Elisa M. D'Angelo

Regulators of heterotrophic microbial potentials in wetland soils

Potential rates of aerobic respiration, denitrification, sulfate reduction and methanogenesis were investigated in 10 different wetland soils with a wide range of biogeochemical characteristics, with the objective of determining relationships between process rates and soil properties. Electron acceptor amendments to methanogenic soils caused gradual (1–13 d) to immediate transitions in electron flow from methanogenesis to alternate electron acceptors. Rates of organic C mineralization ranged between 0.2 and 34 μmol C g−1 d−1 and averaged three times faster with O2 as compared to alternate electron acceptors. There was no significant difference between rates of organic C mineralization (CO2+CH4 production) under denitrifying, sulfate-reducing and methanogenic conditions, indicating that soil organic carbon availability was similar under the different anaerobic conditions. Rates of electron acceptor consumption ranged between 1 and 107 μmol g−1 d−1 for O2, 0.5 and 9.3 μmol g−1 d−1 for NO3−, 0.1 and 11.1 μmol g−1 d−1 for SO42− and 0.1 and 6.2 μmol g−1 d−1 for CO2. Heterotrophic potentials in wetland soils were strongly correlated with inorganic N and several available C indices (total, dissolved and microbial C), but not with pH or dissolved nutrients (P, Ca2+, Mg2+, Fe(II)). Microbial activity–soil property relationships determined in this study may be useful for predicting the fate of pollutants that are influenced by microbial oxidation–reduction reactions in different types of wetland soils.

SOIL CARBON AND MICROBIAL COMMUNITIES AT MITIGATED AND LATE SUCCESSIONAL BOTTOMLAND FOREST WETLANDS

The practice of wetland mitigation has come into question during the past decade because the relative capacity of the mitigated wetlands to perform normal wetland functions is mostly unknown. In this study, we wanted to determine whether soil microbial communities were significantly different in early successional mitigated wetlands (<10 years) (ES) compared to late successional bottomland hardwood forest wetlands (LS) due to differences in soil properties, such as carbon quality and storage and water-holding capacity. Carbon storage in litter and soil was 1.5 times greater in LS wetlands than ES wetlands. Soil water-holding capacity was significantly greater in LS wetlands and was related to soil organic C content (r2=0.87, p-value=0.0007). Gravimetric water content was a moderately strong predictor of microbial respiration (r2=0.55-0.61, p-value=0.001-0.0004) and microbial biomass (r2=0.70, p-value=0.0019). Anaerobic microbial groups were enriched in soils from LS wetlands in both the dry and wet seasons, which suggested that LS soils were wetter for longer periods of the year than ES soils. The capacity of these wetlands to support anaerobic microbial processes depends on soil water retention characteristics, which were dictated by organic matter content. As an integrator of microbial growth conditions in soils, determination of microbial community composition by phospholipid fatty acid (PLFA) analysis may be an important new tool for monitoring successional development of compensatory mitigation wetlands.

Arsenic species in broiler (Gallus gallus domesticus) litter, soils, maize (Zea mays L.), and groundwater from litter-amended fields

Manure and bedding material (litter) generated by the broiler industry (Gallus gallus domesticus) often contain high levels of arsenic (As) when organoarsenical roxarsone and p-arsanilic acid are included in feed to combat disease and improve weight gain of the birds. This study was conducted to determine As levels and species in litter from three major broiler producing companies, and As levels in soils, corn tissue (Zea mays L.), and groundwater in fields where litter was applied. Total As in litter from the three different integrators ranged between <1 and 44 mg kg(-1). Between 15 and 20% of total As in litter consisted of mostly of arsenate, with smaller amounts of roxarsone and several transformation products that were extractable with phosphate buffer. Soils amended with litter had higher levels of bioavailable As (extractable with Mehlich 3 solution and taken up by corn leaves). Arsenic concentrations in plant tissue and groundwater, however, were below the World Health Organization thresholds, which was attributed to strong sorption/precipitation of arsenate in Fe- and Al-rich soils. Ecological impacts of amending soils with As-laden litter depend on the As species in the litter, and chemical and physical properties of soil that strongly affect As mobility and bioavailability in the environment.

