surface runoff

Examples of surface runoff in the following topics:

• The Phosphorus Cycle

  • In addition to phosphate runoff as a result of human activity, natural surface runoff occurs when it is leached from phosphate-containing rock by weathering, thus sending phosphates into rivers, lakes, and the ocean.
  • This sediment then is moved to land over geologic time by the uplifting of areas of the earth's surface .
  • One of the worst dead zones is off the coast of the United States in the Gulf of Mexico, where fertilizer runoff from the Mississippi River basin has created a dead zone of over 8,463 square miles.
  • Phosphate and nitrate runoff from fertilizers also negatively affect several lake and bay ecosystems, including the Chesapeake Bay in the eastern United States, which was one of the first ecosystems to have identified dead zones.
  • Phosphate enters the oceans via surface runoff, groundwater flow, and river flow.

• The Water (Hydrologic) Cycle

  • Rain eventually percolates into the ground, where it may evaporate again (if it is near the surface), flow beneath the surface, or be stored for long periods.
  • More easily observed is surface runoff: the flow of fresh water either from rain or melting ice.
  • Runoff can then make its way through streams and lakes to the oceans or flow directly to the oceans themselves.
  • Rain and surface runoff are major ways in which minerals, including carbon, nitrogen, phosphorus, and sulfur, are cycled from land to water.
  • The cycle is complete when surface or groundwater reenters the ocean.

• The Nitrogen Cycle

  • Human activity can release nitrogen into the environment by two primary means: the combustion of fossil fuels, which releases different nitrogen oxides, and the use of artificial fertilizers in agriculture, which are then washed into lakes, streams, and rivers by surface runoff.
  • A major effect from fertilizer runoff is saltwater and freshwater eutrophication: a process whereby nutrient runoff causes the excess growth of microorganisms, depleting dissolved oxygen levels and killing ecosystem fauna.
  • Some of this nitrogen falls to the ocean floor as sediment, which can then be moved to land in geologic time by uplift of the earth's surface, becoming incorporated into terrestrial rock.

• The Carbon Cycle

  • This carbon can be leached into the water reservoirs by surface runoff.

• Soil Formation

  • Regional surface features (familiarly called "the lay of the land") can have a major influence on the characteristics and fertility of a soil.
  • Topography affects water runoff, which strips away parent material and affects plant growth.
  • Materials are deposited over time, decompose, and transform into other materials that can be used by living organisms or deposited onto the surface of the soil.

• The Sulfur Cycle

  • Sulfur enters the ocean via runoff from land, fallout, and underwater geothermal vents.

• Cell Size

  • Cell size is limited in accordance with the ratio of cell surface area to volume.
  • Therefore, as a cell increases in size, its surface area-to-volume ratio decreases.
  • However, increased surface area can cause problems as well.
  • Notice that as a cell increases in size, its surface area-to-volume ratio decreases.
  • The cell on the left has a volume of 1 mm3 and a surface area of 6 mm2, with a surface area-to-volume ratio of 6 to 1, whereas the cell on the right has a volume of 8 mm3 and a surface area of 24 mm2, with a surface area-to-volume ratio of 3 to 1.

• Limiting Effects of Diffusion on Size and Development

  • Recall that any three-dimensional object has a surface area and volume; the ratio of these two quantities is the surface-to-volume ratio.
  • The surface-to-volume ratio of a sphere is 3/r; as the cell gets bigger, its surface-to-volume ratio decreases, making diffusion less efficient .
  • The larger the size of the sphere, or animal, the less surface area for diffusion it possesses.
  • The surface-to-volume ratio of a sphere decreases as the sphere gets bigger.
  • The surface area of a sphere is 4πr2 and it has a volume of (4/3)πr3 which makes the surface-to-volume ratio 3/r.

• Water’s Cohesive and Adhesive Properties

  • This is also why water forms droplets when placed on a dry surface rather than being flattened out by gravity.
  • Cohesion and surface tension keep the hydrogen bonds of water molecules intact and support the item floating on the top.
  • It's even possible to "float" a needle on top of a glass of water if it is placed gently without breaking the surface tension .
  • In another example, insects such as the water strider use the surface tension of water to stay afloat on the surface layer of water and even mate there.
  • The weight of the needle is pulling the surface downward; at the same time, the surface tension is pulling it up, suspending it on the surface of the water and keeping it from sinking.

• Energy Sources

  • For instance, aquatic plants have photosynthetic tissue near the surface of the water.
  • In wintertime, the surface of lakes found in many northern regions is frozen.
  • In springtime, air temperatures increase and surface ice melts.
  • The oxygen-rich water at the surface of the lake then moves to the bottom of the lake, while the nutrients at the bottom of the lake rise to the surface ().
  • Surface water temperature changes as the seasons progress, causing denser water to sink.