Water quality

Spatial & Temporal monitoring of Bonaire’s near-shore water quality

Internship report

Although Bonaire’s waters harbours one of the richest reefs of the Caribbean, it has not evaded the unprecedented global decline of these unique and precious systems. Recent research suggests a significant impact of local stressors on coral reef functioning. Future intensification of Bonaire's coastal activities may increase run-off, sedimentation, and eutrophication, which, potentially could induce detrimental changes to the system. However, identifying adverse effects of for example nutrient run-off on coral reefs in field conditions remains challenging. Nevertheless, a new local monitoring infrastructure may help to evaluate the risks posed by nutrient pollution by detecting the frequency and origin of harmful concentrations. We aim to create an integrated seawater quality management plan on Bonaire. For this, we measured levels and spatiotemporal variation of dissolved inorganic nutrients (NH4+, NO2-, NO3-, PO43-) and physiochemical water quality parameters (chlorophyll-a and turbidity).

Preliminary data (NOV 2021-Feb 2023) are presented of this ongoing 4-year monitoring project. Spatial water quality data from thirty-seven study sites collected from November 22nd to December 1st (2021) at 5 and 10m depth on the reef slope indicated that DIN concentration at site B12 (marina) and at the sites located in the area North of Kralendijk exceeded the 1μM threshold value set for the phase shift from coral to macroalgae-dominated coral reefs. Furthermore, geographical differences between in nutrient concentrations and relative abundance of nutrient species were found. Ammonium dominated the DIN pool in the areas Kralendijk and North of Kralendijk, whereas in the northern part of Bonaire DIN pool predominantly comprised of nitrate.

The temporal monitoring showed mean chlorophyll-a concentrations across Bonaire’s west coast approached the upper range of the safe threshold value (0.3 μg/L), indicating that Bonaire’s reefs are experiencing a chronic state of eutrophication. The data presented here of short-time span and should be considered as preliminary results. The outcome of this multi-year project, however, will provide more thorough insight spatiotemporal variation in nutrient and physiochemical water quality parameters. This data will help build scientific knowledge into both sources and resilience to external nutrient loading of coral reef ecosystems. Understanding this heterogeneity in local water quality conditions, will aid effective management, help restore reef resilience, and increase our chances of mitigating the global decline in coastal reef systems.

For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
Wageningen Marine Research Student Report
Geographic location
Bonaire
Author

Dynamics of the Deep The influence of spatial heterogeneity of water quality on dominant benthic groups on Bonaire.

MSc thesis

Shifts of coral reefs towards alternative states occur due to local and global stressors. Although global stressors are expected to increase due to climate change, anthropogenic local stressors can be addressed to prevent the loss of important ecosystem services. Identifying and understanding how human activities affect the dynamics in the benthic communities in the reef ecosystems could facilitate more effective reef restoration efforts. But how do human activities affect water quality and subsequently the benthic cover? To answer this question we look towards the coral reefs of Bonaire, home to one of the most pristine reefs in the Caribbean. We combine existing data on human activities and environmental variables with new temporal water quality and benthic cover data generated along the west-coast of Bonaire. We created two sets of models: relating the benthic cover to water quality and explaining water quality with human activity. Because our data collection extended into unexplored deeper parts of the reef we have a unique opportunity to consider the effect of local stressors along a more extensive depth gradient.

We hypothesized that areas with high nutrient loads would be reflected by benthic cover with relatively high algae, sponges and benthic cyanobacterial mats. Our results showed this to be the case for sponges and turf algae, but not for benthic cyanobacterial mats (BCM) and macroalgae. The coral and crustose coralline algae (CCA) cover were expected to be related negatively to the selected water quality variables. The models predicting the coral cover give a mixed result. Both significant positive and negative effects of nutrients on the coral cover have been found, and relatively the positive effects are stronger than the negative effects. The expectation that an increase in human activity leads to a decrease in the water quality is a lot more nuanced, but it is clear that terrestrial human activity plays an important role. The influence of depth on the effects of the water quality on the benthic covers seems to be minimal at most. As the few significant differences in water quality effects found, were more likely to be the effect of under sampling than anything else. However, these results might change as more data becomes available, narrowing both the prediction and confidence intervals and thus increasing the chance of finding significant effects of water quality on the benthic cover and clearer effects of human activity. 

