SITE-SPECIFIC DIFFERENCES, BUT NOT EXPOSURE PROFILES DRIVE THE RESPONSES OF PRIMARY-PRODUCERS TO FRESHWATER SALINIZATION IN A MULTI-SITE MESOCOSM EXPERIMENT

The PRESSUR experiment aimed to characterize the response of model aquatic ecosystems to two different salinity exposure patterns. Fifteen ~500-L, in-lake, closed-bottom, mesocosm were assigned to three treatments (n = 5 each): a control, and two sets of mesocosms treated with NaCl (500 mg CL-/L final concentration) differing on the exposure profile. One received a single spike while the other received the same total amount in 8 events over 21 days. This set up was also replicated at two different locations, an oligotrophic temperate lake (57ºN) and a humic boreal lake (64ºN) both in Sweden. Each mesocosm was outfitted with an array of sensors collecting real time data on temperature, conductivity, pH, dissolved oxygen, chlorophyll-a and phycocyanin fluorescence, and PAR. Other endpoints were also assessed in phyto- and periphyton over the 38 days of the study. Phytoplankton Chll-a fluorescence was reduced by NaCl addition with this effect developing faster in the single application treatment. The gradual application treatment, however, reached similar effect levels after ~2 applications. Interestingly, differences were observed between the two sites, with the northern site showing a late increase in Chll-a 14-20 days post first application (onset earlier in the single-pulse treatment). This late increase on Chll-a levels was not observed in the south site, where Chll-a levels remained low after the initial reduction. This study highlights the importance of original ecosystem characteristics on the sensitivity of aquatic systems to salinization.

Primary Presenter: Jose Luis Rodriguez Gil, IISD - Experimental Lakes Area (joseluis.rodriguezgil@gmail.com)

Authors:

Jose Luis Rodriguez Gil, International Institute for Sustainable Development, Experimental Lakes Area, Canada  (jlrodriguez@iisd-ela.org)

Zorka Dulic, University of Belgrade, Serbia  (sundjerbaby@gmail.com)

Erin Ford, Queen's University, Canada  (ford.e@queensu.ca)

Guangbine Gao, Institute of Hydrobiology, Chinese Academy of Sciences (IHB-CAS), China  (gaoguangbin@ihb.ac.cn)

Aidan Guttormson, International Institute for Sustainable Development, Experimental Lakes Area, Canada  (aguttormson@iisd-ela.org)

Jana Isanta-Navarro, University of Copenhagen, Denmark  (jana.isanta-navarro@bio.ku.dk)

Silke Langenheder, Uppsala University, Sweden  (silke.langenheder@ebc.uu.se)

Mary Mullins, Tarleton State University, USA  (elizabeth.mullins@go.tarleton.edu)

Judit Rodrigo, Uppsala University, Sweden  (juditrodrigo15@gmail.com)

Ingrid Sassenhagen, Institute for Baltic Sea Research in Warnemünde, Germany  (ingrid.sassenhagen@io-warnemuende.de)

Anusha Singh, Institute of Hydrobiology, Biology Centre of the Academy of Sciences of the Czech Republic, Czech Republic  (Anusha.singh@hbu.cas.cz)

Pablo Urrutia Cordero, IMDEA Water Institute, Spain  (pablo.urrutia@imdea.org)

Andrra Zhjeqi, Lund University, Sweden  (an6353zh-s@student.lu.se)

Shelley Arnott, Queen's University, Canada  (arnotts@queensu.ca)