HYDRO-ECOSPHERE Hydro-ecosphere is considered as a more suitable habitat for microorganisms than the atmosphere and lithosphere, mainly because hydrosphere contains water, which is important in microbial metabolism (Atlas and Bartha, 1993). The unique properties of water are also attributes of hydrosphere as a suitable habitat. Due to polarity of water (slightly negative and slightly positive), water is considered as a great solvent, capable of forming hydrogen bonding. Large heat capacity of water is due to its high specific heat (1 calorie/gram); hence a large amount of energy is needed before a 1oC-rise in temperature.
Water also has high heat of fusion (80 cal/g) so it does not freeze easily. Surface tension is high because water molecules stick together, and have ability to attract molecules of surface in contact. This is important in accumulation of non-polar organic compound on the surface layer, which could be used as source of nutrients for microorganisms. With these characteristics of water, aquatic systems are more resistant to extreme environmental fluctuations. However, such water properties can be modified by the presence of dissolved substances.
Aquatic environments are classified as ocean waters and inland waters (groundwater and surface water). Ocean waters contain approximately 35 ppt salt; freshwaters which include lakes, ponds, groundwater, river and spring, has 0. 05 ppt salinity. Special habitats in hydrosphere include bottom sediments, biological and non-biological surface, and interface (between atmosphere and hydrosphere or lithosphere and hydrosphere). There are at least five factors that affect the hydro-ecosphere: light intensity, temperature, pressure, dissolved gases and dissolved solids.
Due to presence of autochthonous microbiota, certain limited general characteristics can be ascribed. Physico-chemical Factors Light. The light from the sun provides energy for primary producers. During daytime, more light is absorbed in water due to the directness of the light; at sunset, lesser light is absorbed because light strikes water more acutely. Dissolved substances, which can confer turbidity, can cause light extinction (since some molecules could absorb and/or reflect light). At different depths, there is a difference in light penetration, which gives rise to zonation (specifically, vertical zonation) in marine and lake habitats.
In lake habitat, the littoral zone is the region where light penetrates the bottom, the limnetic zone is an area of open water away from the shore that descends to the light compensation level, the profundal zone is area of deeper water beyond the depth of effective light penetration, and the benthos (bottom of the lake) represents the interface between the hydrosphere and lithosphere. The profundal zone is not present in shallow waters. In marine habitat, the euphotic zone is the area of effective light penetration to the compensation level, about 0-200 m.
The light compensation level is the depth at which photosynthesis just balances respiration. The aphotic (or disphotic) zone, about 200-6000 m, lies below the euphotic zone. Temperature. Amount of solar energy received, geographical latitude and altitude, and weather conditions determine the temperature in an aquatic environment. Usually, temperature ranges from -1-7oC in the polar regions and 25-30oC in tropical and subtropical waters. In streams and ponds, there are large temperature fluctuations, but in large bodies of water, temperature is quite stable.
The heat distribution in aquatic systems is influenced by depth, amount of water, and differential heating (which part is lighted and not). During summer, differences in temperature in some regions of lake result to layer turnover: epilimnion (warmer, aerobic, uppermost layer with mixing of water), thermocline (the transition between mixed water and bottom) and hypolimnion (colder, anaerobic, bottom layer). The thermocline is characterized by rapid decrease in temperature, across which there is little mixing of water.
In marine waters, thermocline is also present, but the terms used for the mixed water and bottom water are epipelagic and hypopelagic, respectively. The epipelagic and hypopelagic comprise the pelagic zone in marine habitats. Pressure. An important factor in marine waters at great depth is pressure, but not in most inland waters. Generally, there is 1 atm increase for every 10 m depth. It affects water pH since pressure has a role in solubility of nutrients. Dissolved gases. Surface waters are always saturated (the concentration of xygen in water is equal to that in the atmosphere) or even supersaturated (more oxygen in water than in atmosphere) with oxygen. This is due to wind action and wave stirring. Generally, all gases present in the atmosphere can be dissolved in aquatic systems, but the most important dissolved gases are carbon dioxide and oxygen. Carbon dioxide is needed by photosynthetic organisms. It is provided by, decaying organisms, dissolved carbonates from minerals and the atmosphere. Oxygen is needed by heterotrophic organisms, and is supplied by the atmosphere and photosynthetic organisms.
