Effects of animals on the transport of solids (e.g., sediments) can modify earth-surface processes and landforms (role as geomorphic agents) and resources for other organisms (role as ecosystem engineers). Therefore, we studied the impact of crayfish (Orconectes limosus) behavior on sand-gravel erosion and bottom habitat over riffle-pool sequences in experimental streams. We manipulated the availability of crayfish food and refugia. Refugia availability had clear effects on overall crayfish activity. The establishment of dominance hierarchies among the crayfish produced patterns in crayfish activity that differed between riffles and pools. Crayfish activity significantly affected sand and gravel erosion. High local sediment erosion averaged ഠ2.8 (riffles) and ഠ1.4 (pools) kg dry weight mϪ1 when crayfish hierarchies were established and refugia were available. Removing the refugia increased these rates to ഠ4.0 (riffles) and ഠ3.2 (pools) kg dry weight m Ϫ2 d Ϫ1. This direct erosion caused by crayfish should be lower than that caused by floods. Crayfish distinctly (1) increased bedform roughness (riffles), (2) decreased sand dune height (pools), (3) shifted the transition between gravel (riffles) and sand (pools) downstream, (4) decreased sand in gravel interstices (riffles), (5) decreased filamentous algae growth on gravel (riffles), and (6) decreased biofilm cover on sand dunes (pools). These sediment changes due to crayfish activity at baseflow should have opposite effects on sediment erosion during subsequent floods. Crayfish impact on physical habitat at baseflow could largely affect population and community structure of the benthos, as well as egg survival of gravel-breeding fish.

Current approaches to mass spectrometry (MS) require ionization of the analytes of interest. For high-mass species, the resulting charge state distribution can be complex and difficult to interpret correctly. Here, using a setup comprising both conventional time-of-flight MS (TOF-MS) and nano-electromechanical systems-based MS (NEMS-MS) in situ, we show directly that NEMS-MS analysis is insensitive to charge state: the spectrum consists of a single peak whatever the species’ charge state, making it significantly clearer than existing MS analysis. In subsequent tests, all the charged particles are electrostatically removed from the beam, and unlike TOF-MS, NEMS-MS can still measure masses. This demonstrates the possibility to measure mass spectra for neutral particles. Thus, it is possible to envisage MS-based studies of analytes that are incompatible with current ionization techniques and the way is now open for the development of cutting-edge system architectures with unique analytical capability.