Describe natural and anthropogenic sources of organic matter. Give examples and explain why it may be hard to categorise a source as natural or anthropogenic.

Natural sources of organic matter are those derived mainly from plant or microbial residues. Examples include things such as the degradation of plant and animal matter as well as microorganisms and fungi found in soil. Anthropogenic sources of organic matter is organic matter that has come from human activity and can include point and non-point sources. An example of a point source would be discharge pipes, while a non point source would be sediment runoff from farmland. It can be hard to categorise a source as natural or anthropogenic as sometimes you don’t know where the OM has come from - e.g high OM in a lake may be from high aquatic plant degradation or sediment runoff from farmland. It is hard to identify when there are non-point sources around.

· What subcategories can total carbon (TC) be divided into. You may wish to include a diagram in your answer. Total carbon can be divided into the categories shown below:

We can use normal organic matter as a non specific indicator of water quality which is made up of our particulates and dissolved organic carbon We also have our inorganic carbon which has particulates and dissolved but there is a more cyclic behaviour with these processes. Sea creatures take carbon from water and precipitate caco3 to build their shells which give out particulates. When those shells dissolve we move back into the dissolution realm - form carbonate species - carbonic acid, carbonate, and bicarbonate but there is interplay between the inorganic realm and organic realm So we go from dissolved inorganic to our particulate organic which is our primary production - photosynthesis. We can also go from particulate to dissolved organic carbon which is when our material from primary production starts to dissolve again. So everything interplays with each other We measure that through carbon content

· Explain the environmental issues that are related to aqueous organic matter and give three examples. There are 3 main environmental issues related to aqueous organic matter:

1. Toxicity of specific organic compounds - e.g pesticides and their breakdown products

2. Reaction with other aquatic species - Alkylation of metals by microbes e.g. Uses of organotin include in pesticides, preservatives of wood and antifouling paints. • Monomethyl tin (CH3 Sn3+) is more toxic to aquatic biota than inorganic tin because it can cross cell membranes.

3. Consumption of Oxygen - Non-living OM can be oxidised by oxygen and other oxidising agents in water Oxygen deprived water; anaerobic state - not enough o2 for living organisms to breathe. Non living OM can also change the chemistry of the water as organic matter + o2 in water creates carbon dioxide which then reacts with water to form carbonic acid, and then dissociate further into carbonate and H+, making the water more acidic, harming aquatic life

· How is OM matter tested in the laboratory and why is it important to know which test is used?

It is important to know which test is used because different tests may measure different aspects of organic matter, such as its quantity or quality. Understanding the specific test used can help in interpreting the results and making informed decisions about soil management practices.

· Discuss humic material. Your answer should include what it is made up of, the subcategories, how it is formed and features of the structure.

Humic material (HM) is made up of decayed organic material of plant or microbial origin. HM is a class of substances that are produced and reside in soil and water. Humic material has subcategories that include Humin (Hu) •Humic acid (HA) •Fulvic acid (FA). Humic material formation is not well understood. Instead, two main theories hypothesise the formation of Humic Material by two main pathways:

1. Degradation pathway - The degradative pathway hypotheses that the formation of HM occurs from modification of plant biopolymers through degradation. This theory proposes that labile macromolecules (e.g. carbohydrates and proteins) are degraded and lost. While biopolymers (e.g. lignin, macromolecules) are modified to produce the high molecular mass humin, then oxidised to produce the smaller components. Plant biopolymers → humin → humic acid → fulvic acid → small molecule

2. Synthetic pathway - The synthetic pathway hypotheses that plant biopolymers are first broken into small molecules then re-polymerised to form humic material. Individual molecules cannot be identified in humic material, So it is subdivided into 3 categories for operational purposes: •Humin (Hu) •Humic acid (HA) •Fulvic acid (FA) Plant biopolymers → small molecule → fulvic acid → humic acid → humin

The hypothetical structure of HM can vary as there are many possible structures. However, the structure of HM tends to contain many functional groups that interact depending on their proportions. These functional groups are the sites of many important reactions in which HM is involved. They allow specific reactions with inorganic substances and other organic molecules. They also contribute to cation exchange properties of soils and sediments.

· Compare and contrast the various sub-categories of HM. What are the general chemical changes that take place as you move from HM to Fulvic acid? The differences between fulvic acid, humic acid, and humin is Carbon content, oxygen content, acidity, degree of polymerisation, molecular weight and colour. As we move along the pathway of humin → humic acid → fulvic acid we have decreasing : molecular weight (breaking down molecules), carbon and nitrogen content, degree of polymerisation (related to weight, breaking down), intensity of colour. However, we also have increasing: oxygen, and degree of solubility (because molecules smaller, easier to dissolve)

· Discuss interactions of HM. Your answer should include what HM interactions with, the types of interactions, and what influences this has on the water and molecules. Use examples to illustrate your answer. You may want to sketch an example of the interaction (note: a detailed diagram is not required). The interactions of Humic Material are dependent on the environment. The different types of interactions include: vanderwaal forces, charge interactions, hydrogen bonding, hydrophobic interactions, and organic molecules binding to soluble or particulate HM.

