Project

The role of dissolved organic matter in atmosphere-land-river interactions

Goal: This PhD project will assess the potential for intense periods of hydrological activity to dominate the POM and DOM transported from soils into rivers and assess the mechanisms that are responsible for the mobilisation, transport and storage of reactive C in selected natural and disrupted (e.g. peat extraction, agriculture) environments. Furthermore, this study will examine the characteristics of DOM in terms of composition and reactivity from different environments under changing environmental controls in laboratory experiments.

Date: 6 February 2017 - 5 June 2020

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Project log

Sara Trojahn
added 3 research items
Since 2017, we investigated iDOM in tropical and temperate rivers across Amazonia and Scotland using the next-generation liquid chromatography organic carbon detection – organic nitrogen detection system utilised by Pereira et al. (2014). Monthly sampling of rivers including the Cree, the Clyde and the Forth show evidence for iDOM mobilisation, but no clear quantitative relationship between DOC and iDOM. Humic compounds are the dominant DOC fraction (40 to 80%), contrasting with observations from tropical rivers. In order to get a better understanding of short-term temporal changes of iDOM and its mobilisation in headwaters we studied the DOM composition and changes in a small headwater stream of the River Forth in Scotland, the Menstrie Burn.
We investigated the riverine carbon exports from a two headwater peatland environments in the UK, and examined the potential uncertainty of quantification due to the role of optically “invisible” dissolved organic matter (iDOM). Importantly, our work captured compositional changes of riverine DOM in during an exceptionally dry period and compared these with rain events during a generally wetter cooler period in 2018, perhaps an analogue of future climate and weather scenarios. A novel size exclusion chromatography technique allowed elucidation of five different DOM pools including Humics to Biopolymers, Building Blocks, lower molecular weight (LMW) Acids, and LMW Neutrals, without isolating or modifying the original sample.
Sara Trojahn
added an update
The 2nd year of this project comes to an end and 80% of the data is collected.
The fate of dissolved organic matter and the soil as a source needs further investigation in the upcoming month and a new opportunity came up to extend this local Scottish project.
In 2 months a new field campaign in the tropics will start to investigate river carbon exchange in small headwaters with focus on invisible dissolved organic matter (iDOM) and its role in the carbon cycle. We are planning to combine the tropical data of iDOM occurrence with our data from Scottish headwaters.
The next few months will be an interesting time for this project and I cannot wait to see the outcome of the next chapter….
 
Sara Trojahn
added an update
The second intense sampling period of my PhD project came to an end and finally we captured some rain events.
One of my peat-dominated catchment had a really high precipitation of 280mm in 30 days which is much higher than the average precipitation for November in Scotland.
The first data show that high amounts of LMW compounds are transported during dry periods which implies that riverine carbon fluxes are under quantified from peatland environments.
 
Sara Trojahn
added an update
The weather this summer was unusual for Scotland - warm and sunny, almost no rain - difficult conditions when you were planning to collect water samples during rain events.
Nevertheless, ten weeks and almost 600 water samples later we are hopefully closer to clarify in what extent intensified weather events modify the composition of dissolved organic matter (DOM) as it is moving along headwater river systems.
 
Sara Trojahn
added an update
We started our intense river water sampling this week with 2 automated water sampler in Auchencorth moss.
The second peat-dominated catchment by Menstrie (Clackmannanshire , Scotland) will be also equipped with two automated water sampler, one upstream and the other one further downstream.
All 4 water sampler will collect river water every 4 hours over 8 weeks. This period of intense sampling will hopefully provide a more detailed insight into the compositional changes of DOM during low and high flow and the impact of rainfall on the DOM and POM pool.
 
Sara Trojahn
added an update
The baseline is established. One year of fieldwork at Auchencorth moss and Menstrie is completed.
Next step: Installation of Autosampler into both catchments to sample during rain events.
 
Sara Trojahn
added a project goal
This PhD project will assess the potential for intense periods of hydrological activity to dominate the POM and DOM transported from soils into rivers and assess the mechanisms that are responsible for the mobilisation, transport and storage of reactive C in selected natural and disrupted (e.g. peat extraction, agriculture) environments. Furthermore, this study will examine the characteristics of DOM in terms of composition and reactivity from different environments under changing environmental controls in laboratory experiments.