Losing Native Naivety

Our walk to the Elms Environmental Education Center's pond last week was preceded by a slide talk about the importance of using native plants in watershed protection projects. The point was made by +Kurt Reitz, our gracious host, that the reason we want native plants is for the insects.

Photo by Tim Hynes

It takes a while to pull that thread, but what it amounts to is that plants feed insects and insects feed animals and native plants are evolutionarily adapted to the food chain of their area.

I become a little indifferent to the native plant appeals when I recall that I have a food chain that currently doesn't rely on foraging and hunting. In the expectation that this could change rather quickly, I am endeavoring to establish a food forest around my home, but not strictly using natives. Planting natives is a very helpful environmental practice, but environmentmental restoration still takes a back-seat to survival. However, as our fossil-fueled supply chain falters, rejoining the local food chain may become essential to survival.

The more I garden, the more I take pleasure in growing ornamentals. Yet, future reliance on agroforestry for a multitude of resources that will no longer be derived from or made using fossil fuels deters me from planting lots of native ornamentals mainly for environmental preservation.

There are some edible natives, however, that deserve a place in my forest garden. These include: Paw-paw, persimmon, gooseberry, black raspberry, blackberry, blueberry, and elderberry. I already have everything but the first and last of these. They aren't all that I wish to grow in the way of edibles, so non-natives will be in the mix. Then there are the less edible plants that provide other key functions in support of cultivated trees, including the insectary role. The time it takes to harvest, preserve, and consume or distribute the perennial bounty will ultimately determine where my forest farming ends and ornamental gardening begins.

Oh, How the Phragmites Have Fallen

In our Watershed Stewards Academy class visit to Elms Environmental Education Center, our host, +Kurt Reitz showed us a freshwater pond that was walled in halfway around with deep stands of phragmites australis (the common reed), an invasive shoreline plant so tenacious that it requires herculean efforts to eradicate it. Typically, eradication requires cutting, spraying with glyphosate, burning the stubble, and repeat treatments a few years later. The toil and trouble associated with this regimen deters most attempts at restoration, so owners and environmentalists have essentially acceded to allowing phragmites to rob our ecosystems of their natural biodiversity.

These tenacious phragmites will weather this storm, no problem (Photo by Kurt Reitz)

The way phragmites dries up in the fall makes it a tempting target for conversion to biochar. Controlled open burns of phragmites risk turning into conflagrations that could touch off fires in surrounding areas. I wonder, though, if it may be feasible to avoid much of the cutting and spraying and make very hot fires out of phragmites stands by applying traditional charcoal-farming techniques.

Biochar could be made with phragmites similar to the Ankara system. One of the problems we have in the Chesapeake Bay area is that phragmites grows out of dredging deposits, but by using dredging spoils as the covering material for the Ankara-style burn, we would be able to kill the in situ phragmites and the seeds and rhizomes in the dredging material, as well. Open burning has been an ineffective way to eliminate phragmites since the deep rhizomes often survive and come back with a vengeance. With the Ankara approach, heat is concentrated and conducted down deeper into the soil, so there is a better chance that the rhizomes would be killed.

For phragmites, the way to apply this approach might involve cutting three-foot strips about every 12 feet, flattening the reeds in the 12 foot rows and adding the cut pieces, digging out the rhizome-filled soil from the cut areas and spreading it on the flattened reeds, adding dredging spoils (from nearby projects) to create a casing over the whole biomass, making vent holes at the ends and in the top of the ridge as necessary to maintain some air flow, lighting the biomass at both ends and keeping it going by opening or closing air vents while it cooks for several days. After it cools, it can be tilled and planted with winter hardy native plants.

Potential advantages of this approach are its economy, rapidity, sequestering of carbon, creation of a biochar nutrient filter along the shoreline, and improved soil properties for replanting.

Bay Burps

Laura Lapham, et. al., authors of the paper referenced in my previous post state that the methane bubbles suspected to be lurking under the pycnocline are 85% oxidized by the time the layers of the Chesapeake Bay mix in autumn. This leaves 15% of the methane free to circulate into the atmosphere when the final mixing occurs.

Termed "fall turnover," this mixing sometimes occurs as quickly as overnight when air temperatures drop and wind increases wave action. A quick fall turnover, like a tropical storm surge, can result in sudden bursts of methane from the bay. At 15% of the inventory, the amount available is only about half of the hypothetical storm release noted previously. That is only 23 Aliso Canyon incidents spread around the bay, happening overnight (vice 100 days).

Turnover usually does not occur all at once everywhere in the bay, so chances of this much of a release are small, but with wild weather swings from climate change, it is more likely that all the local turnovers will still add up to something close to turnover en masse.

Measurements of surface methane releases showed that there is significant flux into the atmosphere from the bay even when there is no major storm or turnover. What my educated guess adds up to is about (23 + 47) = 70 Aliso Canyon equivalents every 3 years or, on average, 7/3 Tg = 2.33 Tg CH4 annually contributed by the Chesapeake Bay, which is about 6 times the amount spewed annually from the city of Los Angeles.

