Long-Term Trends of Organic Matter Runoff From Large Siberian Rivers Watersheds

Aim. To evaluate the dynamics and load level of dissolved organic matter (DOM) runoff in the river-mouth sections of large Siberian rivers.
Methodology. To calculate the values of chemical runoff, long-term hydrological and hydrochemical information for the period from 1990 to 2020 were used. The dynamics of the organic matter (OM) runoff (including oil products) is considered. A comparative assessment of the runoff of DOM was carried out according to the specific characteristic – the module of chemical runoff – for the mouth sections of such rivers as the Ob, the Pur, the Taz, the Nadym, the Yenisei, the Anabar, the Lena, the Yana, the Indigirka and the Kolyma.
Results. It is shown that the largest values of DOM runoff are typical for the most full-flowing rivers (the Ob, the Yenisei, and the Lena rivers), while the smallest volumes are typical for rivers with a low water runoff. According to such a specific characteristic as the modulus of chemical runoff, the highest runoff values of easily oxidizable OM are recorded for the Pur, the Taz, the Anabar, and the Kolyma rivers, and the highest values of the runoff of hardly oxidizable OM and oil products are recorded for the rivers of the Kara Sea basin. Correlation analysis revealed a statistically significant increase in the runoff of hard-to-oxidize OM in the mouth areas of such rivers as the Ob, the Pur, the Yenisei, the Anabar, the Yana, and the Indigirka. A declining trend of the oil products runoff was identified in the sections of the Ob, the Nadym, the Taz, the Lena and the Kolyma rivers. It has been established that the lower reaches of the Eastern Siberia rivers incur the least total load of the OM runoff and the river-mouth sections of the Kara Sea basin incur the average and high load.
Research implications. Results and obtained data could be used to assess the variability of anthropogenic load and water quality in the mouths sections of the rivers. Also, the findings can be used to study the possible impact of river runoff on the hydrochemical regime of Arctic rivers-mouth ecosystems and coastal marine areas.

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