For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
Student Report
Geographic location
Bonaire
Author

Benthic community composition of the reef on the leeward side of Bonaire; A comparison of water quality with benthic community

MSc internship report

The health and abundance of coral reefs are declining worldwide. Coastal development, terrestrial runoff, the temperature rise of the oceans and coral diseases have decreased the health of coral reef systems in the Caribbean. Terrestrial run off has been shown to affect water quality through nutrient influx. The water quality changes and community composition of the reefs of Bonaire have been recorded in the past but only on smaller scales and most of the time in combination with sites on Curaçao. The project “Resilience Restoration of Nature and Society in the Caribbean Netherlands” (the Resilience project) aims to improve the resilience of the coral reef ecosystem on Bonaire, by implementing an extensive monitoring plan for water quality and benthic community composition. This internship project continues surveys of benthic community composition of Bonaire (1), assess the risk of anthropogenic pollution through nutrient influx (2) and relate the water quality assessment of Bonaire to the benthic community data (3).

Benthic community composition was assessed at 8 sites on the leeward coast of Bonaire, between 5 and 60 meters depth. This was done by Remote Operated Vehicle assisted, picture gathering. Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phospor (DIP) concentrations were also collected at 39 locations around the leeward coast of Bonaire. 11 of the locations were sampled biweekly between November 2021 and May 2022 and nutrient concentrations from these locations were used in a water quality Risk assessment for eutrophic pressure. This was done by calculating a Risk Quotient and comparing it to the percentage of exceedance of a nutrient concentration threshold for eutrophication on coral reefs. Additionally a "Generalized Additive Model" (GAM) was used to explore the relationship between mean coral coverage and mean DIN concentration.

Turf algae showed to be the most dominant functional group between 5 and 20 meters depth, followed by cyanobacteria as the most dominant group between 40 and 60 meters. Coral cover increased until 20 meters depth, up to 25%, and showed a sharp decline afterwards. The benthic index based on AGGRA benthic indicators suggests that the coral reef ecosystem is more dominated by algae and cyanobacteria than corals. DIN concentrations are close to the eutrophic threshold of 1 μm/L and display a relatively high exceedance percentage of that threshold. DIP concentrations stay safely below the threshold value of 0.1 μm/L. Risk assessment of the worst case scenario for DIN shows that almost all locations sampled have low risk or higher for pressure by nutrients. The GAM showed no significant relationship between DIN and coral coverage. Further nutrient concentrations need to be gathered on a temporal scale to get a better view of the water quality over the whole year. The benthic community composition of locations towards the north of the island also need to be mapped to assess the effect of the elevated nutrient concentrations on the coral reef. This study hopes to support the “Resilience Restoration of Nature and Society in the Caribbean Netherlands” project with their extensive monitoring plan.

For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
MSc Internship nr. I0744
Geographic location
Bonaire

Assessing the Relationship between Coastal Currents and Water Quality Indicators on Bonaire: ADCP & CTD approach

MSc internship report

75% of coral reefs worldwide experience degradation of which 60% is caused by local (anthropogenic) stressors. The human welfare of a small islands like Bonaire strongly depends on coral reef ecosystem services. On a global scale the carbon contribution of Bonaire is neglectable, thus their best course of action is to reduce their local stressors. These local stressors include terrestrial runoff of wastewater, sediment and nutrients to the sea. The Project Resilience Restoration of Nature and Society in the Caribbean Netherlands aims to quantify local stressors by monitoring water quality indicators along the leeward coast of Bonaire. Due to their efforts, the site-specific water quality dataset is expanding. However, research on the nutrient transport between the monitoring sites was lacking. To gain insight on local currents, a boat mounted Acoustic Doppler Current Profiler (ADCP) was deployed along the leeward coast of Bonaire. By sailing transects orthogonal to the shore, the ADCP captured the currents in 3D up till 40 m deep. In addition, temperature, salinity and chlorophyll-a were measured using a CTD. Combined the ADCP and CTD data was used to link currents to water quality indicators. The dominant flow was found to be a longshore at all sites. For Bonaire the current is predominantly northward, yet in the Kralendijk area a southward current occurred closer to shore. Around Klein Bonaire, the flow was counterclockwise. Generally, the water masses closest to shore had the highest temperature, salinity and chlorophyll-a concentrations. Local elevated chlorophyll-a layers were observed either in (1) less saline seawater at the surface near shore or (2) in equal saline seawater at 7m depth further offshore. The former could be attributed to terrestrial runoff (local stressor), whilst the latter may originate from open sea. Surface layers of chlorophyll-a were found in both longshore currents on the main island, implying the transport of land-based effluents to the north and to a lesser extent to the south. Exchange between Bonaire and Klein Bonaire seems limited. These results will provide a foot hold on how terrestrial effluents are (re)distributed around the coastal environment. And, hopefully, contribute to successful management practices and monitoring of local stressors.

 

For full report or more information,  please contact erik.meesters@wur.nl or gulsah.dogruer@wur.nl

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
Msc Internship report
Geographic location
Bonaire

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
positions.
- 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.

