Dissolved Oxygen Measurement in Water

Oxygen is vital for the survival of aquatic organisms and enters surface waters through direct absorption from the atmosphere, especially in turbulent streams.

Dissolved Oxygen (DO) indicates the amount of free, non-compound oxygen available in water or other liquids. This oxygen is utilsed by living organisms and decomposing organic matter.

An overabundance of decaying organic material can lead to a depletion of oxygen, which can be deadly for fish. DO is crucial for various forms of aquatic life; fish rely on it for respiration, while plants need it for respiration in the absence of light for photosynthesis. When DO levels fall below a certain threshold, fish mortality rates increase.

Dissolved Oxygen levels are continuously influenced by diffusion, photosynthesis, and decomposition. Additionally, DO can vary due to changes in temperature, salinity, and pressure. Consequently, levels can fluctuate from 1 mg/L to over 20 mg/L. In freshwater environments like lakes, rivers, and streams, DO levels will change with the seasons, making it essential to monitor water quality.

Ammonia Monitoring in Water:

The neutral, uncharged form of Ammonia is a chemical compound consisting of nitrogen and hydrogen, represented by the formula NH3. It primarily originates from fish waste expelled through their gills or urine and poses significant toxicity to aquatic organisms. Ammonia serves as a crucial food source for nitrifying bacteria, which can be lethal to fish. It has the potential to cause damage to gills and internal organs, so it's essential to watch for any signs such as cloudy eyes or frayed fins. This highlights the importance of measuring Ammonia levels when cycling a new aquarium. Any readings above 0.02 mg/l (ppm) are considered harmful.

Another contributor to Ammonia levels is the breakdown of organic matter, including deceased animals or leftover food. As these materials decompose, nitrogen is released, leading to the growth of bacteria that subsequently produce Ammonia. Additionally, Ammonia can result from pollution stemming from domestic, industrial, or agricultural sources, particularly from fertilisers, organic waste, or fecal matter.

pH Measurement:

The portable EcoTestr pH 2 meter measures pH, which indicates the concentration of hydrogen ions in a solution, reflecting its acidity or alkalinity. In natural ecosystems, pH levels can range from approximately 4.5 in acidic peaty upland waters to more than 10.0 in areas with high photosynthetic activity. A pH of 7 is deemed neutral. The term pH stands for 'power of hydrogen,' and its value is calculated based on the molar concentration of hydrogen ions (H+).

Photosynthesis carried out by algae and plants utilizes hydrogen, which raises pH levels. Conversely, respiration and decomposition processes can lead to a decrease in pH levels. An imbalance in water pH can significantly harm aquatic life. Additionally, pH influences the solubility and toxicity of various chemicals and heavy metals present in the water.

Water Temperature:

Physical temperature of the watercourse. Largely dictated by climate, but also of interest around thermal discharges. Temperature extremes can be harmful to aquatic organisms, and also have an effect on other parameters, e.g. pH and dissolved oxygen.

The most common physical assessment of water is temperature. Temperature has a huge impact on both the chemical and biological characteristics of surface water. Temperature affects the dissolved oxygen levels in the water, photosynthesis of aquatic plants and metabolic rates of aquatic organisms. The temperature in water can make aquatic wildlife extremely sensitive to disease. Thermal pollution is where hot water is introduced to water that is at a cooler temperature. This generally appears around power plants as they distribute hot water that has been used to cool equipment directly into streams. As well as this, another common factor contributing to thermal pollution is if there is increased erosion, the sediments in the water absorb heat from the sunlight which then increases the water temperature. Warm water is less capable of holding dissolved oxygen which can be fatal to aquatic wildlife. It can leave aquatic organisms in a weakened physical state making them more susceptible to diseases and pollutants. For this reason temperature should be monitored at the same spot in the water at which dissolved oxygen in monitored

Good water quality leads to happy fish and happy anglers!

