Considerations for the Use of Wetland WWT by Mangroves

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Breaux, A. M. and J. W. Day, Jr. 1999. Considerations for the use of wetlandwastewater treatment by mangroves in the State of Campeche, p. 299-310. In: A.Yez-Arancibia y A. L. Lara-Domnguez (eds.). Ecosistemas de Manglar en

Amrica Tropical. Instituto de Ecologa A.C. Mxico, UICN/ORMA, Costa Rica,NOAA/NMFS Silver Spring MD USA. 380 p.

20Considerations for the Use ofWetland Wastewater Treatment by

Mangroves in the State of Campeche

Andre M. Breaux,1

John W. Day, Jr.2

1Regional Water Board. Oakland, CA

2Coastal Ecology Institute, Department of Oceanography and Coastal Science, LSU

Abst rac t

Two major environmental problems currentlyaffecting the coastal zone of Campeche are loss ofmangrove wetlands and surface water pollution. The

application of treated wastewater to mangroves canbe a means of dealing with both of these problems.The benefits of wetland wastewater treatment includeimproved surface water quality, increased accretionrates to balance sea level rise, improved plantproductivity and habitat quality, and decreased costsfor conventional engineering treatment systems.Wetland treatment systems can be designed andoperated to restore deteriorating wetlands andmaintain existing wetlands. Hydrologically altered

wetlands are appropriate for receiving municipaland some types of industrial effluent. Wetlandwastewater treatment has been shown to be

effective in treating municipal effluent. Both artificialand natural wetlands have been used for treatment.Sea level is rising between 1 and 2 mm/yr and thisrate is projected to increase over the next severaldecades. Effluent discharge to wetlands should beincorporated into comprehensive managementplans designed to increase sediment and nutrientinput into mangrove wetlands, improve waterquality, and result in more economical wastetreatment.

Resumen

Actualmente dos problemas ambientales importantes

afectan la zona costera de Campeche: la prdida depantanos de manglar y la contaminacin de lasaguas superficiales. El uso de los manglares comoplantas de tratamiento de agua de desecho puedeser un medio para enfrentar ambos problemas. Losbeneficios de los humedales como plantas deetratamiento determina mejorar la calidad del aguasuperficial, aumentar la tasa de acrecentamiento delterreno para equilibrar la elavacin del nivel del mar,mejora la calidad del hbitat y la productividad de lasplantas y disminuye costos en comparacin con

sistemas convencionales de tratamiento de aguas.

Los sistemas de tratamiento de pantanos puedendiseZarse y operar para restaurar pantanosdeteriorados y mantener humedales existentes.Los pantanos alterados hidrolgicamente sonreceptores apropiados para recibir descargasmunicipales y algunos desechos de tipo industrial.Los manglares como plantas de tratamiento hamostrado ser efectivos en el tratamiento dedescargas municipales, tanto pantanos artificialescomo naturales se han usado para este propsito.El nivel de mar sube entre 1 y 2 mm/ao y este

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valor se estima aumentar en las prximas dcadas.Las descargas a pantanos deberan incorporarse enlos planes de gestin diseados para aumentar elflujo de sedimentos y el aporte de nutrientes a los

pantanos de manglar, mejorando la calidad delagua, y resultando en un tratamiento de desechosmuy econmico.

Introduction

Wetlands have been used to treat wastewaterfor centuries, but only in the past several decadeshas this process been scientifically analyzed in acomprehensive way (Richardson and Davis,1987). From an ecological perspective, interest inwetlands to purify effluent is based on a belief thatthe free energies of the natural system are bothcapable of and efficient at driving the cycle ofproduction, use, degradation, and reuse (Odum,1978). The basic principle underlying wetlandwaste treatment is that the rate of application mustbalance the rate of decay or immobilization. Theprimary mechanisms by which this balance isachieved are physical settling and filtration,

chemical precipitation and adsorption, andbiological metabolic processes resulting ineventual burial, storage in vegetation, anddenitrification (Patrick, 1990; Kadlec and Alvord,1989; Conneret al., 1989).

Both natural and constructed wetlands are usedto treat wastewater. Constructed wetlands -thosebuilt to treat wastewater on non-wetland sites- canbe designed to treat all forms of effluent fromprimary effluent through tertiary treatment and aredesigned as either surface or subsurface systems.The latter are used extensively in Europe (Watsonet al., 1989) while both systems are used in the

United States. In the US, natural wetlands arelegally limited to providing only tertiary treatmentof secondary waste. By the end of the 1980s,more than 500 natural wetland systems were usedto treat wastewater discharge in the United States(Reed, 1991; EPA, 1987).

