Aerial and Field SAV Observations

Aerial and Field SAV Observations header image 2

Severn River (MD), 7/28 and 7/31/09 (with transects)

July 31st, 2009 by Peter Bergstrom · No Comments

I sampled SAV twice in one week on the Severn (quad 23), first by kayak on 7/28, launching in Brewer Pond at Sherwood Forest, surveying that tidal pond and a bit of the river shoreline outside it.  On 7/31 I worked with Severn Riverkeeper volunteers in the Riverkeeper’s boat to repeat the SAV transect sampling that I coordinated at the same 4 transects in 2007 and 2008.

The overall impression of both sampling events was that the main SAV species are delayed in growth and/or much reduced in abundance compared to 2007 and 2008.  Most of the redhead grass was in bloom or with seeds but none of the sago pondweed or widgeongrass had flowers or seeds, which is very unusual for late July in this region.

Sampling by kayak on 7/28, we found fairly dense but very shallow beds of redhead grass both inside Brewer Pond and along the mainstem just outside it, mixed in some places with moderate sago pondweed and small amounts of widgeongrass (see map).  The beds inside the pond were mostly 0.2-0.4 m deep, sampling a few hours before low tide, while those on the mainstem were a bit deeper, extending out to where it was 1.1-1.3 m deep.  Inside the pond we also found some small patches of Elodea or Ec (reported elsewhere in the Severn from Clements, Weems, and College Creeks, but not from this pond to my knowledge) and milfoil (Ms).  We expected to find mostly milfoil (or no SAV) as we paddled up the increasingly shallow long arm that runs southwest from the main pond, but the scattered small, shallow patches of SAV were all Ppf, Rm or Ppc, except one also had Ms.  The last few beds we found at the upper end of this arm were in water a few inches deep that felt like warm bath water.  Recent ground surveys showed that Zp, Ppf, and Ms were reported in Brewer Pond on the 2004 survey map, while the 2002 survey map reported Zp, Ppf, and Ms plus Ppc here.

We did quantitative SAV sampling along transects on the Severn with Pierre Henkart and other volunteers on 7/31, and the SAV abundance at the 4 transects (see map) was much lower than it was in 2008 or 2007.  See graphs; the 2009 total volume over all sites and species was only 13% of the mean total volume we found for 2007-2008.  (As in past years, we found only 3 species–Ppf, Ppc, and Rm–at these mainstem sites.)  Since the Severn had the best attainment of SAV goals among mesohaline SAV segments north of the Honga River last year, this does not bode well for the forthcoming results of the 2009 SAV survey in this region of the Bay.  The bed outside Asquith Creek (AC transect on the graph, southern tip of bed N4 in 2008) was where SAV was first mapped in the Severn in 1994, and it used to be several acres in size with very dense redhead grass to the surface at low tide.  Today we found only 2 shoots of redhead grass in the transect across part of that bed, and there was no visible flat water that would have indicated dense beds anywhere else on the shoal.  We did a spot check on 7/31 of one other Severn SAV bed (see map), the one outside Rays Pond just south of the bed outside Asquith, part of bed X4 in 2008.  We found some Ppf (redhead grass), but there also appeared to be much less here than there was in past years, with no visible flat water (it was not growing to the surface).

Photos from today show (1) measuring SAV volume with graduated cylinder by water displacement (the person in the water holds and moves boat–note nettle suit), and (2) one of the largest clumps of redhead grass we collected, at the Brewer Pond (BP) transect (not very large compared to past years).  The tongs we use for sampling (shown in this 2007 photo from South River sampling) are modified oyster tongs provided by MD DNR to watershed groups that year.

Tags: Announcements · SAV Observations

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