Potomac River Research Articles

From shell to glass: how beads reflect the changing cultural landscape of the seventeenth-century lower Potomac River valley

ABSTRACTThis article examines over 7,500 beads from eight Native archaeological sites located in the lower Potomac River valley in order to understand how changes in bead assemblages between AD 1300 and 1712 expressed an ever-evolving Chesapeake cultural landscape. This analysis demonstrates clear differences in the types and distributions of beads from mortuary and domestic/nonmortuary contexts. Ossuary contexts contained the highest frequency of beads with the number of beads increasing over time. Following the arrival of English settlers in the 1620s, glass beads begin to appear in ossuary contexts. Beads from domestic or nonmortuary contexts are fewer in number, and those present were manufactured using local materials, including bone and clay, as well as shell. However, after 1680, there is a shift from shell beads being predominate on Native sites, to sites containing exclusively glass beads, red and black glass beads in particular. Post-1680 sites appear to reflect Piscataway displacement and the disruption of indigenous trade routes, leading Natives to obtain beads from colonial vendors. The distribution of bead color, an important attribute for communicating Native states of being, also shifts after 1680, with assemblages once dominated by white shell beads now dominated by black and red glass beads.

Investigation of the metal content of sediments around the historically polluted Potomac River basin in Washington D.C., United States by inductively coupled plasma-optical emission spectroscopy (ICP-OES)

The Potomac and Anacostia rivers have a history of being contaminated with organic and inorganic contaminants. In the past, significant Hg, Pb, and Zn have been found in sediments of these rivers. Thus, monitoring of metals the Potomac River basin sediments has become a high priority. Sediments from ten locations in the Potomac River basin were collected, and the concentrations of Al, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Zn were determined by ICP-OES. Sediments from urban and commercial areas typically had higher concentrations of metals than other locations. The results suggest that the sediments of locations other than our locations, SH and SJ, are likely to have some toxic effect on the environment.

APA Holds Grand Opening of New Headquarters

APA’s new home places it in close proximity to Congress and regulatory agencies in a new neighborhood along the banks of the Potomac River.

Genomic analyses of Northern snakehead (Channa argus) populations in North America.

BackgroundThe introduction of northern snakehead (Channa argus; Anabantiformes: Channidae) and their subsequent expansion is one of many problematic biological invasions in the United States. This harmful aquatic invasive species has become established in various parts of the eastern United States, including the Potomac River basin, and has recently become established in the Mississippi River basin in Arkansas. Effective management of C. argus and prevention of its further spread depends upon knowledge of current population structure in the United States.MethodsNovel methods for invasive species using whole genomic scans provide unprecedented levels of data, which are able to investigate fine scale differences between and within populations of organisms. In this study, we utilize 2b-RAD genomic sequencing to recover 1,007 single-nucleotide polymorphism (SNP) loci from genomic DNA extracted from 165 C. argus individuals: 147 individuals sampled along the East Coast of the United States and 18 individuals sampled throughout Arkansas.ResultsAnalysis of those SNP loci help to resolve existing population structure and recover five genetically distinct populations of C. argus in the United States. Additionally, information from the SNP loci enable us to begin to calculate the long-term effective population size ranges of this harmful aquatic invasive species. We estimate long-term Ne to be 1,840,000–18,400,000 for the Upper Hudson River basin, 4,537,500–45,375,000 for the Lower Hudson River basin, 3,422,500–34,225,000 for the Potomac River basin, 2,715,000–7,150,000 for Philadelphia, and 2,580,000–25,800,000 for Arkansas populations.Discussion and ConclusionsThis work provides evidence for the presence of more genetic populations than previously estimated and estimates population size, showing the invasive potential of C. argus in the United States. The valuable information gained from this study will allow effective management of the existing populations to avoid expansion and possibly enable future eradication efforts.

