The hydro-ecosphere provides a more favorable environment for microorganisms compared to the atmosphere and lithosphere due to the presence of water. Water plays a crucial role in microbial metabolism (Atlas and Bartha, 1993). The unique properties of water also make it suitable as a habitat within the hydrosphere. Water’s polarity, with its slight negative and positive charges, allows it to act as an effective solvent and form hydrogen bonds. Additionally, water has a high specific heat capacity, meaning it takes a substantial amount of energy to increase its temperature by 1oC (1 calorie/gram).
Water possesses a high heat of fusion, measuring 80 cal/g, which grants it resistance to freezing. Additionally, its molecules have a tendency to adhere together and attract molecules from the surfaces they encounter, leading to a notable surface tension. This attribute is crucial as it enables the buildup of non-polar organic compounds on the uppermost layer, providing microorganisms with nourishment. These exceptional characteristics of water play a role in bolstering aquatic systems against drastic shifts in their surroundings. However, the existence of dissolved substances may modify these qualities.
Aquatic environments can be categorized as ocean waters and inland waters, including groundwater and surface water. Ocean waters have a salinity level of approximately 35 ppt, while freshwaters such as lakes, ponds, groundwater, rivers, and springs have a salinity level of 0.05 ppt. The hydrosphere encompasses distinct habitats like bottom sediments, biological surfaces, non-biological surfaces, and interfaces between the atmosphere and hydrosphere or lithosphere and hydrosphere. Several factors impact the hydro-ecosphere including light intensity, temperature, pressure, dissolved gases, and dissolved solids.
The presence of autochthonous microbiota gives certain limited general characteristics to the environment.
Physico-chemical Factors Light. The light from the sun provides energy for primary producers.
During daytime, water absorbs more light because of the directness of the light; at sunset, less light is absorbed because light strikes water more acutely.
Dissolved substances can cause turbidity and contribute to light extinction by absorbing and/or reflecting light.
Different depths have varying levels of light penetration, leading to vertical zonation in marine and lake habitats.
In a lake environment, different zones exist to indicate varying levels of depth and light penetration. The littoral zone is the part where light reaches the lake’s bottom. On the other hand, the limnetic zone is located further away from shore and descends to a point where light becomes ineffective. In even deeper areas known as the profundal zone, photosynthesis cannot occur due to insufficient light. The benthos, which connects the water with the ground beneath it, represents the lake’s bottom. It is important to note that only deeper waters contain a profundal zone; shallow areas lack this feature. Similarly, in marine habitats, there exists an analogous concept called the euphotic zone. This term refers to an area where light effectively penetrates up to about 0-200 meters below sea level.
The light compensation level is the point where photosynthesis and respiration are balanced. This level exists in the aphotic (or disphotic) zone, which extends from 200-6000 m below the euphotic zone. Aquatic environment temperatures are influenced by solar energy, geographical latitude and altitude, and weather conditions. Polar regions typically have temperatures ranging from -1 to 7oC, while tropical and subtropical waters range from 25 to 30oC. Temperature fluctuations are significant in streams and ponds, but large bodies of water have more stable temperatures.
The distribution of heat in aquatic systems is affected by factors such as depth, the quantity of water, and differential heating based on whether a specific part is exposed to light or not. In the summer, temperature variations occur in certain areas of lakes, leading to the formation of different layers: the epilimnion (the uppermost layer that is both warmer and aerobic, with water mixing), the thermocline (the transitional region between mixed water and the bottom layer), and the hypolimnion (the colder and anaerobic bottom layer). The thermocline is characterized by a rapid temperature decrease, which restricts water mixing across this region.
The pelagic zone in marine habitats consists of two zones: the epipelagic, which is mixed water, and the hypopelagic, which is bottom water. Pressure plays a significant role at great depths in these marine waters, with an increase of 1 atm for every 10 m depth. This pressure variation affects both the pH of the water and the solubility of nutrients.
