Runoff chemistry

The processes through which rainfall is turned into runoff, together with the nature of the material through which water moves, control the chemical characteristics of streamflow. Specific runoff mechanisms operating in a landscape control the flowpaths by which water moves through the landscape. Flowpath-depen-dent differences, such as the total time that water spends in contact with different soil horizons or bedrock (residence time), can strongly influence runoff amounts and timing, the relative contribution of event (new) versus stored (old) water, and runoff chemistry. 

The combined influences of runoff generation mechanisms, runoff flowpaths, and soil properties together control runoff chemistry. In spite of the wide range of interactions that characterize terrestrial environments, a few broad generalities can be offered, as the chemical composition of streamflow typically contains... 

Stage 4 marks the runoff chemistry returning to stage 1 values and once again the rate of export equals the weathering rate. However, BS of the soil is now lower and episodic acidihcation is easily induced. 

Hultberg H. and Grennfelt P. (1992) Sulfur and sea-salt deposition as reflected by throughfaU and runoff chemistry in forested catchments. Environ. Pollut. 75, 215-222. 

Wright R. E. (1998) Effect of increased carbon dioxide and temperature on runoff chemistry at a forested catchment in southern Norway. Ecosystems 1(2), 216—225. 

Although the results reported below are not yet sufficient in themselves to produce a materials damage function (i.e., an equation relating damage to one or more environmental factors), they can be used to help evaluate and perhaps modify functions that have been proposed on other bases. This paper tentatively concludes that stone material is lost from skyward-facing surfaces at a rate equivalent to about 15 micrometers of surface recession per year at the field test sites and that an approximate agreement with the results of Reddy s runoff chemistry is found where comparison is now possible, i.e., at sites having low ambient concentrations of sulfur dioxide. 

For limestone, the weight losses were far in excess of expectations based on direct measurements of recession and on runoff chemistry. 

Emphasis in the field tests of stone briquettes is on the long-term damage suffered by exposed marble and limestone. Because the pH variations for the existing test sites are principally variations between one rain and the next rather than from site to site, the separation of the pH effect cannot presently be achieved (except possibly in runoff chemistry on individual rains). The annual... 

Because the chemistry of stream water reflects its source in the soil profile, detailed studies of runoff chemistry from small basins should be very useful in delineating the ways and rates at which various elements are released in weathering. In the Mattole basin, it is apparent that groundwater inflow to the stream at the end of the dry season has a relatively high pH ( 8), relatively high dissolved salts (Spec. Cond. 300), and rather low silica (7-8 mg/liter). Thus, the alkalis and alkaline earths are preferentially removed as compared with silica from rock minerals at or near the water table. In surface soils, however, during storm runoff, quite different conditions prevail. The pH of the water may at first be low (5=t), silica release is relatively rapid (8-12 mg/ liter), and alkalis and alkaline earths are removed rather slowly (Spec. Cond. 70-150). The result is that the rate of silica removal compared... 

River runoff and i situ production are the major sources of U-Th series nuclides (Table 1) to the oceans. The concentrations of the various U-Th series nuclides in rivers vary considerably and depend upon several factors prime among them being their chemical reactivity [13], the chemistry of river water, and the nature of the river bed. 

The chemistry of mixolimnion (0-20m) appears to be controlled by acidic runoff and seepage from the overburden, which contains fragments of sulfide minerals. 

PROFILE is a biogeochemical model developed specially to calculate the influence of acid depositions on soil as a part of an ecosystem. The sets of chemical and biogeochemical reactions implemented in this model are (1) soil solution equilibrium, (2) mineral weathering, (3) nitrification and (4) nutrient uptake. Other biogeochemical processes affect soil chemistry via boundary conditions. However, there are many important physical soil processes and site conditions such as convective transport of solutes through the soil profile, the almost total absence of radial water flux (down through the soil profile) in mountain soils, the absence of radial runoff from the profile in soils with permafrost, etc., which are not implemented in the model and have to be taken into account in other ways. 

The relatively simple interaction between metal ions and particles as described in Fig. 11.4 permits the application of this model (Eqs. 11.2 - 11.5) to make estimates on changes in distribution between particular and dissolved phase and in metal speciation as a function of variations in river chemistry (e.g., a change in turbidity, i.e., in particle concentration as a consequence of increased runoff, or a change in complex forming capacity by complex forming pollutants or a change in pH). 

Analytical Chemistry Drift, Runoff, Volatilization, and Accumulation... 

Biogeochemists are working to construct numerical models that include all of these interlinked feedbacks to explain how the chemistry of seawater has changed over time in response to various forces, including tectonism, biological activity, ocean-atmosphere interactions, crustal weathering, and river runoff To incorporate all of these linkages into a numerical multielemental model of seawater is very complex because most of... 

The overall effect of the terrestrial weathering reactions has been the addition of the major ions, DSi, and alkalinity to river water and the removal of O2, and CO2 from the atmosphere. Because the major ions are present in high concentrations in crustal rocks and are relatively soluble, they have become the most abimdant solutes in seawater. Mass-wise, the annual flux of solids from river runoff (1.55 x 10 g/y) in the pre-Anthropocene was about three times greater than that of the solutes (0.42 x 10 g/y). The aeolian dust flux (0.045 X 10 g/y) to the ocean is about 30 times less than the river solids input. Although most of the riverine solids are deposited on the continental margin, their input has a significant impact on seawater chemistry because most of these particles are clay minerals that have cations adsorbed to their surfaces. Some of these cations are desorbed... 

Bayless, E. R. Olyphant, G. A. 1993. Acidgenerating salts and their relationship to the chemistry of groundwater and storm runoff at an abandoned mine site in southwestern Indiana, USA. Journal of Contaminant Hydrology, 12, 313-328. 

Pinder, G. F. Jones, J. F. 1969. Determination of the groundwater component of peak discharge chemistry of total runoff. Water Resouces Research, 5, 438-445. 

Geochemical modeling is often used to identify the compounds that primarily control the chemistry of arsenic in aqueous solutions. Modeling studies indicate that the arsenic concentrations of Kelly Lake, Ontario, Canada, are controlled by the precipitation and dissolution of Fe(II) arsenates rather than calcium or Fe(III) arsenates (Sadiq et al., 2002). The arsenic in the lake originated from runoff from the nearby Sudbury mining district and airborne particles from local ore smelters (Sadiq et al., 2002). 

The flux of DOC from terrestrial landscapes to surface runoff has wide-ranging consequences for aquatic chemistry and biology. DOC affects the complexation, solubility, and mobility of metals (Perdue et al., 1976 Driscoll et al., 1988 Martell et al., 1988 see Chapter 8) as well as the adsorption of pesticides to soils (Senesi, 1992 Worrall et al., 1997). Formation of trihalomethanes when drinking water is disinfected with chlorine, a worldwide threat to water supplies, is also linked to DOC concentrations (Siddiqui et al., 1997). DOC attenuates ultraviolet-B (UV-B) radiation and thus provides some protection to aquatic biota from exposure to harmful UV radiation (e.g., Williamson and Zagarese, 1994). Finally, DOC affects the heat balance and thus stratification in lakes, which is an important constraint for aquatic organisms with limited habitats (Schindler et al., 1996, 1997). 

Bailey, H.C., Elphick, J.R., Potter, A., Chao, E., Konasewich, D. and Zak, J.B. (1999) Causes of toxicity in stormwater runoff from sawmills, Environmental Toxicology and Chemistry 18, 1485-1491. 

---