Crayfishes of the Potomac River Basin in West Virginia

The high level of endemism displayed by native crayfish taxa, in addition to the recognized displacement abilities of nonindigenous crayfish such as Faxonius virilis and Procambarus acutus represents a serious threat to indigenous crayfish populations. Other major conservation threats to native crayfish fauna in the eastern portion of West Virginia include land development and land-use practices. The goal of this study was to compare recent and historical species distributions and assess conservation standings of native and nonindigenous crayfishes of the Potomac River Basin in West Virginia. Between June and October of 2007 historical and semi-randomly selected sites were sampled throughout the basin. Abundance was determined by catch per unit effort (CPUE) for ten seine hauls. Morphometric data including total carapace length, propodus length, and palm length were recorded in millimeters for each species. Life history parameters were determined from collections made during the study. Native species collected included Cambarus bartonii, Cambarus carinirostris, and Faxonius obscurus. Introduced species collected included Faxonius virilis and Procambarus zonangulus. C. bartoni was present in the Cacapon, North Branch Potomac, Potomac Direct Drains, and South Branch Potomac. F. obscurus was absent from Potomac Direct Drains, and C. carinirostris was only present in the South Branch Potomac. F. virilis and P. zonangulus were only present in Potomac Direct Drains. Though F. limosus was reported in 1989, no specimens were recovered during over the course of this survey, which indicates possible extirpation from the West Virginia portion of its range.

Expansion of Northern Snakehead in the Chesapeake Bay Watershed

AbstractNorthern Snakehead Channa argus, a nonnative species to North America, was discovered in 2004 in tidal freshwater of the Potomac River, the second largest drainage of the Chesapeake Bay watershed. Since then Northern Snakehead has expanded its range throughout much of Maryland's portion of the Chesapeake Bay watershed. We estimated that the species has spread beyond its introduced range at a rate of about 2.7 subwatersheds per year. If that rate is maintained, the species will have spread its range throughout the entire watershed in 52 years. This rate has been consistent over time except for short periods of heightened expansion that followed an introduction of snakeheads into Delaware waters and in years with greater levels of spring precipitation. The expansion by Northern Snakehead is more widespread than that of other invasive fishes of Maryland's portion of the Chesapeake Bay, which include Blue Catfish Ictalurus furcatus and Flathead Catfish Pylodictus olivaris. Attempts to control the spread of the species have included public education, incentives for harvest, agency surveys, and law enforcement. The rapid natural and human‐aided expansion of Northern Snakehead throughout the country's largest estuary highlights the importance of laws that prevent live possession and importation of this species.

Nature and History in the Potomac Country: From Hunter-Gatherers to the Age of Jefferson by James D. Rice

Reviewed by: Nature and History in the Potomac Country: From Hunter-Gatherers to the Age of Jefferson by James D. Rice Isaac J. Emrick Nature and History in the Potomac Country: From Hunter-Gatherers to the Age of Jefferson. By James D. Rice. (Baltimore: Johns Hopkins University Press, 2009. Pp. xvi, 338.) Much like the work of environmental histories from the late twentieth century, Rice's second book connects the regional history of the Potomac River to the ecological interactions of human residents to the development of the region. His 2009 work advances the conversation way beyond the environmental determinism of previous analyses and instead focuses on the similarities and conflicts between human ecological imaginations and their real-world effects across a wide span of history. He begins with the development of indigenous ecological practices along the Potomac in the deep past and traces the complex interplay between human choices and climate change from 900AD till the development of maize agriculture and onward into the height of the Little Ice Age. Mirroring the historical reality, Rice begins placing Europeans in the Indian-controlled landscape and examines the gradual process of shifting influence in ecological decisions in the Potomac throughout the seventeenth century. The second half of the book shifts toward more traditional geopolitical narratives as Rice examines the changes in western Potomac land control and usage during the late seventeenth and eighteenth centuries. The discussion closes where it began, highlighting the legacy of indigenous ecological imagination in the overall history of the human occupation along the Potomac River. Native Americans' active and diverse roles within the Potomac region and beyond are handled with nuanced cultural understanding and scientific supports throughout Rice's writing. Native people are neither determined by their landscape nor are they inscrutable ecological marvels. In fact, Rice's discussions remain grounded in the realities they faced and experimented with regularly to maintain themselves. Likewise, Rice complicates the assumption that English ecological desires were incompatibly different from Indians, as seen in the work of Patricia Seed's Ceremonies of Possession. Rice explains that until the 1670s the English "embraced a diversity of landscapes within an encompassing market economy and thus did not require the Potomac Valley should be remade into a Little England" (82). This desire for cohabitation was marked by a great similarity and compatibility with entrenched Algonquian ecological practices. Far from flattening the indigenous understanding of landscapes and their interactions, Rice is careful to explain different indigenous groups' diverse ecological imaginations, effectively treating them with the same historiographical care as one would when discussing European environmental history. While land ownership always lingers in the background of Rice's discussion in the first seven chapters, the narrative turns away from ecological [End Page 123] and environmental concerns and focuses on more traditional "ownership" and geopolitical mechanisms during the intercultural chaos of the late seventeenth century through the mid-eighteenth century. Though extremely well researched and exciting to read, this section veers away from the environmental focus and strengths of previous chapters. It is a solid and balanced ethnohistorical synthesis of the period but is loosely connected to previous ecological analysis. In the last few chapters, Rice returns to the environmental concerns and what happens as the English gained demographic control over the Potomac above the falls. He explains why the English continued to restrict their settlements below the falls until well into the eighteenth century by focusing on the cross section of tobacco agriculture, Indian-Indian warfare, and limited geographic knowledge of the interior (175). This echoes the prevailing understanding of much of the eighteenth-century historiography. There is a final, noticeable but certainly understandable, shift in the last two chapters that focuses more on the dramatic shifts in landscape allocation through land title and the new economic concerns of small-scale backcountry farmers. The conversation does not ignore Native American involvement; in fact, it underlies each of the decisions of the European settlers in the far western regions of the Potomac River. Rice suggests that the economic shifts of farmers toward "regional exchange economies" is shortlived after the Seven Years' War and Pontiac's Rebellion, and they returned to connected market economy (237). The economic concerns...

