Nutrients

Excess nutrients as a result of agricultural, urban, and industrial runoff are major causes to increases in plankton. Coral reefs are nutrient poor environments to begin with; therefore any increase in inorganic nutrients could potentially alter the balance of these ecosystems. Bonaire is suffering from nutrient input in the coastal waters and said trends are expected to increase in subsequent years. Zooplankton diversity and species richness, photosynthetic pigments, water properties and nutrients were measured at two different sites in Kralendijk, Bonaire. The most common taxonomic groups at each site were copepods and siphonophores. The difference in mean turbidity between the two sites was statistically significant (ttest; n = 14; p = 0.002). Excessively turbid water can be explained by an increased plankton population but also by sediment runoff from events such as coastal construction. A possible trend was found between number of zooplankton individuals, chlorophyll a, turbidity, and ammonia nitrogen concentration. This trend could indicate abnormal amounts of runoff entering the waters surrounding Bonaire. Not only is marine management necessary, but also an additional terrestrial aspect to monitor in the form of wastewater and watershed management. Zooplankton taxonomic groups identified during this study could be used as indicators of reef ecosystem health, reproduction success of organisms with planktonic larvae, or predator-prey impact studies such as with pelagic predators of zooplankton. Overall, this study shows important indicators of management for urban areas on Bonaire, but could also contribute to future ecological studies on zooplankton population dynamics around the Caribbean.

This student research was retrieved from Physis: Journal of Marine Science XVIII (Fall 2015)19: 1-9 from CIEE Bonaire.

Seagrass beds are globally declining due to human activities in coastal areas. We here aimed to identify threats from eutrophication to the valuable seagrass beds of Curaçao and Bonaire in the Caribbean, which function as nursery habitats for commercial fish species. We documented surface- and porewater nutrient concentrations, and seagrass nutrient concentrations in 6 bays varying in nutrient loads. Water measurements only provided a momentary snapshot, due to timing, tidal stage, etc., but Thalassia testudinum nutrient concentrations indicated long-term nutrient loads. Nutrient levels in most bays did not raise any concern, but high leaf % P values of Thalassia in Piscadera Bay (0.31%) and Spanish Water Bay (0.21%) showed that seagrasses may be threatened by eutrophication, due to emergency overflow of waste water and coastal housing. We thus showed that seagrasses may be threatened and measures should be taken to prevent loss of these important nursery areas due to eutrophication.

Land-based nutrient pollution is a major stressor on coral reef communities around the Caribbean region and globally. To assess the status of nutrient enrichment and eutrophication on Bonaire and Curacao’s coral reefs, we conducted a comparative nutrient monitoring program that included seasonal sampling for nutrients (ammonium, nitrate, DIN, SRP, TDN, TDP), phytoplankton biomass (Chl a), stable nitrogen isotopes (ð15N) in reef macroalgae, and biotic cover (point count analysis of video transect data) of shallow and deep reef sites between March 2006 and June 2008. Ammonium dominated the DIN pool on both islands and the highest concentrations (~10 µM) occurred on Bonaire’s reef sites adjacent to the Cargill salt ponds. DIN concentrations averaged > 1 µM on both shallow and deep reefs of both islands, indicating that these reefs are now above the DIN threshold noted to support expansion of algal turf, macroalgae and coral diseases. SRP concentrations averaged ~ 0.1 µM on both islands, a level that also represents the SRP threshold for eutrophication on coral reefs. DON and DOP dominated the TDN and TDP pools; TDN/TDP ratios averaged 52 on Bonaire and 45 on Curacao, indicating strong P-limitation of algal growth. Mean Chl a concentrations were higher on Curacao (0.25 µg/l) than Bonaire (0.19 µg/l) and the highest Chl a concentrations on both islands occurred on reefs adjacent to urbanized, nutrient enriched areas. In contrast, low Chl a values of ~ 0.05-0.1 µg/l occurred at the upstream reef sites and the offshore reference site, underscoring the importance of land-based nutrient enrichment to microbial growth and eutrophication on fringing reefs of both islands. The highest macroalgal ð15N values (> + 3 ‰) occurred at the MegaPier and Piscadera Bay on Curacao, which reflects the highest watershed sewage nitrogen inputs of all reef sites in the study. The lower ð15N (< + 2 ‰) values at the other reef sites reflect lower levels of sewage treatment as well as contributions from other nitrogen sources (nitrogen fixation, atmospheric inputs) that have lower source ð15N values. Reefs on both islands were dominated (~ 75 % cover) by benthic algae but showed distinct differences in algal composition; Bonaire’s reefs had high cover of turf and low cover of macroalgae compared to the opposite pattern on Curacao. Our results suggest that the recent expansion of benthic algae and loss of coral cover on reefs in Bonaire and Curacao are not simply the result of top-down human pressures (e.g., overfishing) alone, but also reflect strong bottom-up effects from land-based nutrient pollution.

