Trophic State and Eutrophication - Freshwater Ecology: Concepts and Environmental Applications - page 363

wetland studies reviewed by Johnston (1991) and 1 of 19 studies reviewed
by Kadlec (1994) showed that the wetlands actually serve as a net source of
phosphorus. Thus, scientific management of wetlands for nutrient removal is
required to ensure that the wetlands serve as nutrient sinks. Wetlands may as-
sist in removal of nutrients from agricultural waters (Woltermade, 2000).
Large areas of wetlands are required for effective nutrient removal. These
wetlands are particularly effective if incorporated into riparian buffer strips.
A concern with using natural wetlands for nutrient removal is that they
may become eutrophic, causing a shift in community composition. This
successional change may not be a problem in constructed wetlands, but
managers should give careful consideration before subjecting natural wet-
lands to high nutrient inputs. Eutrophication of wetlands can be detri-
mental to the natural community (Sidebar 17.3).

SUMMARY

1. Aquatic systems can be classified by trophic state. Eutrophic lakes are
characterized by wide swings in O 2 concentration and pH, anoxia in
the hypolimnion, and algal blooms including increased abundance of
cyanobacteria. Eutrophic streams and
wetlands can be characterized
by high biomass of primary producers.
Eutrophic groundwaters can have high
inputs of organic carbon and be anoxic.
2. Lakes can naturally become more
eutrophic over thousands of years.
However, cultural (human-caused)
eutrophication is currently far more
common.
3. Eutrophication of lakes can lead to
taste and odor problems, toxic algal
blooms, fish kills, lowered water clarity,
and decreased property values.
4. Quantitative equations are available to
calculate expected relationships among
nutrient loading, nutrient concentration,
algal biomass, and Secchi depth in
lakes. These equations are used by lake
managers to make decisions on efforts
to alter lake productivity. Similar
equations are also available for streams.
5. Solving eutrophication problems
generally requires control of point
sources and non-point sources of
nutrients. Control of non-point sources
includes limiting excessive application of
fertilizers, terracing fields, maintaining
riparian and near-shore vegetation, and
keeping livestock out of water bodies
with fences and provision of stock
tanks. Control of point sources includes

Sidebar 17.3.
Eutrophication and the Everglades

The Everglades are naturally oligotrophic wet-
lands on the southern tip of Florida that have
been impacted by agriculture and urbaniza-
tion. Among the negative impacts of the activ-
ities upstream of the Everglades are those on
native plant species assemblages by increased
nutrient input and decreased hydrologic flush-
ing. Preservation of the native wetland plants
is necessary for animal conservation efforts;
approximately one-third of the wading bird
populations have decreased, and several other
species that rely on the wetlands are nearly
extinct, including the Florida panther and snail
kites (Davis and Ogden, 1994). This Everglade
food web is driven by a natural flow regime
that varies seasonally.
The predominant plant cover in the Ever-
glades was historically sawgrass (Cladium ja-
maicense), but it is being replaced by cattail
(Typha). A shift in cyanobacterial community as-
sociated with phosphorus enrichment and hy-
drodynamic alteration has also been docu-
mented (Browder et al., 1994), as have shifts
from Utricularia- to Chara -dominated communi-
ties (Craft et al., 1995). Such community changes
have occurred in areas where phosphorus con-
centrations have increased, mainly from alter-