Aquatic macrophytes are sampled from a boat at stations located at depths from 1 to 4 meters at 0.5-m intervals along transects perpendicular to the lake shoreline of the four primary study lakes in the Madison area (Lakes Mendota, Monona, and Wingra, and Fish Lake) from June to August. A weighted, double-headed garden rake is cast off the front left, front right, rear left, and rear right of the boat and then dragged approximately 2 meters across the bottom by means of an attached line. For each rake cast, filamentous algae and any aquatic macrophyte species present are assigned a density rating from 0-5 based on the extent of coverage of the upper rake head. Determination of extent of coverage involves judgment of the surveyor as to the number of rake teeth and area of teeth covered by each species. It is necessary to separate plants to assess individual species coverage. Ratings from the 4 rake casts at each station can be averaged to compute an overall density rating for each species found at the station.
Detailed Macrophyte Sampling description.
Using the site book and the depth measuring pole, move to the 1 meter depth mark and throw both anchors. From the Macrophyte Depth Table, find the distance to throw out the rake and the meter mark that the line should be drawn to. The table is calculated to determine the starting and ending meter marks to draw in the line to allow the rake to drag 2 meters on the lake bottom. Pull the rake quickly out of the water. Before removing the plant material from the rake, drape the long strands over the rake and gently push the plant material down on the rake. Assign a rake rating (from 1 to 5) depending on how much the plant material covers the rake prongs. The rake prongs are painted in 20 percent increments. If the plant material only covers the lowest 20 percent of the rake prongs, assign the rake rating a 1. If the plant material covers between 20 percent and 40 percent of the rake prongs, the rake rating is a 2, and so on. If a significant amount of dirt has been brought up with the plants (i.e. the weight of the dirt will add significantly to the total weight), wash the plants. Separate the filamentous algae from the rest of the plant material. Separate and identify the individual plant species, throwing out any dead plant material. Give the filamentous algae and each plant species a rake rating (note that it is often necessary to visualize how much space each species would take up on the rake prongs rather than actually placing each species onto the rake). If a plant species can not be identified, take a sample back to the lab by putting it in a ziplock bag with a small amount of water and temporarily storing it in a cooler. Repeat the above steps until 4 rake tosses have been thrown. Normally 2 rake tosses are thrown out each side of the boat to an area where the water depth is known to be at the desired depth. Move to the next half-meter depth. Macrophytes are collected at each half-meter water depth from 1 meter to 4 meters.