Partial pressure of gas in the atmosphere, water temperature, gas pressure, biological activity and dissolved salts in water (salinity) determine the amount of dissolved oxygen. Generally, a decrease in temperature and increase in pressure bring about an increase in the solubility of oxygen. For all gases, the saturation level increases as water temperature decreases and as pressure increases. Water movement is for introduction of oxygen to water, and for nutrient mixing and distribution. It can minimize vertical stratification in rivers and affect the distribution of planktonic organisms.
The velocity of water movement is affected by channel shape and roughness, size or width, depth, wind direction, intensity of rainfall and human intervention. At high velocity with low temperature, there is high dissolved oxygen. Dissolved solids. The dissolved solids can be inorganic matter and organic matter. Amount of inorganic matter is the main distinction between marine and freshwaters. While the marine water is largely composed of Na and Cl which imparts high salinity, the freshwater (or inland water) is mainly composed of Ca, Mg, Na, and K.
In terms of organic matter, freshwater has a higher concentration (1-2mg/L to 26 mg/L) than marine water (0. 4-2mg/L). Due to this, water can be classified according to nutrient concentration: oligotrophic (nutrient-poor but O2 saturated), eutrophic (nutrient-rich, but has anaerobic bottom layer) and mesotrophic (middle of the two types). Marine Habitat Oceans occupy 71% of the earth’s surface. The volume is approximately 1. 46×109 km3, with an average depth of 4000 m. Some oceans have maximum depth of 11, 000 m. The pressure increases by 1 atm for every 10 m depth.
The oceanic salinity is approximately 33-37 ppt (parts per thousand) and pH is within the range 8. 3-8. 5. The temperature below 100 m of depth is usually below 0oC and 5oC. For most part environment conditions in the marine ecosphere are remarkably uniform due to tidal movement, current and thermohaline circulation. Tides are the periodic rise and fall of the ocean waters caused by the gravitational pulls of the Moon and (to a lesser extent) Sun, as well as the rotation of the Earth. Ocean currents are caused by the frictional drag of the wind blowing across the surface of the water.
The effect of land masses on the movements of the ocean currents is called the Coriolis effect. As air moves from high to low pressure in the northern hemisphere, it is deflected to the right by the Coriolis force. In the southern hemisphere, air moving from high to low pressure is deflected to the left by the Coriolis force. Thermohaline circulation is the mixing of water masses vertically due to differences in water densities brought by variations in temperature and salinities. Marine environment contains almost every naturally occurring element but most are in extremely low concentrations.
The major elements aside from H and O are sodium, magnesium, sulfate, calcium, and potassium. Minor elements include carbon, boron, strontium, bromine, silica, and fluorine. Nitrogen, phosphorus and iron are essential for microbial growth. These elements occur in sea water only as trace elements but can typically limit phytoplankton growth. Marine Organisms Since marine habitats lack higher plants for primary production, microscopic algae and photosynthetic bacteria take this role. There is a higher microbial growth in shore, upwelling and estuarine waters.
Marine microorganisms, in general, have been adapted to the salinity of marine waters, usually between 20 and 40 ppt. True marine microorganisms must be able to grow optimally between 33 and 35 ppt. Microorganisms in marine habitat participate in decomposition as they consume organic and inorganic matters. They can also assimilate, and consequently introduce nutrients to the over-all food web. They have a role in mineral cycling as a result of their metabolism and some of them serve as food. Freshwater Habitat Freshwater ecosystem composes about 3% of the Earth’s total water.
Of this 3%, only 1% is available for use and the other 2% is tied up in ice. This type of habitat includes both standing and flowing waters. Freshwater can be found as surface waters or below ground. Surface waters may be divided into two types- lotic (flowing) and lentic (standing). Springs, streams and rivers comprise the lotic habitat. Lentic habitat includes ponds, lakes and wetlands. Springs are places where water flows out of the ground either as a result of gravity or hydrostatic pressure. The characteristic microbial population is quite low in this habitat.
