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Ecohydrology is a new interdisciplinary area linking hydrology with ecological processes involved in the water cycle hydrological cycle. Hydrology (from Greek Yδωρ hudōr, "water" and λόγος logos, "study" is the study of the movement distribution and quality of Ecology (from Greek grc οἶκος oikos, "house(hold" and grc -λογία -logia) is the scientific study of The Earth 's Water is always in movement and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on above These processes generally occur within the water (rivers, lakes, groundwaters) or on land soil and plant foliage. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis. In water, Ecohydrology seeks to understand the dual regulation - how hydrological processes regulate ecological ones (e. g. the discharge regime of rivers regulates the species and their populations that live in it) and conversely, how ecological ones may subsequently regulate hydrological ones (e. g. debris dams in headwaters and wetlands in lower reaches, regulate discharge timing) - on the scale of a river basin. It then integrates the knowledge of those two processes and uses it to find innovative solutions to the problems of river basin degradation. On land, emphasis is put on transpiration and thermodynamic energy balance at the land surface. Transpiration is the Evaporation of water from the aerial parts of Plants especially leaves but also stems Flowers and Roots


Contents

Key Concepts

The hydrologic cycle describes the flow and movement of water through the landscape; the soil plant atmosphere continuum, then the flowing (lotic) and standing (lentic) ecosystems, and ultimately estuarine and coastal marine ecosytems. The Earth 's Water is always in movement and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on above The Soil-Plant-Atmosphere Continuum (SPAC is the pathway for water moving from Soil through the Plant - Animals to the Atmosphere. At all stages water returns to the atmosphere through evaporation and transpiration. One major area of ecohydrological study is the structure and processes of the aquatic ecosystems as they are affected by and affect the hydrology, geomorphology and chemistry of the water. The interactions among vegetation, the land surface, and the vadose zone are the other area major study of ecohydrology. The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic zone or zone of saturation ("vadose"

Principles

The principles of Ecohydrology are expressed in three sequential components:- HYDROLOGICAL: The quantification of the hydrological cycle of a basin, should be a template for functional integration of hydrological and biological processes. ECOLOGICAL: The integrated processes at river basin scale can be steered in such a way as to enhance the basin’s carrying capacity and its ecosystem services. ECOLOGICAL ENGINEERING: The regulation of hydrological and ecological processes, based on an integrative system approach, is thus a new tool for Integrated Water Basin Management.

Their expression as testable hypotheses (Zalewski et al, 1997) may be seen as:- H1: Hydrological processes generally regulate biota H2: Biota can be shaped as a tool to regulate hydrological processes H3: These two types of regulations (H1&H2) can be integrated with hydro-technical infrastructure to achieve sustainable water and ecosystem services

Vegetation and Water Stress

A fundamental concept in ecohydrology is that plant physiology is directly linked to water availability. Where there is ample water, as in rainforests, plant growth is more dependent on nutrient availability. Rainforests are Forests characterized by high Rainfall with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches However, in semi-arid areas, like African savannas, vegetation type and distribution relate directly to the amount of water that plants can extract from the soil. A Semi-arid climate or steppe climate generally describes climatic regions that receive low annual Rainfall (250-500 mm or 10-20 in A savanna or savannah is a Tropical or Subtropical Grassland or Woodland Ecosystem. When insufficient soil water is available, a water-stressed condition occurs. Plants under water stress decrease both their transpiration and photosynthesis through a number of responses, including closing their stomata. Transpiration is the Evaporation of water from the aerial parts of Plants especially leaves but also stems Flowers and Roots Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. In Botany, a stoma (also stomate; plural stomata) is a tiny opening or pore found mostly on the underside of a Plant Leaf This decrease in the canopy water flux and carbon dioxide flux can have an impact on surrounding climate and weather. The canopy is one of the uppermost levels of a Forest, below the emergent layer, formed by the Tree crowns Canopy trees refers to the trees In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time.

Soil Moisture Dynamics

Soil moisture is a general term describing the amount of water present in the vadose zone, or unsaturated portion of soil below ground. Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic zone or zone of saturation ("vadose" Since plants depend on this water to carry out critical biological processes, soil moisture is integral to the study of ecohydrology. Soil moisture is generally described as water content, θ, or saturation, S. Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, In Chemistry, saturation has five different meanings In Physical chemistry, saturation is the point at which a Solution of a substance These terms are related by porosity, n, through the equation θ = nS. Porosity is a measure of the void spaces in a material and is measured as a fraction between 0–1 or as a Percentage between 0–100% The changes in soil moisture over time are known as soil moisture dynamics.

Temporal and Spatial Considerations

Ecohydrological theory also places importance on considerations of temporal (time) and spatial (space) relationships. Hydrology, in particular the timing of precipitation events, can be a critical factor in the way an ecosystem evolves over time. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric For instance, Mediterranean landscapes experience dry summers and wet winters. A Mediterranean climate is one that resembles the Climate of the lands in the Mediterranean Basin, which includes over half of the area with this climate type world-wide If the vegetation has a summer growing season, it often experiences water stress, even though the total precipitation throughout the year may be moderate. Ecosystems in these regions have typically evolved to support high water demand grasses in the winter, when water availability is high, and drought-adapted trees in the summer, when it is low. A drought is an extended period of months or years when a region notes a deficiency in its water supply

Ecohydrology also concerns itself with the hydrological factors behind the spatial distribution of plants. The optimal spacing and spatial organization of plants is at least partially determined by water availability. In ecosystems with low soil moisture, trees are typically located further apart than they would be in well-watered areas.

Basic Equations and Models

Water Balance at a Point

A fundamental equation in ecohydrology is the water balance at a point in the landscape. A water balance states that the amount water entering the soil must be equal to the amount of water leaving the soil plus the change in the amount of water stored in the soil. The water balance has four main components: infiltration of precipitation into the soil, evapotranspiration, leakage of water into deeper portions of the soil not accessible to the plant, and runoff from the ground surface. Evapotranspiration (ET is a term used to describe the sum of Evaporation and Plant Transpiration from the earth's land surface to Atmosphere RUNOFF was the first Computer Text formatting program to see significant use It is described by the following equation:

           nZ_{r} \frac{ds(t)}{dt}=R(t) - I(t) - Q[s(t),t]- E[s(t)] - L[s(t)]

The terms on the left hand side of the equation describe the total amount of water contained in the rooting zone. This water, accessible to vegetation, has a volume equal to the porosity of the soil (n) multiplied by its saturation (s) and the depth of the plant's roots (Zr). Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, The differential equation ds(t) / dt describes how the soil saturation changes over time. A differential equation is a mathematical Equation for an unknown function of one or several variables that relates the values of the The terms on the right hand side describe the rates of rainfall (R), interception (I), runoff (Q), evapotranspiration (E), and leakage (L). These are typically given in millimeters per day (mm/d). Runoff, evaporation, and leakage are all highly dependent on the soil saturation at a given time.

In order to solve the equation, the rate of evapotranspiration as a function of soil moisture must be known. The model generally used to describe it states that above a certain saturation, evaporation will only be dependent on climate factors such as available sunlight. Once below this point, soil moisture imposes controls on evapotranspiration, and it decreases linearly until the soil reaches the point where the vegetation can no longer extract any more water. Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, This soil saturation level is generally referred to as the "permanent wilting point". Permanent wilting point ( PWP) or wilting point ( WP) is defined as the minimal point of Soil moisture the plant requires not to wilt This term is confusing because many plant species do not actually "wilt". WILT (1045 FM) is a Radio station broadcasting a Adult Hits format

References

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