Coastal water quality of Bonaire, St. Eustatius, and Saba during a period of restricted tourism

The traveling restrictions during the Covid-19 pandemic in 2020 and 2021 created a unique possibility
to measure water quality parameters along the coasts of the Dutch Caribbean Islands with minimised
anthropogenic pressure resulting from tourism. Such a baseline dataset could serve as a reference for
future measurements of the monitoring parameters during periods without traveling restrictions,
allowing the determination of the impact of the presence of tourists on the local water quality.

Rijkswaterstaat contracted STINAPA Bonaire and the Caribbean Netherlands Science Institute (CNSI)
to collect water samples along the coasts of Bonaire (STINAPA), and Saba and St. Eustatius (CNSI) in
the period October – December 2020. The samples were stored frozen until transport to the
Netherlands where they were analysed by the NIOZ for nitrogen, phosphorous, and total organic
carbon. Wageningen Marine Research combined the results in the current report and formulated
recommendations for future monitoring of coastal water quality at the Dutch Caribbean Islands.

Although a wide range of samples was collected, especially in Bonaire and St. Eustatius, the number of
samples per site was too low to obtain statistical power in the observations.

Nonetheless, the first insights were achieved as follows:
- The Bonaire locations generally showed lower nitrogen and phosphate concentrations in 2020
than during a sampling campaign in 2012/13.
- In water samples collected at St Eustatius the inorganic nutrient concentrations ranged from
low impacted at positions more remote from the shore to high affected at specific shallow
- At Saba no evident indications were found for negatively affected water quality. However, the
dataset was minimal and covered only a small part of the coastline.
- The available dataset suggests that the NH4-DIN ratio could be a good indicator of a disturbed
nutrient balance in the coastal water.


And following future directions are recommended:
- Extending the dataset in the future with more time points and additional analyses will facilitate
more in-depth data interpretation. Recommendations for future monitoring projects are to work
according to strict protocols regarding selecting parameters, sample identification, sampling
procedure, additional data collection (e.g. weather conditions prior to sampling), sample
storage, and data storage.
- In addition it could be considered to build local analytical capacity in the Dutch Caribbean for
samples from future monitoring projects, which at least allows a safe and secure sample
processing and storage until transport to specific facilities abroad.

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