Flood events are often considered the major hydrologic disturbance structuring lotic communities. Mediterranean climatic regions, however, traditionally experience low- or no-discharge periods on a perennial basis. Recent reductions in alpine snowpack and annual rainfall, combined with increases in mean terrestrial surface temperature and evapotranspriation rates, are predicted to exacerbate seasonal desiccation events and expand the range of Mediterranean climactic zones.
The impact of such desiccation events on lotic periphyton assemblages is poorly understood and two related questions are addressed in this research project:
1.) How does perennial seasonal desiccation affect periphyton community structure?
2.) Does perennial seasonal desiccation constitute a true disturbance event that dramatically alters or resets periphyton community structure on a yearly basis, or does the predictable nature of this frequent abiotic event not dramatically alter community structure?
These questions will be addressed by data from field collections from Mediterranean climatic streams and by imposing different desiccation histories on periphyton assemblages in artificial streams. Predictable desiccation should establish assemblages where desiccation is an important structural component of the assemblage, and does not dramatically alter structure. In contrast, a singular desiccation event imposed on a perennial stream should more severely impact the community structure.