We've long known that estuaries emit methane disproportionately more than their relative geographic extents, but the inclusion of heretofore unnoticed sub-pycnocline burps makes the Chesapeake Bay, and other polluted water bodies with similar methane-storing mechanisms, even larger concerns in the fight against global warming.

Photo by Jason R. Berg

Saving the Bay = Saving the Planet

In addition to sequestering carbon, biochar's capacity for reducing nutrient leaching from cultivated land makes it an especially valuable weapon against global warming around estuaries like the Chesapeake Bay. Other measures are necessary, but in terms of longevity, they are band-aids compared to biochar.  Biochar can throw global warming a one-two punch when prodigiously applied in the Chesapeake's watershed. The carbon sequestration aspect is pretty straightforward, but the nutrient leaching/global warming connection needs more explanation.

In spring and summer, the Chesapeake Bay, due to seasonal changes in its upper and lower water density profiles, is a storehouse of methane-generating detritus in its cold, dense, oxygen-starved lower strata. As hurricane season swings into full gear in mid-summer, a strong storm can bring about the phenomenon know as wind set-up which pushes water level higher on the western shore of the bay and an upwelling of water from the lower layer, pulling methane from the underneath the pycnocline and bringing it to the surface.

From Chesapeake Bay: Introduction to an Ecosystem, Chesapeake Bay Foundation, 1995.

Research by Laura Lapham, Lauren Gelesh, Kathleen Marshall, and +William Boicourt published in February under the title "Methane concentrations increase in bottom waters during summertime anoxia in the highly eutrophic estuary, Chesapeake Bay, U.S.A.", hypothesizes that the methane in the sediment begins to escape into the water and collects under the pycnocline where conditions are anoxic enough to prevent it from oxidizing into more benign substances. When a storm comes through before the methane has a chance to mix with upper layers in the cooling autumn, the sudden upwelling of this methane sends a portion of it into the atmosphere.

We already know that estuaries throughout the world contribute something like 3% of total methane to the atmosphere without the large pulses just described. In such an event, however, the Chesapeake Bay (the U.S.A.'s largest estuary) could almost double that figure, were all the sub-pycnocline gas bubbles to escape. Hurricanes and tropical storms have impacted my Maryland home near the Bay about once every three years, of late. It is worth considering that major storms in late summer, when methane buildup is at its peak, may cause methane bursts of this magnitude.

To grasp the magnitude of such an event, let's say just one-third of the Bay's methane inventory were to bubble out during a major storm in mid-August. That would be 47 times the amount released over a 100 day period in the Aliso Canyon natural gas leak!  (Aliso Canyon incident emitted 0.1 Tg. - the largest such leak ever in the U.S.  Based on annual total worldwide CH4 emissions of 469 Tg, a 1% increase from Chesapeake Bay would be 4.7 Tg.)

We cannot shift the burden of climate change to ocean estuaries and blame the Chesapeake Bay for emitting all these greenhouse gases. These episodes would not occur if the Chesapeake Bay were in a healthy condition in which the lower strata maintained adequate oxygen year-round. This is anthropogenic and the cause is mainly excess nutrients and uncontrolled runoff. The tendency of storm intensity to increase as global temperatures warm also gives this punishing sequence of events a positive feedback quality. To stop it, we need to not only think about how to reduce the concentration of atmospheric CO2, but also how to clean up the water draining into our major estuaries.

I'll Take Biochar Dressing on the Side

In addition to top-dressing, side-dressing with biochar looks like a labor-saving method of application. Not only is it easier, but the resulting black mulch will enhance the appearance of gardens like mine. I've been using free shredded wood mulch on the paths between my garden beds. With cardboard underneath, a thick mulch layer helps keep weeds to a minimum and feeds the underlying soil as it breaks down. The same can be said of biochar, but there are several additional advantages. (1) Biochar will last much longer than decayed wood chips. (2) Walking paths suffer from compaction, making them less hospitable to roots. Walking on the biochar grinds it down. Biochar particles contain pore space that will compensate for compaction, aerating the soil as they are leached in over time. Paths that are less compacted (containing more air) are more inviting to roots and mycelia. If the roots don't reach that far, mycorrhizae can perform their horizontal drilling trick, expanding the resources available to the plants. (3) Charred wood spread all over is more reminiscent of a forest fire, which is a kick-starter for new growth. (4) More carbon sequestration. (5) It looks more attractive and doesn't fade out the way wood chips do. (6) It's a provocative way to make neighboring gardeners interested in biochar.

The beginning of my biochar mulched paths project. 

