In the second quarter of 2012, more than a third of investors are less tolerant of risk than they were at year-end 2011.

That's the key data point from TD Ameritrade's latest survey of investment sentiment, according to Carrie Braxdale, the firm's managing director for investor services.

"It's a significant change," she said, "and it goes hand in hand with a similar decrease in investor optimism."

The previous survey, reported after the first quarter of this year, found that 22% of respondents had reduced their tolerance for investment risk in the prior six months; now, 34% said they had less risk tolerance. Concurrently, the portion of investors feeling optimistic about the stock market fell from 66% to 47%, from April to July of this year.

Reasons for the decline in confidence include weak job creation here, troubles in Europe, and uncertainty about the coming U.S. election, Braxdale believes. Still, those same worries existed three months earlier, when investors were more upbeat. "The latest survey may reflect a continuation of all the uncertainty," she said. "The longer things go on, the more investor concerns are exacerbated."

After reporting an increase in gloom, the TD Ameritrade found a bright spot. More than three-fourths of the respondents are maintaining IRA contributions at previous levels while an additional 10% are contributing more than had been the case. "People may be uncertain how to react to these events," Braxdale said, "but they're still engaged, staying in for the long haul."

Therefore, it's vital for financial planners to maintain communications with their clients now, Braxdale said. "Make sure they're comfortable with their investment positions but try to keep them from over-reacting to short-term swings. After living through the drop and bounce-back of the past few years, we've learned the value of patience and discipline."

Donald Jay Korn writes for Financial Planning.