Jing Feng1*, Johan van de Koppel1,2, Daphne van der Wal1,3
1 NIOZ Royal Netherlands Institute for Sea Research, Department of Estuarine and Delta Systems, Yerseke, Netherlands; 2 Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, Netherlands; 3 Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, Netherlands
Saltmarshes are subject to periodic flooding. Inundation frequency may play an important role in the seaward limit of saltmarsh vegetation. This research focuses on the saltmarshes in the Western Scheldt of the Netherlands. Dominant vegetation species in this area include: (1) Salicornia europaea and Salicornia procumbens (SalSp); (2) Spartina anglica and Spartina townsendii (SpaSp); (3) Bolboschoenus maritimus (BolMa); and (4) Phragmites australis (PhrAu). We address the following two questions: 1) How does the distribution and abundance of different dominant vegetation species relate to the inundation frequency in saltmarshes? 2) What is the relationship between variations of inundation frequency and the biomass dynamics in saltmarshes?
Based on surveys of Rijkswaterstaat, time-series (1993, 1998, 2004, 2010, 2016) of vegetation distribution maps, were analyzed in ArcGIS 10.8.2. Google Earth Engine (GEE) was be used to create a time-series of inundation frequency based on aggregating satellite images from Landsat 5/7/8 (U.S. Geological Survey/NASA). Through counting the times each pixel is classified as water, we can calculate the inundation frequency. Pixel-based analysis was used for further investigation.
First results show changes in the distribution of the selected vegetation species during 1993-2016. For example, a significant increase of SalSp's coverage was observed in the mudflats of both the western and eastern parts of the estuary. SpaSp significantly increased e.g., on the intertidal flat Hooge Platen. As for the total cover area, despite the overall trends of PhrAu, SalSp and SpaSp were increasing and BolMa showed a fluctuant decrease (although it still covers the largest area, in Saeftinghe). For the pioneer species SalSp and SpaSp, the pixels with inundation typically have higher mean vegetation coverage than the ones without inundation, whereas BolMa and PhrAu show the opposite.