Hydrologic variability in black ash wetlands: Implications for vulnerability to emerald ash borer

Black ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non-forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site-dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high-resolution (1-cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB-induced ash mortality, compared to wetter sites where open water evaporation and shallow-rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts.     

The relevance of the 1198 eruption of Solfatara in the Phlegraean Fields (Campi Flegrei) as revealed by medieval manuscripts and historical sources

The Phlegraean Fields (Campi Flegrei) caldera in Italy had one well-documented eruption during the historical period (1538). Another eruption at Solfatara in 1198 is reported by sixteenth and seventeenth-century scholars, and has been commonly regarded as uncertain. In this paper we first discuss the circumstantial evidence and report of this eruption, then discuss the relevance of drawings made in the thirteenth through the fifteenth century illustrating the Solfatara and the primary literary and historical sources describing the site. We infer that the eruption was at most a minor phreatic explosion and we explore the conditions that may have led to the occurrence of this event and the establishment of a small crater pool subsequently used as a thermal bath from the later Middle Ages onward.