Severn Hypoxia 2012: The Edge

Severn Riverkeeper Summer Water Quality Monitoring Program

2012 Weekly Dissolved Oxygen Results—Creek and Edge Stations

Pierre Henkart, PhD

N

SC3 – Our “Saltworks Creek” station is located most of the way up Saltworks Creek, with a depth of about 3.5 meters (a bit over 10 ft). We see some influence of fresh water entering at the tidal head, but beaver dams have created a freshwater marsh upstream.

SC5 – This station is located most of the way up Brewer Creek, with a depth of about 3.5 meters (a bit over 10 ft). We speculate that restoration efforts in this watershed may have improved tidal water quality.

SC4 – Our “Chase Creek” station is located in one of the two branches of this tidal creek, not far from its mouth. We enjoy watching the nesting great blue herons in the treetops at the entrance to this creek.

SC1 – Our “Weems Creek” station is located between the two bridges over the creek., with a depth of 3.5 meters (a bit over 10 ft). The tidal portion of Weems Creek ends at Route 50, and its entire watershed is heavily impacted by development.

SC6 – Asquith Creek is our most interesting creek. Surrounded by forested hills with scattered homes, its watershed is quite small, with minimal expected local nutrient input. But its entrance has a shallow bar over it, and boats enter via a long channel near the adjacent shore, so it’s poorly flushed. Our 4.5 meter deep station typically shows bottom anoxia all summer. Cold salty water left over from the winter forms a layer at the bottom, retarding vertical mixing, but as this dissipates during the summer, anoxia persists.

SR4 – This is our “Edge of Round Bay” site near the end of the Sherwood Forest Pier. This station is ~5 meters deep, and is close to a robust bed of submerged aquatic vegetation and the entrance to Brewer Pond

RBW – This station is in a corner of Round Bay betewen St. Helena Island and the steep cliffs along the shore of the beautifully forested “Green Cathedral” tract. It’s depth is ~6 meters, typical of most of Round Bay, and we have found this station shows the same summer bottom anoxia here as in upper Round Bay.

Severn edge monitoring sites, off the mainstem

Our oxygen depth profiles show habitat stress

Dissolvedoxygen,mg/liter

We show our water quality data as depth profile bar graphs. You can think of yourself as a scuba diver entering the water from our monitoring boat and then heading straight for the bottom. As you go down oxygen levels will change. We’ve plotted the depth in a downward direction, so the longer the bar, the deeper the water. The water quality is color coded, and our graphs show oxygen levels since that has been our principal focus. The colors represent oxygen concentrations needed by different marine organisms. The Severn’s large active fish need at least 5 mg/liter oxygen, and levels greater than that are colored green. Since most oxygen in the water comes from the air, the top of the water column has higher oxygen. In most cases, water near the surface has more than 5 mg/liter, so the tops of most bars are green. Smaller fish like white perch are adapted to live with lower oxygen levels, but will avoid water with less than three mg/liter dissolved oxygen. They will utilize both the green and yellow portions of the water column. Benthic organisms that live in or on the bottom (oysters, worms, etc) are adapted to yet lower oxygen levels down to 1 mg/liter, and they will tolerate bottom water in the orange 1-3 mg/liter oxygen range. Oxygen levels below 1 mg/liter (red) are stressful to tough benthic organisms, even for short durations. Truly anoxic conditions exist below 0.2 mg/liter oxygen, where only anaerobic bacteria can live. This anoxic water will suffocate even the toughest multicellular organisms quickly.

1

0

2

3

4

5

6

Dep

th, m

eter

s

>5

3-5

1-3

.2-1

<.2

D

%

Severn River Dissolved Oxygen, May 23, 2012

Non-mainstem stations

N

1 2 3 40.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

<.2.2-11-33-5>5De

pth,

met

ers

Dissolved oxygenmg/liter

Rte 50

DSevern River Dissolved Oxygen, May 30, 2012

1 2 3 4 5 6 70

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers



NRte 50

DSevern River Dissolved Oxygen, June 6, 2012


1 2 3 4 5 60

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers


NRte 50



1 2 3 4 5 60

1

2

3

4

5

6

<.2.2-11-33-5>5De

pth,

met

ers


NRte 50




N

1 2 3 4 5 6 70

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers

Rte 50

DSevern River Dissolved Oxygen, July 4, 2012



N

1 2 30

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers

Rte 50




NRte 50

1 2 3 4 5 6 70

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers

DSevern River Dissolved Oxygen, August 1, 2012



NRte 50

1 2 3 4 5 6 70

1

2

3

4

5

6

7

8

<.2.2-11-33-5>5De

pth,

met

ers




NRte 50

1 2 3 4 5 60

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers




NRte 50

1 2 3 4 5 6 70

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers




NRte 50

1 2 3 4 50

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers

DSevern River Dissolved Oxygen, September 13, 2012



NRte 50

1 2 3 4 50

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers

DSevern River Dissolved Oxygen, September 20, 2012



NRte 50

1 2 3 4 5 60

1

2

3

4

5

6

7

<.2.2-11-33-5>5De

pth,

met

ers

Severn Hypoxia 2012: The Edge

Sports

Transcript of Severn Hypoxia 2012: The Edge