Carbon in surface waters

Table II, Concentrations of Dissolved Inorganic Carbon, Dissolved C02, and Dissolved Organic Carbon in Surface Waters of Lake N2...

Westerhoff, P., and D. Anning. 2000. Concentrations and characteristics of organic carbon in surface water in Arizona Influence of urbanization. Journal of Hydrology 236 202-222. 

In most models of the global C02 cycle the relationship between the partial pressure of C02 dissolved in water (pc) and the general concentration Cjj of inorganic carbon in surface waters is calculated based on the buffer coefficient ... 

Because of the high concentrations of inorganic carbon in surface waters of the ocean, it is rarely thought about as a potential hmiting factor for plankton growth. However, several recent studies taking confluent research tracks have shown elevated Die stimulates both growth and N2 fixation in Trichodesmium. 

Carbon isotopes of dissolved inorganic carbon in surface waters... 

The hydrophobic/hydrophilic fractionation of organic carbon in ground-water is different than the fractionation of organic carbon in surface water. Table 3 shows that the amount of hydrophobic material in the groundwaters studied was less than 35%, and in surface waters the amount of hydrophobic... 

Describe the speciation of carbonates in surface waters in accordance with their pH and CO2 content. 

In addition to the biological factors noted above, the isotopic composition of inorganic carbon is influenced by the exchange of carbon between surface waters and the atmosphere. Carbon isotopes are fractionated with the transfer of carbon between water and the atmosphere (Siegenthaler and Munnich 1981 Zhang et al. 1995), with equilibrium fractionation resulting in atmospheric carbon dioxide about 8%o depleted relative to the ocean. This effect is temperature dependent, with a change in fractionation of approximately -0.1%o per K (Mook 1986). Thus, at equilibrium, DIC in colder waters is enriched in C relative to warmer waters. In natural waters, the time required for isotopic equilibration is slow relative to the residence time of carbon in surface waters... 

They constitute 75% w/w of the organic matter in most soils and 50% of the organic carbon in surface waters. Humic substances are composed of complex heterogeneous mixtures of organic compounds and are characterized as being yellow to brown in color, of high relative molecular mass, and refractory. Unlike many other natural organic products, they cannot be described in terms of unique chemical structures and are operationally defined by the technique used for their extraction and fractionation. 

In addition to its presence as the free element in the atmosphere and dissolved in surface waters, oxygen occurs in combined form both as water, and a constituent of most rocks, minerals, and soils. The estimated abundance of oxygen in the crustal rocks of the earth is 455 000 ppm (i.e. 45.5% by weight) see silicates, p. 347 aluminosilicates, p. 347 carbonates, p. 109 phosphates, p. 475, etc. 

This frontier s practical opportunities were first developed with submarines, which until the nuclear ones were limited to depths of only a few hundred feet. Many thousands of feet can now be navigated. The crushing pressures below the surface, which increase at a rate of about V2 psi per foot of depth, make corrosion a major threat to the operation and durability of many materials. For example, the life of uncoated magnesium bolts in contact with steel nuts is less than seventy-two hours, aluminum buoys will corrode and pit after only eleven months at just four hundred feet, and low-carbon steel corroded at a rate one-third greater than in surface waters. 

Oceanic surface waters are efficiently stripped of nutrients by phytoplankton. If phytoplankton biomass was not reconverted into simple dissolved nutrients, the entire marine water column would be depleted in nutrients and growth would stop. But as we saw from the carbon balance presented earlier, more than 90% of the primary productivity is released back to the water column as a reverse RKR equation. This reverse reaction is called remineralization and is due to respiration. An important point is that while production via photosynthesis can only occur in surface waters, the remineralization by heterotrophic organisms can occur over the entire water column and in the underlying sediments. 

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today s oceans. Below the lysocline is the level where no carbonate remains in the sediment this level is termed the carbonate compensation depth. 

Dissolved humic substances (DHS) are the main constituents of the dissolved organic carbon (DOC) pool in surface waters (freshwaters and marine waters), groundwaters, and soil porewaters and commonly impart a yellowish-brown color to the water system. Despite the different origins responsible for the main structural characteristics of DHS, they all constitute refractory products of chemical and biological degradation and condensation reactions from plant or animal residues and play a crucial role in many biogeochemical processes. 

Anionic surfactants are present in surface water, resulting in serious environmental pollution. Therefore, adsorption of surfactants, such as sodium dodecylsulfate [155,156], on Mg/Al LDHs has received considerable attention. Ulibarri et al. also published the results of sorption of an anionic surfactant (sodium dodecylbenzenesulfonate) from water by LDHs and calcined samples (773 K), focusing both on their potential application as a sorbent and on the possibility of their recycling [154,157]. They found that anionic exchange was complete when the interlayer anion in the LDH precursor was Cl", reaching 100 % of AEG, and calcined LDH-carbonates were better adsorbents than those derived from LDH-chloride samples, however. It was also claimed that an increase in the crystallinity of the LDH samples probably leads to better ordered calcined mixed oxides, facilitating reconstruction of the layers and enlarging the absorption capacity. 

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