Upland Sources Research Articles

Early Miocene continental-scale sediment supply to the Gulf of Mexico Basin based on detrital zircon analysis

The early Miocene was a period of major continental margin progradation in the Gulf of Mexico Basin that accompanied prominent tectonic and climatic changes in North America. However, sediment pathways from continental upland sources to deep basinal sinks remain poorly constrained. This study presents 2192 new detrital zircon U-Pb analyses from 19 Lower Miocene samples spanning the entire northern Gulf of Mexico margin to elucidate early Miocene sediment provenance and paleodrainage systems. The U-Pb age patterns indicate that the Great Plains, southern Rocky Mountains, and mid-Cenozoic volcanic field were the major source terranes for the western-central Gulf of Mexico coast, whereas the Appalachian foreland basin and Appalachian Mountains mainly contributed sediment to the eastern Gulf of Mexico coast. Local source terranes included the Llano uplift and Edwards Plateau in central Texas and the Ouachita Mountains and foreland basin in Oklahoma and Arkansas. A comparison to previous detrital zircon studies around the Gulf of Mexico indicates that sediment recycling was important during the early Miocene. Sediment associated with major paleorivers, including the Rio Bravo, Rio Grande, Houston-Brazos, Red, Mississippi, Tombigbee, and Apalachicola Rivers, can be differentiated using the detrital zircon U-Pb analyses. These data help to better define the early Miocene source-to-sink system in the northern Gulf of Mexico, by relating the basin fill to hinterland tectonic and geological evolution. In comparison to the Paleocene−Eocene Wilcox drainage system, the early Miocene drainage system of the northern Gulf of Mexico was smaller and received less input from western Mexico arc terranes and Archean basement in Wyoming. This drainage area reduction, related to regional thermal uplift and Basin and Range−Rio Grande rifting, likely explains the reduced sediment volume of the Lower Miocene strata in the Gulf of Mexico relative to the Paleocene−Eocene Wilcox Group.

Application of SPARROW Modeling to Understanding Contaminant Fate and Transport from Uplands to Streams

AbstractUnderstanding spatial variability in contaminant fate and transport is critical to efficient regional water‐quality restoration. An approach to capitalize on previously calibrated spatially referenced regression (SPARROW) models to improve the understanding of contaminant fate and transport was developed and applied to the case of nitrogen in the 166,000 km2 Chesapeake Bay watershed. A continuous function of four hydrogeologic, soil, and other landscape properties significant (α = 0.10) to nitrogen transport from uplands to streams was evaluated and compared among each of the more than 80,000 individual catchments (mean area, 2.1 km2) in the watershed. Budgets (including inputs, losses or net change in storage in uplands and stream corridors, and delivery to tidal waters) were also estimated for nitrogen applied to these catchments from selected upland sources. Most (81%) of such inputs are removed, retained, or otherwise processed in uplands rather than transported to surface waters. Combining SPARROW results with previous budget estimates suggests 55% of this processing is attributable to denitrification, 23% to crop or timber harvest, and 6% to volatilization. Remaining upland inputs represent a net annual increase in landscape storage in soils or biomass exceeding 10 kg per hectare in some areas. Such insights are important for planning watershed restoration and for improving future watershed models.

Livelihood Dynamics as a Response to Natural Hazards: A Case Study of Selected Places of Basanti and Gosaba Blocks, West Bengal