Conclusion

Conclusion

EMC personality profile

Every year in August, the EMC community convenes for the IEEE International Symposium on Electromagnetic Compatibility, Signal and Power Integrity. In 2017 we met in the Washinghton DC area on the banks of the picturesque Potomac River in the National Harbor. The event was characterized by a high quality technical program as well as a remarkable social program, including a dancing performance by members of the EMC Society Board of Directors. With this Personalty Profile column, I woud like to introduce a colleague to you, who worked hard to make the 2017 IEEE International Symposium on EMC+SIPI happen. The person I am talking about is Michael F. Violette, an active member of our Society, particularly involved in marketing as well as in the Washington DC/Northern Virginia EMC Society Chapter.

Early American Studies in the Age of Trump

Early American Studies in the Age of Trump Anna Mae Duane (bio) Press and Speech under Assault: The Early Supreme Court Justices, the Sedition Act of 1798, and the Campaign against Dissent wendell bird New York: Oxford University Press, 2016 568 pp. Self-Evident Truths: Contesting Equal Rights from the Revolution to the Civil War richard d. brown New Haven, CT: Yale University Press, 2017 400 pp. A Temperate Empire: Making Climate Change in Early America anya zilberstein New York: Oxford University Press, 2016 264 pp. As 2017 drew to a close, CNN impaneled a group of experts to respond to a pressing question (State of the Union). Did Barack Obama overstep the bounds of political decorum—and historical accuracy—when he made a historical analogy that compared Donald Trump to Adolf Hitler? Earlier that week, Obama had warned an assembled group that they needed to guard against complacency if they wanted to avoid finding themselves, as Germans had in 1933, overtaken by a horror they had been too complacent to fight when they had the chance. Was Obama, the moderator wanted to know, being inflammatory by invoking the terrors of the past to motivate voters in the present? At least one of the respondents didn't feel that pulling from history was the problem, but took the former president to task for using the wrong history in his argument. Nazi Germany was not an apt analogy for our current moment, the pundit declared, but Watergate surely was. Even with this quibble about the choice of example, everyone [End Page 953] on the panel seemed to agree on one thing: we need the past as a gauge to explain the present. We can only know where we are by looking at where we've been. For scholars in early American culture who have long endured allegations that our scholarship had little applicability to the problems of "real life," this current hunger for historical knowledge can seem a bit disorienting. Beyond the questions of what the study of early US culture can tell us about our current moment, there is much in our present that puts pressure on how we can study the past. Throughout academia, but especially within the field of early American studies, every post-2016 conversation is newly fraught with questions about how we can do our work and why it matters. Even as scholars find ourselves in a bewilderingly postfactual era, pundits have blamed academics for causing this mess in the first place. Late 2016 and early 2017 were awash in think pieces that suggested that it was the intellectual turn away from the notion of universal truth that allowed an inveterate conman to snag the highest elected office in the land. "Derrida and his fellow deconstructionists have uncoupled words from meaning," chided a March 2016 article, and it was the spread of such a destabilizing approach to truth that allowed Trump to "get away with saying one thing and then its opposite" (Kelly; see also Heer and Williams). While it stretches credibility to blame Jacques Derrida for an election effectively decided by a handful of voters in midwestern states, Trumpism's sustained attack on authority—in academia, in journalism, in government itself—has forced us all to reassess, if not realign, our own relationship to truth, and our own methodologies for excavating it. Consider, as just one example among many, the confrontation between Trump—who loves to invoke the word history when touting his own accomplishments—and the historians who pointed out that he was, quite simply, making stuff up. Back in 2015, the New York Times reported on a plaque Trump had erected at one of his golf courses in Virginia, claiming that particular green as an important site of American history. The plaque read: "Many great American soldiers, both of the North and South, died at this spot. The casualties were so great that the water would turn red and thus became known as 'The River of Blood.' It is my great honor to have preserved this important section of the Potomac River!—Donald John Trump." When the Times reporter cited historians who insisted that there had actually been no Civil War battles at...

