Karst Springs

Karst Spring: Bill Walker-Karst Conservancy.

Introduction

A Karst topography is formed when rock is dissolved, causing small fissures within the geologic structure. This soluble rock material is often limestone, dolomite, or gypsum. This caustic solution creates sinkholes in the soil surface and as it digs further into the rock, can create underground caverns and passageways. This allows precipitation and surface runoff to penetrate the soil horizons and fill subterranean caverns. This water can be held within the underground caverns, or exit though hydric tunnels. Karst springs are formed when water exits the subterranean matrix (though eroded tunnels) and forms surface pools.

Importance of Karst Systems

Karst systems host a wide variety of endemic species due to the unique nature of the habitat. With anthropogenic disturbance taking a heavy toll on the natural landscape, the potential for great harm to the karst topography exists. The microclimate of a karst means that any inputs to the system will remain isolated within that pocket and persists for a much greater time period. An introduction of toxic pollutants could potentially kill an entire species inhabiting this kind of system. Furthermore, with the expansion of the urban environment, the interaction between man and karst is increasing. Whether it be urban sprawl (depleting water levels and the species that reside with it) or ecotourism, humans are interaction more heavily with karst landscapes.

Physio-chemical Environment

Diagram of a Karst Formation.

Chemical

The formation of the karst topography begins with the "carbon dioxide cascade." Rainfall absorbs CO₂ from the atmosphere during droplet formation, while it falls as precipitation, or as it moves through the soil horizons. This forms carbonic acid (H₂CO₃).

H₂O + CO₂= H₂CO₃

As the acid comes in contact with the alkaline rock the two react, forming an aqueous solution that will further dissolve small channels within the soil. Slowly over decades channels will expand allowing larger volumes of water to pass through it. Due to the high solute concentrations within the water, karst systems are often found to be alkaline, having reacted with the calcareous environment and forming the karst.

Physical

The movement of water through any ecosystem effects the physical structure of that system. This is especially true for a karst. A karst is not only borne of the chemicals within water eroding away bedrock, but also the physical scrapping of rock due to water movement.

Flowing water within a karst can hold a significant load of microorganisms and nutrients. The transportation of which can yield changes in the biological and chemical environments both at the source and sink regions of the karst watershed.

Biological interactions

In addition to the abundance of microbial organisms found in a karst, there are a plethora of higher organisms as well. Bats, birds, reptiles; animals associated with cavernous habitats, reside in karst systems. Consequently, there exists an relationship between the higher order inhabitants of these subterranean landscapes and the microorganisms that rely on the biological activities of these organisms.

Pollution

Karst systems are one of the greatest suppliers of aquifers, with nearly 25% of the drinking water (in the United States) flowing through a karst. The rapid recharge of the subterranean aquifers does mean that little filtration may occur with certain water sources. This may lead to potential pollution and contamination hazards.

Are there important biological interactions that are important in this environment? Do these interactions influence microbial populations and their activities? How do these interactions influence other organisms? Describe biological interactions that might take place in this environment, using as many sections/subsections as you require. Look at other topics available in MicrobeWiki. Create links where relevant.

Microbial processes

The bacteria within the Karst landscape build and define the channels of the system. Through the cycling of carbon, carbon dioxide is utilized to build up, and break down calcium deposits. This action creates the sinkholes from which

What microbial processes define this environment? Describe microbial processes that are important in this habitat, adding sections/subsections as needed. Look at other topics in MicrobeWiki. Are some of these processes already described? Create links where relevant.

Key Microorganisms

Bacteria

Phylum/Class	Genus
α-proteobacteria	Rhizobium
	Bradyrhizobium
	Sphingomonas
β-proteobacteria	Acidovorax
	Deefgea
	Duganella
	Iodobacter
	Janthinobacterium
	Massilia
	Pigmentiphaga
	Polaromonas
	Rhodoferax
γ-proteobacteria	Acinetobacter
	Aeromonas
	Buttiauxella
	Erwinia
	Escherichia
	Pantoea
	Pectobacterium
	Pseudomonas
	Rahnella
	Rheinheimera
	Serratia
	Shewanella
	Stenotrophomonas
	Yersinia
Bacteroidetes	Chryseobacterium
	Flavobacterium
	Hymenobacter
	Pedobacter
	Sphingobacterium
Firmicutes	Bacillus
	Sporosarcina
Actinobacteria	Arthrobacter
	Leifsonia
	Nocardia
	Rhodococcus

Algae

As with any open air body of water, karst springs host a number of different algal species including cholorphyta and bacillariophyceae.

Fungi

Ascomycetes:

Histoplasma capsulatum is a fungus found in karst systems and is often associated with the presence of bats (Myotis spp.). This fungus grows on the guano of bats on the floor of caverns and Karst systems.

Also found in karsts are fungi of zygomycetes

Current Research

1)One study analyzed the bacterial diversity and community composition in three karst cave system with different hydrologic and chemical traits. Specifically, they looked at the assemblage of microbes by the use of the 16S rRNA genes for identification. Accroding to the study, "Unexpectedly high microbial phylotype richness was found even in the two pools without groundwater contact and with low concentrations of organic carbon and total cell numbers (< 104 ml-1)." The conclusion of the analysis was that karst water provides a means of bacteria from a terrestrial ecosystem to a freshwater habitat via subsurface flow.

2) The composition of 681 aerobic and heterotrophic strains that were isolated on two different media was assessed at four sampling points along a ~300 m stretch of a karst water rivulet.

Based on partial sequence analysis of 16S rRNA genes, members of 35 genera were identified; however, only a few species dominated as their representatives were repeatedly isolated at different sampling sites. Determination of the phylum affiliation showed that the isolates included members of Bacteriodetes (especially the genus Flavobacterium) and Proteobacteria (mainly Pseudomonas and Stenotrophomonas). MALDI-TOF analysis and/or similarities of partial sequences of flavobacterial strains resulted in the generation of almost complete 16S rRNA gene sequences for 100 isolates, about 60 of which may represent novel phylospecies. The number as well as the intra-phylum distribution of the isolates changed with distance from the discharge site. While phylogenetically restricted at the spring, diversity increased at downstream sampling sites.