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Earthworms have an enormous impact on most terrestrial ecosystems. As saprophytes they also will be an excellent species for use in Nauvik, a CELSS ('Closed Ecological Life Support System; a project to develop ecological systems for use in space). Earthworms will intercept un-used energy for use by higher organisms. Using this energy, however indirectly, for human consumption will reduce primary production. Since a smaller growing area could then be used earthworms will reduce biosphere energy and space requirements.
Taking earthworms from the soil regeneration system will remove some nutrients. This loss is more than offset by the quality of the casts (feces). These casts are composed of earthworm wastes (like urine), humus, other undigested organic compounds and ingested soil particles. Casts can be used directly as soil, applied as fertilizer or soaked to produce a hydroponics solution.
There are more than 1,800 known species of earthworms (Minnich, 1977). Nauvik will provide food & environment similar to that provided by commercial earthworm growers. This simplifies species selection because we can use one of the species that have been developed commercially. A short analysis of the more useful species follows (Minnich, 1977; Appelhof, 1982): Lumbricus terrestris, commonly called the native night crawler, is the largest earthworm commonly found in North America. Though popular for bait they are difficult to raise commercially and would be unsuitable for Nauvik due to their slow reproduction rates, low temperature requirements and their tendency to migrate. Allolobophora caliginosa, the field or gray worm, is an important agricultural worm. Although their casts are excellent fertilizer with high mineral content they probably won't be suitable for use in Nauvik for the same reasons as L. terrestris. It may, however, prove useful for some of the cooler, soil based crop systems for it can survive on infertile soils. Lumbricus rubellus, or red wiggler, is the most popular earthworm for commercial production. Several of the characteristics which make it ideal for commercial production also make it a likely candidate for Nauvik. Although it is a smaller earthworm at 5-12 cm (2-5") long it is a prolific breeder with one pair of worms capable of producing nearly 2,000 in a year's time. It does well inside, is quick to reduce organic refuse into compost, and is quite odorless. Eudrilus eugeniae is a commercially popular earthworm called the African night crawler. It can be difficult to raise commercially due to it's high temperature requirements. This is in it's favor for use in Nauvik since our temperatures shall be quite warm. Unfortunately it not as efficient a compose maker as L. rubellus, nor can it survive in infertile soils. We shall try this species, but it is not expected to be as good as L. rubellus. Pheretimas species are Asiatic 'swamp worms' that are becoming common in the American south. It is a very active species that probably destroys Escherichia coli (Khambata, 1973), a handy feature for Nauvik! Though requiring a somewhat warmer temperature, Pheretimas' other environmental requirements are similar to A. caliginosa and it could be a useful addition to the soils of Nauvik.
It may prove beneficial to have more than one species of earthworms. Final species selection will be made after Nauvik is partially functional, so each promising species can be tried in an appropriate niche.
Earthworms, like all life, have particular environmental parameters within which they flourish. Most important among these are soil moisture, pH and temperature. Food requirements, limiting light and soil composition are also important.
Earthworms have few mechanisms to preserve body moisture. Their moist body surface requires a moist environment, without which they perish in short order (personal observation). Optimum cocoon production occurs between 28 and 42 percent soil moisture (Evans, 1982) and population densities are usually the highest between 12 and 30 percent (Minnich, 1977). In practice this means keeping the earthworm medium moist but not wet.
Earthworms are very sensitive to pH. They prefer a soil with a neutral pH, or slightly alkaline (Lee, 1985). This should not be a problem in Nauvik except where urine might be mixed with the feces. This can be remedied by soaking the urine from the feces. I noted an interesting phenomenon when I soaked chicken manure in a hydroponics solution: it became alkaline! I haven't explored why but if it is repeatable this could prove an excellent method to adjust soil acidity. Earthworms also tend to neutralize soil pH (see table 1,) which will be handy to regulate the pH of hydroponics solutions produced from earthworm casts.
