Case study: Tommelen bomb craters (Hasselt)

1. Case study: Tommelen bomb craters (Hasselt) (Part of WP1: Biodiversity at multiple spatial scales: patterns and driving variables) WWII - 1944 High density ponds (ca 110 ponds;12 ha), similar age, same soil (light sandy loam)

2. Aims 1) Investigate how diversity is structured in a pond complex (high density, small spatial scale) for a diverse set of organisms groups 2) What are the main drivers of communities inhabiting ponds 3) Recommendations concerning pond(complex) management and conservation (in combination with management-experiment).

3. Survey Survey of 49 ponds (spring & summer 2007): - physical & chemical variables (nutrients, turbidity, oxygen,…) - morphology (depth, surface,…) - fluctuations in groundwater

4. Survey Macrophytes Cladocerans Benthic diatoms Bacteria Amphibians Macroinvertebrates Phytoplankton © D. Ercken © D. Ercken

5. Structure of diversity in a pond complex Alpha diversity:diversity within a particular area or ecosystem (e.g. number of species in a pond) Beta diversity:change in species diversity between two ecosystems Gamma diversity:overall diversity for different ecosystems within a region (e.g. Tommelen) GAMMA ALPHA A C BETA D D E C B

6. Structure of diversity in a pond complex BACTERIA (total 55; average 11.2) Regional species/taxa richness (gamma) 90% CUMULATIVE NUMBER OF SPECIES/TAXA 18 poelen 110 NUMBER OF PONDS

7. Why is structure of diversity important? SIMILAR GAMMA DIVERSITY HIGH ALPHA DIVERSITY BUT: different effect on diversity if ponds disappear CUMULATIVE NUMBER OF SPECIES/TAXA HIGH BETA DIVERSITY NUMBER OF PONDS

8. Zooplankton (21; 5) Phytobenthos (221; 35.6) 33 ponds 37 ponds Phytoplankton (135; 23) Macrophytes (21; 4 – 111; 17) 29 ponds 34 ponds Macroinvertebrates (65; 28.6) Amphibians (5*; 4) 11 ponds 3 ponds

9. Turnover rate per sample (beta diversity) Based on Shannon diversity 0 = no turnover 1= each sample is completely different from every other sample

10. Main drivers?

12. Main drivers? Hydrology (data 1994-1995 inbo)

13. Community composition • Strong zonation: phytobenthos, phytoplankton, bacteria • Spatially correlated eutrophication gradient • Important role of periodically filled ditch, polluted up to 1996

14. Community composition Diatoms

15. Community composition Most important structuring variables linked with eutrophication gradient & vegetation cover Bacteria: total nitrogen, % open water, surface, oxygen Phytoplankton: emerse vegetation, oxygen, SO4 Phytobenthos: total nitrogen, % open water, presence of fish, alcalinity Zooplankton: total phosphorus, maximum depth, density of Hydra, successional stage Macroinvertebrates: transparency, fish, oxygen, temperature Macrophytes: maximum depth, degree of sludge, pH Amphians: (only larvae): fish (remark, fish only in ponds connected to ditch)

16. Prospectives & Management recommendation • Species poor ponds > subset of species rich ponds? (nestedness analysis) • Relatively high beta diversity within most groups of organisms: loss of ponds can result in pronounced loss of diversity • But strong variation in beta diversity between groups of organisms • Zonal/spatial patterns (mainly linked with local pond characteristics) • Strong effect of « ditch » on pond communities (introduction of fish, variable quality of incoming water,…)