Dale W. Cole

Anion mobility in soils: Relevance to nutrient transport from forest ecosystems

Nutrient transport from forest ecosystems is strongly regulated by the availability of anions in soil solution. Each of the major anions in forest soil solutions has some unique properties which affect its production and mobility. The production of bicarbonate, one of the most common anions, is regulated by soil CO2 pressure and pH. The mobility of phosphate is most strongly affected by adsorption reactions. The mobility of nitrate is regulated almost solely by biological processes, whereas chloride is relatively uninvolved in either biological or inorganic chemical reactions. Sulfate is intermediate, being involved in both biological and inorganic chemical reactions. Knowing these properties of the major anions, it is possible to assess and to predict the effects of several diverse site manipulations on soil leaching rates. Case studies from a site in Washington State consistently demonstrate the importance of accounting for bicarbonate transformations following site manipulations. Although organic anions are frequently dominant in cold-region soil solutions, very little information on the complex factors affecting their mobilities is available. Further research into organic anion mobility and futher attention to bicarbonate mobility should add greatly to the body of knowledge on nutrient transport processes in forest soils.

Sulfate mobility in an outwash soil in Western Washington

The effect of acidic precipitation on cation leaching in a second-growth Douglas-fir ecosystem at the Thompson Research Center is reviewed. Sulfate mobility and soil pH buffering power were tested by applications of heavy doses of H2SO4 to the study plot. Sulfate at high concentrations proved to be immobilized, presumably by adsorption to soil sesquioxide surfaces. Soil sulfate adsorption was determined at varying sulfate concentrations, and two mechanisms of adsorption are implied by the shapes of the isotherms.

Soil nutrient supply in natural and managed forests

Soils differ in their ability to supply the nutrients necessary to sustain forest productivity. Nutrients are added through natural processes such as weathering of primary and secondary soil minerals, mineralization of soil organic matter including the forest floor layer, fixation of nitrogen primarily through symbiotic microorganisms, and natural or induced atmospheric deposition. Nutrients become unavailable for plant uptake through immobilization by soil microorganisms and through chemical and mineralogical reactions including precipitation and adsorption reactions and ionic fixation within lattice structures of clay minerals. Losses of nutrients can take place through soil leaching and erosional processes. Nutrients can also be added or lost through human activities such as fertilization and harvesting. Nutrient supply continually shifts with the rate and direction dependent on the prevailing processes in the soil system, but subject to overriding human influence. Over relatively short periods of time, the soil nutrient supply can be subject to seasonal fluctuations. Factors affecting long-term nutrient availability are functions of soil mineralogy, the rate of mineralization of the organic matter of the soil and forest floor layer, and plant-soil relationships of the species occupying the site (deciduous vs. coniferous species, deep vs. shallow rooting, symbiotic nitrogen fixation).The long-term stability of the soil nutrient supply is of increasing concern in the face of a diminished forest land base, increased demand for forest products, and reluctance to apply nutrients to many forest areas because of environmental or economic constraints.There are questions to consider in evaluating the nutrient sustainability of forest areas if we expect to maintain the long-term nutrient stability of natural and managed forest ecosystems.

Acid precipitation and soil sulfate adsorption properties in a tropical and in a temperate forest soil

Atmospheric sulfuric acid inputs and leaching in a tropical and temperate forest are compared. In both cases, H/sup +/ is mostly removed in the forest canopy. The tropical forest appears to be accumulating SO/sub 4//sup 2 -/ whereas the temperate forest is near steady-state. The tropical soil has a high capacity permanently to retain sulfate, which is probably related to its high sesquioxide content. It is proposed that the high sesquioxide content of the tropical soil renders is very resistant to leaching by atmospheric sulfuric acid inputs.

Phosphorus cycling and soil P fractions in Douglas-fir and red alder stands

Abstract Nitrogen-fixing species can dramatically increase soil acidity and organic matter content, and potentially alter biogeochemical P dynamics. We compared ecosystem P cycling in adjacent stands of N 2 -fixing red alder ( Alnus rubra Bong.) and non-fixing Douglas-fir ( Pseudotsuga menziesii Franco) in order to determine whether P-cycling rates within stands were related to soil P forms as measured by sequential P fractionation. Above-ground annual P uptake was 61% greater in the red alder stand, although soil available P, as measured by Bray (NH 4 F–HCl) extraction, was only 10% of that found in the Douglas-fir stand. Total ecosystem P in the alder stand was only 69% of that found in the Douglas-fir stand, and could indicate a pre-establishment difference between stands. However, the percentage of total soil P released by Bray or NaOH extraction was also lower in the alder stand, which suggests that differences in total P alone did not control the patterns observed in P fractions. Concentrations of inorganic P sorbed to Fe and Al minerals and contained in Fe minerals and apatite were greater under Douglas-fir, while organic P was slightly greater under red alder. While fluxes of P in litterfall, uptake and resorption were 94, 60 and 292% higher in the alder stand, soil extractable fractions meant to represent available P were lower under alder. Static measures of available P do not appear to adequately reflect P supply, and the development of techniques to assess P turnover is needed to better understand cycling and plant availability of P.

