North Temperate Lakes LTER: Zooplankton - Madison Lakes Area 1997 - current

Zooplankton samples for the 4 southern Wisconsin LTER lakes (Mendota, Monona, Wingra, Fish) have been collected for analysis by LTER since 1995 (1996 Wingra, Fish) when the southern Wisconsin lakes were added to the North Temperate Lakes LTER project. Samples are collected as a vertical tow using an 80-micron mesh conical net with a 30-cm diameter opening (net mouth: net length ratio = 1:3) consistent with sampling conducted by the Wisconsin Dept. Natural Resources in prior years. Zooplankton tows are taken in the deep hole region of each lake at the same time and location as other limnological sampling; zooplankton samples are preserved in 70% ethanol for later processing. Samples are usually collected with standard tow depths on most dates (e.g., 20 meters for Lake Mendota) but not always, so tow depth is recorded as a variate in the database. Crustacean species are identified and counted for Mendota and Monona and body lengths are recorded for a portion of each species identified (see data protocol for counting procedure); samples for Wingra and Fish lakes are archived but not routinely counted. Numerical densities for Mendota and Monona zooplankton samples are reported in the database as number or organisms per square meter without correcting for net efficiency. [Net efficiency varies from a maximum of about 70% under clear water conditions; net efficiency declines when algal blooms are dense (Lathrop, R.C. 1998. Water clarity responses to phosphorus and Daphnia in Lake Mendota. Ph.D. Thesis, University of Wisconsin-Madison.)] Organism densities in number per cubic meter can be obtained by dividing the reported square-meter density by the tow depth, although adjustments for the oxygenated depth zone during the summer and early fall stratified season is required to obtain realistic zooplankton volumetric densities in the lake's surface waters. Biomass densities can be calculated using literature formulas for converting organism body lengths reported in the database to body masses. Sampling Frequency: bi-weekly during ice-free season from late March or early April through early September, then every 4 weeks through late November; sampling is conducted usually once during the winter (depending on ice conditions). Number of sites: 4 Note: for a period between approximately 2011 and 2015, a calculation error caused density values to be significantly greater than they should have been for the entire dataset. That issue has been corrected.

自1995年起，长期生态研究（Long-Term Ecological Research, LTER）项目团队便开始采集威斯康星州南部4个LTER湖泊（门多塔湖、莫诺纳湖、温格拉湖、菲什湖）的浮游动物（Zooplankton）样本用于分析（其中温格拉湖与菲什湖的样本采集始于1996年）——彼时威斯康星州南部的这批湖泊被纳入北温带湖泊LTER研究项目。样本采用垂直拖网方式采集，使用网口直径30厘米、网目尺寸80微米的锥形网（网口与网长之比为1:3），该采样方法与此前威斯康星州自然资源部采用的标准一致。浮游动物拖网采样均在各湖泊的深水区进行，采样时间与地点与其他湖沼学采样同步；采集后的浮游动物样本将保存于70%乙醇溶液中，以待后续处理。多数采样日期的拖网深度均采用标准值（如门多塔湖为20米），但并非全部如此，因此拖网深度作为变量被记录于数据库中。研究人员会对门多塔湖与莫诺纳湖的甲壳类动物物种进行鉴定与计数，并对鉴定出的各物种的部分个体测量其体长（计数流程详见数据规程）；温格拉湖与菲什湖的样本仅作归档保存，不进行常规计数。数据库中记录的门多塔湖与莫诺纳湖浮游动物数值密度单位为个/平方米，未对网具捕获效率进行校正。[网具捕获效率在清水条件下最高可达约70%；当藻类水华密集时，捕获效率会出现下降（引自Lathrop R.C. 1998年发表于威斯康星大学麦迪逊分校的博士论文《门多塔湖磷与水蚤对水体透明度的影响》）]若要换算为单位立方米的浮游动物个体密度，可将数据库中记录的平方米密度值除以拖网深度；但在夏季与早秋的水体分层期，需对含氧深度带进行校正，才能获得湖泊表层水体中符合实际情况的浮游动物体积密度。可利用已发表文献中的计算公式，将数据库中记录的个体体长转换为生物量，进而计算生物量密度。采样频率：在无冰期（3月末至4月初至9月初）每两周采样一次，9月初至11月末每四周采样一次；冬季通常采样一次（具体取决于冰层状况）。采样点位数量：4个。备注：在2011年至2015年左右的一段时期内，因计算误差导致整个数据集的密度值显著偏高，该问题现已得到修正。