Severn Riverkeeper Summer Water Quality Monitoring Program 2012 Weekly Dissolved Oxygen Results—Mainstem Stations Pierre Henkart, PhD
Severn mainstem monitoring stationsSR7 – Our shallow N SR6 – Our Severn Narrows station with a depth of 5 meters. We generally notice fresher water near the surface, the influence of the(~1.5m) upper fresh Severn Run entering to the northeast. Summer bottom anoxiastation with is pronounced here.fresher water fromnearby SevernRun, especially SR5 – Our mid Round Bay station with a depth of 7after rains. meters. Bottom anoxia usually sets in by early July, andTurbidity is high. in the absence of storms, persists until September.RBN – Our “Round Bay North” SR3 – Our “Joyce” station in a deep holestation, with a typical Severn depth south of Joyce Point, at a depth of 12-13of ~ 7 meters. This is the heart of meters (~40 feet). There are a few otherthe Severn summer dead zone. deep spots like this in the Severn. RBS – Our “Round Bay South” SR1 – Our “USNA” station in station, which is interesting because the mid-channel opposite College bottom sometimes gets anoxic in the Creek, with a depth of 7 meters summer. It has a typical Severn depth of ~ 7 meters. SR2 – Our “Rte 50 bridge” station with a depth of 7 meters. We get to watch the peregrine falcons that nest on the bridge. We also get to compare our data with the The distance monthly MD DNR monitoring data (their station WT7.1) Annapolis from SR0 to SR7: on the “Eyes on the Bay” website. 18 km = 11 miles SR0 – Our “near Chesapeake” station south of Greenbury Point, in the channel, with a depth of 6 meters (a bit less than 20 ft). SR0 is near the NOAA “Annapolis” buoy providing great continuous on-line water quality data at 1 meter depth.
Our oxygen depth profiles show habitat stress Dissolved We show our water quality data as depth profile bar graphs. You can oxygen, think of yourself as a scuba diver entering the water from our monitoring 0 mg/liter 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 >5 the longer the bar, the deeper the water. The water quality is color 1 coded, and our graphs show oxygen levels since that has been our principal focus. The colors represent oxygen concentrations needed by 2 3-5 different marine organisms. The Severn’s large active fish need at least 5Depth, meters 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 3 column has higher oxygen. In most cases, water near the surface has 1-3 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 4 water with less than three mg/liter dissolved oxygen. They will utilize .2-1 both the green and yellow portions of the water column. Benthic organisms that live in or on the bottom (oysters, worms, etc) are adapted 5 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 <.2 below 1 mg/liter (red) are stressful to tough benthic organisms, even for 6 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.