Organic Geochemistry – Fossil Fuels: · Explain how coal was formed and what contaminants are found in it.

Coal was formed over 300 million years ago due to dead plant matter that fell into swampy water. Anaerobic conditions caused the plant matter to not decompose and over time it was buried and built up. Overall, pressure, heat, and time converted the organic matter into coal. This process is called coalification. Contaminants that are found in coal are primarily sulphur due to sulphur being present in salt water swamps due to bacteria in the swamp that converted sulphate in saltwater to pyrite (FeS2 ) which became a part of the coal. Low sulphur coal was formed in freshwater swamps. There is also some mercury in coal present due to its affinity for sulphur.

· Describe the conditions required to form petroleum. Petroleum comes from OM that is deposited on seabed which is buried by sediments which are then broken down and transformed over millions of years. There are special conditions that are required to form petroleum. All seven conditions need to exist in one place, hence why petroleum is only found in certain areas of the world.

1. Source rock with a High organic content (marine organisms) - would come from marine organisms because most petroleum reserves found from old oceans

2. Rapid burial to create a reducing environment - anoxic conditions (no O2) as we don’t want organisms to degrade

3. Overburden pressure – created by burial to depths of ~7-15 km -> helps in maturation process

4. Structure (e.g Anticline trap) - fold structure with an arch of non-porous rock overlying reservoir rock to trap oil and gas Special conditions are required to form petroleum: - need structure, mostly anticline which acts as a trap

5. Cap rock – Impermeable rock to prevent fluids and gas escaping upward

6. Reservoir rock – a porous permeable rock where petroleum and natural gas are found - has to move upwards as it forms and needs rock porous to hold oil and fluids need to be able to move from one rock to another - so important where capping layer occurs

7. Movement easiness from the source rock to the reservoir rock

· How are components of petroleum separated and what property allows this separation to occur? Components of petroleum are separated through fractional distillation and it is the boiling point of each fraction that allows this separation to occur

· If there is an oil spill at sea what will happen to the different fractions? Light fractions will evaporate and heavy fractions will float/sit on top of the water

· Discuss what a biomarker is. Your answer should include how they are formed, important features and what they are used for. Biomarkers are organic molecules that are derived from living matter but are resistant to degradation. Biomarkers are formed by organic material that dies and undergoes anaerobic diagenesis, which turns organic matter into kerogen (we do this by losing oxygen, nitrogen, and sulphur ). With increasing temp and pressure we push kerogen into oil (biomarker) through catagenesis. Important features of biomarkers include that they need to be stable over time so that they do not break down, they need to have an identifiable structure so that they can be easily analysed in small quantities, and need to have various concentrations in different oils so we can relate them to whatever oil it is being linked to. Biomarkers are used for characterising oil by looking at the molecules present. This allows for differentiation and correlation of oils to oil spills, allowing for identification of contamination (e.g if there was an oil spill) and allows for the monitoring of its breakdown for its relation to the environment and environmental effects.

· Discuss the different compounds that are biomarkers, and what compounds they originate from Three classes of biomarkers in petroleum are: Cyclic structures -> Hopanes – from bacteria -> Steranes – sterols present in plants and animals. These are single bonded ring structures Polyaromatic hydrocarbons (PAHs) also ring structures but has alternating single and double bonds Terpanes – open chain alkane with branches derived from terpenes. They are fully saturated (carbons bonded to 4 other things and all bonds are taken) (terpenes contain double bonds, terpanes contain single bonds) Sterane is a terpane that is derived from steroids or sterols via diagenesis and catagenesis breakdown Hopane (C30H48) is a triterpene that originates from bacteria There are over 150 naturally occurring hopanoids. These have been identified in soils, sediments and other organic matter

· What technique is used to analyse biomarkers? Give a brief overview of how this instrument separates compounds? How is the data interpreted to identify compounds? How are samples compared? In order to analyse biomarkers, Gas Chromatography Mass Spectrometry is used to separate compounds through two phases: Stationary phase (column) a stationary phase which is coated with material that interacts whatever compound we are looking for and it slows it down, giving a chance to separate out into fractions Mobile gas phase (He gas – inert and does not react with the compounds) and that carries that through the system and is heated. Over the course of analysis, the oven temperature is increased and compounds elute (come off) the column in order of their boiling point Different compounds interact differently with the column and this causes some compounds to flow through the column slower than others. As the temperature increases compounds begin to move with the helium through the column instead of sticking to the column. Substances with a greater affinity (attraction) for the mobile phase reach the detector at the end of the column more quickly. Substances with a greater affinity for the stationary phase move more slowly through the column. The more volatile that a compound is, the faster it will move through the column. Therefore separation is based on molecular weight. Once the compounds exit the column, they are ionised (i.e. the compound becomes charged). They are separated by mass (occurs in a quadrupole) and then detected to produce abundance vs. time plots. The compounds can be identified based on their retention time.