Guest Blog: Humic substances in freshwater aquariums By Vince Dollar

Editor's note- I was contacted by today's guest author, Vince Dollar, some weeks ago, after he stumbled on the Tannin Aquatics website. Intrigued by our offerings and ideas, he proferred that there is way more to the concept of "aquatic botanicals" than just great-looking aquariums!  A very enthusiastic, experienced aquarist, Vince is as into the "tinted" aquarium concept as I am.

However, his intellectual curiosity led him even further, beyond the simple aesthetics, to research the more "practical" aspects of botanical-influenced aquariums- specifically, their production of humic substances and the benefits they offer aquarium fishes. His research and personal experiments have led to some remarkable findings and conclusions that, in our opinion, will change the way we think of our aquarium water composition and its impact on our fishes' health and well being. Enjoy! 

 

Humic Substances in Freshwater Aquariums 

By Vince Dollar  (aka Kmuda)

All natural bodies of water contain dissolved organic carbon (DOC), with 40% to 80% of DOC being comprised of Humic Substances. Humic substances are, in turn, comprised of humic and fluvic acids, both of which are produced by the biodegradation of dead organic matter. 

Humic substances are introduced into lakes, rivers, and streams by leaves and wood falling into these bodies of water, forming the “leaf litter” substrate that all Apisto enthusiasts are familiar with, and by rain runoff flowing across the forest/jungle floor, where dead leaves and wood are plentiful. As the water runs across the forest floor, dead and decaying organic matter release tannins. These tannins, which stain the water a tea color, contain humic substances.

A tannin-laden South American Jungle Stream

Up until the last decade, science considered any influence of humic substances on aquatic life as “anecdotal”. Research conducted within the last 10 years has proven that humic substances have an important direct physiological influence on aquatic life. In extreme blackwater conditions, they are what make it possible for fish to survive in pH as low as 3.9.

In less extreme conditions, we are just now beginning to understand the role they play. However, they have been documented to play a major role in the functionality of a fish’s immune system, influence growth, improve lifespan, prevention of oxidative DNA damage, detoxification of heavy metals and organic pollutants, suppression of cyanobacteria, regulation of gill function, protection of fish from environmental physiological stress (low oxygen levels, temperature swings, pH shifts, TDS changes, Ammonia, Nitrite, etc…) and faster recovery from these environmental stressors. Humic substances have also proven to possess antifungal, antiparastic, and antibacterial properties, inhibiting the growth of Aeromonas hydrophila, A. sobria, Edwardsiella iclaluri, E. tarda, Pseudomonas fluorescens, and Escherichia coli.

It is important to understand that all natural bodies of water contain humic substances. From Ocean water, to the Mississippi river, to the Amazon River, to ice covered lakes in Antartica. This should be a lesson to everyone. Life has a way of producing what is needed to prolong life. If humic substances are found in lakes covered by hundreds of feet of ice in Antarctica, there is a reason they are there. It's because they are a foundational necessity. In some environments, such as Blackwater environments, they make life possible. Fish could not exist in these conditions without them. In other environments, such as Central American aquifer fed streams or African Rift Lakes, they make life better. This is perhaps best stated in a March 2008 Study conducted by Humboldt University at Berlin, Institute of Biology, Freshwater and Stress Ecology, Germany, in which they came to the conclusion that “It appears that dissolved HS have to be considered abiotic ecological driving forces, somewhat less obvious than temperature, nutrients, or light.”

There you go: Humic substances, once considered a "fringe" aspect of the aquarium hobby- products previously employed only by blackwater enthusiasts- should instead be considered an essential component of every aquarium, almost as important as temperature and food.

Many will think it does not matter; perhaps thinking, “..Surely my tap water contains enough of this stuff.” The issue is that Humic Substances interact with chemicals used during drinking water purification, resulting in the release of other chemicals (byproducts) determined to be harmful for consumption (check your tap water for Haloacetic Acids and Trihalomethanes, these are the byproducts resulting from the interaction of humic substances with chlorine). As a result, our water companies attempt to remove humic substances from our drinking water prior to the introduction of purification chemicals. This means that our aquarium water is basically void of the compounds millions of years of evolution has enabled fish to utilize, even depend on.

