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Wetland Biogeochemistry

Narin Boontanon

Faculty of Environment and Resource Studies

Mahidol University

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The field of biogeochemistry involves scientific study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the hydrosphere, the pedosphere, the atmosphere, and the lithosphere), and the cycles of matter and energy that transport the Earth's chemical components in time and space.

What is biogeochemistry?

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In ecology and Earth science, a biogeochemical cycle is a circuit or pathway by which a chemical element or molecule moves through both biotic ("bio-") and abiotic("geo-") compartments of an ecosystem. In effect, the element is recycled, although in some such cycles there may be places (called "sinks") where the element is accumulated or held for a long period of time.

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Biogeochemistry is an interdisciplinary science. It has it roots in biochemistry to understand the metabolic reactions of organisms, which obtain raw materials from the environment and cast their chemical waste into nature (ex. cycle of reduction and oxidation)

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Wetland SoilsMust show signs of being a wetland (hydric) soil

» mottling» color» deep organic layer

Soils can still be saturated with a water table 1 foot or more below the surface

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Wetland SoilsTypes and Definitions

Wetland soil are both the medium in which many of the wetland chemical transformations take place and the primary storage of available chemicals for most wetland plants.

They are often described as hydric soils: formed under conditions of saturation long enough to develop anaerobic conditions.

Gray or neutral color is caused by “reduction”, which is a bio-chemical process involving soil microbes in waterlogged soils.

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Wetland SoilsTypes and Definitions

Wetland soil are of two types:

1. mineral soils: less than 20-35% OM (on dry-weight basis)

2. organic soils have a specific definition dependent upon degree of saturation and soil texture.

Organic soils differ from mineral soils in these categories:

- Bulk density and porosity (lower bulk density)

- Hydraulic conductivity (depends on degree of decomposition)

- Nutrient availability (more nutrients are tied up in unavailable organic forms)

- Cation exchange capacity (greater cation exchange capacity)

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n

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Wetland Soils Identification

Hydric soilsLacking oxygen

Soil Colorgrayish and may have black and white mottling patterns.

Soil Permeabilityorganic (high) or mineral (poor)

Soil Texturefine particles, silts, and clays

Soil Smellsulfurous (rotten egg)

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Jarosite is a basic hydrous sulfate of potassium and iron with a chemical formula of KFe3+

3(OH)6(SO4)2. This mineral is formed in ore deposits by the oxidation of iron sulfides.

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Chemical Transformations in Wetlands

Oxygen and Redox PotentialOxygen diffuses slowly in water, so slowly, in fact, that it is often

used up by microbial activity faster than it can be replenished. This affects root respiration, and impacts nutrient availability. Some soil components are changed to toxic forms.

Redox potential is the measure of electron availability in a solution. Reduction is the opposite of oxidation. It involves releasing oxygen, gaining hydrogen, or gaining an electron. It is driven down by microbial activity, as metabolizing organisms seek terminal electron acceptors to allow their harvest of energy from substrate compounds.

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Oxygen and Redox Potential

Organic decomposition can occur in the presence of any number of terminal electron acceptors, including O2, NO3

-, Mn4+, Fe3+, SO4=. It occurs most rapidly in the presence of oxygen, and slower for other electron acceptors. Redox potential drops through the sequence of electron acceptors, as O2 is the acceptor at 400-600 mV. Nitrate becomes an acceptor at 250 mV, manganese at 225 mV, iron between+100 and -100 mV, and sulfides at -100 to -200 mV. Carbon, or CO2, will become the terminal electron acceptor below -200 mV.

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Sequence in time of transformations in soil after flooding.

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The thickness of oxidized layer is directly related to:

1. The rate of oxygen transport across the atmospheric-surface water interface

2. The small population of oxygen-consuming organisms present

3. Photosynthetic oxygen production by algae within the water column

4. Surface mixing by convection currents and wind action

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Carbon TransformationsMethanogenesis occurs when certain bacteria use CO2 as an

electron acceptor and produce gaseous methane (CH4).

