Identifying sources of dissolved organic carbon in agriculturally dominated rivers using radiocarbon age dating: Sacramento–San Joaquin River Basin, California

We used radiocarbon measurements of dissolved organic carbon (DOC) to resolve sources of riverine carbon within agriculturally dominated landscapes in California. During 2003 and 2004, average Δ¹⁴C for DOC was ?254‰ in agricultural drains in the Sacramento–San Joaquin Delta, ?218‰ in the San Joaquin River, ?175‰ in the California State Water Project and ?152‰ in the Sacramento River. The age of bulk DOC transiting the rivers of California’s Central Valley is the oldest reported for large rivers and suggests wide-spread loss of soil organic matter caused by agriculture and urbanization. Using DAX 8 adsorbent, we isolated and measured ¹⁴C concentrations in hydrophobic acid fractions (HPOA); river samples showed evidence of bomb-pulse carbon with average Δ¹⁴C of 91 and 76‰ for the San Joaquin and Sacramento Rivers, respectively, with older HPOA, ?204‰, observed in agricultural drains. An operationally defined non-HPOA fraction of DOC was observed in the San Joaquin River with seasonally computed Δ¹⁴C values of between ?275 and ?687‰; the source of this aged material was hypothesized to be physically protected organic-matter in high clay-content soils and agrochemicals (i.e., radiocarbon-dead material) applied to farmlands. Mixing models suggest that the Sacramento River contributes about 50% of the DOC load in the California State Water Project, and agricultural drains contribute approximately one-third of the load. In contrast to studies showing stabilization of soil carbon pools within one or two decades following land conversion, sustained loss of soil organic matter, occurring many decades after the initial agricultural-land conversion, was observed in California’s Central Valley.     

Characterization of microsatellite loci in chinook salmon (Oncorhynchus tshawytscha) and cross‐species amplification in other salmonids

Previous studies of population genetic structure of fall‐run chinook salmon (Oncorhynchus tshawytscha) in California’s Central Valley have either not focused on or have been unable to resolve intertributary differences within the San Joaquin River basin. The authors describe the isolation, the polymerase chain reaction conditions, and characterize the cross‐species amplification of 17 microsatellite loci in six species of salmonids. Fourteen of these loci are polymorphic in fall‐run chinook from the San Joaquin River drainage. These results indicate the potential utility of microsatellite markers developed for one species, for both congenerics and species within a closely related genus.     

Seasonal population dynamics of Draeculacephala minerva (Hemiptera: Cicadellidae) and transmission of Xylella fastidiosa

The grass sharpshooter, Draeculacephala minerva Ball (Hemiptera: Cicadellidae), is a very common and often abundant grass-feeding leafhopper in California. Its population dynamics and ability to transmit Xylella fastidiosa were monitored over a 2-yr period in California's San Joaquin Valley. Collections of individuals from natural populations in irrigated pastures and alfalfa, Medicago savita L. fields adjacent to X. fastidiosa-infected almond (Prunus spp.) orchards indicated the occurrence of three discrete generations per year that peaked during the summer. Population densities varied significantly among experimental field survey sites. Insects captured on intercepting mesh traps, yellow sticky cards, and UV-light traps indicated local movement of these insects into and surrounding X. fastidiosa-infected, almond orchards. Local movement and seasonal transmission of X. fastidiosa from infected almonds to Catharanthus roseus (L.) G. Don indicated that this insect may be partly responsible for the slow spread of almond leaf scorch now recently observed in California's San Joaquin Valley.     

