Water Quality Parameters Associated with Aquatic Animal ...€¦ · animal health and homeostasis. Water quality parameters also affect the aqueous environment, both physically and

Water Biology PHC 6937; Section 4858; G201 HPNP

Water Quality Parameters Associated with

Aquatic Animal Homeostasis

Andrew S. Kane University of Florida - Aquatic Pathobiology Laboratory

College of Health and Health Professions – Environmental Health Program Emerging Pathogens Institute - [email protected]

Water quality is a critical component of the aquatic environment in order to maintain aquatic animal health and homeostasis. Water quality parameters also affect the aqueous environment, both physically and chemically, since water serves as a medium for animal locomotion, production of food resources, reproduction, excretion, deriving oxygen, and maintaining ionic balance. Water quality varies in different aquatic habitats: • salinity (freshwater vs. brackish vs. saltwater)

salinity tolerance (stenohaline vs. euryhaline) • water flow (lotic vs. lentic) • substrate type/tanks (consideration for optimal surroundings and disinfection) • benthic vs. pelagic species • warm vs. cool vs. cold water species

temperature tolerance (stenothermic vs. homeothermic) • Other factors affecting water quality and habitat adequacy Factors which affect aquatic animal health:

Host Environmental stressors:

!!transport

!!handling

!!water quality

!!contamination/pollution

Pathogens/Parasites

Compromise/Infection

A.S. Kane, Water Quality & Life in Water, page 2

Temperature. Different aquatic organisms have different upper and lower thermal tolerances, and different optimal temperatures for growth, food conversion, egg incubation and larval growth, and resistance to specific diseases and parasites. The uptake/toxicity of organic and inorganic substances/contaminants may vary with temperature. • Specific-specific tolerances • Thermal shock • Effect on chemical reactions and solubility of gasses • Effect on respiration, uptake and metabolism.

Temperature affects density of water: • Thermal stratification • Inversion of water masses • Ice

Light. Visible radiation, or light, from the Sun is important to the world's ocean systems for several reasons. It provides the energy necessary for ocean currents and wind-driven waves. Conversion of some of that energy into heat helps form the thin layer of warm water near the ocean's surface that supports the majority of marine life. Most significantly, the transmission of light in sea water is essential to the productivity of the oceans. Visible wavelengths of light are captured by chlorophyll-bearing marine plants, which then make their own food through the process of photosynthesis. The organic molecules created by this process are an important energy source for many small organisms that are the base of the entire marine food chain. All life in the oceans is ultimately dependent upon the light and the process of photosynthesis that it initiates. Similarly, light transmission is a key factor in the ecology of lakes, streams and other freshwater environments.

• Reflection, Refraction, and Color.

The uppermost, sunlit layer of the ocean where 70 percent of the entire amount of photosynthesis in the world takes place is called the euphotic zone. It generally extends to a depth of 100 meters (330 feet). Below this is the disphotic zone, between 100 and 1,000 meters (330 and 3,300 feet) deep, which is dimly lit. Some animals are able to survive here, but no plants. Although the amount of light is measurable at this range of depths, there is not enough available for photosynthesis to take place. The layer of the ocean where no light at all penetrates—over 90 percent of the entire ocean area on Earth—is called the aphotic zone, where depths are more than 1,000 meters (3,300 feet).

• Light Penetration A certain amount of incoming light is reflected away when it reaches the ocean surface, depending upon the state of the water itself. If it is calm and smooth, less light will be reflected. If it is turbulent, with many waves, more light will be reflected. The light that penetrates the surface is refracted due to the fact that light travels faster in air than in water. Once it is within the water, light may be scattered or absorbed by solid particles. Most of the visible light spectrum is absorbed within 10 meters (33 feet) of the water's surface, and almost none penetrates below 150 meters (490 feet) of water depth, even when the water is very clear. Greater abundances of solid particles in the water will decrease the depth of light penetration.


Therefore, water near the seashore that is more turbid (cloudy) due to particles will show a decrease in light transmission, even in shallow water. This is due to large numbers of particles brought in by river systems, and biological production by microorganisms, as well as waves, tides, and other water movement picking up debris on the ocean floor.

