Market volatility over the past several trading days has been as high as it’s been all year, as investors fear the possibility of a double-dip recession amid a stagnant economy. But as market participants note, it will be difficult to sustain the increased activity for the long haul.

Trading volume for much of 2011 has been down from the levels seen last year. There can be many reasons for this, including a lingering fear from investors that economic growth has grinded to a halt, leading many to simply sit on the sidelines until things take a turn for the better. Some critics note that trading volume is down from 2010 because last year saw an unusually large amount of trading volume, and that sustaining it would have been difficult.

The different types of macro events that have occurred during 2011 have each provided temporary boosts to market volatility and trading activity. Starting from the Earthquake in Japan earlier in the year, through the U.S. debt ceiling situation and ongoing European debt concerns, and most recently, the Standard & Poor’s downgrade of U.S. credit, each event has stimulated trading activity.

The most recent bout during the first part of August has boosted trading volumes to their highest levels all year, culminating in nearly 18 billion equity shares changing hands on Aug. 8. In fact, total equity volume has remained over 10 billion shares per day since Aug. 3, and above 16 billion since Aug. 5. While the numbers are high, it remains to be seen if they can stay this high for an extended period of time.

“In 2011, volumes have been particularly depressed, but in the last week, because of the volatility, volumes have been particularly frothy,” said Bernie McDevitt, vice president of institutional trading for Cheevers & Co. “It’s been substantially greater than balance of the year, but I don’t know if it will last.”

The trading volume is showing signs of slowing down. On Aug. 9, there was about 16.97 billion shares traded, down from the previous day’s 17.97 billion, which was the highest single day volume of the year.