Delbert L. Mokma

Regional scale analysis of denitrification in north temperate forest soils

Large scale analyses of biogeochemical processes are necessary for understanding anthropogenic effects on global climate and environmental quality. Regional scale estimates of denitrification from forest soils in southern lower Michigan USA were produced by stratifying the region into landscape experimental units using soil texture and natural drainage classes, and extrapolating data to larger areas using a geographic information system (GIS). Previous landscape-scale research established relationships between soil texture and drainage and denitrification and quantified annual denitrification N loss in nine soil texture/drainage groups. All forest soils within the region (64 series) were assigned to one of these nine groups based on their texture and drainage characteristics and were assigned an annual denitrification N loss value. A regional estimate of denitrification was produced by multiplying the areal extent of each of the nine soil groups by their annual denitrification N loss value. Loam-textured soils underlie 47% of the regional forest and accounted for 73% of the forest denitrification. Sandy soils were found under 44% of the regional forest but produced only 5% of the regional denitrification. Clay loam soils underlie 9% of the regional forest and produced 22% of the denitrification. Annual denitrification N loss for the region was estimated as 1.4×107 kg N/yr. We used denitrification enzyme activity (DEA) as a proxy for annual denitrification N loss to determine if the relationship between denitrification and soil texture and natural drainage that we observed at the landscape scale held up at the regional scale. DEA was measured in 22 soils across the region and was strongly related to soil texture and natural drainage (r2=0.61), suggesting that extrapolation of data from the landscape to the regional scale was justified.

A numerical index of Podzol and Podzolic soil development

A numerical index of soil development, the POD Index, was developed and applied to 723 pedons of United States soils that either exhibit, or are developing, Podzol (Spodosol) morphology. The index is determined solely from morphologic (field) criteria, and provides the first soil development index for Podzol and Podzol-like soils that does not use chemical data. The index assumes that pedogenesis and profile development in these soils produces the following morphologic changes; (1) the E (eluvial) horizon becomes “whiter,” (2) the B (illuvial) horizon becomes “redder” and “darker,” and (3) the number of B subhorizons increases. Results indicated that the index was useful for differentiating between non-Podzols and Podzols, and between Entic and Typic subgroups of Spodosols. A comparison of POD Indices for Spodosols of differing drainage revealed that maximum development occurred in wet soils (somewhat poorly drained), with minimal development on the driest sites. This finding is consistent with current th...

Differentiation of surficial glacial drift in southeastern Michigan from 7-Å/10-Å X-ray diffraction ratios of clays

Woodfordian till deposited by the juxtaposed Saginaw and Huron-Erie glacial lobes in southeastern Michigan appears similar in many respects but may be differentiated on the basis of certain mineralogical characteristics of clay-sized particles. This is apparent from X-ray diffractograms of basally oriented, magnesium-saturated, and glycerol-solvated specimens. Thirty-five till samples from the converging Kalamazoo (Saginaw lobe) and Mississinewa (Huron-Erie lobe) moraines and their interlobate tract have 7-A/10-A peak height ratios that differ significantly according to provenance. Every sample from locations within and proximal to the Kalamazoo moraine has a ratio of 0.91 or more. All but one of the samples from the Mississinewa moraine and areas to the east have ratios less than 0.91. Data from several other sources indicate that the same relationships also exist on a larger scale in southeastern Michigan. The findings are consistent with previous interpretations of the area9s geology and may provide a reliable basis for the placement of the surficial boundary between drifts deposited in a complex interlobate area.

Predicting the Onset of Metal Leaching from Land Application of Wastewater Using Soil Sensors and Microbial Community Analyses

Several food processors use land application to treat process wastewater. Excessive organic and hydraulic loadings can result in environmental harm through surface water runoff and groundwater contamination. A recently recognized impact is the mobilization of heavy metals from the soil. The metals serve as the electron acceptors when oxygen is depleted and anaerobic microorganisms predominate. The objective of this research is to determine the feasibility of using moisture and oxygen sensors to predict changes in the soil environment resulting from the addition of wastewater that leads to anaerobic conditions. Eight 46-cm diameter, 0.97-m tall columns were constructed, filled with clean sand, and instrumented with sensors at three depths. Three organic loadings were tested: 7-, 56-, and 112-g biological oxygen demand/ m2 /day . The sensors predicted soil conditions that led to the leaching of Mn and chemical oxygen demand from the more highly loaded columns. Trends from the phospholipid and respiratory qu...

Formation of a cultivated Spodosol in East-Central Finland

Karkeille hietamaille syntyneet podsolit ovat Suomen kehittyneimpia maannoksia. Niita tutkimalla saadaan uutta tietoa taman koko pohjoisella havumetsavyohykkeellayleisen maannostyypin kehittymiseen johtaneista prosesseista, joista edelleenkin vallitsee erilaisia kasityksia. Taman tutkimuksen kohteena oli Sotkamossa karkealla hietamaalla oleva noin 50 vuotta viljelty maa, joka on ollut kuivillaan noin 10 700 vuotta. Muokkauskerroksen alapuolella oli huuhtoutumiskerros (valkomaa), joka sisalsi lahes pelkkaa kvartsihiekkaa. Sen alapuolella oli noin 10 cm paksu rautapalsi eli iskostunut horisontti, johon ylempaa orgaanisina kompleksiyhdisteina huuhtoutuneet rauta ja alumiini ovat saostuneet. Mikroskoopilla voidaan nahda, miten nama saostuneet ainesosat peittavat kvartsihiekan jyvaset ja sitovat ne yhteen. Tassa horisontissa oli erittain runsaasti heikosti kiteytynytta rautaoksidia, joka on uutettavissa ammoniumoksalaattiliuoksella, kun taas valkomaassa tallaista rautaa oli erittain vahan. Rikastumiskerroksen alumiinista valtaosa oli pyrofosfaattiin uuttuvassa, oletettavasti orgaanisen aineksen sitomassa muodossa, mika viittaa aineiden kulkeutuneen tahan horisonttiin nimenomaan kelaatteina eika epaorgaanisina kolloideina. Syva kynto on nostanut valkomaata ja kappaleita rikastumiskerroksen iskostumasta myos muokkauskerrokseen. Rikastumiskerroksen alapuolella kvartsihiekkajyvasten pinnoilla ei ollut paljonkaan rautasaostumia, mutta mikroskoopilla nakyi runsaasti rapautumatonta biotiittia. Rikastumiskerroksen rauta lienee suureksi osaksi peraisin juuri biotiitista, joka on kokonaisuudessaan rapautunut pintamaasta. Vahemman biotiittia sisaltaviin maihin ei todennakoisesti kehity nain vahvaa rikastumiskerrosta maan pienemman rautapitoisuuden takia. Podsoloituminen on luultavasti pysahtynyt sen jalkeen, kun maa on otettu viljelyyn ja sen pintaosien pH on kalkituksen seurauksena noussut.