Influence of potassium supply on growth and nutrient storage by water hyacinth

The net productivity and nutrient storage of potassium (K), nitrogen (N), and phosphorus (P) by water hyacinth (Eichhornia crassipes [Mart.] Solms) were evaluated at several K concentrations in the culture medium (between 2 and 52 mg K liter−1) using 1000-liter outdoor tanks for a period of about 4 months. Maximum plant biomass (3·1 kg (dw) m−2) was reached at culture medium K concentrations of 12–52 mg K liter−1. Potassium storage in water hyacinth tissue steadily increased at K supplies of up to 52 mg K liter−1 with a maximum tissue K content of 72 mg K g−1. Maximum N and P storage in the plant biomass was reached at K concentrations of 12 and 22 mg K liter−1, respectively; further increases in K concentration did not increase either N or P storage.

Biomass yield and nutrient removal by water hyacinth (Eichhornia crassipes) as influenced by harvesting frequency.

Abstract The effects of harvesting frequency on productivity, nutrient storage and uptake, and detritus accumulation by water hyacinth ( Eichhornia crassipes /Mart/ Solms) cultured outdoors in nutrient-enriched waters were evaluated for a period of 13 months. Significant differences in hyacinth standing crop and productivity were measured with harvesting regimes of 1, 3 (harvest at maximum density) and 21 harvests over a 13-month period. The average plant standing crop decreased from 65 to 20 kg (fresh wt) m −2 for systems with 1 and 21 harvests, respectively. Total harvested plant biomass was 67 kg (fresh wt) m −2 , 110 kg (fresh wt) m −2 and 162 kg (fresh wt) m −2 for 1, 3 and 21 harvests, respectively. The mean net productivity increased from 7·7 to 16·5 and 24·5 g (dry wt) m −2 day −1 for 1, 3 and 21 harvests, respectively. Nutrient storage in water hyacinth biomass (live, dead and detrital) at the end of the study decreased from 93 to 46 and 30 g N m −2 , and from 20 to 12 and 5 g P m −2 , for 1, 3 and 21 harvests, respectively. For the system with one harvest, 46% of the stored N and 25% of the stored P were recovered in dedrital tissue at the bottom of the tank. For the systtem with 21 harvests, only 11% of the stored N and 15% of the stored P were recovered in detrital tissue at the bottom of the tank. Ammonium-N and soluble reactive P concentrations in the water column were significantly higher for the treatment with one harvest compared to the treatments with 3 and 21 harvests.

PHOSPHORUS SORPTION CAPACITY AND EXCHANGE BY SOILS FROM MITIGATED AND LATE SUCCESSIONAL BOTTOMLAND FOREST WETLANDS

A central tenet of wetland mitigation is that replacement wetlands can sequester nutrients and perform other functions at the same level as natural wetlands. This study evaluated phosphorus (P) sorption capacity and P exchange in flooded soil microcosms obtained from eight early successional (ES) mitigated and eight late successional (LS) bottomland forest wetlands in western Kentucky, USA. The LS soils had three times greater capacity to remove and retain soluble inorganic P than ES soils, which was mostly due to higher amounts of amorphous aluminum (Al) oxides (oxalate extractable), organically-bound Al (CuCl2 extractable), and organic carbon in LS soils. Phosphorus exchange rates between the soil and water column were not significantly different in LS and ES microcosms, but rates in both systems were strongly related to the molar ratio of Mehlich III extractable P to Al + Fe in the soil (r2=0.64). Relationships between P sorption/exchange and organic C, Mehlich III- and oxalate-extractable forms of P, Al, and Fe determined in this study could be useful for (i) identifying suitable mitigation sites that would be P sinks rather than P sources to the water column and (ii) determining replacement ratios that would fairly compensate for P retention capacity losses caused by destruction/alteration of Kentucky bottomland hardwood forest wetlands.