To a large extent, conventional treatment plantsuse the same physical and biological processesas those operating in both natural and constructedwetland systems. But whereas filtration,sedimentation, oxidation, reduction, and nutrientcycling occur in natural systems by the interactionof soils, water, vegetation, and microorganisms,these same processes occur in conventionalplants only with substantially greater amounts ofenergy and chemical additives to compensate forthe reduced space and time required to treat largevolumes of effluent. Constructed wetlandsgenerally fall in between the two extremes,depending on design and loading rates.

In any treatment system -natural, constructed,or conventional- a large number of variables canbe manipulated to achieve pollutant reductiongoals. While conventional plants use highly

engineered, energy intensive systems toaccommodate the microbial mineralization oforganic carbon, natural wetland treatmentsystems are designed to take advantage ofexisting site and climatic conditions such assoils, plants, pH under submerged conditions,temperatures, precipitation, and floodingregimes. The primary management controls inthe natural system are loading rates andresidence times, though design of thedistribution system can increase the number ofoutfalls and take advantage of or creategradients or slopes.

Our objective in this paper is to discuss theconsiderations for the use of wetland wastewatertreatment in the coastal zone, with specialreference to the coastal zone of Campeche. Wefirst put the issue into a conceptual framework,that of restoration ecology. Then we develop adetailed analysis based on examples from anumber of coastal areas followed by adiscussion of the benefits and concerns ofwetland treatment. Much of this paper is basedon Breaux and Day (1993).

Before continuing further, we want to stressseveral points which are essential to our main

hypothesis that wetland waste treatment is notonly possible, it is desirable. First, mangrovewetlands are disappearing due mainly topressure from agriculture and urban expansion.Coastal wetlands which are most amenable towetland wastewater treatment are generallythose which are most threatened, and we arguethat wastewater application will benefit thesewetlands. Thus, the nutrients and organic matterin the effluent are used as a resource ratherthan treated as a pollutant.

Second, there is surface water qualitydeterioration in the coastal zone of Campeche,

mostly due to inputs of high levels of nutrientsand non-toxic organic matter. Conventionaltreatment methods alone are often impractical oruneconomic. Most of the wastewater isgenerated in areas that are located adjacent tolarge tracts of wetlands so that water does nothave to be transported over long distances. TheCity of Campeche is a good example of this withwastewater presently flowing into mangroves.Wetland wastewater treatment can be the mostcost-effective means of treatment.


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Figure 1. Conceptual model of the effects of treated effluent on wetland elevation. Addition of wastewater effluentstimulates wetland elevation both directly (through deposition of sediment) and indirectly (through increased plantproduction). In the Louisiana Coastal Zone wetland elevation is lowered due to sea level rise and subsidence, and thuscontinual accretion is necessary if plant communities are to be maintained

Finally, coastal wetlands are threatened by sealevel rise. Conversely, effluent application canstimulate vertical accretion thus helping to offsetwaterlogging resulting from inundation. Thisaccretion leads to rapid permanent burial ofmaterials and thus wetland wastewater treatmentsystems will not become saturated. Since sealevel rise is predicted to accelerate in the next

century (Warrick and Oerlemans 1990),wastewater can be used as a resource to helpoffset the impacts of rising water levels (Fig. 1).

Restoration Ecology

Restoration ecology has been defined as thereassembly or partial assembly of an ecologicalsystem (Jordan et al., 1987). In attempting torestore and maintain coastal wetlands, theaddition of sediments and nutrients to wetlandsthrough effluent application constitutes a form ofwetland restoration. The chief component of arestoration plan would be the selection of an

adequate design and effective loading rates toensure adequate hydrologic control and the healthof the ecosystem. The success of wetlands astertiary treatment systems has been amplydemonstrated under conditions where populationsare not large and natural wetland acreage isavailable (Nichols, 1983; Richardson and Nichols,1985; Khalid et al., 1981; Best 1987). Wetlandwastewater treatment could be incorporated as acomponent of coastal management in Campechewhere these conditions exist. The situation in

Campeche presents the opportunity toinvestigate the assimilative capacity of wetlandsto serve as more than tertiary systems (i.e., totreat effluent less than secondary). For example,in a recently completed a study of the use ofwetlands to treat wastes from a potato chipfactory in Louisiana, a system was designed toeffectively treat less than secondary wastes(Breaux, 1992).

