Water quality surveys in Culebra: comprehensive assessment of inorganic nutrient and human dietary tracer concentrations 2023-05-03 to 2024-05-21

This record provides dissolved inorganic nutrient and human dietary tracer (caffeine and sucralose) concentration metrics collected monthly between May 2023 to May 2024 to provide reference data of nearshore and watershed water quality on the island of Culebra, Puerto Rico. The water quality monitoring was conducted at 18 fixed stations. Five stations were selected to quantify Land Based Sources of Pollution (LBSP) stressor loads at key point and non-point sources in the Cabra, Coronel, and Aeropuerto watersheds. Levels of LBSP exposure were measured at 13 nearshore stations co-located with long-term seagrass monitoring sites. Nearshore monitoring sites were selected to identify watershed discharge points, coastal hydrodynamics, as well as the existing level of LBSP exposure and anticipated changes to LBSP exposure due to management actions. Nearshore monitoring stations were designated based on their land based sources of pollution management implementation status (LBSP Treatment Group), as follows: 1) LBSP Restoration stations: Located downstream where land-based pollutant management has or is being implemented. 2) LBSP Control stations: Representing a range of land-based pollutant impairments, including sites with no LBSP management and no known direct discharge of LBSP but are representative of the range of external factors that may be encountered at the LBSP Restoration stations. 3) Negative Reference stations of know significant -anecdotal and quantified- LBSP impairment. 4) Positive Reference stations of low LBSP impairment.

Nearshore water quality samples for nutrients were collected at two depths: surface (10-25 cm ) and bottom (2 m deep). Human dietary tracer water samples were collected at surface, only collected at the 13 nearshore monitoring stations. Watershed water quality samples were collected only at surface. Metrics include: Nitrite, nitrate, ammonium, total nitrogen, orthophosphate, total phosphorus, and silicate; caffeine and sucralose. The data presented herein was collected with financial support from NOAA Restoration Center and NOAA Coral Reef Conservation Program, and the National Fish and Wildlife Foundation (NFWF). The research questions, survey design and monitoring localities were specific to this study and the associated water quality data is unsuitable in a regulatory framework.

This work is an integral component of the Culebra Ridge-to-Reef Monitoring Program; a spatiotemporally coordinated effort designed to evaluate the effectiveness of the NOAA management strategies and actions in priority watersheds to reduce land-based sources of pollution (LBSP) impacts to the nearshore marine ecosystems of the island. This ridge-to-reef monitoring framework implements a Multiple Lines of Evidence approach consisting of: 1) Monitoring of LBSP stressors that are being managed through NOAA funding including sediment accumulation at unpaved road stabilization projects, water quality monitoring at key points throughout the watershed, and watershed modeling to estimate pollutant loads into the nearshore coastal environment. 2) Monitoring of LBSP exposure through nearshore water quality and sediment trap monitoring at nearshore fixed stations. 3) Monitoring of nearshore habitat responses that is co-located with the aforementioned nearshore water quality fixed stations and includes data collection via seagrass monitoring transects. Within this context, water quality is characterized and tracked to quantify the land-based pollutant loads and exposure levels in the receiving coastal environment and the associated seagrass and coral reef communities, which are ultimately the focal point of the NOAA LBSP management efforts on Culebra.

These data address LBSP pollutant stressor and exposure monitoring, specifically inorganic nutrient concentrations, which together with LBSP habitat response monitoring represent the basis of Culebra's integrated LBSP Monitoring and Evaluation Framework with which to successfully assess progress and effectiveness toward achieving NOAA LBSP management goals and outcomes on Culebra. The parameters selected for monitoring are known to be good indicators of water quality condition (U.S. Coral Reef Taskforce Watershed Partnership Initiative Priority Ecosystem Indicators). In particular, indicators that are linked to both the LBSP management that is conducted in the watershed while also being linked to potential changes in habitat response.

Human dietary tracers were collected to identify the sources of LBSP pollution; human or environmental.

https://www.ncei.noaa.gov/data/oceans/coris/library/NOAA/CRCP/NMFS/OHC/Projects/30033/Culebra_LBSP_RidgeToReef_Monitoring_Program/Vargas-Angel2024_Culebra_LBSP_RidgeToReef_Monitoring_Program.pdf

https://www.ncei.noaa.gov/data/oceans/coris/library/NOAA/CRCP/NMFS/OHC/Projects/30033/Culebra_LBSP_RidgeToReef_Monitoring_Program/Vargas-Angel2024c_Nearshore_WaterQuality_Monitoring_WorkPlan.pdf