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Nitrogen TransformationsOne of the more significant ways that nitrogen is lost to the

atmosphere is in wetlands. Organic N is mineralized to ammoniumNH4

+. In aerobic conditions, nitrification occurs through the mediations of Nitrosomonas then Nitrobacter, resulting in nitrite then nitrate. Nitrate is often then subjected to uptake or leaching, as it is very mobile in solution. If not, it may be subjected to denitrification, which results in gaseous nitrogen forms that are lost to the atmosphere. Denitrification is inhibited in acid wetland soils.

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Phosphorus TransformationsPhosphorus is a major limiting nutrient in freshwater marshes,

northern peatlands and deepwater swamps. It is more available in agricultural wetlands and saltmarshes. Phosphorus retention is often considered to be an important ecosystem function in wetlands and is often designed into constructed wetlands.

Phosphorus occurs in a sedimentary rather than gaseous cycle like nitrogen. It is often present in wetlands as a cation. It may be tied up in organic litter in peatlands or in inorganic sediment in other wetlands. It can be made unavailable for uptake as the result ofprecipitation as phosphates with ferric iron and aluminum (acid soils), or calcium and magnesium (basic soils) under aerobic conditions. In water columns, anaerobic conditions render it soluble.

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Sulfur TransformationsAt low redox potentials, sulfur is reduced and H2S, hydrogen

sulfide, is released. Because the concentration of sulfates is higher in salt water wetlands, sulfide emission is also higher, and toxicity greater. Toxicity can occur as the result of contact with roots, or with reduced availability of sulfur to plants because it precipitates with trace metals. Zinc and copper can also be limiting because theyprecipitate with sulfur. If ferrous iron is present, it will precipitate with sulfides. Ferrous sulfide (FeS) give many wetland soils their black color, and is the source of sulfur commonly found in coal deposits.

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Chemical Transport Into Wetlands

PrecipitationLevels of chemicals entering wetlands in precipitation are variable,

but such solutions are very dilute. Higher magnesium and sodium are associated with maritime influences, while calcium is associated with continental influences. Sulfate concentrations from industrial atmospheric pollution could have an impact in oligotrophic systems, though sulfate levels have decreased. Nitrates from auto exhausts have not decreased and may similarly impact poorly buffered systems.

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Streams, Rivers, GroundwaterDissolved substances in groundwater often depend upon the ease of dissolution of the mineral, with limestone and dolomite yielding high levels of dissolved materials and granite and sandstone low levels.

Arid regions tend to have higher salt concentrations in surface waters.

Geography: there is often an inverse correlation between streamflowand dissolved materials; sediment load and dissolved materials.

Human uses impact sediment, nutrients, herbicides, pesticides, and organic loading (BOD).


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EstuariesEstuaries have quite variable chemistry, different from both that of the adjacent ocean or the tributary rivers.


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Chemical Mass Balances of WetlandsWetlands may serve as sources, sinks or transformers of chemicals.

There are seasonal patterns of uptake and release, and they are different for colder, low productivity systems and warmer, high productivity systems. Wetlands are frequently couple to adjacentecosystems through chemical exchanges that are significant to both systems. Wetlands can be highly productive or systems of low productivity. Nutrient cycling is different in aquatic and terrestrial systems.

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Many wetlands act as sinks for inorganic substances and may be major providers of organic material for downstream systems.

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Survey and measurement methods

Gases emission

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Gases emission

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Dissolved gases

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Sediment

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Greenhouse gases emission from wetlands

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I Initial stage

II Intermediate stage

III Present stage (before drainage)

IV Present stage (after drainage)

drainage canal

Melaleuca leucadendron sedges, reeds and ferns predominate

accumulation of peat and development of fresh water swamp forest

development of marsh vegetation

closed lagoon or depression

closed lagoon or depression

sandy beach sandy beach sea

sea

sea

sea

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Figure Monthly precipitation in Narathiwat and the flow rate of Bang Nara River flow during January, 1997 and April, 1998.

