James P. M. Syvitski

Geomorphic/Tectonic Control of Sediment Discharge to the Ocean: The Importance of Small Mountainous Rivers

Analysis of data from 280 rivers discharging to the ocean indicates that sediment loads/yields are a log-linear function of basin area and maximum elevation of the river basin. Other factors controlling sediment discharge (e.g., climate, runoff) appear to have secondary importance. A notable exception is the influence of human activity, climate, and geology on the rivers draining southern Asia and Oceania. Sediment fluxes from small mountainous rivers, many of which discharge directly onto active margins (e.g., western South and North America and most high-standing oceanic islands), have been greatly underestimated in previous global sediment budgets, perhaps by as much as a factor of three. In contrast, sediment fluxes to the ocean from large rivers (nearly all of which discharge onto passive margins or marginal seas) have been overestimated, as some of the sediment load is subaerially sequestered in subsiding deltas. Before the proliferation of dam construction in the latter half of this century, rivers probably discharged about 20 billion tons of sediment annually to the ocean. Prior to widespread farming and deforestation (beginning 2000-2500 yr ago), however, sediment discharge probably was less than half the present level. Sediments discharged by small mountainous rivers are more likely to escape to the deep sea during high stands of sea level by virtue of a greater impact of episodic events (i.e., flash floods and earthquakes) on small drainage basins and because of the narrow shelves associated with active margins. The resulting delta/fan deposits can be distinctly different than the sedimentary deposits derived from larger rivers that discharge onto passive margins.

Impact of Humans on the Flux of Terrestrial Sediment to the Global Coastal Ocean

Here we provide global estimates of the seasonal flux of sediment, on a river-by-river basis, under modern and prehuman conditions. Humans have simultaneously increased the sediment transport by global rivers through soil erosion (by 2.3 ± 0.6 billion metric tons per year), yet reduced the flux of sediment reaching the worlds coasts (by 1.4 ± 0.3 billion metric tons per year) because of retention within reservoirs. Over 100 billion metric tons of sediment and 1 to 3 billion metric tons of carbon are now sequestered in reservoirs constructed largely within the past 50 years. African and Asian rivers carry a greatly reduced sediment load; Indonesian rivers deliver much more sediment to coastal areas.

Anthropogenic sediment retention: major global impact from registered river impoundments

In this paper, we develop and apply a framework for estimating the potential global-scale impact of reservoir construction on riverine sediment transport to the ocean. Using this framework, we discern a large, global-scale, and growing impact from anthropogenic impoundment. Our study links information on 633 of the worlds largest reservoirs (LRs) (≥0.5 km3 maximum storage capacity) to the geography of continental discharge and uses statistical inferences to assess the potential impact of the remaining >44,000 smaller reservoirs (SRs). Information on the LRs was linked to a digitized river network at 30′ (latitude×longitude) spatial resolution. A residence time change (ΔτR) for otherwise free-flowing river water is determined locally for each reservoir and used with a sediment retention function to predict the proportion of incident sediment flux trapped within each impoundment. The discharge-weighted mean ΔτR for individual impoundments distributed across the globe is 0.21 years for LRs and 0.011 years for SRs. More than 40% of global river discharge is intercepted locally by the LRs analyzed here, and a significant proportion (≈70%) of this discharge maintains a theoretical sediment trapping efficiency in excess of 50%. Half of all discharge entering LRs shows a local sediment trapping efficiency of 80% or more. Analysis of the recent history of river impoundment reveals that between 1950 and 1968, there was tripling from 5% to 15% in global LR sediment trapping, another doubling to 30% by 1985, and stabilization thereafter. Several large basins such as the Colorado and Nile show nearly complete trapping due to large reservoir construction and flow diversion. From the standpoint of sediment retention rates, the most heavily regulated drainage basins reside in Europe. North America, Africa, and Australia/Oceania are also strongly affected by LRs. Globally, greater than 50% of basin-scale sediment flux in regulated basins is potentially trapped in artificial impoundments, with a discharge-weighted sediment trapping due to LRs of 30%, and an additional contribution of 23% from SRs. If we consider both regulated and unregulated basins, the interception of global sediment flux by all registered reservoirs (n≈45,000) is conservatively placed at 4–5 Gt year−1 or 25–30% of the total. There is an additional but unknown impact due to still smaller unregistered impoundments (n≈800,000). Our results demonstrate that river impoundment should now be considered explicitly in global elemental flux studies, such as for water, sediment, carbon, and nutrients. From a global change perspective, the long-term impact of such hydraulic engineering works on the worlds coastal zone appears to be significant but has yet to be fully elucidated.