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
Wageningen University & Research report C026/22
Geographic location
Bonaire
Saba
Saba bank
St. Eustatius
Author

Een natuurwetenschappelijk onderzoek gericht op het behoud van het Lac op Bonaire

After news was received that the Netherlands Antilles' largest and as yet
almost unspoiled lagoon would be involved in development plans, a
scientific survey was organised for obtaining new data on the present
condition of Lac, Bonaire.
The field work took place between i and 28 August, 1967, by Dr. P. J.
Roos, Amsterdam - who had already studied the coral fauna of Lac
in 1965 - and between 7 August and 23 September by Dr. P. WAGENAAR
HUMMELINCK, Utrecht, who first visited the lagoon in 1930. Roos did
most of the underwater work whereas HUMMELINCK collected biological
specimens from about 60 localities. The survey was initiated by the
Foundation for Scientific Research in Surinam and the Netherlands
Antilles (STUDIEKRING) and was financed by the Netherlands Foundation
for the Advancement of Tropical Research (WOTRO). The material is
being studied in the Zoological Laboratory of the State University at
Utrecht, in cooperation with specialists; most of the results will be
published in the Foundation's "Studies on the Fauna of Curacao and
other Caribbean Islands".
The Lac covers about 8 km^; of this one third is mangrove and shallow
mud flats (Figs. 3-5, 12). The transparency of the water is striking,
compared with that of other inland bays in the Lesser Antilles. Dearth of
nutrients may cause the absence of mangrove-oysters and other mollusks
known to occur in abundance in other mangrove lagoons, and also the
scarcity of balanids and other animal species which are common in
similar Caribbean environments.
Lac is separated from the sea by a barrier of coral debris; a shallow
flat of white sand occurs inshore (Figs. 3-4, 5, 12). The basin has vast
7"Aa/assj'a flats, whose shallower parts may be very muddy, often with
abundant Ha/twerfa. Syrtngorfjum grows near the entrance of Lac and
in other sandy areas. .4uraiwwV/ea is common in several inlets, where it
may grow in profusion. i?w/>£ia is found in creeks and ponds of high
salinity. .Di/j/an/Wa has been collected only once (Figs. 7, 12, 52).
More data on the fauna and flora are shown in Figs. 8-11. The distribution
of the small form of Afe/ongena we/ongena appears to have been
much larger some 30 years ago. CAfowe cawee/Za/a was not found in Lac
recently but it was abundant a few thousands years ago when the lagoon
extended further inland (Figs. 11, 51). It is likely that the fauna of Lac
has become poorer in recent times. The big heaps of S/tt>m6«s £tgas have
not visibly increased in size during the last thirty years (Figs. 8, 35-36).
During the last century the landscape has changed considerably.
Formerly the broad sandy barrier which separates the basin from the
mangrove-flat in the north (Figs. 12, 17-18, 24, 26, 46-47) had several
large openings through which the water could circulate. Afterwards part

Date
1968
Data type
Research report
Geographic location
Bonaire
Image

How does water quality correlate with coral disease, bleaching, and macroalgal growth on coastal reefs? A comparative study of various anthropogenic threats on Bonaire, N.A.

Coral reefs worldwide are currently jeopardized by anthropogenic factors such as land-based pollution, coastal development, and sediment erosion. In the Caribbean alone, nearly two-thirds of coral reefs have been deemed as threatened. This study investigated the potential negative effects of water quality and eutrophication, Enterococci bacteria (found in human gut), and sedimentation on coral disease, bleaching, and macroalgal growth on the near shore reefs of Bonaire, N.A. Monitoring sites were defined according to their proximity to anthropogenic activity: “more impacted” or “less impacted” (< 200 m and > 200 m from coastal development, respectively). Water samples at 5 m were collected weekly and at 12 m biweekly from each site and tested for nutrient concentrations (NO3, NO2 - , NH4-N, PO4), Most Probable Number of Enterococci bacteria, sedimentation rates, and particle size distributions. Video transects (100 m) were also taken at defined depths and analyzed for live coral cover and diversity, percent disease and bleaching, and macroalgal cover. Data showed elevated NH4-N levels at all sites, Enterococci bacteria present at 3 of the 4 sites (mainly at 5 m), and sediment particle counts showed significant differences among sizes at both depths and between the interaction of size and impact at 12 m. There was also a strong trend of finer grained sediments at high impact sites and coarser grained sediments at low impact sites. Very little overall coral disease (1.105 ± 1.563 % at more impacted sites and 0.400 ± 0.566 % at less impacted sites in 12 m) and bleaching (3.245 ± 0.615 % at more impacted sites and 1.390 ± 1.966 % at less impacted sites in 12 m) was found on the reefs however, neither were present at 5 m. There was significantly more macroalgae at 12 m and a strong trend of more macroalgae at the deeper, more impacted sites. This study suggests that increased anthropogenic activity on Bonaire is contributing to the increased NH4- N levels, Enterococci bacteria presence, and finer particle sediments, which future studies may correlate significant interactions between these parameters and coral disease, bleaching, and macroalgal growth.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 35-43 from CIEE Bonaire.

