PH Sensor
What is it, and why study it?
By measuring pH, you are checking the concentration of hydrogen ions (H+) in a liquid. An acidic solution has a high concentration of hydrogen ions (H+), greater than that of pure water. A basic solution has a low H+ concentration, less than that of pure water. The pH of an aqueous solution can be measured on a scale from 0-14. The lower the number, the more acidic the solution. The higher the number, the more basic the solution.
///<insert PH_Scale.png\> [tag Wikimedia Commons as source]
The pH scale is used to rank solutions in terms of acidity or basicity (alkalinity). Since the scale is based on pH values, it is logarithmic, meaning that a change of 1 pH unit corresponds to a ten- fold change in H+ ion concentration. The pH scale is often said to range from 0 to 14, and most solutions do fall within this range, although it’s possible to get a pH below 0 or above 14. Anything below 7.0 is acidic, and anything above 7.0 is alkaline, or basic.
///<insert PH_Scale-_Acidic_vs._Basic_(Alkaline).png\> [tag Wikimedia Commons as source]
For reference, most drinking water has a pH range of 6.5 to 9.5. Many animals cannot live in a pH level below 5 or above 9. Once the normal pH range for water has been established, a rise or fall in pH can indicate chemical pollution, acid rain, treatment plant issues, or problems with the supply pipe network. Low pH levels can precipitate a negative feedback loop in the environment, facilitating the solubility of heavy metals. As the level of hydrogen ions increases, metals such as aluminum, lead, copper, and cadmium are released into the water instead of being absorbed into the sediment.
While important in environmental systems health and water treatment, measurements of pH are also important in chemistry, soil management for crops, and medicine.
Scientific Uses1
From waterways to soils to even our drinking water, scientists measure pH to monitor safe levels for human, plant, and animal health alike. It is important to establish a baseline for pH levels to determine if external factors are affecting the pH of an environment.
FRESHWATER
Measuring pH can help in monitoring freshwater lakes and rivers. As pH fluctuates out of its natural ranges, it can put stress on animals, leading to reduced hatching and survival rates. There are increased dangers when pH reaches extreme levels. These conditions can facilitate the solubility of toxic elements and compounds, thus increasing the risk of absorption by aquatic life.
Not only does pH serve as a metric to test for safe living conditions for organisms, but changing levels can also serve as an indicator of increased pollution, acid rain, or wastewater and mining discharges. Some states, such as Alaska, are attempting to maintain a pH standard for water quality. The Alaska Water Quality Standard requires pH levels between 6.5 and 8.5 to protect the many salmon populations.
Oceans2
Over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2 pH. For millions of years, the oceans maintained a relatively stable level of acidity, creating ideal conditions for complex webs of ocean life to flourish. The industrial revolution arose some 200 years ago, precipitating the release of billions of tons of carbon dioxide into the atmosphere. Since the ocean absorbs about a third of those human-generated CO2 emissions, the pH of the ocean has dropped 0.1 pH units, putting it currently around 8.1 pH, representing a 25-percent increase in acidity over the past two centuries. Projections based on these numbers show that by the end of this century, continued emissions could reduce ocean pH by another 0.5 units. Shell- forming animals including corals, oysters, shrimp, lobster, many planktonic organisms, and some fish species are in danger from these changes, in effect impacting the entire food chain and ecosystem.
<insert WOA05_GLODAP_del_pH_AYool.png\> [caption: Estimated change in sea water pH caused by human created C02 between the 1700s and the 1990s, from the Global Ocean Data Analysis Project (GLODAP) and the World Ocean Atlas [Creative Commons]]
Soil
Precision agriculture is a farm management strategy based on information technology which can help optimize soil and crop quality, production levels, sustainability, and food safety. The nutrition growth and yields of most crops decrease where pH is low and increase as pH rises to an optimum level.
Specifically, pH levels influence the solubility of nutrients while also affecting the ability of micro-organisms to break down organic matter and transform the chemistry of the soil. Additionally, most pesticides are labeled for specific soil conditions. If soils have a pH outside the allowed range, the pesticides may become ineffective, changed to an undesirable form, or may not degrade as expected, which results in problems for the next crop period.
Hydroponics3
Managing pH levels in a soil-less hydroponic system are essential to maintaining plant health. In these systems, plants absorb nutrient solutions through their roots. In this scenario, the absorption capacity is affected by the pH of the solution. For example, acidic solutions facilitate the absorption of aluminum, hydrogen, and manganese which can be toxic to the plant. Conversely, at low pH, calcium and magnesium are less readily absorbed. This can lead to deficiencies of these nutrients. The same is true in alkaline environments, which increase the availability of molybdenum and macronutrients and decrease availability of phosphorus, iron, zinc, copper, and cobalt.
Acid Rain4
Acid rain, defined as precipitation with a pH level less than 5.0. is one of the best known examples of human influence on the pH of water. Mining and smelting operations produce nitrogen oxides and sulfur oxides. These are then transported by wind and air in the atmosphere and react to form sulfuric and nitric acids before combining with water and falling back to earth as wet depositions. High C02 levels associated with fossil fuel combustion also contribute to the acidity of rain.
Acidic particles and gases can also deposit from the atmosphere in the absence of moisture as dry deposition. The acidic particles and gases may deposit to water bodies, vegetation, and even buildings. When the accumulated acids are washed off a surface by the next rain, this acidic water flows over and through the ground, and can harm plants and wildlife.
(to be cont'd....)
1 https://www.fondriest.com/environmental-measurements/parameters/water-quality/ph/ https://www.usgs.gov/special-topic/water-science-school/science/ph-and-water?qt-science_center_objects=0#qt-science_center_objects
2 https://www.noaa.gov/education/resource-collections/ocean-coasts-education-resources/ocean-acidification https://www.sciencedirect.com/science/article/abs/pii/S0165993612002427 https://www.nationalgeographic.com.au/nature/ocean-acidification.aspx