Search

Blue oak tree-ring chronologies correlate highly with winter–spring precipitation totals over California, with Sacramento and San Joaquin river stream flow, and with seasonal variations in the salinity gradient in San Francisco Bay. The convergence of fresh and saline currents can influence turbidity, sediment accumulation, and biological productivity in the estuary. Three selected blue oak chronologies were used to develop a 625-year-long reconstruction of the seasonal salinity gradient, or low salinity zone (LSZ), which provides a unique perspective on the interannual-to-decadal variability of this important estuarine habitat indicator. The reconstruction was calibrated with instrumental LSZ data for the winter–spring season, and explains 73% of the variance in the February–June position of the LSZ from 1956 to 2003. Because this calibration period post-dates the sweeping changes that have occurred to land cover, channel morphology, and natural streamflow regimes in California, the reconstruction provides an idealized estimate for how the LSZ might have fluctuated under the seasonal precipitation variations of the past 625 years, given the modern geometry and bathymetry of the estuary and land cover across the drainage basin. The February–June season integrates precipitation and runoff variability during the cool season, and does not extend into the late-summer dry season when LSZ extremes can negatively affect Sacramento–San Joaquin Delta (Delta) agriculture and some aquatic organisms. However, there is such strong inter-seasonal persistence in the instrumental LSZ data that precipitation totals during the cool season can strongly pre-condition LSZ position in late summer. The 625-year-long reconstruction indicates strong interannual and decadal variability, the frequent recurrence of consecutive 2-year LSZ maxima and minima, large-scale ocean atmospheric forcing, and an interesting asymmetrical influence of warm El Niño–Southern Oscillation (ENSO) events.

We present four reconstruction estimates of Arkansas River baseflow and streamflow using a total of 78 tree‐ring chronologies for three streamflow gages, geographically spanning the headwaters in Colorado to near the confluence of the Arkansas‐Mississippi rivers. The estimates represent different seasonal windows, which are dictated by the shared limiting forcing of precipitation on seasonal tree growth and soil moisture—and subsequently on the variability of Arkansas River discharge. Flow extremes that were higher and lower than what has been observed in the instrumental era are recorded in each of the four reconstructions. Years of concurrent, cross‐basin (all sites) low flow appear more frequently during the 20th and 21st Centuries compared to any period since 1600 A.D., however, no significant trend in cross‐basin low flow is observed. As the most downstream major tributary of the Mississippi River, the Arkansas River directly influences flood risk in the Lower Mississippi River Valley. Estimates of extreme high flow in downstream reconstructions coincide with specific years of historic flooding documented in New Orleans, Louisiana, just upstream of the Mississippi River Delta. By deduction, Mississippi River flooding in years of low Arkansas River flow imply exceptional flooding contributions from the Upper Mississippi River catchments. [ABSTRACT FROM AUTHOR]

Severe ground shaking and the formation of Reelfoot Lake during the great New Madrid earthquakes of A.D. 1811-1812 had a profound effect on baldcypress trees that still survive in Reelfoot Lake of northwestern Tennessee. Inundation greatly increased baldcypress radial growth from 1812 to 1819 and permanently decreased wood density after 1811. Ground shaking fractured the baldcypress stems that were present during the 1811-1812 event, but fractures are absent in the post-1811 growth. In contrast, the growth of old baldcypress trees in the St. Francis sunkland of northeastern Arkansas was severely suppressed for almost 50 yr following the 1811-1812 New Madrid earthquakes. Thus, there are two opposite but profound growth responses to the same earthquake events preserved in baldcypress trees of the New Madrid seismic zone. The tree. ring chronology at Reelfoot Lake extends from A.D. 1682 to 1990, but the 1812-1819 growth surge was the only extreme growth anomaly in this 309 yr period. The St. Francis sunkland chronology extends from A.D. 1321 to 1990, and the 1812-1857 growth suppression is the most severe and prolonged growth anomaly of this entire 670 year period. Thus, the tree-ring record indicates that there was not a great earthquake during the 129 yr prior to 1811 in the Reelfoot Lake basin, nor during the 490 yr prior to 1811 in the St. Francis sunkland.

