Carbon Cycle in Soils

Photosynthesis in green leaves CO₂ in air synthesised into sugars
Sugars transported in stems to all parts of plant
Exudates from roots deposited in soil and becomes food for microorganisms
Plants eaten by animals and respiration produces energy and CO₂ returned to atmosphere
Leaf litter forms from dead leaves, bark and stems
Soil organic matter
Microrganisms
CO₂ is released during respiration by insects and microorganisms and
Inorganic plant nutrients are released into the soil in a soluble form available to plants.

WATER and CARBON in GARDEN SOILS

Vigorous plant growth, irrigated by water harvesting will establish carbon sinks in urban gardens.

Water cycle

Water harvesting: Water collected from the roof of a house and used to irrigate the home garden. Water can be stored in a water tank and used in dry times or water from the roof spread directly on the garden during rain periods.

When raindrops come to earth they are absorbed by the soil or if there is too many of them they will flow down hill over the soil surface.

Transpiration is the movement of water from soils up the roots and stems of plants and into atmosphere. Water movement up roots and stems is essential to carry plant nutrients from soils to the growing parts of the plant.

Excess rainfall is not absorbed by soils and flows downhill over the land surface into drains and creeks. Flooding is reduced when more water is absorbed by soils and less water allowed to enter drains.

Water harvesting reduces downstream flooding and reduces severity of droughts in gardens. Organic matter improves water penetration into soils and increases water storage in soils.

Irrigation increases plant growth. The use of town water may not be available in the future and to ensure good plant growth in urban gardens water harvesting is necessary. Water tanks are very useful and storage of water in soils will help plants to grow in dry times.

Water collected on the roof of a house and spread over a garden area of equal size to the house, doubles the total rainfall. For this to work the soil has to be well prepared. The ground surface needs to be very permeable to allow water to soak down into the earth.

IMPROVING WATER INFILTRATION INTO GARDEN SOILS

Increase plant cover to protect soil surface
Encourage plants with deep roots
Improve soil structure
Add mulches, green manures and compost
Encourage earth worms
Add soil improvers such as gypsum
Maintain rough soil surface
Protect the soil from raindrop impact
Reduce soil compaction
Improve subsurface drainage
Use organic fertilizers and animal manures

Growing plants encourages water to penetrate deep into soils. A variety of plants with different root systems will allow water stored in the soil at different depths to be utilized.

Carbon sinks

Carbon dioxide in the atmosphere causes greenhouse effect and air temperatres to rise. A carbon sink is created when carbon is removed from the atmosphere and locked up in a form away from the atmosphere and not causing a rise in air temperature.

Photosynthesis: In green chlorophyll of plant leaves, organic compounds are synthesised using energy from sunlight, water from soils and atmospheric carbon dioxide CO₂.

Photosynthesis is the basic process producing food and energy by plants. Animals eat plants and each other and there food and energy is originally synthesised by photosynthesis.

Respiration:Plants and animals use oxygen from atmosphere and living compounds to produce energy and exhale carbon dioxide CO₂ to atmosphere. All living organisms respire including plants, animals and microorganisms.

In a mature native forest the rate of photosynthesis is nearly equal to the rate of respiration. There is a balance and no CO₂ is added or subtracted from the atmosphere. If the forest is cut down photosynthesis in trees stops and respiration by soil microorganisms continues and extra CO₂ is added to the atmosphere increasing the greenhouse effect. If trees are planted and nurtured in cleared land and photosynthesis is faster than respiration a carbon sink will form.

Carbon sinks can be formed from any plants growing at a faster rate than total respiration. In most farming land respiration is faster than photosynthesis so CO₂ is added to the atmosphere.

Carbon sinks in urban gardens are created by living plants growing above and below the ground surface. Green plants absorb carbon dioxide from the air and manufacture plant material by photosynthesis in leaves.

Below ground level, organic matter in soils is a very important carbon sink. Leaves and stems fall onto the soil surface, forming a leaf litter. Many small animals and microorganisms break down large dead plant remains into small pieces, incorporating broken down plants into soil organic matter.

Benefits of soil organic matter

Food for microorganisms and soil animals
Nutrient cycling
Store plant nutrients in soils
Reduce harmful changes in soil acidity and alkalinity
Improve soil structure
Improve soil aeration
Reduce erosion
Increase water infiltration
Improve water holding capacity
Create healthy soils and encourage vigorous plant growth
Are a very good carbon sink and reduce greenhouse gases

Organic matter in soils is found in varying stages of decay. On the soil surface plant residues occurs including leaf litter and mulches. Particulate organic carbon is small plant remains, humus is very small particles synthesized by microorganisms. Charcoal is mainly carbon and is resistant to decay, lasting for hundreds of years.

Plants are made from sugars, starches, cellulose, fats, oils, proteins and lignin. Sugars are very quickly eaten by microorganisms, cellulose is slowly converted to sugars and lignin is very resistant to decay and may survive in soils for hundreds of years. Organic matter is mainly dead, decomposing plant material. Only a small proportion originates from animals. Animal bones, CaCO₃ is a inorganic compound containing carbon.

The amount of carbon is often equal above and below ground level. Carbon in soils increases in cold or wet conditions. Woody plants, containing lignin, forms humus resistant to microbial breakdown and will persist in soils for hundreds of years.

