TY - JOUR
T1 - Long-term change of phytoplankton in Lake Kivu
T2 - The rise of the greens
AU - Rugema, Edouard
AU - Darchambeau, François
AU - Sarmento, Hugo
AU - Stoyneva-Gärtner, Maya
AU - Leitao, Maria
AU - Thiery, Wim
AU - Latli, Adrien
AU - Descy, Jean Pierre
N1 - Funding Information:
The data used in this study, originating from different projects supported by CUD (Coopération Universitaire pour le Développement, FRS-FNRS (Fonds National de la Recherche Scientifique), CTB (Coopération Technique Belge), and BELSPO (Belgian Scientific Policy Office), were gathered during the EAGLES project, supported by BELSPO (Belgian Scientific Policy Office; www.belspo.be) under the Science for Sustainable Development (contract SD/AR/02A). The collaboration with the teams from ISP Bukavu and University of Rwanda was invaluable. H.S.'s work was supported by CNPq (grant 309514/2017-7) and FAPESP (process 2014/14139-3). The authors are grateful to the editor of FWB and to one referee, who both made constructive comments that helped improve the manuscript.
Publisher Copyright:
© 2019 John Wiley & Sons Ltd.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - Phytoplankton time-series enable the observation of recurrent seasonal patterns on community composition, but drastic shifts in community structure are rarely observed, unless linked to anthropogenic impacts (e.g. changes in nutrient inputs). Here, we report a unique case of non-seasonal, multiannual regime shift of phytoplankton community structure in Lake Kivu, East Africa, and explore the possible causes for such changes. We recorded phytoplankton biomass every 2 weeks over a period of 12 years (from 2002 to 2015). Phytoplankton community previously dominated by cyanobacteria and diatoms changed considerably from 2012, with a conspicuous rise in the biomass of green algae (from 3 to 33% lake-wide), and a decline of cryptophytes and cyanobacteria along with an increase in total chlorophyll a concentration. Concomitantly, we observed significant differences in the mixed layer depth between the two periods, resulting from changes in the thermal gradient. The euphotic zone depth was also reduced in 2012–2015, probably from the higher phytoplankton biomass. Moreover, mean particulate nitrogen and phosphorus increased as well as the particulate N:P ratio. Desmids (Cosmarium laeve) now dominate the mixolimnion, probably due to atelomixis, observed in high-frequency temperature measurements. We believe that decadal or multidecadal variability of climate on the Indian Ocean may be the reason for this regime shift in thermal stratification, with a strong impact in phytoplankton community structure. In conclusion, our study demonstrates that tropical lakes may be subject to non-seasonal fluctuations that generate multiannual regime shifts. These regime shifts have probably never been reported previously because of the lack of long phytoplankton time-series in low latitudes.
AB - Phytoplankton time-series enable the observation of recurrent seasonal patterns on community composition, but drastic shifts in community structure are rarely observed, unless linked to anthropogenic impacts (e.g. changes in nutrient inputs). Here, we report a unique case of non-seasonal, multiannual regime shift of phytoplankton community structure in Lake Kivu, East Africa, and explore the possible causes for such changes. We recorded phytoplankton biomass every 2 weeks over a period of 12 years (from 2002 to 2015). Phytoplankton community previously dominated by cyanobacteria and diatoms changed considerably from 2012, with a conspicuous rise in the biomass of green algae (from 3 to 33% lake-wide), and a decline of cryptophytes and cyanobacteria along with an increase in total chlorophyll a concentration. Concomitantly, we observed significant differences in the mixed layer depth between the two periods, resulting from changes in the thermal gradient. The euphotic zone depth was also reduced in 2012–2015, probably from the higher phytoplankton biomass. Moreover, mean particulate nitrogen and phosphorus increased as well as the particulate N:P ratio. Desmids (Cosmarium laeve) now dominate the mixolimnion, probably due to atelomixis, observed in high-frequency temperature measurements. We believe that decadal or multidecadal variability of climate on the Indian Ocean may be the reason for this regime shift in thermal stratification, with a strong impact in phytoplankton community structure. In conclusion, our study demonstrates that tropical lakes may be subject to non-seasonal fluctuations that generate multiannual regime shifts. These regime shifts have probably never been reported previously because of the lack of long phytoplankton time-series in low latitudes.
KW - atelomixis
KW - climate variability
KW - community structure
KW - East Africa
KW - tropical great lake
UR - http://www.scopus.com/inward/record.url?scp=85070867957&partnerID=8YFLogxK
U2 - 10.1111/fwb.13383
DO - 10.1111/fwb.13383
M3 - Article
AN - SCOPUS:85070867957
SN - 0046-5070
VL - 64
SP - 1940
EP - 1955
JO - Freshwater Biology
JF - Freshwater Biology
IS - 11
ER -