Paying the Piper

The amount of sediment that is allowed to runoff into the Chesapeake Bay is forty times by weight the amount of nitrogen and 500 times the amount of phosphorus allowed. Now that the Conowingo Dam is silted to the point that scoured sediment is washing through, it will become harder to meet the decreasing sediment limits without dredging. However, the real problem is phosphorus since the sediment contains much more than a 1:500 ratio. Who will pay for the dredging?

Exelon, which operates the power generating station at Conowingo, will benefit from dredging due to less wear and tear on their hydraulic turbines and improved output. Environmentalists have estimated that Exelon could afford to fund dredging at $27 to $44 million per year out of revenues from selling hydroelectricity.  Yet, Exelon did not cause the problem. The dam didn't cause the sediment to flow into the river. It was allowed to run off by poor land management practices. Some silting does occur naturally, but the lack of attention to stormwater management and soil conservation is largely to blame for the rate of buildup. Maryland is taking on the job of dredging, but Pennsylvania should be the ones paying for it. Pennsylvania loses twice as much sediment to the Chesapeake Bay watershed as Maryland. They are not on track to meet their 2017 TMDL target for sediment and have not even committed to doing so.

Just the 25,000 cu. yd. dredging (representing 1% of the total targeted for removal) in the pending demonstration project entails removing 80 million lbs. of sediment. To stop the buildup in Conowingo Reservoir and carryover into the bay, removal would have to proceed at nearly 30 times that rate, i.e. the annual total sediment flow for Pennsylvania (2.4 billion lbs). Should dredging stop after reaching the target amount, the reservoir will refill in a few years.

Pennsylvania cannot be expected to eliminate all of their sediment runoff. Their target is 1.945 billion lbs. of sediment flow per year by 2025, which would equate to about a 55 million lb. per year annual reduction. This means that interstate nutrient trading would not begin to pay for the 8 billion lbs. of  dredging necessary to correct the problem.

Once we dredge Conowingo Reservoir (and I'm afraid Marylanders will be stuck with the bill) , there are two other dams upstream that have the same problem. Pennsylvania should work on those, too. Exelon's bid for a new 46-year lease to run the hydroelectric station should be rejected unless they offer to foot the dredging bills (not to exceed $44 million/yr) as long as they hold the lease. If they do not, as soon as dredging is substantially complete, perhaps we should prepare to dismantle each of these dams. It would ultimately restore the lower Susquehanna River and ensure that we do not have to keep paying the piper.

Anchara

If phragmites australis were to be charred under a cover of dredge spoils, the affected area could be immediately nitrogen-deficient due to the loss of N gas in the exhaust. Dredge material from upstream of the Conowingo Dam is nitrogen-rich, however, and the underlying soil would also contain great amounts of nitrogen which could wash up into the biochar. The heat of charring could even create microsites of char from the organic matter mixed in with the dredge spoils.

Nitrogen that was held in the reeds and added organic matter could be entrapped by the sediment casing, making it available when subsequent planting takes place (as with ankara practiced in Cameroon). Nitrogen that is trapped in the sediment cover or char due to an increase of reactive sites on clay or biochar could be sequestered, avoiding the greenhouse gas release or eutrophication that would accompany simply dumping of the spoils on the shore. Inoculating seedling roots with mycorrhizal fungi would be a very helpful step. If native legumes or other nitrogen-fixing species can be found, planting their seedlings preceded by a dip in the proper bacterial inoculum could be all it takes to jump start the nitrogen cycle after charring. Plants that are easy to grow would be necessary in any case, since the soil would be otherwise devoid of microbes. The roots should be placed no deeper than the baked sediment layer, though the underlying baked sediment should be broken up to allow the roots to grow into the charred phragmites layer.

One currently followed method of phragmites eradication is described in this brochure and a more interesting slideshow. It may be less expensive than my method, but it is potentially more harmful to the environment (glyphosate) and takes two years to reach the point of replanting or initial restoration. My method can be performed in a matter of weeks and it sequesters carbon while recycling dredge spoils. Since applying glyphosate must be done in a way that avoids overspray and contacts all the targeted foliage, current methods may also be more labor intensive (adding expense) and pose a health hazard to the exterminators.

Another common method of eradicating phragmites involves burning in addition to herbicides. This video shows what a good tinder phragmites is. My covered method would be more controlled and hopefully much less smoky.

Demonstration Projects

Though installing rock dams at the outfalls to my local lake will require a lot of preparing, planning, organizing, and coordinating, my higher ambition involves another dam, also affecting the Chesapeake Bay, but to a much greater extent. Tomorrow the Maryland Environmental Service (MES) will begin evaluating bids for the contract competition to dredge 25,000 cubic yards of sediment from the Maryland portion of the Susquehanna River upstream of the Conowingo Dam and recycling the dredge spoils in an innovative fashion. The idea is to select a company that offers a promising plan for disposal of 1,000 times this much sediment by using this contract as a demonstration of how it can be accomplished on a small scale.

Conowingo Dam photo by Aaron Harrington

I am not in the dredging business, but the amount of dredge spoils requiring disposal from this dam  could be an ideal opportunity for me to try my idea for phragmites eradication. A successful small scale grant-funded demonstration would be a good way to gain the interest of MES and whichever compan(ies) they eventually award contract(s) totalling $3 billion. Before I even seek a grant,  backyard experimentation with charring under earth and/or sediment cover would be a good first step. Once I finish building my cob oven, I will be able to practice a few techniques, but will eventually want to replicate charring of dry grasses using a configuration like that in my eradication concept.

On top of that, following a year of training and practice, I am happy to report that tonight I got my certificate naming me a Master Watershed Steward. And I got the t-shirt. That oughta make 'em sit up and pay attention to my ideas on saving the bay.