Becoming Hallowed Ground

Becoming Hallowed Ground Edwin A. Martini (bio) Micki McElya. The Politics of Mourning: Death and Honor in Arlington National Cemetery. Cambridge: Harvard University Press, 2016. 395 pp. Photos, notes, and index. $29.95. On his first Memorial Day as President, Barack Obama sent two wreaths to commemorate Civil War soldiers. The first was delivered to the African American Civil War Memorial, near the U Street Metro stop in the Shaw neighborhood, an overwhelmingly black district in an overwhelmingly black city. The second was sent from the White House across the Potomac River to a very specific area of Arlington National Cemetery, Section 16, specifically set aside for the bodies of Confederate soldiers. In the former case, Obama was the first U.S. President to send a wreath memorializing the sacrifice of black soldiers who fought to end slavery. In the latter case, he continued a century-old tradition, dating back to Theodore Roosevelt, recognizing the sacrifice of white, southern soldiers who fought to preserve it (p. 160). Each case, however, as Micki McElya demonstrates in The Politics of Mourning: Death and Honor in Arlington National Cemetery, is the product of long, complicated histories, and a range of battles involving race, gender, nation, and historical memory. Throughout this fascinating book, McElya makes a strong case indeed that the struggle over who lived, worked, and was allowed to be laid to rest in Arlington is a powerful window into nearly the full sweep of United States history, particularly from the mid-nineteenth century on. As she writes in her introduction: Since before its inception as a cemetery during the Civil War, Arlington has been the scene of pitched struggles over the use and shape of the place, struggles that have always been about the larger meanings of freedom, sacrifice, citizenship, honor, state authority, and the nation itself and about which bodies, alive and dead, are most representative, most capable and valuable, and most difficult to lose (p. 10). These battles were consistently defined by several themes, including the dominant cultural narrative of sectional reconciliation after the Civil War, the establishment and maintenance of a white, patriarchal, and military definition [End Page 497] of national service and sacrifice, and a powerful shift from the bodies of the dead defining the landscape to the landscape itself defining the bodies. McElya traces these struggles over seven chapters, along with an introduction and conclusion. The chapters proceed largely by chronology, weaving in thematic elements throughout. McElya makes use of a rich array of sources, including archival materials from several relevant collections in Maryland, Virginia, and Washington, D.C., a number of historical periodicals, and other, more contemporary cultural texts. The entire project is also very well grounded in the secondary literature on history, memory, and the negotiation of meaning over memorials and other contested landscapes. The first three chapters explore Arlington's long journey to becoming hallowed ground, beginning with land taken from "several Algonquian-speaking Indian communities" and colonized by white settlers to the large plantation bought and maintained by John Custis, stepson to George Washington and father-in-law to Robert E. Lee; from a union-occupied fortress during the Civil War to Freedman's Village; and, finally, from one of a network of national cemeteries to the national cemetery (p. 14). McElya begins her narrative with a long look at the early history of Arlington through the lens of a few key, but lesser-known figures. She takes a number of twists and turns in getting readers there, but ultimately it is worth the wait. McElya makes a compelling case that while Arlington House was made both famous and infamous by memorializing Robert E. Lee (who never actually owned the plantation), it is Lee's wife, Mary, who is a far more intriguing and complicated figure in the struggle over the meaning of the house and its place in Arlington. In tracing Mary Lee's efforts to maintain and recover the homestead during and after the Civil War, McElya effectively deals with Lee's gendered connections to the landscape without glossing over the clear role of racialized hierarchies in Lee's assertions of her rights to Arlington. An angry letter from Lee, written...

