Submersed Macrophyte Vegetation and Distribution Within Lakes: Line Transect Sampling

ABSTRACT

Line transects often provide a practical basis for quantitative, nondestructive sampling of aquatic vegetation; here four types of line transect arrangements are briefly compared: 1) transects perpendicular to the shoreline have been widely used, but may oversample nearshore areas where shorelines are convex; 2) transects parallel to each other at regular intervals may provide the best basis for mapping an area; but 3) parallel transects at (stratified) random intervals may reasonably represent different areas within the site and avoid possible biases of regular sampling. The tendency of all three methods to oversample some depth ranges and to combine data from different community types may be obviated by using 4) transects along depth contours near a given shoreline of nearly uniform exposure. Line transects may in some cases be sampled with a line intercept method, which is probably best suited for floating-leaved species, but most often a belt transect consisting of contiguous quadrats is more practical. For each sampling unit, data may be gathered on species presence or percent cover, although the former may yield more information per unit effort. Five field examples are given to illustrate sampling schemes, macrophyte community heterogeneity, and straightforward data summary procedures.

Key Words:

• aquatic plant sampling
• macrophyte communities
• line transects
• heterogeneity
• adequate sample
• compositional change