TY  - JOUR
A1  - Kamjunke, Norbert
A1  - Rode, Michael
A1  - Baborowski, Martina
A1  - Kunz, Julia Vanessa
A1  - Zehner, Jakob
A1  - Borchardt, Dietrich
A1  - Weitere, Markus
T1  - High irradiation and low discharge promote the dominant role of phytoplankton in riverine nutrient dynamics
JF  - Limnology and oceanography / American Society of Limnology and Oceanography
N2  - Rivers play a relevant role in the nutrient turnover during the transport from land to ocean. Here, highly dynamic planktonic processes are more important compared to streams making it necessary to link the dynamics of nutrient turnover to control mechanisms of phytoplankton. We investigated the basic conditions leading to high phytoplankton biomass and corresponding nutrient dynamics in eutrophic, 8th order River Elbe (Germany). In a first step, we performed six Lagrangian sampling campaigns in the lower river section at different hydrological conditions. While nutrient concentrations remained high at low algal densities in autumn and at moderate discharge in summer, high algal concentrations occurred at low discharge in summer. Under these conditions, concentrations of silica and nitrate decreased and rates of nitrate assimilation were high. Soluble reactive phosphorus was depleted and particulate phosphorus increased inversely. Rising molar C:P ratios of seston indicated a phosphorus limitation of phytoplankton, so far rarely observed in eutrophic large rivers. Global radiation combined with mixing depth had a strong predictive power to explain maximum chlorophyll concentration. In a second step, we estimated nutrient turnover exemplarily for N during the campaign with the lowest discharge based on mass balances and metabolism-based process measurements. Mass balance calculations revealed a total nitrate uptake of 423 mg N m(-2)d(-1). Increasing phytoplankton density dominantly explained whole river gross primary production and related assimilatory nutrient uptake. In conclusion, riverine nutrient uptake strongly depends on the growth conditions for phytoplankton, which are favored at high irradiation and low discharge.
Y1  - 2021
U6  - https://doi.org/10.1002/lno.11778
SN  - 0024-3590
SN  - 1939-5590
VL  - 66
IS  - 7
SP  - 2648
EP  - 2660
PB  - Wiley
CY  - Hoboken
ER  -