Wastewater application to wetlands does notusually lead to biological communities identicalto those either preceding application orsurrounding the receiving site, though suchcommunities might be desirable. The ultimateaim of the discharge would be to make use ofthe assimilative capacity of the wetland to treatwastewater in order to maintain biologicalproductivity and to offset sea level rise.Monitoring and research should be an integralpart of any program that attempts to make useof wetland waste treatment to enhance theenvironment. Duplication of wetland functions is

the important point. This is emphasized byJordan et al. (1987) in their discussion ofrestoration ecology as both environmentaltechnology and ecological technique:

What is needed...is not rote copying, butimitation - the distinction being that copyingimplies reproducing systems item for item,while imitation implies creating systems thatare not identical but that are similar in criticalways and that therefore act the same.


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The authors state further that it is imitation thatwill ultimately provide the understanding critical forthe reproduction of natural systems.

Wetland treatment systems in Campeche canbe used to gain an understanding of the responseapplication of sewage effluent. In so doing,knowledge of natural processes will be bothexpanded and refined. The natural processesinvestigated underlie the hypothesis that wetlandsimprove water quality and that added sedimentsand nutrients will benefit wetlands facing sea levelrise. Maintaining coastal wetlands will prevent theloss of not only water purification functions andvalues but also flood control benefits, wildlifehabitat and diversity, direct economic use,education, and research.

Benefits of Wetland

Wastewater Treatment

The following are the primary benefits of wetland

wastewater treatment in the coastal zone ofcoastal Campeche: 1) improved surface waterquality, 2) increased accretion rates to balance

subsidence, 3) increased productivity ofvegetation and improved habitat quality, and 4)the financial savings of capital not invested inconventional tertiary treatment systems.

A number of factors associated with wetlands ingeneral, and with Louisiana coastal wetlands inparticular, lead to efficient reductions in biologicaloxygen demand, total suspended sediments, totalorganic carbon, and nitrogen and phosphoruslevels contained in typical municipal or food

processor effluent. These factors include 1) a highrate of burial due to subsidence and 2) highdenitrification rates due to warm temperatures andwetland plants which enhance denitrification.Relatively high temperatures are also favor highermetabolic rates, and higher plant productivity ingeneral. A third factor related to phosphorusremoval is the adsorption and precipitation ofinorganic phosphorus which is facilitated byreactions with iron and aluminum under theneutral conditions of saturated wetland soils(Nichols, 1983; Patrick, 1990). Phosphorusremoval rates in the southeast are variable butpotentially high. Nixon and Lee (1986), in a review

of field studies of wetlands and water quality,found overall phosphorus removal rates in thesoutheast to range from 9% to 98% for a range ofloading rates between 0.4 to 46 gP/m

2/yr. By

using conservative hydraulic and nutrient loadingrates and employing design criteria to optimizecontact time, complete removal rates for all waterquality constituents could be achieved.

Finally, the current mean relative sea level riserate in the Mississippi Delta is about ten times thatof eustatic sea level rise (Penland et al., 1988;

Conner and Day, 1988; Baumann et al., 1984;Gornitz et al., 1982) This means that theMississippi delta can serve as a model for theeffects of sea level rise other coastal systems(Day and Templet 1989). Wetland restorationattempts through the stimulation of biomass inthe rapidly subsiding Mississippi delta can,therefore, prove useful in the management of

endangered wetlands and the creation of newwetlands beyond the reach of encroaching sealevels.

Potential Problems and Concerns

There are a number of potential concernsabout the use of wetlands for wastewatertreatment. We believe that proper design andoperation of these systems in hydrologicallyaltered areas in coastal Louisiana can overcomethese concerns.