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Nitrification (Oxic) Denitrification (Anoxic)

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Org. N NH4+ NO2

- NO3-

N2O

O2 H2ONitrificationNitrification

δ15N (N2O) ≤ δ15N (NO3- or NH4

+) and

δ18O (N2O) < δ18O (O2 and H2O)

DenitrificationDenitrification

NO2-NO3

- N2O N2

NO2-

δ15N and δ18O (N2O) ≥ δ15N and δ18O (NO3-)

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Time

[N2O]

δ15N

δ18O

Figure Schematic illustration of nitrous oxide and its isotopic compositions in Bang Nara River during rainy season (after Boontanonet al., 2000).

Coupling of nitrification & denitrification or denitrification nitrification

Coupling of nitrification & denitrification or denitrification

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The Greenhouse Effect & Wetlands

We are all familiar with the idea that the greenhouse effect could make our environment (including wetlands) warmer. Warmer conditions speed reactions -including decomposition reactions- and so this could help to release carbon that was previously safely stored away.

The consequently reduced rainfall could seriously undermine peatland ecosystem stability by inducing a transition to a less waterlogged (more aerobic), state.

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Wetland BiogeochemistryPossible global impacts on Wetlands

This could occur as a shift in the nature of the biogeochemical exports that leave the wetlands. Effects could occur through increases in two mechanisms;

1: Export of gases to the atmosphere (e.g. re-releasing carbon dioxide), and

2: Export of leachates into waterbodies such as lakes, rivers and the oceans (e.g. nutrients and dissolved carbon compounds).

These solutes could even add to the greenhouse effect as the dissolved organic compounds are broken down to carbon dioxide, or adversely affect water quality with possible implications for human health.

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Storage (Gt C) Reservoir type Author(s)860 Gt Peats, world-wide Bohn (1976)300 Gt Peats Sjors (1980)202 Gt Peats Post et al. (1982)500 Gt Peats Houghton et al. (1985)249 Gt Northern peatlands Arm.& Men. (1986).210 Gt Boreal peatlands Oeschel (1989)461 Gt Subarctic and boreal peat Gorham (1992)1576 Gt Global soils (present-day) Eswaran et al. (1993)500 Gt Global peats Markov et al. (1988)

- How big is the problem?Many studies have focussed on the potential for

destabilisation of peat carbon stores. Various authors have estimated the peatland carbon that could be released:

Units are in gigatonnes of carbon (1 Gt = 1 billion tonnes = 1 Petagram = 1 x 1015 g).

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Wetland EnzymesEnzymes are biological catalysts. They speed up chemical

reactions, often very dramatically. Many biochemical reactions would not occur at environmental temperatures and pressures without enzymes. In short, enzymes allow the processes of life to occur.

Enzymes play a key role in breaking down "complex" organic materials and releasing the "simple" chemicals which are locked-up within them (biogeochemical cycling). If climate change does cause our vast stores of peat to begin to break down, then it will have been a stimulation of enzyme activities that will have allowed it.

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Sustainable use and management

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Why do we have to "Klaeng Din"?Ever since 1973, each year His Majesty the King would temporarily

reside in the South and take the occasion to regularly visit the local people there. His Majesty has perceived numerous problems that the people in Narathiwat and nearby provinces were facing. One of the major problems wasthe lack of productive land to carry out a living. By nature, after water was drained out from the boggy region, the soil in that area would become strongly acidic. This occurred because of the oxidation process between pyrite and oxygen from the air which consequently released the sulphuric acid. If the sulphuric acid content in soil is high, it would be harmful to the crops planted and thus reduces the yields. Therefore in 1981, His Majesty initiated the establishment of the "Pikun Thong Royal Development Study Center" in Narathiwat Province to study and improve the soil in boggy region so that this land would become productive for agricultural and other purposes.

http://www.chaipat.or.th/chaipat/journal/dec97/eng/k/k1.html

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His Majesty paid a royal visit to observe the "Klaeng Din" Projectat the Pikun Thong Royal Development Study Center.

http://www.chaipat.or.th/chaipat/journal/dec97/eng/klaengdin.html

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How is the process of "Klaeng Din" implemented? The Pikun Thong Royal Development Study Center carried out

research study and activities to improve the soil by using His Majesty's royally initiated "Klaeng Din" approach. To "Klaeng Din" involved causing the soil to become strongly acidic, by leaving the soil dry and then making it wet. Actually, water is released into the experimentation field and stored for a period of time before being drained out, thus creating periods of wet and dry conditions. This process of alternate drying and flooding of the area will accelerate the acidification of the soil.


