Dissolved silica dynamics, transfer and retention in a temperate groundwater flow-through shallow lake of the Pampean Plain, Argentina

Abstract

Mainly through BSi processing, shallow lakes regulate DSi retention, transport, and delivery to the ocean. However, these DSi fluxes in southern lakes are little known. This work evaluated the spatio-temporal variation and the main factors that affect DSi dynamics and retention in a temperate groundwater flow-through shallow lake in Argentina. Water samples from streams, the lake, and groundwater were collected from Los Padres Lake Watershed for DSi determination. DSi retention was calculated through a mass balance approach. The BSi pool from macrophytes was quantified using biomass, BSi production, and satellite images. The phytoplankton community was described by chlorophyll content, species quantification, and alpha diversity metrics. The contribution of Si-enriched water from groundwater (≈ 50 mg L−1) mainly controlled DSi concentrations in the inflow stream (≈ 54 mg L−1). Lake DSi concentration was lower than streams and groundwater, and increased over time (14–34 mg L−1). BSi contribution by macrophytes (≈1.4 Mg Si year−1) has little variation, therefore, the reduction of diatoms due to cyanobacteria increase is the most likely factor controlling DSi dynamics, influencing the role of the lake as a DSi sink/source. These biogeochemical processes regulated the DSi transfer from the lake to the outflow stream, and the delivery to the ocean (≈ 630 Mg Si year−1). Given the importance of small lakes in nutrient cycling and retention along flow paths within a watershed, in-lake Si processes and Si sources to these water bodies are critical to quantifying limnetic contributions to the global Si cycle.