https://www.ncei.noaa.gov/data/oceans/coris/library/NOAA/CRCP/NMFS/OHC/Projects/30033/Culebra_LBSP_RidgeToReef_Monitoring_Program/Vargas-Angel2024e_Seagrass_Monitoring_Transects_WorkPlan.pdf

https://www.ncei.noaa.gov/data/oceans/coris/library/NOAA/CRCP/NMFS/OHC/Projects/30033/Culebra_LBSP_RidgeToReef_Monitoring_Program/Vargas-Angel2024b_Watershed_WaterQuality_Monitoring_WorkPlan.pdf

https://www.ncei.noaa.gov/data/oceans/coris/library/NOAA/CRCP/NMFS/OHC/Projects/30033/Culebra_LBSP_RidgeToReef_Monitoring_Program/Vargas-Angel2024f_Appendix-A_Identifying_Priority_Fixed-Site_Monitoring_Locations.pdf

https://www.coris.noaa.gov/activities/uscrtf_watershed_tools/Priority_Ecosystem_Indicators_Final%202_18_16.pdf

Discrete water samples (125 mL) were collected for the analysis of nutrients including nitrate, nitrite, orthophosphate, ammonium, total nitrogen, total phosphorus, and silica. Watershed samples were hand collected at surface (10-25 cm); nearshore samples were collected at the surface and bottom (~2 m deep; employing a Niskin bottle). Sterile nitrile gloves were worn at all times to avoid sample contamination. Samples were frozen and sent to the TDI-Brooks Laboratory for analyses. For further instrumentation and methodological details please review the Culebra Nearshore and Watershed Water Quality Monitoring Work Plans listed under "Other Citation Details" and "Lineages".

Nitrate and nitrite analyses are based on the methodology of Armstrong et al. (1967) and utilize a ground Cd column for reduction of NO3- to NO2-. Orthophosphate is measured using chemistry based on the investigations of Bernhardt and Wilhelms (1967) with the modification of hydrazine as a reductant. Silicate determination is accomplished using the methods of Armstrong et al. (1967) using stannous chloride. Ammonium analysis is based on the method of Harwood (Harwood and Kuhn, 1970) using dichloro-isocyanurate as an oxidizer. Laboratory intercomparisons have been conducted and results are available. In order to increase processing efficiency and speed, voltage streams from the colorimeters are logged via a National Instruments acquisition board and data is acquired and stored using Labview. Peak processing is accomplished using software written in Matlab and software development continues. Peak voltage values associated with standards and samples can be determined with the written software, but manual checks and adjustment are still required at the present. The total concentrations of nitrogen and phosphorus are determined after an initial decomposition step. This method involves persulfate oxidation while heating the sample in an autoclave (115 degrees Celsius, 20 minutes) (Hansen and Koroleff 1999). After oxidation of the samples nutrient determination is conducted on the Technicon II analyzer. Samples are processed in batches of 30 with a full range of standards and blanks. All samples, standards, and blanks are run in a standard format as described above. Sample weight is recorded before and after oxidation treatment (and cooling) to detect any loss in volume. In order to determine total nitrogen and phosphorus a separate sample in addition to the volume taken for determination of dissolved components above must be provided. A 20 ml volume in the above-mentioned 30 ml Nalgene containers suffices. Currently five standards are run in duplicate at the beginning of each day. Line regression calculations are conducted to generate conversion equations. Correlation coefficients of 0.99 or better are achieved prior to analysis. At the end of each day's run all standards are analyzed again and regression analysis is conducted. The results of these regression analyses are compared to the initial determinations and adjustments can be made for instrument drift. Low-end standards are also analyzed along with an internal standard (Spex certified standard, Certiprep Inc.) between each batch of 10 samples with blank determination before and after each standard check. Blanks are also analyzed after each calibration in order to bracket each batch of 10 samples. These blanks are used to adjust the baseline and to monitor drift. Duplicate samples are analyzed with each batch. The %RPD must be less than 30% for each of the analytes measured if the detected analytes are detected at greater than 3x MDL. These methods are based on the following references:

-Aminot, A. and R. Kerovel. 1982. Dosage automatique de l'uree dans l'ea de mer: une methode tres sensible a la diacelylmonoxime. Can. J. Fish. Aquat. Sci. 39: 174-183.

-Armstrong, F. A. J., C. R. Stearns, et al. (1967). "The measurement of upwelling and subsequent biological processes by means of the Technicon Autoanalyzer and associated equipment." Deep-Sea Research 14(3): 381-389.

-Bernhardt, H. and A. Wilhelms (1967). The continuous determination of low level iron, soluble phosphate and total phosphate with the AutoAnalyzer. Technicon Symposium.