This method will have me applying biochar to paths at a greater rate than most of my garden beds, but they will eventually catch up, due to repeated dosing with biochar-infused compost. Biochar application rates over 150 t/ha have been shown to be excessive. For 10 cm of soil, that comes out to almost 50% biochar, which I take to be the target for my gardens. Most gardeners and farmers won't shoot that high, because diminishing returns come into play around 10 t/ha, but I should be able to make this much biochar, and diminishing returns or not, I hope to see some marginal improvement for 10 successive years all the way up to 50% concentration by using biochar on both my beds and paths. Once applications are maxed out, the infiltration of biochar on the paths will continue to promise some improvement for years afterward.

Sunshine Insurance

Composting biochar and digging it into the soil before planting is a best practice that needn't be followed in all situations. When mulch is needed, especially for warmth-loving plants, biochar could be a better choice than straw or other common dressings. As I pointed out in my previous post, this mimicking of a natural fire's residue gives the biochar an opportunity to become somewhat charged and inoculated while holding moisture in the ground.

My pepper plants basking in the heat from a top-dressing of biochar and black plastic

Plants need three things to exist: Nutrients, Water, and a suitable atmosphere that contains Light. Charging biochar with nutrients and getting it wet make it an excellent buffer for the first two needs. For the sake of completeness, I've been trying to imagine how biochar could also buffer a plant's need for light, allowing it to make sugar without total reliance on photosynthesis. If it does this, it would be by use of an alternative energy source, e.g. electric current.

The discharge of electrical currents around plants is touted by some to aid plants in many ways, including improvement of their capacity for photosynthesis. Or perhaps, rather than using light in conjunction with chlorophyll, plants can use electricity through their roots to power the transformation of CO2 and water into sugar.

Biochar has a quasi-graphene micro-crystalline structure that could make it able to generate photoelectrons by sunlight impingement, which it might then store capacitively until its conductivity is raised by filling with rainwater, allowing the electrons to discharge into the ground. Alternatively, rain could deposit cations on the graphene-like micro-crystals to trigger current. In these ways, biochar top-dressings might act as a photosynthesis buffer on rainy days when sunlight is lacking.

These conjectures enable me to maintain the notion that biochar can provide assurance of plants' three essential inputs. If biochar provides sufficient assurance, then maybe the government will see fit someday to subsidize farmers with biochar instead of crop insurance.

Now, (speaking of assurance) I doubt that exposure to the elements is going to fully prepare biochar for incorporation into the soil over a single season. Using a 50-50 mix of compost and biochar as a top-dressing, however, might be just the ticket.

Making Biochar, Rain or Shine

My small scale biochar production cycle is weather-driven. When rain is infrequent, I make char while the sun shines and pour out the new biochar into a framed area dubbed my "biochar patch." Quite a bit can accumulate before rain comes to rinse the biochar and fill up its macropores, making it ready for the next step. I like to allow no more than a day to pass after a good rain before I crush the moistened biochar with a tamper and screen it through a salvaged patio tabletop into a bin. Dry biochar makes too much hazardous dust when crushing and sifting, so rain is welcome, though a couple of dry days are then needed for my feedstock to dry again. This gives me time to split more wood in preparation for the next round. 

My biochar patch with screening tools

Screened biochar

The admittedly tedious process of sifting biochar by hand has the advantage that any remaining torrefied pieces can be culled and sent back for more charring. Torrefied wood, i.e. pieces not charred completely through, inhibits plant growth, and does not belong in the final product. A less laborious (but more polluting) method of granulation is pouring damp biochar into a chipper/shredder. Occassionaly, I do this and then purge the machine by shredding leaves or sticks to prevent the residual biochar from corroding the metal and to avoid having a black dust cloud emerge when the machine is started up the next time. I've seen others use gas powered portable blower vacs to grind up biochar. (My electric blower may do the trick with dry biochar - something to try out.) The output from my shredder is a gelatinous concentration of biochar particles that needs to be mixed well with the soil or compost so that it becomes aerobic once again.

My biochar patch serves as a unique area of water retention for the garden that I am working to turn into something of a tropical paradise. Aside from getting free water to rinse and moisten the biochar, staying in rhythm with nature this way includes the benefit of a nitrogen charge whenever a new storm comes through. During lightning storms, some of the diatomic nitrogen (N2) that predominates in the atmosphere is ionized. These nitrogen-rich ions become entrained by raindrops that deposit it on the soil where it is mineralized into a form that plants can use and biochar can store as a slow-release fertilizer. If enough rain falls on biochar, I suppose it accumulates a sufficient charge of nitrogen to make it garden-ready.

Particles needn't be so fine as from a shredder when biochar is added to the soil. It helps earthworms to ingest them, but the larger (< 2 cm) particles that drop through the expanded metal screen used in a manual approach will break down from freeze-thaw cycles over time and the larger size doesn't reduce biochar's effectiveness in the meanwhile. Some situations are well suited to top-dressing with raw biochar in bulk form. Weathering eventually breaks up these unground particles, so they leach into the soil beneath. In the interim, they acquire nitrogen from above and pioneering microbes from below that make this labor-saving method of biochar application most economical. In my next post, I want to talk about one more reason top-dressing could be preferable to burying biochar.