Water quality

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

Abstract

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.

Date
2022
Data type
Research report
Theme
Research and monitoring
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

A baseline water quality assessment of the coastal reefs of Bonaire, Southern Caribbean

Bonaire is considered to harbor some of the best remaining coral reefs of the Caribbean, but faces multiple pressures including eutrophication. We measured multiple water quality indicators twice annually, from November 2011 to May 2013, at 11 locations at the west coast of Bonaire. This study resulted in 834 data points. DIN concentrations ranged from below quantification to 2.69 μmol/l, phosphate from below quantification to 0.16 μmol/l, and chlorophyll-a from 0.02 to 0.42 μg/l. Several indicators showed signs of eutrophication, with spatial and temporal effects. At southern and urban locations threshold levels of nitrogen were exceeded. This can be a result of brine leaching into sea from salt works and outflow of sewage water. Chlorophyll-a showed an increase in time, and phosphorus seemed to show a similar trend. These eutrophication indicators are likely to exceed threshold levels in near future if the observed trend continues. This is a cause for concern and action.

doi:10.1016/j.marpolbul.2014.06.054

 

Date
2014
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire

Water quality of the coastal zone of Bonaire Results field monitoring 2011-2013

Approach:

Eutrophication is a common threat to the integrity of coral reefs as it can cause altered balance and integrity of the reef ecosystem. On the island Bonaire the former waste water treatment is limited which is a point of concern to the quality of the marine park. The reef of Bonaire faces nutrient input by various sources, of which enriched groundwater outflow from land is considered to be a substantial one. It is assumed that groundwater is enriched with nutrients e.g. due to leaking septic tanks.

In order to reduce the input of nutrients on the reef via enriched groundwater, a water treatment plant is being built on Bonaire. The treatment of sewage water is extended in 2012 with a sewage system covering the so called sensitive zone, the urbanised area from Hato to Punt Vierkant, including Kralendijk, the islands largest town. Based on the dimensions of the treatment plant and estimated connections to the plant, it is estimated that a total of 17.5 to 35 tonnes of nitrogen a year will be removed from the sensitive zone, and will not leach out to the sea. No estimates are known of the contribution of other sources to the total nitrogen load.

Limited information was available about concentrations of nutrients in the marine local environment and its eutrophic state. Therefore, Rijkswaterstaat asked IMARES to conduct a study on water quality aspects. The goal of this coastal monitoring study was to collect baseline water quality data to be able to study the impact of the water treatment plant in coming years. The following research questions are discussed based on the results:

  • Are environmental safe threshold levels of water quality exceeded?
  • Is temporal (over the years), or seasonal variation (November-May) of water quality observed?
  • Does water quality vary among locations or regions in Bonaire?
  • Based on experience and results, what are recommendations for future monitoring of water quality?

The study area was the west coast of Bonaire, and included 12 field locations. Water was sampled during early morning field trips at each location twice a year (May and November) starting November 2011 till May 2013. Indicators for water quality related to the nutrient status on the reef were selected and analyzed.

Based on their relevance to general water quality aspects and steering primary production, their relevance to the outflow of enriched (polluted) groundwater (and thus possible impact of the treatment plant in future) the following indicators were included:

  • Inorganic nutrients
    • NO2, NO3, NH4, PO4
    • DIN (calculated based on NO2+ NO3+ NH4)
  • Organic nutrients
    • Total nitrogen, ureum and total phosphorus
  • General water parameters
  • Chlorophyll-a
  • Fecal bacteria

Concentrations were assessed against environmental threshold values from peer reviewed literature or (inter)national standards. If not available, outlying concentrations were highlighted taking the 80th percentile as a representative level.

Results and discussion

Water quality indicators measured at the west coast of Bonaire show signals of eutrophic conditions. Spatial and temporal variation in water quality is however observed. At some locations and certain moments environmental safe levels of nutrients are exceeded (see overview of data in Figure 1- Figure 4). Especially at locations in the south and in the sensitive zone concentrations of nitrogen and phosphorus exceed the threshold levels. Southern locations are probably affected by the salt pans, and locations in the sensitive zone by outflow of sewage water.

Furthermore, an increase of phosphorus and chlorophyll-a is observed in the last 2 years, whereas nitrogen (DIN) decreases slightly over the years. However, despite the decrease of nitrogen, its threshold levels are exceeded at Red Slave, Tori’s reef, Angel City, 18th Palm, Cliff. Phosphorus and chlorophyll-a do not yet exceed environmental threshold levels, but if the increase continues, this might be relevant in near future.

The risk of higher nutrient levels is that algal growth can outcompete corals, and can change the structure of the ecosystem. Furthermore, increased levels of nutrients affect the coral reefs integrity due to decreased stability of the skeleton.

