Abstract

The dissolved organic matter (DOM) quality or quantity of stream waters reflects catchment functioning. Dissolved organic matter features, pH, and Fe content in the main stream and tributaries of the forested Wüstebach catchment in Germany were examined for a 4-yr weekly sampling period (2009–2013). The catchment outlet (Wu14) discharge (Q) ranged from 0.22 to 72.5 L s−1, with minima and maxima around the summer and winter seasons, respectively. Discharge clearly followed precipitation in the late autumn to early spring period. Dissolved organic C (DOC) values at Wu14 ranged between 0.8 and 7.4 mg L−1, with a mean of 2.7 mg L−1. Annual periodicities in DOC and temperature (T), and DOC and Fe concentrations were positively correlated, reflecting DOM transport via organo-mineral complexes. The watershed tributaries dominated by surficial water (Wu01, Wu08, and Wu09) exhibited relatively high DOC, Fe, pH, and specific DOC UV absorbance (SUVA) and high variability. Groundwater-dominated tributaries (Wu03, Wu12, and Wu15) had lower, less variable contents. The extremely dry 2011 spring had limited effect on stream water chemistry. Outlet (Wu14) stream water DOC reflected seasonally variable contributions of surficial water and groundwater, annually 65 vs. 35%. Critically, a 4-yr lowering of SUVA (reduction of the DOM aromaticity and increased biodegradability) was observed in headwater tributaries (Wu01 and Wu08) but not at Wu14. Our long-term spatial-temporal explicit data set, covering both tributaries and main stream water DOM quality and quantity, was critical in apportionment of contributing sources and drivers of sub- and whole-catchment stream water DOM dynamics.

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