The Indian Sundarban with a shore length of 130 km is topographically a low lying flat alluvial plain, dissected by a large number of tidal rivers, estuaries and creeks. The reclamation activity in the islands of Sundarbans for resource generation and resource consumption was accentuated in the latter half of the 19th century replacing mangroves by the Colonial Government of India. The premature reclamation was done by raising embankments all along the river banks which has reduced the spill areas of rivers leading to in channel siltation. Thus the tidal floodplain, devoid of silt is always at a lower level than the water level of the rivers. Moreover the creeks of Sundarban are severed from their freshwater upland sources and record increase in salinity. Comparison of data of 1984 and that of 2001 shows drastic increase in the salinity of the outer estuary (26 ppt to 36.2 ppt) and that of mid estuary from 20 ppt to 26 ppt for summer of the eastern sector. (Chand et al, R. K Trivedi, S. K. Dubey and M. M. Beg, 2012) Ref [4]. The study area comprising of places Hogolduri, Kalahazra, Katrakhali, Bagulakhali, Chunakhali, Parbatipur, Masjidbati of Basanti block and Sambhunagar of Gosaba block of West Bengal, India are highly vulnerable to hazards and disasters like tropical cyclones, embankment breaching and subsequent salt water incursion. This has led to occupational shift as agricultural lands are transformed to aquaculture farms. This paper takes into account this budding problem over the years and studies the livelihood pattern of the study area. Survey Of India toposheets of 1969 (79 B/12, 79 B/15 and 79 B/16) followed by satellite images (LANDSAT 4, 5 and LANDSAT 7, Path – 138, Row – 45, from USGS Earth Explorer) and Google Earth imageries have been used. Questionnaire surveys have also been conducted. It has been found that the area of aquaculture farms have been increasing at the cost of agricultural lands. Since the transformation of agricultural lands to aquaculture farms is permanent and the people need to adapt to this transformation, it is highly recommended to run the aquaculture farms on a co – operative basis so that the profits will be distributed among the stakeholders according to their share of land.

Dating of debris flow fan complexes from Lantau Island, Hong Kong, China: The potential relationship between landslide activity and climate change

Five debris flow fan complexes bordering the coastal foothills of western Lantau Island, Hong Kong, have been the subject of a stratigraphic and dating study to explore the potential relationship between past periods of climate change and landslide activity. Luminescence (OSL) ages from the fan complexes, supported by a few calibrated radiocarbon (14C) ages on duplicate samples, suggest six main periods of accumulation: 28,000–20,000ka, 14,500–10,500ka, 5800–5000ka, 4370–4230ka, 3560–3320ka, and 1350–1050ka. The younger periods (<10,000ka) appear to be dominated by relatively thin (0.5–1.5m) units deposited mainly by debris flood events whereas the older periods are dominated by thicker (1.0–3.5m) units deposited by debris flow events. We hypothesise that immediately prior to the Last Glacial Maximum (LGM, i.e., 21,000ka), the climate was cool and dry. Upland areas were probably devoid of vegetation, providing favourable conditions for sediment production in source areas. These debris-laden source areas are likely to have been mobilised during periodic rainstorm activity, rapidly channelised over relatively short drainage courses, and then deposited as thick, sediment-rich, debris flow deposits along the coastal foothills. During the early to middle Holocene, the climate was warmer and more humid. Pluvial conditions dominated; forests occupied the upland source areas, leading to possibly reduced sediment yields, more frequent flash floods and deposition dominated by debris floods. Compared with recent studies on the weathering and erosion history of the Pearl River Delta, our landslide age data are indicative of a potential link between increased landslide activity and intensification of the East Asian monsoon during the early to middle Holocene.

Patterns of Population Differentiation in Early Traits of Development in Elymus glaucus: Implications for Restoration

Restoration of native plant communities is a foundational practice in restoration ecology, but land managers and biologists don’t often take into account the role of intraspecific variation in establishment of restoration seedings. Although ecologists have known for decades that lack of adaptation to local conditions may interfere with the success of ecological restoration, there is little information about the extent to which species demonstrate adaptive divergence among populations. If adaptive divergence occurs for early establishment, knowing which populations have better germination and early growth can maximize restoration performance. Restoration of California grassland requires species establishment in both riparian and upland habitats. To what degree does local adaptation to these habitats influence early growth traits? In this study, we compared time to germination and early growth rate of riparian, upland, and commercial seed sources of blue wild rye ( Elymus glaucus ) under contrasting water regimes in a controlled environment. Two hypotheses were tested: 1) plants grown from commercial seeds will outperform plants grown from locally-collected seeds under controlled conditions; and 2) plants will demonstrate local adaptation by high performance of riparian sources under high water treatments and high performance of upland sources under low water treatments. We saw no evidence of local adaptation but did observe population differentiation. Time to germination was significantly shorter for upland seeds. In addition, the rate of shoot growth for upland plants was significantly higher than riparian or commercial plants. Understanding if sourcing from similar microhabitats is more important than sourcing from nearby populations will allow us to develop more successful restoration seedings.

