HYDROLOGY Hydrology is the science that encompasses the occurrence, distribution, movement and properties of the waters of the earth and their relationship with the environment within each phase of the hydrologic cycle. The hydrologic cycle is a continuous process by which water is purified by evaporation and transported from the earth's surface (including the oceans) to the atmosphere and back to the land and oceans.

All of the physical, chemical and biological processes involving water as it travels its various paths in the atmosphere, over and beneath the earth's surface and through growing plants, are of interest to those who study the hydrologic cycle.

There are many pathways the water may take in its continuous cycle of falling as rainfall or snowfall and returning to the atmosphere. It may be captured for millions of years in polar ice caps. It may flow to rivers and finally to the sea. It may soak into the soil to be evaporated directly from the soil surface as it dries or be transpired by growing plants. It may percolate through the soil to groundwater reservoirs (aquifers) to be stored or it may flow to wells or springs or back to streams by seepage. They cycle for water may be short, or it may take millions of years.

HYROLOGIST The hydrologist studies the fundamental transport processes to be able to describe the quantity and quality of water as it moves through the cycle (evaporation, precipitation, streamflow, infiltration, groundwater flow, and other components).

SURFACE WATER Most cities meet their needs for water by withdrawing it from the nearest river, lake or reservoir. Hydrologists help cities by collecting and analyzing the data needed to predict how much water is available from local supplies and whether it will be sufficient to meet the city's projected future needs. To do this, hydrologists study records of rainfall, snowpack depths and river flows that are collected and compiled by hydrologists in various government, agencies. They inventory the extent river flow already is being used by others.

Groundwater Groundwater, pumped from beneath the earth's surface, is often cheaper, more convenient and less vulnerable to pollution than surface water. Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes, including the Great Lakes. In some areas, groundwater may be the only option. Some municipalities survive solely on groundwater. Hydrologists estimate the volume of water stored underground by measuring water levels in local wells and by examining geologic records from well-drilling to determine the extent, depth and thickness of water-bearing sediments and rocks.

Extreme Environments These can include temperature (high or low), pressure, acid or alkali and high salts.

DEEP SEA Open ocean the photic zone can extend to 300m, causing a good deal of biological growth down to 1,000m. Below this level (75% of ocean volume) the biological activity is less. 3 problems are faced Low temperature below 1,000m it is a constant C High pressure 1 atm/10m. eg at 1,000m it is? Low nutrient levels Phytoplankton falls to the sea bed as marine snow which is seasonal following growth. The journey down takes over 1 month and 99% is already decomposed. Below 100m the bacteria are psychrophilic. Some bacteria isolated are barotolerant (down to ~ 300m), grow at atmospheric pressure, will not grow above 500atm.

Temperature Classes Psychrophile – hyperthermophiles

Growth at cold temperatures. Psychrophile opt growth below 15 0 C and max below 20 0 C, grows at 0 0 C. Psychrotolerant grows at 0 0 C but opt C. Psychrophiles found in any permanently cold environment, can be rapidly killed by room temp. Best known are algae that grow in the bottom of sea ice in polar regions. Growing in summer months on the bottom of ice ~ 2m thick. In summer months also get alga growing under the surface of snowfields and glaciers giving it a red or green colour.

Hydrothermal Vents. Associated with moving tectonic plates on the ocean floor. Hot basalt and magma near the sea floor. Seawater seeping into it becomes superheated and rich in minerals. Two types of vents. Warm vents C and hot vents. Hot vents emit at C. The mineral rich liquid forms black smokers as the mineral rich liquid mixes with cold water.

pH

Organisms have optimum pH values for growth. Most microorganisms are neutrophiles pH opt Bacteria cannot survive if the internal pH drops below ~ 5.0. Acidophiles must maintain an internal pH above this or their proteins will denature. There membranes can be impermeable to protons. Thiobacillus are important acidophiles that oxidise sulphide minerals generating sulphuric acid, they are used to help leach Cu from low grade ore. They cause environmental problems of acid mine drainage from coal mining waste, acid and dissolved metals are toxic. They need air to oxidise the pyrite, so coal below the surface is OK. Cyanidium caldarum and Sulfolabus acidocaldarius live in acidic hot springs.

Acid mine Drainage From coal mine

Osmotic – Halophiles. The water availability (activity) is also dept. on the conc. of solutes. The cytoplasm of cells usually has a higher solute conc. than the surrounding media so water tends to move in, balanced by cell wall.. Seawater 3.5%, marine organisms have a requirement for Na+. At high solute conc. water will tend to move out Mild halophile 1-6% Moderate 6-15% Extreme halophile 15-30% Organisms cope by using internal solutes, often organic compounds like glycine betaine, proline or glycerol to balance the osmotic pressure without damaging proteins or K+ (Halobacterium).