Water sampling is the process of collecting a portion of water from various sources such as natural environments, industrial sites, or water distribution systems, in order to analyze its quality and composition. This process is crucial for monitoring and ensuring that water meets safety and quality standards for its intended use, whether it be for drinking, recreational activities, or as part of an industrial process. Water sampling can be performed using different techniques, such as discrete or grab sampling, where a single sample is collected at a specific time and place, or through more complex procedures involving multiple samples and electronic equipment. The collected samples are then transported, often under controlled conditions, to a laboratory for analysis.
A rosette sampler, also known as a CTD-rosette or carousel, is a device used for water sampling in deep water bodies such as oceans and large inland water bodies. The name “rosette” comes from the circular arrangement of the sampling bottles around a central cylinder. The rosette sampler is made up of an assembly of 12 to 36 sampling bottles, each with a volume ranging from a minimum of 1.2 L to a maximum of 30 L. Each bottle can be programmed to open at a specific depth, allowing for the collection of water samples from different depths in the water column. The opening of each sampling bottle can be automatic (triggered by reaching a certain depth) or manual (remotely controlled).
The central cylinder of the rosette sampler houses a sensing system called a CTD, which stands for “Conductivity, Temperature, and Depth”. Modern CTDs can also measure other variables such as water turbidity, dissolved oxygen concentration, chlorophyll concentration, and pH.
The rosette sampler is lowered into the water using a wire rope attached to a winch on board the boat. It can approach the seabed at a distance from 1 to 5 m, depending on the particular sea conditions
Rosette samplers are a key piece of equipment in oceanography and are used for various applications such as chemical analysis and ecotoxicological assessment of water. They are preferred over other types of samplers for collecting water samples at different depths due to their ability to collect multiple samples at once and their integrated CTD sensors.
How Rosette Sampler Work
Rosette samplers are devices used to collect water samples from various depths in a body of water for scientific analysis. The CTD (Conductivity, Temperature, and Depth) Rosette is a specific type of rosette sampler that combines water sampling with the measurement of physical water conditions.
Here’s how a typical CTD Rosette sampler works:
1. Assembly of Niskin Bottles: The Rosette sampler consists of an array of Niskin bottles, which are cylindrical containers that can be triggered to close at specific depths, capturing a water sample inside. A standard Rosette may have anywhere from 8 to 12 bottles, but smaller versions with fewer bottles are also used.
2. Integration with Sensors: The Rosette is equipped with sensors that measure conductivity (to determine salinity), temperature, and depth. These sensors provide real-time data on the water column’s physical characteristics as the Rosette is lowered into the water.
3. Deployment: The Rosette sampler is lowered into the water body from a research vessel. It is typically connected to a winch with a cable that transmits sensor data back to the ship and is used to trigger the closing of the Niskin bottles at predetermined depths.
4. Sample Collection: As the Rosette descends, the Niskin bottles are open, allowing water to flow through them. When the desired depth is reached, a signal is sent from the surface to close a bottle, trapping the water sample inside. This process is repeated at various depths to collect samples from different layers of the water column.
5. Retrieval and Analysis: Once the sampling is complete, the Rosette is retrieved back to the ship. The collected water samples are then analyzed for various chemical, biological, and physical parameters to understand the water body’s characteristics.
6. Microcontroller Systems: Some modern Rosette samplers use microcontrollers and can be operated through applications, allowing for more efficient and precise operations. These systems may include additional sensors for dissolved oxygen (DO), total dissolved solids (TDS), temperature, and pressure.
The Rosette sampler is an essential tool for oceanographers and marine researchers as it allows for the collection of water samples at different depths, which is crucial for studying the stratification of water bodies, including temperature and salinity gradients, nutrient profiles, and biological activity.
Rosette Sampler Strengths and Weaknesses
Strengths of the Rosette Sampler include:
- Simplicity: It is relatively simple to use
Comprehensive Data - Collection: The Rosette Sampler can measure physical parameters including temperature, salinity, oxygen, fluorescence, light transmittance, nitrate, and photosynthetically active radiation (PAR)
High Sampling - Resolution: The CTD-Rosette is lowered at different speeds at different depths to improve the sampling resolution in areas with significant hydrological and biological gradients
- Real-Time Data: The CTD electronic sensor array sends real-time data to a shipboard computer
Weaknesses of the Rosette Sampler include:
- Heavy to Transport/Deploy: The Rosette Sampler is heavy, making it difficult to transport and deploy
- Fragility: The Rosette Sampler may be very fragile
- Requires High Capacity Boat: Due to its size and weight, a high capacity boat is needed for its deployment
- Limited Depth: The CTD-Rosette is typically lowered to a terminal depth of 515 meters (1690 feet), which may limit its use in deeper oceanographic studies
Writer : Rifqi Diyan Nugraha
