DOI: 10.5061/dryad.rxwdbrvn9
title: Calibration of the transparency tube for estimating turbidity in estuarine systems

description: Turbidity, quantified in turbidity units (nephelometric or formazin), is a
 common and valid measure of water quality related to transparency. A
 transparency tube (TT) is an economical tool developed to estimate water
 clarity as an alternative to the Secchi disk, but it is also frequently
 used to estimate turbidity. Although the relationship between TT measures
 and turbidity is well characterized for freshwater river and lake systems,
 this relationship has not been tested for estuarine waters. The objective
 of the current study was to empirically determine the TT-turbidity
 relationship for estuarine waters and compare these results with the
 traditional freshwater system conversions. We obtained 107 measurements of
 TT depth, turbidity, total suspended solids, CDOM absorbance, Secchi
 depth, and chlorophyll a at 22 estuarine locations in South
 Carolina over a one-year period. Linear regressions provide conversion
 equations that can be applied to estuarine waters. The TT-turbidity
 relationship for estuaries was compared with freshwater systems. Our
 results suggest that the slope of the relationship differs between systems
 (-1.11 vs. -1.41), resulting in different turbidity estimates for TT
 measurements for estuarine vs. inland waters. We propose a combined
 conversion table incorporating estuarine and freshwater (riverine and
 lacustrine) systems. A TT-turbidity conversion for estuarine waters
 significantly benefits current coastal water quality programs and citizen
 science groups by producing more accurate turbidity estimates for
 screening and routine monitoring efforts.
description: A total of 22 estuarine locations were sampled 107 times in 2022
 - 23, stretching from North Myrtle Beach to Port Royal Sound along the
 coast of South Carolina (Fig. 2). The goal was to include a range of water
 types with different turbidity characteristics from tidal regions of
 coastal waterbodies. Site selection was determined based on accessibility,
 usually from a boat dock or launch ramp. Water
 transparency, photosynthetically available radiation (PAR) depth profiles,
 salinity, and temperature were obtained on-site. Transparency was measured
 using a 120 cm “transparency tube” (Eisco Labs, Victor, NY, PN
 PH1120148120SPR). The transparency tube (TT) was filled with well-mixed
 water from the sample site using a 1 m bailer and carboy. While looking
 through the top opening of the tube, water was slowly drained out of the
 bottom until the Secchi disk at the bottom of the tube was visible, and
 the depth of the remaining water (in cm) was recorded. The water column
 length in the TT was recorded as the average of two independent
 measurements taken by observers. The Secchi depth was determined using a
 20 cm black and white Secchi disk and measured in centimeters. Both Secchi
 and TT measurement methodologies follow the protocol by Ohrel and Register
 (2007). A Li-Cor LI-250A portable light meter with a LI-COR LI-193
 spherical underwater quantum sensor was lowered into the water column to
 measure photosynthetically available radiation (PAR, 400 – 700 nm)
 available throughout the water column (LI-COR, Lincoln, NE, USA). PAR
 values were recorded as 15 s averages at 0.25 m depth intervals, in units
 of µmol photons m<sup>-2</sup> s<sup>-1</sup>.
 Measurements continued until the PAR equaled 0, or, if the sample depth
 was exceptionally shallow, until the bottom of the water column was
 reached (the maximum depth for the cable was 8 m). The equation used for
 calculating the diffuse attenuation coefficient for PAR
 (k<sub>d(PAR)</sub>) was: E<sub>z
 </sub>=
 E<sub>o</sub>e<sup>-kz</sup>
 Where z is water depth (m), E<sub>z </sub>is the PAR
 at a depth (z), E<sub>o</sub> is the PAR at the surface, and k
 is the diffuse attenuation coefficient (Kirk 2011). Salinity was
 determined using a refractometer, and temperature was measured with a
 digital thermometer. GPS coordinates, tidal stage, and weather conditions
 were recorded during sampling. The remaining sample water in the carboy
 was mixed well, poured into an opaque 1 l Nalgene bottle, and stored in an
 ice cooler for 3-5 hours before laboratory analysis.
 Total suspended solids (TSS), turbidity (NTU), chromophoric
 dissolved organic matter (CDOM), and phytoplankton biomass (as chlorophyll
 <em>a, </em>chl<em> a</em>) were measured for each
 sample. Water for TSS measurements was filtered through pre-weighed
 filters (GF/F, 47 mm, 0.7 µm nominal particle retention), dried at 45 °C
 for 24 h, and reweighed to determine the dry weight of suspended solids.
