Cascade Project at North Temperate Lakes LTER: Nutrients 1991 - 2007

Physical and chemical variables are measured at one central station near the deepest point of each lake. In most cases these measurements are made in the morning (0800 to 0900). Vertical profiles are taken at varied depth intervals. Chemical measurements are sometimes made in a pooled mixed layer sample (PML); sometimes in the epilimnion, metalimnion, and hypolimnion; and sometimes in vertical profiles. In the latter case, depths for sampling usually correspond to the surface plus depths of 50percent, 25percent, 10percent, 5percent and 1percent of surface irradiance. The 1991-1999 chemistry data obtained from the Lachat auto-analyzer. Like the process data, there are up to seven samples per sampling date due to Van Dorn collections across a depth interval according to percent irradiance. Voichick and LeBouton (1994) describe the autoanalyzer procedures in detail. Nutrient samples were sent to the Cary Institute of Ecosystem Studies for analysis beginning in 2000. The Kjeldahl method for measuring nitrogen is not used at IES, and so measurements reported from 2000 onwards are Total Nitrogen.理化变量的监测工作在每个湖泊最深处附近的中心监测站开展。绝大多数情况下，监测于晨间08:00至09:00时段进行。监测采样采用不同深度间隔的垂直剖面方案。 化学组分测定可采用三种方式：一是采集混合层混合水样（pooled mixed layer sample, PML）进行分析；二是分别于表水层（epilimnion）、斜温层（metalimnion）与底水层（hypolimnion）分层采样测定；三是开展垂直剖面采样。若采用垂直剖面采样，采样深度通常设置为表层，以及表层辐照度的50%、25%、10%、5%与1%对应的深度。 1991年至1999年的化学组分数据通过Lachat自动分析仪（Lachat auto-analyzer）获取。与过程数据一致，每个采样日最多可采集7份样本，这些样本通过范多恩采水器（Van Dorn sampler）按辐照度占比对应的深度区间采集得到。Voichick与LeBouton（1994）已详细阐述了该自动分析仪的操作流程。 自2000年起，营养盐样本被送往卡里生态系统研究所（Cary Institute of Ecosystem Studies）开展分析。IES未采用凯氏定氮法（Kjeldahl method）测定氮含量，因此2000年及之后报告的氮测量值均为总氮（Total Nitrogen）。