Lagrangian profiles of riverine autotrophy, organic matter transformation, and micropollutants at extreme drought

Detailed process knowledge is rare in large rivers, in particular at hydrological extremes. We investigated autotrophic processes, heterotrophic carbon utilization, and micropollutant concentrations applying a Lagrangian sampling design in the River Elbe, at historically low discharge. Phytoplankton biomass and photosynthesis increased from upstream to downstream sites but maximum chlorophyll concentration was lower than at mean discharge. Concentrations of dissolved macronutrients decreased to almost complete phosphate depletion and low nitrate values. The longitudinal increase of bacterial abundance and production was less pronounced than in wetter years and bacterial community composition changed downstream. Molecular analyses revealed a longitudinal increase of many DOM components due to microbial production. In decomposition experiments, DOM components with high O/C ratios and high masses decreased whereas those with low O/C ratios, low masses, and high nitrogen content increased at all sites. Radiocarbon age analyses showed DOC was relatively old, whereas the mineralized fraction was much younger suggesting predominant oxidation of algal lysis products and exudates particularly at downstream sites. Micropollutants determining toxicity for algae, hexachlorocyclohexanes and DDTs showed higher concentrations from the middle towards the downstream. Autotrophic and heterotrophic process rates and micropollutant concentrations increased from up- to downstream reaches.

KAMJUNKE Norbert;  BECKERS Liza-Marie;  HERZSPRUNG Peter;  VON TÜMPLING Wolf;  LECHTENFELD Oliver;  TITTEL Jörg;  RISSE-BUHL Ute;  RODE Michael;  WACHHOLZ Alexander;  KALLIES Rene;  SCHULZE Tobias;  KRAUSS Martin;  BRACK Werner;  COMERO Sara;  GAWLIK Bernd;  SKEJO Helle;  TAVAZZI Simona;  MARIANI Giulio;  BORCHARDT Dietrich;  WEITERE Markus; 

2022-03-17

ELSEVIER

JRC128235

0048-9697 (online),   

https://www.sciencedirect.com/science/article/pii/S0048969722013353,    https://publications.jrc.ec.europa.eu/repository/handle/JRC128235,   

10.1016/j.scitotenv.2022.154243 (online),