So, what are we to do? All natural humic substances have been removed from our tap water, and here is this nut claiming our fish require them, although no one has worried about these things since the beginning of aquarium keeping (which is not actually true)! Asian and SE Asian breeders have long known about the beneficial properties of Peat, Indian Almond (Cattapa) leaves, tree bark, and alder cones, employing them in the breeding of everything from Betas to Tilapia. While they may not have been aware of the physical interactions tannins released from these products had with the fish in their care, they were well aware of the end results, as are Apisto enthusiasts, for whom tannin leaching botanical tanks are common.  And while people may have experienced long term success with fish, there is a reason fish such as Astronotus ocellatus (Oscars) develop diseases such as HITH, which is only experienced by fish in captivity, and have an average captive lifespan of 8 years, when it should be closer to 15. I claim this is partially because of an absence of humic substances in our tank water.

Oscar. (Photo by Jón Helgi Jónsson, used under CC BY SA 3.0)

What needs to change is that all aquarium enthusiasts need to understand the influence these substances have on our fish and to take actions to ensure there is a replenished supply. While we don’t have the ability to collect rain water from the jungle floor, we can simulate the end result, either by the manufacture of “tank tea”, via the maintenance of a “botanical aquarium”, or via the use of commercial conditioners.

Tank Tea

“Tank Tea” involves the manufacture of tannin laden water using various materials such as Peat, Indian Almond Catappa Leaves, Alder Cones, Oak Leaves, Maple Leaves, and any number of leaf/wood products determined to be “aquarium safe” (check out tanninaquatics.com/). 

I manufacture “tank tea” in a 20 gallon aquarium, although you can use anything from a 5 gallon bucket to a large (clean) Rubbermaid trashbin. Or you can make it as needed by boiling (and cooling) the same products in a pot on the stove. However, one important aspect I’ve discovered is that as long as the “tea” is under aeration, it is fine but when sealed up in a jar or milk jug, it changes from a clean earthy smell to something more sinister, a bit funky.

My "tea" is the color of coffee (using Peat, Catappa, alder cones, roiboss tea bags, green tea bags). Water is constantly run through 3 to 4 cups of Peat (in a media bag) in a AC70 filter hung on a 20 gallon tank. The Peat is on the bottom of the filter, with the stock AC sponge on top of the peat. The sponge will need to be rinsed whenever you see bypass coming from the intake tube section of the filter. Catappa leaves are left free floating, alder cones are in a media bag, and used roiboss/green tea bags are just tossed into the tank. Old media bags of peat removed from the filter are dropped into the tank to further soak.

 

The Peat in the filter is replaced every couple of months. Each week, following water changes, I'll add 2 Catappa Leaves to the tank. Each month, I'll add a handful of Alder cones to the media bag.

An important concept that needs to be understood is that no two humic substances are alike. Humic substances, for instance, from the Rio Negro will be the result of hundreds, perhaps thousands, of different source materials, compiled up into a consolidated mixture of “humic substances”. In addition, Rio Negro humic substances will be completely different than those found in Rio Inirida water, for example. To provide an optimal simulation of these substances, it is of utmost importance to provide as varied a source of humic substances as possible, to include using multiple types of peat from different locations, various types of leaf material, different woods, etc... While any source of humic substance is better than no source, multiple sources are better than a single source. 

In addition to the AC 70, I have a small AC 20 running, stuffed with generic filter floss. This is to help remove the big particles of loose peat and broken down catappa from the water column.

The filters are not absolutely necessary. If using a 5 gallon bucket, a trashbin, or even another aquarium, the only absolute requirement is aeration (and water movement), which can be accomplished with nothing more than air pumps and air stones, although I would recommend a heater.

You can use any brand of Peat, even garden store peat (provided it has no other additives). My favorite Peat to use is the Sera Brand, because I like the small condensed pellets (makes less mess, last longer) but I also use the Laguna Pond brand extensively, because of cost. I don't like using garden brands of peat because they are very dusty (and twiggy), although this is absolutely the least expensive route.

For those of you who are afraid of "tinting" your water. Here is my 65 gallon Discus tank. I add 2 gallons of the above tea to this water each water change (3x70% water changes per week) AND I add two catappa leaves directly to the tank each week. The "tinting" is hardly noticeable unless you drain water into a white bucket.

 

The TDS in my tanks generally runs at 100 or below. Excluding the Discus tank, where I am intentionally altering the water chemistry, I notice no difference in the tanks where I am using Peat tea and the tanks where I am not.