Watershed export of fine sediment, organic carbon, and chlorophyll-a to Chesapeake Bay: Spatial and temporal patterns in 1984–2016

Chesapeake Bay has long experienced nutrient enrichment and water clarity deterioration. This study provides new quantification of loads and yields for sediment (fine and coarse grained), organic carbon (total, dissolved, and particulate), and chlorophyll-a from the monitored nontidal Chesapeake Bay watershed (MNTCBW), all of which are expected to drive estuarine water clarity. We conducted an integrated analysis of nine major tributaries to the Bay to understand spatial and temporal export patterns over the last thirty years (1984–2016). In terms of spatial pattern, export of these constituents from the MNTCBW was strongly dominated (~90%) by the three largest tributaries (i.e., Susquehanna, Potomac, and James). Among the nine tributaries, the ranking of constituent export generally follows the order of their watershed sizes, with other factors such as land use and reservoir playing important roles in some exceptions. In terms of partitioning, suspended sediment (SS) export was dominated by fine-grained sediment (SSfine) in all nine tributaries; overall, ~90% of the MNTCBW SS is SSfine. Total organic carbon (TOC) export was dominated by dissolved organic carbon (DOC) in all tributaries except Potomac River; overall, ~60% of the MNTCBW TOC is DOC. A comparison with literature shows that the MNTCBW SS and TOC yields were ~80% and ~60% of the respective medians of worldwide watersheds. In terms of temporal pattern, flow-normalized yields from the MNTCBW show overall increases in SS (both long-term [1984–2016] and short-term [2004–2016]), SSfine (long-term and short-term), TOC (long-term), and chlorophyll-a (short-term). The rises in SS, SSfine, and TOC were largely driven by Susquehanna River where Conowingo Reservoir's trapping efficiency has greatly diminished in the last twenty years. Overall, these new results on the status and trends of sediment, organic carbon, and chlorophyll-a provide the foundation for building potential linkages between riverine inputs and estuarine water clarity patterns.

Water Resources Adaptation to Climate and Demand Change in the Potomac River

AbstractThe effects of climate change are increasingly considered in conjunction with changes in water demand and reservoir sedimentation in forecasts of water supply vulnerability. Here, the relat...

Applying high-frequency surrogate measurements and a wavelet-ANN model to provide early warnings of rapid surface water quality anomalies

It is critical for surface water management systems to provide early warnings of abrupt, large variations in water quality, which likely indicate the occurrence of spill incidents. In this study, a combined approach integrating a wavelet artificial neural network (wavelet-ANN) model and high-frequency surrogate measurements is proposed as a method of water quality anomaly detection and warning provision. High-frequency time series of major water quality indexes (TN, TP, COD, etc.) were produced via a regression-based surrogate model. After wavelet decomposition and denoising, a low-frequency signal was imported into a back-propagation neural network for one-step prediction to identify the major features of water quality variations. The precisely trained site-specific wavelet-ANN outputs the time series of residual errors. A warning is triggered when the actual residual error exceeds a given threshold, i.e., baseline pattern, estimated based on long-term water quality variations. A case study based on the monitoring program applied to the Potomac River Basin in Virginia, USA, was conducted. The integrated approach successfully identified two anomaly events of TP variations at a 15-minute scale from high-frequency online sensors. A storm event and point source inputs likely accounted for these events. The results show that the wavelet-ANN model is slightly more accurate than the ANN for high-frequency surface water quality prediction, and it meets the requirements of anomaly detection. Analyses of the performance at different stations and over different periods illustrated the stability of the proposed method. By combining monitoring instruments and surrogate measures, the presented approach can support timely anomaly identification and be applied to urban aquatic environments for watershed management.