• Light Spectrum Water selectively scatters and absorbs certain wavelengths of visible light. The long wavelengths of the light spectrum—red, yellow, and orange—can penetrate to approximately 15, 30, and 50 meters (49, 98, and 164 feet), respectively, while the short wavelengths of the light spectrum—violet, blue and green—can penetrate further, to the lower limits of the euphotic zone. Blue penetrates the deepest, which is why deep, clear ocean water and some tropical water appear to be blue most of the time. Moreover, clearer waters have fewer particles to affect the transmission of light, and scattering by the water itself controls color. Water in shallow coastal areas tends to contain a greater amount of particles that scatter or absorb light wavelengths differently, which is why seawater close to shore may appear more green or brown in color.

Cartoon illustrating penetration of visible light in seawater.

Dissolved oxygen (D.O.). For most aquatic poikilothermic vertebrates, oxygen is derived from the water via gill structures (amphibians and some fish have dermal respiration as well). • Species-specific optimal ranges • Solubility and supersaturation • Effect on respiration rate and uptake • Analytical techniques Gases dissolve in liquids to form solutions. This dissolution is an equilibrium process for which


an equilibrium constant can be written. For example, the equilibrium between oxygen gas and dissolved oxygen in water is O2(aq) <--> O2(g). The equilibrium constant for this equilibrium is K = p(O2)/c(O2). The form of the equilibrium constant shows that the concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution. This statement, known as Henry's law, was first proposed in 1800 by J.W. Henry as an empirical law well before the development of our modern ideas of chemical equilibrium. Values of the Henry's law constants for many gases in many different solvents have been measured. The table below gives a few selected values of Henry's law constants for gases dissolved in water. Table: Molar Henry's Law Constants for Aqueous Solutions at 25oC

Gas Constant (Pa) (Pa/(mol/litre))

Constant (atm) (atm/(mol/litre))

He 282.7 x 106 2865.0 O2 74.7 x 106 756.7 N2 155.0 x 106 1600.0 H2 121.2 x 106 1228.0

CO2 2.9 x 106 29.76 NH3 5.7 x 106 56.9

The value of the Henry's law constant is found to be temperature dependent. The value generally increases with increasing temperature. As a consequence, the solubility of gases generally decreases with increasing temperature. One example of this can be seen when water is heated on a stove. The gas bubbles that appear on the sides of the pan well below the boiling point of water are bubbles of air, which is evolved when water which was air-saturated at lower temperatures is heated and the amount of air which it can contain (the molar solubility of air) decreases. Addition of boiled or distilled water to a fish tank will cause the fish to die of suffocation unless the water has been allowed to reaerate before addition. The decrease in solubility of gases with increasing temperature is an example of the operation of Le Chatelier's principle. The heat or enthalpy change of the dissolution reaction of most gases is negative, which is to say the reaction is exothermic. As a consequence, increasing the temperature leads to gas evolution.


General effects of dissolved oxygen on fish (and other aquatic organisms). Note that various species have different requirements and tolerances to shifts in DO and other water quality parameters.

pH. By definition, pH is -log[H+], or the negative logarithm of the hydrogen ion concentration. The pH scale varies from 0 to 14, and is negatively logarithmic, i.e., for a decrease in 1 pH unit there is a 10-fold increase in hydrogen ion concentration. Values of pH less than 7.0 are considered acidic; values greater than 7.0 are alkaline; pH 7.0 is neutral (equal concentrations of hydrogen and hydroxyl ions). • optimal range for homeostasis • natural environmental fluctuation • diel fluctuations • pKa of xenobiotics/drugs


Effect of pH on relative proportions of H2CO3, HCO3

- and CO32-. The mole fraction of a

component is its decimal fraction of all the moles present.

Diel fluctuations in pH in freshwater ponds of varying buffering capacity.

