Abstract
Benthic vegetation at the land-water interface is recognized as a filter for silica fluxes, which represents an important but under-investigated subject. This paper aims to analyze stocks and fluxes of biogenic (BSi) and dissolved (DSi) silica in relation to nitrogen (N) and phosphorus (P) in the littoral zone of a deep lake. Specifically, we evaluated how different primary producers can influence BSi retention and DSi release. The study was performed from April to October in 2017, in three different benthic communities: submerged aquatic vegetation (SAV) and microphytobenthos (MPB), both occurring in soft bottom sediments, and epilithic macro- and microalgae (EA) on rocky substrates. The main result was that SAV and MPB were a DSi source and a N and P sink with the DSi efflux from SAV nearly three times as much as in MPB patches. These findings corroborate the hypothesis that SAV mediates the DSi transport from pore water to the water column. Conversely, EA communities were a DSi sink and a N and P source. Overall, these results highlight the fact that the littoral zone of lakes plays a key role in regulating aquatic Si cycling, which is likely to depend on the health status of SAV communities.
Highlights
Silicon (Si) is an essential element for the growth of many aquatic primary producers like siliceous algae, especially diatoms, a key component of phytoplankton and phytobenthos communities [1,2].Despite its importance, Si biogeochemistry in aquatic environments is still poorly understood compared to N and P, limiting our capacity to explain the mechanisms regulating aquatic food web structure and functioning [3,4].The global Si cycle consists of continental and oceanic sub-cycles, which are connected through the hydrographic network [4]
Several papers focus on dissolved silica (DSi) fluxes in similar systems, i.e., shallow brackish and freshwater ecosystems, but less is known about the biogenic silica (BSi) content of surface sediments, epilithic macro- and microalgae (EA), and submerged aquatic vegetation (SAV) biomass
While DSi fluxes measured in the present study fall within the ranges reported in the literature (Table 6), comparisons are less reliable for sedimentary BSi, since there is scarce data available
Summary
The global Si cycle consists of continental and oceanic sub-cycles, which are connected through the hydrographic network [4] Within this network, the dissolved silica (DSi) delivered to coastal seas is thought to depend mainly on biologically mediated processes through the synthesis and decomposition of biogenic silica (BSi), on interactions with the geosphere and, on hydrology and land use [3,5]. The dissolved silica (DSi) delivered to coastal seas is thought to depend mainly on biologically mediated processes through the synthesis and decomposition of biogenic silica (BSi), on interactions with the geosphere and, on hydrology and land use [3,5] In this context, fluvial ecosystems connecting the continental and marine domains are not water conveyors, but rather comprise of a number of subsystems acting as filters and reactors, which strongly regulate Si transport [6]. These subsystems include lentic waters, especially wetlands and lakes, which
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