The main mechanism of phosphorus removal

in wetland treatment systems is the adsorptionand precipitation of iron, and aluminumcomplexes (Richardson, 1985). After longperiods of effluent application, soils havebecome saturated and phosphorus removalefficiency has decreased (Faulkner andRichardson, 1989; Hemond and Benoit, 1988;Richardson, 1985; Nichols, 1983). Where naturalsoils do not contain sufficient amounts of iron,aluminum, or calcium to effectively removephosphorus (Nichols, 1983), other techniqueshave been employed successfully in the field orlab such as the addition of an anaerobic zone ina section of the activated sludge system at the

Walt Disney World treatment system (Knight etal., 1987). When phosphorus loadings are highor a wetland lacks the assimilative capacity totransform or remove it, Richardson and Davis(1987) suggest pretreatment using alum or iron,or aeration to decrease BOD and suspendedsolids. Khalid et al. (1982) found phosphorusremoval from municipal wastewater to beenhanced both by the addition of calciumcarbonate and by the pre-reduction of thesoil/plant system. Finally, Louisiana wetlandscan assimilate much higher levels of phosphorusthan elsewhere due to the high rate of burialresulting from the high rate of subsidence.

Because of this latter factor, properly designedtreatment systems in the coastal zone will neverbecome saturated.

Two other commonly voiced concerns over theissue of wetlands used as wastewater treatmentsystems include the suggestion of incompletepathogen removal and the implications oftreatment to wildlife populations. Questions havebeen raised by some researchers (e.g., Shiaris,1985 and Grimes, 1985) about the effectivenessof wetland treatment in removing pathogens. At


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the same time, however, successful pathogenremoval by natural die-off has been reported byEPA (1987), and measured in the field or lab byMeo et al. (1975), and Gersberg (1987) amongothers. Kadlec (1989) reported that fecal coliformsare generally reduced to acceptable water qualitystandards after passage through wetlands, as areviruses and bacterial indicators such as fecal

streptococcus. He found no reported incidents ofadverse effects to animals or humans resultingfrom wetland wastewater treatment.

Finally, concerns for the potentially adverseeffects of wastewater treatment to wildlife aresometimes expressed and the suggestion madethat more artificial wetlands be built to serve asnatural systems (e.g., Guntenspergen and Sterns,1985). But others acknowledge that there is nosubstitute for a natural system, and that speciesdiversity is usually lower in artificial systems (EPA,1987). Many believe that the use of properlyoperated natural wetlands as treatment systems

has benefited, and can continue to benefit, wildlifepopulations (e.g., Best, 1987). Wentz (1987) ofthe National Wildlife Federation also concludedthat wetland waste treatment was not incompatiblewith wildlife management.

The fact that 1991 waterfowl survey figures forten species of diving and dabbling ducks show adecline for nine of those species from the 1955-1990 average, with the northern pintail showing adecrease of 62% (US Fish and Wildlife Service1991), emphasizes the need for full-scale habitatprotection measures. The importance of Louisianawetlands as waterfowl habitat, and the high

wetland loss rates require efforts to increase andimprove existing wetland acreage.

A careful design can combine the techniques ofthe engineer in terms of flow rates, holding ponds,stormwater diversions, and the pretreatmentmethodologies described above, with theimpoundments, spoil banks, levees and sheerspace available in the natural system to produceboth effective wastewater treatment systems andproductive wetlands. Wentz (1987) explains thebenefit of and need for the carefully plannedmultiple use of wetlands: We must take peoplebeyond the idea that because wetlands are

valuable they cannot and should not be`managed. It is very important that peopleunderstand that manipulation of wetlands is notnecessarily a bad thing. Indeed, manipulation ofaltered natural systems is essential in order tocontrol the changes brought about by humaninterference. This is especially the case forLouisiana where human impacts threaten the veryexistence of the coastal zone. We believe thateffluent application will enhance the long-termsurvival of coastalwetlands.

Current Political and Regulatory

Climate

EPA

The US Environmental Protection Agency(EPA) has recognized the benefits and efficiencyof wetland treatment systems. The Agencys

Report on the Use of Wetlands for MunicipalWastewater Treatment and Disposal states:Wetlands appear to perform, to at least somedegree, all of the biochemical transformations ofwastewater constituents that take place inconventional wastewater treatment plants, inseptic tanks and their drainfields, and in otherforms of land treatment. The report furtherstates that both natural and constructed wetlandtreatment systems have been found to achievehigh levels of removal from wastewater fornutrients, BOD, suspended solids, nutrients,heavy metals, trace organic compounds, andpathogens, as well as natural die-off of

pathogens from wastewater (EPA, 1987).While the Agency acknowledges that

constructed wetlands are often more costly andrarely achieve the same level of biologicalcomplexity as natural wetlands systems, itsstated policy is that currently, use ofconstructed, rather than natural wetlands, isgenerally preferred by EPA when projects forwastewater treatment are proposed (EPA,1987). One reason for preferring constructedover natural wetland treatment systems is thereluctance to alter biotic communities of naturalwetlands when using natural systems astreatment areas. The no action approach to

wetland preservation in coastal Louisiana,however, is more likely than not to lead to theelimination of existing wetland species as theybecome increasingly and permanentlyinundated. Sediment and nutrient additions tothe subsiding wetlands could help reverse thetrend toward submergence.