-Hansen, H. P. and F. Koroleff (1999). Determination of Nutrients. Methods of Seawater Analysis. K. Grasshoff, K. Kremling and M. Ernhardt. New York, Wiley-VCH: 159-251.

-Harwood, J. E. and A. L. Kuhn (1970). "A colorimetric method for ammonia in natural waters." Water Research 4: 805 - 811.

Discrete nearshore surface (10-25 cm) water samples (250 mL) were collected for the analysis of human dietary tracers of caffeine and sucralose. Sterile nitrile gloves were worn at all times to avoid sample contamination, and purified water was used as blank. Water samples were frozen and sent to the TDI-Brooks Laboratory for analyses. For further samping and methodological details please review the Culebra Nearshore Water Quality Monitoring Work Plan listed in this Summary Package under "References". Caffeine and Sucralose were extracted in water by Solid Phase Extraction followed by determination in water by liquid chromatography following the protocols outlined in:

-Sanatsania, C.œApplication Report 266: LC-MS Analysis of Sucralose and Sucrose Octacetate on Ascentis RP-Amide, Supelco. 2005.

-Wu, M., Qian, Y., Boyd, J., Hrudey, S., Le, X., Li, X. Direct large volume injection ultra-high performance liquid chromatography-tandem mass spectrometry determination of artificial sweeteners sucralose and acesulfame in well water. Journal of Chromatography A. 2014.

-Batchu S, Ramirez C, Gardinali P (2015) Rapid ultra-trace analysis of sucralose in multiple-origin aqueous samples by online solid-phase extraction coupled to high-resolution mass spectrometry. Anal. Bioanal. Chem. 407 (2015), pp. 3717-3725.

-Wang C (2012) Assessment of the occurrence and potential effects of pharmaceuticals and personal care products in south florida waters and sediments. Florida International University Electronic Theses and Dissertations (2012), p. 689. https://digitalcommons.fiu.edu/etd/689.

These protocols resulted in method detection limits (MDLs) of 2.806 and 0.984 ng/L, for caffeine and sucralose respectively

Raw data include monthly individual water quality parameter measurements.

The temporal data for each survey station include: survey year, date, and time.

The physical data for the survey stations include: station name, Latitude (decimal degrees), and Longitude (decimal degrees). Watershed (i.e., contributing drainage area), and land-based sources of pollution management implementation status is also included.

Water quality parameters include: nitrate, nitrite, ammonium, total nitrogen, orthophosphate, total phosphorus, silica, caffeine, and sucralose.

While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.

We welcome the opportunity to collaborate on research issues contributing to the scientific basis for better management of marine ecosystems.

The following recommendations are for your consideration as you use this data:

1) Data analyses should take all field exigencies into account. The most effective way to do this would be active collaboration with principal investigators.

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3) If you collect or generate data for the same study areas, NOAA requests that you share relevant information on complimentary data collections.

Data can be accessed online via the NOAA National Centers for Environmental Information (NCEI) Ocean Archive.

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Data were collected once monthly from May 2023 to May 2024 and provide a quantitative baseline of nutrient stressor loads and key point and non-point sources in the watersheds, and nutrient stressor exposure in the nearshore waters. The data is spatially explicit; not all watershed and nearshore habitats on island are represented.

Water quality measurement were made implementing state-of-the-art laboratory instrumentation.

Handheld GPS units were used to locate sites and mark site locations.

Nutrient concentrations in non-eutrophic tropical marine coastal ecosystems are typically low and laboratory analyses often times return values below the instrument's detection limit (BDL). Numeric concentration values BDL for January-May 2024 are not provided; the analytical chemistry laboratory processing the samples (TDI-Brooks Analytical Laboratory) modified their data output and Tech Report format.

The research questions, survey design and monitoring localities are specific to this study and the associated water quality data is inadequate for regulatory purposes.

Data gaps may originate from, but not limited to, instrument malfunction or weather conditions.

Handheld GPS units were used to locate sites.

Instrument Detection Limit:

Nitrate: <0.0099 mg/L

Nitrite <0.0006 mg/L

Ammonium: <0.0035 mg/L

Orthophosphate: <0.0068 mg/L

Total Phosphorus: <0.03 mg/L

Survey methods were consistent across all sites.

The quality control occurred at three major stages - 1) instrument calibration; 2) data entry; and 3) data management. Data entry quality control included both review and manual error correction steps.

This data addresses LBSP pollutant loads and exposure monitoring, specifically nutrient concentrations, which together with LBSP habitat response monitoring represent the basis of Culebra's Integrated LBSP Monitoring and Evaluation Framework with which to successfully assess progress and effectiveness toward achieving NOAA LBSP management goals and outcomes on Culebra.