Custom System Case Studies

Impact of Rainfall on River Water Quality: A Guide to Aquaprobe Monitoring

Sudden or heavy rainfall events can drastically alter river water quality, introducing a complex cocktail of pollutants through surface run-off. Understanding and monitoring these changes is crucial for environmental protection. Omni Instruments offers a comprehensive suite of Aquaprobes, ranging from the AP-Lite, for single parameters, up to the advanced AP-7000, with self-cleaning and able to monitor up to 17 parameters. Each is designed to monitor the effects of run-off following heavy rain and identify what has been transferred to the water.

How Runoff Pollutes Rivers During Heavy Rainfall

When heavy rain falls, it creates an increased volume of surface run-off that picks up pollutants from land before discharging into rivers. This run-off can carry a variety of contaminants:

Sediment: Eroded soil particles increase turbidity, reducing light penetration and affecting aquatic life.
Nutrients: Fertilisers from agricultural land and septic systems, rich in nitrates and phosphates, can lead to eutrophication, promoting excessive algal growth.
Chemicals: Pesticides, herbicides, and other industrial or urban chemicals can be washed into waterways, posing toxic threats.
Pathogens: Bacteria and viruses from overflowing sewage systems or agricultural waste pose significant health risks to humans and wildlife.
Dissolved Solids: Salts and other dissolved substances can alter the water’s conductivity and overall chemical balance.

Monitoring Pollution with the Aquaprobe Range:

The Aquaprobe series provides robust and versatile solutions for water quality monitoring, from spot checks to permanent deployments. All Aquaprobes are constructed with marine-grade aluminum, finished with hard anodising for excellent corrosion and biofouling resistance, ensuring durability in challenging environments. This metal construction provides a characteristic weight and high-quality feel.

Core Parameters Monitored by Aquaprobes:

Most Aquaprobes come pre-fitted with common water quality testing sensors, including:

pH: Measures the acidity or alkalinity of the water. Runoff can introduce acidic or alkaline substances, shifting the pH outside the optimal range for aquatic organisms.
ORP (Oxidation-Reduction Potential): Indicates the water’s ability to break down contaminants. Changes can signify the introduction of oxidising or reducing pollutants.
Conductivity (EC), TDS (Total Dissolved Solids), Resistivity, Salinity, and Seawater Specific Gravity (SSG): These parameters are interconnected and reflect the concentration of dissolved inorganic compounds in the water. Sudden increases can point to contamination from industrial discharge, road salts, or agricultural run-off.
Dissolved Oxygen (DO): Essential for aquatic life. Run-off containing organic matter can lead to a changes in DO as microorganisms consume oxygen during decomposition.
Temperature: Water temperature affects chemical reaction rates, gas solubility (like oxygen), and biological activity. Run-off can alter thermal regimes, impacting aquatic ecosystems.

Differences and Enhanced Capabilities Across the Range:

While the core parameters are consistent, the Aquaprobe models offer varying capacities for additional sensors and different cleaning mechanisms, catering to diverse monitoring needs:

AP-LITE: This compact and lightweight Aquaprobe serves as an entry-level solution for water quality monitoring. It features a single auxiliary socket specifically designed for customer-selected optical sensors. This makes the AP-LITE a highly portable and cost-effective option for focused measurements where specific optical parameters are required.
AP-2000: This model provides a robust set of features beyond the entry-level probes. It includes the core parameters and comes with two empty auxiliary sockets, one limited to the optical sensors only. The standard AP-2000 doesn’t include a depth sensor, but the AP-2000-D version has a depth sensor added. This covers a measurement range of 0-60m with a resolution of 1cm.
AP-5000: This model offers increased sensor capacity compared to the AP-2000. It is equipped with four empty auxiliary sockets, all of which are available for both the full range of Ion Selective Electrodes (ISEs) and optical sensors to be fitted. The AP-5000 also has a depth measurement range of 0-60m with a resolution of 1cm.
AP-6000: This advanced multi-parameter probe features all common water quality testing sensors pre-fitted. Crucially, it includes four empty auxiliary sockets for customisation with either Ion Selective Electrodes (ISEs) or optical sensors. The AP-6000 boasts a new, much smaller self-cleaning mechanism with two rotating brushes, making it suitable for both spot monitoring and permanent deployments. Its diameter of 55mm makes it the smallest self-cleaning Aquaprobe.
AP-7000: The largest probe in the range has a 77mm diameter and increased capacity, potentially covering up to 17 parameters on a single device with space for 6 additional sensors. The AP-7000’s improved self-cleaning system enables prolonged deployment with minimal maintenance. The AP-7000’s depth measurement range is 0-100m with a resolution of 1cm and an accuracy of ±0.2% FS, which is greater than the AP-2000/AP-5000 models. The AP-7000 has a diameter of 77mm.

Specialised Sensors (Compatible probes for any AquaProbe unit):

For a more detailed analysis of pollution, compatible Aquaprobes can be fitted with:

Ion Selective Electrodes (ISEs):
- Ammonium and Ammonia: High levels are often indicators of pollution from sewage or agricultural runoff.
- Chloride: Elevated chloride levels can indicate road salt runoff or industrial discharge.
- Nitrate: A common pollutant from agricultural fertilisers and wastewater.
- Fluoride and Calcium: Can be present due to industrial waste, natural deposits, or construction runoff.
Optical Electrodes:
- Turbidity: Measures the cloudiness of water due to suspended particles. Heavy rainfall increases sediment runoff, leading to higher turbidity.
- Chlorophyll, Phycocyanin (freshwater BGA), and Phycoerythrin (marine BGA): These detect photosynthetic pigments and specific types of harmful algal blooms, indicating nutrient pollution and eutrophication.
- Rhodamine WT Dye and Fluorescein Dye: These dyes can be used as tracers to study water flow patterns and the dispersion of pollutants.
- Refined Oil: Detects petroleum hydrocarbons, indicating spills or leaks.
- CDOM/FDOM (Coloured Dissolved Organic Matter/Fluorescent Dissolved Organic Matter): Measures dissolved organic matter, which can originate from natural sources or pollution.

The Optical Electrodes use fluorescence measurement, which are ideal for researchers who are interested in detecting the presence or absence of a specific substance in reasonable concentrations and measuring relative fluorescence changes that can be used as an indication of increasing or decreasing concentrations. For accurate results, the data obtained with fluorescent electrodes should be post-calibrated with data from standard laboratory analysis of grab samples acquired during testing.

Self-cleaning Sensors

The self-cleaning mechanisms on models like the AP-6000 and AP-7000 are crucial for maintaining sensor accuracy during long-term deployments in turbid river environments. The wiper cleaning frequency can be configured when used with an Aqualogger, or if used with a telemetry system, the wiper will run every 6 hours to reduce battery drain.

All Aquaprobe packages can include the BlueLink Bluetooth interface to allow for wireless connection to the sensors. Providing live data viewing and recording to a mobile phone or tablet. The AquaLink software is free and allows for easy data download, analysis, reporting, and Google Map creation, providing a comprehensive solution for monitoring the complex impacts of heavy rainfall on river ecosystems.