more of the incoming nutrients and suspended solids during the growing season
(e.g., Toth 1972; Lee, Bentley, and Amundsen 1975; Spangler, Fetter, and Sloey
Fetter, Sloey, and Spangler 1978;
1980; Sinclair and Forbes
and Adams 1984; Weidenbacher and
1980;
1983;
bring 1984; Willenbring 1985).
(1983) describes the deterioration of Clear Lake, Minnesota
To protect the
257 ha; drainage area = 1,518 ha) due to urban
(area
lake from further impacts, storm runoff was diverted to a
marsh, com-
posed of peat underlain with clay loam and having a reed canary grass
The marsh was divided into cells con-
plant community.
Nutrients and suspended solids were removed by percolation
trolled by gates.
The marsh was harvested to remove nutrients and to maintain
through the peat.
During the winter, storm flows were
the absorption potential of the peat.
Filtration sig-
diverted through the marsh rather than through the cells.
nificantly reduced nutrient concentrations, especially phosphorus (90 per-
6
cent), and suspended solids (70 percent). In 1982, 897
10
was filtered,
Where possible, a 5-day detention time was
removing 526 kg of phosphorus.
used.
Sinclair and Forbes (1980) examined the removal capacity of a swamp, a
reservoir dominated by waterhyacinth (Eichhomia
and a
0.4-ha reservoir dominated by the submergent plant Najas sp. The latter two
systems were effective nutrient sinks, but the aerobic system
was most
effective.
The authors believe that in comparison with the swamp, the
waterhyacinth- and naiad-dominated systems have the greatest potential to be
nutrient sinks because they can be harvested.
The systems could be used in
series.
Sinclair and Forbes
following the suggestion of Boyd
also recommended cattail systems for removal of nutrients and suspended solids
due to their large standing crop, rapid growth rate, high nutrient value to
cattle, and ease of harvest.
Limitations and Concerns
Many of the problems that could be encountered with the use of any of
these prereservoir treatments will be site- and problem-specific.
Therefore
only a general listing of the most likely problems is given here.
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