By Jan TenBruggencate
Advertiser Columnist

Waimanalo Stream is an example of many of the bad things that happen to streams in the Islands.

Edward Laws, a University of Hawai'i oceanographer who is studying the stream, said it is the main source of sediment and nutrients that end up in Waimanalo Bay.

Sediment and nutrients can be bad things on a coral reef shelf. The sediment can smother corals. The nutrients can change the chemical makeup of the water and can act as fertilizer for seaweeds that compete with corals.

"Waimanalo Stream is a disaster waiting to happen," Laws said.

Some changes are already visible, including the increase in certain species of algae or seaweed, he said.

With money from the Hawai'i Coral Reef Initiative Research Program, Laws is working on a project to identify the problems and make recommendations for how to improve conditions in the stream — and, as a result, in the near-shore waters.

"Waimanalo Bay is home to coral reefs that ... have received very little attention from the scientific community," said Michael Hamnett, the coral reef project's director.

A major problem is that the stream has been significantly altered along much of its length, as have the surrounding areas.

The watershed around the stream has been developed and is no longer the complex native forest that once existed there.

"The result of the change in the watershed of Waimanalo Stream is that it no longer behaves like a sponge, where it soaks up rainwater and releases it at a slow rate during dry weather. Instead, much of the rainwater rapidly enters the stream via storm drains," Laws said.

Also, the streambed itself is dramatically changed, in some places choked by grass and in other areas turned into concrete channels.

"Hardened portions of the stream have no capacity to process nutrients, so the nutrient concentrations rise off the charts and flow downstream into the ocean," he said.

Laws said he hopes his project, which is scheduled to be finished at the end of the year, will include recommendations for changing land-use activities in ways that reduce the effects of the flow of nutrients into the ocean.

The 4-year-old coral reef initiative is jointly run by the state Division of Aquatic Resources and the University of Hawai'i. It pays for projects that provide information on the management and protection of the state's reefs. Information on the various projects it supports is available at its Web site.

Hamnett said the information gained at Waimanalo can be applied to watersheds upstream from coral reefs in Hawai'i and around the world.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Reach him at (808) 245-3074 or jant@honoluluadvertiser.com.