Surface waters in marine habitats are always saturated or even supersaturated with oxygen due to wind action and wave stirring. Aquatic systems can dissolve all atmospheric gases, but carbon dioxide and oxygen are particularly important. Photosynthetic organisms need carbon dioxide from sources like decaying organisms, dissolved carbonates, or the atmosphere. Oxygen is essential for heterotrophic organisms and comes from both the atmosphere and photosynthetic organisms.
Several factors affect the amount of dissolved oxygen in water, including atmospheric gas partial pressure, water temperature, gas pressure, biological activity, and salinity. Lower temperatures and higher pressures generally increase oxygen solubility. This applies to all gases because colder water and higher pressure lead to greater saturation levels. Water movement introduces oxygen into the water and helps distribute nutrients. Additionally, it has a crucial role in reducing vertical stratification in rivers and influencing the distribution of planktonic organisms.
Several factors influence the velocity of water movement, such as channel shape and roughness, size or width, depth, wind direction, intensity of rainfall, and human intervention. When the velocity is high and the temperature is low, there is a significant amount of dissolved oxygen in the water. Additionally, the water contains dissolved solids which can be either inorganic or organic matter. The distinction between marine water and freshwater depends on the level of inorganic matter present. Marine water consists primarily of Na and Cl elements, resulting in high salinity. In contrast, freshwater (or inland water) is mainly composed of Ca, Mg, Na, and K.
Freshwater has a higher amount of organic matter compared to marine water. In freshwater, concentrations range from 1-2mg/L to 26 mg/L, while in marine water it ranges from 0.4-2mg/L. The nutrient concentration determines how water is classified: oligotrophic (low nutrients but high oxygen), eutrophic (nutrient-rich but anaerobic bottom layers), and mesotrophic (in between).
Marine habitats, which include oceans covering 71% of the earth’s surface, have a total volume of about 1.46×109 km3 with an average depth of 4000 m. Some areas can reach depths up to 11,000 m. It is worth noting that for every increase of 10 m in depth, there is a corresponding increase in pressure by 1 atm.
The ocean has a salinity of approximately 33-37 ppt (parts per thousand) and a pH range of 8.3 to 8.5. Below a depth of 100 m, the temperature typically ranges from below 0°C to 5°C. Tidal movement, ocean currents, and thermohaline circulation help maintain the stability of the marine environment. Tides occur as the gravitational forces of the Moon and Sun, along with the Earth’s rotation, cause periodic changes in ocean water levels. Ocean currents are formed by wind blowing across the water surface and creating frictional drag.
The Coriolis effect impacts ocean currents when they come into contact with land masses. In the northern hemisphere, air that moves from areas of high pressure to low pressure is redirected to the right as a result of this force. Conversely, in the southern hemisphere, it is deflected to the left. The vertical mixing of water masses caused by variations in temperature and salinity, known as thermohaline circulation, results in differing water densities. Within the marine environment, almost all naturally occurring elements are present but at very low levels.
Seawater consists of hydrogen (H), oxygen (O), sodium, magnesium, sulfate, calcium, potassium, carbon, boron, strontium, bromine, silica, and fluorine. Nitrogen, phosphorus, and iron are essential for microorganism growth but exist in seawater as trace elements. Nevertheless, these elements frequently restrict the growth of phytoplankton. In marine environments lacking higher plants, primary producers encompass microscopic algae and photosynthetic bacteria. Shorelines,
upwellings,
and estuarine waters generally exhibit a higher microbial growth concentration.
Marine microorganisms are well-adapted to survive in the salinity range of marine waters, typically between 20-40 ppt. To be considered truly marine, these microorganisms thrive best when the salinity is around 33-35 ppt. Their crucial role within their marine environment involves decomposing both organic and inorganic matter. By consuming these materials, they introduce nutrients into the food web and aid in mineral cycling. Furthermore, certain marine microorganisms serve as a source of sustenance. In contrast, freshwater ecosystems account for merely 3% of Earth’s total water supply.
