Nearly half of Bonaire water samples contain unhealthy levels of nitrogen
KRALENDIJK – Unhealthy levels of nitrogen were measured in nearly half of the water samples examined around Bonaire between 2022 and 2024. In addition, persistently high concentrations of oil-related contamination were found in the seabed sediment near the former BOPEC site. Researchers warn that the poor water quality is putting further pressure on the already vulnerable coral reef.
This is according to a study by Wageningen Marine Research into the coastal waters of Bonaire, Saba and St. Eustatius. For the study, water quality data were collected and contaminants in sediment were analysed between 2022 and 2025. According to Wageningen, this is the first time that nutrient pollution and chemical contamination have been assessed jointly for the three islands and over multiple years.
Of the three islands, Bonaire showed the greatest risk of excessive nutrient loading. DCNA reports based on the same study that between 2022 and 2024, nitrogen levels above a healthy threshold were measured in nearly half of all water samples around Bonaire.
The researchers mainly point to land-based sources. Wastewater, polluted groundwater and stormwater runoff likely contribute significantly to the elevated concentrations of nitrogen and phosphorus in the coastal water. Natural processes, such as inflow from South American rivers and upwelling of deeper seawater, may also explain part of the high values.
BOPEC stands out
The chemical contamination also yields striking results. At the monitoring location near the former BOPEC site, the highest concentrations on Bonaire were found for nearly all of the polycyclic aromatic hydrocarbons (PAHs) examined.
According to the report, BOPEC differed clearly from all other monitoring sites. Between November 2022 and January 2025, concentrations above international assessment values were repeatedly measured there. For some substances, the exceedances were considerable. In the report, the researchers themselves speak of “highly concerning results at BOPEC”.
PAHs are formed, among other things, during combustion and are strongly associated with oil products and industrial activities. Some PAHs can have harmful effects on marine life.
Elevated PAH concentrations were also found elsewhere on Bonaire, including at Buddy’s Reef, the marina and Lagun, but according to Wageningen these were more likely incidental peaks. At BOPEC, by contrast, the values were persistently elevated.
More chemical substances found
In addition to PAHs, the researchers also found PCBs, PFOS and the globally banned tributyltin (TBT) at various locations in the Caribbean Netherlands. These substances break down slowly and can accumulate in the environment and in food chains. Among other things, they can disrupt the growth, reproduction and development of marine animals.
For Bonaire, the BOPEC contamination is not new. After the major fire at the site in 2010, PFOS and PAHs were already found in the surrounding area. However, the new study shows that at the coastal location near BOPEC, more than twelve years later, there is still a clearly deviating and persistent contamination profile.
The former BOPEC site has since been taken over by Curoil Bonaire Terminals. A separate foundation has been established for the remediation of the site. Among other things, oil, PFOS and other soil contamination are being addressed.
Coral restoration possibly affected
The study also suggests a possible link with coral restoration. At three coral restoration sites on Bonaire, the location with the highest sediment contamination also had the lowest survival rate of outplanted young corals.
The researchers stress that this does not prove a direct causal link, but that local pollution is likely one of the factors influencing the success of coral restoration.
According to coral researcher Erik Meesters of Wageningen, improving water quality is the most important local measure to make reefs more resilient to climate change. Higher nutrient levels make coral more susceptible to bleaching and disease, while chemical substances can impair, among other things, their defences and reproduction.
The study also points to a governance problem: the Caribbean Netherlands does not yet have a specific assessment framework for water quality. As a result, according to Wageningen, measurement data are insufficiently translated into concrete environmental targets and management measures.
