Macrophyte Sampling - Yahara Lakes District

Macrophyte Sampling Schedule

1. Macrophytes are sampled on Lakes Mendota, Monona, Waubesa, Wingra, and Fish Lake. Follow past years sampling order (Waubesa, Wingra, Fish, Monona, Mendota) and keep the dates as consistent to past years as possible (see list of dates). Working around the routine LTER sampling, schedule the macrophyte sampling well in advance in order to sign out a vehicle and boat when necessary.

Macrophyte Sampling Preparation

1. With a list of the plants found in past years in the southern lakes, study the macrophytes using the available keys and the plant presses.

2. Collect the equipment listed on the Macrophyte Equipment List.

3. Remark and remeasure the line on the two-sided rake from 2 to 6 meters in 0.1-meter increments.

4. Remark and remeasure the pole from 1 to 3 meters in 0.5 meter increments (Note that it would be helpful to devise a 1 meter extension so that the pole could measure to 4 meters. The extension would have to be removable in order for the pole to fit in the Suburban.)

5. Test the spring balances against more accurate electronic balances.

Macrophyte Sampling Method

1. Using the site book and the depth measuring pole, move to the 1 meter depth mark and throw both anchors. It seems easiest to first throw the anchor opposite the direction the boat is moving and throw the second anchor in the opposite direction after the line from the first anchor is taught.

2. From the Macrophyte Depth Table, find the distance to throw out the rake and hold that mark in one hand. Also determine 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. The table assumes that the line is held 1meter above the water surface while dragging in the line.

3. Throw the rake horizontally out the side of the boat stopping it at the correct meter mark on the line. Allow the rake to sink to the bottom. Draw in the line, holding it approximately 1 meter above the water surface. Stop drawing in the line at the correct meter mark.

4. Pull the rake quickly out of the water. In order to retain the plants that are attached to the rake, it may be beneficial to rotate the rake 180 degrees once the rake handle is grabbed (so that the prongs that were dragged along the bottom are facing up). Then pivot the rake against the side of the boat and bring it into the boat.

5. 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% increments. If the plant material only covers the lowest 20% of the rake prongs, assign the rake rating a 1. If the plant material covers between 20% and 40% of the rake prongs, the rake rating is a 2, and so on (see page on rating description).

6. 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. Depending on the volume of the plants, wash them either by keeping them in your hands and dunking them in the lake or by putting them in the white bucket with the drain holes.

7. 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. Temporarily assign each unknown species with a common symbol or name on the data sheet (to be changed to the correct species name when identified). Stan Nichols at the WGNHS can be used as a resource (263-7389).

8. Combine all of the plant species, keeping the filamentous algae separate, and squeeze out as much water as possible (it may be necessary to divide up the plant material into portions to effectively squeeze out the water). Weigh the plant material (minus the filamentous algae) and record the total weight. Weigh the filamentous algae and record the weight.

9. 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.

10. Move to the next half-meter depth. Macrophytes are collected at each half-meter water depth from 1 meter to 4 meters. In the case of Lake Wingra, look at past year’s data to determine the deepest sampling depth for each transect (often 3 meters). In areas of steep drop-offs, it can be difficult to anchor the boat at the proper depth and it may be necessary to drop the anchor upwind and drift to the desired depth.

Macrophyte Sampling Equipment List

Data Sheets

Rake with marked line

Anchors

Pole with meter marks

Depth finder

Site Map (and photos?)

Cooler with ice

Tubs

Pail with holes

Bags (zip-lock)

Seat cushions