Fluvial Load Research Articles

Sediment accumulation patterns and fine-scale strata formation on the Waiapu River shelf, New Zealand

Multiple sediment transport and reworking processes influence fine, cm-scale strata formation and long-term accumulation on the Waiapu River shelf, New Zealand. Gravity cores collected during two cruises, in August 2003 and May 2004, were analyzed using 7Be and 210Pb geochronologies, bulk carbon, δ 13C, X-radiographs, and grain-size to investigate sediment mixing and accumulation patterns. The presence of 7Be on the inner- and mid-shelf regions (< ~ 80m) indicated recent (within the last 4–5 months) deposition of fluvial muds, whereas the distribution of excess 210Pb accumulation rates revealed that the middle to outer shelf (50–130 m) acted as fine sediment repositories on longer time scales. Excess 210Pb accumulation rates were high, with an area weighted average of 1.1 ± 0.1 cm/yr and ranging between 0.2 and 3.5 cm/yr, yet were localized such that only an estimated ~ 23% (ranging between 17 and 38%) of the fluvial load was retained on the shelf between 40 and 200 m depths over the last 80 to 100 yr. Sediments not retained on the shelf were either transported to deeper waters or along the shelf beyond the sampling area. Several cores collected from the high sediment accumulation zone on the middle to outer shelf exhibited non-steady state excess 210Pb profiles, suggesting that multiple transport processes influenced fine-scale strata formation. Layers of low excess 210Pb activity and predominantly terrestrial δ 13C and C/N values were likely formed during floods, when sediments were rapidly deposited and buried on the shelf. These event layers were sufficiently thick (up to ~ 20 cm), such that all or a portion of the initial flood layer immediately transited through the surface mixing layer, ensuring preservation in the sediment record. Sediments inter-bedded with these event layers reflected a relatively marine source indicating either that they were not deposited rapidly or were significantly bioturbated. A gradient of physical and biological mixing signatures, extending radially from the Waiapu River mouth, suggested that high background accumulation rates and flood deposits negatively impacted the preservation of biological structures and enhanced preservation of event-produced beds.

Net Ecosystem Metabolism and Nonconservative Fluxes of Organic Matter in a Tropical Mangrove Estuary, Piauí River (NE of Brazil)

Net ecosystem metabolism (NEM) was measured in the Piaui River estuary, NE Brazil. A mass balance of C, N, and P was used to infer its sources and sinks. Dissolved inorganic carbon (DIC) concentrations and fluxes were measured over a year along this mangrove dominated estuary. DIC concentrations were high in all estuarine sections, particularly at the fluvial end member at the beginning of the rainy season. Carbon dioxide concentrations in the entire estuary were supersaturated throughout the year and highest in the upper estuarine compartment and freshwater, particularly at the rainy season, due to washout effects of carbonaceous soils and different organic anthropogenic effluents. The estuary served as a source of DIC to the atmosphere with an estimated flux of 13 mol CO2 m−2 year−1. Input from the river was 46 mol CO2 m−2 year−1. The metabolism of the system was heterotrophic, but short periods of autotrophy occurred in the lower more marine portions of the estuary. The pelagic system was more or less balanced between auto- and heterotrophy, whereas the benthic and intertidal mangrove region was heterotrophic. Estimated annual NEM yielded a total DIC production in the order of 18 mol CO2 m−2 year−1. The anthropogenic inputs of particulate C, N, and P, dissolved inorganic P (DIP), and DIC were significant. The fluvial loading of particulate organic carbon and dissolved inorganic nitrogen (DIN) was largely retained in two flow regulation and hydroelectric reservoirs, promoting a reduction of C:N and C:P particulate ratios in the estuary. The net nonconservative fluxes obtained by a mass balance approach revealed that the estuary acts as a source of DIP, DIN, and DIC, the latter one being almost equivalent to the losses to the atmosphere. Mangrove forests and tidal mudflats were responsible for most of NEM rates and are the main sites of organic decomposition to sustain net heterotrophy. The main sources for this organic matter are the fluvial and anthropogenic inputs. The mangrove areas are the highest estuarine sources of DIP, DIC, and DIN.

