What’s in the bog water?
Whilst on the road, in classrooms and communities, The Living Bog is often asked about the colour of water coming from, or near a bog, and if it’s safe to drink that water. The yellowy-brown water is a familiar sight to anyone from the midlands (or indeed the uplands), and some of our rivers are sometimes coloured. What causes the colour? Dissolved Organic Matter, or DOM.
Project hydrologist John Cody had prepared a blog on the subject which, we hope, will make people more aware of their DOC’, POC’s and THM’s, and outline just some of the hydrological work ahead in 2020, how restoration will allay some fears over the ‘bog water’…
What’s in the Bog Water by John Cody, Project Hydrologist, The Living Bog.
“Water discharged from the bogs contains Dissolved Organic Matter (DOM). DOM is principally composed of natural acids and proteins that are stable in the bog environment, and are responsible for the characteristic yellow brown colour of bog water. Generally DOM is stable, and the organic nitrogen, carbon and phosphorous compounds are not immediately available as plant nutrients, hence DOM is not considered as a water pollutant in its own right. Ecologically DOM provides a substrate for bacteria and once in a receiving water course can also acts as a natural sunscreen, reducing the depth that UV light penetrates through the water column, protecting communities of decomposers (bacteria and protozoans) responsible for a streams ability to attenuate pollutants.
Once discharged into a receiving water course with comparatively high levels of dissolved oxygen DOM is broken down by decomposers, resulting in the production of carbon dioxide, nitrates and phosphates.
The carbon dioxide released in this way is considered a fugitive emission in current studies of bogs in relation to climate change and is a major cause of uncertainty in estimates of the climate change potential of degraded bogs. Some recent research has suggested that the carbon flux associated with DOM can exceed direct atmospheric exchange by orders of magnitude and account for the majority of the carbon flux from a ditched bog.
Research has shown that 90% of the carbon lost from degraded bogs is exported via drainage discharge. Nitrates and phosphates, are released as by-products from the degradation of DOM through natural processes. These are considered as water pollutants by the EPA. This is not due to potential impacts on human or animal health, but because they contribute to a process known as Eutrophication, which has a negative impact on the ecology of the water course. Consequently, production bogs are identified as a significant pressure on 8% of Irish rivers at risk of not meeting their environmental quality objectives under the water framework directive. The other significant pollutant from production sites are fine grained sediments. There is also evidence that ammonium (a natural by-product of decay processes) is present at elevated levels downstream of production bog sites. Ammonium is a recognised water pollutant as it is toxic to fish at low concentrations, there is no direct risk to human health posed by ammonium. Nitrates in water are implicated as a cause of methemolobinemia (blue-baby syndrome), where nitrogen combines with oxygen in the blood stream in preference to iron. The epidemiological evidence indicates that this is likely to be a risk only where vitamin C deficiencies exist, and hence is not likely to be a significant health risk in Ireland.
For example, the concentration of Nitrate at the discharge point on Killyconny Bog, Co Cavan on 23/09/2019 was less than 0.44 mg/L, which is an order of magnitude lower than existing Maximum Allowable Concentrations (MAC’s). Bear in mind that this concentration would be reduced by dilution on entering the receiving water course. DOC had a concentration of 45.1 mg/L and TOC 46.7 mg/L. Particulate Organic Matter (POC) present in a concentration of 1.6 mg/L. There are no published MAC’s for these parameters, so the project will seek to compare the concentrations from restored sites with the data the EPA has available on production sites over the course of the next 12 months, in order to determine how drain blocking impacts on water quality ecosystem services.
Tri-halo methanes (THM’s) are formed by a reaction between chlorine and organic compounds (principally DOM). THM’s are thought to be carcinogens as there is epidemiological evidence that prolonged exposure to THM’s leads to elevated rates of some stomach cancers. As DOM is dissolved in the bog water it cannot be removed from water via filtration or coagulation /flocculation, which are the traditional primary stages in water treatment. Hence treating water with high levels of DOM is expensive. Consequently water sources that have high levels of DOM or are highly coloured have been avoided by water supply utilities to avoid the costs of associated with treatment.
Traditionally water entering a pipeline from a water treatment plant is dosed with chlorine. This acts as a disinfectant and is an effective treatment of the main pathogens that cause serious diarrhoeal diseases such as cholera and dysentery. It is considered an essential part of the treatment process as the chlorine dose provides a residual disinfection effect as water is in the transmission pipeline, ensuring potable quality at the consumers tap.
THM’s are not formed naturally in concentrations that would impact human health under natural conditions. They are part of a wider group of compounds collectively known as Chlorine by-products (CBP’s). There are maximum acceptable concentration limits set by the EC Drinking Water Directive for THM’s and CBP’s, and compliance monitoring is undertaken routinely by the EPA. Hence the occurrence of DOM in a peatland catchment is only likely to be a health risk if there is a water abstraction point downstream of the bog. This is highly unlikely as no sensible utility would abstract surface water from a source with high DOM concentrations, it would be cheaper to pump it from a borehole. Drinking bog water without treatment will not result in death by cancer from THM’s over a course of years. You are more likely to die in a couple of days from bloody diarrhoea.
From the above it can be concluded that restoring the bogs will have the following net benefits to the ecological status of the receiving water courses:
- Reduce the amount of sediments entering the receiving water course;
- Reduce the amount of ammonium being directly discharged into the water course.
- The impacts in relation to DOC are less clear. From first principles increasing the residence time of water on the bog surface will increase DOM concentrations, as will increased coverage of Sphagnum, as the amino acids produced by the sphagnum is a contributing factor to low pH on bogs. However there are no negative health impacts associated with the DOC and it is not considered a pollutant, and increased concentrations could well be considered an important ecosystem service function of bog restoration. The production of ammonium resulting in microbial breakdown of DOM is unlikely to cause toxicity as this process will be naturally regulated. The project will monitor the impacts of drain blocking on DOC concentrations using FDOM sensors installed in hydraulic measuring structures.
Blocking drains on the bogs will have a net positive impact on water quality. As the ecological status of the bog improves, so too will the ecological status of the receiving water course. There will be no negative human health impacts associated with water quality as water supply companies are required to control THM concentrations as part of their treatment processes.
LINKS TO NOTE:
EPA Catchment Unit, Significant pressures (peat) – https://www.catchments.ie/significant-pressures-peat/
Local Authorities Water Programme http://watersandcommunities.ie/
‘An overview of dissolved organic carbon in groundwater and implications for drinking water safety’ by Dr Shane Regan, Paul Hynds & Ray Flynn.