People require lots of resources. Population momentum (population growth at the national level that would occur even if levels of child bearing immediately declined to replacement level). Rare earth metals (set of 17 chemical elements in the periodic table, specically the 15 lanthanides plus scandium and yttrium). Carrying capacity is an ecological term that refers to the population that an area (in this case, the entire planet) can support without environmental deterioration. Water + sustainability. The hydrologic or water cycle describes the movement and storage of water between different spheres on the planet. Water is constantly mov ing between these spheres through the processes of evaporation, precipitation, inltration, melting, and groundwater ow. Only 3 percent of the Earths water is freshwater (not salty), and close to 70 percent of that freshwater is frozen in ice caps at the poles and in glaciers. Beyond our obvious uses of freshwater for drinking, bathing, and washing, our society makes use of water for many other purposes. Scientists break these uses down into categories known as consumptive and instream. Consumptive (or extractive) uses involve removing water from its source for drinking or other residential purposes as well as for industrial use and for irrigation of crops. Instream (or nonextractive) uses involve deriving benets from water without removing it from where it is located. Examples of instream uses include transportationnavigation, recreation, habitat for sh and other aquatic life, hydroelectric power generation, and waste processing. The sustainable management of water supplies frequently involves tradeoffs andor conicts between consumptive and instream uses. This was dramatically illustrated in recent years in the Pacic Northwest when irrigation water from rivers was denied to farmers in order to maintain water levels needed for salmon populations. Over three fourths of all underground water is considered nonrenewable since it is found in aquifers that formed tens of thousands of years ago that are not replenished. (ex. Ogallala Aquifer. In contrast, renewable groundwater refers to aquifers that are regularly replenished by rainfall or snowmelt. Even though groundwater resources are renewable, they can be seriously mismanaged. Examples include when water is removed faster than it is replenished and when pollutants or waste products from the surface are allowed to seep into them. The movement of water through the hydrological cycle comprises the largest of the three cycles (airwatersoilfood) ows, delivering an estimated 110,000 cubic kilometers (km) of water to the land each year as snow and rainfall. Driven by solar energy. Renewable fresh water provides many services essential to human health and well being, including water for drinking, industrial production, and irrigation, and the production of sh, waterfowl, and shellsh. Fresh water also provides many benets while it remains in its channels (nonextractive or instream benets), including ood control, transportation, recreation, waste processing, hydroelectric power, and habitat for aquatic plants and animals. Some benets, such as irrigation and hydroelectric power, can be achieved only by dam ming, diverting, or creating other major changes to natural water ows. Such changes often diminish or preclude other instream benets of fresh water, such as providing habitat for aquatic life or maintaining suitable water quality for human use. People have been demanding exponentially more water. Despite this greatly increased consumption, the basic water needs of many people in the world are not being met. Currently, 1.1 billion people lack access to safe drinking water, and 2.8 billion lack basic sanitation services. These deprivations cause approximately 250 million cases of waterrelated diseases and ve to ten million deaths each year. How fresh water is managed in particular basins and in individual watersheds is the key to sustainable water management. Most of the earth is covered by water, more than one billion km3 of it. The vast majority of that water, however, is in forms unavailable to landbased or freshwater ecosystems. Less than 3 percent is fresh enough to drink or to irrigate crops, and of that total, more than twothirds is locked in glaciers and ice caps. Freshwater lakes and rivers hold 100,000 km3 globally, less than one tenthousandth of all water on earth. Water vapor in the atmosphere exerts an important inuence on climate and on the water cycle, even though only 15,000 km3 of water is typically held in the atmosphere at any time. This tiny fraction, however, is vital for the biosphere. Water vapor is the most important of the socalled greenhouse gases (others include carbon dioxide, nitrous oxide, and methane) that warm the earth by trapping heat in the atmosphere. Water vapor contributes approximately twothirds of the total warming that greenhouse gases supply. 