An assessment of anthropogenic source impacts on mercury cycling in the Willamette Basin, Oregon, USA

In Oregon's Willamette River Basin (Basin), methylmercury levels in fish triggered health advisories and required development of a mercury Total Maximum Daily Load (TMDL) for the Willamette River. A seasonally-responsive dynamic systems model is used to identify the principal sources of natural and anthropogenic mercury, the relative contributions of these sources to the river, the impact of hypothetical reductions in specific natural and anthropogenic sources on mercury levels in surface water, sediment, and fish tissue, and the degree to which any such changes would be clearly discernible to environmental managers and Basin stakeholders. Two scenarios are modeled: “PRES”, which considered all currently known natural and anthropogenic mercury sources and “LEEM”, which (hypothetically) eliminated all local, but not global, anthropogenic sources and greatly lowered native soil erosion rates. Elimination of local air emissions reduces runoff of air-deposited mercury by ≈34% and advection from the Basin by ≈12%, while lowering erosion rates reduces particulate runoff by ≈57%, deposition from the water column to surficial sediment by ≈33%, and fluvial load by ≈24%; for a net reduction of 25.6% in the total mercury load to the river. Such hypothetical reductions bring methylmercury concentrations in predatory fish to levels that would allow restoration of fish consumption as a beneficial use. However, several factors, primarily technical feasibility and global sources, may impede attempts to attain this beneficial use. Actualizing the hypothetical 100% elimination of local anthropogenic sources and a > 50% reduction in erosion could pose significant technical challenges. Because local anthropogenic emissions make relatively smaller contributions to the Basin than do persistent global sources (sources over which there is little, if any, possibility of local control), localized environmental management actions alone may not be adequate to address mercury impacts within the Basin.

The merging of human activity and natural change: temporal and spatial scales of ecological change in the Kokemäenjoki river delta, SW Finland

Human cultures have had important influences and major impacts on nature and its natural state along rivers. Riversides have been settled for thousands of years and human interpenetration of nature along rivers is multilevel both in time and space. In this descriptive article, we discuss how human activities have changed in the Kokemäenjoki river delta in the northern Baltic, SW Finland and how these altered activities have influenced the formation structure and ecological dynamics of the delta. Vegetational changes during the last 100 years are used as a proxy of environmental change. We study the complicated human culture–nature interpenetration at different temporal and spatial scales. The Kokemäenjoki river delta was formed during deglaciation after the last Ice Age. Because of rapid land uplift (about 0.7 cm per year) and the fluvial load transported by the river, the delta is moving towards the sea at a quick pace. Livestock farming has kept meadows open and shaped their vegetation for thousands of years, and field clearing has had significant impacts on the delta since the 16th century. Further, disturbances such as damming or the establishment of factories along rivers have also shaped the Kokemäenjoki river delta for centuries, changing the river’s role in transporting organisms and debris. Remarkably, structural changes associated with agricultural land use in the late 19th and in the middle of 20th century and damming for hydropower purposes in the 1920s and 1940s, seem to have had only a minor influence regarding the vegetation dynamics in this wetland habitat. It seems that the delta can retain its conservation value in the future. Land uplift ensures that new wetland habitats are constantly created. Since the delta has experienced human impact from the very beginning of its formation, it appears that the occurring vegetation has adapted to those influences and the interrelation of human presence.

Temporal and Spatial Patterns of Trace Elements in the Patuxent River: A Whole Watershed Approach

Trace element distributions, partitioning, and speciation were examined at 15 sites in the Patuxent River watershed from May 1995 through October 1997 to determine possible sources of trace elements to the river and estuary, to examine the relationship of the trace element discharges to freshwater discharges as well as to land use and geographic region, to validate previous estimates of loadings to the river, and to provide baseline data for trace elements in the Patuxent River watershed and estuary. Six freshwater sites were examined, representing different basins and geographic provinces, and nine sites along the estuarine salinity gradient. Subregions within the watershed varied considerably in concentrations and areal yields for some elements. Concentrations of As, Cd, Ni, Pb, and Zn were elevated in the Coastal Plain sites compared to the Piedmont sites, while Cu and Hg were more evenly distributed. Cadmium, Cu, Hg, Ni, Pb, and Zn showed overall positive correlations with river flow while As and methylHg (meHg) showed negative correlations with river flow. Concentrations of trace elements in the estuarine portion of the river were generally low, and consistent with mixing between Patuxent River water with elevated concentrations and the lower concentrations of the Chesapeake Bay. Interesting features included a local Cd maximum in the low salinity region of the estuary, probably caused by desorption from suspended sediments, and a significant input of water containing high As concentrations from the Chesapeake Bay and from As being released from bottom sediments in summer. Comparisons between the estimated annual flux of trace elements and the estimates of suspected source terms (atmospheric deposition, urban runoff, and known point sources) suggest that, except for Hg, direct atmospheric deposition is small compared to fluvial loads. Current estimates of trace element inputs from point sources or from urban runoff are inadequate for comparison with other sources, because of inappropriate techniques and/or unacceptably high detection limits. A complete examination of trace element dynamics in the Patuxent River (and in other coastal systems) will require better data for these potential sources.