Geology, Geography, and Humans Battle for Dominance over the Delivery of Fluvial Sediment to the Coastal Ocean

Sediment flux to the coastal zone is conditioned by geomorphic and tectonic influences (basin area and relief), geography (temperature, runoff), geology (lithology, ice cover), and human activities (reservoir trapping, soil erosion). A new model, termed “BQART” in recognition of those factors, accounts for these varied influences. When applied to a database of 488 rivers, the BQART model showed no ensemble over‐ or underprediction, had a bias of just 3% across six orders of magnitude in observational values, and accounted for 96% of the between‐river variation in the long‐term (±30 years) sediment load or yield of these rivers. The geographical range of the 488 rivers covers 63% of the global land surface and is highly representative of global geology, climate, and socioeconomic conditions. Based strictly on geological parameters (basin area, relief, lithology, ice erosion), 65% of the between‐river sediment load is explained. Climatic factors (precipitation and temperature) account for an additional 14% of the variability in global patterns in load. Anthropogenic factors account for an additional 16% of the between‐river loads, although with ever more dams being constructed or decommissioned and socioeconomic conditions and infrastructure in flux, this contribution is temporally variable. The glacial factor currently contributes only 1% of the signal represented by our globally distributed database, but it would be much more important during and just after major glaciations. The BQART model makes possible the quantification of the influencing factors (e.g., climate, basin area, ice cover) within individual basins, to better interpret the terrestrial signal in marine sedimentary records. The BQART model predicts the long‐term flux of sediment delivered by rivers; it does not predict the episodicity (e.g., typhoons, earthquakes) of this delivery.

Fjords: Processes and Products

1 Introduction.- 1 Fjords and Their Study.- 1.1 Definition, Distribution, and History.- 1.2 Environmental Setting and Study.- 1.3 The Past, Present, and Future of Fjord Research.- 2 Environmental Setting.- 2.1 Geomorphology.- 2.2 Climate.- 2.3 Oceanographic Characteristics.- 2.4 Sediment Sources and Transport Mechanisms.- 2.5 Fjord History.- 2.6 Characteristic Features of Fjord Coastlines.- 2.7 Summary.- 2 Processes and Products.- 3 The Fluvial-Deltaic Environment.- 3.1 Runoff.- 3.2 Sediment Transport.- 3.3 Paraglacial Sedimentation.- 3.4 Fjord-Head Deltas.- 3.5 Summary.- 4 Circulation and Sediment Dynamics.- 4.1 Fjord Estuarine Circulation.- 4.2 Hypopycnal Sedimentation.- 4.3 Hyperpycnal Flow.- 4.4 Flushing and Deep Water Renewal.- 4.5 Ice Influences.- 4.6 Mixing Processes and the Seafloor Environment.- 4.7 Summary.- 5 Subaqueous Slope Failures.- 5.1 Mass Sediment Properties and Subaqueous Slope Stability.- 5.2 Release Mechanisms.- 5.3 Mass Transport Processes.- 5.4 The Products of Subaqueous Slope Failure.- 5.5 Summary.- 6 Biotic Processes.- 6.1 Pelagic and Littoral Processes.- 6.2 The Fjord Benthic Environment.- 6.3 Summary.- 7 Biogeochemistry.- 7.1 Particulate Sediment.- 7.2 Aerobic Diagenetic Reactions.- 7.3 Anoxic Environments.- 7.4 Summary.- 3 Implications/Applications.- 8 Environmental Problems: Case Histories.- 8.1 Introduction.- 8.2 Agfardlikavsa Fjord, Greenland.- 8.3 Resurrection Bay, Alaska.- 8.4 Port Valdez, Alaska.- 8.5 Howe Sound, British Columbia.- 8.6 Rupert Inlet, British Columbia.- 8.7 Saguenay Fjord, Quebec.- 8.8 Iddefjord, Norway/Sweden.- 8.9 Saudafjord, Southwest Norway.- 8.10 Sorfjord, West Norway.- 8.11 Ranafjord, Northern Norway.- 8.12 Loch Eil, Scotland.- 8.13 By fjord, Sweden.- 8.14 Summary of Impacts in Other Fjords.- 9 Future Fjord Research.- 9.1 Oceanographic Problems and Projects.- 9.2 Biogeochemical Problems and Projects.- 9.3 Biological Problems and Projects.- 9.4 Geological-Related Problems and Projects.- 9.5 Approaches.- References.- Fjord Index.