Little more information to learn;

Water has a significantly lower capacity to hold oxygen compared to air; approximately 20% of air consists of oxygen, while water can only retain about one part of oxygen for every 100,000 parts of water at most. The amount of oxygen dissolved in water is influenced by various factors, with temperature being the most critical. As the temperature of water increases, its ability to hold oxygen decreases. For instance, water at 5˚C can contain a maximum of 12 milligrams of oxygen per liter (mg/L or 12 parts per million), while at 20˚C, this maximum drops to 9.1 mg/L.

As a result, organisms have access to less oxygen in warmer water. This is particularly significant for fish species, which require more oxygen at elevated temperatures due to their poikilothermic nature, meaning they are more active in warmer conditions and less so in cooler ones. When water reaches its maximum concentration of dissolved oxygen at a specific temperature, it is referred to as "saturated" or "at saturation." The concentration of dissolved oxygen is often expressed as a percentage of this saturation level. Therefore, an oxygen meter might display a reading of xx percent.

It is crucial to note that 75% saturation at 5˚C indicates a higher actual oxygen level than 75% at 20˚C. In certain situations, water may temporarily exceed the expected levels of dissolved oxygen, a phenomenon known as super-saturation. This can occur during sunny, warm, and calm weather, particularly when there is abundant plant or algal growth that produces oxygen through photosynthesis at an accelerated rate

Factors Leading to Deoxygenation: The depletion of oxygen in aquatic environments can stem from various influences, which can be categorized into two primary groups: bacterial activity and weather-related factors.

Bacterial Activity: Bacteria are simple organisms found in diverse habitats, thriving on both living and decaying matter. In aquatic ecosystems, the bacteria that significantly affect oxygen levels are those involved in decomposition.

These microorganisms can proliferate rapidly in warm environments, while their activity diminishes in cooler temperatures. Most bacteria, like many other life forms, require oxygen for survival. As their population grows, so does their oxygen consumption.

When ample food sources are present, bacteria can reproduce swiftly, potentially depleting nearly all dissolved oxygen in the water, which adversely affects other organisms, including fish. Situations or actions that provide abundant nutrients for bacteria often result in deoxygenation. (Technical note: The oxygen demand exerted by bacteria in water is referred to as Biochemical Oxygen Demand (BOD), measured as the amount of oxygen consumed in a standard volume of water over five days at 20˚C. Generally, a BOD of 5 mg/l or lower is adequate for coarse fish, while 3 mg/l or lower is suitable for trout.)

Organic Loading: In aquatic environments, bacteria typically break down organic material in water rapidly, playing a crucial role in natural processes. However, when the influx of organic matter exceeds the capacity for decomposition, it can accumulate on the beds of lakes, rivers, or canals, leading to the formation of thick layers of organic silt. This silt serves as a rich food source for bacteria, particularly during the summer months when bacterial activity can be quite pronounced.

Generally, this process results in only minor fluctuations in the levels of dissolved oxygen in the water. However, in autumn, the additional organic load from falling leaves and the decay of aquatic plants, combined with reduced photosynthesis, can exacerbate these changes. A sudden influx of organic matter at any time can lead to significant de-oxygenation. The deeper layers of silt at the bottom of water bodies may become anoxic, meaning they lack oxygen, which can cause them to appear black and emit a foul odor. Disturbing this deep silt can trigger rapid and severe de-oxygenation. Organic matter can enter water bodies through various means. A substantial amount of leaf litter can wash into the water from deciduous trees and shrubs along the banks. Leaves may also be blown in from nearby land or carried in by feeder streams.

Additionally, excessive use of bait by anglers, droppings from waterfowl, and livestock waste can contribute organic material to the water. Certain common pollutants, particularly those rich in animal and plant waste, such as sewage and agricultural runoff, can lead to deoxygenation issues in fisheries by promoting bacterial growth.

Highbridge Angling Association Objectives for Bank Management:

It is far more sensible to prevent problems caused by low oxygen in fisheries than to rely on emergency action once the problems have become manifest. By identifying the potential causes of de-oxygenation and, where necessary, rectifying them, it should never be necessary to take last-minute action.