Range-wide molecular analysis of the western pond turtle (Emys marmorata): cryptic variation, isolation by distance, and their conservation implications

We analysed phylogeography and population genetic variation across the range of the western pond turtle (Emys marmorata) using rapidly evolving mitochondrial and nuclear DNA sequence data. Nuclear DNA sequences from two unlinked introns displayed extremely low levels of variation, but phylogenetic analyses based on mtDNA recovered four well-supported and geographically coherent clades. These included a large Northern clade composed of populations from Washington south to San Luis Obispo County, California, west of the Coast Ranges; a San Joaquin Valley clade from the southern Great Central Valley; a geographically restricted Santa Barbara clade from a limited region in Santa Barbara and Ventura counties; and a Southern clade that occurs south of the Tehachapi Mountains and west of the Transverse Range south to Baja California, Mexico. An analysis of molecular variance (amova) based on regional hydrographic units revealed that populations from the Sacramento Valley north to Washington were virtually invariant, with no evidence of population substructure among northern river drainage basins. In other areas, E. marmorata contains considerable unrecognized variation, particularly in central and southern California and in northern Baja California, Mexico. Our northern clade is congruent with the distribution of the subspecies Emys marmorata marmorata (Washington-central California). However, no clade is congruent with the distribution of the southern subspecies Emys marmorata pallida from central California-Baja. Thus, recognition of the current subspecies split is not warranted, based on the available genetic evidence. Our amova and phylogenetic results, in conjunction with a growing comparative database for other codistributed aquatic taxa, confirm the occurrence of genetic breaks across the Tehachapi Mountains and Transverse Range bounding the southern end of the Great Central Valley, and point to southern California as a rich source of cryptic genetic variation.     

Selenium in animal nutrition: The Oregon and San Joaquin Valley (California) experiences—Examples of correctable deficiencies in livestock

White muscle disease and other selenium deficiency syndromes, once extremely common in young calves and lambs in Oregon, especially in the areas of volcanic origin east of the Cascade mountain range, prompted extensive investigations in the Oregon Agricultural Experiment Station that resulted in the implementation of large-scale selenium supplementation programs. Although selenium deficiency in livestock is consequently now rare in Oregon, selenium-deficient soils and attendant selenium deficiency conditions have been reported near the Kesterson Wildlife Refuge in the Northern part of the San Joaquin Valley, California, where, paradoxically, selenium toxicity in wildfowl, nesting near evaporation ponds, occurred and attracted wide attention. This review cites studies which explain why there is no evidence of selenium toxicity in livestock, but some selenium deficiency on the east side of the San Joaquin Valley. They also show that there is no threat to the food supply owing to excessive selenium in this area and that the consumption of meat and milk from the herds would not exceed the safe range of selenium for humans.     

Toxic effect of water-soluble fractions of crude, refined, and weathered oils on the growth of a marine bacterium.

The water-soluble fractions of three crude and two refined oils reduced the growth rate and maximum cell density of the marine bacterium Serratia marinorubra grown in batch culture. The weathering of a crude and a refined oil was simulated in the laboratory. The water-soluble fractions remaining from this process were more toxic to S. marinorubra than were the parent unweathered oils. Increases in the magnitude of toxic effect of 3 to 30 times were observed as a function of decreasing the concentration of yeast extract in the cultures from 0.1 to 0.05 and 0.01%. The toxicity did not correlate with the concentration of total water-soluble fraction or of aromatic hydrocarbons in the water-soluble fraction. Affected cultures did not exhibit a residual toxicity after being back-inoculated into control media.     

Taxon-specific multiplex-PCR for quick,easy, and accurate identification of encyrtid and aphelinid parasitoid species attacking soft scale insects in California citrus groves

Citricola scale, Coccus pseudomagnoliarum Kuwana (Hemiptera: Coccidae), is a serious pest of citrus in California’s San Joaquin Valley, but not in southern California where a complex of Metaphycus spp. Mercet (Hymenoptera: Encyrtidae) suppress it. This has created interest in using these (and other Metaphycus) species for biological control in the San Joaquin Valley. A critical step in assessing an organism’s potential for biological control is the ability to accurately identify it. For Metaphycus spp., this currently requires slide mounted adult specimens and expert taxonomic knowledge. We present a simple, quick and accurate method to identify any life stage of the ten major parasitoids of soft scales in California citrus, based on amplification of ribosomal DNA, using the polymerase chain reaction (PCR). Three multiplex-PCR protocols amplify products of taxon-specific sizes, allowing direct diagnosis of taxa accommodated by the PCR, and reducing identification time to a fraction of that of existing methods.     