Alkalinity and Hardness. Total alkalinity. The total concentration of titratable bases in a water, expressed as equivalent calcium carbonate, is referred to as total alkalinity. Bicarbonate, carbonate, ammonia, hydroxide, phosphate, silicate, and some organic acids can react to neutralize hydrogen ions, so these substances are all bases and contribute alkalinity to water. Alkalinity can be divided into bicarbonate alkalinity, carbonate alkalinity, and in some waters, hydroxide alkalinity. Total alkalinity levels for natural waters may range from less than 5 mg/L to more than 500 mg/L. Seawater has an average total alkalinity of 116 mg/L. Total hardness. The dissolution of limestone is a major source of alkalinity in natural waters. Limestones are carbonates of calcium and magnesium. Therefore, the milliequivalents of calcium plus magnesium are often similar to the milliequivalents of carbonate and bicarbonate in a natural water. Because divalent alkaline earth elements (Ca+2 and Mg+2) react with soap to form a precipitate, waters containing relatively high concentrations of alkaline earth metals are referred to as “hard” waters. Calcium and magnesium are the most abundant alkaline earth metals in normal freshwaters, and their concentration as equivalent calcium carbonate, usually has been taken as a measure of total hardness. Below is a relative scale of hardness of freshwaters:


0-75 mg/L soft 75-150 mg/L moderately hard 150-300 mg/L hard >300 mg/L very hard

Carbonate hardness is also called temporary hardness because it precipitates upon boiling. If the total hardness of a water exceeds the total alkalinity the water is said to contain non-carbonate hardness (total hardness – carbonate hardness = non-carbonate hardness). Non-carbonate hardness is called permanent hardness because it cannot be removed by boiling. If total alkalinity and total hardness are equal, calcium and magnesium can be thought of as being associated entirely with bicarbonate and carbonate. When the total alkalinity of a water sample exceeds its total hardness, some of the bicarbonate and carbonate is associated with potassium and sodium, rather than only with calcium and magnesium. Likewise, if the total hardness is greater than the total alkalinity, some of the calcium and magnesium is associated with sulfate, chloride, silicate, or nitrate instead of only with bicarbonate and carbonate. The total hardness of seawater averages 6,600 mg/L. Brackish waters, and ponds in arid regions will also have relatively high total hardness. Salinity. Salinity is a measure of total dissolved salts, and is expressed as g/kg, or more often parts per thousand (‰). Salinity of freshwater is usually <0.5 ‰; full-strength seawater 34 ‰; brackish (estuarine) water in-between. Closed basin lakes can have salinities as high as 300 ppt. • Changes in salinity; effects on gills and kidney • Measurements (conductivity meter, refractometer, hydrometer) • Chlorinity (measure of total halides; salinity = 0.03+1.805 Chlorinity ‰) • Use in parasite treatment and stress reduction for holding and transport Nitrogen, phosphorus, nutrients


Bibliography and Source Material Boyd, C.D. 1990. Water quality in ponds for aquaculture. Alabama Experiment Station, Auburn University, Auburn, AL. Birmingham Publishing Co, Birmingham, AL. Davis, Richard A. Oceanography: An Introduction to the Marine Environment, 2nd ed. Dubuque, IA: Wm. C. Brown Publishers, 1991. Gross, M. Grant. Oceanography: A View of the Earth, 3rd ed. Englewood Cliffs, NJ: Prentice Hall, 1982. Piper, R.G., et al. 1982. Fish Hatchery Management. US Department of the Interior. Fish and Wildlife Service, Washington, DC. Water Enclyclopedia (on-line): http://www.waterencyclopedia.com/ Thurman, Harold V., and Elizabeth A. Burton. Introductory Oceanography, 9th ed. Upper Saddle River, NJ: Prentice Hall, 2001.

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WATER QUALITYWATER QUALITY FACTORSFACTORS

Water BiologyPHC 6937

Andrew S. Kane, Ph.D.University of Florida

Environmental Health Program, PHHPCenter for Environmental and Human Toxicology

Emerging Pathogens Institute

Diel fluctuations in pH

Diel fluctuations in pH

2

Effect of pH on carbonates

Effects of D.O. on Aquatic Organisms

Diel fluctuations in O2

3

D.O. Saturation Nomogram

Thermal Stratification

Light Penetration in Water

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Light Penetration in Water

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Water Quality Parameters Associated with Aquatic Animal ...€¦ · animal health and homeostasis. Water quality parameters also affect the aqueous environment, both physically and