Evaluating the Performance of PyroScience AquapHOx Loggers With New Antifouling Sensors for Long-Term pH and Oxygen Monitoring in Coastal Waters

Introduction

Accurate and consistent real-time in situ monitoring of oxygen, pH, and temperature is essential for understanding biogeochemical processes and ecosystem dynamics in coastal waters. These aquatic environments are vital habitats for diverse marine life and play a significant role in global carbon cycling and nutrient regulation. However, they are often affected by anthropogenic stressors such as industrial discharge, agriculture, and urban runoff. It is important to understand the impact of these stressors on such environments, as well as climate-driven changes like ocean acidification and hypoxia, which threaten the well-being of aquatic organisms. Advanced sensor technology that allows for autonomous, long-term monitoring of essential parameters is needed for understanding these processes and dynamics.

Both short and long-term monitoring in these environments often face significant challenges, like biofouling, which occurs when microorganisms, algae, or invertebrates attach to sensor surfaces, causing sensor drift, reduced accuracy, and higher maintenance requirements. To address these challenges, PyroScience recently developed innovative oxygen and pH sensor caps with a new antifouling layer that are compatible with their flexible plug-and-play AquapHOx loggers and transmitters. 

The new antifouling pH caps are designed for monitoring pH between 7 and 9 (+-0.5) (PHCAP-PK8-AF-SUB) including total scale option (PHCAP-PK8T-AF-SUB, see pic. 1) and the oxygen sensor cap (OXCAP-AF-SUB, see pic. 2) is used for monitoring DO.

For additional protection, all pH and oxygen sensor caps, as well as AquapHOx devices, can be combined with copper protection cages (APHOX-CAGE-AF and APHOX-CAP-AF, see pic. 3 and 4) which can be easily attached as an additional protective layer to prevent sensor biofouling.

To assess the effectiveness of these new sensor caps in preventing biofouling and ensuring long-term, accurate data collection in challenging shallow water coastal environments, PyroScience carried out separate deployments at two locations: Kiel Fjord (Western Baltic Sea, Germany) and Rovinj (Northern Adriatic Sea, Croatia). The main focus of this study was on comparing the absolute difference between two sensor versions – one equipped with the antifouling layer and one without.

• 2 x AquapHOx-L-pH loggers: 1 x PHCAP-PK8T-SUB, 1 x PHCAP-PK8T-AF-SUB
• 2 x AquapHOx-L-O2 loggers: 1 x OXCAP-SUB, 1 x OXCAP-AF-SUB

The loggers were mounted on a stainless-steel frame and positioned at ca. 1.5m below the water surface. pH and oxygen levels were recorded at 1-minute intervals, ensuring high-resolution data collection.

To provide additional biofouling protection, the loggers and sensor caps were equipped with an antifouling cage (APHOX-CAGE-AF) and a protective cap (APHOX-CAP-AF).

The second deployment in the nutrient-rich waters of Rovinj, Croatia took place over 6 months with some sensor servicing in between due to the longer deployment period. A total of six AquapHOx shallow water loggers were deployed (see Pic. 6):

• 3 x AquapHOx-L-pH loggers: 2 x PHCAP-PK8T-SUB, 1 x PHCAP-PK8T-AF-SUB
• 3 x AquapHOx-L-O2 loggers: 1 x OXCAP-SUB, 2 x OXCAP-AF-SUB

One of the PHCAP-PK8T-SUB, the PHCAP-PK8T-AF-SUB, and all of the oxygen sensors were protected from biofouling additionally with copper cages (APHOX-CAGE-AF, APHOX-CAP-AF). The measurement interval for all pH and oxygen sensors was set to 1-minute.

It is clear from the images that some significant biofouling occurred on device and sensor surfaces during both deployments, but data shows that the antifouling protection cages have provided a good level of resistance enhancing the results quality in comparison to what they would have been without using the cages.

To learn more, download the full white paper: “Evaluating the Performance of PyroScience AquapHOx Loggers with New Antifouling Sensors.” If you’d like discuss how this technology could be tailored to your needs, feel free to contact us.