Urea losses in flooded soils with established oxidized and reduced soil layers

SummaryLaboratory batch incubation experiments were conducted to determine in fate of urea-15N applied to floodwater of four rice soils with established oxidized and reduced soil layers. Diffusion-dependent urea hydrolysis was rapid in all soils, with rates ranging from 0.0107 to 0.0159 h-1 and a mean rate of 0.0131 h-1. Rapid loss of 53%–65% applied urea-15N occurred during the first 8 days after application, primarily by NH3 volatilization. At the end of 70 days, an additional 20%–30% of applied urea-15N was lost, primarily through nitrification-denitrification processes. The soil types showed significant differences in total applied urea-15 recovery. Conversion of urea-15N to N2-15N provided direct evidence of urea hydrolysis followed by nitrification-denitrification in flooded soils.

Effect of aerobic and anaerobic conditions on chlorophenol sorption in wetland soils

ant between the solid phase and dissolved phase (sorption), which is governed by the physical and chemical Sorption of four chlorophenols (CPs) was studied in ten wetland properties of the solute, the sorbent, and the solvent. soils with organic C contents between 1 and 44%, which were incuMuch research on organic pollutant sorption has dembated under aerobic or anaerobic conditions to simulate wetland conditions. The objectives of the study were to (i) determine the influence onstrated a strong link between the distribution ratio of aerobic and anaerobic processes on sorption, and (ii) develop sorp(Kp) and the lipophilicity of hydrophobic organic polluttion models to predict the distribution coefficient based on chemical ants, as expressed by its Kow, and the fractional amount characteristics of soils and compounds. Aerobic soils consistently had of organic C of the sorbent (foc): lower pH than anaerobic treatments, which was a function of the amount of oxidizable constituents present in the sample. Depending Kp foc a(Kow) [1] on the pKa of the compound relative to the pH shift, a greater fraction where a and b are empirical constants that differ deof the CP was in the neutral form in the aerobic treatments, which pending primarily on the nature of the pollutant. The was sorbed to a much greater extent than the ionic form (by about relationship has been very useful for predicting sorption 25 times). The organic C normalized distribution coefficient (Koc) was of many hydrophobic organic pollutants by a wide varistrongly related to the octanol-water distribution coefficient (Kow) and soil pH. Sorption models accurately predicted distribution coefficients ety of sorbents; on occasion, however, it has been found within a factor of 2 from the Kow and pKa of the compounds and the to be deficient for ionizable organic compounds such pH and organic C content of the sorbent. The role of sorption on CP as CPs. retention was partially negated by the formation of the nonseparable In studies on the sorption of CPs in soils and sediphase, which composed up to 8.6% of the total solid mass (depending ments, Schellenburg et al. (1984) and Lagas (1988) on the soil redox status) and had similar distribution coefficients as found that the model for hydrophobic compounds had the separable phase. This study demonstrated that microbial redox limited application because it did not account for the processes significantly influenced the soil properties and CP retention contribution of both the neutral species and the phecharacteristics, and should be considered when designing a bioremedinolate anion to overall sorption. Shimizu et al. (1992) ation plan for these compounds. derived a model that accounted for the contribution of both species to the distribution coefficient of PCP (pKa 4.74): C are common contaminants in soils, sediments, surface waters, and groundwater, largely Kp Ko p φ K p (1 φ) [2] because of their worldwide utilization in the last 50 yr where Ko p and K p are the distribution coefficients, and as wood preservatives, and general biocides in industry φ and 1 φ are the fractional amounts of the neutral and agriculture (ATSDR, 1998). Chlorophenols are also species and phenolate species, respectively. They found by-products of pulp mill effluent chlorination (Paasithat pentachlorophenolate sorption accounted for varta et al., 1983; Kringstad and Lindstrom, 1984), and 90% of overall sorption when the pH was 6, even chloro-aromatic transformations (Mikesell and Boyd, though the distribution coefficient for the anion (K p ) 1985). Pentachlorophenol (PCP) is toxic to all life forms, was up to 60 times lower than for the neutral species is commonly found at National Priorities List sites (Ko p). They also observed that outside the pH range 6 (about 20%), and is classified as a priority pollutant by to 8, there were considerable changes in the chemical the USEPA. nature of the sorbent and solvent that decreased the Chlorophenols are subject to several abiotic and accuracy of the model. They warned that the model biotic processes, including photodegradation (Wong should be appropriately amended under these condiand Crosby, 1981), volatilization (Pignatello et al., 1983), tions. plant and animal uptake (Weiss et al., 1982; Larsson et In natural ecosystems, microbial breakdown of plant al., 1993), and microbial degradation (Laine and Jorgendetritus, solubilization of humic substances, erosion, resen, 1997; D’Angelo and Reddy, 2000). A major factor suspension, and bioturbation events can contribute sigcontrolling these processes is distribution of the pollutnificant levels of dissolved and suspended organic and E. D’Angelo, Univ. of Kentucky, Soil & Water Biogeochemistry Lab., Abbreviations: CP, chlorophenol; CR, Crowley soil; DCP, 3,5-dichloDep. of Agronomy, N-122 Agricultural Science Building North, Lexrophenol; DOC, dissolve organic C; HLPI, Houghton Lake Peat– ington, KY 40546-0091; K.R. Reddy, Univ. of Florida, Soil and Water impacted by domestic waste; HLPU, Houghton Lake Peat–unimScience Dep., 106 Newell Hall, P.O. Box 110510, Gainesville, FL pacted by domestic waste; KOC, organic C normalized sorption 32611-0510. Florida Agricultural Experiment Station Journal Series coefficient; KOW, octanol water distribution coefficient; Kp, linear sorpNo. R-09194. Received 13 Feb. 2001. *Corresponding author (edangelo@ tion coefficient; LSM, Louisiana salt marsh; PCP, pentachlorophenol; uky.edu). TAL, Talladega soil; TeCP, 2,3,4,5-tetrachlorophenol; TCP, 3,4,5trichlorophenol. Published in Soil Sci. Soc. Am. J. 67:787–794 (2003).

