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Plants in the Inland Aquatic Environment:Their Role in a Healthy Ecosystem
Katherine Gerein and Marlene Evans
National Water Research Institute, 11 Innovation Blvd., Saskatoon, SK, S7N 3H5
Plants are a crucial component to the functioning of a healthy aquatic ecosystem. As in
terrestrial ecosystems, plants form the base of the food web and interactions between
plants and animals ultimately affect food web structure. Aquatic plants provide habitat
for invertebrates, fish, both migratory and nesting waterfowl and other wildlife, such as
beavers and moose. As well, they are an important source of dissolved oxygen in the
water column, stabilize the sediments of the littoral (near-shore) zone, and provide sites
for the growth of epiphytic algae. Some aquatic plants have medicinal properties.
Aquatic plants exhibit great morphological diversity, varying from microscopic algae to
large macrophytes (rooted plants). Within a freshwater lake, the littoral zone is
subdivided into different zones characterized by their plant community. Emergent
macrophytes, such as cattails (Typha) and bulrushes (Scirpus), are found along the
nearshore region; whereas floating macrophytes, such as pond weed (Potamogeton) and
water lilies (Nymphaea and Nuphar), occur in waters up to 3 m. Submerged
macrophytes, such as stoneworts (Chara), grow on the substrate in waters up to 10 m,
depending on water clarity. Macrophytes also provide substrate for epiphytic algae.
Plants in the pelagic (open-water) zone of a lake are dominated by algae, ranging from
single-celled (e.g., Chlamydomonas) to large, colonial algae (e.g., Aphanizomenon). The
rapid movement of water in rivers limits plant growth to rooted macrophytes and
epiphytic algae growing along the shoreline.
While a naturally balanced flora is necessary, problems arise if plant growth becomes
excessive. Many Saskatchewan lakes are naturally eutrophic, although algal blooms are
frequently exacerbated by human activities, such as sewage effluent discharge and runoff
of fertilizers from agricultural lands. In eutrophic lakes, when blooms of large colonial
algae die, bacteria decompose the algae which can result in anoxia causing the death of
fish. Algal blooms are also aesthetically unpleasant as they decrease water clarity, and
can have an odour. As well, certain algal species release toxins into the water that can
poison wildlife and cattle. Excess nutrients also lead to increased macrophyte growth
which can foul recreational areas.
Saline lake aquatic plant communities have reduced diversity as a result of the elevated
salinity. Saline lakes are unique ecosystems and until recently, their importance has been
overlooked. They are vital to the shorebirds ecology, and several of these saline lakes in
Saskatchewan have been declared protected areas. Phosphorus and nitrogen
concentrations in saline lakes are high, but the total plant biomass is generally lower than
expected. Macrophytes are often absent in these ecosystems and the algal community
appears to be dominated by single-celled taxa, and have fewer colonial forms.
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