An additional reason for encouraging the useof constructed over natural wetland systems isthe presumed greater level of control in theformer. Two points in regard to the issue ofcontrol need to be addressed here. First, inLouisianas case at least, it can be argued that

the large number of isolated impounded or semi-impounded areas allow for as much control asmight be available in a constructed wetland.Second, control in an artificially-createdenvironment which lacks the diversity of anatural one, is not as instructive scientifically interms of revealing the functions and processesof the wetland ecosystem. Again, Jordan et al.(1987) describe the situation appropriately withan emphasis on the value of control in naturalsystems, as opposed to artificial ones:


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The essential idea is control -the ability not onlyto restore quickly, but to restore at will, controllingspeed, decelerating change as well asaccelerating it, reversing it, altering its course,steering it, and even preventing it entirely (whichof course is actually a frequent objective of theecological manager).

Louisianas needs to control or prevent wetlandloss and deal with surface water pollution suggestthat wetland wastewater treatment would bebeneficial. The use of hydrologically alteredwetlands to treat wastewater will enable thetesting of hypotheses regarding ecosystemresponse and land loss, and will contribute to theoverall knowledge of wetland ecosystems.

EPAs preference for constructed over naturalwetlands as treatment systems has undoubtedlyinfluenced national policy. In 1987 the Agencyitself acknowledged that the lack of EPA waterquality criteria for wetlands and the resulting

absence of State water quality standards forwetlands is one of the most serious impedimentsto a consistent national policy on use of wetlandsfor wastewater treatment or discharge (EPA,1987). Florida is the only state to have institutedits own regulations for wetland treatment systems.Prior to the institution of those regulations in themid-1980s, H.T. Odum (1978) used Florida as anexample of a state whos regulatory authoritylacked an appreciation of the environmentsassimilative capacity: An economy is vital whenenvironment and economic developments aremutually reinforced and protected. Unfortunately,well-meaning efforts to draft laws to protect the

environment have not always been made with anunderstanding of the ecological principles ofsymbiosis and recycling by which nature andhumanity are best combined.

The regulations which Florida subsequentlyadopted allow for progressively stricter loadingrates depending on the type of wetland to whicheffluent is discharged. The Florida plan allows forthe following applications:

1. Hydrologically altered wetlands are allowedto receive a maximum of 75 g/m

2/yr of total

nitrogen and 9 g/m2/yr of total phosphorus;

2. Treatment wetlands are used to treatreclaimed water that has gone throughsecondary treatment with nitrification, and areallowed to receive 25 gN/m

2/yr and 3 gP/m

2/yr;

3. Receiving wetlands are used to receivereclaimed water that has gone throughadvanced (tertiary) treatment, and can acceptonly wastewater treated to 3 mg/liter totalnitrogen and 1 mg/liter total phosphorus(Harvey, 1988).

Floridas ranking of wetlands to treatwastewater is a response to environmentalproblems which include a high degree of waterlevel reductions with relatively little subsidence.Discharge to treatment and receiving wetlandsare generally prohibited in Class I and II watersand in non-cattail dominated herbaceouswetlands. Hydrologically altered wetlands in

Florida are defined as those where uplandvegetation has encroached and wheresubstantial reductions in water levels haveoccurred. While Louisiana does have alteredwetlands that fit this description due to drainageprojects or deprivation of flows to some wetlandareas, the problem of subsidence and risingwater levels is a far more serious threat. Effluentwith higher sediment and nutrient loads shouldbe considered for discharge to submergingwetlands to increase accretion rates andproductivity. While Florida needs to deal with theproblem of wetland loss as a result of decreasedwater levels and the consequent transition to

uplands, Louisiana needs to deal with theproblem of wetland loss as a result of increasedwater levels, sediment starvation, and theconsequent transition to open water.