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How is the process of "Klaeng Din" implemented? Based on this logic, His Majesty provided a suggestion to

imitate nature which has a dry and raining season each year, except the duration would not be as long as the period of each season. First leave the soil to dry for one month. Then release water into the field and let it remain flooded for two months. Repeat these two steps four times a year alternately is just like having four dry and raining seasons annually. After such process, there will be a study to find ways to improve the soil so that it is possible to grow economic crops.


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"Klaeng Din" first, then improve the soil: an important method

After executing the process of "Klaeng Din" , there are several methods which can be used to improve the acid soil condition forcultivation purposes.

Mix lime such as marl or lime dust together with the soil. The lime will react with sulphuric acid to create a compound mixture thus decreasing the amount of acidity in the soil. And if an appropriate amount of lime has been used, the soil would be neutralized.


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"Klaeng Din" first, then improve the soil: an important methodUse water to directly leach the acid and poisonous substance from the soil. This method will take longer than using lime because acid will slowly be leached away. Nevertheless, it is as effective.

Create raised beds in order to cultivate fruit or perennial trees and dig ditches on the side. Use the soil from the ditch to cover the top edge of the raised bed to create a thicker soil surface. As for the soil which contains pyrite, it will be used to support the sides so when water leaches acid down from the sides of the raised bed, acid will bewashed into the ditches and later be drained.

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"Klaeng Din" first, then improve the soil: an important methodControl the underground water level above layer of mud and sediments which helps to prevent the pyrite from reacting with oxygen, thus sulphuric acid will not be further released.

Grow plants which can tolerate strongly acidic soil condition.

Use all of the above mentioned methods together.


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Cross section view of acid soil layer.


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Conditions of the boggy region which make farming practices impossible and need to be developed.


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What do the people gain after the implementation of "KlaengDin"?

After achieving desirable results from the study, the Pikun Thong Royal Development Study Center disseminated these findings to the people living in areas with strong acid soil problem. For this matter, His Majesty provided the following directive, " The areas of Ban Khok It and Ban Khok Nai are made up of acid soil, however, farmers there would like to grow rice. The Royal Irrigation Department has supplied the areas with irrigated water. Through coordination with the Royal Irrigation Department, the acid soil needs to be improved to serve different purposes. "As a result of the land development at Ban- Khok It and Ban Khok Nai, farmers were able to significantly increase rice yields. To His Majesty's content that He mentioned " I have been to Ban Khok It and Ban Khok Nai before to observe the cultivation area in which the farmers used to gain only 5-10 buckets (one bucket=15 kg) of rice. But now they can harvest up to 40-50 buckets which is good enough. This is owing to the process of creating maximum acidity in the soil, by repeating the process of digging to accelerate acidity and then drain out. The farmers are getting better. This is the victory to be proud of. As the land is now productive, farmers' lives will also improve. Before The farmers needed to buy rice, but now, the rice yields they have may even be enough for selling."

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However, the "Klaeng Din" Project does not end in any particular areas, the implementation must go on. "The work to improve acid soil should be continued, in terms of both the experiment study and dissemination of the concept. "At present, the project findings have been disseminated to the people in Narathiwat and other provinces. In progress, this accomplishment will be transferred to Nakhon Nayok and NakhonSrithammarat. Thus, the "Klaeng Din" Project is one project which provides benefits to people in all parts of the country. The Thai people are extremely proud and touched by His Majesty the King's personal sacrifice to initiate schemes of "Klaeng Din" or "aggravate the soil" in order to pull His people out of poverty and placethem into the state of ecstacy.

"...if soil is put to work, it will no longer be angry..."

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The rice cultivation area at Ban Khok It and Ban Khok Naiproduced an increasing yield from 5-10 buckets(one bucket=15 kg.) to 40-50 buckets.