Organic matter compositions and loadings in soils and sediments along the Fly River, Papua New Guinea

The compositions and loadings of organic matter in soils and sediments from a diverse range of environments along the Fly River system were determined to investigate carbon transport and sequestration in this region. Soil horizons from highland sites representative of upland sources have organic carbon contents (%OC) that range from 0.3 to 25wt%, carbon:nitrogen ratios (OC/N) that range from 7 to 25mol/mol, highly negative stable carbon isotopic compositions (δ13Corg<−26‰) and variable concentrations of lignin phenols (1<LP<5mg/100mgOC). These compositions reflect inputs from local vegetation, with contributions from bedrock carbon in the deeper mineral horizons. Soils developed on the levees of active floodplains receive inputs of allochthonous materials by overbank deposition as well as autochthonous inputs from local vegetation. In the forested upper floodplain reaches, %OC contents are lower than upland soils (0.8–1.5wt%) as are OC/N ratios (9–15mol/mol) while δ13Corg (−25 to −28‰) and LP (2–6mg/100mgOC) values are comparable to upland soils. These results indicate that organic matter present in these active floodplain soils reflect local (primarily C3) vegetation inputs mixed with allochthonous organic matter derived from eroded bedrock. In the lower reaches of the floodplain, which are dominated by swamp grass vegetation, isotopic compositions were less negative (δ13Corg>−25‰) and non-woody vegetation biomarkers (cinnamyl phenols and cutin acids) more abundant relative to upper floodplain sites. Soils developed on relict Pleistocene floodplain terraces, which are typically not flooded and receive little sediment from the river, were characterized by low %OC contents (<0.6wt%), low OC/N ratios (<9mol/mol), more positive δ13Corg signatures (>−21‰) and low LP concentrations (∼3mg/100mgOC). These relict floodplain soils contain modern carbon that reflects primarily local (C3 or C4) vegetation sources. Total suspended solids collected along the river varied widely in overall concentrations (1<TSS<9000mg/L), %OC contents (0.1–60wt%), OC/N ratios (7–17mol/mol) and δ13Corg signatures (−26 to −32‰). These compositions reflect a mixture of C3 vascular plants and freshwater algae. However, little of this algal production appears to be preserved in floodplain soils. A comparison of organic carbon loadings of active floodplain soils (0.2 and 0.5mgC/m2) with previous studies of actively depositing sediments in the adjacent delta–clinoform system (0.4–0.7mgC/m2) indicates that Fly River floodplain sediments are less effective at sequestering organic carbon than deltaic sediments. Furthermore, relict Pleistocene floodplain sites with low or negligible modern sediment accumulation rates display significantly lower loadings (0.1–0.2mgC/m2). This deficit in organic carbon likely reflects mineralization of sedimentary organic carbon during long term oxidative weathering, further reducing floodplain carbon storage.

