Drivers of planktonic chlorophyll a in pampean shallow lakes

Abstract

Although agricultural intensification has been linked with the increment of lake eutrophication and shallow lake research has demonstrated the importance of submerged macrophytes for maintaining water clarity, less is known about the role of macrophytes and the effects of agriculture on shallow lakes of the global south. Shallow lakes in the Pampean region of Argentina are subjected to high anthropic pressure and are classified as eutrophic and hypereutrophic and, in spite of most of them are turbid and dominated by phytoplankton biomass, some remain in a clear-vegetated regime with profuse submerged macrophytes. We studied the potential drivers of phytoplankton biomass (estimated as Chlorophyll-a - Chla) by applying a regional approach and a model selection process for a dataset of 58 shallow lakes that represent the variability of the Pampean region. For the 58 lakes, the presence of submerged macrophytes, total nitrogen, and nearby agriculture of each lake were the main drivers of Chla with −1.55, 0.19 and 0.02 coefficient values, respectively. Moreover, a high proportion of the variance in this dataset (37.7 %) was explained by the regional location of each lake (hydrographic systems). For lakes with macrophytes (N = 8), Chla exhibited a positive relationship with total phosphorus (coefficient value = 3.05), whereas for lakes without macrophytes (N = 50) Chla showed a positive relationship with nearby agricultural development (coefficient value = 0.02) and 36.4 % of variance explained by the hydrographic system. Our regional approach highlighted the importance of submerged macrophytes in shaping phytoplankton biomass in Pampean shallow lakes. Our results support the idea that the conservation of submerged macrophytes, as well as the control of agriculture in the riparian zones of lakes, will help to stabilize the shallow lakes in clear regime, even in regions highly impacted by agriculture and in lakes under eutrophic conditions.