 Water for chl <em>a</em> was vacuum filtered onto 25 mm
 filters (GF/F) and stored at -80 ˚C until analysis. For CDOM measurements,
 50 ml of water was syringe-filtered through a dried 25 mm GF/F filter and
 stored at 4 ˚C for no longer than one month. A calibrated Hach 2100Q
 turbidimeter (PN: 2100Q01) was used to measure turbidity in NTU, following
 the U.S. EPA Method 180.1 (US EPA 1993). An average of at least three
 independent readings was recorded. A Jasco V-730 UV-visible
 spectrophotometer was used to measure the absorbance of CDOM at a
 wavelength of 355 nm. The absorbance at this wavelength represents CDOM
 concentration in coastal environments (Blough and Del Vecchio 2002; Kirk
 2011). CDOM raw absorbance data were converted into absorption
 coefficients (<em>a</em>) using the equation (Hu et al.
 2002): <em>a</em><sub>(355)
 </sub>= 2.303
 *<em>A</em><sub>(355)</sub>/0.05
 Where <em>A</em>(<em>l</em>) is the raw
 wavelength-dependent absorbance, and 0.05 is the optical path length of
 the cuvette in meters. High-performance liquid chromatography (HPLC) was
 used to determine chl <em>a</em>.. Samples were lyophilized
 for 24 h at -50 °C, placed in 90% acetone (0.750 ml), sonicated, and
 extracted at -20 °C for 18 - 20 h. Filtered extracts (250 µl) were
 injected into a Shimadzu 2050 HPLC equipped with a monomeric (Rainin
 Microsorb-MV, 0.46 x 10 cm, 3 µm) and a polymeric (Vydac 201TP54, 0.46 x
 25 cm, 5 µm) reverse-phase C18 column in series. A nonlinear binary
 gradient consisting of the solvents 80% methanol: 20% 0.50 M ammonium
 acetate and 80% methanol:20% acetone was used for pigment separations
 (Pinckney et al. 2001a).
 <strong>Statistics</strong> All
 data were log<sub>10</sub> transformed before analysis. IBM
 SPSS Statistics (v. 29.0) was used for the correlations and linear
 regressions, and slope comparisons were made using OriginPro
 2025.
description: # Calibration of the transparency tube for estimating turbidity in
 estuarine systems Dataset DOI:
 [10.5061/dryad.rxwdbrvn9](10.5061/dryad.rxwdbrvn9) ## Description of the
 data and file structure The primary objective of our study was to
 empirically determine the transparency tube (TT) to turbidity (ntu)
 relationship for estuarine and coastal waters and compare these results
 with traditional freshwater system conversions. Our aim was to evaluate
 the accuracy of the freshwater system conversions for estuarine systems. A
 second objective was to examine the correlations between TT, Secchi depth,
 total suspended solids, chromophoric dissolved organic matter (CDOM), and
 the diffuse attenuation coefficient (kd) for photosynthetically available
 radiation (PAR). Estuarine locations (22 sites) were sampled for a total
 of 107 times in 2022 - 23, stretching from North Myrtle Beach to Port
 Royal Sound along the coast of South Carolina. The goal was to include a
 range of water types with different turbidity characteristics from tidal
 regions of coastal waterbodies. Site selection was determined based on
 accessibility, usually from a boat dock or launch ramp. Water
 transparency, photosynthetically available radiation (PAR) depth profiles,
 salinity, and temperature were obtained on-site. Transparency was measured
 using a 120 cm “transparency tube” (Eisco Labs, Victor, NY, PN
 PH1120148120SPR). The transparency tube (TT) was filled with well-mixed
 water from the sample site using a 1 m bailer and a carboy. While looking
 through the top opening of the tube, water was slowly drained out of the
 bottom until the Secchi disk at the bottom of the tube was visible, and
 the depth of the remaining water (in cm) was recorded. The water column
 length in the TT was recorded as the average of two independent
 measurements taken by observers. The Secchi depth was determined using a
 20 cm black and white Secchi disk and measured in centimeters. Both Secchi
 and TT measurement methodologies follow the protocol by Ohrel and Register
 (2007). A Li-Cor LI-250A portable light meter with a LI-COR LI-193
 spherical underwater quantum sensor was lowered into the water column to
 measure photosynthetically available radiation (PAR, 400 – 700 nm)
