Madison Wisonsin Lakes Zooplankton 1976 - 1994

Zooplankton of the four Yahara River chain of lakes (Mendota, Monona, Waubesa, and
Kegonsa) were sampled and analyzed by the Wisconsin Department of Natural Resources (WDNR)
during 1976 to 1994 as part of a long-term limnological sampling program directed by Richard
C. Lathrop. Methods for zooplankton sampling and laboratory analyses were previously
summarized for Lake Mendota (Lathrop 1998); methods were similar for the other three Yahara
lakes although Waubesa and Kegonsa were only sampled for zooplankton during 1976-1985. In
general, zooplankton were sampled at the deepest location of each lake by pulling a conical
net vertically through the water column (i.e., vertical tow sample) during 1976-1994.
Sampling was usually done on a biweekly schedule during the open water period and at least
once through the ice at the deepest region of each lake, although in some years lakes
Waubesa and Kegonsa were only sampled monthly during the open-water period. On a few dates
during high winds or during winter, sampling was conducted in slightly shallower water than
at the deepest lake location. Tow depths for Mendota and Monona are included in the data
set. Tow depths for Waubesa and Kegonsa have not been transcribed yet, but generally ranged
between 9.5-10.0 meters and 7.5-8.0 meters, respectively. The conical zooplankton net had a
15-cm diameter opening ("small net") and a net filtering area to opening area ratio of about
11. The net was made of Nitex screening with a mesh size of 75-80 um (#20 net) for all years
except for 1976 when the mesh size was about 153 um (#10 net). The smaller-meshed net was
initially chosen so that rotifers would be quantitatively collected along with crustacean
zooplankton. For the small net, a vertical tow sample was taken from approximately 0.5 m off
the lake bottom. The net was pulled to the lake surface at approximately 0.3 m per sec.
After the net was raised and the sides rinsed, the sample was transferred to a bottle and
preserved with formalin in early years, sugared formalin for a few years, and then formalin
plus seltzer water was the preservative used after 1986. For each zooplankton sample
obtained by the small net, organisms were identified to species and enumerated in three
separate 1-mL subsamples obtained by a Hensen-Stemple pipette. Subsamples were taken
directly from the sample bottle (sample volume ca. 150-250 mL), transferred to a 1-mL
Sedgewick-Rafter cell and counted using a compound microscope. For each subsample,
individual body lengths for all Daphnia encountered were recorded using an eyepiece
micrometer; 5-10 organisms of other cladocerans and various life stages of copepods (i.e.,
nauplii, copepidites, and adults) were also measured. Based on specified size criteria,
juvenile and adult Daphnia of each species were recorded separately. These size criteria
were given in Luecke et al. (1990) for samples collected in 1976-1989. The criteria varied
in subsequent years but were generally 1.3 mm for D. pulicaria, 1.2 mm for D. mendotae, the
most common Daphnia species encountered. If smaller Daphnia were encountered with eggs in
their brood chamber, then the adult size was adjusted. Thus, the distinction of adult versus
juvenile Daphnia densities recorded in each sample must be viewed as only an index of the
two age groups. Calanoid and cyclopoid copepodites were counted separately as two distinct
groups without regard to species or life stages. All nauplii were counted as a single group
with no distinction made between calanoid and cyclopoid species. All densities and length
measurements in the three subsamples were then averaged for each species' life stage.
Numerical density estimates (N per meter squared) for each species or zooplankton group as
reported in the data set were then computed by multiplying the average subsample count by
the subsampling dilution factor (i.e., volume of sample in bottle) and then dividing by the
net opening area (0.01767 meter squared). Biomass estimates for each species or zooplankton
group (gram per meter squared) can then be computed using the average length (mm) recorded
in the data set using length-weight relationships published in the literature. One caveat
for interpreting the zooplankton data for 1976-1994 is that the net efficiency of the
vertical tow net used is less than 100%, and also variable depending on the amount of algae
clogging the net (Lathrop 1998). Under clear water conditions (Secchi disc greater than 8
m), the net efficiency of the small net was determined to be approximately 58%. However, net
efficiency was only about 42% during a period with moderate blue-green algal densities
(Secchi disc 1.8 m). The relatively small mesh size (75-80 um) of the net was initially
chosen in order to capture rotifers, which are recorded in the database. Beginning in 1991 a
larger 30-cm diameter ("large") net with a 75-80 um mesh size was also used, which became
the standard sampling net used in 1995 coincident with the lake sampling program being
conducted by the North Temperate Lakes Long-Term Ecological Research (NTL-LTER) Project.
After 1994, the "small" net was no longer used for sampling zooplankton on the Yahara lakes.
This data set also contains large net data for years 1991 through 1994 for Mendota and for
1994 for Monona. Leptodora counts from the small net are available for Mendota (1976-1989),
Monona (1976-1987), Kegonsa and Waubesa (1976-1985). Leptodora counts from the large net are
available for Mendota (1991-1993). All Leptodora counts were performed on the entire sample
by dumping the sample bottle into a container. Individual length measurements for some
zooplankton sampled with the small net are available for Mendota (1988-1989, 1992-1994) and
Monona (1994). Individual length measurements for zooplankton sampled with the large net are
available for Mendota (1991-1993). Daphnia eggs counts (number of eggs per adult daphnia in
the sample) from samples taken with the small net are included for Mendota (1976-1991),
Monona (1976-1993 except 1989), and Kegonsa and Waubesa (1976-1985). Egg counts represent
the combined number of free eggs found in each subsample plus eggs still remaining in adult
Daphnia as many times adult Daphnia had eggs expelled from their brood chambers once the
preservative was added (especially in years when the preservative was just formalin). Once
the total number of eggs for either D. pulicaria or D. mendotae was counted, then the
estimate of the number of eggs per adult Daphnia was calculated while recognizing that the
criteria for separating adult versus juvenile Daphnia is not without error. Thus, the number
of eggs per adult number is best used as an index to determine if the Daphnia population was
increasing or not growing due to food limitation. Number of sites: 4 Sampling Frequency:
varies