Carbon Sequestration Processes in Temperate Soils With Different Chemical Properties and Management Histories

A variety of biochemical, physical, and chemical processes protect organic carbon from decomposition in soils; however, the influences of land use and soil properties on the relative importance of these processes are not well known. In this study, amounts of organic C in unprotected, physically protected, and 10 chemically and biochemically protected pools in agricultural and forest soils and soils with different mineralogical composition were investigated using a combination of organic C mineralization and sequential chemical extraction techniques. Results from the mineralization procedure with intact and disrupted aggregates showed that unprotected, physically protected, and biochemically/chemically protected organic C made up 1 to 7%, 0.1 to 2%, and more than 90% of soil organic C, respectively. The most important biochemically and chemically protected organic C pools, as revealed by the sequential extraction procedure, were (i) acid-hydrolyzable organic C, representing fulvic acid, amino sugars, and polysaccharides (34-58% of soil organic C), (ii) pyrophosphate-extractable organic C, representing compounds complexed with Fe and Al cations and oxyhydroxides and mineral surfaces (12-21%), (iii) nonextractable organic C, representing lignin and humin (7-29%), and (iv) base-hydrolyzable organic C, representing humic acids (3-21%). Cultivation of soils significantly decreased the amount of organic C in all pools except for those in the physically protected, humic acid and mineral-intercalated fractions. Results from the study showed that organic C in these soils was protected primarily by a combination of biochemical and chemical processes and that these were dictated by land management practices (organic matter inputs and quality) and soil chemical properties (levels of Fe and Al cations and oxyhydroxides).