Ecohydrology
These interactions may take place within water bodies, such as rivers and lakes, or on land, in forests, deserts, and other terrestrial ecosystems.
Areas of research in ecohydrology include transpiration and plant water use, adaption of organisms to their water environment, influence of vegetation and benthic plants on stream flow and function, and feedbacks between ecological processes, the soil carbon sponge and the hydrological cycle.
In terrestrial ecosystems (such as forests, deserts, and savannas), the interactions among vegetation, the land surface, the vadose zone, and the groundwater[1] are the main focus.
In aquatic ecosystems (such as rivers, streams, lakes, and wetlands), emphasis is placed on how water chemistry, geomorphology, and hydrology affect their structure and function.
The general assumptions of ecological hydrology is to decrease ecosystem degradation using concepts that integrate terrestrial and aquatic processes across scales.
As seasonal or event-scale flows occur, changes in connectivity of a watershed affect flowpath, residence time, and biogeochemical reactions.
A fundamental concept in ecohydrology is that the development of the soil carbon sponge and plant physiology is directly linked to water availability.
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.
Plants under water stress decrease both their transpiration and photosynthesis through a number of responses, including closing their stomata.
[5] Insufficient soil moisture produces stress in plants, and water availability is one of the two most important factors (temperature being the other) that determine species distribution.
One of the earliest responses to insufficient moisture supply is a reduction in turgor pressure; cell expansion and growth are immediately inhibited, and unsuberized shoots soon wilt.
An increase in moisture stress in the rooting medium (soil carbon sponge) as small as five atmospheres affects growth, transpiration, and internal water balance in seedlings.
The two conifers Norway spruce and Scots pine show larger differences in water potential between leaf and substrate than do the hardwoods.
[10] Transpiration rate decrease less in Norway spruce than in the other three species as soil water stress increases up to 5 atmospheres in controlled environments.
In field conditions, Norway spruce needles lose three times as much water from the fully turgid state as do birch and aspen leaves, and twice as much as Scots pine, before apparent closure of stomata (although there is some difficulty in determining the exact point of closure).
Since plants depend on this water to carry out critical biological processes, soil moisture is integral to the study of ecohydrology.
Recent global studies using water stable isotopes show that not all soil moisture is equally available for groundwater recharge or for plant transpiration.
[12][13] Plant available water in sandy soils can be increased by the presence of sepiolite clay.
([15] Watersheds can have increased and decreased ability to cycle nutrients within their overall system given their grade, discharge and velocity.
However, mankind has also had significant impact in this area, leading to the overall degradation of watershed system health in many cases.
"Agricultural, urbanization, and resource extraction have dramatically increased nutrient loading and altered dissolved organic matter (DOM) delivery and production....In the past 60 years, human activity has more than doubled global nitrogen fixation and quadrupled phosphorus loading.
At the same time, human land-use has directly disturbed half of global land surface, fundamentally altering the capacity of ecosystems to buffer or process [or cycle] these nutrient inputs.
"[16] Ecohydrological theory also places importance on considerations of temporal (time) and spatial (space) relationships.
If the vegetation has a summer growing season, it often experiences water stress, even though the total precipitation throughout the year may be moderate.
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.
The terms on the left hand side of the equation describe the total amount of water contained in the rooting zone - the soil carbon sponge.
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.
The law was formulated by Henry Darcy in the early 1800's when he was charged with the task to bring water through an aquifer to the town of Dijon, France.
Henry conducted various experiments on the flow of water through beds of sand to derive the equation.
