Lake Wingra Exclosure Experiment at North Temperate Lakes LTER: Secchi Disk Depth 2005 - 2008

Starting in late summer 2005, Wisconsin Dept of Natural Resources (WDNR), Dane County,
Friends of Lake Wingra (FOLW), and NTL-LTER initiated a 3-year experiment in Lake Wingra to
test the response of the native macrophyte community to clearer water produced from a major
carp reduction program. This demonstration-scale experiment includes the construction of a
1.0-hectare rectangular carp exclosure with its solid vinyl walls extending from the lake
shoreline to a water depth of 2.9 meters. NTL-LTER conducts the routine limnological
monitoring of the lake and exclosure and is leading the science evaluation of potential lake
restoration activities. The exclosure experiment was terminated in the fall of 2008. The
exclosure was removed from Lake Wingra at that time. Sampling is done both within the
exclosure and at a control site located nearby in the littoral zone. The sample location
within the exclosure is equidistant from the side walls and approximately 75 meters from the
shore in a water depth of approximately 2.5 meters. The control site sample location is
approximately 75 meters west of the exclosure sample site at the same approximate distance
from shore and water depth. Samples are taken at the same time and on the same schedule as
the NTL-LTER limnological sampling on Lake Wingra, e.g., biweekly spring through summer,
every 4 weeks in the fall, and once during the winter depending on ice conditions.
Parameters measured within the exclosure and at the control site include water temperature,
dissolved oxygen, secchi depth and chlorophyll-a. Additional parameters measured only within
the exclosure include total Kjeldahl nitrogen, nitrate + nitrite nitrogen, ammonia nitrogen,
total phosphorus, dissolved reactive phosphorus and dissolved reactive silica. Secchi disk
depth is measured within the exclosure and at a nearby control site in the littoral zone .
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 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. Other parameters measured at depth include water temperature and dissolved
oxygen. Auxiliary data include time of day, air temperature, cloud cover, wind speed and
direction, and wave height. Sampling Frequency: generally bi-weekly during ice-free season
from late March or early April through early September, then every 4 weeks through late
November. Number of sites: 2