What seawater conductivity measurement really reveals

Seawater conductivity: what role does it play in multiparameter monitoring?

In a coastal or port area, or near an estuary, seawater conductivity helps quickly identify a change in the monitored water mass. This measurement is useful for detecting that a change is occurring, but it does not explain the cause on its own. This is why it is compared with other parameters depending on the context and the cause being investigated: turbidity near a construction site, dissolved oxygen in a sensitive area, pH or redox potential to complete the analysis of water conditions.

Key points of the article

  • Seawater conductivity varies with salinity and temperature, and its interpretation depends on the measurement conditions.
  • Depending on the site, it can be combined with turbidity, dissolved oxygen, pH or redox potential to better characterize the changes observed.
  • The choice of a multiparameter measurement chain depends on the application: marine construction activities, coastal environment, marine discharges, spot checks or continuous monitoring.
Eau de mer surveillée dans le cadre d’un suivi multiparamètre en environnement marin.

What does seawater conductivity reveal?

Conductivity depends on the dissolved ions present in the water. The higher their concentration, the more the water conducts electrical current. It is expressed in microsiemens per centimetre (µS/cm) or millisiemens per centimetre (mS/cm).

In seawater, this measurement is strongly linked to salinity. An unusual decrease or increase may lead operators to look for freshwater input, runoff or a nearby discharge. The measurement is therefore mainly used to identify a change that must be interpreted alongside site conditions and the other parameters being monitored.

What is the link between conductivity, salinity and temperature?

Salinity is determined from the measured conductivity, after taking temperature into account. The calculation is based on a standardised relationship between conductivity, temperature and salinity, rather than on a simple direct conversion.

Temperature also influences conductivity: with the same amount of salts, warmer water conducts electrical current more effectively. Sensors therefore also measure temperature in order to apply the necessary compensation. Without this correction, comparing two measurements taken under different thermal conditions would be misleading.

Why combine conductivity with other parameters?

Conductivity is combined with other parameters according to the application. Near marine construction activities , turbidity can be used to check whether a variation is also accompanied by an increase in suspended particles. In a sensitive coastal area, dissolved oxygen provides another perspective on environmental conditions. pH, redox potential and temperature can also be integrated depending on the project context. The aim is not to monitor every parameter, but to retain those that provide genuinely useful information about the phenomenon being observed.

In which marine environments should multiparameter monitoring be integrated?

Zone portuaire où la conductivité de l’eau de mer peut être intégrée à un suivi multiparamètre.
Port area
Zone maritime surveillée dans le cadre d’un suivi multiparamètre de la qualité de l’eau.
Marine construction sites
Environnement côtier surveillé par des mesures de conductivité et de qualité de l’eau.
Coastal environments
vNavire concerné par le contrôle de la qualité des eaux de ballast avant rejet en mer.
Ballast water

Multiparameter monitoring of marine construction activities

Near coastal works, several phenomena can simultaneously modify the characteristics of the water. Monitoring must therefore be organised in a way that distinguishes the influence of the works from natural inputs or other sources present in the area.

Aqualabo has deployed this type of monitoring as part of a project carried out in Genoa, Italy. The port authority wanted to monitor seawater 24/7 near a river mouth and coastal construction site in order to detect potential pollution. Two points were equipped at sea, at a depth of approximately four metres. The solution combined two NTU probes, one C4E sensor and AquaConnect to ensure data retrieval and transmission.

Multiparameter monitoring of coastal environments

In a coastal area, water conditions may change as a result of freshwater inputs, discharges from the shoreline, movements of water masses or activities taking place along the coast.

In Mauritius, Aqualabo took part in a continuous seawater quality monitoring project developed as part of the Blue Resilience programme. The system combined conductivity and salinity sensors, turbidity, dissolved oxygen, pH, redox potential and temperature. Data was transmitted continuously via a LoRaWAN network to an IoT platform in order to monitor changes in the seven parameters simultaneously. This configuration met the need to monitor sensitive coastal environments, particularly near coral reefs.

Sensors for connected buoys

Monitoring ballast water and marine discharges

Marine discharges are subject to regulatory requirements  that vary depending on their origin, the area concerned and the applicable regulatory framework. Ballast water, treated wastewater on board or certain effluents from maritime activities may be subject to analysis before discharge in order to verify compliance with the required criteria.

On board, these checks must also take space constraints into account, while remaining simple to perform. For example, Aqualabo equipped a cruise company with a customised solution combining ODEON Open X, a PHEHT sensor for pH and temperature, a C4E sensor for conductivity and an NTU sensor used for TSS. A Photopod LS completed the measurements for chlorine, ammonium, copper, hardness and COD, with a dedicated system for coliform testing.

How can a multiparameter measurement chain be implemented in seawater?

Capteur C4E pour mesurer la conductivité, la salinité et la température

Measuring conductivity and salinity with the C4E sensor

The C4E sensor measures conductivity, salinity and temperature. It can be used as part of a fixed station or integrated into a measurement chain comprising several sensors, depending on the required parameters and the data retrieval method.

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Appareil portable ODEON pour le suivi multiparamètre de la qualité de l’eau.

Carrying out multiparameter field checks

For spot measurements in the field or on board, ODEON makes it possible to connect several sensors to a portable instrument. It can measure several physicochemical parameters using Aqualabo digital sensors, including conductivity, salinity, pH, redox potential, dissolved oxygen, turbidity, TSS and temperature.

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Système LOG AQUA pour l’enregistrement et la transmission des mesures de qualité de l’eau.

Recording and transmitting data

For a fixed installation, LOG AQUA records measurements and transmits them remotely via the GSM network. Up to four sensors can be connected simultaneously. The data can be viewed from a web browser. SMS or email alerts can also be configured according to the thresholds defined for the site.

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Biofouling sur un capteur immergé utilisé pour surveiller la qualité de l’eau de mer.

How can reliable measurements be maintained during prolonged immersion?

Anticipating biofouling in marine environments

Prolonged immersion exposes sensors to biofouling: algae and other organisms can accumulate on the sensors and reach the measurement area. Fouling may alter the measurements and eventually make the data difficult to use. For installations intended to remain immersed for several weeks, it is recommended to favour sensors equipped with suitable anti-fouling protection.

Adapting maintenance to installation conditions

Anti-fouling protection does not remove the need for maintenance. Cleaning frequency varies from one site to another, depending on the sensor used and the speed at which it becomes fouled. A visual inspection makes it possible to check the condition of the measurement area and intervene before deposits disrupt the data. Access to the sensors must therefore remain sufficiently simple to facilitate maintenance operations.

Adapting multiparameter monitoring to the constraints of the marine environment

At sea, measurement quality depends as much on the choice of parameters as on how the system is integrated into the constraints of the site. Aqualabo, a French company with an international presence, supports water professionals in monitoring projects with solutions adapted to real operating conditions. Contact our teams today to find out how to adapt your measurement system  to the constraints of your marine environment and your monitoring needs.

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