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LIGHT ENERGY by Sam Gamble Aquarium.Net

This month Sam Gmables discusses light energy in the aquarium, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Light Energy

by Sam Gamble

LIGHT ENERGY

In the aquarium industry much of our experience has been derived by the products offered to us. A two sided coin. The quantity and quality of lighting for fresh or marine aquariums has improved within recent years. Most often the quality has been rated using the sun as the standard. There are many products that measure up acceptably. We've all seen the charts, graphs, and spectral ratings that compare what we can produce and what the sun produces. What the sun emits is termed natural, and what we manufacture is artificial. Both have photon bundles of energy that characteristically have traits of mass, and mass traveling at very high speed. Commonly we refer to energy levels of light using the terms wave length and spectrum.

It is apparent we can reproduce sunlight well enough to sustain the biology of our aquariums. However, we are still having husbandry problems that can be traced to supply and management of energy. Light, like all electromagnetic radiation, is a result of either an accelerating electric charge or a nuclear fusion or fission reaction. In nuclear reactions, a photon is produced in the same manner as other elemental partial products of the reaction. However, with the exception of sunlight and starlight, light usually results from changes in the electronic structure of atoms and molecules as they absorb and readmit energy. In all situations the key word is ENERGY. Light is a transport of energy.

This is one of the ways the concept of metabolism fits into our husbandry protocol. Metabolism is the sum of all the chemical reactions in the living cell that are used for the production of useful work and the synthesis of cell constituents. In nature the essential or beginning source of energy in living organisms comes from the sun. For our aquariums we use another suitable source of electromagnetic radiation. The energy arrives by units of light and is trapped by the pigment chlorophyll. Chlorophyll is present in the cells of green plants, and accumulates as chemical energy within the different foodstuffs. Without the sun, there would be no life on this planet. Almost all the energy cellular reactions are catalyzed by complex protein molecules called enzymes, which are capable of speeding up reaction rates by a factor of hundreds to millions. Some of them are light reactive.

However, keep in mind the sequence traces back to the fact the essential source of energy in living organisms comes from the sun (natural). It is easy to see optics may be important to the production and utilization of energy by cells in direct and indirect ways. Let's take a closer look at light to better understand energy concepts that ultimately control the equilibrium of the aquarium. To do so we employ the field of optics.

In simplest terms, the concept of OPTICS is generally defined as that branch of physics dealing with the integration of light with its containment medium as the light propagates through that medium. For the reef aquarium this concerns the moment the light leaves the bulb (artificial), the distance through the air, effects of striking the surface, traveling through the water, interacting with ALL that is associated in, including the water, and finally interacting with the living cell.

In reality, when analyzing energy, optics includes the biology of the interaction with the cell membrane, cytoplasm, mitochondria and cytochromes and all their enzymes. What seems like only a fraction of an instant, is actually a long and interactive trip. All the aspects of the journey are important. Because fundamentally it effects the cell's health and ability to reproduce. From the micro scale to the macro scale, this would determine equilibrium of the ecological system that you are trying to maintain.

When considering the route light energy (photons) must travel, more principles come into consideration. Photon energy represents a range from low to high with an area in the middle we can see. Commonly called visible light, the spectrum is from red to violet, respectively. The low energy photons are affected first when interacting with other forces and particularly other mass. From the spectrum we perceive this would be first the red band. I think we are all aware that red light is absorbed more quickly in water than the other wavelengths of the spectrum.

So it's easy to consider that the more that comes between the light source and the desired destination - the organelle - the more affect there is to get or not to get, crucial energy. In view of the fact that the mass of light photons is very minute, it stands to reason, all substances including water are capable of transforming the photons along the way. The how, why, and how much is subject of countless physics books. It's not my intention to generate a large glossary here, so we'll stick to energy's role and the route.

Let's go back to the trail energy must follow and see what detours and dead end streets occur. First is the air above the water interface. The distance is short with little in it, unless there is a lot of surface splashing etc. to cause aerosol. Most often this is not the case. So there is little for the photon to interact with other than normal elements of the atmosphere. A short and open street.

Next is the water surface to air interface. Here, surface agitation, surface film, and surface bubbles have an effect. How much, would have to be measured. If you have a system with all the above obstacles for light, then light could be lost from detours and absorption at dead end streets. The agitation would scatter the light to be perhaps absorbed elsewhere (detour). Surface film would absorb some of the light energy (dead end street). All the tiny little bubbles would also scatter light and some of the matter adhering to the bubbles would absorb light energy (detour and a dead end street). The absorption and scattering effects would remove measurable amounts, making less energy available at the desired metabolic locations.

The underside of the water's surface has function which is reflectance. Light that penetrates the surface interface, may be reflected back toward the surface. If the surface is turbulent then the light scattering is again possible and another potential traffic problem occurs. When we maximize surface exchange of a light dependent aquarium like a reef tank with strong aeration, strong current, and wave action; are we actually facilitating energy pathways?

Good question.