My KH is very low straight from the tap (somewhere between 0 and 1 degrees German Hardness..... changes color on first drop) so it should be (is) very easy to completely crash the KH resulting in a sharp pH decline. I know, because I do this, intentionally, for the Discus tank (and a few other tanks). 

 

Can I add enough Peat tea to result in a dropped pH? Absolutely. But I am adding 1 gallon of my "Tank Tea" to my 120 gallon Oscar tank, with each water change, along with 3 catappa leaves every other week, and 1 cup of peat in an Aquaclear filter (monthly), and it's not influencing pH. So If I can do all of this to 120 gallons of my water, which has virtually no existing carbonate buffer, without dropping pH, then others with much harder water should have no issues at all, even adding much more.

“Tank Tea” will not soften water or influence pH other than via dilution.  As an exercise, let’s pretend we have “Tank Tea” with pH of 4 that has zero hardness (chances of your tank tea reaching this level is very slim, only if you start with extremely soft water). If you add 1 gallon of this tea to a 20 gallon tank, you will reduce hardness by 1/20^th (or 5%) - negligible. The pH of the tea itself is basically irrelevant because the impact to carbonate hardness is negligible (decreased by 5%), so while there may be a momentary slight decrease in pH (again resulting from only from dilution), it will soon return to normal as the carbonate buffer reestablishes. Yes, peat softens water by exchanging humic acids for magnesium and calcium but this requires active peat filtration (the water running over the peat itself). The resulting “tea” itself has no such properties.

The first question everyone will ask is “how much “Tank Tea” should I add? I wish I could provide a mathematical answer to that question but the real answer is “as much as you can”. There are two factors at play here. The most important factor is how much “Tank Tea” can you add without harmfully influencing water chemistry? Start with a small amount (a cup or so), test the pH, and keep adding until you see a change (of course, you can also monitor KH and GH). If there is a change, you added too much, go back to however many cups you added before it changed, and that should be set as your max. You will likely be surprised at how much can be added, especially if you have hard water. 

The second factor is aquarist preference. How much tint can you stand? Personally, I have come to prefer a dark tint to my tanks.

 

Tinted tanks are, after all, the most natural and healthiest environment, in my opinion, but I understand those who want the crystal clear, pristine, “swimming-in-air-tanks”. For these environments, you add as much “Tank Tea” as you can stand. As you can see from my photo of my Discus tank, I get two gallons of tea in a 65 gallon aquarium without significantly altering water color or clarity. Even if you are just adding a cup or two per 55 gallons of water, you are introducing a higher level of humic substances than existed before. An important side note, the brighter the lighting, the less noticeable the tinting.

Here's a link to a lively discussion on the topic on the oscarfish.com forum

 

The Botanical Aquarium

A botanical aquarium is best described as a Natural Aquarium, an aquarium in which we attempt to duplicate actual conditions of our fish in the wild. Botanical Aquariums may include driftwood, a leaf litter substrate, along with various “twigs and nuts”. Unlike the typical crystal clear “swimming-in-air” type tanks that so many seek to achieve, botanical aquariums tend to be tannin stained because of the “botanicals” in use, although botanical aquariums are not limited only to tannin stained water (more on this later). For details on the preparation and actual setup of a botanical aquarium, I recommend the following article. http://tanninaquatics.com/blogs/news/52807553-woah-slow-down-there-theres-no-rush

Of the three mentioned options to provide humic substances to our fish, a botanical aquarium can be considered the best option, while also being the most involved. It’s not a simple matter of dropping a bunch of leafs, twigs, and nuts into an aquarium. It takes planning, preparation, and an understanding of pH, KH, and (to a lesser extent) GH. You’ll need to identify the affect individual botanicals have on these parameters of your tap water.

Below are three photographs, one is an underwater photo from a South American stream, the other a botanical aquarium simulating a South American stream, and the third, your stereotypical aquarium. Which would you rather have? Which do you think provides the healthiest environment?

 

Underwater Photo South American Stream

 

  Botanical aquarium representing a South American Stream by Tai Strietman

 

( Photo by Nevit Dilmen Used under CC BY-SA 3.0)

While many who build a botanical aquarium will first attempt to boil out the tannins (again, trying to maintain that crystal clear water) before adding the wood, leaves, and other “twigs and nuts” to the actual tank, I would encourage not doing so. Soak the products long enough to get them to sink, then add them directly to the tank, or even add them to tank to soak, until they sink. Allow those tannins to leach into the water. It’s what we want. It’s what our South American Cichlids have evolved to live in.

