Adsorption of Dissolved Organic Carbon and Nitrogen in Soils of a Weathering Chronosequence

Adsorption of DOM by soil has been implicated as a very important factor in controlling the loss of DOM Leaching of dissolved organic matter (DOM) and the associated from ecosystems in stream water (McDowell and Wood, nutrient elements can be a significant form of loss from developing 1984; Nelson et al., 1993; Qualls et al., 2002). Several ecosystems. We studied how the adsorption of dissolved organic C (DOC) and N (DON) changes during soil development and deterauthors have found positive correlations between pamined which soil characteristics control adsorption. We sampled 77, rameters derived from DOC adsorption experiments 255, 616, and about 1200 yr-old andesitic soils at five depths and and soil characteristics such as clay content, oxalate did adsorption isotherm experiments fit to a modified Langmuir equaextractable Al and Fe, dithionite-citrate-bicarbonate tion. We measured DOC and DON in soil solution at the 10to 20-, (DCB) extractable Fe, and surface area (Donald et al., 40-, and 150-cm soil depths during the snowmelt period to compare 1993; Moore et al., 1992; Nelson et al., 1993). Few studies with adsorption experiments. Ability of the soils to adsorb DOM inexist, however, on the adsorption of DON (Kaiser and creased with soil age. Regression analyses were performed between Zech, 2000b) despite N being the limiting nutrient in adsorption capacity or the null point concentration of either DOC or most terrestrial ecosystems (Schlesinger, 1997). DON and the independent variables soil organic C (SOC), N, alloWhile several authors have studied the adsorption of phane, oxalate extractable Fe, crystalline Fe, and specific surface area. The best relationships were found between adsorption capacity and DOC to ferrihydrite and aluminum hydroxides, much the allophane/SOC ratio (r2 0.88), and between the null point less is known about the adsorption of DOC to allophane, concentration of DOC or DON and the SOC/allophane ratio (DOC: an aluminosilicate. Allophanic soils are known to accur2 0.85; DON: r2 0.77). Stepwise multiple regression indicated mulate organic matter rapidly and this has been attribthat oxalate-extractable Fe and specific surface area contributed only uted to their large surface area and positive surface small increases in the multiple R2. High correlations between the nullcharge (Wada, 1989; Parfitt, 1990). The short-rangepoint adsorption of DOC or DON and the DOC (r2 0.92) or DON order aluminosilicates, allophane, and imogolite strongly (r2 0.86) field soil solution concentrations indicated that results adsorb DOC (Parfitt et al., 1977; Yuan et al., 2000). obtained in laboratory experiments were applicable to field condiDahlgren and Marrett (1991) attributed the strong adtions. The cause of the increased ability of the soils to adsorb and sorption of DOC in the Bs horizon of a volcanic Spodoretain DOM during soil development appears to be an increase in allophane concentrations. sol to high concentrations of ferrihydrite and imogolite. Dahlgren et al. (1991) also found that most DOC was removed from solution in the A horizon of a nonallophanic Andisol in Japan. The mechanism of adsorption D organic matter plays an important role of organic matter to allophane surfaces is probably by in soil development and influences the potential ligand exchange. for leaching of nutrient elements (Duchaufour, 1982). Carbon and N cycles change during ecosystem develDissolved organic N is the dominant form of dissolved opment (Dickson and Crocker, 1953; Sollins et al., 1983). N lost from many minimally disturbed forest ecosystems Soils of the Mt. Shasta soil weathering chronosequence (Perakis and Hedin, 2002; Qualls et al., 2002). In stream were aged at 77, 255, 616, and 1200 yr in 2001 with C water from 100 unpolluted watersheds in Chile and Arand N accretion rates increasing linearly with age by gentina, DON comprised on average 80% of the total 121 kg C ha 1 yr 1 and 4.5 kg N ha 1 yr 1, respectively N. In streams draining 19 minimally disturbed waterover the first 616 yr (Lilienfein et al., 2003). Concentrasheds in the USA, with atmospheric N deposition rates tions of allophane and ferrihydrite as well as SSA, also ranging from 1.0 to 7.5 kg ha 1 yr 1, DON comprised increased with soil age. As we have discussed, there are 47% of total N and 63% of total dissolved N (Lewis, many factors that influence adsorption of DOM in soils, 2002). In some areas of high atmospheric N deposition, and these factors tend to change during soil developnitrate dominates the total dissolved N in stream water ment. Consequently, we hypothesized that adsorption (Perakis and Hedin, 2002; Lewis, 2002) or water draincharacteristics would differ between the soils of our ing from the forest floor (Michalzik and Matzner, 1999), chronosequence. but DON can still be the dominant form (59%) in some The aim of this work was to determine: (i) how the watersheds with high N deposition (Campbell et al., 1999). adsorption of DOC and DON in andesitic soils changes with soil development, (ii) which soil characteristics conJ. Lilienfein, R.G. Qualls, S.M. Uselman: Dep. of Environmental and trol the adsorption of DOM in these soils, (iii) if there Resource Sciences, MS 370, University of Nevada-Reno, Reno, NV are any differences in the adsorption characteristic of 89557; S.D. Bridgham: Ecology and Evolutionary Biology, University of Oregon, Eugene, OR 97403. Received 15 Oct. 2002. *CorrespondAbbreviations: DOC, dissolved organic carbon; DOCnp, null-point ing author ([email protected]). DOC concentration; DOM, dissolved organic matter; DON, dissolved organic nitrogen; DONnp, null-point DON concentration; Fe0, oxalate Published in Soil Sci. Soc. Am. J. 68:292–305 (2004).  Soil Science Society of America extractable iron; IM, initial mass; SOC, soil organic C; SSA, specific surface area; TN, total nitrogen. 677 S. Segoe Rd., Madison, WI 53711 USA