Next, consider light has transmitted to the bulk water of the aquarium. The properties of the molecular content of the containment medium will further effect transmission to the final destination. Purposely omitting salinity (salt density) from the discussion for simplicity, there are many other elements to consider. The two most important are dissolved organic carbon (DOC) and suspended minerals (SM).

Commonly DOC is often considered to mean the yellow water we see in aged aquariums. In considering the properties of light transmission the effects start before yellowing occurs. Yes, nutrient rich yellow water has absorptive characteristics. But so does clearer water with dissolved nutrients. The coloring agents are usually related to phenols. Water high in dissolved organic carbon, does not have to have these coloring agents. To the human eye, much of the dissolved organic carbon has little perceived color. Urea for example, is rather clear when mixed with water, however, it has light changing abilities. It is also a big time waste product from fish and a source of nitrate (roughly 46% by weight). A reef tank with a fish population could be very nice and clear, but producing sizable amounts of nitrate with an energy shift away from equilibrium.

We have seen that the combination of the processes, absorption and scattering, control the manner in which impinging radiation propagates through a body of water. The nature and magnitude of those absorption and scattering processes are controlled by the bulk optical properties of the water. The bulk optical properties are in turn, direct consequences of each optically significant organic and inorganic component in the water body.

It has been discovered that increasing the suspended mineral (SM) concentration in a water body containing a dissolved organic carbon (DOC) concentration (2mg C/l) results in a more rapid volume reflectance, increasing more in the red end of the spectrum than in the blue. Large concentrations of SM quite clearly result in volume reflectance values that are an order of magnitude greater than those resulting from other components like chlorophyll in phytoplankton blooms. Keep in mind the greater the amount of reflectance, the less transmittance, and subsequently absorption becomes possible. Simply stated, less light passage, with an electron shift.

Let's apply some of this to an aquarium. A mythical case history. The aquarium has an increase in nitrate, giving us suspicion that there is an increase in available nutrients (DOC). With that there is a drop in pH and ORP. Most likely the metabolism of extra organic carbon (nutrients) by microbial mediation is causing a mild acid, which tries to buffer itself. Hence, the decrease in pH and ORP and a flux in the alkalinity.

Conventional wisdom; stabilize pH with a buffer, add increased buffering capacity with Kalkwasser or the like, and may be even toss in a few additives to make sure necessities like strontium are there to help - whatever (SM). Crank up the power heads and wave makers to get "better" surface exchange of gases like CO2, and throw in some extra air bubbles to increase DO.

Calcium is a suspended mineral, reacting quickly with most nonmetals. It reacts with all halides like iodine and bromine, often forming a film on metals. Calcium reacts spontaneously with water and acids to form hydrogen gas.

The addition of kalkwasser then not only buffers, but shifts reactions of other components and adds scattering and reflectance to the scenario, making less light (photons of energy) available to the bulk water (SM).

The lower or more negative millivolt readings indicates there is less absorption of light, including red band. However, that is not to be attributed to better blue/violet passage which the cnidarians desire. Increased passage of blue/violet would look like; increased or higher pH, DO, and ORP. The case history is just the opposite.

The extra water to air interface turbulence increases the refraction and reflectance of incoming energy. Some light is reflected away from the surface and some is scattered. It may improve gas exchange, however the loss of energy is the concern.

The light energy that does make it through and into the containment medium must also pass the nutrient layer at the water to substrate interface. This barrier can act almost as a screening mechanism. Again energy is lost or shunted. Unfortunately this all adds to the attractiveness for primary production by algae and some diatoms.

Many diatoms, bye the way, get much of their silica from carbon metabolism and the production of organic acids. The rearrangement of light energy through the containment medium can also facilitate their appearance from much the same processes as nuisance algae. Simply, the right amount of light and nutrients.

So then, have our maintenance changes to the mythical case history done much to alter metabolic shift away from energy equilibria? That's a good question to analyze.

The goal is to maintain increased light parameters and a steady level to absorb the flux by spontaneous equilibrium shifts. Energy is required in amounts and conditions, at specific energy levels, at all times to achieve balance. Photon energy is a tremendous source, but it can be detoured easily. With proper chemical and radiant energy, the enzymes can respond to changes at rates measured in very small fractions of a second with reactions that can number in the millions. They require the proper transportation system. A lighted energy highway for starters.

There seems to be a fine line between stable and unstable nutrients (life balance) in any environment. When sincerely investigating sources of energy and the results, it helps illustrate more and more that any single ppm additive is overkill to a system mainly for the reason of being a single active or reactive phenomenon. Also, that everything in nature is multifaceted or acting. When a shift occurs, all phenomena must adjust. Conducive factors include, adequate optics for the passage of light energy to its destination down the energy highway. With fewer obstacles, there are fewer detours and dead ends. This equates with better transportation of energy, and natural balance.

Question or comments

Sam Gamble

102170,3150@compuserve.com

Created by liquid
Aquarium.Net
Last modified 2006-11-19 01:26
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