Carbon sinks will be bigger when there is extra plant growth in soils with desirable physical properties.

The build up of soil organic matter by returning garden cuttings, compost and mulches to soils will add nutrients to the soil. The addition of organic materials to soils will improve soil physical properties. Structure is stable, improving soil aeration and water movement. Water holding capacity is increased, improving drought tolerance. Damage from erosion and the beating action of raindrops is decreased.

Cultivation and digging soils can reduce soil organic matter. Digging soils increases aeration and this can increase the decay of organic matter. Cultivation kills plants and this can reduce the build up of organic matter.

Hardwood trees and shrubs and especially gum trees form long lasting humus in soils.

Well managed garden soils will contain up to 10% organic matter. A small gum tree can store up to 1 tonne of carbon with ½ half above ground and ½ half in the soil. It is possible to store 4 tonnes of carbon in 100 square meters of garden containing several trees.

During a hot summers day trees will cool a backyard garden and strategically positioned plants will cool a house. Tall trees provide welcoming shade and growing plants transpire water from their leaves into the air producing a cooling effect.

Community Involvement

Whites Creek Wetland A Mini Aquatic Sanctuary In Sydney

A Mini Aquatic Sanctuary In Sydney

Why Build a Wetland?

An old polluted drain flows between the Sydney suburbs of Annandale and Lilyfield. The native bush was chopped down over a hundred years ago, swamps filled in and Whites Creek was turned into a concrete stormwater drain, forming a hostile environment for frogs and fish.

The original concept was initiated by Friends of the Earth in 1996, who had a vision to reduce pollution in Sydney Harbour by mimicking nature and using natural means.

What happened?

The landscape architects, Oculus, prepared a concept plan and University of Technology Sydney, undertook initial feasibility studies. These services were donated to Friends of the Earth.

Leichhardt Council built the wetlands in 2002. Council held meetings and produced newsletters to help keep local people informed of progress during construction.

A local bushcare company selected and planted the aquatic seedlings and the immediate area surrounding the water was planted by volunteers.

On Sunday 20th Oct 2002 an Open Day was held where people enjoyed a bbq and visited stalls held by local organisations.

Funding was received by Council from the Stormwater Trust program for construction and education projects. Additional grants from the Trust funded a demonstration water tank installed at the community gardens and a team of volunteers were trained to give tours of the wetlands.

A special effort was made to involve local schools. North Annandale Public School have adopted the wetlands as an outdoor classroom and students planted trees in bush regeneration project areas.

St Scholastica’s High School monitors chemicals in the water.

Debbie Faint, a local artist exhibited “Wetlands”, an intimate glimpse of life in a fragile ecosystem, rendered with extreme sensitivity.

An informative educational DVD, “Creating an urban wildspace”, was produced by Al Media Productions.

Next to the wetlands is the “Labyrinth” where children like to play. This area was a tangled mass of Lantana, Privet, and many other weeds and made a good hiding place for children. To improve biodiversity, native species were planted to replace the weeds. The wetlands and the “Labyrinth” are now connected into one natural biodiversity unit.

The wetlands are an important component of a greenway along Whites Creek Valley. Every year more bushland is added to the valley between the wetlands and Rozelle Bay.

The greenway connects the wetlands to the old railway goods line. The Hawthorn Canal and the old railway are very important greenways in the densely populated inner Western suburbs of Sydney.

The concrete sides of Whites Creek act as a barrier to the movement of many ground dwelling animals. Replacing the concrete sides with more nature friendly materials will improve aquatic biodiversity and help animals on the move.

Local community groups have played a prominent role in the wetlands and the Valley. The members of Rozelle Bay Nursery are a driving force in the establishment of native bush. Plans are well advanced for the nursery to move to a new site, next door to the wetlands.

Friends of Whites Creek Valley Park have supported the wetlands and the establishment of native bush in the parklands. A community center with facilities for environmental education may soon become a reality after a long campaign by this organisation.

Ramin Communications is a local computer company who have provided free services to community organisations. The Ramin website has information on the wetlands, bird lists and a web page on Rozelle Bay Nursery: http://www.ramin.com.au/creekcare/ .

Why are the wetlands valuable?

Many people value the wetlands, often for different reasons.

The wetlands mimic nature adding a little aquatic wildlife to inner Sydney.

They look good while many water management structures made from concrete and steel look ugly.

Nature is enhanced where fish, frogs, turtles and little critters make their home. A good view of aquatic life can be seen from the path running beside the wetlands.

Water is continually pumped from the creek up into a sediment pond where heavy polluted particles are traped and removed. Nitrogen and phosphorus are nutrient pollutants and are removed by plants growing in the water.

Local residents have developed an ownership of the wetlands and soon complain to the Council if the water is polluted or if other problems are occurring.

Education values are high for all ages.

The wetlands are truly multi-functional and have helped to stimulate better water management practices and new biodiversity projects in an extensive area surrounding Whites Creek.

“Why build a wetland? Because it wasn’t there.”

Ted Floyd www.ramin.com.au/creekcare

This article was first published in WetlandLink

creeksbyted

WATER AND CARBON IN SOILS