Tracking polychlorinated biphenyls (PCBs) congener patterns in Newark Bay surface sediment using principal component analysis (PCA) and positive matrix factorization (PMF)

PCB congener data for Newark Bay surface sediments were analyzed using PCA and PMF, and relationships between the outcomes from these two techniques were explored. The PCA scores plot separated the Lower Passaic River Mouth samples from North Newark Bay, thus indicating dissimilarity. Although PCA was able to identify subareas in the Bay system with specific PCB congener patterns (e.g., higher chlorinated congeners in Elizabeth River), further conclusions reading potential PCB source profiles or potential upland source areas were not clear for the PCA scores plot. PMF identified five source factors, and explained the Bay sample congener profiles as a mix of these Factors. This PMF solution was equivalent to (1) defining an envelope that encompasses all samples on the PCA scores plot, (2) defining source factors that plot on that envelope, and (3) explaining the congener profile for each Bay sediment sample (inside the scores plot envelope) as a mix of factors. PMF analysis allowed identifying characteristic features in the source factor congener distributions that allowed tracking of source factors to shoreline areas where PCB inputs to the Bay may have originated. The combined analysis from PCA and PMF showed that direct discharges to the Bay are likely the dominant sources of PCBs to the sediment. Review of historical upland activities and regulatory files will be needed, in addition to the PCA and PMF analysis, to fully reconstruct the history of operations and PCB releases around the Newark Bay area that impacted the Bay sediment.

From mountains to sound: modelling the sensitivity of Dungeness crab and Pacific oyster to land–sea interactions in Hood Canal, WA

AbstractMany diagnoses of declining marine species and habitats along US coasts point to upland and freshwater sources of imperilment. Yet, little work has examined how and whether activities on land affect marine resources. Similarly, the impacts of climate change on coastal systems are among the most certain; yet, few studies have explored how alternative management and climate scenarios will affect the delivery of diverse benefits to people from coasts. We estimated how Dungeness crab (Metacarcinus magister) and Pacific oyster (Crassostrea gigas) harvest in Hood Canal, WA, may change given predictions of land uses and effects of climate change. These two marine species are critical components of local commercial and recreational fisheries and thus represent key “ecosystem service” endpoints. We found that Dungeness crab harvest responds strongly to effects of climate change, as mediated by increased ocean temperature, whereas Pacific oyster harvest is more responsive to projected change in land-use/land-cover due to increased nutrient loading to the marine system. These changes vary spatially throughout Hood Canal. These results can be used as a heuristic framework to help decision-makers, planners, and other stakeholders in the region as they work to target conservation and restoration activities and plan for future growth in a changing climate.

Influence of Rhizosphere Microbial Ecophysiological Parameters from Different Plant Species on Butachlor Degradation in a Riparian Soil

Biogeochemical processes in riparian zones regulate contaminant movement to receiving waters and often mitigate the impact of upland sources of contaminants on water quality. However, little research has been reported on the microbial process and degradation potential of herbicide in a riparian soil. Field sampling and incubation experiments were conducted to investigate differences in microbial parameters and butachlor degradation in the riparian soil from four plant communities in Chongming Island, China. The results suggested that the rhizosphere soil had significantly higher total organic C and water-soluble organic C relative to the nonrhizosphere soil. Differences in rhizosphere microbial community size and physiological parameters among vegetation types were significant. The rhizosphere soil from the mixed community of Phragmites australis and Acorus calamus had the highest microbial biomass and biochemical activity, followed by A. calamus, P. australis and Zizania aquatica. Microbial ATP, dehydrogenase activity (DHA), and basal soil respiration (BSR) in the rhizosphere of the mixed community of P. australis and A. calamus were 58, 72, and 62% higher, respectively, than in the pure P. australis community. Compared with the rhizosphere soil of the pure plant communities, the mixed community of P. australis and A. calamus displayed a significantly greater degradation rate of butachlor in the rhizosphere soil. Residual butachlor concentrations in rhizosphere soil of the mixed community of P. australis and A. calamus and were 48, 63, and 68% lower than three pure plant communities, respectively. Butachlor degradation rates were positively correlated to microbial ATP, DHA, and BSR, indicating that these microbial parameters may be useful in assessing butachlor degradation potential in the riparian soil.