The molecular phylogenetics of endangerment: cryptic variation and historical phylogeography of the California tiger salamander, Ambystoma californiense

A primary goal of conservation genetics is the discovery, delimitation and protection of phylogenetic lineages within sensitive or endangered taxa. Given the importance of lineage protection, a combination of phylogeography, historical geology and molecular clock analyses can provide an important historical context for overall species conservation. We present the results of a range-wide survey of genetic variation in the California tiger salamander, Ambystoma californiense, as well as a summary of the past several million years of inundation and isolation of the Great Central Valley and surrounding uplands that constitute its limited range. A combination of population genetic and phylogenetic analyses of mitochondrial DNA variation among 696 samples from 84 populations revealed six well-supported genetic units that are geographically discrete and characterized by nonoverlapping haplotype distributions. Populations from Santa Barbara and Sonoma Counties are particularly well differentiated and geographically isolated from all others. The remaining units in the Southern San Joaquin Valley, Central Coast Range, Central Valley and Bay Area are separated by geological features, ecological zone boundaries, or both. The geological history of the California landscape is consistent with molecular clock evidence suggesting that the Santa Barbara unit has been isolated for at least 0.74-0.92 Myr, and the Sonoma clade is equally ancient. Our work places patterns of genetic differentiation into both temporal- and landscape-level contexts, providing important insights into the conservation genetics of the California tiger salamander.     

Evaluation of the dermal carcinogenic potential of liquids produced from the Cold Lake heavy oil deposits of northeast Alberta

This study assessed the dermal carcinogenic potential of raw bitumen derived from the Cold Lake Oil Sands deposit (located in Northeast Alberta, Canada) and two liquids which were under evaluation as part of a process to refine the crude bitumen at the Cold Lake site. The crude bitumen was dermally carcinogenic, inducing tumors in 26% of the treated animals with a median latency of 106 weeks. This response was significantly greater than the tumor yield previously reported for a raw bitumen derived from Athabasca tar sands by the Syncrude process, but was not substantially different from the carcinogenic potential of two crude petroleum oils. The GO-FINING product, a high boiling (259-519 degrees C), catalytically cracked gas oil was a relatively potent dermal carcinogen, inducing tumors in 86% of the treated animals with a median latency of 46 weeks. This result is consistent with the fact that the GO-FINING product contained appreciable levels of high boiling aromatic compounds. The HYCRACKING product, a high boiling (102-498 degrees C), severely hydroprocessed liquid was noncarcinogenic. This result was also consistent with the compositional data; the high boiling components were predominantly saturated species. Thus the carcinogenic properties of the liquid products prepared by these two processes were as predicted from the compositional information.     

Seasonal abundance of Draeculacephala minerva and other Xylella fastidiosa vectors in California almond orchards and vineyards

Almond leaf scorch (ALS) disease is caused by the bacterium Xylella fastidiosa and transmitted by xylem-feeding insects. Reports of increased incidence of ALS-diseased trees in California prompted surveys in three almond [Prunus dulcis (Mill.) D. A. Webb]-growing regions, from June 2003 to September 2005, to determine insect vector species composition and abundance. For comparison, sampling in and near vineyards in the San Joaquin Valley, California, also was completed. Sampling in or near almond orchards collected >42,000 Cicadomorpha of which 4.8% were xylem feeders, including 1912 grass sharpshooter, Draeculacephala minerva Ball; five Xyphon fulgida Nottingham; and a single spittlebug, Philaenus spumarius L. The most abundant vector was D. minerva. Season-long sampling indicated that D. minerva was a year-round resident in and/or near almonds in the Sacramento Valley, but not in the San Joaquin Valley. Similarly, D. minerca was rare in vineyards in the San Joaquin Valley, but was abundant in irrigated pastures near vineyards. D. minerva was most frequently collected along orchard margins, and peak densities were observed in summer, the period of time when bacterial titers are reported to increase in infected trees. Screening of D. minerva for presence of X.fastidiosa found that 1.1% of insects collected near almond orchards and 4.5% of insects collected from pastures tested positive. The X. fastidiosa subspecies and genotype detected in insects collected from orchards matched those collected from ALS-diseased almond trees in the same orchard. Of the few X. fulgida and P. spumarius collected, none tested positive for X. fastidiosa. Results are discussed with respect to X. fastidiosa vector control and detection methods.     

