Hydrogeology and Bugs

An actual issue of the “Hydrogeology Journal” is dedicated to an interesting approach for hydrogeological research and exploration – the possibility and the use of animal and plants for evaluating and prospecting springs and aquifers. Here I present a summary of this interdisciplinary research, with some personal experiences and considerations.

Maybe one simple definition of a spring is that it is a point(s) in which the groundwater table intersects with the Earth’s surface, so that the water spills over and become an open water body. Groundwater represents an important source of potable water – and so to understand the hydrogeology of springs is an important challenge for geologist.
Research on and the classification of spring in hydrogeology is traditionally done by physical parameters, like temperature, electric conductivity and discharge. These are important parameters that can provide clues of the catchment’s area, conductivity of the underground and connections to the surface, and capacity of the aquifer. But geologist are still searching for even more clues to understand the hidden paths of water in the underground, and use geophysical methods, geochemistry, prospecting by drilling, prospecting by satellites and maybe in future bugs…

A droplet of drinkwater from London (UK) as habitat, in a satirical caricature of the journal “Punch” from 1850. London got his first canalisation system in the first half of the 19th century – consisting simple of a collecting system discharging in the rivers of the city, where then again the drinkwater was won. The hygienic conditions were disastrous, causing epidemics spread trough the consumption of infected water, like typhus and cholera.

Springs are not only source for drink water for our daily use – but in first place they are places that can provide sustain and microhabitats for a large array of aquatic, wetland and terrestrials plant and animal species. This can be common species, not strictly bound to a spring habitat, but also species, bound strictly to the ecological conditions that provide springs – but because the habitat “spring” is often changed by human activity, in form of depleting the aquifer that feeds the spring, or using the spring itself for his uses, most of this life forms are seriously endangered.

Springs as habitats are still underevaluated and poorly understand – they represent ecotones – a connecting habitat between two different ecosystems, the groundwater and the surface(-water). Hydrogeologists have traditionally dealt with the point of emergence, paying little attention to springs after the point of discharge, where they are more interesting to biologists. Classification systems of surface waters or groundwater ecosystems have more incidentally included springs – in fact, there exist a lots of classifications systems, but no integrated system considering the mayor physical, biological and socio-cultural variables of springs.
The consideration of these variables can help to understand the hydrology of an aquifer, and unify the language between hydrogeologist and biologists, so that they can exchange information’s and ideas.

Step 1. – Unifying theory

The presence of a spring is constricted by some parameters. The proposed classification of SPRINGER 2008 include 12 spheres of discharge, controlled by geomorphic considerations (hydrostratigraphic units, emergence environment, orifice geomorphology, sphere of discharge, channel dynamics), forces bringing water to the surface (confined aquifer and artesian springs), flow properties (persistence, consistency, rate, variability), water quality (temperature and geochemistry), habitats (climate, surrounding ecosystems, habitat size and microhabitat variability), springs biota (species composition and diversity, vegetation) and spring management and use.

- Cave: Emergence in a cave (for example carst)
- Exposure springs: Cave, rock shelter fractures or sinkholes where uncounfined aquifer is exposed near the land surface
- Fountain: Artesian fountain or gas propelling the water column
- Geyser: Explosive flow of hot water from confined aquifer
- Gushet: Discrete source flow gushes from a cliff wall of a perched, unconfined aquifer
- Hanging garden: dripping flow emerges usually horizontally along a geologic contact along a cliff wall
- Helocrene: Emerges from low gradient wetlands; often indistinct or multiple sources seeping from shallow, unconfined aquifers
- Hillslope: Emerging of a un-/confined aquifers by indistinct or multiple sources seeping out on a hillslope
- Hypocrene: A buried spring where flow does not reach the surface, typically due the very low discharge and high evaporation or transpiration (“wetland”)
- Limnocrene: Emergence of un-/confined aquifers in pool(s)
- (Carbonate) mound-form Rheocrene: Flowing spring, emerges into one or more stream channels

REFERENCES:

SPRINGER, A.E. & STEVENS, L.E. (2009): Spheres of discharge of springs. Hydrogeology Journal 17: 83-93