亚哈拉河链四湖（门多塔湖、莫诺纳湖、沃贝萨湖与凯贡萨湖）的浮游动物样本由威斯康星州自然资源部（Wisconsin Department of Natural Resources, WDNR）于1976至1994年间采集并分析，该工作是Richard C. Lathrop主导的长期湖沼学采样计划的一部分。此前Lathrop（1998）已对门多塔湖的浮游动物采样与实验室分析方法进行过总结；其余三座亚哈拉湖的采样方法与之类似，但沃贝萨湖与凯贡萨湖仅在1976-1985年间开展了浮游动物采样。

总体而言，1976-1994年间，研究人员在各湖的最深点位通过锥形网垂直拖过水柱（即垂直拖网样本）采集浮游动物。通常在开阔水期每两周采样一次，并在各湖最深区域至少开展一次冰下采样；不过部分年份中，沃贝萨湖与凯贡萨湖仅在开阔水期每月采样一次。在强风或冬季的少数日期，采样点位会略浅于湖最深区域。门多塔湖与莫诺纳湖的拖网深度已纳入本数据集。沃贝萨湖与凯贡萨湖的拖网深度尚未转录，但通常分别介于9.5-10.0米与7.5-8.0米之间。

该锥形浮游动物网网口直径为15厘米（简称“小型网”），网过滤面积与网口面积之比约为11。除1976年网孔尺寸约为153 μm（#10网）外，其余年份均采用孔径75-80 μm的Nitex筛绢（#20网）。最初选择更小网孔的网具，是为了能定量采集轮虫与甲壳类浮游动物。针对小型网，采样时从湖底上方约0.5米处开始垂直拖网，以约0.3米每秒的速度将网提拉至湖面。收起网具并冲洗网身后，将样本转移至样本瓶中，早年采用福尔马林固定，部分年份采用加糖福尔马林，1986年后则统一使用福尔马林加苏打水作为固定液。

