AP Environmental Science Unit 5 Review (Everything you Need to Know!)

This section introduces Unit 5, focusing on land use and its environmental consequences. It explains the 'Tragedy of the Commons' as the overuse of shared resources due to individual monetary benefits, assuming others will also overuse them, or a lack of immediate consequences. Examples of common resources (oceans, groundwater, public rangelands) and non-common resources (private lakes, mining sites) are provided. Solutions include imposing regulations, quotas, fees, or fines to manage resource consumption and fund restoration efforts.

Clear-cutting, the practice of cutting down all trees in an area for lumber, agriculture, or development, offers short-term economic benefits. However, it leads to long-term environmental degradation: soil erosion, warmer and drier soil, increased runoff, flash floods, and landslides. It also warms and turbids nearby streams and rivers, decreasing dissolved oxygen and harming aquatic life. Furthermore, clear-cutting reduces air quality and accelerates climate change by removing trees that absorb air pollutants and sequester carbon dioxide.

The Green Revolution introduced technological advancements in agriculture, increasing food production by focusing on higher yields per acre. Key practices include mechanization (tractors, combines) which increases efficiency but releases CO2 and causes soil compaction. GMOs enhance pest or drought resistance and growth, but reduce genetic diversity and can deplete soil nutrients. Synthetic nitrate-based fertilizers dramatically increase yields but require fossil fuels for production, releasing greenhouse gases, and contribute to eutrophication from agricultural runoff. Synthetic pesticides kill pests, increasing yields, but can harm non-target species and lead to pesticide resistance. Advanced irrigation methods prevent crop loss but deplete groundwater and surface water sources.

Monocropping, the practice of growing a single crop type, increases efficiency and lowers costs but decreases biodiversity, making crops vulnerable to disease and pests. It also leaves soil bare, increasing erosion. Tilling loosens soil for planting but breaks root structures, leading to erosion and releasing CO2 from decomposing organic matter. Slash-and-burn agriculture clears land and returns nutrients but releases greenhouse gases and reduces carbon sequestration, especially in biodiverse tropical regions. The section differentiates synthetic fertilizers (concentrated chemicals for plant growth, highly soluble, no organic matter) from organic fertilizers (natural, return organic matter, retain moisture, wider range of nutrients, slower release, nourish soil microbes).

Irrigation prevents crop loss and supports agriculture in dry regions, but accounts for 70% of global freshwater use, leading to groundwater and surface water depletion. The Ogalala aquifer serves as a prime example of an essential groundwater source undergoing rapid depletion due to irrigation. The efficiency of different irrigation methods is discussed: furrow irrigation (low cost, 33% water loss), flood irrigation (simple, cheap, 20% water loss, causes water logging), spray irrigation (more efficient, less water loss, higher cost), and drip irrigation (95% efficient, conserves water in dry climates, high cost). Soil salinization, caused by salts in groundwater accumulating after irrigation water evaporates, can become toxic to plants. Solutions include flushing fields, using drip irrigation, or switching to freshwater sources like rivers or lakes.

Pesticides (rodenticides, insecticides, herbicides, fungicides) are chemicals designed to kill pests, increasing crop yields and farmer profits. However, they can kill non-target species and lead to pest resistance as organisms with genetic mutations survive and pass on resistance. GMO crops, such as Bt crops, are engineered with pest resistance genes, which can reduce pesticide use but also decrease genetic diversity, making crops vulnerable to catastrophic loss from disease or environmental changes if the entire crop is genetically identical.

Meat production involves methods like Concentrated Animal Feeding Operations (CAFOs) and free-range grazing. CAFOs raise large numbers of animals in small, indoor spaces on grain-based diets, offering economic efficiency (maximum meat per acre/time, low cost) but have significant environmental drawbacks. Meat production is inefficient compared to plant protein (20 times less land), leading to increased topsoil erosion and nutrient depletion from corn monocropping. CAFOs also create manure lagoons, which can leak and pollute water with E.coli, antibiotics, hormones, and excessive nutrients, causing eutrophication. Free-range grazing, in contrast, reduces disease, spreads waste as natural fertilizer, and produces higher-quality meat. However, it requires more land, resulting in higher consumer costs, and risks overgrazing, which can lead to desertification, soil compaction, and permanent damage to ecosystems.

Meat production, whether CAFO or free-range, significantly contributes to greenhouse gas emissions (CO2, methane, nitrous oxide) and requires large amounts of water for animals and feed crops. Reducing meat consumption is a crucial sustainability step to lessen emissions, habitat loss, and topsoil erosion. Overfishing occurs when fish are harvested faster than they reproduce, leading to fishery collapse (90% population decline), reduced genetic diversity, and potential inability to recover. It can destabilize food webs, and bycatch (unintended species) further reduces biodiversity. Destructive fishing methods like bottom trawling damage coral reefs and increase water turbidity, affecting marine ecosystems.

Mining extracts valuable ore by removing overburden (soil, rock, vegetation). Surface mining, including mountaintop removal, destroys habitats, increases soil erosion, and adds particulate matter to the atmosphere. Mine tailings (non-valuable rock) can contaminate soil and water with toxic metals (selenium, arsenic, mercury) due to runoff. Acid mine drainage, highly acidic rainwater from abandoned mines, further mobilizes toxic metals and harms plant and animal growth. Coal mining releases methane, a potent greenhouse gas. These valuable resources are finite and as shallow deposits are exhausted, deeper, more costly, and hazardous subsurface mining becomes necessary, leading to health risks for workers and increased resource prices. The video concludes by emphasizing the importance of reviewing these concepts for the AP Environmental Science exam.