Erosion-driven drawdown of atmospheric carbon dioxide: The organic pathway

Rapidly eroding, coastal mountain belts, where steep rivers and submarine channels connect upland sources to nearby marine sinks are hotspots of organic carbon transfer from life biomass, soil and exhumed bedrock into geological storage. Using observations from the Southern Alps of New Zealand, and Taiwan, we have mapped this organic pathway to geological carbon sequestration, and can evaluate the magnitude and efficiency of transfers between sources and sinks. We demonstrate that POC is harvested by landsliding, but importantly also by common and widespread surface runoff on steep hillslopes. Although terrestrially sourced POC is found in many sedimentary environments associated with mountain belts and frontier basins, it appears to be most abundantly trapped and preserved in marine turbidites. The loss of all forms of POC in onward transport through short, steep routing systems to this repository is limited. This is in marked contrast to larger routing systems, in which only the most resilient forms of POC survive into long-term deposition.

Importance of the Water Table in Controlling Dissolved Carbon along a Fen Nutrient Gradient

Boreal fens are minerotrophic peatlands that act as important control points for dissolved C between upland and aquatic ecosystems. Fens occupy a minerotrophic continuum from “rich,” having high water tables and large nutrient contributions from upland sources, to “poor,” having low water tables and small nutrient contributions. Dissolved C within these fens will be influenced by the degree of minerotrophy, which in turn impacts peat pore water acidity and alkalinity and downstream productivity. To examine how dissolved C concentrations change along the minerotrophic gradient and to explore possible mechanisms controlling their concentration, pore water chemistry was analyzed from piezometers at 25‐, 50‐, and 100‐cm depths in rich, intermediate, and poor fens during the snow‐free periods of 2005, 2006 (dissolved organic C [DOC] only), 2007, and 2008. We found that dissolved inorganic C (DIC) concentrations increased with higher water tables (poor &lt; intermediate &lt; rich) and wetter years (2005 &lt; 2007 ∼ 2008). In contrast, DOC concentrations decreased with higher water tables (rich &lt; intermediate &lt; poor), but the effect differed among years. Wetter conditions resulted in high DOC concentrations in the intermediate fen, low concentration in the poor fen, and no change in the rich fen. Correlation analyses suggest that DIC concentrations may be linked to groundwater contribution of carbonate materials and DOC to ionic strength and mechanisms of productivity and decomposition. Although further experimentation is required to verify these mechanisms, the evidence points to the importance of minerotrophic status when considering the role of peatlands in watershed C balances and their response to changing climate.

Exposure-age constraints on the extent, timing and rate of retreat of the last Irish Sea ice stream

We report 23 cosmogenic isotope exposure ages ( 10Be and 36Cl) relating to the maximum extent and deglaciation chronology of the Irish Sea Ice Stream (ISIS), which drained the SW sector of the last British–Irish Ice Sheet. These show that the ISIS failed to reach the Preseli Hills of North Pembrokeshire yet extended southwards to impinge on northern Isles of Scilly (50°N) during the last glacial maximum. Four samples from western Anglesey demonstrate deglaciation of the southern Irish Sea Basin by c. 20–18 ka, and two from the Llŷn Peninsula in northwest Wales, if valid, suggest deglaciation by c. 23–22 ka followed by gradual oscillatory northwards retreat of the ice margin for over 3000 years. An alternative interpretation of our data suggests that ice reached Scilly as late as 22–21 ka then retreated 450 km northwards within the following three millennia, possibly in response to sea level rise and/or intrinsic reorganisation within the last British–Irish Ice Sheet. Samples from upland source areas of the ISIS in NW England and SW Scotland produced exposure ages ≤14.3 ka, suggesting possible persistence of ice in such areas into the Lateglacial Interstade of 14.7–12.9 ka.

Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management1

Vidon, Philippe, Craig Allan, Douglas Burns, Tim P. Duval, Noel Gurwick, Shreeram Inamdar, Richard Lowrance, Judy Okay, Durelle Scott, and Steve Sebestyen, 2010. Hot Spots and Hot Moments in Riparian Zones: Potential for Improved Water Quality Management. Journal of the American Water Resources Association (JAWRA) 46(2):278‐298. DOI: 10.1111/j.1752‐1688.2010.00420.xAbstract: Biogeochemical and hydrological processes in riparian zones regulate contaminant movement to receiving waters and often mitigate the impact of upland sources of contaminants on water quality. These heterogeneous processes have recently been conceptualized as “hot spots and moments” of retention, degradation, or production. Nevertheless, studies investigating the importance of hot phenomena (spots and moments) in riparian zones have thus far largely focused on nitrogen (N) despite compelling evidence that a variety of elements, chemicals, and particulate contaminant cycles are subject to the influence of both biogeochemical and transport hot spots and moments. In addition to N, this review summarizes current knowledge for phosphorus, organic matter, pesticides, and mercury across riparian zones, identifies variables controlling the occurrence and magnitude of hot phenomena in riparian zones for these contaminants, and discusses the implications for riparian zone management of recognizing the importance of hot phenomena in annual solute budgets at the watershed scale. Examples are presented to show that biogeochemical process‐driven hot spots and moments occur along the stream/riparian zone/upland interface for a wide variety of constituents. A basic understanding of the possible co‐occurrence of hot spots and moments for a variety of contaminants in riparian systems will increase our understanding of the influence of riparian zones on water quality and guide management strategies to enhance nutrient or pollutant removal at the landscape scale.

A geospatial approach for assessing denitrification sinks within lower-order catchments

Local decision makers can influence land use practices that alter N loading and processing within the drainage basin of lower-order stream reaches. Because many practices reduce water retention times and alter the timing and pathways of water flow, local decisions regarding land use can potentially exert a major influence on watershed N export. We illustrate a geospatial approach for assessing the role of denitrification sinks in watershed N delivery at the local level using: (a) widely available geospatial data, (b) current findings from peer-reviewed literature, (c) USGS stream gage data, and (d) locally based data on selected stream attributes. With high resolution, high quality GIS data increasingly available to local communities, they are now in a position to guide local management of watershed N by targeting upland source controls and by identifying landscape sinks for protection and/or restoration. We characterize riparian wetlands, lentic water bodies, and stream reaches as N sinks in the landscape and use geospatial particle tracking to estimate flow paths from N sources and evaluate N removal within sinks. We present an example analysis of the Chickasheen drainage basin, RI, USA, comparing N flux from three equivalent hypothetical N source areas situated in different regions of the watershed and illustrating the role of each N sink type in mediating N flux. Because our goal is to generate a tool that is used by and useful to decision makers we are exploring methods to better understand how decision makers understand and respond to the manner in which information is presented.

Impact of Microbial Partitioning on Wet Retention Pond Effectiveness

Wet detention basins are among the most common best management practices (BMPs) being implemented as means of complying with United States Phase II storm-water rules and impending Total Maximum Daily Load limits. The effectiveness of these basins for removal of microbial contaminants, one of the most frequent causes of water quality impairment, may be significantly affected by the degree to which microbes associate with particles in storm water. Little is known with regard to where microbial-particle associations are initiated within the storm-water transport chain as flow travels from upland sources (e.g., lawns, parking lots) through storm sewer systems and BMPs and finally on to receiving waters. A similar lack of information exists on the relative concentrations of microbes at each point in the transport chain. Both of these factors have important implications for the location of wet detention basins within a watershed, as well as their anticipated effectiveness. This study tracked the concentrations and partitioning behavior of three indicator organisms (fecal coliform, E. coli, and enterococci) at several locations in the transport chain and also explored the impacts of partitioning on wet pond removal efficiency. Results suggest that microbial-particle association is primarily initiated at upland sources and the degree of microbial partitioning does not vary greatly throughout the transport chain; therefore, treatment ponds will likely be most effective if located near upland contaminant sources. The overall reduction in microbial concentration brought about by the ponds was less than that assumed by most regulatory agencies, but the ponds did show some evidence of preferentially removing particle-associated fecal coliform and E. coli, suggesting that sedimentation is a key removal process. These findings should provide insights useful in the design and implementation of storm-water management strategies.

