Spatiotemporal Dynamics of Submerged Aquatic Vegetation in a Deep Lake from Sentinel-2 Data

Abstract

We mapped the extent of submerged aquatic vegetation (SAV) of Lake Iseo (Northern Italy, over the 2015–2017 period based on satellite data (Sentinel 2 A-B) and in-situ measurements; the objective was to investigate its spatiotemporal variability. We focused on the southern sector of the lake, the location of the shallowest littorals and the most developed macrophyte communities, mainly dominated by Vallisneria spiralis and Najas marina. The method made use of both in-situ measurements and satellite data (22 Sentinel 2 A-B images) that were atmospherically corrected with 6SV code and processed with the BOMBER (Bio-Optical Model-Based tool for Estimating water quality and bottom properties from Remote sensing images). This modeling system was used to estimate the different substrate coverage (bare sediment, dense stands of macrophytes with high albedo, and sparse stand of macrophytes with low albedo). The presented results substantiate the existence of striking inter- and intra-annual variations in the spatial-cover patterns of SAV. Intense uprooting phenomena were also detected, mainly affecting V. spiralis, a species generally considered a highly plastic pioneer taxon. In this context, remote sensing emerges as a very reliable tool for mapping SAV with satisfactory accuracy by offering new perspectives for expanding our comprehension of lacustrine macrophyte dynamics and overcoming some limitations associated with traditional field surveys.

Impact of upstream landslide on perialpine lake ecosystem: an assessment using multi-temporal satellite data

“…Operational mid-resolution satellite data have recently been used for environmental applications on aquatic systems focusing, for example on: riparian vegetation classification (Stratoulias et al, 2015), mapping water quality and submerged macrophyte cover (Dörnhöfer et al, 2016;Fritz et al, 2019), estimating aquatic vegetation biomass (Gao et al, 2017), assessing the spatio-temporal evolution of primary producers Ghirardi et al, 2019), analysing the seasonal dynamics of wetland plant communities , and mapping cyanobacteria blooms (Sòria-Perpinyà et al, 2020).…”

“…The specific water absorption and backscattering coefficients were the same used by Ghirardi et al (2019) for Lake Iseo. The concentrations of water constituents were set differently for each processed Sentinel-2 date and parameter, namely: i) suspended particulate matter values from ACOLITE turbidity outputs, by assuming a unity conversion factor (Jafar-Sidik et al, 2019); ii) coloured dissolved organic matter absorption values at 440 nm assumed fixed at 0.1 m -1 ; and iii) chlorophyll-a concentration varying according to the month, i.e.…”

Silica Storage, Fluxes, and Nutrient Stoichiometry in Different Benthic Primary Producer Communities in the Littoral Zone of a Deep Subalpine Lake (Lake Iseo, Italy)

“…In contrast with what we found at the RS site, SAV species at VS efficiently accumulated N and P. These elements exhibited a seasonal pattern similar to the BSi one, with a peak in the early phase and a sharp decrease in the later part of the season (Figure 2). Such a pattern can be explained by both leaf detachment [78,79] and element translocation from leaves to roots and rhizomes. Both processes usually occur at the end of the vegetative growth phase.…”

“…This pattern was probably due to the fast decay of detrital BSi from different sources, primarily SAV and its epiphytes, which are known to have a short half-life of just a few weeks [29]. It is likely that part of the lost BSi was taken up and retained by SAV, but then exported from the meadow as detached leaves [79]. The Si assimilation by MPB accounted for a slight BSi increase at the BS site ( Figure 2) but, at <1 g m −2 , it was not sufficient to compensate for the total BSi loss.…”

“…Like many other littoral zones, the southern part of Lake Iseo is under the influence of coastal runoff [88]. Such stressors can affect the health status of the extensive SAV meadows, which also undergo a great inter-annual variability [79]. Here, in soft, shallow sediments, meadows of V. spiralis, and to a much lesser extent N. marina, can produce dense biomass covering up to 100 ha, while zones with sparse SAV usually spread over an additional 300-400 ha [79].…”