Drivers of planktonic Chlorophyll a in Pampean shallow lakes: a regional approach

SÁNCHEZ, MARÍA LAURA; IZAGUIRRE, IRINA; ZAGARESE, HORACIO; SCHIAFFINO, MARÍA ROMINA; CASTRO BERMAN, MANUEL; LAGOMARSINO, LEONARDO; CHAPARRO, GRISELDA; BALIÑA, SOFIA; VERA, MARÍA SOLANGE; CHERUVELIL, KENDRA S.

Congreso; 10th International Shallow Lakes Conference; 2021

The Pampean plain of South America hosts thousands of shallow lakes Most of them areeutrophic or hypereutrophic, subjected to anthropic activities The majority of these lakesare turbid with high phytoplankton biomass However, some of them are in a clear statewith beds of submerged macrophytes and low phytoplankton abundance Therefore, weask what are the main drivers of phytoplankton biomass in Pampean shallow lakes? Weperformed a linear mixed model with data of 60 shallow lakes located in 10 differentregions that were sampled irregularly from 2015 to 2019 Our model was performed withLN(Chla) as dependent variable and land use, limnologic, morphometric, and hydrologiccharacteristics as independent fixed factors We also included the region membership ofeach lake as a random factor We performed a model selection process to obtain the bestfitted model according to Akaike Index Criteria The best fit model indicated a non linearrelation between LN(Chla) and TP in these lakes This model included the interactionbetween TP and macrophytes in combination with Agriculture (estimated in a 1 km bufferarea) Agriculture was statistically significant and positive, while the presence ofsubmerged macrophytes was statistically significant and negative Region membershipexplained 30 of the variance For a more detailed analysis, we split the data set intolakes with (n=9) and without submerged macrophytes (n=51). For shallow lakes withsubmerged macrophytes, the only statistically significant driver variable was TP with apositive coefficient On the other hand, lakes without macrophytes exhibited a small butnegative relationship with TP These results demonstrate that 1 for these Pampeanshallow lakes, the relationship between TP and LN(Chl)a is non linear, 2 in most of theselakes, TP is not a limiting factor for algal growth, and 3 in clear lakes, the presence ofsubmerged macrophytes is a key factor modulating the relation between LN(Chla) and TP