An additional factor favoring wetlandwastewater treatment in Louisiana is itsrelatively low population density and availableland area. While Florida ranks first in thecoterminous United States for total wetlandacreage and Louisiana ranks second (Dahl,1990), Louisiana has a substantially lowerpopulation density, with 97 persons per squaremile of land area compared to 240 for Florida(US Bureau of the Census, 1991). In addition,the general tendency for populations inLouisiana to be distributed along natural leveeridges backed by wetlands facilitates use ofthose wetlands as treatment systems.

Since 1987, EPA has attempted to designstandards that would be more appropriate forwetlands than the aquatic standards developedfor surface water bodies. The Agency hasrecently published a manual describingnumerical or narrative biological standardsdesigned to prevent a decrease in wetlandproductivity or diversity (U.S. EPA, 1990). Whilethe Agency is still willing to permit the use of

wetlands as tertiary treatment systems in someLouisiana cases, it will not allow such use as aform of wetland enhancement. The term wasused in the report on wetlands to treat municipalwastewater (EPA, 1987) primarily as a possibilityonly in areas where insufficient water exists tomaintain a wetland as occurs in the westernUnited States, not in areas facing the possibilityof conversion to open water as occurs inLouisiana. There appears to be a reluctance toadmit, or a basic disagreement with, the


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hypothesis that a natural but degraded wetlandmight adequately purify wastewater, whilebenefiting ecologically at the same time.

Consequently, EPA has discouraged wetlandwastewater treatment in Louisiana as a form ofenhancement, and encouraged the state toapprove wetland projects according to theantidegradation rule which requires that the stateprovide for the protection of existing uses inwetlands... (EPA, 1990). In Louisianas case,where sea level rise is predicted to drown a vastexpanse of coastal wetlands (Park et al., 1989;Day and Templet, 1989), such an emphasis onpresent uses appears short-sighted anddesigned to accommodate only those who use orwill use the wetland areas directly over the next 2to 3 decades or less.

The Louisiana DEQ has granted permission todischarge secondarily treated wastewater towetlands near Thibodaux and is considering thesame permission for Breaux Bridge, but only as a

naturally dystrophic waters exception on thepremise that dissolved oxygen levels are naturallylower than the EPA standard of 4.0 mg/l inestuarine waters. State DEQ personnel havegenerally sought to establish expedient permittingof wetland treatment systems, though workingwithin the inflexible national framework of EPApolicy has been a deterrent. A memo from onestaff member to the Secretary emphasized theneed for prompt consideration and processing ofwetland treatment system permitting:

If we are to make wetlands enhancement bywastewater application feasible in Louisiana,

we must provide the regulatory structure toallow expedient permitting of such discharges.The establishment of appropriate wetlandspecific standards is the first step in providingthe regulatory structure for permitting (Knox,no date).

Recently the state has developed a set oftentative standards for the Thibodaux wastewatertreatment site which include the followingprohibitions designed to protect wetlands from anyadverse effects due to wastewater application:

1. No more than 20% decrease in naturallyoccurring litter fall or stem growth.

2. No significant decrease in the dominanceindex or stem density of bald cypress.

3. No significant decrease in faunal speciesdiversity and no more than a 20% decrease inbiomass.

Monitoring of the site after effluent applicationbegins in the Spring of 1992 will test the validity ofthese criteria and serve as a basis for theirexpansion or refinement.

EPA has already acknowledged the capabilityof wetlands to effectively treat wastewater. Itremains for the agency to review the potential fortreated effluent to benefit Louisianas wetlands inlight of the unique problems of the state. If thebasic premise that effluent can contributevaluable sediment and nutrients to the wetlandsis accepted, then wetland wastewater treatment

could be incorporated as a major component ofan overall comprehensive plan to protect andrestore the states wetlands. Seven years agoGosselink and Gosselink (1985) suggested thatwetland wastewater treatment be incorporatedinto plans to divert freshwater from theMississippi River to the coastal plain. Templetand Meyer-Arendt (1988) have emphasized thatthe wetland sediment deficit is a primary reasonfor Louisianas land loss. Their suggested policyis to use Mississippi River water, sediments, andnutrients to revive and nourish coastal wetlandsby helping to maintain surface elevationssufficient for plant growth. They state further

that:

The greater the number of conduits deliveringwater, sediments, and nutrients into thewetlands, the greater is the level of restoration ofa formerly viable ecosystem.

Strategy: Provide maximum distribution of thewaters of the Mississippi River across the deltaicplain by using the maximum number ofdistribution points to move water, sediment, andnutrients into the coastal wetlands.

