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

ZAGARESE H.; LAGOMARSINO L.; VERA M.S.; IZAGUIRRE I.; CASTRO BERMAN M.; BALIÑA S.; SANCHÉZ M. L.; SCHIAFFINO M. R.; CHAPARRO G.; CHERUVELIL K. S.

Natal

Congreso; Shallow lakes 2021; 2021

The Pampean plain of South America hosts thousands of shallow lakes. Most of them are eutrophic or hypereutrophic, subjected to anthropic activities. The majority of these shallow lakes are turbid with high phytoplankton biomass. However, some of them remain in the clear regime with beds of submerged macrophytes and low phytoplankton abundance. Therefore, we ask: what are the main drivers of phytoplankton biomass in Pampean shallow lakes? We performed a linear mixed model with data of 60 shallow lakes located in 10 different regions that were sampled irregularly from 2015 to 2019. Our model was performed with LN(Chla) as the dependent variable and land use, limnologic, morphometric, and hydrologic characteristics as independent fixed factors. We also included the region membership of each lake as a random factor. We performed a model selection process to obtain the best fitted model according to AIC criteria. The best-fit model indicated a non-linear relation between LN(Chla) and TP in these shallow lakes. This model included the interaction between TP and macrophytes in combination with Agriculture percentage (estimated in a 1 km buffer area). Agriculture was statistically significant and positive, while the presence of submerged macrophytes was statistically significant and negative. Region membership explained 30% of the variance. For a more detailed analysis, we split the data set into lakes with (n=9) and without submerged macrophytes (n=51). For shallow lakes with submerged macrophytes, the only statistically significant driver variable was TP with a positive coefficient. On the other hand, lakes without macrophytes exhibited a small but negative relationship with TP. These results demonstrate that: 1) for these Pampean shallow lakes, the relationship between TP and LN(Chla) is non-linear, 2) in most of these lakes, TP is not a limiting factor for algal growth, and 3) in the less abundant clear lakes, the presence of submerged macrophytes is a key factor modulating the relation between LN(Chla) and TP.