Biota of Lakes and Reservoirs - Hydro-Environmental Analysis: Freshwater Environments - page 433

extent the copepods (Wetzel 2001). For zooplankton, most species migrate to the surface at night,
and retreat to the bottom layers with the dawn.

15.3.2 L IttoraL z one
The organisms of the littoral zone are diverse and include a complex mixture of plants, animals, and
microorganisms. Plants of the littoral zone include those that grow on some substrate, the periphy-
ton, and the larger plants, the macrophytes.

15.3.2.1 Periphyton
Periphyton refers to a community of organisms that is associated with some surface, such as rocks,
debris, macrophyte leaves, etc. Macrophytes, discussed in the next section, comprise the large
(“macro”) plants while periphytons are typically members of the small or microbiota. Microbiota,
both plants and animals, grow on or attach to virtually any surface immersed or growing in water:
living, dead, organic, or inorganic (Wetzel 2001).
The periphyton are largely composed of the same algal groups as the phytoplankton (e.g., diatoms,
cyanophyta, and eugleonophyes). However, while the planktonic members of these algal groups are
ecologically important, probably greater than 90% of all algal groups grow attached to a substrate. The
attached algae often dominate the algal biomass of small streams and shallow lakes (Wetzel 2001).

15.3.2.2 Macrophytes
Macrophytes, also briely introduced in Chapter 6, represent a diverse assemblage of plants that
grow in the littoral zone of most lakes and reservoirs. Primary forms of macrophytes include emer-
gents, loating-leaved and/or free loating, and submerged species (Westlake 1975).
Emergents : Emergent macrophytes are typically rooted in the lake bottom with the tops of the
plant extending into the air. Thus, they can obtain nutrients from the sediments and water, oxygen
and carbon dioxide from the air, and light from above the water surface (so they are not impacted
by light attenuation in the water column). They must also be strongly rooted since they are subject
to the wind and waves. The root and rhizome system (underground stems) exists under anaerobic
conditions, as do the very young foliage for a brief period. Examples include cattails, bulrushes,
pickerelweed, and others (Figure 15.22). Most emergent macrophytes are perennials (plants or plant

Iris

Spatterdock

Cattails

Bulrush

Pickerelweed

FIGURE 15.22 Examples of emergent macrophytes. (From Ohio Pond Management Plant Identiication,
Ohio Department of Natural Resources.)