Introduction:
Soil hydrophobicity is the inability of a soil to readily wet or allow water to infiltrate a dry soil (Figure 1, Doerr et al., 2010). Understanding soil hydrophobicity is important to soil scientists and land managers because it directly affects runoff and erosion. The primary cause of hydrophobicity in soils is burning. Post-fire soil hydrophobicity causes decreased infiltration rates which lead to observed increases in post-fire runoff and erosion (Doerr et al., 2010). This study will focus on the effects that fire-induced hydrophobicity has on infiltration and runoff.
Figure 1: Water droplets that are resisting infiltration into a highly porous hydrophobic soil (Doerr, 2007).
A better understanding of the causes of soil hydrophobicity is warranted to understand its effects on infiltration and runoff. Fire isn’t the only factor that can induce water repellency in soil. Soils can be slightly hydrophobic at low or moderate moisture contents in burned or unburned conditions (Doerr et al., 2010). Different combinations of vegetation and soil type can develop strong soil water repellency. Soils under certain types of vegetation with oil or wax rich leaves (i.e. shrubs, conifers, and eucalyptus) are more susceptible to becoming hydrophobic than soils under broad-leaved vegetation (Doerr et al., 2010). Soil particle size also plays a role in the susceptibility of developing water repellency. Coarser soils are more prone to becoming water repellent than finer soils because of smaller surface area and number of potential adsorption sites for organic molecules (DeBano, 1981).
How does fire cause soil hydrophobicity? Burning induces soil water repellency by volatilizing the hydrophobic organic compounds in the litter and topsoil (Doerr et al., 2010). This results in the development of a pressure gradient within the leaf litter or topsoil that causes some compounds to be driven into the atmosphere while others are forced into the soil (Doerr et al., 2010). As the gas infiltrates the soil it cools with depth causing it to condense onto soil particles at or below the soil surface. This phenomenon creates a waxy coating around the soil grain which causes it to repel water. Laboratory studies show that soil water repellency is intensified at soil temperatures of 175-270°C, but is destroyed at temperatures above 270-400°C (Doerr et al., 2010).
Once a soil becomes hydrophobic it doesn’t always remain that way; in fact, most soils become less hydrophobic or lose their hydrophobicity with time. Both burned and unburned soils become less hydrophobic or completely lose their hydrophobicity as soil moisture increases.
Plants that grow in the vast arid and semi-arid regions of Australia are prone to fires simply because of the desert climate they grow in. High temperatures, low fuel moisture contents, little humidity and drying winds that sweep across the landscape encourage small patches of plants to burst into flames.
Sill P - Planning Prediction I predict that as the concentration of salt solution (molar dm-3) is increased, meaning that the water potential outside the carrot decreases, the water potential inside the carrot will decrease. As the water potential outside of the carrot cell is decreased, the water potential inside the carrot will increase, when the salt solution is more dilute. This change in water potential will occur because of a net movement of water molecules called osmosis. Osmosis is; The movement of water molecules from an area of high water potential to an area of low water potential, down the concentration gradient, across a partially permeable membrane. A partially permeable membrane, which is found in plant cells, such as the ones in a carrot, is a membrane that only allows certain molecules to pass through it, in this case, the membrane will allow water molecules to pass through it, but will not let the salt molecules pass through.
Another interesting characteristic of chaparral plants is their ability to respond to fire and other natural disasters. Due to the dry and arid nature of the area, the sage and grasslands can easily cause brush fires. When the area is burned, the shrubs and plant life d...
Water that has changed throughout the hydrologic process travels from the irrigation treatment and enters into the aquifers. First...
If a plant cell is places in a hypotonic solution the cell has a lower water concentration to that of the solution. Water will move into the cell by osmosis from a high water concentration outside the cell to a lower water concentration inside the cell through a selectively permeable membrane. The cell becomes turbid
Biological Impact: What is the impact? Water's cohesive properties are especially crucial to the survival of plants. Cohesion due to hydrogen bonding contributes to the transport of water against gravity in plant xylem. As transpiration, water evaporation, in leaves occurs, water in the plant xylem is "tugged" into the leaves to replace evaporated water. This upward pull is transmitted along the vessel all the way to the roots.
Sandberg, D.V., R.D. Ottmar, J.L. Peterson, and J. Core. 2002. Wildland Fire on Ecosystems: Effects of Fire on Soil and Water. Published by The United States Department of Agriculture, Forest Service. Retreived on line July 7, 2005
Most of the fires have some effect on inland waters. Inland waters are described as “permanent water bodies inland from the coastal zone and areas whose properties and use are dominated by the permanent, seasonal, or intermittent occurrence of flooded conditions” (GreenFacts Scientific Board, 2017). This includes any body of water that we may encounter except the ocean. This is the same water from which we treat for use in our homes for drinking, cooking, bathing and even cleaning. A wildfire burning next to a stream of which we collect water from couldn’t be expected not to have some type of effect from this
Osmosis is the passage of water molecules from a weaker solution to a stronger solution through a partially permeable membrane. A partially permeable membrane only allows small molecules to pass through, so the larger molecules remain in the solution they originated in. Solute molecule [IMAGE] [IMAGE] Water molecule [IMAGE] The water molecules move into the more concentrated solution. When water enters a plant cell it swells up. The water pushes against the cell wall and the cell eventually contains all that it can hold.
S Soil saturation - this may cause a river to flood as the water would
Fire at any level can be devastating, yet the effects that wildfires have on every worldwide country really has left its mark on the land. As written by world renowned wild fire spokesperson Smokey the Bear, “Every year, wildfires sweeps through parts of the United States setting wilderness and homes ablaze. On average these raging infernos destroy about four to five million acres of land a year. But in 2012, wildfire burned more than 9.3 million acres, an area about the size of Massachusetts and Connecticut combined” (U.S. Wildfires). Destroying homes, crops, towns and of course forests. Yet the effects of these fires can be seen from a negative perspective as well as some positive. Plus there are natural causes as well as manmade that makes these destructive fires erupt and become almost unstoppable in seconds.
Cook, R.J. “Influence of Water Potential of Soils and Plants on Root Disease”. Annual Reviews: A
Saline soil is also vulnerable to erosion due to the death of vegetation that held the soil together. Soil that is eroded can ‘pollute’ water too.
Agriculture also leads to soil erosion, both through rainfall and wind. This soil can damage the aquatic ecosystems it ends up in, an...
Other factors that contribute to natural bushfires are dry, hot climates with minimal rainfall, the availability of fuel and the presence of oxygen. Disposal of excess fuels in the forms of dried and or dead leaves or vegetation must be encouraged to reduce the chances of ignition by diminishing the medium for fires.