 

There is a perception that in such a tank, you cannot maintain a stable pH. I could not disagree more. While the pH of your tap will almost certainly be different than the tank water, with regular water changes, the pH will not continually decline. In essence, you cannot decrease the pH of orange juice by adding more orange juice and while there may be an initial influence on the pH, it will eventually stabilize. 

There are many variables that define what our final water parameters may be, these include the botanicals in use (some will leach more acids than others), the chemistry of our source water (KH, GH, pH), and stocking levels. With very hard water, it will be difficult to achieve any long term success in modifying the pH because the leached acids must first erode the carbonate buffer (KH) in order to drop the pH. However,  when you really get down to it, unless I am trying to keep Altum Angels or breed blackwater fish (in which case, you probably need to be starting with R/O water), I’m not worried about pH, although it is imperative that we are aware of it.

The only rule that needs to be clearly understood is that you make the chemistry of the replacement water match, as closely as possible, the tank water. This cannot be stated with enough importance. Chances are, because of the influence of botanicals on the water, there will be a significant difference between tank water and tap water chemistry. It is essential we get our water change replacement water near the chemistry of our tank water otherwise we run the risk of a water change killing our fish by osmotic shock. By far, the easiest way to accomplish this is to “double up”. If building a 20 gallon botanical aquarium, don’t stand up one aquarium, stand up two. I utilize Titan "EZ stands", placing my primary tank on top, the water aging tank on the bottom.

If you adopt this setup, when purchasing botanicals, purchase two of everything. For instance, if you are going to add 5 catappa leaves to the top tank, add five to the bottom as well. If you are going to add 5 pieces of cholla wood to the top tank, add 5 to the bottom as well. If you are adding a couple of monkey pots to the top tank, add a couple to the bottom tank as well.

The bottom tank is used to age water for water changes. If you are including the same botanicals in this tank as the top, then the water chemistry between the two tanks should be close enough. Certainly much safer than attempting to refill with unmodified water directly from the tap. After using water from the aging tank for the water change, refill the aging tank with unmodified water directly from the tap.  Monitor the pH, KH, and GH between the two tanks.

If the bottom tank starts to fall a bit behind, add a catappa leaf or two to get it caught back up. With a little testing and experience, before long, you’ll know exactly what to add and when, to keep chemistry between the two tanks aligned. As the botanicals deteriorate and are replaced, just continue adding and replacing both the top and bottom tanks. For quick adjustments, SeaChem Acid Regulator and SeaChem Alkaline Regulator can work wonders. Do not confuse these products with Neutral Regulator and Discus Buffer, which should not be used for this application.

If the added expense of a second tank (which would also require a filter for water flow and a heater) is not to your liking, any container that holds the same volume of water as your primary tank will suffice. I’ve used Rubbermaid trashbins extensively for this purpose. A Rubbermaid trashbin with a strong airpump or powerhead, gets the job done. However, being a firm believer in always being prepared, a second tank can also become an emergency home for your livestock should a leak develop in the main tank!

Understanding your end resulting pH is essential. If the pH of your tank drops to below 6.5 degrees (German Hardness), you are limiting yourself to South American blackwater type fish (which I happen to think are some of the most fascinating of all fish).  At a pH of 6.5 to 8.0, the door is wide open as to the types of fish (although you would not want African Cichlids at the lower end of that pH range). Your end resulting pH depends completely on the chemistry of your tap water. In other words, there are no guarantees a botanical aquarium will achieve a low pH. The end resulting pH can be anywhere from 4.0 to 8.0, depending on the hardness and buffering capacity of your tap water. But again, this article is not about achieving a “blackwater” tank. It’s about introducing humic substances as a foundational necessity of our aquariums. For the purpose of this discussion, we are after the tannins, not creating a low pH blackwater tank.

The "Botanical" aquarium without the "tinting..."

For those who just cannot stand the idea of their water being a tea color, but would like the natural appearance of a botanical aquarium, achieving this result may be easier than you think. The simplest method, in my opinion, is a combination of processes. Setup a water aging container to be utilized for the manufacture of “Tank Tea”, placing all “Botanicals” to be used in the main tank into the aging container. Those items that need to be boiled can be boiled, with the resulting “brew” dumped into the water aging container (we don’t want to waste those valuable tannins).

