Fine-scale spatial homogenization of microbial habitats: a multivariate index of headwater wetland complex condition.

With growing public awareness that wetlands are important to society, there are intensifying efforts to understand the ecological condition of those wetlands that remain, and to develop indicators of wetland condition. Indicators based on soils are not well developed and are absent in some current assessment protocols; these could be advantageous, particularly for soils, which are complex habitats for plants, invertebrates, and microbial communities. In this study, we examine whether multivariate soil indicators, correlated with microbial biomass and community composition, can be used to distinguish reference standard (i.e., high condition) headwater wetland complexes from impacted headwater wetland complexes in central Pennsylvania, USA. Our reference standard sites existed in forested landscapes, while our impacted sites were situated in multi-use landscapes and were affected by a range of land-use legacies in the 1900s. We found that current assessment protocols are likely underrepresenting sampling needs to accurately represent site mean soil properties. On average, more samples were required to represent soil property means in reference standard sites compared to impacted sites. Reference standard and impacted sites also had noticeably different types of microbial habitats for the two multivariate soil indices assessed, and impacted sites were more homogenized in terms of the fine-scale (i.e., 1 and 5 m) spatial variability of these indices. Our study shows promise for the use of multivariate soil indices as indicators of wetland condition and provides insights into the sample sizes and scales at which soil sampling should occur during assessments. Future work is needed to test the generalizability of these findings across wetland types and ecoregions and establish definitive links between structural changes in microbial habitats and changes in wetland soil functioning.

In vivo modulation of hippocampal epileptiform activity with radial electric fields.

PURPOSE: Electric field stimulation can interact with brain activity in a subthreshold manner. Electric fields have been previously adaptively applied to control seizures in vitro. We report the first results from establishing suitable electrode geometries and trajectories, as well as stimulation and recording electronics, to apply this technology in vivo. METHODS: Electric field stimulation was performed in a rat kainic acid injection seizure model. Radial electric fields were generated unilaterally in hippocampus from an axial depth electrode. Both sinusoidal and multiphasic stimuli were applied. Hippocampal activity was recorded bilaterally from tungsten microelectrode pairs. Histologic examination was performed to establish electrode trajectory and characterize lesioning. RESULTS: Electric field modulation of epileptiform neural activity in phase with the stimulus was observed in five of six sinusoidal and six of six multiphasic waveform experiments. Both excitatory and suppressive modulation were observed in the two experiments with stimulation electrodes most centrally placed within the hippocampus. Distinctive modulation was observed in the period preceding seizure-onset detection in two of six experiments. Short-term histologic tissue damage was observed in one of six experiments associated with high unbalanced charge delivery. CONCLUSIONS: We demonstrated in vivo electric field modulation of epileptiform hippocampal activity, suggesting that electric field control of in vivo seizures may be technically feasible. The response to stimulation before seizure could be useful for triggering control systems, and may be a novel approach to define a preseizure state.