That most singular of singer-songwriters, Imogen Heap, stunned Houston audiences last night at Verizon Wireless Theater with her whiley vocals, and an unexpected shout-out to local nonprofit, Buffalo Bayou Partnership.

It's all part of her $54,000 campaign to raise cash for local charities on her current North American tour — but the tactic has its own Imogen-edge.

During each performance, she composes and plays a completely improvised piece of music, influenced by the audience's suggestions on key, tempo and time signature. The song is then made available as a digital download after the show, with proceeds given to a chosen local charity suggested by Imogen's fans.

A simple e-mail to Imogen by Buffalo Bayou Partnership's director of development Jennifer Gaines earned that non-profit the spotlight yesterday evening.

"She's assigned an instrument and loops it back," explains Gaines, who is an avid Imogen fan. The artist works with a Monome, the open-source beat machine pioneered by Daedelus, in her lap, to produce majestic layered sounds. Minute microphones decorate her wrists, capturing the sounds of her medley of instruments.

"The crowd picked the sound of a chirping bird," says Gaines, "and Imogen began jokingly whistling, 'This is annoying.' Her use of technology is stunning."

"We were completely shocked when we saw her put Buffalo Bayou Partnership on display," says Brian Thorp, a patron of BBP. "It revealed what an urban oasis the Bayou's become as a place where people can play sports, or just for dreamers to go escape from the concrete jungle.

"The show itself was terrific," Thorp attests. "She has an amazing presence."

After the show, Imogen gratefully tweeted, "Thanks for those who came tonight in Houston. We had a great time even with a bird in improv choice. Silliness. xxx."

Last night's tune is not yet available, but once it's up, it will only be on the Web site for two months. To date, the tour has raised $2,754 for various charities, including Detroit's Urban Farming, Orlando's Sea Turtle Preservation Society and the Lower East Side Ecology Centre of New York. Heap donates $1 to the charity each time a fan downloads the track.

Such generosity is all the more impressive considering the artist's own economic straits: Last week, she revealed that she may stop touring because it is too expensive and "not easy keeping afloat in this climate."

"I need to feed myself and this isn't going to help me, if I keep touring till the end of the year like I wanted to," Heap told BBC before performing in Miami, adding, "I just can't afford it. I'm going to be broke." The Grammy-winning Londoner is a classically trained pianist and recipient of the prestigious Ivor Novello songwriting award. It's a formula that encourages word-of-mouth mania, but doesn't necessarily fill stadiums.

The banks of Buffalo Bayou were merely yards away as Heap performed her latest self-produced album, Ellipse, at Bayou Place.

The Buffalo Bayou Partnership is responsible for developing and facilitating improvements to the Buffalo Bayou greenway system. In the past seven years, it has raised and leveraged over $45 million for improvements along a 10-mile stretch of Buffalo Bayou from Shepherd Dr. to the Ship Channel Turning Basin.

What's more, the organization has developed a 20-year master plan, Buffalo Bayou and Beyond, three miles of trails east of downtown, Sesquicentennial Park, the North Side Trail and the purchase of over 35 acres of land in the East End for future parks.