You use the water aging container to allow the botanicals to leach out tannins (and to lose buoyancy), moving the botanicals over to your main tank once this is achieved. Subsequently, the resulting “tea” in the aging tank can be added to the main tank as described in the “Tank Tea” section.

Using this concept, you should be able to maintain a botanical aquarium without significantly altering the water chemistry, clarity, or color, while introducing the humic substances we are looking for.

 

Commercial Conditioners

I am often asked, “Will commercially available Blackwater Extracts work?” My short answer is “I don’t know”. I have no clue what is actually in these products. You can kind-of read between the lines to determine if they are acceptable products but fact of the matter is, if I honestly thought what they were producing was as good as the Tank Tea I am making on my own, I would be using their products instead! The advantage of the "Tank Tea" is that I am able to add things I know provide medicinal benefits, such as Catappa, Alder Cones, Roibos Tea, and other plants with medicinal uses. I control it. That's my preference. Homemade “Tank Tea” is certainly much more cost effective.

As for individual products, there are some that are better than others, in my opinion. I would not trust certain products, and others might not provide exactly what I'm looking for. The Sera product claims it will not alter pH, which means it does not contain the substances we are looking for, it just tints the water. Remember, Humic Substances are comprised of Humic and Fluvic acids, and if the Sera product contained these acids, it could not claim it will not alter pH.

(fulvic acid)

Two other products I'm familiar with are Marc Weiss's "Instant Amazon", which is made from Catappa Leaves, Carob Tree beans, and the Karaya Gum tree, each viable and desirable products with known medicinal properties, and Kent Blackwater Extract, a product for which ingredients are not clear. So, in my mind, as a commercial extract, the Marc Weiss product would be preferred, although at $22 for 16-Ounces, with a dosage of 1 teaspoon per 10 gallons, you will spend several hundred dollars per year vs. making your own tank tea, and your own tank tea will be a superior product, in my opinion.

If a commercial extract is all you are willing to do, then by all means, utilize that option. The introduction of humic substances from these products would be preferred over a continued total absence.

Scientific Resources:

Humic substances. Part 2: Interactions with organisms. Meinelt T1, Schreckenbach K, Pietrock M, Heidrich S, Steinberg CE.

• zleibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany

Humic substances. Part 1: Dissolved humic substances (HS) in aquaculture and ornamental fish breeding Meinelt T1, Schreckenbach K, Pietrock M, Heidrich S, Steinberg CE.

• leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany

Humic acid and moderate hypoxia alter oxidative and physiological parameters in different tissues of silver catfish (Rhamdia quelen) Riffel, Ana P; K; Saccol, Etiane M; H; Finamor, Isabela A; Ourique, Giovana M; Gressler, Luciane T

• Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology184.4 (May 2014): 469-82.

Dissolved organic carbon from the upper Rio Negro protects zebrafish (Danio rerio) against ionoregulatory disturbances caused by low pH exposure; Rafael M. Duarte, D. Scott Smith, Adalberto L. Val & Chris M. Wood

• Scientific Reports 6, Article number: 20377 (2016) doi:10.1038/srep20377 Published online: 08 February 2016

Can dissolved aquatic humic substances reduce the toxicity of ammonia and nitrite in recirculating aquaculture systems?; Thomas Meinelta, , , Hana Kroupovab, , Angelika Stübera, Bernhard Rennerta, , Andreas Wienkec, , Christian E.W. Steinbergd

• Martin-Luther-University Halle-Wittenberg, Medical Faculty, Institute of Medical Epidemiology, Biostatistics and Informatics, Magdeburger Straße 8, 06112 Halle (Saale), Germany

The Use of Aqueous Humic Substances for in-situ Remediation of Contaminated Aquifers; D.R. van Stempvoort, S. Lesage, J. Molson

• National Water Research Institute

Role of Humic Substances in the Complexation and Detoxification of Heavy Metals: Case Study of the Dnieper Reservoirs; P.N. Linnik, T.A. Vasilchuk

• Department of Hydrochemistry, Institute of Hydrobiology, National Academy of Sciences

Use of Humic Substances to Remediate Polluted Environments: From Theory to Practice; Irina V. Perminova, Kirk Hatfield, Norbert Hertkorn

• Proceedings of the NATO Advanced Research Workshop on Use of Humates to Remediate Polluted Environments: From Theory to Practice Zvenigorod, Russia 23–29 September 2002

Mitigating Activity of Humic Substances: Direct Influence on Biota; N.A. Kulikova, E.V. Stepanova, O.V. Koroleva

• Department of Soil Science, Lomonosov Moscow State University

Cytotoxic and Radical Scavenging Potential of Indian Almond (Terminalia catappa) Leaf Extracts; D. R. Behera, Sunita Bhatnagar* and A.K.Mahapatra

• Medicinal and Aromatic Plants Division, Regional Plant Resource Centre, Nayapalli, Bhubaneswar-751015, India.

