Relationships between diatom metrics based on species nutrient traits and agricultural land use

We assessed how diatom metrics were related to different ranges of agricultural land use. Diatom assemblage composition, nutrients, and landscape characteristics were determined at 232 sites in eight agriculturally dominated study areas of the continental United States. Two regional groups based on differences in diatom relations to human disturbance were determined. Changes in diatom species composition were related to nutrients, pH, and conductivity in the eastern study areas (due to more wetlands) and more exclusively to nutrients in the west-central study areas. Homogenization of diatom flora among streams was related to high agricultural disturbance at this transcontinental scale. Species traits were developed separately for the east and west-central study groups and calculated two ways: indicator species analysis for taxa in low and high TN or TP conditions and weighted average partial least squares models of TN and TP concentration. These diatom metrics were significantly related to many indicators of agricultural land use in watersheds, especially percent row crops. Further analysis was conducted on only the west-central region due to its larger sample size. Overall, diatom metrics using species responses to N gradients were better related to agricultural land use than were species responses to P gradients. Most nutrient-based diatom metrics changed greatly in response to low ranges of percent row crops, but only a few high N diatom metrics responded to high row crop conditions. The greater response of diatoms to changes in low agriculture conditions may be due to past diatom evolution occurring when most waters had low nutrient conditions.

The green alga, Cladophora, promotes Escherichia coli growth and contamination of recreational waters in Lake Michigan

A linkage between Cladophora mats and exceedances of recreational water quality criteria has been suggested, but not directly studied. This study investigates the spatial and temporal association between Escherichia coli concentrations within and near Cladophora mats at two northwestern Lake Michigan beaches in Door County, Wisconsin. Escherichia coli concentrations in water underlying mats were significantly greater than surrounding water (p < 0.001). Below mat E. coli increased as the stranded mats persisted at the beach swash zone. Water adjacent to Cladophora mats had lower E. coli concentrations, but surpassed EPA swimming criteria the majority of sampling days. A significant positive association was found between E. coli concentrations attached to Cladophora and in underlying water (p < 0.001). The attached E. coli likely acted as a reservoir for populating water underlying the mat. Fecal bacterial pathogens, however, could not be detected by microbiological culture methods either attached to mat biomass or in underlying water. Removal of Cladophora mats from beach areas may improve aesthetic and microbial water quality at affected beaches. These associations and potential natural growth of E. coli in bathing waters call into question the efficacy of using E. coli as a recreational water quality indicator of fecal contaminations.

Control of photon beam dose profiles by localized transverse magnetic fields

Unlike electron beams, scant attention has been paid in the literature to possible magnetic field effects on therapeutic photon beams. Generally, dose profiles are considered to be fully determined by beam shape, photon spectrum and the substances in the beam path. Here we show that small superconducting magnets can exercise potentially useful control over photon dose profiles. The magnet produces a locally strong transverse field with large gradients and is applied to the tissue surface below which the photon beam is passing. For one practical magnet design, our simulations, which use the EGS-4 Monte Carlo code modified to include magnetic field effects, show significant intensification and shielding effects. In water phantoms, the effects extend to 3-4 cm or more beyond the warm face of the cryostat and greater distances are achieved in phantoms simulating lung (density approximately 0.3). Advances in applying the concept and in superconducting materials and magnet design hold promise for extending these ranges.