Principles, methods, and application of particle size analysis

List of contributors Preface Acknowledgements Part I. Introduction: 1. Principles and methods of geological particle size analysis I. N. McCave and James P. M. Syvitski 2. The effect of grain shape and density on size measurement Martin D. Matthews 3. The effect of pretreatment on size analysis Martin D. Matthews Part II. Theory and Methods: 4. Principles, design and calibration of settling tubes James P. M. Syvitski, Kenneth W. Asprey and D. A. Clattenburg 5. Methodology of sieving small samples and calibration of sieve set Kristian Dalsgaard, Jens Ledet Jensen and Michael Sorenson 6. Image analysis method of grain size measurement Stephen K. Kennedy and Jim Mazzullo 7. Quantitative grain form analysis Julian D. Orford and W. Brian Whalley 8. Electroresistance particle size analyzers T. G. Milligan and Kate Kranck 9. Laser diffraction size analysis Y. C. Agrawal, I. N. McCave and J. B. Riley 10. SediGraph technique John P. Coakley and James P. M. Syvitski 11. Size, shape, composition and structure of microparticles from light scattering Miroslaw Jonasz 12. Textural maturity of arenaceous rocks derived by microscopic grain size analysis in thin section Song Tianrui 13. Interlaboratory, interinstrument calibration experiment James P. M. Syvitski, K. William G. LeBlanc and Kenneth W. Asprey Part III. In Situ Methods: 14. In situ size measurements of suspended particles in estuarine and coastal waters using laser diffraction A. J. Bale and A. W. Morris 15. The Floc Camera Assembly David E. Heffler, James P. M. Syvitski and Kenneth W. Asprey Part IV. Data Interpretation and Manipulation: 16. Suite statistics: the hydrodynamic evolution of the sediment pool William F. Tanner 17. The hyperbolic distribution Christian Christiansen and Daniel Hartmann 18. Factor analysis of size frequency distributions: significance of factor solutions based on simulation experiments James P. M. Syvitski 19. Experimental-theoretical approach to interpretation of grain size frequency distributions Supriya Sengupta, J. K. Ghosh and B. S. Mazumder Part V. Applications: 20. Application of suite statistics to stratigraphy and sea-level changes William F. Tanner 21. Application of size sequence data to glacial-paraglacial sediment transport and sediment partitioning Jay A. Stravers, James P. M. Syvitski, and Dan B. Praeg 22. The use of grain size information in marine geochemistry Dale E. Buckley and Ray E. Cranston 23. Grain size in oceanography Kate Kranck and T. G. Milligan 24. The need for grain size analyses in marine geotechnical studies Francis J. Hein Index.

Predicting the terrestrial flux of sediment to the global ocean: a planetary perspective

A new model for predicting the long-term flux of sediment from river basins to the coastal ocean is applied to a global data set of 340 river basins. The model is based on relief, basin area (or, averaged discharge), and basin-averaged temperature. Basinaveraged temperature is determined from basin location (latitude, longitude) and the lapse rate across the basin relief (hypsometric approximation). The sediment flux model incorporates climate through basin temperature and hydrologic runoff. Solutions are provided for each of the major hemispheric climate regions (polar, temperate and tropic). The model successfully predicts the pre-anthropogenic flux of sediment to within the uncertainties associated with the global observations (within a factor of two for 75% of rivers that range across five orders of magnitude in basin area and discharge). Most of the ‘‘problem’’ rivers are associated with low observational loads (often smaller rivers where anthropogenic impacts are often magnified, and temporal variability is high). Model predictions provide a baseline for researchers: (1) to question the quality of observational data where available and disagreement is greatest, (2) to examine a river basin for unusually large anthropogenic influences (i.e. causes of erosion or causes of hinterland sediment retention), and (3) to uncover secondary factors not addressed by our model (lithology, lakes). The model provides a powerful tool to address the impact of paleo-climate fluctuations (warmer/colder; wetter/drier) on the impact of sediment flux to the coastal ocean. D 2003 Elsevier B.V. All rights reserved.