Antiparasitic, Antibacterial, and Antifungal Activities Derived from a Terminalia catappa Solution against Some Tilapia (Oreochromis niloticus) Pathogens; C. Chitmanat, K. Tongdonmuan, P. Khanom, P. Pachontis and W. Nunsong

• Department of Fisheries Technology College of Agricultural Production Maejo University, Chiang Mai, 50290 Thailand

Humic substances affect physiological condition and sex ratio of swordtail (Xiphophorus helleri Heckel) Thomas Meinelt, Kurt Schreckenbach, Klaus Knopf, Andreas Wienke, Angelika Stüber, Christian E. W. Steinberg

• Meinelt, T., Schreckenbach, K., Knopf, K. et al. Aquat. Sci. (2004) 66: 239. doi:10.1007/s00027-004-0706-9

The effect of some tannins on trout erythrocytes exposed to oxidative stress; Donatella Fedelia, Marco Berrettinia, Teresa Gabryelakb, Giancarlo Falcionia

Department of General Biophysics, University of Lodz, Banacha, 12/16, Lodz 90-237, Poland Received 15 July 2003, Revised 28 January 2004, Accepted 10 June 2004, Available online 23 August 2004

Antibacterial Properties of Tannic Acid and Related Compounds against the Fish Pathogen Cytophaga columnaris; Guojing Zhao , King-Thom Chung , Kimberly Milow , Wenxian Wang & S. Edward Stevens Jr.

• Published online: 09 Jan 2011 Department of Microbiology and Molecular Cell Sciences, University of Memphis

Growth Inhibition of Selected Aquatic Bacteria by Tannic Acid and Related Compounds: King-Thom Chung , Guojing Zhao , Edward Stevens Jr. , Bill A. Simco & C. I. Wei

• Published online: 09 Jan 2011 Department of Microbiology and Molecular Cell Sciences, University of Memphis

Antileishmanial activity and immune modulatory effects of tannins and related compounds on Leishmania parasitised RAW 264.7 cells; Herbert Kolodzieja, Albrecht F. Kiderlenb

• Robert Koch-Institut, Department of Infectious Diseases, Nordufer 20, D-13353 Berlin, Germany Revised 14 December 2004, Available online 12 February 2005

Antibacterial action of several tannins against Staphylococcus aureus; Hisanori Akiyama*, Kazuyasu Fujii, Osamu Yamasaki, Takashi Oono and Keiji Iwatsuki

• Department of Dermatology, Okayama University Graduate School of Medicine and Dentistry, Shikata-cho 2-5-1, Okayama 700-8558, Japan

Humic substances affect physiological condition and sex ratio of swordtail (Xiphophorus helleri Heckel) Meinelt, T., Schreckenbach, K., Knopf, K. et al. Aquat. Sci. (2004) 66: 239. doi:10.1007/s00027-004-0706-9

• Aquatic Sciences June 2004, Volume 66, Issue 2, pp 239–245

DISSOLVED HUMIC SUBSTANCES FACILITATE FISH LIFE IN EXTREME AQUATIC ENVIRONMENTS AND HAVE THE POTENTIAL TO EXTEND THE LIFESPAN OF CAENORHABDITIS ELEGANS. Steinberg, Christian E. W.; Saul, Nadine; Pietsch, Kerstin; Meinelt, Thomas; Rienau, Stefanie; Menzel, Ralph

•  Annals of Environmental Science . Feb2007, p81-90. 10p. 

Physiological effects of humic substances on higher plants: Serenella Nardia, , , Diego Pizzeghelloa, Adele Muscolob, Angelo Vianelloc Received 16 July 2001, Revised 15 July 2002, Accepted 19 August 2002, Available online 28 October 2002

• Dipartimento di Biologia ed Economia Agro-industriale, Sezione di Biologia Vegetale, Università di Udine, Via Cotonificio 108, 33100 Udine, Italy

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