Seasonal Variation in Spectral Response of Submerged Aquatic Macrophytes: A Case Study at Lake Starnberg (Germany)

Abstract

Submerged macrophytes are important structural components of freshwater ecosystems that are widely used as long-term bioindicators for the trophic state of freshwater lakes. Climate change and related rising water temperatures are suspected to affect macrophyte growth and species composition as well as the length of the growing season. Alternative to the traditional ground-based monitoring methods, remote sensing is expected to provide fast and effective tools to map submerged macrophytes at short intervals and over large areas. This study analyses interrelations between spectral signature, plant phenology and the length of growing season as influenced by the variable water temperature. During the growing seasons of 2011 and 2015, remote sensing reflectance spectra of macrophytes and sediment were collected systematically in-situ with hyperspectral underwater spectroradiometer at Lake Starnberg, Germany. The established spectral libraries were used to develop reflectance models. The combination of spectral information and phenologic characteristics allows the development of a phenologic fingerprint for each macrophyte species. By inversion, the reflectance models deliver day and daytime specific spectral signatures of the macrophyte populations. The subsequent classification processing chain allowed distinguishing species-specific macrophyte growth at different phenologic stages. The analysis of spectral signatures within the phenologic development indicates that the invasive species Elodea nuttallii is less affected by water temperature oscillations than the native species Chara spp. and Potamogeton perfoliatus.

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

“…The results show that SAV coverage significantly changes across seasons and years in Lake Iseo, as expected for deep lakes [52] and also reported by Bolpagni et al (2016) [1]. In this context, remote sensing seems a viable tool to detect and investigate very rapid successional processes (i.e., inter and intra-annual variation), as well as to quantify the surface areas involved-processes that would, instead, be impossible to adequately evaluate using classical approaches (e.g., by macrophyte survey along transects as imposed by the Water Framework Directive implementation) [53,54]. This stresses the pivotal contribution that remote sensing can play in the analysis of underlying processes of aquatic ecosystems in the coming years.…”

Ecological Responses of Lakes to Climate Change

“…Traditional field sampling of SAV is labor-intensive and costly. In this special issue, Fritz et al [36] explore the efficacy of a remote sensing method-studying changes in the SAV community in Lake Starnberg, Germany, in the growing seasons of 2011 to 2015 based on ground-truthed reflectance spectra. They develop 'phenologic fingerprints' for each SAV species and characterize changes in the plant assemblage with some degree of error that needs to be addressed with further research.…”

Community stability and seasonal biotic homogenisation emphasize the effect of the invasive tropical tanner grass on macrophytes from a highly dynamic neotropical tidal river

“…A myriad of interactive ecological factors contributes to explain biodiversity in ecosystems. It is well established for aquatic macrophytes that spatial and temporal changes in species composition are explained by a combination of processes, including seasonal changes, dispersion, hydrological variation and environmental filtering (Lacoul and Freedman 2006 ; Bornette and Puijalon 2011 ; Fritz et al 2017 ; Ceschin et al 2017 ). At larger scales, dispersion and landscape (including hydrology) are common drivers of the diversity of aquatic plants (Rolon et al 2010 ).…”