Saturday, September 17, 2016

Drought Streamflow

OCTOBER 1 UPDATE: after two inches of rain in the last two days, Salisbury Brook has risen dramatically!  (Two photos at the very bottom of the post.)  I am astonished: since you seldom see surface runoff--except on pavement--I assumed nearly all the rain would sink into the soil and begin the long process of restoring soil moisture.  

I expect two inches might penetrate half a foot or so into dry soil on level ground, reaching most plant roots.

Instead, a good deal of rain has almost directly entered this brook (or others, or the sewers)The bad news: by running off rather than sinking in, most of this water will be lost from the system.  And eastern Massachusetts is still about 10 inches below normal rainfall for the year.

Original post of September 17:
A news report a couple of weeks ago said the Ipswich River in the northeast part of Mass was at its lowest level since records began, back in the 1930s.  Meanwhile, the Boston Globe yesterday reported that half of Massachusetts is now in extreme drought (an official designation--the second worst possible), and rainfall in the Boston area is 9.5 inches below normal for the year, and 18.5 inches below normal since January, 2015.  

I have been taking photos of a bit of Salisbury Brook here in Brockton every so often this year.  Here are photos early and late in the year.  

 February 2

late February

March 11

By chance, I took no photos for more than three months, not having planned a complete chronicle.

 July 29

 August 5

August 13

 August 29

 Sept 3

  September 17

Water still trickles among stones it once splashed over, but the flow is only perceptible if you stop and look awhile.
Of course, there is regular seasonal variation in streamflow, but around here it shouldn't be too extreme: rainfall is typically pretty even throughout.  Here is a climate diagram for nearby Taunton to contrast with the current drought.  Climate diagrams* show average monthly rainfall (thicker line, millimeter scale on right) and temperature (thinner line, Celsius temperatures on left) throughout the year (tic marks at bottom).  The scales are made to line up so that when the two lines cross ("temperature higher than rainfall"), water evaporates more quickly than it is replaced by rain--producing dry conditions.  As you can see, that rarely happens around here--even though rainfall dips in summer.

*Climate Diagram World Atlas

 Late morning, Saturday, October 1, after 2 inches of rain in two days.

Saturday, September 3, 2016


I came across this little  tan leaved branch on a trail near Ponkapoag Pond, Blue Hill Reservation.  The dead, dried leaves mark it as an American chestnut (Castanea dentata).  If you walk these trails you will meet them often; always small, they are remnants of the great chestnuts of old. 

Until a century ago, American Chestnut was a major--sometimes dominant--tree of eastern forests, reaching three feet in diameter and a hundred feet in height.  In about 1904 a new fungal disease--probably imported on Asiatic chestnut trees--appeared on American chestnuts in the New York Zoological Park, infecting and killing trees and spreading like wildfire.  Today the tree is all but extinct in its natural range, existing only as stump sprouts that the fungus kills back regularly.

The tree I saw may have died of the severe drought; it is too small to be targeted by the fungus--certainly something killed it in mid-season.  The little thing had sprouted from the base of a somewhat-larger tree (upright near center), likely killed three or four years ago by chestnut blight.

When chestnut trunks reach two or three inches in diameter the fungus enters through cracks in the bark.  The fungus girdles the trunk before creating the orange sporangia on the bark that spread the spores that reproduce it.  The trunk dies but the roots often survive to send up another sprout, however these sprouts almost never become mature enough to flower and set seed.  In a cruel irony, by hanging on these trees maintain the fungus population.  But even if the chestnuts died for good, red oak is able to host the fungus without suffering serious harm; we will likely never be rid of it. 

So these "ghost trees" have existed for a century in a sort of limbo, not completely dead nor entirely alive.  The rotted stump at the base (below) must have been dead about a century: it could not have reached that diameter after the fungus arrived in the area.  Now, after a hundred years of stubbornness, this tree might finally be dead.*  

Efforts to breed resistant trees have been underway for decades; perhaps newer recombinant DNA technology will finally bring the tree back.

  Chestnut blight fungus (Cryphonectria parasitica aka Endothia parasitica) has almost entirely wiped out mature chestnuts from their natural range.  Only stump sprouts remain.

*Or have I just noticed in the photo a new sprout with a couple of long, dark green, saw-toothed chestnut leaves between stump and shoots?