WQM: 9.22.23 – Conditions in the Severn River Offer A Puzzling Story

Published: September 23, 2023

An Odd Mix in the Severn – Great Oxygen, Poor Clarity

Water Quality Is Excellent – In Some Areas

Some areas of the Severn River last week enjoyed better than normal levels of dissolved oxygen (DO) and consistently high salinity levels. 

The best news is in the area between the Rt. 50 and USNA Bridges, which is home to our five oyster restoration reefs. This area enjoys a mix that is perfect for oyster spawning – warm water, oxygen levels greater than 5 mg/L and salinity levels greater than 10 parts per thousand (ppt). 

That’s why our new Chesapeake Conservation Corps member, Grace Weeks, is smiling in the above picture. She’s pointing to conditions she recorded Sept. 20 right on the bottom of the river that is home to our Manresa oyster restoration reef. At 4 meters depth, water is a toasty 24.0 degrees Celsius, oxygen is 5.72 mg/L and salinity is a whopping 12.11 ppt!  

Yet in other areas, our water quality monitoring (WQM) teams find some pesky hypoxic oxygen conditions (aka “dead zones”) where water contains less than 2 mg/L of dissolved oxygen (DO). 

For example, our Round Bay North monitoring station consistently shows low oxygen levels that can suffocate fish and crabs. This hypoxic area covers the bottom 1/3 of the water column. See the data sheet below.  Despite this, there’s plenty of oxygen on the top 2/3 of the water column. This phenomenon of good and bad oxygen layers is known as “hypoxic squeezing,” which forces fish to concentrate near the surface where the water is too warm for their comfort.

The other bad news is the increasing murkiness of the river, especially in the areas near the mouth of the Severn. In Meredith Creek and Lake Ogleton on Sept. 22, our clarity readings were downright horrible. In Meredith Creek clarity was down to 0.33 m and 0.42 m. Clarity readings in Lake Ogleton were 0.30 m, 0.37 and 0.33 m. Not good. The Chesapeake Bay Program gives a failing score of F to any clarity reading of less than 0.60 m.  

The murkiness is due to a spike in algae activity, which is fueled by the nitrogen pollution in stormwater runoff. That nitrogen is junk food for algae and their population explodes when they feast on the nitrogen in warm water on sunny days. 

Special thanks to Delaplaine Foundation for their support that enables SRA to manage ’our extensive water quality monitoring program. Our teams visit 52 stations throughout the entire waterway – every week.