BACKGROUND READING
Freshwater - What is pH?
Background reading & resources on aspects of the FWC field chemistry - pH
FreshWater Catalogue Chemistry - What Is pH?
pH is the measurement of the hydrogen-ion concentration in the water. This basic chemistry parameter is a key part of our freshwater cataloguing field measurement programme.
A pH below 7 is acidic (the lower the number, the more acidic the water), and a pH above 7 (to a maximum of 14) is basic (the higher the number, the more basic the water). High pH values tend to facilitate the solubilization of ammonia, heavy metals and salts, whereas low pH levels tend to increase carbon dioxide and carbonic acid concentrations. Lethal effects of pH on aquatic life occurs below pH 4.5 and above pH 9.5.
Sensitivies of Freshwater life to pH (DEFRA, UK)
In our freshwater systems there are numerous drivers that can influence pH levels, including both natural and anthropogenic sources. Natural sources include geology, hydrology, precipitation, and temperature, whereas anthropogenic sources include mining, agriculture, industrial effluents, wastewater discharge, and acid rain. Given the rural nature of Salt Spring Island, we can likely eliminate many of the anthropogenic sources as drivers for changes in our creek's pH values. However, regular monitoring is valuable, to understand today's seasonal freshwater variability (establishing a "baseline") and to investigate/ establish what the changes we do see, relate to...
Selected FWC creeks - pH variability (trends?) over time.
Based on data collected through the SSI FWC, our streams are generally neutral or slightly basic (alkaline). The acidity of freshwater is naturally variable, but most lakes and rivers have a pH within the range of 6 to 9, thus, our streams fit within this pH range. However, our pH data also show variations that are not entirely seasonal, thus, there could be other local drivers influencing these streams.
pH can also be used (assuming no anthropogenic overprints...) to measure natural variations in the composition of groundwater. As temperatures change seasonally, as the water table rises and falls, or as recharge rates vary, the chemical hydrogen-ion state will change and, as a result, so will the composition of groundwater. pH is often positively correlated with groundwater inputs into a hydrologic system; however, this does not entirely explain the trends observed in our island stream pH data. A relationship between areal, watershed vegetative cover growth (plant species richness) and groundwater baseflow (pH values; Kuglerova et al., 2014) is intriguing and supports the importance of the role of groundwater in our surface freshwater systems... TBD...
Do you have any insights into what could be influencing pH values in Salt Spring Island streams, or interested in investigating?
Please, let us know your thoughts - contact the SSIFWC Project Lead!
Resources
Further reading...