Tree-ring chronologies can provide surprisingly accurate estimates of the natural variability of important climate parameters such as precipitation and temperature during the centuries prior to the Industrial Revolution. Bald cypress tree-ring chronologies have been used to reconstruct spring rainfall for the past 1000 years in North Carolina, South Carolina, and Georgia. These rainfall reconstructions explain from 54% to 68% of the spring rainfall variance in each state, and are well verified against independent rainfall measurements. In fact, these tree-ring data explain only 6% to 13% less statewide rainfall variance than is explained by the same number of instrumental raingage records. The reconstructions indicate that the spring rainfall extremes and decade-long regimes witnessed during the past century of instrumental observation have been a prominent feature of southeastern United States climate over the past millennium. These spring rainfall regimes are linked in part to anomalies in the seasonal expansion and migration of the subtropical anticyclone over the North Atlantic. The western sector of the Bermuda high often ridges strongly westward into the southeastern United States during dry springs, but during wet springs it is usually located east of its mean position and well offshore. Similar anomalies in the western sector of the Bermuda high occurred during multidecadal regimes of spring rainfall over the Southeast. During the relatively dry springs from 1901 to 1939, the high often ridged into the Southeast, but the western periphery of the high was more frequently located offshore during the relatively wet period from 1940 to 1980. Spring and summer rainfall extremes and decade-long regimes over the Southeast are frequently out of phase, and the tendency for wet (dry) springs to be followed by dry (wet) summers also appears to reflect anomalies in the zonal position of the Bermuda high during spring and summer.

The native population collapse in 16th century Mexico was a demographic catastrophe with one of the highest death rates in history. Recently developed tree-ring evidence has allowed the levels of [...]

Informed multi-family dwelling (MFD) waste reduction and recyclables collection programs require empirical knowledge of the composition, variability, and generation rates of recyclables associated with the waste disposal behavior of MFD residents. A full sampling of MFD residents' non move-out, non-bulky disposal over four study periods was undertaken at a 28-unit apartment complex having no children in Fayetteville, Arkansas. Generation rates for commonly collected categories of recyclables were calculated based on the results of the test for significant difference between period means. Using analysis of variance and a 10% significance level, no significant difference was found between the period means for corrugated boxes, rigid paperboard, mixed paper, HDPE bottles and jugs, steel cans and lids, aluminum cans, and clear glass constituent recyclable material groups. Significant differences were, however, found between the period means for newspaper, PET bottles and jugs, the glass material group brown glass, green glass, and total recyclable disposal. The period average total recyclable generation rate ranged from 1.97 kg/person/wk to 2.77 kg/person/wk across the periods. Fifty-two percent of the average resident's generated weekly solid waste was recyclable—an amount that would likely have been noticeably higher had cats not been permitted. Implications for future MFD waste characterization studies are discussed. [ABSTRACT FROM AUTHOR]

Development of successful multi-family dwelling (MFD) organics and household hazardous waste (HHW) diversion programs require empirical knowledge of the composition, variability, and generation rates of compostables and HHW associated with the disposal behavior of MFD residents. A full sampling of MFD residents non-bulky, non move-out disposal over a fall and spring study period was undertaken at a 28-unit apartment complex having no children in Fayetteville, Arkansas. Per capita weekly generation rates for organics and HHW categories were calculated based on the results of the test for significant differences between period means. Significant differences were found between the period means for total compost-target material (CTM) disposal. On a period average basis, generation rates for CTM ranged from 1.337 kg/person/wk for the fall period to 1.045 kg/person/wk for the spring period. No significant difference, however, was found between the period means for total HHW disposal and cat litter. HHW across the two periods averaged 0.078 kg/person/wk. Cat litter, a material collected as part of at least one large municipal waste diversion program's organics collection, was found to represent a significant portion of total generated disposal. Implications for future CTM and HHW-focused MFD waste characterization studies are discussed. [ABSTRACT FROM AUTHOR]