1 Historic developments in macrozoobenthos of the Rhine-Meuse estuary: 2 From a tidal inlet to a freshwater lake 3 4 S. Wijnhoven *, W. Sistermans, H. Hummel 5 6 Monitor Taskforce, Netherlands Institute of Ecology, Centre for Estuarine and Marine 7 Ecology (NIOO-CEME), Korringaweg 7, P.O. Box 140, NL-4401 NT, Yerseke, The 8 Netherlands 9 10 *Corresponding author. Tel.: +31-113-577357; Fax: +31-113-573616; E-mail: 11
[email protected] 12 13 Abstract 14 15 Water works during the 1960s and 70s changed the northern part of the Rhine-Meuse estuary 16 in the south-west of the Netherlands into a freshwater lake, from west to east divided into 17 three basins called the Haringvliet, the Hollands Diep and the Biesbosch. Concurrently water 18 quality parameters (e.g. nutrients and pollutants) changed drastically during the last 50 years. 19 This study combines macrozoobenthic monitoring data from the region from 1960 to 2001 20 with trends in abiotic parameters to evaluate historic developments of the communities, 21 including densities, species numbers and diversity, and assess future developments as a first 22 step to a rehabilitation of the estuary as planned for January 01, 2008. During the 1960s, the 23 macrozoobenthic densities of Oligochaeta and/or Polychaeta dominated communities 24 increased with a gradual decrease of salt water intrusion and salinity variability. The first 25 years after the basins became stagnant, the species numbers per sample and the Shannon 26 diversity were high due to coexistence of salt and freshwater species. An increase in nutrient 27 and pollutant loads led to a decrease in the macrozoobenthos densities.