The Legacy of Leaded Gasoline in Bottom Sediment of Small Rural Reservoirs

The historical and ongoing lead (Pb) contamination caused by the 20th-century use of leaded gasoline was investigated by an analysis of bottom sediment in eight small rural reservoirs in eastern Kansas, USA. For the reservoirs that were completed before or during the period of maximum Pb emissions from vehicles (i.e., the 1940s through the early 1980s) and that had a major highway in the basin, increased Pb concentrations reflected the pattern of historical leaded gasoline use. For at least some of these reservoirs, residual Pb is still being delivered from the basins. There was no evidence of increased Pb deposition for the reservoirs completed after the period of peak Pb emissions and (or) located in relatively remote areas with little or no highway traffic. Results indicated that several factors affected the magnitude and variability of Pb concentrations in reservoir sediment including traffic volume, reservoir age, and basin size. The increased Pb concentrations at four reservoirs exceeded the U.S. Environmental Protection Agency threshold-effects level (30.2 mg kg-1) and frequently exceeded a consensus-based threshold-effects concentration (35.8 mg kg-1) for possible adverse biological effects. For two reservoirs it was estimated that it will take at least 20 to 70 yr for Pb in the newly deposited sediment to return to baseline (pre-1920s) concentrations (30 mg kg-1) following the phase out of leaded gasoline. The buried sediment with elevated Pb concentrations may pose a future environmental concern if the reservoirs are dredged, the dams are removed, or the dams fail

Differences in onset of Greenness: A multitemporal analysis of Grass and Wheat

ABSTRACT The time when vegetation emerges (begins active photosynthesis) each year can be monitored using remotely sensed data obtained from Earth observation satellites. This measurement, called the onset of greenness, can be calculated using time series data sets of the Normalized Difference Vegetation Index (NDVI), a ratio of red and near infra-red (NIR) light that is strongly correlated to plant biomass. The date at which the onset of greenness occurs varies depending on the region, type of vegetation present, weather conditions, land management practices, and other factors. Time series NDVI data are proving useful for a wide variety of applications including vegetation mapping, crop monitoring, and yield modeling. The onset of greenness metric values were extracted from bi-weekly AVHRR satellite data over the state of Kansas from 1989 through 2000. Four different locations in Kansas were sampled: 1) winter wheat from Sumner County, 2) winter wheat from Thomas County, 3) tall grass rangeland from Chase County, and 4) short grass rangeland from Logan County. The onset date was recorded from 20 AVHRR pixels from each location for each year of data. Samples from the same location were analyzed to detect differences in onset date between years and samples from different locations were compared to identify differences in onset date within the same year. Results show a significant difference in the onset of greenness date between cover types and a significant difference in onset dates between years for the same cover type at the same location. Regression analysis shows that the grasslands and wheat of northwestern Kansas have a negative slope (earlier onset), while the lines of best fit for grasslands and wheat in south central Kansas did not indicate a substantial change in onset date