North Temperate Lakes LTER: Secchi Disk Depth; Other Auxiliary Base Crew Sample Data 1981 - current

Secchi disk depth is measured in the deepest part of each lake for the eleven primary lakes (Allequash, Big Muskellunge, Crystal, Sparkling, Trout lakes, unnamed lakes 27-02 [Crystal Bog] and 12-15 [Trout Bog], Fish, Mendota, Monona and Wingra). The disk is circular, 20 cm in diameter, and has alternating black and white quadrants. It is lowered using a calibrated Kevlar rope to minimize stretching. Readings are made on the shaded side of the boat both with and without the aid of a plexiglass viewer. The points at which the disk disappears while being lowered and reappears while being raised are averaged to determine Secchi depth. Auxiliary data include time of day, air temperature, cloud cover, wave height, wind speed and direction and whether the lake was ice covered on the sampledate. Sampling Frequency: fortnightly during ice-free season - every 6 weeks during ice-covered season for the northern lakes. The southern lakes are similar except that sampling occurs monthly during the fall and typically only once during the winter (depending on ice conditions). Number of sites: 11

针对11个核心监测湖泊（包括Allequash湖、Big Muskellunge湖、Crystal湖、Sparkling湖、Trout湖，以及未命名湖泊27-02[Crystal Bog]、12-15[Trout Bog]，还有Fish湖、Mendota湖、Monona湖与Wingra湖），我们在每个湖泊的最深处测量赛氏盘透明度（Secchi disk depth）。该赛氏盘为圆形，直径20厘米，带有交替分布的黑白象限。使用经校准的凯夫拉绳索（Kevlar rope）下放以尽可能减少绳索拉伸。测量操作均在船体背阴侧完成，分别采用有机玻璃观测器（plexiglass viewer）辅助与不辅助两种方式。将赛氏盘下放过程中完全隐没的深度与上提过程中重新显现的深度取平均值，以此计算得到赛氏盘透明度。辅助测量参数包括当日时刻、气温、云量、浪高、风速、风向，以及采样当日湖泊是否处于冰封状态。采样频率：无冰期内为每两周一次；北部湖泊的封冰期内为每6周一次。南部湖泊的采样规则略有差异：秋季为每月采样一次，冬季通常仅采样一次（具体取决于冰封状况）。监测点位数量：11个