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The Artificially Constructed Wetland System

This waste water treatment system involves digging out a shallow, square-shaped pond which will contain waste water at lightly sloping depths of 15-30 centimeters. The plants cultivated in the pond have short stalks, grow in dense clumps, and have dispersed roots which are rooted well into the soil. These include Cyperuspapyrus, Arundo donax, and similar species which are able to grow well in areas that usually remain flooded. In this waste water treatment system, water is released into one end of the wetland and slowly passes down to the other end.

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Cyperus papyrus Arundo donax

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While waste water remains in the artificial wetland, nature, wind, and sunlight also contribute, to a certain degree, to treating the waste water. However, a significant factor in reducing pollutants are these plants: they help to absorb both organic and inorganic substances present in the waste water. Moreover, the microbes that are attached to the stalks and roots effectively help to eliminate organic substances which pollute the water. The system improves the water quality, thus allowing the water to exit from the lower end of the artificial wetland with a quality suitable for consumption, household uses and irrigation purposes.

Nevertheless, this system is still in the study and experiment stage.

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Constructed wetland system

http://www.chaipat.or.th/chaipat_old/n_stage/activities_e/pakbia/pb1.html


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Constructed wetland system



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The grass filtration waste water treatment system is very similar to the artificially constructed wetland system except for the filtering stage in which waste water is retained periodically. The experimental study revealed that the appropriate level for the water is 30 centimeters for a period of five days; after this period of flood the area will be left to dry out for three days. Wastes in the water will be reduced due to the grass planted on the plot which filters wastes and thus reduces pollutants in the water. It was established that plants which grow fast and possess a great waste water treatment potential include Cyperus corymbosus, Indonesian vetiver grass, Typhaangustifolia, Leptoschlosa fusca, Cynodon dactylon, and Sporoborusvirginicus. The appropriate ratio of sand to organic soil mixture for growing such plants for treating waste water is 3:1.

The grass filtration system

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Constructed area of the grass filtration plot

The model used in the research study for the grass filtration system consists of:

1) Seven plots of plants grown for consumption as well as for animal feeds at a size of 5x100 meters each.

2) Seven plots of plants grown in inundated fields at a size of 5x25 meters each.Rural government agencies with limited budgets such as the Sukhapiban (a local government agency lower in authority than a municipality) can use this study as a demonstration model for future application and adaptation to their own waste water treatment systems.


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Grass filtration system




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Cyperus corymbosus

Indonesian vetiver grass

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Typha angustifolia Cynodon dactylon

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This system has been used in a research study on the treatment of waste water through natural means. It involves using mangrove forest to absorb as well as filter waste water. The water from the central waste water drain will flow through a pipeline into the mangrove area before it is released into the sea. Thus, water quality will be improved and the impact on the ecological balance can be controlled.

The Red and White Mangrove System

A natural mangrove forest in the project area


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In this study, mangrove was used to treat waste water by allowing the water to pass through the existing mangrove forest as well as through newly planted mangrove trees. The mangrove forest is capable of filtering and absorbing toxins and other pollutants present in the water, thus producing good quality water. The clean water can be used for agricultural purposes and can be further released safely into the sea.

A mangrove plantation plot for waste water treatment


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A natural mangrove forest in the project area


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A mangrove plantation plot for waste water treatment


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Organic C CH4

CO

CO2

SOIL

AtmosphereVegetation

Ground Water Surface Water

POC

DOC

CO2

VOC

CO2, HCO3,CO3

(Heterotrophic Respiration)

(Methanogenesis)

(Methanotrophy)

(Leaching) (Leaching)

(Litterfall)

(NPP)

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Atmospheric CH4 Concentration (AM)

Ebullition(EB)

Plant-MediatedEmission (PM)

Diffusion (DSA)

(Oxic Soil)

CH4 Consumption (MC)

(Anoxic Soil)CH4 Production (MP)

Water Table

Lower Boundary

Soil / Water Surface

Upper Boundary

Net Methane (CH4) Exchange

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NO3Organic N NH4

NH3

NO

N2O

N2

SOIL

AtmosphereVegetation

Ground Water Surface Water

PON

DON

(Nitrification)

(Denitrification)

(Mineralization)

(Leaching)(Leaching)

(Litterfall)(Uptake)

N2

(Symbiotic fixation)

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sustainable use and management

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