Petrography and Mineral Content of Sea-floor Sediments of the Tigris-Euphrates Delta, North-west Arabian Gulf, Iraq

Sea-floor sediments of the Iraqi territory of the Arabian Gulf have been studied in detail petrographically and mineralogically. The carbonate fraction of these sediments comprises various allochems in order of abundance: skeletal remains, ooids, peloids, and composite grains. On the other hand, the insoluble residues of the sediments studied consist of quartz, feldspars and mica. The matrix is carbonate micrite, containing various percentages of clays.Mineralogically the carbonate fraction consists of calcite, Mg-calcite, aragonite and dolomite. Mg-calcite, forming the radial cortex of the ooids, is the most unexpected and significant of such components. In addition, the Mg-calcite micritic cement is the most commonly observed diagenetic product resulting in the formation of hardgrounds in some areas. The clay minerals of the (<2 μm) grade are: illite, smectite, chlorite, illite-smectite, kaolinite and palygorskite. They are mainly detrital in origin.The fluvial loads of the Shatt Al-Arab (i.e. Tigris and Euphrates rivers) and Karun rivers, sand and dust from north-westerly storm winds (Shamal) are the main potential sources for the detrital sediments accumulating in the area of study. The indigenous marine organisms and some inorganic precipitation (as Mg-calcite), are additional sources of the sediments and increase in percentage toward the open waters.

Comparison of Nutrient and Trace Element Distributions in the Delta and Shelf Outflow Regions of the Mississippi and Atchafalaya Rivers

Nutrient and trace element distributions were determined in the outflow region of the Mississippi and Atchafalaya rivers during high river discharge. This outflow region can be divided into two physiographic areas: the broad, shallow Louisiana Shelf off the Atchafalaya River and the narrow shelf off the Mississippi Delta. The physiographic differences between these two areas lead to observable differences in the chemical distributions. During high discharge conditions, nutrient depletion occurs at lower salinities on the Louisiana Shelf, relative to the delta outflow plume, and significant uptake of nickel and cadmium is apparent in these shelf waters, too. Important factors that appear to connect the physiographic to the chemical include the fate of the fluvial suspended load, rates of mixing, and the extent of productivity supported by recycled nutrients. The results suggest that the Mississippi-Atchafalaya outflow region may provide a natural laboratory for examining the possible effects of sea-level change on the biogeochemistry of estuarine and coastal environments.

Behavior of Cd, Pb, and Cu in the marine deltaic area of the Po River (North Adriatic Sea)

An analysis of the spatial trend of concentrations and of the correlation between heavy metals and total suspended matter was performed in a multidisciplinary study of transport of pollutants in the marine coastal area involving in situ investigations, remote sensing techniques and modeling. This paper presents results concerning the chemical behavior of heavy metals (Cu, Cd, Pb) in the North Adriatic Sea and in particular in the marine deltaic area of the Po river. The samples were collected during the JRC Remote Sensing Campaigns ADRIA 84 and ADRIA 85, carried out in the entire North Adriatic Sea and in the selected area in front of the Po when passing from the fluvial to the marine environment. In the dissolved phase, Cu undergoes a dilution process consistent with the mixing theory, while there is a tenfold increase in Pb concentrations. A pronounced tendency to augment the level in the dissolved phase is observed for all three elements in the pelagic waters. In the particulate phase, Cd and Cu, after a diminution in the nearshore stations, their concentration increases as the pelagic area is approached. The total amount of heavy metals in solid phase of the water decreases according to the dispersion and the sedimentation processes of the fluvial load in the marine water. A satisfactory correlation was found between the Cu and Pb with the total suspended matter (TSS). An attempt was made to characterize sediments and suspended matter in order to assess the role of the organic and mineralogical components on heavy metal behavior.

Stratigraphy and Hydrocarbon Potential of Muddy Sandstone, Wind River Basin, Wyoming: ABSTRACT