Soil and sediment properties affecting the accumulation of mercury in a flood control reservoir

Abstract Mercury accumulations in some fish species from Grenada Lake in north Mississippi exceed the Food and Drug Administration standards for human consumption. This large flood control reservoir serves as a sink for the Skuna and Yalobusha River watersheds whose highly erodible soils contribute to excessively high sediment yields and impaired water quality. This study was conducted to characterize the distribution of total Hg in watershed soils and determine the relationship between the easily transportable clay, organic C (OC), and Fe oxide fractions and the movement of Hg from upland sources to reservoir sinks. Cores were collected from soils, of different land-use, representative of the three soil orders (Alfisols, Entisols, and Vertisols) found in the watersheds. Sediment cores were collected from the Yalobusha River and Grenada Lake. In the laboratory, soil cores were sampled by horizon while sediment cores were sampled in 10 cm increments. These samples were characterized for total Hg, particle size distribution, OC, Fe oxide contents, and pH. Mercury concentrations ranged from 10 to 112 µg kg − 1 in the soil profiles, with average regression coefficient ( r 2 ) values of 0.104, 0.362, and 0.06 for Hg versus clay, OC, and Fe oxides, respectively. River sediment cores had Hg concentrations ranging from 0 to 38 µg kg − 1 , and significant (1% level) r 2 values of 0.611, 0.447, and 0.632 versus clay, OC, and Fe oxides, respectively. Mercury concentrations in the lake sediment ranged from 0 to 125 µg kg − 1 . The r 2 values for Hg versus clay, OC, and Fe oxides in the lake sediment were 0.813, 0.499, and 0.805, respectively, all significant at the 1% level. These results indicate that total Hg is poorly correlated with the clay, OC, and Fe oxide fractions at depth in the soil profiles because maximum Hg concentrations occur in the surface horizons due to atmospheric in-fall. The statistically significant r 2 values for Hg versus these components in the sediment cores are the result of particulate clay, Fe oxides, and finely divided OC sorption of Hg from solution during the runoff and sediment transport process. The higher correlations for the lake sediment reflect an enrichment of the Hg-laden clay fraction relative to stream sediment through flocculation and sedimentation processes in the slack-water environment of the reservoir.

English

The USACE-Norfolk District (NAO) and the City of Petersburg, VA are working toward restoring the former Appomattox River Federal Navigation Channel. In this effort, ~350,000 cubic yards of deposited sediment will be removed from -14 feet MLLW up to + 6 feet MLLW over a ~1 mile reach of the Appomattox River. Historical industrial uses have resulted in PAH contamination exceeding 500 mg/kg on average, with hotspots detected in excess of 5,000 mg/kg based on USACE 2004 analytical data. To support the NAO with its assessment of contaminant distribution, upland source control measures, dredge sequencing, sediment capping requirements to address residual contaminants and beneficial reuse options for the dredged material have been evaluated. In support of beneficial reuse as agricultural soil, a lab treatability study has been completed to assess biodegradation potential. Total PAH concentrations in three laboratory test pans after 46 weeks of treatment indicated an overall 80% contaminant reduction using an enhanced bioremediation process. The results of this bench-scale study were used as the basis for the design of a pilot field-scale landfarm study demonstration undertaken during July 2007. After five months of treatment, LMW PAHs in landfarm material appear to have degraded first while HMW PAHs are degrading more slowly, a process which generally mimics the results of the laboratory investigation. Conclusions based on the laboratory and landfarm activities as well as the technical and regulatory issues that must be resolved to allow eventual placement of the material at a mine reclamation site for revegetation purposes will be presented.