Only 1% of the total freshwater available is usable, with the remaining 2% trapped as ice. This environment contains both stagnant and moving bodies of water, which can be found on the surface or underground. Surface waters can be categorized as flowing (lotic) or standing (lentic). Lotic habitats consist of springs, streams, and rivers, while lentic habitats encompass ponds, lakes, and wetlands. Springs act as natural outlets where water emerges from the ground due to gravity or hydrostatic pressure. The microbial population in this habitat tends to be relatively low.
The main types of microorganisms found are mainly gram-negative rods and stalked bacteria. Some of the common bacterial genera include Hyphomicrobium, Caulobacter, Gallionela, and Pseudomonas. Streams and rivers can be divided into three categories based on how the water moves. The riffle section has shallower water and more turbulence. It has high oxygen levels and a relatively low temperature because of the shade provided by the surrounding forest. As a result, primary productivity is also low in this area. In the middle section, known as the run, the water flows smoothly and the temperature is higher compared to the riffle section due to less forest shade.
Primary productivity is higher in the first location due to deeper water and slow water movement, resulting in excessive silt deposition at the end of the pool. The specific conditions vary locally, leading to different dominant microorganisms in each area. In particular, bacterial species from the Family Bacillaceae, Pseudomonadaceae, and Enterobacteriaceae can be found. Observations have been made on genera like Azotobacter, Nocardia, Micrococcus, Vibrio, Streptomyces,Sarcina,Cytophaga,Spirillum,and Thiobacillus.
The presence of epilithic microalgae can also be observed. Lakes and ponds have a higher concentration of nutrients due to the accumulation of deposited materials and nutrients. Lakes are divided into three layers based on temperature. The epilimnion is the upper layer of warm water that circulates and is usually no more than 6 m (20 ft) deep. In this layer, the concentration of dissolved oxygen is moderate to high. The thermocline is a thin layer where the temperature and oxygen levels decrease rapidly with depth, separating the upper and lower layers. The hypolimnion is characterized by a cold, deep-water layer that does not circulate and has low or no oxygen.
In both uncontaminated and polluted water, the presence of Achromobacter, Flavobacterium, Brevibacterium, Micrococcus, Sarcina, Bacillus, and Pseudomonas can be observed. Additionally, lake sediments and marine sediments have high bacterial counts. When conditions are calm in the hydrosphere and atmosphere, microorganisms form a surface microlayer called neuston. This uppermost layer is favorable for phototrophic mcgs because primary producers have easy access to CO2 from the atmosphere and light radiation.
The ocean has high surface tension, allowing nonpolar organic compounds to accumulate. This accumulation, along with the oxygen from the atmosphere, can be used by secondary producers. There are two main categories of aquatic sampling devices for marine habitats: qualitative and quantitative. Qualitative devices collect individuals of various species to provide basic information on the fauna and flora.
These devices include plankton nets and traps, as well as quantitative devices that estimate the total abundance or biomass of the area. The quantitative devices collect samples of a defined volume from the water column or area from the sediment. Examples of these devices are grabs, corers, and water bottles such as the Niskin bottle. The study of microorganisms in the sea can be conducted through electron microscopy and Automated Ribosomal Intergenic Spacer Analysis (ARISA), which provides estimates of microbial diversity and community composition.
DNA extraction and PCR amplification are part of the process. Mud in the sea can be sampled using various methods, including surface samplers like dredges and benthic grabs, as well as gravity corers and Winogradsky columns. Dredges are suitable for collecting samples from hard surfaces like rocky bottoms, while benthic grabs are ideal for soft, sandy sediments without rocks. Gravity corers can sample sediment layers up to 6 feet deep. These sampling tools offer advantages such as simplicity, durability, reliability, ease of use, and low maintenance requirements.
However, deploying and recovering heavy and awkward devices can be cumbersome. The Winogradsky column offers a solution by providing numerous gradients that support the growth of a large diversity of microorganisms. In freshwater habitats, the J-Z sampler is used for bacterial samples, while the Van Veen Grab Sampler is used for sediments. The Suspended Sediment Sampler utilizes a water-sediment mixture to determine 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.