The most favorable temperature for most earthworms is 13-18 degrees C (55-65 degrees F) (Minnich, 1977). Earthworms can't stand to be frozen, so their lower limit is 0 degrees C (32 degrees F), and most species do not thrive in temperatures above 22 degrees C (72 degrees F). This upper limit may restrict the number of species which can be used in Nauvik, for the temperature will be maintained around 25 degrees C (77 degrees F). Soil temperatures will be lower than air temperature due to evaporative cooling (personal observation), so a more suitable temperature range may be supportable--especially in areas adjacent to the outside wall. Another common heat problem encountered in commercial earthworm production is heating of the soil by bacteria. This can be fatal to the earthworms, and needs to be avoiding by limiting the amount of food introduced at one time.
Light can injure or kill earthworms, especially ultra-violet light. The only concern this will pose is keeping the earthworm 'farm' away from the intense crop lighting.
Earthworms can survive in a wide range of natural soil types (Darwin, 1897). After correcting for such things as pH 'soils' of sand, loam, peat, silt, compost and manure are all acceptable to the earthworm. Unfortunately earthworms can't tolerate things like rock wool or Pearlite due to the physical sharpness of the medium tearing up their internal organs when consumed (Chambers, 1990). This severely limits the use of these mediums in Nauvik. It also limits the use of mediums like vermiculite, which contains these materials.
Earthworms are primarily saprophagous animals. The bulk of their diet consists of decaying organic waste of almost any origin. Living microorganisms like fungi and bacteria are also ingested (usually along with decaying organic matter) and there is evidence that this forms an important part of the diet (Lee, 1985).
All earthworms thrive on manure (Minnich, 1977). Most species also thrive on vegetable wastes, and many live in soils. Nauvik will have several of different food types for the earthworms: soils containing dead roots, plant and kitchen wastes that are of such low quality that higher animals like chickens can't consume them and animal feces. Different species of earthworms may be required to maximize production from each food source.
Earthworms consume their body weight in food every day (Minnich, 1977). This is primarily because of the low quality of their diet, and much of what is consumed simply passes through the earthworm (Darwin, 1897). In soil systems this leads to a high turn-over rate, and in some very long term experiments Charles Darwin proved that the 'sinking' of objects through the soil over 30 years is due to earthworm action (Darwin, 1897). High turn-over rates yields naturally plowed soils, a fact that could be very handy for Nauvik.
In natural systems earthworms are often nutrient stressed (Dotson, 1989; Aplet, 1990). In Nauvik we expect to provide our earthworm growth chambers an ample supply of nutrients. However those earthworms which might be used to improve soil productivity (i.e. growing symbiotically with Nauvik's plants) grow at a much slower rate, and are much less productive due to lower quality of food and nutrients. Though slower they are still expected to make a significant contribution to Nauvik productivity.
Earthworms are capable of growing at very high population densities. The best natural ecosystem (the Nile Valley) has roughly a million earthworms per acre (Hopp & Slater, 1948). This works out to around 5,000/m2. Commercial growers can support densities of 100,000 earthworms per cubic meter (3,000 earthworms/cubic foot) (Minnich, 1977). We hope our soil systems will approach the 5,000/m2, and in our growth chambers we expect to maintain between 50,000 and 100,000/m3. A growth chamber 60 cm x 30 cm x 40 cm (12x15x24") (0.072 m3) will produce 5,000 earthworms annually (Kennerly, 1965). Since the average earthworm weighs slightly more than a gram (Minnich, 1977), it would take 15 such growth chambers (roughly a cubic meter) to produce 200 g daily--which is an estimate of the daily requirement for Nauvik. This is a population of some 75,000 earthworms weighing 30-40 kg. It is uncertain at this time whether Nauvik could support this population.
Earthworms are a disease vector (Hampson & Coombes, 1989). This poses two problems for their use in Nauvik: first they may import disease from outside and second they may spread disease within Nauvik.
It is possible to create axenic earthworms (Whiston & Seal, 1988) but it may prove unwise. Deleterious micro-organisms frequently colonize sterile medium & populations since there is no competition from normal microflora. Thus the introduction of sterile earthworms into a semi-sterile environment could encourage unwanted micro-organisms.