Nitrogen balances in forest ecosystems of the Pacific Northwest

Abstract In order to understand the role of nitrogen in the forests of the Pacific Northwest, especially Douglas-fir, a great number of studies have been initiated to evaluate both static and dynamic aspects of the nitrogen balance. This paper presents a summary of many of these past results covering 20 yr research with the specific intent of defining the nitrogen economy of these systems and the long- and short-term changes that are occurring. Variations of nitrogen in both soils and vegetation are discussed with some sampling techniques applicable to coniferous forests given. It appears that the soil total nitrogen, in different soils, varies several fold more than the nitrogen in the forest crops of these soils. The dynamics of nitrogen transfer within the ecosystem, together with gains and losses from the system, are presented.

Use of municipal sludge to restore and improve site productivity in forestry: The pack forest sludge research program

Abstract Municipal wastewater residuals—sludge or biosolids—represent a major waste by-product from society that must be managed in responsible ways, and not released into aquatic systems or allowed to contaminate ground waters. Because of its high nutrient and organic matter content, sludge can be beneficially recycled into forest sites for site improvement purposes. Research to date on forest application of sludge has been very encouraging, clearly demonstrating the validity of this management technique. Forest sites typically display benefits in two ways: (1) an immediate growth response by both overstory and understory species; (2) a long-term improvement to the productivity of the site. However, for this practice to have broad utility and acceptance, it is critical that the concerns of the regulatory agencies and general public be addressed regarding public health and environmental issues through continued research. These concerns include the fate of trace metals, including movement, uptake and potential phytotoxicity, and passage into wildlife and human food cahin, the fate of pathogens, and leaching of nitrates into ground water systems. Many concerns are a result of misconceptions or misunderstandings of the potential problems involved and require working with these agencies and the general public through education and demonstration programs. This paper addresses the opportunities and problems that researchers at the University of Washington, College of Forest Resources have encountered while working in forest sludge applications during the past 20 years.

Sulfur Cycling in Five Forest Ecosystems

The cycling and retention of sulfur were studied in five forest ecosystems: a chestnut oak and yellow poplar stand on Walker Branch Watershed, Tennessee; a mixed oak stand on Camp Branch Watershed, Tennessee; and a red alder and Douglas-fir stand at the Thompson site, Washington. Calculations from foliage sulfur turnover indicate that about one-half of total sulfur input was dry in the Tennessee sites, whereas only one-tenth was dry in the Washington sites. Atmospheric sulfur inputs exceeded forest sulfur requirements in all cases, but three sites (chestnut oak, mixed oak, and red alder) showed a net ecosystem retention of atmospherically deposited sulfur. Net ecosystem sulfur retention was consistent with laboratory-determined sulfate adsorption isotherms within a given location (Walker Branch, Thompson site) but not between locations because of differing deposition histories and consequent differing degrees of soil sulfate saturation. No consistent relationships between soil sulfate adsorption capacity and other soil properties (pH, base saturation, iron, and aluminum oxides) were found.

Recovery from Acidification

Acidification and, to a lesser extent, alkalinization occur in all soils. That they do so indicates these reactions are of great importance because they affect such vital ecological processes as the solubility and exchange reactions of inorganic nutrients and toxic metals, the activities of soil animals and microorganisms, and the weathering of soil minerals.

Long-term effects of heavy applications of biosolids on organic matter and nutrient content of a coarse-textured forest soil

Abstract Long-term changes in soil properties due to a single heavy application of municipal biosolids (municipal sewage sludge) on a coarse-textured glacial outwash soil were evaluated. Study sites, located at the University of Washingtons Pack Experimental Forest, 100 km south of Seattle, were clearcut, cleared, fertilized with 500 Mg ha −1 of municipal biosolids and planted a variety of tree species in 1975. Soil samples were taken in 1990 from three biosolids-amended forest stands and adjacent unamended control sites by horizon to a depth of 185 cm. Biosolids-amended samples had higher C (139 vs. 67 mg g −1 ), N (12 vs. 3.4 mg g −1 ), P (14 vs. 2.2 mg g −1 ) and S (2.5 vs. 0.4 mg g −1 ) contents in 0–7 cm mineral soil and other surface soil horizons compared with adjacent unamended soil horizons, but showed no significant differences below 25 cm. Soil pH ranged from 0.4 to 1.0 units lower in biosolids-amended vs. unamended soil throughout the sampled soil horizon. Soil cation exchange capacity was higher in the surface soil horizons (30 vs. 18 mmol c kg −1 in 0–7 cm soil), but there were no significant differences below 50 cm. Biosolids-amended samples had higher total Ca (13 vs. 6.1 mg g −1 in 0–7 cm soil) and K (1.9 vs. 1.5 mg g −1 in 0–7 cm soil) throughout the sampled soil profile. Total Mg was relatively constant (2.0–3.0 mg g −1 ) throughout the sampled soil profile. Study results indicate that one of the primary objectives of the original biosolids application (increasing total nutrients in the rooting zone of the forest soil) extended at least 15 years from the application date.