 3.3mm/yr. Students and leads were responsible for data collection, data analysis, and data interpretation of the project.

本研究在三条采样断面上采集了沉积岩芯（同步记录GPS坐标）：其中一条断面位于犹他湖（Utah Lake）北端，另外两条设于约旦河（Jordan River）沿岸、距该湖1公里范围内的区域。岩芯以5厘米的分辨率进行分样，用于沉积物粒度分析、碳氮稳定同位素（carbon and nitrogen stable isotope）测定、碳氮比（C/N ratio）分析以及铅-210（lead-210）检测。所有采样流程均经过标准化处理，采样数据为单次夏季野外采集所得。碳、氮稳定同位素组成分别在55厘米深度处出现4‰与2‰的正向偏移；碳氮比在55厘米以浅的深度区间内波动幅度较大（9~18），而在更深深度则保持相对稳定（11~14）。上述结果表明，犹他湖的有机质来源在55厘米深度处发生了显著转变，该深度大概率对应了1847年前后该流域拓殖活动的前后地层分界。在55厘米深度以深的地层中，沉积物有机质主要来源于陆生C3植物与本土自生C4植物；而在55厘米以浅的地层中，有机质主要来源则为陆生植被、粪肥/污水衍生有机质以及湖生藻类。基于上述数据，我们估算该湖区拓殖后的沉积速率约为3.3毫米/年。本项目的数据采集、分析与解读工作由学生及项目负责人共同完成。