10 of the 425k km^3 of ocean water evaporated by solar energy falls on land. If this were the only source of rainfall, the earth would be a semiarid region (desert). Evapotranspiration is the second source of water recycled from plants and soil. Also helps with the cycling of materials such as carbon and nitrogen. This second source of recycled water con tributes twothirds of the 70 cm of precipitation that falls over land each year. Taken together, these two sources account for the 110,000 km3 of renewable freshwater available each year for terrestrial, freshwater, and estuarine ecosystems. The extra water returns to the oceans. A number of factors affect how much of this water is available for human use on its journey to the oceans. These factors include whether the precipitation falls as rain or snow, the timing of precipitation relative to patterns of seasonal temperature and sunlight, and the regional topography. Approximately 99 percent of all liquid fresh water is in underground aquifers, and at least a quarter of the worlds population draws its water from these groundwater supplies. Renewable aquifers depend on current rainfall for relling and so are vulnerable to changes in the quantity and quality of recharge water. Where extraction of ground water exceeds recharge rates, the result is lower water tables. Water tables: the uppermost level of an aquifer, below which the ground is saturated with water. When a waterbearing rock readily transmits water to wells and springs, it is called an aquifer. Wells can be drilled into the aquifers and water can be pumped out. Precipitation eventually adds water (recharge) into the porous rock of the aquifer. The rate of recharge is not the same for all aquifers, though, and that must be considered when pumping water from a well. Pumping too much water too fast draws down the water in the aquifer and eventually causes a well to yield less and less water and even run dry. The majority of water used for self supplied domestic and livestock purposes came from groundwater sources. Currently, humans expropriate 54 percent of all available fresh water from rivers, lakes, streams, and shallow aquifers. As a global average, most freshwater withdrawals69 percent are used for agriculture, while industry accounts for 23 percent and municipal use (drinking water, bathing and cleaning, and watering plants and grass) just 8 percent. Humans have basically destroyed everything. Examples: China, the Aral Sea, Lake Chad. Solutions: In places lacerated by poverty, the problem is often a lack of infrastructure wells, pipes, pollution controls, and systems for disinfecting water. Though politically challenging to execute, the solutions are fairly straightforward: investment in appropriately scaled technology, better governance, community involvement, proper water pricing, and training water users to maintain their systems. Lithosphere. Soil functions: sponges, faucets, supermarkets, strainers, detoxify. Not soil: Geologic materials = Sediments (pieces of broken and weathered rock that have been carried by water, wind, or ice and then deposited [left behind]) or regolith (a layer of loose or broken up rock above solid bedrock). Soils have horizons, or layers, in them that form roughly parallel to the earths surface (Table 3.1). These layers are created by the physical and biogeochemical weathering processes that formed the soil from parent materials. Geologic sediments may have layers in them, but these layers are created by processes such as moving water, wind, or ice that left the sediments behind. The properties of soils are very different than the properties of sediments and regolith, and these differences are important in some environmental health applications, such as the placement of septic system. Urban soils differ from natural soils because they have been altered to some degree. They have been excavated, compacted, disturbed, and mixed and may no longer possess their natural soil properties and features. Soil texture affects water and air movement through the soil as particles of different sizes pack together and thus determine the size and spacing of pores and channels. Water movement in urban soils is described in three ways: 1) inltration into the soil surface, especially from rainfall 2) Percolation within the soil drain lines from septic systems, which is especially important in the soil below the drain line and above a restrictive layer 3) Permeability within the soil from the surface to a restrictive layer. (Restrictive layers have high density (high weight in a given volume of soil) and low porosity (limited space between particles), so that water cannot ow into or through them.) Cation exchange capacity (the degree to which a soil can adsorb and exchange cations; cations are positively charged ions). The surfaces of most clays and organic matter have a net negative charge, giving