The distributions of 9 species of aquatic vascular macrophytes were examined in relation to interstitial water patterns (based on temperature) in the beds of three northern Michigan (U.S.A.) streams. Ranunculus septentrionalis Poir., Caltha palustris L. and Nasturtium officinale R.Br. were associated with areas of groundwater discharge. Sparganium chlorocarpum Rydb., Veronica catenata Penn., Potamogeton fili/ormis Pers. and P. richardsonii (Benn.) Rydb. occurred most often at the downstream end of a hyporheic zone (corresponding to the foot of a riffle) where interstitial water was of surface origin. Sagittaria lati[olia Willd. occurred where interstitial temperatures were cool; the water origin was not determined. Potamogeton gramineus L. occurred most often where interstitial temperatures were warm, primarily at the upstream ends and middles of hyporheic zones (heads of riffles) in areas of surface-water infiltration. Complex patterns of interstitial water movement and related physicochemical complexity combined with differences in plant requirements, in part, may determine observed local distributions.
The ability to resolve 2-3Å structurally and 20-50Å chemically has made high resolution electron microscopy (HREM) and microanalysis the preferred techniques for a number of interface studies. The interfaces are usually examined in thin cross-sections cut normal to a major crystallographic direction along which the structure at the interface appears particularly simple in projection. A large number of such studies have now been carried out in a number of different laboratories, including the studies of semiconductor-oxide, semiconductor-semiconductor, and semiconductor-metal interfaces. An exciting new aspect of the studies is exploring the chemistry at the interface using a high resolution probe-forming instrument and either energy-dispersive X-ray spectroscopy(EDXS) or electron energy loss spectroscopy(EELS), since these studies can usally be performed on the same specimens as used for HREM, and a good correlation between the detailed atomic structure and the chemical composition can be achieved.
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