Seasonal and Scale Size Relationships between Citricola Scale (Homoptera: Coccidae) and Its Parasitoid Complex (Hymenoptera: Chalcidoidea) on San Joaquin Valley Citrus

The phenology of citricola scale, Coccus pseudomagnoliarum (Kuwana), and its associated parasitoid complex were studied on citrus in the San Joaquin Valley of central California over the period April 1995–March 1997. A total of 10,237 parasitoid specimens of 10 species were collected. Two of these species, Marietta mexicana (Howard) and Encyrtus lecaniorum (Mayr), each recovered from individually isolated scales, represent new parasitoid records for citricola scale. A third species, Encarsia citrinus citrinus (Craw), may represent a new parasitoid record, but this requires further confirmation because a single (male) specimen was recovered from individually isolated scales. The three most dominant parasitoid species, Coccophagus lycimnia (Walker), Metaphycus helvolus (Compere), and Metaphycus luteolus (Timberlake), accounted for the majority (>97%) of the specimens recovered. In contrast to the situation on citrus in southern California, where citricola scale is under effective biological control and is very rarely seen, citricola scale on citrus in the San Joaquin Valley is reemerging as a major pest, especially in groves employing integrated pest management with minimal use of broad-spectrum insecticides. Possible reasons uncovered in this study for the lack of effective biological control of citricola scale in the San Joaquin Valley include: (i) reduced presence of Metaphycus spp. because of hyperparasitism by the heteronomous hyperparasitoid C. lycimnia; (ii) absence of alternate hosts for those species of Metaphycus present; and (iii) absence of hosts of suitable size for Metaphycus at critical times of the year. Recommendations for improving the level of biological control in the San Joaquin Valley are discussed.     

Book Reviews

Book reviewed in this article:
The Epidemic of 1830–1833 in California and Oregon . S. F. C ook
The Aboriginal Population of the San Joaquin Valley, California . S. F. C ook     

Effects of Temperature and Crude Oil Composition on Petroleum Biodegradation

The biodegradability of seven different crude oils was found to be highly dependent on their composition and on incubation temperature. At 20 C lighter oils had greater abiotic losses and were more susceptible to biodegradation than heavier oils. These light crude oils, however, possessed toxic volatile components which evaporated only slowly and inhibited microbial degradation of these oils at 10 C. No volatile toxic fraction was associated with the heavier oils tested. Rates of oil mineralization for the heavier oils were significantly lower at 20 C than for the lighter ones. Similar relative degradation rates were found with a mixed microbial community, using CO2 evolution as the measure, and with a Pseudomonas isolate from the Arctic, using O2 consumption as the measure. The paraffinic, aromatic, and asphaltic fractions were subject to biodegradation. Some preference was shown for paraffin degradation, especially at low temperatures. Branched paraffins, such as pristane, were degraded at both 10 and 20 C. At best, a 20% residue still remained after 42 days of incubation. Oil residues generally had a lower relative percentage of paraffins and higher percentage of asphaltics than fresh or weathered oil.     

Effects of pyriproxyfen on California red scale (Hemiptera: Diaspididae) development and reproduction

Two life stages of a laboratory colony of California red scale, Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae), were exposed to 10 concentrations of pyriproxyfen to evaluate the effect of this insect growth regulator (IGR) on scale development and fecundity. First instars exposed to pyriproxyfen responded with mortality during the first and second molts. Second instars were more tolerant of pyriproxyfen than were first instars, indicating that growers should treat California red scale in the field before the first molt to achieve maximum efficacy. Male scales responded with an LC50 12-fold lower and an LC90 47-fold lower than was observed for female scales. Female scales that survived first instar exposure to pyriproxyfen experienced reduced fecundity with increasing pyriproxyfen concentration. Reduced fecundity was due to reduced survival of the females rather than sterility. Results from this study provide baseline California red scale susceptibility data for pyriproxyfen, and they suggest that 1 ppm pyriproxyfen can be used as a concentration that would discriminate between susceptible and resistant populations of scales. Field monitoring for incipient pyriproxyfen resistance in California red scale should be implemented in the San Joaquin Valley of California, and if resistance is detected, integrated resistance management strategies should be used to slow the progression of resistance.     