Diel and Seasonal Patterns in Continuously Monitored Water Quality at Fixed Sites in Two Adjacent Embayments of the Tidal Freshwater Potomac River

Water quality patterns in two adjacent embayments of the tidal freshwater Potomac River were compared using continuously monitored data. The two embayments, the tidal Occoquan and Gunston Cove, are shallow embayments fed by tributaries which vary in their watershed attributes. The tidal Occoquan has a larger watershed and a dam just upstream from the head of tide whereas Gunston Cove has a large wastewater treatment plant just upstream of the embayment. Water temperature, specific conductance, dissolved oxygen (DO), and pH were collected at 15 min intervals at representative locations in the two embayments from April through November of 2012. Mean daily values of water quality variables exhibited similar seasonal patterns at both sites which were related to seasonal patterns of forcing functions such as temperature, light and freshwater inflows. Three two-week intervals were examined in great detail. During a mid-summer period of stable conditions and low flow, both embayments exhibited strong and consistent diel (light cycle-based) periodicity in temperature, DO, and pH. Specific conductance exhibited semi-diel (tidal cycle-based) periodicity. The two other two-week intervals were punctuated by substantial flow events which resulted in major changes in daily mean values and disruptions to the typical diel or semi-diel cycles. The large rainfall event related to Hurricane Sandy caused a major disruption in diel and semi-diel cycles. Some cycles were quickly re-established and others took a week or more. The two embayments exhibited similar behavior in most aspects. Site-specific factors such as differences in the frequency and magnitude of tributary flow pulses and the presence of treated sewage discharge at Gunston Cove helped explain some of the differences observed between the two embayments.

Assessing strategies for protecting transportation infrastructure from an uncertain climate future

This paper investigates the importance of explicitly considering the stochastic nature of future climate impact predictions and predictive accuracy for optimal investment planning in the protection of coastal and inland transportation infrastructure against climate impacts. Such impacts include sea level rise, coastal and riverine flooding resulting from more frequent and intense precipitation events, storms, storm surges and other extreme events. For this purpose, numerical experiments utilizing stochastic optimization based methodologies were conducted on a case study of the Washington, D.C. Greater Metropolitan area proximate to the Potomac River under varying climatic predictions. Results from the numerical experiments suggest a 54% reduction in added costs due to the implementation of chosen protective infrastructure investments. They also indicate a reduction in added costs (capital investment and added delays) on the order of 19% when the investments are chosen to hedge against probable future flooding events as compared with planning for the 50th percentile SLR prediction with associated weather events. A potential gain of nearly 27% in reduced costs through improved predictive accuracy in climatic forecasts is also noted, suggesting significant value in more accurate forecasts.

Successes of Restoration and Its Effect on the Fish Community in a Freshwater Tidal Embayment of the Potomac River, USA

After a local wastewater treatment plant significantly reduced phosphorus loading into a phytoplankton-dominated tributary of the Potomac River in the early 1980s, water quality and biological communities were monitored bi-weekly from April to September. After a 10-year time-lag, submerged aquatic vegetation (SAV), once abundant in this freshwater tidal embayment, returned to the area in 1993. After additional reductions in nitrogen load starting in 2000, the system switched to an SAV-dominated state in 2005. Fish abundance did not change during these distinct phase changes, but the fish community structure did. Increases in SAV provided refuge and additional spawning substrate for species with adhesive eggs such as Banded Killifish (Fundulus diaphanus), which is now the most abundant species in the embayment. Other changes observed were a decrease in the relative contribution of open water dwelling species such as White Perch (Morone americana), and an increase of visual predators such as Largemouth Bass (Micropterus salmoides). The 30-year record of data from this Potomac River tributary has revealed important long-term trends that validate the effectiveness of initiatives to reduce excess nutrient inputs, and will aid in the continued management of the watershed and point-source inputs.