 available throughout the water column (LI-COR, Lincoln, NE, USA). PAR
 values were recorded as 15-s averages at 0.25 m depth intervals, in units
 of µmol photons m-2 s-1. Measurements continued until the PAR equaled 0,
 or, if the sample depth was exceptionally shallow, until the bottom of the
 water column was reached (the maximum depth for the cable was 8 m). The
 equation used for calculating the diffuse attenuation coefficient for PAR
 (kd(PAR)) was: Ez = Eoe-kz Where z is water depth (m), Ez is the PAR at a
 depth (z), Eo is the PAR at the surface, and k is the diffuse attenuation
 coefficient (Kirk 2011). Salinity was determined using a refractometer,
 and temperature was measured with a digital thermometer. GPS coordinates,
 tidal stage, and weather conditions were recorded during sampling. The
 remaining sample water in the carboy was mixed well, poured into an opaque
 1 l Nalgene bottle, and stored in an ice cooler for 3-5 hours before
 laboratory analysis. Total suspended solids (TSS), turbidity (NTU),
 chromophoric dissolved organic matter (CDOM), and phytoplankton biomass
 (as chlorophyll *a, chl* a) were measured for each sample. Water for TSS
 measurements was filtered through pre-weighed filters (GF/F, 47 mm, 0.7 µm
 nominal particle retention), dried at 45 °C for 24 h, and reweighed to
 determine the dry weight of suspended solids. Water for chl *a* was vacuum
 filtered onto 25 mm filters (GF/F) and stored at -80 ˚C until analysis.
 For CDOM measurements, 50 ml of water was syringe-filtered through a dried
 25 mm GF/F filter and stored at 4 ˚C for no longer than one month. A
 calibrated Hach 2100Q turbidimeter (PN: 2100Q01) was used to measure
 turbidity in NTU, following the U.S. EPA Method 180.1 (US EPA 1993). An
 average of at least three independent readings was recorded. A Jasco V-730
 UV-visible spectrophotometer was used to measure the absorbance of CDOM at
 a wavelength of 355 nm. The absorbance at this wavelength represents CDOM
 concentration in coastal environments (Blough and Del Vecchio 2002; Kirk
 2011). CDOM raw absorbance data were converted into absorption
 coefficients (*a*) using the equation (Hu et al. 2002): *a*(355) = 2.303
 **A*(355)/0.05 Where *A*(*l*) is the raw wavelength-dependent absorbance,
 and 0.05 is the optical path length of the cuvette in meters.
 High-performance liquid chromatography (HPLC) was used to determine chl
 *a*. Samples were lyophilized for 24 h at -50 °C, placed in 90% acetone
 (0.750 ml), sonicated, and extracted at -20 °C for 18 - 20 h. Filtered
 extracts (250 µl) were injected into a Shimadzu 2050 HPLC equipped with a
 monomeric (Rainin Microsorb-MV, 0.46 x 10 cm, 3 µm) and a polymeric (Vydac
 201TP54, 0.46 x 25 cm, 5 µm) reverse-phase C18 column in series. A
 nonlinear binary gradient consisting of the solvents 80% methanol: 20%
 0.50 M ammonium acetate and 80% methanol:20% acetone was used for pigment
 separations (Pinckney et al. 2001a). ### Files and variables #### File:
 Datafile\_for\_Dryad.csv **Description:** Data are in comma-separated form
 and available for future analyses and comparisons. Column headers are as
 follows: ##### Variables Site: Name of sampling location in South
 Carolina, USA Date: Date the samples were collected Latitude and
 Longitude: Sampling location in digital degrees (north latitude and west
 longitude) Secchi Depth: Maximum depth (m) for detecting the Secchi disk
 Transparency Tube: Length of the water column (cm) for minimum detection
 of the disk at the bottom of the tube Turbidity: Water turbidity in
 nephelometric turbidity units (ntu) Salinity: Water salinity measured in
 practical salinity units (PSU) Temperature: Water temperature in degrees
 Celsius (°C) Kd(PAR): The diffuse attenuation coefficient for
 photosynthetically available radiation (PAR, 400 – 700 nm) Water Depth:
 Water depth at the sampling location (m) TSS: Total suspended solids (mg
 l-1) A355: Absorption coefficient for water containing CDOM at 355 nm
 (m-1) Chlorophyll a: Phytoplankton concentration in units of chlorophyll a
 (µg l-1) Missing data are denoted by “-999”