Upper Midwest Environmental Sciences Center

Submersed aquatic vegetation was collected using a long-handled, double-headed rake modified from Jessen and Lound (1962) and Deppe and Lathrop (1992). The rake is 36 cm (14 inches) wide, has 14, 5 cm (2 inches) long teeth on each side, and was made by welding two square-headed garden rakes together. The teeth are divided and marked into five equal parts (or 20% increments). The handle is about 3 m long, with a rope extension, and is scaled at 10-cm increments. Aquatic vegetation or aquatic species refer to the following plant types or life forms: submersed (S) and rooted floating–leaf (F).

Each site had six subsampling areas, each of which was a rectangular area approximately 1.5 m long and 0.35 m wide (the width of the rake head). One subsampling area was located off each corner of the boat and the other two were located, one each, off the left and right sides.

Individual species and different life forms of aquatic vegetation (e.g., submersed and rooted floating–leaf) were recorded as either present or absent at each subsampling area based on visual examination and a rake sample. When present, submersed species and the filamentous algae were given a density rating (see table at lower left) based on their thickness on the rake teeth. When present, rooted floating–leaf and emergent species were given a percent cover rating (see table at lower right). Species that had not been recorded in the six subsampling areas but were observed at the site were recorded and marked as "additional species." Fassett (1957), Voss (1972, 1985) and Gleason and Cronquist (1991) were the primary references used for plant identification. Scientific nomenclature and common names are based on those found in the U.S. Department of Agriculture's PLANTS Database on the Internet (http://plants.usda.gov/).

Frequency values in this report are computed by dividing the number of sites where a species was recorded by the number of sites investigated in the stratum, and then multiplied by 100 to convert it into a percentage.
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The frequency value in a pool is computed by averaging the frequency values of the shallow water strata, weighted by acreage:
where F_j is the frequency in stratum j and S_j is the acreage of stratum j.

An index is created to measure the quantity of a submersed species using both presence or absence and plant density rating data recorded in the six subsampling areas. We call it the abundance index to differentiate it from the frequency index. The abundance index is computed according to the following formula:

where V_i is the presence or absence (1,0) and R_i is the plant density ranking (0,1,2,3,4,5) data for the i^th subsampling areas at the site (i=1,2,3,4,5,6). Data are treated before computation so that V_i=1 if R_i>=1 and, vice versa, R_i>=1 if V_i=1. The abundance index for a stratum is computed as the simple average of all its sites . The abundance index for a pool is computed as the average of all shallow water strata, weighted by acreage:
where A_j is the abundance index of the species in stratum j and S_j is the acreage of stratum j.

The percent cover of rooted floating–leaf life forms in a stratum is computed using the following formula: where L_j is the cover rating at individual sites and A is the midpoint of the corresponding percent cover (Table 3), and M is the total number of sites in the stratum. Percent cover in a pool is computed as the average of all shallow water strata, weighted by acreage:
where C_j is percent cover in stratum j and S_j is the acreage of stratum j.