(Repost from Liz Foote, Coral.org West Maui Watershed News, March 2013) Back in December, you may have seen some press (here, here, and here) on the results of a study conducted by the University of Hawaii to investigate the connection of treated wastewater effluent (disposed of through gravity-fed injection wells) to the water emerging as freshwater seeps amongst the nearshore reefs of North Ka’anapali.
You can find the study in its entirety - all 513 pages of it – at the EPA site. The EPA’s official news release can be found here.
Don’t feel like reading 513 pages of a technical report? Here are several take-home messages that we wanted to highlight.
For years, warm freshwater has been visibly emerging from the seafloor at a few locations in the North Ka’anapali Beach region. They are known as “freshwater seeps” or “submarine seeps.”
Here is a look at one of the areas (‘seeps’) where freshwater emerges from the seafloor at a shallow depth very close to shore (The blurry area in the photo is due to freshwater mixing with salt water.)
A tracer dye was added to the treated wastewater effluent injected at the Lahaina Wastewater Treatment Facility. It took 84 days to be detected in the nearshore waters in North Ka’anapali, emerging from the submarine springs. The study determined that the monitored springs consist primarily of the treated wastewater effluent from the LWTF. This is not the first study to provide evidence of a linkage of the injected wastewater to the water emerging just offshore, but its methodology using the fluorescing tracer dye further solidified our understanding about the pathway and transport time of the treated effluent .
It is encouraging to note that ostensibly due to the disinfection of the treated effluent, bacterial levels of the water emerging from the springs are within the range deemed by the Department of Health as safe for humans. In October 2011, the LWTF began using chlorine as a disinfectant, and is in the process of transitioning to ultraviolet disinfection, slated for the end of 2013.
This study was also the first to document a “thermal anomaly” in the region. The map below was created through aerial infrared remote sensing, and shows the location of warmer surface water in relation to the seeps.
While there may be causes for this warm water other than the emerging effluent (known to be warm to begin with), such as geothermal activity and decomposition reactions, the study noted that “the warmest area of the entire coastline mapped corresponds to the geographic location where effluent enters the ocean through submarine springs.”
Though warmer (and fresher) water may not be that much of a concern to humans, it is certainly a concern to coral reefs. Corals are animals with a narrow range of tolerance for many characteristics of the physical environment, particularly temperature and salinity.
Many questions remain about the dynamics and impact of the treated wastewater on Ka‘anapali’s coral reefs; further study and analysis are needed to determine the relative contribution of this stressor in the face of multiple and diverse threats to our reefs. While the scientific community is still working to understand exactly why and how our reefs are degrading, the key message to keep in mind is that West Maui’s reefs have declined at an alarmingly fast pace, and will continue to do so without intervention and effective conservation strategies.