Test 2 Review Flashcards
What are the types of rocks, and how can the distribution of these rocks influence the landscape?
The three types of rock are igneous, sedimentary, and metamorphic. The distribution of these rocks can have drastic effects on the landscape because they weather at different rates. For example, an intrusive deposit of igneous rock into sedimentary rock can create a landform over a long period of time, because the sedimentary rock around the deposit will weather faster than the igneous rock. This is what formed Mont Royal and Mt-Saint-Hilaire. The distribution of rocks is also important because they have unique mineralogical features. For example, sedimentary rock often contains many nutrients and organic material, while igneous rock can be susceptible to chemical alteration that releases certain elements into the environment.
What are the major patterns of minerology in igneous rock? Give some examples of igneous rocks.
The simplest form of igneous rock is made of silicates in different proportions and structures, giving different types of rock that have different levels of resistance. In these structures, oxygen is shared with silicon atoms. Sometimes, these silicon ions are replaced by other ions in a process called isomorphous substitution. Aluminium, for example, can often substitute for silicon, creating aluminosilicate minerals. There is no change in structure, but other ions often have to be incorporated to balance the charges (Si is 4+, while Al is only 3+.) Quartz, mica, pyroxene, and feldspar are examples of igneous minerals.
What are the major patterns of minerology in sedimentary rock? Give some examples.
There are two varieties of sedimentary rock. The clastic variety does not exhibit the same type of regimented structure, because it is formed by compressing together many different mineral particles. The chemical variety are new minerals formed in the sedimentary environment, like limestone, which has a precise chemical formula.
Give a brief overview of physical weathering processes.
The types of physical weathering we covered are freeze-thaw weathering, thermal changes, wetting/drying, biological, salt weathering, and pressure release. (You should be able to explain each of these thanks to GEOG272 so I won’t repeat what these are here.)
Give a brief overview of chemical weathering processes.
The types of chemical weathering we covered are solution, hydration, redox, chelation, carbonation, and hydrolysis. (Here, chelation was defined as the reaction of normally insoluble minerals with products of biological decomposition. Carbonation is the reaction of carbonic acid with carbonates. Hydrolysis was defined as the reaction of H+ ion with a cation in the mineral.)
Explain the relationship between minerology and ease of weathering. (Think of oxygen.)
As more and more substitution occurs, removing silicon from the minerals and replacing it with aluminium, iron and magnesium, and sodium/potassium/calcium, the strength of the bonding to the oxygen decreases and the rock is therefore more easily weathered.
What is the role of soils in mediating environmental processes?
Soils are incredibly important to the environment because they regulate four key areas in environmental processes. They are related to the (1) radiation budget because their moisture and thermal conductivity interact with heat transfer. They are also related to (2) the environment’s hydrological budget, because the soil texture and properties affect levels of moisture, support plant growth, and thus influence evapotranspiration rates. Thirdly, they influence (3) nutrient cycling, as organic matter collects and decays within them, and their microbiomes enable processing and decomposition of certain compounds so they are biologically available for new plant growth or for export. Finally, soils have a role to play in (4) gas exchange due to their complex microbiomes, which take in a variety of gases (notably oxygen) while exporting others (like carbon dioxide and N2O).
Define biogeochemical cycling.
Biogeochemical cycling is the movement of chemicals within an environmental system. Important aspects to consider involve the inputs and outputs of the chemicals, as well as how long they remain in the system, both of which can differ between chemicals.
Give a brief overview of soil textures, particle sizes, and what this effects in the environment.
Soil texture and particle size play a crucial role in determining the moisture content and water storage of a soil. The clast properties of the individual soil particles is important here – soils with large particles, like a coarse sand, will store more water than a dense and fine clay. These properties influence infiltration capacity and rates (and thus propensity for overland flow), the ease of plant roots and life to take root in the soil, as well as available moisture and water storage for plant growth. Most importantly, it determines the cation exchange capacity for retention of important minerals (mainly alkali metals) that are needed by plants and can buffer against the effects of acid rain.
What is cation exchange capacity?
Cation exchange capacity is a property of the soil that is determined by its clast properties, mineral structures, and organic matter present in a soil. It describes the total capacity of the soil to hold cations that are important as essential nutrients and buffers against acification. It is also important when considering the presence and formation of clay minerals.
What are clay minerals? Give some examples.
Clay minerals are intricately and regularly structured chemical formations, often consisting of sheets of ions bound to one another (oxygen and silicon or aluminium). The metal ions in clay minerals are often substituted for one another, causing changes in availability of certain beneficial (e.g. calcium) or harmful (e.g. aluminium) metal ions. Some examples are kaolinite, which has a 1:1 structure of aluminium to silicon, and which is formed of alternating layers of octahedra and tetrahedra, with oxygen sandwiched between to be shared. This structure is relatively stable because the layers share the same oxygen atoms. Another example is Montmorillonite, a 2:1 silicon to aluminium mineral that has a high cation exchange capacity.
What is the importance of organic matter in soils? What are potential inputs and outputs of organic matter to the soil system?
Organic matter is important for several reasons. Firstly, it improves the soil’s structure and porosity, increases the infiltration rate, and increases the water capacity. It also supplies essential nutrients to plants (e.g. calcium, magnesium, potassium, nitrogen, phosphorous) by slowly decomposing and releasing them over time. Humus, a complex chemical structure made of decayed organic matter, has a good cation exchange capacity for buffering against acid rain, because it tends to retain cations like Ca, Mg and K which help to this end.
What are the factors that control soil formation and determine what the character of local soil is?
Five factors influence soil formation. (1) The climate, including temperature and precipitation. (2) The parent material being weathered, which influences minerology, sediment type, and ease of weathering. (3) Local vegetation, since the forest type may result in very different patterns of organic matter input, e.g. coniferous trees do not lose their leaves. Also important is the environment itself – is it even a forest? Are we talking about a grassland, or an agricultural environment? (4) Topography of the landscape, which controls the water regime and rates of erosion. Finally, (5) is time – older soils will be more developed than young soils.
Explain systems of cycling of calcium, nitrogen, and phosphorous. Order them in terms of ease of loss.
Calcium is mainly stored in the soil, in clay minerals. It can be introduced to the environment through precipitation. Plants absorb calcium from the soil to use, and calcium is returned to the soil when these plants lose their leaves or other matter. The main output of calcium is dissolved calcium leaving the soil by percolating into the groundwater system. Magnesium and potassium have similar cycling.
Nitrogen can be input to a system through precipitation (acid rain). It can also be added through fertilizer to promote plant growth. It can be lost to groundwater (“leaching”). Nitrogen mainly stored in the atmosphere as gaseous nitrogen. This nitrogen is pulled into the soil by bacteria (“fixation”), who process it in several steps, including “nitrification”, which takes the ammonium ions stored on the cation exchange complex and turns them into easily soluble nitrate, which is suitable for plant use. Decaying plants and animals can release nitrogen back into soil (“mineralization”). Finally, after being used by plants and reduced to nitrite, it can be released by bacteria back into the atmosphere (“denitrification”).
Ease of loss is generally N > K > Ca > P.
How does nutrient cycling differ between disturbed and undisturbed systems?
In undisturbed systems, the storage of these minerals is relatively stable, as inputs are about equal to outputs. In disturbed systems, cycling can be “loose” meaning that outputs are greater than inputs, leading to a net loss of the nutrient from the soil.