Spread of disease within Nauvik is quite a different matter. No effort will be made to make individual populations sterile. However earthworms from those growth chambers that are fed feces will be sterilized (probably by cooking) before being fed to another tropic level. This will help prevent the spread of micro-organisms from, say, human to chicken.
On the positive side earthworms will reduce fungus infestations. This is from both competitive interactions (fungi are opportunistic saprophytes) and physical consumption (Minnich, 1977). Other micro-organisms also may be reduced/controlled by earthworms.
There are many methods of extracting earthworms from their soil environment. Complete extraction is possible (Judas, 1988) with mechanical washing and straining. Except on occasions when exact counts are needed this won't be used. Extraction by simple sorting will be the preferred method. This is quite easy to perform and, if one doesn't care to obtain every specimen, quick to do. A pile of soil containing earthworms is placed on the table or sorting bench and 1-2 cm of the surface is scrapped off at a time. The earthworms will move to escape the disturbance and the light, and when you get to the bottom of the pile there will be a ball of earthworms (Minnich, 1977; personal observation). Other mechanical extractors are available for commercial operations, but Nauvik will not need to extract sufficient quantities to make this an economical alternative to hand sorting.
It may be desirable to track earthworm populations in soil systems. This means sampling earthworm populations. Dickey & Kladivko (1989) determined the most efficient sampling method was digging 10 cm (4") along the row by 45 cm (18") across the row, and 20 cm (8") deep. In Nauvik it will be necessary to dig completely through the soil to the bottom of the "container," for the soil will be fertile and able to support earthworms throughout. Sorting earthworms from extracted soil will be either by hand (Bouche & Gardner, 1984) or with a mechanical washer such as the one described by Judas (1988).
Earthworms add to soil fertility by releasing nutrients (Petrussi et al, 1988). Experiments with corn residue (e.g. stalks) have a 30% greater breakdown rate with earthworms than without (Zachmann & Linden, 1989). Earthworm casts have long been touted for use as fertilizer (Darwin 1897; Home Farm & Garden Research Inc, 1954; Minnich, 1977; Lee, 1985). Indeed they are so rich in nutrients (see table 1) that hydroponics solutions can be made from soaking their casts (DeKorne, 1978; Hydro Greenhouse Corp, 1983).
Table 1. Properties of earthworm casts and of soil from cultivated fields.
|Organic carbon (%)||5.17||3.35||1.11|
|Carbon : Nitrogen ratio||14.7||13.8||13.8|
|Nitrate nitrogen (ppm)||21.9||4.7||1.7|
|Available phosphorus (ppm)||150.0||20.8||8.3|
|Exchangeable calcium (ppm)||2,793.0||1,993.0||418.0|
|" magnesium (ppm)||492.0||162.0||69.0|
|" potassium (ppm)||358.0||32.0||27.0|
|Total calcium (%)||1.19||0.88||0.91|
|Total magnesium (%)||0.545||0.511||0.548|
|Moisture equivalent (%)||31.4||27.4||21.1|
Source: Lunt, H. A. and G. M. Jacobson, The Chemical Composition of Earthworm Casts.
Soil Science, 58:5 (1944).
The solution produced by soaking earthworm casts is similar to that produced by inorganic hydroponic salts. A solution made from soaking a 1:1 ratio of earthworm casts and water should yield a nutrient solution very similar in chemical make-up to the casts. A comparison between table 1 and table 2 will show that the only macro-nutrient that might be inadequate is nitrogen. Calcium is almost an order of magnitude higher than that of artificial solutions, but calcium in not toxic at these levels (Resh, 1987).
Earthworms also contribute to the soil by loosening it, creating tunnels and moving the soil from one place to another. Besides physical movement they break soil particles down (Darwin, 1897), aid in aeration (Edwards & Lofty, 1972) and movement of nutrients from lower in the soil strata to the surface (Darwin, 1897) where rain (watering!) will wash many nutrients to the plant's roots. Thus all soils in Nauvik that are capable of supporting earthworms will be stocked with them.
Table 2. Properties of artificial hydroponics solutions.
Derived from: Resh, Howard M. (1987). Hydroponic
Food Production. Woodbridge Press Publishing
Company, Santa Barbara, CA.