Date
2009
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Author

Effects of Nutrient Enrichment and Water Quality on Coral Disease Prevalence in Bonaire, Dutch Caribbean

Trying to understand the extent to which anthropogenic stressors impact coral reefs globally has led to an increase in studies which analyze the effects of nutrient enrichment on the frequency and severity of coral disease. Bonaire, Dutch Caribbean currently has no sewage treatment facility in place, resulting in the percolation of wastewater to the surrounding coastal marine environment. On the reefs near resorts, there is a large volume of groundwater used and subsequently discharged into the ocean. As a result, the reefs directly in front of major resorts are likely to have higher disease levels than reefs without resorts nearby. The goal of this study was to evaluate the difference in prevalence of coral disease between sites located in close proximity to groundwater discharge and sites located further away. In order to achieve this objective, six sites with varying gradients of exposure to sewage discharge were surveyed by laying down 1 m x 30 m transect belts parallel to the shore at 6 m, 12 m and 18 m depths. During each survey, nutrient enrichment, macroalgal cover, water depth and coral colonies displaying signs of disease were recorded. Water quality was assessed using a number of parameters including nutrients (ammonium, ammonia, phosphate and dissolved oxygen), Enterococci bacteria and sedimentation. At sites closer to resorts there were higher nutrient levels and percent cover macroalgae, however sedimentation rates and mean percent coral disease frequency were highest at medium impacted sites. Low impacted sites had a greater presence of coral disease at shallower depths, compared to high impacted sites. This data will be used to illustrate a relationship between coral disease and anthropogenic stressors and provide a baseline for future studies.

This student research was retrieved from Physis: Journal of Marine Science IX (Spring 2011)19: 1-11 from CIEE Bonaire.

Date
2011
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Author

Coastal marine water quality based on the presence of Polychaetes, coliforms,

A lack of sufficient wastewater treatment practices on the island of Bonaire, Dutch Caribbean suggests that contaminated groundwater seepage or runoff could be impacting the health of the coastal habitats and fringing reefs that surround the island. Bonaire does not monitor the health of its coastal waters, although effects of pollution have been observed. This study aims to learn more about the coastal water quality at three stations along the coast of the city of Kralendijk, Bonaire. Both indicator bacteria (coliform bacteria, Escherichia coli, and enterococci) and polychaete assemblages were monitored. IDEXX ColilertTM and EnterolertTM test kits were used to monitor bacteria levels in samples taken over a five-week study period. Polychaetes were identified to the family level from soft sediment samples. Polychaete family abundance, richness, and diversity were compared between stations. Grain size of the soft sediments at each station was measured. Polychaete assemblages varied between stations, but not enough data was gathered to eliminate the possibility of unexpectedly large grain size differences in explaining this variability. Typical water samples from each station showed narrow variability within U.S. Environmental Protection Agency standards for indicator bacteria levels. Two outliers occurred. The Marina station experienced a wider variance in all bacteriological indicator levels than the other two stations, and all surface stations experienced a significant spike in enterococci levels after a heavy rainstorm. If elevated enterococci levels consistently occur during heavy rainstorms, this could present a

This student research was retrieved from Physis: Journal of Marine Science XII (Fall 2012)19: 22-32 from CIEE Bonaire.

Date
2012
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Author

Pelagic plankton diel vertical movement, diversity, and density in relation to nitrate concentration in Bonaire, Dutch Caribbean

Plankton are the base of the marine food web and are studied for a broad range of research relating to diversity and ocean health. These organisms have not been well studied in Bonaire and this study provided a preliminary assessment for the pelagic net plankton movement and diversity. Water samples and plankton tows were collected using a Niskin bottle and 20-micrometer closable plankton net respectively at four depths: 90 m, 60 m, 30 m, and 10 m. The water samples were processed for nitrate concentration and the 5-meter vertical plankton tows were analyzed for plankton abundance using the following categories: diatoms, dinoflagellates, copepods, and other zooplankton. Dinoflagellates displayed diel vertical migration with higher density at 10 m and 30 m during the day and lower density at 10 m and 30 m at night. Simpson’s Diversity Index (SDI) did not show a significant difference in the diversity at 90 m and 10 m during the day or night. Nitrate concentration and plankton density were not found to be correlated. This study created a preliminary assessment for further research into the effects of the lunar cycle, nitrate, and movement of the pelagic net plankton of Bonaire.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 28-34 from CIEE Bonaire.

Date
2016
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Author