Hydrocarbon bioremediation of a mineral-base contaminated waste from crude oil extraction by indigenous bacteria

The susceptibility to bioremediation of the hydrocarbons contained in a waste from crude oil extraction was examined. Laboratory scale batch reactors were inoculated with indigenous bacteria and biodegradation was followed for 45 days. The total hydrocarbon content was reduced to 70% of its initial value at the end of the experiments. Saturated and aromatic hydrocarbons were the most readily degraded fractions with, respectively, 70% and 60% of the fraction remaining at the end of the experiment. A minor degradation was observed in the resins fraction (20%), whereas the asphaltenes fraction remained almost constant.The substrate preferences of the natural population towards various fractions of the crude oil were determined by both the length of the lag phase and the slope of the exponential growth in a mineral salt-base medium containing either of the different hydrocarbon fraction as the sole source of carbon. The highest consumption rate for every fraction during the time course experiments was in agreement with the shortest lag phase and the greatest exponential growth slope in the corresponding selective media, indicating changes in the population composition.     

Genetic analysis reveals two distinct Sacramento splittail (<Emphasis Type="Italic">Pogonichthys macrolepidotus</Emphasis>) populations

The Sacramento splittail is an endemic cyprinid fish of the San Francisco estuary and its tributaries, which is a highly manipulated, constantly changing ecosystem. Splittail is the only extant member of its genus and is listed as a federal and California Species of Special Concern due to uncertainties regarding long-term abundance trends. Determining population structure for splittail is important because unique populations may contain different adaptive genetic variation, which can allow one population to persist through future environmental or demographic stochasticity while others become extirpated. To assess splittail population structure, 13 microsatellite markers were used to genotype 489 young-of-year splittail from five major rivers draining into the estuary: Cosumnes, Napa, Petaluma, Sacramento, and San Joaquin Rivers. Two genetically distinct populations were found to exist within our study region; one largely comprised of splittail collected from the Petaluma and Napa Rivers and the second comprised of splittail collected from tributaries in Californiaȁ9s Central Valley: Cosumnes, Sacramento, and San Joaquin Rivers. These results were replicated in two consecutive years with both distance and model-based algorithms. The genetic distinction between these two populations appears correlated with salinity differences between migratory regions and spawning grounds. Splittail from the Petaluma River exhibited a significantly higher degree of differentiation from the Central Valley population than did Napa River splittail. Our results suggest on-going monitoring programs are probably highly biased towards sampling splittail from the Central Valley population. Understanding population dynamics of splittail could be improved if monitoring programs were expanded to include all splittail populations.     

Inter-regional differences in baseline toxicity of Bemisia argentifolii (Homoptera: Aleyrodidae) to the two insect growth regulators, buprofezin and pyriproxyfen.

A survey of 53 Bemisia argentifolii Bellows & Perring populations from different agricultural regions in California and Arizona was conducted from 1997 to 1999 to establish baseline toxicological responses to buprofezin and pyriproxyfen. Although both compounds proved to be highly toxic even in minute quantities to specific stages, geographical and temporal differences in responses were detected using a leaf spray bioassay technique. Monitoring for three years revealed that six to seven populations had higher LC50 values but not greater survival when exposed to these two insecticides. A significant difference in relative susceptibility to buprofezin was first observed in late season 1997 in San Joaquin Valley populations with LC50s ranging from 16 to 22 microg (AI)/liter(-1) compared with IC50s of 1 to 3 mg (AI)/liter(-1) in Imperial, Palo Verde Valley and Yuma populations. Whiteflies collected in subsequent years from these and other locations showed an increase in susceptibility to buprofezin. Regional differences in susceptibilities to pyriproxyfen were minimal within the same years. Three years of sampling revealed consistently higher LC50s to pyriproxyfen in populations from Palo Verde Valley, CA, compared with whiteflies from Imperial, San Joaquin Valley or Yuma. As was the case with buprofezin, a decline in LC50s to pyriproxyfen was observed in whiteflies from all locations sampled in 1999. However, no correlation was observed between buprofezin and pyriproxyfen toxicity in any of the strains. The variable toxicities observed to both compounds over a period of 3 yr may be due principally to inherent differences among geographical populations or due to past chemical use which may confer positive or negative cross-resistance to buprofezin or pyriproxyfen.     