The data of the study can be found here

The Nature Foundation carried out water quality tests on the 22nd, 23rd, and 24th of July 2012 at seven sites surrounding St. Maarten. These tests, which are conducted bi- annually, are carried out in order to determine the levels of pollutants and other factors affecting wetlands and beaches on St. Maarten. Tests were carried out in order to determine Nitrates (which shows that the water is polluted), Phosphates (which shows the presence of Sewage), Nitrogen, Dissolved Oxygen, and the acidity of the water. Tests were carried out on seven sites; Cole Bay Lagoon, Simpson Bay Lagoon, Mullet Pond, Kim Sha Beach, Great Bay Beach, Belair Pond, Fresh Pond, and the Great Salt Pond. The sites of Great Bay Beach and Kim Sha Beach were particularly chosen to test the swimming quality of the beaches.

It was determined that the sites Cole Bay Lagoon, Kim-Sha Beach, Mullet Pond, and Great Bay had medium levels of both phosphates and nitrates in samples tested. Elevated levels of nitrates and phosphates show that there is a presence of various types of pollutants and sewage which can cause toxic algal blooms and mortality events (large scale dying of fish, turtle and crabs) in wetlands and coastal areas. The highest level was recorded in the Great Salt Pond and indicates the presence numerous pollutants and sewage in the tested water. This may cause fish die offs and algal blooms. Taking this into consideration levels will continuously be monitored by the Nature Foundation.

It was further established that the sites Cole Bay Lagoon, Kim-Sha Beach, Mullet Pond, and Great Bay had low levels of Nitrogen in samples tested. Elevated levels of Nitrogen, caused by pollutants, can cause massive fish die-offs in wetlands and coastal areas. The highest level was recorded in the Great Salt Pond at .6 ppm, which is a relatively high number and indicates the presence of elevated nitrogen levels which can pose a threat to aquatic organisms and which may cause fish die-offs between now and the end of the year. The Nature Foundation will continuously monitor Nitrogen Levels at this site in order to give an approximation when fish die offs may be expected.

Almost all levels of oxygen recorded were at sufficient levels to maintain healthy life. The lowest level was recorded in the Great Salt Pond. This site should be closely monitored for a further drop in oxygen levels which may result in fish kills and breeding of airborne insects (i.e. Midges). It is interesting to note that previously recorded levels in April 2011 of Oxygen in the Fresh Pond indicated a low level present. Current levels have been recorded at healthy levels, which is a significant improvement. This is probably related to the installation of aeration pumps in the Fresh Pond by the Public Works (ROB) Department of the Ministry VROMI.

Despite the fact that many sites showed Low to Medium readings, the Nature Foundation will follow up on a monthly basis during the summer months to carefully monitor for changes in the respective levels. Similarly the levels recorded in the Great Salt Pond show that there exists the possibility of fish die-offs and increased midge activity between now and end of 2012.