Because of the dispersed nature ofdischargers in the coastal zone, wide distribution

to wetlands could easily be achieved. Forexample, 147 distribution points were identifiedas appropriate for discharge to subsidingwetlands in the Terrebonne and BaratariaBasins in coastal Louisiana. These distributionpoints consist of dischargers of secondarilytreated effluent, primarily from sewage treatmentplants, oxidation ponds, subdivisions, schools,and trailer parks (Breaux, 1992). Total rural flowin the two basins is about 52 MGD, of which 38.1MGD was appropriate in terms of effluent qualityand total volume per discharger. Based ontypical effluent composition of secondarilytreated municipal wastewater of 25 mg/l

suspended sediments, 20 mg/l total nitrogen,and 10 mg/l total phosphorus (Richardson andNichols, 1985), and a total wetland area ofapproximately 783,000 ha in the study area(Louisiana Department of Environmental Quality,1990), the following loading rates would beapplied to the two basins: 0.17 g/m

2/yr of

suspended sediments; 0.13 g/m2/yr of total

nitrogen; and 0.067 g/m2/yr of total phosphorus.

Applied to the total wetland area, these additionsof sediments and nutrients would be too small tomake much of a difference to accretion.


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Concentrated at only 148 receiving wetlands,however, they could be distributed in a mannerthat would help build up the wetland withsediment, and fertilize the vegetation withnutrients.

In sum, water, sediment, and nutrients fromsmall industries and municipalities throughout thecoastal region could enhance coastalmanagement by increasing both the total volumeand the maximum number of distribution points.Money saved from the construction ofconventional or constructed wetland treatmentsystems, could be applied toward thoroughpreproject review of potential wetland treatmentareas and a sophisticated monitoring andmodeling system designed to prevent anydetrimental impacts to natural areas.

In attempting to restore altered wetlands withadded sediment and nutrients, a number ofgeneric questions arise that pertain to themaintenance of virtually all Louisiana wetlands.

Wetland wastewater treatment could be used as acomponent of a restoration plan to return nutrientsand sediments to the wetland, but only afterknowledge of the system and goals for itsmaintenance are established.

In addition to the question of exactly what werethe historic hydraulic and nutrient levels thatformed and nourished the wetland before it wasaltered, other questions that need to be addressedinclude: is the present vegetation identical orsimilar to previous types, or have different speciesestablished themselves? Are natural rates ofsuccession occurring, or have human alterationssped up or changed the natural course? Wherehuman intervention has brought about changes,then what is the ultimate goal - to revert to theprevious system, maintain the present one, ormanipulate the present one to achieve functionalgoals or aesthetic values deemed desirable bysome segment or all of the present population?Clearly a comprehensive management plan isneeded to save coastal Louisiana, and wetlandwastewater treatment can be an integral part ofsuch a plan. While the primary benefit of wetland

treatment will be the improvement of waterquality, it can contribute to the halting of wetlandloss by increasing the number of sediment andnutrient distribution points to subsiding wetlands.Holding ponds, pretreatment techniques, rotatingreceiving areas, and multiple outlet distributionssystems could be incorporated into wetlandtreatment systems in order to restore sediment

and nutrients to the coastal plain.

Summary

Wetland wastewater treatment systems arewidely used and have proven to be especiallyeffective in warm regions such as the southernUnited States. When combined with carefuldesigns and monitoring programs, wetlandtreatment systems show great promise for bothenhancing the mangrove wetlands of Campecheand improving water quality. Specific benefits ofwetland wastewater treatment include improvedsurface water quality, increased accretion rates

to balance rising sea level, increasedproductivity as a result of the additions ofnitrogen and phosphorus, and decreasedfinancial outlays on conventional sewagetreatment systems.

The sediments and nutrients contained insecondarily treated municipal effluent and insome types of industrial effluent (e.g., seafoodprocessors) can be beneficially applied towetlands in the coastal zone. The warmtemperatures, relatively low population densityand abundance of wetlands make theCampeche coastal zone an especially

appropriate region for wetland wastewatertreatment.

The use of natural wetlands as treatmentsystems conforms to the general principle ofecological engineering described by H.T. Odum(1978) who emphasized the challenge tomodern culture as: Recognizing the high valuesin existing landscapes and finding ways to fitmans further developments without waste of theprevious landscape values.

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