Respiration of mitochondria from the gonads of the sea urchin, Strongylocentrotus droebachiensis: the effects of petroleum fractions on oxygen consumption

The respiration of mitochondria from gonads of Strongylocentrotus droebachiensis has been studied in the presence of 2-oxoglutarate, glutamate and succinate. The rate of oxygen consumption increased with temperature between 4 and 20 degrees C. Removal of gametes from ripe gonads was necessary to obtain good respiring mitochondria. Equilibration of respiration media with various petroleum fractions reduced the rate of oxygen consumption and the coupling of O2 consumption to ADP utilization. Lighter fractions (leaded gasolines, unleaded gasoline and related fractions) were more deleterious than medium fractions (kerosene and fuel oil). Heavy fraction (bunker C, vacuum bottoms and crude oil) were least deleterious. Tetraethyl lead contributed to the toxicity of the leaded fractions.     

Salt toxicosis in ruddy ducks that winter on an agricultural evaporation basin in California

Agricultural evaporation basins are used as a means to dispose of highly saline underground-tile-drainage water in the San Joaquin Valley (California, USA). The hypersaline water conditions encourage high aquatic invertebrate production, primarily brine shrimp (Artemia franciscana), which attract birds to these sites. Cool winter temperatures (< 4 C) and hypersaline water conditions (> 70,000 mumhos/cm) resulted in feather salt encrustation and salt toxicosis in ruddy ducks (Oxyura jamaicensis). During December 1998 and January 1999, approximately 200 dead and sick ruddy ducks were collected from an evaporation basin and five healthy control ruddy ducks were collected from a freshwater wetland. Brains contained > or = 1,890 ppm sodium (wet tissue mass) in seven dead birds and contained < or = 1,150 ppm sodium in the control birds. Liver arsenic, lead, and mercury concentrations were < 1 ppm in all birds examined. Manganese, molybdenum, and copper liver concentrations did not differ significantly (P > 0.05) between the two groups of ducks. The dead ducks had significantly higher liver selenium, cadmium, iron, and zinc than the controls, but the concentrations were not sufficient to cause toxicity. Significant gross and microscopic lesions in most of the dead birds included conjunctivitis, lens opacity and cataract formation, vascular congestion in various organs most notably in the meninges of the brain, and myocardial and skeletal muscle degeneration.     

Gene flow among San Joaquin kit fox populations in a severely changed ecosystem

The San Joaquin kit fox (Vulpes macrotis mutica) was once ubiquitous throughout Californias San Joaquin Valley and its surrounds. However, most of its habitat has been lost to irrigated agriculture, urban development, and oil fields. The remaining foxes are concentrated in six areas, although there are several small pockets of foxes throughout the Valley. To help conserve kit foxes, we sought an ecological understanding of the level of genetic variation remaining in these locations and the extent of gene flow among them. We collected tissue from 317 kit foxes from 8 sites and estimated genetic variability in and gene flow among sites using data from 8 polymorphic, microsatellite markers. We found no differences in both observed and expected heterozygosity between locations using Bonferonni corrected paired t-tests. We found differences in mean number of alleles per locus, even after we used Monte Carlo simulations to adjust for sample size differences. Population subdivision was low among sites (F_st=0.043), yet a matrix of pairwise F_st values was correlated with a matrix of pairwise geographic distances. An assignment test classified only 45% of the individuals to the site where they were captured. Overall, these data suggest that kit fox dispersal between locations may still maintain genetic variation throughout most of the areas we sampled.