通过小型网获取的每份浮游动物样本，均采用Hensen-Stemple移液管分取三份独立的1mL子样本，对其中的生物进行物种鉴定与计数。子样本直接从样本瓶中获取（样本体积约150-250 mL），转移至1mL的塞奇威克-拉夫特计数板（Sedgewick-Rafter cell）后，使用复合显微镜进行计数。针对每份子样本，使用目镜测微尺记录所有水蚤属（Daphnia）个体的体长；其余5-10种枝角类以及桡足类的各发育阶段（即无节幼体、桡足幼体与成体）也需测量体长。根据既定体长标准，将各物种的幼龄与成年水蚤分开记录。1976-1989年的采样体长标准参见Luecke等（1990），后续年份的标准有所调整，但常见优势种水蚤的阈值通常为：蚤状溞（D. pulicaria）1.3 mm、孟氏水蚤（D. mendotae，最常见的水蚤物种）1.2 mm。若小型水蚤个体的育卵室中带有卵，则需调整成年个体的体长判定标准。因此，每份样本中记录的幼龄与成年水蚤密度仅可作为两个年龄组的相对指标。

哲水蚤目与剑水蚤目的桡足幼体按两个独立类群分别计数，不区分物种与发育阶段；所有无节幼体统一作为一个类群计数，不区分哲水蚤与剑水蚤物种。将三份子样本的所有密度与体长测量结果取平均值，得到各物种/浮游动物类群的对应值。本数据集报告的各物种/浮游动物类群的数值密度估计值（单位：个/平方米），通过以下公式计算：将子样本平均计数乘以子样本稀释因子（即样本瓶中样本体积），再除以网口面积（0.01767平方米）。各物种/浮游动物类群的生物量估计值（单位：克/平方米），则可通过数据集中记录的平均体长（mm），结合已发表文献中的体长-体重关系计算得到。

解读1976-1994年的浮游动物数据需注意：本次使用的垂直拖网网效率未达100%，且会因网具被藻类堵塞的程度而变化（Lathrop 1998）。在清水条件下（透明度盘读数大于8米），小型网的网效率约为58%；而在蓝藻密度中等的时期（透明度盘读数1.8米），网效率仅约为42%。最初选择较小网孔（75-80 μm）的网具，正是为了捕获数据库中记录的轮虫。1991年起，研究人员开始同时使用网口直径30厘米（简称“大型网”）、网孔尺寸75-80 μm的网具；1995年，该大型网成为标准采样网具，此时亚哈拉湖的采样计划由北温带湖泊长期生态研究（North Temperate Lakes Long-Term Ecological Research, NTL-LTER）项目接手。1994年后，小型网不再用于亚哈拉湖的浮游动物采样。本数据集同时包含1991-1994年门多塔湖的大型网采样数据，以及1994年莫诺纳湖的大型网采样数据。

小型网采集的薄皮溞（Leptodora）计数数据如下：门多塔湖（1976-1989年）、莫诺纳湖（1976-1987年）、凯贡萨湖与沃贝萨湖（1976-1985年）。大型网采集的薄皮溞计数数据仅见于门多塔湖（1991-1993年）。所有薄皮溞计数均通过将样本瓶中的全部样本倒入容器后完成。部分采用小型网采集的浮游动物个体体长数据如下：门多塔湖（1988-1989年、1992-1994年）与莫诺纳湖（1994年）。采用大型网采集的浮游动物个体体长数据仅见于门多塔湖（1991-1993年）。

小型网采样获得的水蚤卵计数数据（即样本中每只成年水蚤的卵数）包含：门多塔湖（1976-1991年）、莫诺纳湖（1976-1993年，1989年除外）、凯贡萨湖与沃贝萨湖（1976-1985年）。卵计数统计了每份子样本中发现的游离卵数，以及仍附着在成年水蚤育卵室中的卵数——这是因为加入固定液后，部分成年水蚤的卵会从育卵室中排出（尤其是仅使用福尔马林作为固定液的年份）。在统计完蚤状溞或孟氏水蚤的总卵数后，即可计算每只成年水蚤的平均卵数，但需注意区分幼龄与成年水蚤的判定标准存在误差。因此，每只成年水蚤的卵数仅可作为指示水蚤种群是否因食物限制而增长或停滞的相对指标。

采样点位数量：4个；采样频率：不固定。