Field evidence for the influence of weathering on rock erodibility and channel form in bedrock rivers

AbstractErosion processes in bedrock‐floored rivers shape channel cross‐sectional geometry and the broader landscape. However, the influence of weathering on channel slope and geometry is not well understood. Weathering can produce variation in rock erodibility within channel cross‐sections. Recent numerical modeling results suggest that weathering may preferentially weaken rock on channel banks relative to the thalweg, strongly influencing channel form. Here, we present the first quantitative field study of differential weathering across channel cross‐sections. We hypothesize that average cross‐section erosion rate controls the magnitude of this contrast in weathering between the banks and the thalweg. Erosion rate, in turn, is moderated by the extent to which weathering processes increase bedrock erodibility. We test these hypotheses on tributaries to the Potomac River, Virginia, with inferred erosion rates from ~0.1 m/kyr to >0.8 m/kyr, with higher rates in knickpoints spawned by the migratory Great Falls knickzone. We selected nine channel cross‐sections on three tributaries spanning the full range of erosion rates, and at multiple flow heights we measured (1) rock compressive strength using a Schmidt hammer, (2) rock surface roughness using a contour gage combined with automated photograph analysis, and (3) crack density (crack length/area) at three cross‐sections on one channel. All cross‐sections showed significant (p < 0.01 for strength, p < 0.05 for roughness) increases in weathering by at least one metric with height above the thalweg. These results, assuming that the weathered state of rock is a proxy for erodibility, indicate that rock erodibility varies inversely with bedrock inundation frequency. Differences in weathering between the thalweg and the channel margins tend to decrease as inferred erosion rates increase, leading to variations in channel form related to the interplay of weathering and erosion rate. This observation is consistent with numerical modeling that predicts a strong influence of weathering‐related erodibility on channel morphology. Copyright © 2017 John Wiley & Sons, Ltd.

An interbasin comparison of tree‐ring reconstructed streamflow in the eastern United States

AbstractTree‐ring reconstructions of streamflow are uncommon in the eastern United States compared with the western United States. Although the east has not experienced severe drought on the scale of the west over the last 100 years, multiyear droughts have stressed the water management systems throughout the east. Here, we reconstruct mean May–September streamflow of three rivers serving population centers in the northeast (Beaver Kill River serving New York, NY), mid‐Atlantic (Potomac River serving Washington, DC), and southeast (Flint River serving Atlanta, GA) to demonstrate the efficacy of reconstructing streamflow in the eastern United States. Then, we conducted an interbasin comparison to identify periods of common variability and examined the influence of the North Atlantic subtropical high on reconstructed streamflow. Our models explained 40–61% of the variance in the instrumental record and passed verification tests in all basins during the period 1675–2000 CE. Droughts and pluvials showed some synchrony across all basins, but the mid‐Atlantic region acted as a hinge, sometimes behaving more like the northeast, and other times like the southeast. Climatic analyses suggest a relationship exists between the North Atlantic subtropical high and reconstructed streamflow that influences the probability of drought and pluvial events. Given the many factors influencing tree growth in closed‐canopy systems, we have shown that careful standardization of individual tree‐ring series, nested regression models, and the use of multiple species can produce robust proxies of streamflow across the eastern seaboard.

Pharmaceutical chemicals, steroids and xenoestrogens in water, sediments and fish from the tidal freshwater Potomac River (Virginia, USA)

ABSTRACTSelected pharmaceutical chemicals, steroids and xenoestrogens (PCSXs) consisting of 29 endocrine modulators, therapeutic drugs, pesticides, detergents, plastics, and active ingredients in household products were measured in water, riverbed sediments and fish collected in a tributary embayment of the Potomac River (Hunting Creek, Alexandria, VA, USA) in the vicinity of wastewater discharge. A total of 17 PCSXs were found in the Hunting Creek samples, with steroid hormones (e.g., progesterone and 17α-ethinylestradiol), triclosan, dextromethorphan and bisphenol A being the most prominent micropollutants detected.The geospatial distribution of the PCSXs in Hunting Creek indicated that the steroids correlated with wastewater treatment plant discharge in all matrices, but such an association is tentative in Hunting Creek given the complex nature of urban sources of PCSXs and hydrodynamics in an urban tidal river. The sediment PCSX concentrations correlated with sediment total organic carbon content at all sampling sites. For the most part, the PCSXs showed an enrichment in fish tissue relative to sediments when concentrations were normalized to lipids and sediment organic carbon contents, but the influence of endogenous steroids is also an important consideration for these chemicals.