Salinity and stable isotope dataset for Guayas estuary waters

The Guayas estuary is an ecologically and economically vital, large estuarine system located on the western coast of South America. A suite of ∼400 water samples was collected and analyzed to enable investigation of the sources of water types within this estuary, as well as environmental processes active within various portions of it. These samples were obtained at sites distributed across the major areas of the inner and outer portions of the estuary at the ends of consecutive dry (December/January) and rainy (May) seasons. At each site, Van Dorn bottles were lowered into the water from a boat (or bridge) and then triggered when they reached specified depths. When the Van Dorn bottles were brought back aboard the boat, aliquots of water from them were promptly sealed in glass containers for later analysis. These were transported to onshore laboratories where their salinities, and their oxygen (δ18O) and hydrogen (δ2H) isotopic compositions were measured. Established analytical procedures and standards were employed to obtain a robust set of resultant data. The samples, analyses, and data presented here support the associated research article, “Stable isotope evidence for the origins of waters in the Guayas estuary and Gulf of Guayaquil” [1], to which readers are referred for interpretation.

© 2021 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Table   Subject Earth and Planetary Sciences Specific subject area Oceanography Type of data Table  How data were acquired Water samples were collected in the field. Salinities were determined using a HACH HQ14d conductivity meter; oxygen and hydrogen isotope ratios were determined using a Picarro L2120i cavity ring-down spectroscopy (CRDS) analyzer. Data format Raw and analyzed data Parameters for data collection Water sample collection date, latitude ( °), longitude ( °), depth (m), salinity (PSU), oxygen isotope ratio ( ‰ ), and hydrogen isotope ratio ( ‰ ) Description of data collection Sampling devices were deployed from boats to collect waters at sites and water depths distributed across the Guayas estuary. Their salinities were determined from measured conductivity ( ±0.1 precision on PSS-78 practical salinity scale) at INOCAR, and their stable isotope ratios of oxygen ( δ 18 O) and hydrogen ( δ 2 H) were measured at Texas A&M University using a CRDS analyzer at (precisions of individual δ 18 O and δ 2 H analyses relative to VSMOW are ±0.1 ‰ and ±1.0 ‰ , respectively).

Specifications
Data source location Water samples were collected in the Guayas estuary of Ecuador (see Table 1 for specific coordinates). The samples were analyzed at these institutions:

Value of the Data
• Salinity, δ 18 O, and δ 2 H values for Guayas estuary waters indicate the origins of estuarine waters and environmental processes that affect these waters. • Researchers interested in estuarine dynamics benefit from knowledge of abundances of water types and movement of water within various parts of the estuary. • This dataset can be used to support studies of nutrient cycling and pollutant transport, and it can inform the further studies of estuarine circulation and the impacts of seasonal and inter-annual climate variability on the estuary's physical and biological components.

Methods
The water samples were collected using Van Dorn bottles lowered into the water with lines, typically from 9.5-m-long survey boats and at a few sites from bridges. Geographical coordinates of the boats were determined using C-Nav GPS systems. The Van Dorn bottles were triggered when they reached specified depths and then brought back aboard the boats, where aliquots of water for salinity and stable isotope analyses were promptly put in 250 ml glass bottles and 20 ml glass vials, respectively, and sealed using conic plastic caps and electrical tape. These bottles were kept under refrigerated conditions prior to being analyzed.
The 250 ml bottles with Guayas estuary water samples were taken to the Department of Chemical Oceanography at the Instituto Oceanográfico de la Armada (INOCAR) in Guayaquil, Ecuador, where a HACH HQ14d meter with conductivity probe was used to determine their salinities. A water sample's conductivity depends on the amount of dissolved salts in it and the temperature at which conductivity is measured. The response of the conductivity probe was calibrated by inserting it into solutions of known salinity and temperature, then the probe was inserted into aliquots of water from the Guayas estuary samples and their conductivity and temperature were measured. Based upon the established probe response, the salinity of each water sample was calculated from its measured conductivity and temperature. Standard procedures for instrument calibration and the direct measurement method were followed (for example, see Ref. [3] ).
To assess the consistency of salinity measurements, aliquots of a standard solution were periodically analyzed with the Guayas estuary samples. The estimated precision of an individual salinity analysis is ±0.1 on the PSS-78 practical salinity scale, as indicated by the standard deviation of the replicate analyses of standards. Replicate analyses of the salinities of several randomly selected Guayas estuary samples were also made. In each instance, the difference between each pair of measured values was smaller than the estimated precision of the individual measurements, so a single value for each sample is presented in Table 1 .
The salinity values of discrete water samples determined in the laboratory were compared to in situ profiles of salinity obtained with a SeaBird CTD at the sites where the water samples were collected. The water sample values agreed well with the in situ profile values, indicating the Van Dorn bottles triggered at the intended water depths and the samples were not affected by handling prior to being analyzed.