Blame the High Water!

That's the word from local VDGIF biologist Chad Boyce in answer to my question earlier today about what caused the current low-oxygen levels on our waterways.

As Chad (right) explained it, that stretch of high water we had around here recently pushed far back into areas that depleted the oxygen (specifically, "dissolved oxygen" or DO) content, and when the water level retreated, all that oxygen-depleted water drained back into the main body and its tributaries.

In response, local anglers are being asked to forego their regularly scheduled tournaments at both Bob's Fishing Hole and West Neck Marina for the time being. "We don't want to stress the fish any more than they already are," said Chad in our phone conversation today. Some dead ones already have been turning up, and there likely will be more.

What will it take to remedy this situation? As Chad noted, "Some days with not-so-hot water, certainly no high water, and, ideally, days without much rain." In other words, weather like we haven't seen around here for a fair spell now.

According to information I found online, the generally accepted minimum amount of DO required to support a large population of various fishes is from 4 to 5 mg/L. When the DO drops below 3 mg/L, even hardy fish will die. Following is a sampling of how various fish species differ in their DO requirements (e.g., lowest DO at which they survived for 24 hours in summer):

Northern Pike - 6.0 mg/L

Black Bass - 5.5 mg/L

Common Sunfish - 4.2 mg/L

Yellow Perch - 4.2 mg/L

Black Bullhead - 3.3 mg/L

For the sake of comparison, consider that Chad obtained the following readings in his travels around the local area today: surface DO - 1.18 and just off the the bottom - 0.8. "Both of these are well below the desirable range for most all game fish," he noted. "Having said that, the juvenile fish generally have a much higher tolerance for low-oxygen conditions."

As explained in a paper written by the U.S. Geological Survey (USGS), "You can't tell by looking at water that there is oxygen in it (unless you remember the chemical makeup of a water molecule is hydrogen and oxygen). But, if you look at a closed bottle of a soft drink, you don't see the carbon dioxide dissolved in that either, until you shake it up and open the top. The oxygen dissolved in lakes, rivers and oceans is crucial for the organisms and creatures living in them. As the amount of dissolved oxygen drops below normal levels in water bodies, the water quality is harmed and, if not rectified, creatures begin to die off.

"Although water molecules contain an oxygen atom, this oxygen is not what is needed by aquatic organisms living in natural waters. A small amount of oxygen, up to about 10 molecules of oxygen per million of water, is actually dissolved in water. Oxygen enters a stream mainly from the atmosphere and, in areas where groundwater discharge into streams is a large portion of streamflow, from groundwater discharge. This dissolved oxygen is breathed by fish and zooplankton and is needed by them to survive.

"Rapidly moving water, such as a mountain stream or large river, tends to contain a lot of dissolved oxygen, whereas stagnant water contains less. Bacteria in water can consume oxygen as organic matter decays. Thus, excess organic material in lakes and rivers can cause eutrophic conditions, which is an oxygen-deficient situation that can cause a water body to die. Aquatic life can have a hard time in stagnant water that has a lot of rotting, organic material in it, especially in summer (the concentration of dissolved oxygen is inversely related to water temperature), when dissolved-oxygen levels are at a seasonal low. Water near the surface of the lake--the epilimnion--is too warm for them, while water near the bottom--the hypolimnion--has too little oxygen. Conditions may become especially serious during a period of hot, calm weather, resulting in the loss of many fish. You may have heard about summertime fish kills in local lakes that likely result from this problem.

"As the accompanying chart shows, the concentration of dissolved oxygen in surface water is controlled by temperature and has both a seasonal and a daily cycle. Cold water can hold more dissolved oxygen than warm water. In winter and early spring, when the water temperature is low, the dissolved-oxygen concentration is high. In summer and fall, when the water temperature is high, the dissolved-oxygen concentration is low.

"Dissolved oxygen in surface water is used by all forms of aquatic life; therefore, this constituent typically is measured to assess the 'health' of lakes and streams. Oxygen enters a stream from the atmosphere and from groundwater discharge. The contribution of oxygen from groundwater discharge is significant, however, only in areas where ground water is a large component of streamflow, such as in areas of glacial deposits. Photosynthesis is the primary process affecting the dissolved-oxygen/temperature relation. Water clarity and strength and duration of sunlight, in turn, affect the rate of photosynthesis. Dissolved-oxygen concentrations fluctuate with water temperature seasonally, as well as daily."

I can only speak for myself, but I have no desire to chase any kind of fish around when they're already having a hard time just finding enough oxygen. The way I see it, Dennis, from down at Bob's, has it right. Let's all concentrate on "preserving our little green buddies."