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Monitoring dissolved organic carbon and nitrate concentrations using wavelet analysis

 

Understanding the cycle of nitrogen and carbon in water ecosystems is critical to estimating human impacts on these cycles. Although water ecosystems are capable of recycling nitrogen and carbon, the concentrations in many water bodies such as streams have been increasing over the last two decades. This is a major concern, contributing to environmental problems such as air pollution, eutrophication (a form of water pollution that encourages algae growth) and climate change. 

In an article published in the March issue of Vadose Zone Journal, researchers report using a data analysis method known as Wavelet Transform Coherence (WTC) analysis to study variations in carbon and nitrogen in stream and groundwater in the forested Wustebach catchment (Germany).  WTC is a method that accounts for non-stationary relationships between data sets, to find hidden correlations in data that vary with time, thus overcoming limitations of classical data analysis methods.

The study revealed that water transit times, or the amount of time it takes for a drop of water to travel from one location (e.g. soil) to another (e.g. stream), significantly influences the amount of carbon and nitrogen in the water. Carbon and nitrogen concentrations in stream waters can be explained by the mixing of groundwater and subsurface runoff. WTC analysis, unlike previous methods used, allows for the discrimination between the influence of groundwater and subsurface runoff to the stream water. The WTC analysis also revealed strong negative correlations between carbon and nitrogen that were consistent over long time scales but weak and inconsistent over short timescales, suggesting further study covering time scales from minutes to years to better understand the hydrological and biogeochemical processes at play. 

Read the full open access article in VZJ.