Cycles of Matter - Chapter 2 Notes

There is a finite amount of water, which is re-used through the hydrologic cycle.
Water is a universal solvent of polar molecules.
Water is essential to humans and ecosystems.
The hydrologic cycle plays a central role in nutrient cycles (biogeochemical cycles).

Carbon, oxygen, sulfur, and nitrogen are found in living organisms and in the land, atmosphere, and water. They are recycled through biotic and abiotic processes.
Phosphorus is found in living organisms and in the land and water. It is recycled through biotic and abiotic processes.
Disruptions in one biogeochemical cycle can affect another.

Biotic and abiotic processes maintain the balance of matter and energy exchange in the biosphere.
Natural processes and human activities can affect the transfer of energy and the cycling of matter through the biosphere.

Pacific Northwest coastal rainforest trees rely on the Pacific Ocean as their source of nitrogen, obtained from the urine and feces of bears and scavengers that consume Pacific salmon.
Around $60$ million kg of nitrogen-containing salmon tissue feeds the forest soil.
Salmon require healthy forests and streams to reproduce, while forests and bears need abundant salmon; streams need standing trees to retain soil and provide shade.

There is a need for integrated forest, wildlife, and fish management due to the close relationship between salmon and trees.

Some suggest extending human rights to all living things, while others propose giving natural entities like streams, oceans, and forests legal standing in courts.
Homes built in wild areas may impact other species' habitats; laws protecting organisms may affect loggers' livelihoods; tourist activities may harm delicate alpine terrain and sensitive wetlands.

As salmon decompose, nutrients like nitrogen are released to the soil.
Tree ring studies show trees grow up to three times faster when salmon are abundant.

Water is naturally recycled, making it available to living organisms.
The routes that water and other chemical nutrients take through the biotic and abiotic components of the biosphere are known as biogeochemical cycles.
The water cycle, or hydrologic cycle, connects ecosystems separated by great distances and involves all phases of water.
More than $97$ percent of the water in the biosphere exists in liquid form due to water’s relatively high boiling point.
About $86$ percent of the global evaporation of water is from the oceans.
Water vapor is a greenhouse gas that traps and transfers heat, distributing it from the tropics toward the Poles.
Ocean currents transfer warm water from hotter to cooler regions, moderating temperatures over nearby land.

Water carries substances as it moves, such as nutrients like nitrogen and phosphorus, and toxic compounds like methylmercury.
A water molecule consists of two hydrogen atoms covalently bonded to one oxygen atom, making it a polar molecule with a slightly positive hydrogen end and a slightly negative oxygen end.
Polarity allows water to form hydrogen bonds between molecules.

Hydrogen bonding allows water to remain liquid over a large temperature range and dissolve/transport substances.
Many hydrogen bonds together are quite strong, requiring a large amount of energy to break, resulting in a relatively high boiling point ( $100$ °C).
Frozen water (ice) has a relatively high melting point ( $0$ °C) due to hydrogen bonds.
Frozen water is less dense than liquid water because hydrogen bonds hold water molecules in an open crystal structure.
Water reaches its greatest density ( $1 \text{kg/L}$ ) at $4$ °C.
As water sinks and rises, nutrients and dissolved oxygen are cycled with it.
Water percolating into rocks expands when it freezes, weathering rocks and unlocking nutrients. Ice insulates deep water in lakes during winter, providing a refuge for aquatic life.

Cohesion is the attraction of water molecules to each other, responsible for surface tension.
Adhesion is the attraction of water molecules to molecules of other substances.
Cohesion and adhesion together explain how water travels from the roots of a tree up to its leaves against gravity during transpiration.

Water has a high heat capacity due to hydrogen bonding, requiring large amounts of energy to change temperature.
Water heats up more slowly and holds its temperature longer.
This property enables organisms to maintain constant internal temperatures and moderates air temperatures of nearby land.
Water’s heat capacity and ability to hold heat allows surface currents to distribute heat from warm equatorial regions to higher latitudes.

Water comprises more than $50$ percent of all plant and animal tissue by mass.
The adult human body is composed of about $70$ percent water, and a radish is composed of $95$ percent water.
Animals obtain water directly by eating, drinking, and absorbing water, as well as through cellular respiration.
They lose water through breathing, sweating, urine, and feces.
Plants obtain water through their roots but lose large amounts by transpiration.

Natural features providing for human needs are called ecosystem services; fresh water provides an essential ecosystem service.
Droughts are major natural disasters.
Increased global temperatures may increase evaporation, potentially making regions drier.
Population growth, along with agricultural and industrial use, has increased water demand.
Water quality affects the amount of water available for drinking and other uses; toxic chemicals and pathogens can harm ecosystems.
Water is a renewable resource if used wisely.

A $4000 \text{ m}^2$ cornfield can transpire $16000 \text{ L}$ of water daily.
When water is scarce, plants close their stomata, reducing transpiration and photosynthetic activity.
Simulated drought experiments show that trees grow deeper roots and slow trunk growth, with many of the largest trees dying.
Changes in the hydrologic cycle affect other cycles of matter and ecosystems.