Like most animals earthworms accumulate toxins. This could pose serious hazards to the human inhabitant(s) of Nauvik if toxins are present in the environment. Even if the human(s) weren't eating earthworms toxins can move up the food chain, often gaining in concentration as they do. Thus chickens would likely have a higher concentration than that of the earthworms, as would the fish.
Very few of all the possible toxins have been looked at with respect to earthworms. Two industrially important toxins (and hence likely to be present in Nauvik) are lead and polychlorinate biphenyls (PCBs). These two toxins represent the heavy metal toxins and the organic toxins, and though earthworms reactions may differ within each group looking at these will give us an idea of what these toxins do in earthworms.
Sewage sludge is used as a fertilizer in Switzerland, and this sludge has concentrated PCBs (compared to the environment). Use of this sludge as fertilizer allows comparison between earthworm populations exposed to elevated concentrations of PCBs, and those in fields that weren't fertilized with sludge. Results of a study done by Kreis et al (1987) show that earthworms are, as a whole, more contaminated than the soils they inhabit. This concentrating of PCBs continues up the food chain. Thus, while the contaminant in the soil may not be deleterious, by the time the toxin works up the food chain to man it may be present in dangerous concentrations.
Lead is a common element in modern manufacturing. Lead solder, though now outlawed (Jones, 1990), is common in water pipes. Lead is a key component of many electrical appliances, lights, dehumidifiers, and many a other industrial items present in Nauvik. Since lead will be so common in Nauvik it will be critical to monitor for contamination. This monitoring will be crucial in the earthworm habitats, for earthworms will transfer lead to higher tropic levels, though lead concentrations in earthworms will usually remain below that of soil concentrations (Morgan & Morgan, 1988).
The two examples of toxins presented show the necessity of careful control of potential toxins. Any release of dangerous elements or chemicals into Nauvik' environment is likely to end up being consumed by the human(s).
Earthworms feeding on the entire spectrum of Nauvik's harvest may prove a viable method for monitoring toxic build-up. Occupying a key position in regard to the transfer of toxins to higher trophic levels (Kreis et al, 1987) earthworms are a good biological indicator of contamination (Bouche, 1984).
The primary function of the earthworm in Nauvik is to capture energy that would otherwise be used by microbes and put it back on a pathway that can be used by human(s). This 'energy' enters the earthworm niche in many forms. It can be ineatable remnants of animals, feces, plant matter, microbes and any other organic waste Nauvik generates. The energy thus captured is passed on to higher tropic levels by feeding the fish and chickens, who in turn feed the human(s).
Feces are a by-product of most animal's digestion process. They are generally composed of bacteria, fiber, minerals and organic compounds which couldn't be digested. Earthworms thrive on this, using the energy present to create body tissue and releasing many of the nutrients that were bound in the feces. This process, with sufficient numbers of earthworms is completely odorless. Indeed I have an experiment that I have been running since the middle of November in which I buried feces in a tray of earthworms and compost--and that tray is in my bedroom!! Thus earthworms are the idea answer to feces 'disposal'.
Earthworms daily produce casts equal to their weight. Though they will frequently re-consume their casts (Minnich, 1977) large amounts of high-quality soil that can be produced by a few earthworm growth chambers. These casts can be used directly as soil medium, as a fertilizer or as a means to make a hydroponics solution. Thus earthworm casts are expected to provide a significant proportion of Nauvik' crop nutrient needs.
We can see that Nauvik will need a healthy earthworm population. Since waste production for Nauvik has yet to be determined the population required to break that waste down can't be determined. It is expected that a minimum of 75,000 earthworms will be needed to yield 200/day. Since the fish and chickens are expected to need at least this many for supplemental feeding (their main diet being vegetarian) it is hoped that Nauvik will be capable of producing sufficient organic by-products to support a minimum of 75,000 earthworms.
Zachmann, J. E. and D. R. Linden (1989). Earthworm Effects on Corn Residue Breakdown and Infiltration. Soil Sci. Soc. Am. J., vol. 53. pp 1846-1849.