Linking Water Treatment with Wetland Restoration - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 364

There are as many as six thousand constructed wetlands currently in operation
in North American and Europe. In addition to municipal wastewaters, constructed
wetlands are used to treat stormwater, a wide range of industrial effluents including
pulp and paper, food processing, landfill leachate, and acid mine drainage, as well as
agricultural runoff from both feeding-lot operations and crop fields (France 2003).
Wetland design and performance data are readily available. Three books that
CH2MHILL engineers regularly consult include Constructed Wetlands for Waste
Water in Europe (Vymazal et al. 1998); Treatment Wetlands , 2nd ed. (Kadlec and
Wallace 2004); and Natural Systems for Waste Water Treatment: WEF Manual
of Practice (Water Environmental Federation 2005). All these documents provide
ready guidance for anyone charged with having to apply this information, and Bays
(2004) believes that if any wetland engineer went to Iraq today, he or she would want
to bring books such as these in order to begin progress.
There is a set of questions that people often ask about treatment wetlands. The
first: do the wetland systems need to be harvested? In point of fact, it is actually
desirable and important for plants to accumulate in the wetlands in order for them
to build up a new layer of soil. On the other hand, it is possible, and sometimes
necessary for vector and hydraulic purposes, to periodically harvest plants. For the
marshes in southern Iraq, the harvesting and commercial use of the reeds is actu-
ally an important part of the heritage (Ochsenschlager 2004) which could represent
another somewhat novel end product of constructed treatment wetlands (Bays 2004).
The point is that it is certainly possible to harvest plants successfully if there are
reasons for doing so but it is not necessary to undertake this task in relation to the
performance of the treatment system.
Do accumulating sediments need to be removed? Because accumulation rates are
very slow (usually in order of mm or perhaps a cm a year at the most in the most
extreme case) the need for removal is extremely rare for municipal systems. In the
case of stormwater treatment wetlands, the high inorganic load of sand and silt par-
ticles is usually pretreated and removed in a special forebay, and as such, there is no
need to remove them from the marsh itself.
Is there an ecological risk to these wetlands? Most treatment wetlands receive
water in which the toxic constituents are relatively dilute and not at levels that would
bioaccumulate or be harmful. Industrial effluents, however, may deserve extra atten-
tion. And selenium, which has been identified in some of the waters in the Iraq
marshes (France 2011), may be a concern that requires special assessment and con-
sideration (Bays 2004).
Mosquitoes and wildlife can be problems that have resulted in decades of wetland
destruction in attempts to try to control these vectors. But we know from experience
that vector control is a tractable problem which can be solved by management and
design approaches (Bays 2004). Odors are not a problem in treatment wetlands; they
simply smell like marshes and ponds and not like sewage.
NATURAL TREATMENT PROCESSES
Consider a shallow wetland where there's about a foot or so of water overlying a
layer of soil (Bays 2004). As the plants grow and die through their annual cycle of