TY - JOUR
T1 - Long-term impacts of nutrient control, climate change, and invasive clams on phytoplankton and cyanobacteria biomass in a large temperate river
AU - Minaudo, Camille
AU - Abonyi, András
AU - Leitão, Maria
AU - Lançon, Anne Marie
AU - Floury, Mathieu
AU - Descy, Jean Pierre
AU - Moatar, Florentina
N1 - Funding Information:
Authors are thankful to the water basin authorities (Agence de l'Eau Loire Bretagne) for providing long term water quality data, and allowing the publication of phytoplankton data. Authors are also grateful to “Eléctricité de France” for providing data on Corbicula densities and continuous water temperature measurements in the Middle Loire River. The short-term phytoplankton sampling would have been impossible without the help of Laurence Lanctin, Yannick Bennet, André Dubois, Hervé Couet and Didier Louvel. We thank the two anonymous reviewers for their comments and suggestions that helped improve the manuscript, and G. Flaim for providing English language editing.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2021/2/20
Y1 - 2021/2/20
N2 - Recent studies suggest that climate change, with warmer water temperatures and lower and longer low flows, may enhance harmful planktic cyanobacterial growth in lakes and large rivers. Concomitantly, controlling nutrient loadings has proven effective in reducing phytoplankton biomass especially in North America and Western Europe. In addition, the impact of invasive benthic filter-feeder species such as Corbicula on phytoplankton has largely been overlooked in large rivers, leading to even more uncertainty in predicting future trajectories in river water quality. To investigate how nutrient control, climate change and invasion of benthic filter-feeders may affect phytoplankton biomass and composition, we assembled a large database on the entire water course of the River Loire (France) over three decades (1991–2019). We focus on cyanobacteria to provide an in-depth analysis of the 30-year trend and insights on future possible trajectories. Since 1991, total phytoplankton and cyanobacteria biomasses have decreased 10-fold despite warmer water temperature (+0.23 °C·decade−1) and lower summer flow (−0.25 L·s−1·km−2·decade−1). In the long-term, the contribution of planktic cyanobacteria to total biomass was on average 2.8%. The main factors driving total phytoplankton and cyanobacteria biomasses were total phosphorus (4-fold decrease), the abundance of Corbicula clams (from absence before 1998 to 250–1250 individuals·m−2 after 2010), the duration of summer low flows and the intensity of summer heatwaves. The River Loire constitutes an example in Europe of how nutrient control can be an efficient mitigation strategy, counteracting already visible effects of climate change on the thermal regime and flow pattern of the river. This may hold true under future conditions, but further work is needed to account for the climate trajectory, land and water use scenarios, the risk of enhanced benthic biofilm and macrophyte proliferation, together with the spread of invasive filter-feeding bivalves.
AB - Recent studies suggest that climate change, with warmer water temperatures and lower and longer low flows, may enhance harmful planktic cyanobacterial growth in lakes and large rivers. Concomitantly, controlling nutrient loadings has proven effective in reducing phytoplankton biomass especially in North America and Western Europe. In addition, the impact of invasive benthic filter-feeder species such as Corbicula on phytoplankton has largely been overlooked in large rivers, leading to even more uncertainty in predicting future trajectories in river water quality. To investigate how nutrient control, climate change and invasion of benthic filter-feeders may affect phytoplankton biomass and composition, we assembled a large database on the entire water course of the River Loire (France) over three decades (1991–2019). We focus on cyanobacteria to provide an in-depth analysis of the 30-year trend and insights on future possible trajectories. Since 1991, total phytoplankton and cyanobacteria biomasses have decreased 10-fold despite warmer water temperature (+0.23 °C·decade−1) and lower summer flow (−0.25 L·s−1·km−2·decade−1). In the long-term, the contribution of planktic cyanobacteria to total biomass was on average 2.8%. The main factors driving total phytoplankton and cyanobacteria biomasses were total phosphorus (4-fold decrease), the abundance of Corbicula clams (from absence before 1998 to 250–1250 individuals·m−2 after 2010), the duration of summer low flows and the intensity of summer heatwaves. The River Loire constitutes an example in Europe of how nutrient control can be an efficient mitigation strategy, counteracting already visible effects of climate change on the thermal regime and flow pattern of the river. This may hold true under future conditions, but further work is needed to account for the climate trajectory, land and water use scenarios, the risk of enhanced benthic biofilm and macrophyte proliferation, together with the spread of invasive filter-feeding bivalves.
KW - Corbicula clams
KW - Large rivers
KW - Loire
KW - Oligotrophication
KW - Phosphorus
KW - Trend analysis
UR - http://www.scopus.com/inward/record.url?scp=85097480306&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2020.144074
DO - 10.1016/j.scitotenv.2020.144074
M3 - Article
C2 - 33303198
AN - SCOPUS:85097480306
SN - 0048-9697
VL - 756
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 144074
ER -