The Role of Molecular Dissolved Organic Matter (DOM) Composition to Identify Sources and Release of DOM and Trace Elements in Catchments of Drinking Water Reservoirs in Mid-Latitude Mountain Areas – (DOMtrace) A Solid Phase Analytic Pyrolysis (Py-GC-MS, THM-GC-MS) Approach
Mineralogy, Petrology and Geochemistry
Final Report Abstract
Project DOMtrace has shown that it is likely that, in general terms, the proportion of the DOM in our study area that originates from deteriorating spruce forests should not be underestimated. Focusing the management of the ecosystems on peat systems alone (drainage, rewetting), and the corresponding research effort, does not seem to be the right approach. Peat environments do deliver DOM to the system, which can be reliable recognized based on molecular fingerprinting using THM-GC-MS, but is only a major source in stream water samples that were taken in the vicinity of peat deposits. The effect of discharge (catchment hydrology, connectivity) is also clear, giving rise to slightly higher proportion of peatland-derived DOM during periods of low precipitation, probably because the forest soils, which are largely positioned on hillslopes, because disconnected from the water flow paths under such conditions. Nevertheless, even under those circumstances, downstream water samples have a DOM fingerprint that is very similar to that of the forest environments. Hence, vegetation and vegetation status (spruce fitness) have a significant control on DOM composition, modulated by hydrological parameters such as precipitation and catchment connectivity. With detailed molecular studies of reference materials from the Harz Mountains and their leachates, we believe that we have pushed DOM provenancing to a higher level. We proposed a series of proxies that can be used to determine the balance between polyphenols from peatland and forest environments. Here it is worth noticing that the vegetation patterns of the study area (and hence the reference materials studied) are roughly representative of temperate mountain ranges in Central Europe, with abundance of coniferous forests and wetlands. These environments are currently subjected to dramatic environmental change, causing the collapse of the wood economy that it sustains (for instance in Germany, the Czech Republic and Slovakia). Therefore, our approach can be useful to understand the link between forest dieback, peat degradation and water quality deterioration in a wider geographic area. This is the reason why further research using the Harz National Park as a natural laboratory to further explore the nature of the organometallic and organomineral complexes (including pollutant (co-)transport) is an opportunity to understand the consequences of environmental change and effects of future management (such as reafforestation using other tree species than Norway spruce) on surface water quality in Central Europe. DOMtrace has confirmed a major role of DOM in the biogeochemical cycles of many elements (Fe, Al, Pb, As, Cu, Ti) and pointed towards different transport mechanisms of different elements on the basis of seasonal differences between the elements regarding the effects of season and positioning of a sampling position within the catchment. The combination of molecular fingerprinting and metal(loid) analyses suggests that spruce-derived polyphenols have a major role in metal transport, a role that is apparently much stronger than that of the peatland DOM efflux. But we need further research to evaluate the link between specific molecular structures and specific elements to identify controlling factors on pollutant transport, because the general correlations between DOM concentrations and the metals are so strong that non-causal ones are difficult to distinguish from those that result from actual binding mechanisms between DOM and the studied metal(loid)s. We pretend to do so by studying the organic and metal composition of different colloidal size fractions. One of the main surprises during DOMtrace was to observe how fast the environment is changing, in particular the rapid disappearance of spruce forests, and the impact of dry heat waves during summer on the spruce stands, showing massive loss of spruce leaves during periods in which they shouldn’t. Another surprise was the similarity in the composition of Ecker and Abbe stream DOM samples and the leachates of fresh (and decayed) spruce wood, and simultaneously the big contrast with the phenolic patterns of the leachates from peat and peat forming plants. This gave rise to the formulation of new proxies on DOM provenance, and laid the foundation for future research.
Publications
- 2020. Origin of dissolved organic matter in the Harz Mountains (Germany): A thermally assisted hydrolysis and methylation (THM-GC–MS) study. Geoderma 378, 114635
Kaal, J., Plaza, C., Nierop, K.G.J., Pérez-Rodríguez, M., Biester, H.
(See online at https://doi.org/10.1016/j.geoderma.2020.114635) - 2020. Towards understanding ecological disaster in the Harz Mountains (Central Germany) by carbon tracing: pyrolysis-GC-MS of biological tissues and their water-extractable organic matter (WEOM). Analytical Pyrolysis Letters, APL008, 1-17. ISSN 2659-5605
Kaal, J., Plaza, C., Pérez-Rodríguez, M., Biester, H.