The increase of bioavailable phosphate alters the nutrient ratio (DIN:SRP ratio) and species composition can evolve from this change in relative nutrient availability. Relating these data with observations in benthic composition and chlorophyll-a trends is advised to support this hypothesis.

Fecal bacteria numbers exceed several standards for human health safety. High fecal bacteria numbers are more frequently found in the south and in the sensitive area, and are likely to be related to rainfall events. Bacteria are found in surface samples as well; indicating surface run off as a possible source.

Actual rainfall, especially just before or during sampling is an important steering factor in the concentrations measured. Rainfall is very scattered during the rainy season, and we believe so is the outflow of nutrients to the reef.

In short it is recommended to continue the monitoring of water quality over several years at the same frequency and locations. Next to the regular program, make sure that interval sampling during heavy rains are included as these moments indicate point source discharges which can be missed when rainy season is shifted. No locations should be discarded from the program. In order to prepare the monitoring program for future measures taken outside the current zone (Hato- Punt Vierkant) additional locations just north and south of the sensitive zone are advised to be included. The set of indicators can remain the same, with some slight adaptations such as the addition of coprostanol (measure of faecal discharge) and discard of ureum.

As nutrient levels are in a constant flux, data should be considered in an ecosystem context. Benthic surveys focusing on macro algae, turf algae and cyanobacteria, were not included in this study, but add largely to a whole ecosystem assessment on eutrophication issues.

Monitoring of water quality in the coastal zone alone will not provide satisfactory indication of the impact of the treatment plant in reducing emissions to the marine environment. To monitor the impact of the treatment plant, several factors should be considered. These are related to the treatment plant itself, groundwater quality, coastal water quality, benthic coverage and benthic quality. Actual reduction of emissions to the marine environment can be retrieved from monitoring and reporting of the efficiency of the treatment plant. Monitoring of groundwater wells provides knowledge on the groundwater quality that outflows to the reef. Water quality monitoring in the coastal zone gives knowledge on conditions contributing to environmental health. It is advised to synchronize the monitoring programs, and to analyze the datasets in a coherent way.

In the end, eutrophication is not the only pressure potentially affecting a reef. Besides the focus on the research related to the treatment plant it is advised to consider additional research on a “whole ecosystem basis” in which the contribution of other pressures as well, such as run off via canals and overflows of salinas with nutrients and sediments (in rainy season), fisheries impact and the impact of climate change/acidification on the reef are included. 

Date
2013
Data type
Research report
Theme
Research and monitoring
Report number
C158/13
Geographic location
Bonaire

Saba Bank research expedition 2011 – Progress Report

Abstract:

The Saba Bank is a large submerged carbonate platform of approximately 2,200 km2 in the Caribbean Sea which lies partially within the Exclusive Economic Zone of the Netherlands and partially within the territorial waters of Saba and St. Eustatius. It was declared a protected area by the Dutch Government on 15 December 2010 and has been registered as such in the Specially Protected Areas and Wildlife (SPAW) protocol of the Cartagena Convention for the Protection and Development of the Marine Environment of the Wider Caribbean. Applications for a Particularly Sensitive Sea Area (PSSA) at IMO and Ecological or Biological Significant Area (EBSA) at CBD are pending.

As part of the Saba Bank research program 2011-2016, commissioned by the Dutch Ministry of Economic Affairs (EZ), an expedition to the Saba Bank was conducted from 22 to 29 October 2011. The Saba Bank research program aims to obtain information on the biodiversity, key ecological processes and carrying capacity for commercial fisheries to facilitate sustainable management of the area. The primary objectives of the 2011 research expedition were to collect data on benthic and reef fish communities; sponges and nutritional sources of the sponge community; seabirds and marine mammals; water quality, water velocity and other physical parameters. A multidisciplinary team conducted video and visual surveys on benthos, fish and sponges during 10 SCUBA dives at 20-30m depth, while sea birds and marine mammals were surveyed by means of on-board visual surveys and acoustic data loggers. Water velocity and water quality were also measured on-board using an Acoustic Doppler Current Profiler (ADCP) and Conductivity, Temperature and Depth (CTD) device.

During the expedition 8 sponge species were collected and 37 scleractinian coral species and 85 fish species were identified.Fish biomass varied per site between 1.3 kg to 4.4 kg.
Part of the measurements on water velocity, water quality and benthic cover are still in the process of being analysed. Data collected will also be used as baseline for future monitoring and analyses of biodiversity and key ecological processes within the framework of the 2011-2016 research program. 

Date
2013
Data type
Research report
Theme
Research and monitoring
Report number
C018/13
Geographic location
Saba bank