Isotope values (δ15N and δ13C) and elemental composition (%N and %C) of aquatic insects, biofilm, transported organic matter, leaves, and elk muscle tissue collected from mainstem Big Creek, Middle Fork Salmon River, USA (2010-2011).

We collected aquatic insects from the an elk carcass (May 2011) for isotope analysis. We also collected aquatic insects at sites without a carcass in March 2011 for reference samples (no-carcass treatment). We were restricted to compare the isotope values of aquatic insects on an elk carcass in May 2011 and aquatic insects at sites without a carcass in March 2011 because of logistical constraints. Additionally, we collected potential food sources of aquatic insects for isotope analysis including elk muscle tissue (Mar. 2011), biofilm (Dec. 2010 – May 2011), seston (i.e. transported organic matter, Feb. – Mar. 2011), and leaves (Dec. 2010). All samples were frozen until analysis. In the laboratory, samples were dried in a drying oven at 60 °C, except samples of elk muscle tissue were freeze-dried. After drying, we homogenized the samples with a mortar and pestle or grinding mill. All samples were analyzed with the Elemental Combustion System 4010 (Costech Analytical Technologies Inc., Santa Clarita, CA, USA) interfaced to a Delta V Advantage Mass Spectrometer through the ConFlo IV System (Thermo Scientific, Waltham, IL, USA). All samples were analyzed for isotope ratios of δ13 carbon (δ13C) and δ15 nitrogen (δ15N). Isotope ratios of δ13C are reported as per mil (‰) values relative to the VPDB scale; whereas δ15N values are reported as per mil (‰) values relative to air N2. Additionally, all samples were analyzed for elemental composition of percent nitrogen and carbon. All isotope and elemental analyses were conducted at the Center for Archaeology, Materials and Applied Spectroscopy (CAMAS) Laboratory at Idaho State University, Pocatello, ID.本研究于2011年5月从一具马鹿（elk）尸体上采集水生昆虫，用于同位素分析。2011年3月，本研究同时在无马鹿尸体的采样点采集水生昆虫作为对照样本（无尸体组）。受后勤条件限制，本研究仅能对比2011年5月附着于马鹿尸体的水生昆虫与2011年3月无尸体采样点水生昆虫的同位素数值。此外，本研究还采集了水生昆虫的潜在食物源以开展同位素分析，包括2011年3月采集的马鹿肌肉组织、2010年12月至2011年5月采集的生物膜（biofilm）、2011年2月至3月采集的浮游碎屑（seston，即输运性有机质）以及2010年12月采集的植物叶片。所有样本均冷冻保存直至实验分析阶段。实验室内，除马鹿肌肉组织样本采用冷冻干燥处理外，其余样本均置于60℃烘箱中烘干。烘干完成后，使用研钵或研磨机对样本进行均质化处理。所有样本均通过元素燃烧系统4010（Elemental Combustion System 4010，美国加利福尼亚州圣克拉里塔市Costech Analytical Technologies Inc.生产），经ConFlo IV接口系统（ConFlo IV System，美国伊利诺伊州沃尔瑟姆市Thermo Scientific生产）连接至Delta V Advantage型质谱仪进行分析。所有样本均检测了碳同位素比值（δ¹³C）与氮同位素比值（δ¹⁵N）。其中，δ¹³C同位素比值以相对于VPDB标准的千分比（‰）形式报告，δ¹⁵N同位素比值则以相对于大气氮（air N₂）的千分比（‰）形式报告。此外，本研究还对所有样本的氮、碳百分含量组成进行了检测。所有同位素与元素分析工作均在美国爱达荷州波卡特洛市爱达荷州立大学考古、材料与应用光谱学（Center for Archaeology, Materials and Applied Spectroscopy, CAMAS）实验室完成。