GRAZING AFFECTS THE GREENHOUSE GAS EMISSIONS

Grazing Affects The Greenhouse Gas Emissions In UK Floodplain Meadows



Table of Content

CHAPTER I: INTRODUCTION3

CHAPTER II: LITERATURE REVIEW5

Carbon Dioxide: Grazed Lands Can Act As A Sink For Carbon Dioxide7

U.S. Agriculture and Forestry Greenhouse Gas Inventory: 1990-20057

CHAPTER III: METHODOLOGY9

Site Description9

Measuring Greenhouse Gases In The Field13

Extraction Of Inorganic Nitrogen From Soils14

Determination Of Water Content And Loss On Ignition15

CHAPTER IV: RESULTS17

Carbon dioxide17

Graph 2:5 samples of carbon dioxide gas from ungrazed floodplain meadow19

Graph 3: CO2 emissions (mean numbers) from grazed and ungrazed meadows.24

Methane25

Graph 4: 5 samples of CH4 emissions from grazed floodplain meadow25

Graph 5: 5 samples of CH4 emissions from ungrazed floodplain meadow29

Graph 6: Mean CH4 emissions from grazed and ungrazed meadows29

CH4 at grazed site (ppm)30

CH4 ungrazed site (ppm)30

Grazed Sites Description32

Ungrazed Sites Description32

CHAPTER V:DISCUSSION AND CONCLUSION34

Carbon Dioxide34

Methane35

Nitrous Oxide36

Conclusion36

REFERENCES38

CHAPTER I: INTRODUCTION

The amount of greenhouse gases has considerably increased since pre-industrial times. Carbon dioxide, the main greenhouse gas has increased by about 30 % since that time. Each year it grows with the rate of 0.4% mostly due to fossil fuel burning and land use changes (Hoffmann et al, 2009). Methane the second most important greenhouse gas has doubled since 1970. Although methane is minor contributor to global warming compared to carbon dioxide its warming potential is 21 times that of CO2. Not all emitted greenhouse gases stay in atmosphere, but some of them are absorbed by oceans and terrestrial biospheres. Soils that hold about 1500 Gt organic carbon are considered to be the main carbon sink (Hoffmann. 2009). Even small changes to organic soil carbon can play an important role in atmospheric carbon concentrations. Therefore erosion is an important process of carbon removal from soil on one hand and carbon burial through sediment deposition on floodplains on the other hand.

Floodplains are seasonally inundated sites with high biological activity, which strongly influence carbon dynamics. They are generally known as important sinks of carbon and sources of greenhouse gases, such as carbon dioxide, methane and nitrous oxide, at the same time. These sites are characterised by high rates of organic production and frequent anaerobic conditions (Ballester and Santos, 2001). The process of carbon remineralisation by methanogenic bacteria is the main pathway of methane emission under these conditions (reference). Methane emissions from floodplains are of big importance for global methane cycling. Natural wetlands account for more than 25% of atmospheric methane of all biogenic emissions (Pulliam, 1993). Anaerobic conditions within the soil slow down SOM decomposition thus enable big quantities of carbon to accumulate and to act as a sink to atmospheric CO2. Moreover floodplains play a crucial role in nitrate removal from rivers through the process of denitrification. This is the main biological process responsible for emitting and reducing nitrous oxide (Pinay et al, 2007).

Under different conditions floodplains can act as positive or negative feedback to global warming. Any little changes are significant to alter the balance. For instance, drainage of floodplains alters greenhouse gas emissions, with CH4 and N2O decreased in favour of greater CO2 ...