De impact van antropogene en klimatologische druk op vijvers en hun macrofyten- en macro-invertebratengemeenschappen

Ponds are increasingly exposed to the combined and interacting impacts of multiple environmental stressors. Due to their small size, shallow water depth and high surface-area-to-volume ratio, ponds are especially sensitive to global change pressures, including nutrient enrichment and climate warming. The overarching objective of this thesis was to improve understanding of how pond ecosystems respond to these stressors. Specifically, I examined (i) how pond primary producer communities respond to increasing nutrient levels and rising growing-season temperatures, (ii) whether mitigation measures such as terrestrial vegetated buffer strips can effectively reduce nutrient and sediment runoff into ponds from surrounding agricultural land, and (iii) how variation in water permanence influences macroinvertebrate communities. In Chapter 1, I analysed a dataset comprising 220 ponds (147 permanent and 73 temporary) distributed across a broad climatic gradient spanning the United Kingdom, Denmark, Belgium, Germany, Switzerland, Spain, Turkey and Uruguay. The aim was to assess how nutrient concentrations, growing-season temperature, and their interaction influence phytoplankton biomass and the coverage of submerged, free-floating, and emergent macrophytes. Results showed that permanent ponds with low total nitrogen (TN) concentrations were typically dominated by submerged vegetation, whereas at elevated TN levels, submerged macrophytes were replaced by either phytoplankton or free-floating plants. Higher temperatures lowered the nutrient concentrations at which such changes in dominance occurred in permanent ponds. By contrast, submerged plant communities in temporary ponds displayed greater tolerance to increased nutrient concentrations. In Chapter 2, using the same 147 permanent ponds, I explored the relationships between submerged macrophyte cover, taxonomic richness, and functional richness. I further evaluated how increasing nutrient concentrations influence submerged plant cover, species richness, functional richness, and functional redundancy, and investigated nutrient-driven changes in functional type composition. A strong positive association was observed between taxonomic and functional richness, resulting in generally low functional redundancy across ponds. Species richness was significantly lower in ponds with minimal plant cover (0-25%) compared to ponds exhibiting higher cover (>25%). However, richness levels did not differ among moderate to high cover categories, due to cases where dense plant cover occurred despite low species diversity. Submerged plant cover, species richness, functional richness and functional redundancy all declined with increasing TN. Functional groups showed contrasting nutrient responses: Utricularia spp. were most abundant at low TN levels, while Ceratophyllum/Elodea spp. and Characeae showed no apparent sensitivity to the TN gradient. In Chapter 3, I investigated the effect of terrestrial vegetated buffer strip width on pond nutrient concentrations, total suspended solids, and phytoplankton biomass in 34 agricultural ponds in Belgium (Flanders) and Germany (Brandenburg). In Germany, buffer strip width had a strongly negative effect on total nitrogen, total phosphorus and total suspended solids concentrations, with improvements in water quality detectable even at 5 m width, although wider buffers yielded greater reductions. In Belgium, no such relationship was observed, likely due to differences in landscape characteristics, historical eutrophication and pond hydroperiod. Buffer strip width did not significantly influence phytoplankton biomass in either region, most likely because nutrient concentrations remained consistently high, even in ponds surrounded by buffer strips. In Chapter 4, I assessed how hydroperiod affects local species richness and community structure of aquatic Coleoptera, Odonata and Gastropoda in 13 permanent and 17 temporary ponds in northeastern Germany (Brandenburg). Coleoptera species richness (both larvae and adults) was consistently higher in temporary ponds, whereas no significant richness differences were observed for Odonata or Gastropoda. In contrast, species composition differed between hydroperiod types for Gastropoda, but not for Coleoptera or Odonata. Water permanence significantly influenced species turnover in Gastropoda communities. Temporary ponds contributed disproportionately to regional diversity of Coleoptera and Gastropoda, whereas permanent ponds supported a greater proportion of regional Odonata diversity. Most recorded taxa were generalists with traits enabling survival under periodic drying. Species of national conservation concern were detected in both pond types, particularly among gastropods.