| مستخلص: |
Ponds used mostly for fish production are man-made equivalents of natural shallow lakes. Due to the excessive nutrient input, they experience heavy cyanobacterial blooms and common oxygen deficits over the season. Recently, they have also been identified as playing an important role in biogeochemical cycles and the transformation of organic carbon. From July–September 2019, we conducted three diurnal campaigns in which we measured the spatial variability of environmental conditions (temperature, oxygen, chlorophyll-a) and CH 4 fluxes in the hypertrophic Dehtář fishpond. In July, we observed that wind events of several hours resulted in cyanobacterial bloom accumulation in the downwind part of the fishpond, a ~ 4 °C temperature fluctuation, and order of magnitude differences in oxygen concentration along the north-south axis. Methane fluxes were highly variable both spatially and over the season. In July and September, we observed horizontal gradients, while in August spatial heterogeneity was characterised by remarkable patchiness and hotspot formation showing an increase of two orders of magnitude over the rest of the fishpond. Diffusive fluxes accounted for only a minor fraction of total CH 4 fluxes (seasonal average 10.5%, range 0.03–87%), emphasising the dominant role of ebullition (bubble production) in the CH 4 exchange between water and the atmosphere in the hypertrophic fishpond. Linear mixed-effects models identified water depth as the only significant predictor of methane fluxes. Our findings necessitate complex sampling strategies involving seasonal and spatial variability for reliable estimates of the role of fishponds in a global methane budget |