Estimating fluvial sediment transport: the rating parameters

Correlations between suspended sediment load rating parameters, river basin morphology, and climate provide information about the physical controls on the sediment load in rivers and are used to create predictive equations for the sediment rating parameters. Long-term time-averaged values of discharge, suspended load, flow duration, flow peakedness, and temporally averaged values of precipitation, temperature, and range in temperature were coupled with the drainage area and basin relief to establish statistical relationships with the sediment rating parameters for 59 gauging stations. Rating parameters (a and b) are defined by a power law relating daily discharge values of a river (Q) and its sediment concentration Cs, where Cs = aQb. The rating coefficient a (the mathematical concentration at Q = 1 m3/s) is inversely proportional to the long-term mean discharge and is secondarily related to the average air temperature and the basins topographic relief. The rating exponent b (the log-log slope of the power law) correlates most strongly with the average air temperature and basin relief and has lesser correlations with the long-term load of the river (which is related to basin relief and drainage area). The rating equation describes the long-term character of the suspended sediment load in a river. Each river undergoes higher-frequency variability (decadal, interannual, and storm event) around this characteristic response, controlled by weather patterns and channel recovery from extreme precipitation events.

Sediment flux and the Anthropocene.

Data and computer simulations are reviewed to help better define the timing and magnitude of human influence on sediment flux—the Anthropocene epoch. Impacts on the Earth surface processes are not spatially or temporally homogeneous. Human influences on this sediment flux have a secondary effect on floodplain and delta-plain functions and sediment dispersal into the coastal ocean. Human impact on sediment production began 3000 years ago but accelerated more widely 1000 years ago. By the sixteenth century, societies were already engineering their environment. Early twentieth century mechanization has led to global signals of increased sediment flux in most large rivers. By the 1950s, this sediment disturbance signal reversed for many rivers owing to the proliferation of dams, and sediment load reduction below pristine conditions is the dominant signal today. A delta subsidence signal began in the 1930s and is now a dominant signal in terms of sea level for many coastal environments, overwhelming even the global warming imprint on sea level. Humans have engineered how most water and sediment are discharged into the coastal ocean. Hyperpycnal flow events have become more common for some rivers, and less common for other rivers. Bottom trawling is now widespread, suggesting that even continental shelves have received a significant but as yet quantified Anthropocene impact. The Anthropocene attains the level of a geological climate event, such as that seen in the transition between the Pleistocene and the Holocene.

Global variability of daily total suspended solids and their fluxes in rivers

The daily variability of river suspended sediment concentration (Cs) and related yield (Y) is studied at 60 global stations. The data set covers natural conditions (e.g. pre-reservoir data), ranging from the humid tropics to subarctic and arid regions, located in all types of relief (yearly runoff q* from 0.1 to 55 l s � 1 km � 2 ). Basin area ranges from 64 km 2 to 3.2 million km 2 . Survey lengths range from 1 to 20 years with a median of 3 years. Median values (Cs50, q50, Y50) and discharge-weighted averages for Cs* and Y* range from 5 to 29000 mg l � 1 and 10 to 5000 kg km � 2 day � 1 , respectively. A set of indicators of variability are proposed for sediment concentration, water and sediment discharges including mean to median ratios (Cs*/Cs50, Y*/Y50), the percentage of sediment flux discharged in 2% of time (Ms2), the percentage of time necessary to carry half of the sediment flux (Ts50), and quantiles of Cs, q and Y distributions corresponding to the discharge-weighted averages. Since most of the sediment flux is discharged in less than 25% of the time, ‘‘truncated rating curves’’ metrics are proposed between the Cs vs. q relationship for periods of high flux. Temporal variability decreases with increasing basin size, lake abundance, and is higher for basins influenced by glaciermelt and snowmelt. The least variable sediment flux regimes are noted for the Mississippi at its mouth, the Rhone Lacustre, the St. Lawrence and the Somme, a medium-sized French phreatic river. The most variable flux regimes were for small- to mediumsized basins (i.e. <1000 to 10000 km 2 ) such as steep Andean Bolivian basins, Thai basins, the Eel (CA) and Walla Walla (OR) rivers. A proposed global scale typology is based on six classes key variability indicators. D 2003 Elsevier Science B.V. All rights reserved.