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Mechanisms of the air-surface exchange of organic pollutants and mercury in a

Chinese subtropical forest

Luca Nizzetto Norsk Institutt for Vannforskning

Gaustadelléen 21, Oslo

Luca.nizzetto@niva.no

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The Project numbers

• NFR – NorKlima : 3,000,000 NOK

• About 2,000,000 NOK as counterpart from Chinese partners

• Period 2009-2012

• 2 PhD students and 2 Post Docs involved

• 1 year of field work in Southern China forests

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NIVA Norwegian Institute for Water Research Luca Nizzetto, Katrine Borgå, Thorjørn Larssen

State Key Lab. for Organic Geochemistry (Chinese Academy of Sciences (CAS)) –

Guangzhou (Prof. Gan Zhang) State Key Lab. for Environmental

Geochemistry (CAS) – Guiyang (Prof. Xinbin Feng)

The Partners

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Scientific objectives

• To investigate the mechanisms linking the environmental cycling of persistent pollutants and Biogeochemical cycles, in subtropical/tropical forests.

• To assess the relationship between organic matter turn-over and contaminants air-soil exchange

• To derive parameters useful for monitoring

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The scientific case: Semivolatile Persistent Pollutants

• Long/indefinite residence time in the environment

• Bioaccumulation/toxicity

• Long range transport/ubiquitous contaminants

Examples: Hg, PCBs, DDTs, HCBs, new POPs

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The scientific case

• Multimedia partitioning /speciation in the environment

• Long term storage in soils, vegentation, sediments

• Re-mobilization can be controlled

by climate and biogeochemistry.

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The scientific case

• Tropical and Subtropical forest: 60% of global terrestrial productivity.

• Very important stores of organic carbon (and contaminants?) • Fast organic matter turn-over in soil

What are the implications for contaminant cycling?

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Dinghushan Biosphere Reserve - Subtropical forest

primary tropical rainforest

Jianfengling -Hainan

Dinghu Mountain

The study location

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Passive Exchange Meter

(PEM)

The experiments and tools

Active Exchange Meter

(AEM)

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PUF

Deposition of:

- Organic matter

- Rain

- ”Native” pollutants

+ Environmental and

climatic conditions

Sorbant for

pollutants

Forest litter

collected in-situ

deposition

volatilization

Leaching

Passive exchange meter

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Low

volume air

sampler

Soil core 10 c

m

Low volume air

sample

Polyurethan

foam

sorbent

Active Exchange meter

Sampling of:

-Potential volatilization

-Distribution in litter and

soil core over time

-Leaching

Mini-polyurethan foam plugs

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The results

• Higher mobilization from soil surface were observed under

canopy conditions.

• Losses by leaching were dependent on compound

hydrophobicity, suggesting biogeochemical control.

• Litter dry masss loss correlated with contaminant losses.

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The results

• Exchange properties controlling

Contaminant accumulation in

forest litter from air

determinesusing the PEM

• Their dependence on compound

properties determined

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The results

• Rapid incorporation of contaminants to soil

controlled by litter degradation rate

• Elevated mobility within soil controlled by

leaching of dissolved organic matter

• Soil pools of contaminants compared

between boreal and tropical forests

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Follow-up

• Consolidated/on-going collaboration with Chinese partners

• 2 Visits from Chinese researcher after the end of the project

• New complementary studies carried out.

• Additional outputs related to EXPOLL

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Follow-up results

• Soil OC distribution strongly control

PCB distribution

• Exposure of mineral soils is higher

in southern climates (sensible to

temperature and precipitation)

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Follow-up results

• Distribution of flame retardants in

soil depends on primary source

distribution.

• Soil contamination correlated to an

index of anthropic impact

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The overall picture

• We investigated, for the first time, the processes that drives contaminant fate in tropical and sub-tropical environments.

• We developed new robust tools for chemical flux analysis

• We shed some light on the interaction between climate and contaminant fate and distribution

• We have greatly tighten our partnership and set conditions for long term collaboration in this field

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Thanks Acknowledgments: NFR-NORKLIMA for funding All coauthors of our studies

Luca.nizzetto@niva.no