Aquatic Plant Management: One frequent cause of de-oxygenation in water bodies is the inadequate planning and execution of fisheries management related to aquatic "weed" issues. The overgrowth of aquatic plants typically reaches its peak during the summer months, leading to the temptation to address large areas using herbicides or through cutting and raking methods. While these management strategies can be quite effective, improper execution may result in the decomposition of plant material, which can trigger a rapid increase in bacterial populations. This sudden drop in oxygen levels can have serious consequences for the fish community. Additionally, the natural decay of algae and rooted aquatic plants can also lead to de-oxygenation, particularly in the autumn when these plants begin to die off and decompose due to bacterial activity.

Water Plants: Their Role and Management Water plants are prevalent in nearly all aquatic environments across Britain and play a vital role in the ecosystems of rivers and lakes. These details outlines their significance in aquatic habitats, the circumstances under which they should be managed, and the methods for doing so. Green plants depend on sunlight for growth, and their development is highly influenced by water clarity.

Functions The functions of water plants can be summarised as follows:

Water Aeration Through the process of photosynthesis, which occurs during daylight hours, submerged plants release oxygen as a by-product. This process can enhance the dissolved oxygen levels in the water. However, at night, the plants consume some of this oxygen through respiration, which can lead to critical oxygen depletion in dense weed beds, potentially endangering fish life.
Habitat for Wildlife Larger aquatic plants offer shelter for various animals, providing protection from currents and predators. Many fish and invertebrate species lay their eggs on these plants. By offering this refuge, they contribute to the overall productivity of the water. Generally, a plant-rich pool supports a greater food supply for fish compared to one devoid of vegetation. However, excessive plant growth can result in water quality issues and may pose challenges for anglers.
Nutritional Source for Other Organisms Both living and decaying plants serve as a food source for numerous animals. For instance, plant detritus is a significant nutritional resource for many invertebrates and certain fish species.

Plants can be classified into main groups:

Emergent Plants These plants feature upright aerial leaves that emerge from either open water or muddy substrates. They thrive in areas where the water level fluctuates from just below the surface to approximately half the plant's maximum height. Long, slender-leaved species, commonly referred to as reeds, include examples such as common reed (Phragmites australis), bur-reed (Sparganium erectum), reedmaces (Typha latifolia and Typha angustifolia), reed-grass (Glyceria maxima), and bulrush (Scirpus lacustris). Broad-leaved varieties consist of water plantain (Alisma plantago-aquatica), arrowhead (Sagittaria sagittifolia), and great water dock (Rumex hydrolapathum). Floating-Leaved Plants This category encompasses water lilies (Nymphaea alba and Nuphar lutea).

Most of these plants are anchored to the substrate with long, flexible stems, although some, like duckweed (Lemna minor) and frog-bit (Hydrocharis morsus-ranae), float freely on the water's surface.

Members of this group are typically found alongside emergent and submerged plants in waters that are just over one meter deep, or deeper for those that are free-floating. Submerged Plants These plants are generally rooted in the sediment, as seen with Canadian pondweed (Elodea canadensis) and water milfoil (Myriophyllum spp).

However, a few species, such as ivy-leaved duckweed (Lemna trisulca) and hornwort (Ceratophyllum), float just beneath the water's surface. When in bloom, most of these plants extend their flowering shoots above the water. Water milfoil (Myriophyllum spp) and mare’s tail (Hippuris vulgaris) are notable examples of this behavior.

Other ways to manage our lake

De-silting: If we have 1m of silt, that when disturbed, gives off a rotten-egg smell, there may be potential problems. Solutions include removing the accumulated silt (de-silting) and helping to prevent excessive input of organic matter from other sources.

De-silting will help to reduce bacterial activity and prevent associated de-oxygenation. It will also deepen the fishery, increase the volume of water and reduce the impact of extreme weather conditions. Lake de-silting is an expensive and disruptive process that is usually best accomplished after removing the fish and draining the fishery.

