Heterogeneity and Resilience Dynamics of Submerged Macrophytes in the Littoral Zone of Lake Constance (HRSC) Analysis of spatio-temporal changes of submerged macrophytes and their interactions with ecosystem functions by integrating knowledge-based, multi-sensor remote sensing and GIS methods
Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
Final Report Abstract
Lake Constance underwent major changes of water quality in the last 100 years with a peaking eutrophication in the late 1970s and a subsequent re-oligotrophication process. Longterm development of submersed vegetation was analysed based on remote sensing techniques and GIS application. Macrophyte spatial distribution data of 1911, 1967, 1978 and 1993, 2009-2016 and 2019 were analysed and compared. For the analysis of spatial heterogeneity, landscape metrics were calculated based on functional groups of submersed macrophytes. Metrics on species level were adapted from indices developed for running waters. Moreover, habitat suitability indices for fish were developed using a GIS- and factor-based approach. Data from 1911 were digitized from litteral descriptions and compared with data from 2019 and 2021 to assess resilience of submersed vegetation. The longterm development of macrophyte species composition and distribution is closely related to the longterm changes in trophic state of Lake Constance. In the time of eutrophication, stoneworts and broad-leaved pondweeds declined, while narrow-leaved pondweeds and Zannichellia palustris greatly increased. Nine Chara and nine Potamogeton species vanished in the period of high eutrophication in the 70s and could not recover so far. Nevertheless, for 2019, charophytes increased their dominance in Lower Lake Constance, which indicates a further re-oligotrophication. In 1911 the distribution of Characeae and Potamogetonaceae was exactly equal, whereas 2019/2021 the Characeae are clearly in the majority. Thus, the ecosystem has visibly changed today and has not returned to its former state of the beginning of the 20th century, but shifted more towards a high dominance of Characeae-species. From 1967 to 2019, an increase of vegetated area and relative class diversity was observed. In contrast, the macrophyte vegetation of Lower Lake Constance underwent a homogenization in 1978 caused by the peak of eutrophication. This shows that the heterogeneity of the underwater landscape provided by macrophytes increased with the re-oligotrophication and demonstrates the usefulness of landscape metrics for monitoring aquatic ecosystems. Habitat suitability indices for refuge habitat of European perch and bream as well as for spawning habitat of three-spined stickleback showed spatial and temporal variations but also continuous locations of suitable habitats. A validation and further development of the indices could contribute to a better understanding of population dynamics of fish species. LiDAR data analyses showed the potential of this technique for automated classification processes, structural heterogeneity and biomass estimation of submersed macrophytes.