them the ability to attract, hold, and exchange positively charged ions, or cations. Another important soil property: Aggregates are masses of sand, silt, clay, and organic matter all stuck together into clumps in the soil. Soil is an important part of the hydrologic cycle (the natural sequence through which water passes into the atmosphere as water vapor, precipitates to the earth in liquid or solid form, and ultimately returns to the oceans). Exposure to heavy metals (metal elements that have densities greater than 4500kgm3) through soil contact is a major human health concern. Arsenic is actually a metalloid (a chemical element with properties that are inbetween or a mixture of those of metals and nonmetals), but is commonly grouped with the heavy metals for the purpose of human health discussions. Ewastes, or wastes associated with electronic appliances such as computers and mobile phones, are also becoming an increasing source of heavy metals such as lead, antimony, mercury, cadmium, and nickel in the soil. Organic chemicals (molecules that possess carbonbased atoms) that end up in soil are also a major health concern. The main concern with organic chemicals comes from materials known as persistent organic pol lutants (POPs). These are organic chemicals that resist decomposition in the environment or that bioaccumulate through the food chain (a process producing an increase in the concentration of chemicals [usually toxicants] in the tissues of organisms with each increase in the trophic level in the food chain), and therefore pose a risk of causing adverse effects to human health and the environment. Soil Health Management: Manage more by disturbing less Diversify soil biota with plant diversity Keep a living root growing throughout the year Keep the soil covered as much as possible Reduce wind erosion. Atmosphere. The air that surrounds us is a complex mixture of gases. It is active and changes dramatically as you go higher up away from the surface of the earth. This air is called the atmosphere, and it is composed of 78.09 nitrogen (N2) and 20.95 oxygen (O2). The remaining 1 is composed mostly of argon (Ar) at 0.93, and carbon dioxide (CO2) at 0.039, with lower concentrations of methane and other minor gases. Carbon dioxide and methane concentrations are increasing due to the actions of humans. The concentration of water vapor varies widely between locations and time of day, and is, on average, about 1. Four layers (from closest to ground to space): 1) Troposphere (the atmospheric layer closest to the surface and extends up to about 10 km (32,000 ft), but this can vary from 8 to 18 km (26,00059,000 ft) depending on the position of the earth and the season of the year. This is the region of the atmosphere that is heated by the surface of the earth and can harbor life. It con tains most of the water vapor in the atmosphere and is where weather occurs.) 2) Stratosphere (top is called the stratopause) 3) Mesosphere (frozen water vapor due to low temperatures called noctilucent clouds). 4) Thermosphere (The air in this area is so raried that a molecule may have to travel a kilometer before hitting another molecule. Aurora can be seen in this area). The heat source for our planet is the sun. Energy from the sun is transferred through space and through the earths atmosphere to the earths surface. Since this energy warms the earths surface and atmosphere, some of it is or becomes heat energy. There are three ways heat is transferred into and through the atmosphere: radiation (the transfer of heat energy through space by electromagnetic radiation) conduction (the transfer of heat energy from one substance to another or within a substance) convection (the transfer of heat energy in a uid. Air in the atmosphere acts as a uid. The suns radiation strikes the ground, thus warming the rocks. As the rocks temperature rises due to conduction, heat energy is released into the atmo sphere, forming a bubble of air which is warmer than the surrounding air. This bubble of air rises into the atmosphere. As it rises, the bubble cools with the heat contained in the bubble moving into the atmosphere.) The earthatmosphere energy balance is the balance between incoming energy from the Sun and outgoing energy from the Earth. Energy released from the Sun is emitted as shortwave light and ultraviolet energy. When it reaches the Earth, some is reected back to space by clouds, some is absorbed by the atmosphere, and some is absorbed at the Earths surface. However, since the Earth is much cooler than the Sun, its radiating energy is much weaker (long wavelength) infrared energy. Anaerobic: not using oxygen. Weather Climate. Global Circulations explain how air and storm systems travel over the Earths sur face. The global circulation would be simple (and the weather boring) if the Earth did not rotate, the rotation was not tilted relative to the sun, and had no water.