Biogeochemical characterization of carbon sources in the Strickland and Fly rivers, Papua New Guinea

The highstanding islands of Oceania are recognized as a source of significant particulate organic carbon delivered to nearshore marine environments. The existing data on carbon export in Oceania are largely derived from small mountainous watersheds (&lt;10,000 km2) with little or no sediment storage capacity and located in subtropical to temperate regions. The Fly‐Strickland fluvial dispersal system is the largest in tropical Oceania and has high sediment yields, aged organic matter in its suspended‐sediment load, and lowland sediment storage capacity. The Fly River system also has very high soil organic carbon content and conditions favorable to perennially high production, oxidation, and discharge within the watershed. We used stable and radiogenic isotopes (δ13C, Δ14C, and δ15N), lignin phenols, and X‐ray photoelectron spectroscopy to examine the organic and inorganic composition of particulate and dissolved carbon at several lowland sites in the Fly and Strickland rivers and on the Strickland River floodplain. Isotopic, elemental, and biomarker results suggest that organic carbon in the Strickland River was more degraded than in the Fly River, with a greater input of ancient organics from upland sources, and that aquatic production constituted a larger source in the Fly River. Radiocarbon results indicate that all carbon fractions were older in the Strickland than in the Fly and that Strickland floodplain sediments were also depleted in radiocarbon. Collectively, these results suggest that rivers of New Guinea export a comparable amount of particulate organic carbon to the Amazon, with a significant contribution from radiocarbon‐depleted sources.

Spatial Analysis of a Large Magnitude Erosion Event Following a Sierran Wildfire

High intensity wildfire due to long-term fire suppression and heavy fuels buildup can render watersheds highly susceptible to wind and water erosion. The 2002 "Gondola" wildfire, located just southeast of Lake Tahoe, NV-CA, was followed 2 wk later by a severe hail and rainfall event that deposited 7.6 to 15.2 mm of precipitation over a 3 to 5 h time period. This resulted in a substantive upland ash and sediment flow with subsequent down-gradient riparian zone deposition. Point measurements and ESRI ArcView were applied to spatially assess source area contributions and the extent of ash and sediment flow deposition in the riparian zone. A deposition mass of 380 Mg of ash and sediment over 0.82 ha and pre-wildfire surface bulk density measurements were used in conjunction with two source area assessments to generate an estimation of 10.1 mm as the average depth of surface material eroded from the upland source area. Compared to previous measurements of erosion during rainfall simulation studies, the erosion of 1800 to 6700 g m(-2) mm(-1) determined from this study was as much as four orders of magnitude larger. Wildfire, followed by the single event documented in this investigation, enhanced soil water repellency and contributed 17 to 67% of the reported 15 to 60 mm ky(-1) of non-glacial, baseline erosion rates occurring in mountainous, granitic terrain sites in the Sierra Nevada. High fuel loads now common to the Lake Tahoe Basin increase the risk that similar erosion events will become more commonplace, potentially contributing to the accelerated degradation of Lake Tahoe's water clarity.

Timing of surficial process changes down a Mojave Desert piedmont

We measured 10Be and 26Al in 29 sediment samples to infer the history and millennial-scale rates of change down a low-gradient piedmont, a common but enigmatic landform that dominates the Mojave Desert. Nuclide data suggest that a large volume of sediment was deposited on the proximal East Range Road piedmont in Fort Irwin, California, ∼ 75,500 yr ago. Since then, this material has been stable or eroding slowly. In contrast, on the distal piedmont (3.5 km from the upland source basins) soil stratigraphy suggests that there have been alternating periods of surface stability, erosion, and deposition over the last 70,000 yr. Nuclide data from samples amalgamated along cross-piedmont transects suggest that long-term average down-gradient sediment speeds range from 9 cm yr − 1 near the uplands to 22 cm yr − 1 6 km down-piedmont. These speeds are similar to 10Be-estimated sediment speeds down three other piedmonts in the Mojave Desert, suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates. The timing of surface process change down the East Range Road piedmont is determined by a combination of sediment available in the source basins, sediment transport rates, and the size of the piedmont.