Microorganisms present are predominantly gram-negative rods and stalked bacteria. Among the common bacterial genera are Hyphomicrobium, Caulobacter, Gallionela and Pseudomonas. Streams and rivers are composed of three courses based on the movement of water. The water in the riffle is shallower and more turbulent. Oxygenation is high and temperature is relatively low due to forest shade and hence, primary productivity is also low. In the middle course, called the run, water flows smoothly and temperature is higher than the riffle due to less forest shade.
Primary productivity is higher than the first. The pool, last course, is characterized deeper water level and slow water movement resulting to excessive silt deposition. Rivers have variable conditions depending on the local conditions which makes the dominating microorganisms differ in different in different locality. In particular, bacterial species present found are of the Family Bacillaceae, Pseudomanadaceae and Enterobacteriaceae. Among the observed genera are Azotobacter, Nocardia, Micrococcus, Vibrio, Streptomyces, Sarcina, Cytophaga, Spirillum and Thiobacillus.
Epilithic microalgae can also be observed. Lakes and ponds have higher nutrient concentration because of build-up of deposits and nutrients. Lakes have three stratifications based on temperature. Epilimnion, an upper layer of circulating warm water, usually no more than 6 m (20 ft) deep, where dissolved oxygen concentrations are moderate to high. Thermocline, a layer of rapid temperature and oxygen decrease with depth, often quite thin, separates the upper and lower layers. Hypolimnion characterized by cold, deep-water, non-circulating layer in which oxygen is low or absent.
In clean waters, Achromobacter, Flavobacterium, Brevibacterium, Micrococcus, Sarcina, Bacillus, and Pseudomonas can be observed. However, on polluted waters, heterotrophic bacteria increase in counts. Like in marine sediments, lake sediments also have high bacterial counts. Under quiescent conditions, microorganisms form a surface microlayer between the hydrosphere and atmosphere. It is the uppermost layer of the hydrosphere and is called neuston. It is favorable for phototrophic mcgs, since primary producers have unrestricted access to CO2 from the atmosphere and to light radiation.
It also has high surface tension where nonpolar organic compounds can accumulate and it can be used by secondary producers (plus the oxygen available from the atmosphere). Sampling Methods Methods/Sampling Devices for Marine Habitat Aquatic sampling device can be classified into two main categories according to the quality of the results obtained from their use- qualitative and quantitative. Qualitative devices provide basic information on the fauna and flora by means of collection of individuals of various species.
These include plankton nets and traps. Quantitative devices, on the other hand, provide an estimate of the total abundance or biomass of the area in question. Devices of this type take samples of defined volume (from the water column) or area (from the sediment). These include grabs, corers and water bottles (e. g. Niskin bottle). Studying microorganisms in the sea can be done by electron microscopy and Automated Ribosomal Intergenic Spacer Analysis (ARISA). ARISA provides estimates of microbial diversity and community composition.
It involves DNA extraction and PCR amplification. Sampling of mud in the sea can be done by using surface samplers (dredges, benthic grabs), gravity corers and Winogradsky column. Dredges are used when collecting samples from hard surfaces such as rocky bottoms while benthic grabs good for collecting soft, sandy sediments that do not contain rock. Gravity corer samples sediment layer up to 6 feet. Advantages of these sampling materials are simple, robust, relatively reliable and also extremely easy to use and require little maintenance.
However, these are heavy and awkward to deploy and recover. The Winogradsky column can be used for culturing large diversity of microorganims provides numerous gradients from which microorganims can grow. Methods/Sampling Devices for Freshwater Habitat For bacterial samples, J-Z sampler can be used and on sediments, Van Veen Grab Sampler is used. Suspended Sediment Sampler uses water-sediment mixture to determine the mean suspended sediment concentration, particle size distribution and specific gravity. REFERENCES Atlas R. M. , and R. Bartha. 1993. Microbial Ecology. Fundamentals and Applications. 3rd ed. USA: Benjamin/Cummings Publishing Co. , Inc. • Prescott, L. M. , J. P. Harley and D. A. Klein. 2005. Microbiology. 6th ed. USA: McGraw Hill Co. , Inc. • Rodina, A. G. 1972. Methods of Aquatic Microbiology. Baltimore: Univ. Park Press • Wood, E. J. F. 1965. Marine Microbial Ecology. London: Chapman & Hall, Ltd. • Zobell, C. E. 1946. Marine Microbiology. USA: Chronica Botanica Co.