Bermuda Inshore Waters

The Bermuda Inshore Waters Investigations (BIWI) is a time series of monitoring of pollution around the island of Bermuda. This process started in the 1970s and continues today.  What do "time series" & monitoring mean?  Monitoring means keeping an eye on something and "time series" means monitoring at regular time intervals for a certain length of time.

The BIWI monitoring took place every month from 1976 until 1996 and was funded by the Bermuda government.  This kind of research is like taking the pulse of the environment by measuring possible indicators of the health of the ecosystem.  In addition to health reasons, the Bermuda Government is concerned about the tourism industry which relies on a clean environment to continue to attract visitors to our island. 

BBSR conducts two time series monitoring programs:  Sewage Pollution Monitoring and Toxic Trace Metals.  Sampling of the Bermuda Inshore Waters is accomplished by monthly visits to eight stations around the platform: St. George's Harbor, Castle Harbor, Harrington Sound, Great Sound, Hamilton Harbor, Inner Hamilton Harbor, Inner North Lagoon and Outer North Lagoon.  There has been a station added at the incinerator, near the cooling water outfall.  Each month samples are collected for salinity, nutrient and pigment analyses.  Physical measurements such as water temperature and water turbidity are recorded at each station.

Sewage Pollution Monitoring

Bermuda does not have a sewage treatment plant.  For houses, we rely on pits dug into the limestone to store and process the sewage and household "grey" water from laundry and sinks.  The mixture gradually percolates into the porous limestone and mixes with underground lakes of freshwater that are fed by rainfall or it mixes with seawater and diffuses out into the water around the island.  Large sources such as hotels and towns rely on pipes to transport the waste offshore. 

By the 1970s, there were quite a few such pipes going into the marine environment and naturally there were concerns about the effects.  Many of these sources are no longer present but raw sewage continues to be discharged into nearshore waters. BBSR is monitoring a site on the South Shore where the Corporation of Hamilton discharges (Hamilton is the capital of Bermuda).


What kinds of effects could human sewage have on the marine environment?  One possible effect is the stimulation of plant growth due to the nutrients in the sewage.  Human sewage is a valuable fertilizer (called night soil in Asia since it is collected from houses at night and taken to farms) although now concerns about diseases require it to be composted before use so that the disease organisms are killed.  Human sewage might cause the plants on the reef (algae) to grow so fast that they would overgrow and shade the corals and eventually kill the reef.  In addition, there are obviously visual concerns about seeing raw sewage near where you are swimming.  In addition, there are some more subtle effects.  The extra nutrients might not only stimulate algae growing on the bottom but the microscopic plants growing in the water called phytoplankton.  As phytoplankton increase in number, the water begins to turn green and is no longer as crystal clear as it should be in Bermuda! 

The BIWI project began measuring the concentration of the two most important nutrients, nitrate and phosphate, at various sites around the island.  One important site was the harbor in the capital,  which is surrounded by numerous houses whose sewage enters the harbor by slowly draining from a sewage pit  down the hills and  into the surrounding waters.   The measurements were made every month for many years to determine if there was a trend as the

population increase in Bermuda.  The graph illustrates that the population began increasing significantly from the 1920s and continued to increase until the population stabilized at about the 60,000 people that we have today. 

The measurements began  in 1975 and the project ceased monthly sampling in 1996 after finding no evidence for increased nutrients in the waters around Bermuda.  If you look at these figures, there is some variability over the first 15 years or so that is

due to sampling at different tides or times of month or after a rainfall which would wash more nutrients into the ocean.  This variability is especially obvious in the nitrate data because nitrates move quite freely through the limestone rock of the island. Phosphates on the other hand tend to stick to the surface of the rock and so do not reach the sea as quickly.  The high values of phosphate in 1991 are hard to understand but because the values returned to "normal" immediately afterwards, there was no cause for concern. 


Since no evidence for pollution was found, one might think that the work was not needed.  Although that is easy to say after the fact, if  there had been a change, the BIWI sampling program would have made it possible for government to take steps to prevent the problem from getting worse before it was too late.