The Lower Cretaceous (late Albian) Muddy Sandstone in the Wind River basin and adjacent areas rests unconformably upon the Thermopolis Shale and is disconformably overlain by and interfingers with the lower part of the Shell Creek Shale. The Muddy Sandstone is divided into five informal members: the Lazy B, Rozet, lower Recluse, upper Recluse, and Cyclone members. These members, defined as chronostratigraphic units bounded by bentonite beds, transgressive disconformities, and/or unconformities, consist of asymmetrical, coarsening and thickening-upward progradational deltaic/strand-plain and bay-fill deposits and/or asymmetrical, fining and thinning-upward aggradational valley-fill deposits. The Lazy B and Rozet members are marine progradational strand-plain deposits bounded by unconformities. They occur as discontinuous, erosional remnants in the western and northwestern parts of the study area. Following Rozet deposition, a major sea level fall resulted in the development of a headward-eroding valley system. During a subsequent sea level rise these valleys aggraded with fluvial/estuarine deposits of the Grieve member. Eventually the study area was blanketed by landward-stepping, progradational bay-fill, nearshore, and offshore marine deposits of the lower Recluse, upper Recluse, and Cyclone members. In addition to localized production from anticlinal or fault-bounded structural closure, the most significant oil and gas production is from updip pinch-outs ofmore » sand-rich valley fill of the Grieve member in the southeastern Wind River basin. Extensive outcrop and core analysis reveals these sand-rich paleovalleys, which range up to 10 mi wide and 100 ft thick, contain numerous scour-and-fill sequences composed of either fluvial bed load, fluvial suspended load, or abandoned channel deposits. Individual scour-and-fill sequences range up to 300 ft wide and up to 50 ft thick.« less

ON THE FORMATION PROCESSES OF RIVER TERRACES DISTRIBUTED ALONG THE SARU RIVER, HOKKAIDO, JAPAN

The author investigated the river terraces along the Saru river, Hokkaido, Japan. First, he divided the Quarternary age into four stages by means of the age of marker tephra layers, such as Spfa-1 (ca. 33, 000 yrs. B. P.), En-a (ca. 15, 000yrs. B. P.), Ta-d (ca. 9, 000yrs. B. P.) and Ta-d (ca. 550 yrs. B. P.) which were named Ms, Mw-I, Mw-II, and F stages in the descending order (Fig. 1). Secondly, the river terraces were classified into four topographic surfaces based on topographic continuties, which were named I, II, III, and IV surfaces in the ascending order. Comparing M_??_F stages with I_??_IV topographic surfaces, respectively, he found that there was a time lag within the formation of each topographically continuous terrace surface (Figs. 4 and 5). One case of time lag is shown by the convergence of terraces, (e. g., II_??_IV surfaces converge into one surface in the middle course; the lag of which is estimated 2_??_4×104 yrs). The other is attributed to the translocation of downcutting place of river bed (e. g., I surface is considered to have formed whithin a time of about 1×104 yrs.). I and II surfaces along the lower course were formed in the Postglacial age. While, III and IV surfaces were formed by the translocation of knick-point, accompanied with the lowering of sea level during the Lastglacial age. Judging from the field evidences and longitudinal profiles (Figs. 4 and 5), down-cutting of II surface was initiated from the middle course, slowly proceeding to upward and downward. It is supposed that this phenomenon was caused by the complex influence of the following factors: (1) increasing of curvature in river profile, probably effected by the relative decrease of fluvial load and sea level rise in the Postglacial age, (2) slight falling of sea level after the maximum phase of Jomon transgression, (3) other unknown factors. The river traces distributed along the course of the Saru have been formed as a result of successive translocation of down-cutting, lateral erosion, and depositional areas to upward and downward along the river course. Fig. 7 shows the presumed changes of river bed altitudes since Lastglacial time along the Saru.

Cation-exchange characteristics of Amazon River suspended sediment and its reaction with seawater

The cation-exchange characteristics of Amazon River suspended sediment have been studied in order to determine the contribution of exchangeable cations to the geochemical fluxes from the river. Sediment samples were obtained throughout most of the Amazon Basin. The range of exchangeable cation compositions is very narrow in the river and in seawater as well. In river water, the exchangeable cation complement (equivalent basis, exclusive of H +) is 80% Ca 2+, 17% Mg 2+, 3% Na + plus K +. In seawater Na + and Mg 2+ are about equal (38%) while Ca 2+ ~ 15% and K + ~ 9%. On reaction with seawater, river suspended sediment took up an amount of Na + equal to nearly one-third of the dissolved river load, as well as amounts corresponding to 15–20% of the dissolved fluvial K + and Mg 2+. These estimates reflect an unusually high suspended-sediment:dissolved-solids ratio of 6.4 at the time of sampling. At a more representative world average ratio of four, the uptake of Na + would be 20% of the dissolved fluvial load, and that for K + and Mg 2+ about 10%. Over the annual cycle of the Amazon, it is estimated that ion exchange has a still smaller effect, as a consequence of the low average suspended-solids:dissolved-solids ratio of 1.7. Variations in the ratio X Ca X Mg , the equivalent fraction of exchangeable Ca 2+ and Mg 2+, throughout the river, can be described by a single isotherm. This same isotherm accurately describes the distribution of exchangeable Ca 2+ and Mg 2+ on sediment equilibrated with seawater, despite that a high proportion of exchange sites is occupied by Na + and K +.