Managing the vegetation along our banks is essential for controlling the accumulation of organic silt. Trees and shrubs in these areas not only enhance the ecosystem but also serve as crucial habitats for various wildlife and plant species that contribute to a thriving aquatic environment. Therefore, it is advisable to perform only light and selective trimming of overhanging branches. One highly effective strategy for minimizing silt build-up is the annual removal of floating leaves before they settle on the bottom.

Siltation: Removing silt from a coarse fishing lake to enhance water quality and fishing yields The process of siltation in a lake is often hastened by the accumulation of leaf litter from the surrounding deciduous trees and adjacent land. Leaves that float on the surface can be blown into specific corners of the lake, where they become saturated and eventually sink. Over time, the continuous buildup of leaves in these locations leads to siltation, which can ultimately make parts of the lake unfit for fishing. For enclosed still waters, the most effective material is crushed limestone, sized from ‘quarter inch to dust,’ which can be spread into the water—potentially from a boat—at a rate of approximately 300 to 350 pounds per acre. Powdered chalk is also a viable alternative. This process is ideally carried out in winter, ensuring that the crushed limestone or chalk is applied before spring weather arrives. If phosphate-rich fertilizers are to be used, it is crucial to apply the limestone or chalk several weeks prior to introducing the manure or triple-super phosphate. Applications should be limited to silted regions. If the entire lake requires treatment, it is advisable to apply the material to no more than a quarter of the lakebed at a time, allowing at least a month between treatments for the subsequent quarter.

Calcium: A Vital Component Fertilizers rich in calcium fulfill multiple roles. Primarily, calcium acts as a crucial 'building block' for fish and many invertebrates that serve as their food sources, such as water snails, shrimp, and insect larvae. By incorporating chalk or limestone, the availability of food for fish is enhanced, which in turn promotes their growth rates. Additionally, both chalk and limestone contribute to raising the pH levels, which has various benefits, and they facilitate the decomposition of organic matter on the lake bottom. These materials are commonly used to help reduce silt accumulation in fisheries. Fertilization can significantly enhance your fishery, and this guide outlines the process. A notable characteristic of many still-water coarse fisheries is the clarity of the water, which can impact fish populations and fishing quality. For instance, clear-water lakes may experience low survival rates for naturally spawned fish fry. This issue is often linked to a scarcity of suspended algae and the small, planktonic invertebrates that feed on them. Young fish need to consume plankton shortly after hatching. When there is an abundance of these tiny food sources, fry tend to grow quickly and accumulate enough energy reserves to survive their critical first winter. Conversely, in clear-water fisheries where plankton is scarce or present in limited quantities, young fish typically remain smaller and have insufficient food reserves to endure the winter months.

Dedicated Water Monitoring for Healthier Fisheries

Water Monitoring

Little it bit of more learning…. Causes of deoxygenation, climate control, and strategies to mitigate

Water Temperature:

To enhance our awareness and management practices, 4 of the Highbridge Angling Association's water quality team have participated in a 2 day course organised in collaboration with the Environment Agency and the Institute of Fisheries Management (IFM) over the past few years.

Understand practical fishery management techniques

Stay in the Loop!

Dedicated Water Monitoring for Healthier Fisheries

Water Monitoring

Little it bit of more learning…. Causes of deoxygenation, climate control, and strategies to mitigate

Water Temperature:

To enhance our awareness and management practices, 4 of the Highbridge Angling Association&#039;s water quality team have participated in a 2 day course organised in collaboration with the Environment Agency and the Institute of Fisheries Management (IFM) over the past few years.

Understand practical fishery management techniques

Stay in the Loop!

To enhance our awareness and management practices, 4 of the Highbridge Angling Association's water quality team have participated in a 2 day course organised in collaboration with the Environment Agency and the Institute of Fisheries Management (IFM) over the past few years.