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Thermokarst (thaw) lakes are an important source of atmospheric CH4; however, few studies have examined the composition and biodegradability of their sediment organic matter (OM). We have quantified the (i) composition of bulk sediment OM (bulk SOM) using pyrolysis gas chromatography-mass spectrometry (GC-MS) and (ii) statistical relationships between bulk SOM properties and anaerobic incubation CH4 production rate at 3 °C in sediment core samples from a thermokarst lake system. The study extended through the full vertically-thawed profile (0–550 cm) of Vault Lake, a small thermokarst lake near Fairbanks, Alaska, USA, and into the permafrost thawing beneath the lake (551–590 cm). Compared with the underlying mineral-dominated sediments (153–590 cm depth in core), the surface organic-rich sediment horizon (0–152 cm) had higher CH4 production rate, greater substrate availability indicated by percent organic carbon and total nitrogen, and greater proportions of terrestrially-associated bulk SOM compounds (alkanes, alkenes, lignin products, and phenols and phenolic precursors). Correlation and principal component analyses indicated that CH4 production potential values measured in the core were positively associated with initial substrate availability and terrestrially-derived OM compounds. We observed positive correlation (p ⩽ 0.05) between CH4 production and bulk SOM compounds classified as phenols and phenolic precursors, a pattern different from previously observed relationships in natural aquatic anaerobic environments.

Cold (22 oC) and hot water (80 oC) extractions have been used to estimate labile organic carbon (C) and nitrogen (N) in soils. Sequentially extracted cold and hot water organic matter (WEOM) from 14 Alaskan soils under different land uses were characterized by ultraviolet and fluorescence spectroscopies. Compared to cold WEOM, the ultraviolet (UV) absorptivity at 254 nm and fluorescence index were significantly (P < 0.05) decreased in hot WEOM of all soils. The biodegradability, assessed in a 21-d solution incubation, of hot WEOC and WEON was significantly (P < 0.05) greater than that of cold WEOC and WEON in all soils. The biodegradability of cold or hot WEOC was correlated with the protein-like component, indicating that a protein-like fluorophore is a labile fraction in both cold and hot WEOM pools. Information derived from this work contributed to better understanding of subarctic soil WEOM properties and their biodegradability.

Land use conversion induces quantitative change of soil water-soluble organic matter (WSOM), but knowledge of such change is still limited. In this study, field moist and air-dried soils sampled from subarctic Alaska under three land use managements (i.e., forest, agriculture, and grassland converted from agricultural use and under a Conservation Reserve Program [CRP]) were extracted with deionized water and separated by filtration into different size fractions (2.5 μm, 0.45 μm, and 1 kDa). Water-soluble organic C (WSOC), water-soluble organic N, and fluorescence spectroscopy of each fraction were determined. There were few differences in quantitative data between samples from different land uses with air-dried samples, implying that air-dried samples were not suitable for characterizing the impact of soil management practices on soil WSOM. For field moist soil samples, the WSOC contents decreased in the order forest > CRP > agricultural land. Furthermore, WSOC was dominated by large (>0.45 μm) and small (

Water-extractable organic matter (WEOM) contains labile organic carbon (C) and nitrogen (N) and is sensitive to soil management. The objective of this study was to determine the quantity and spectral properties of soil WEOM responding to types of nutrient addition and tillage managements. Soil samples were taken from treatments (con- ventional tillage, no-tillage, poultry litter, and NH4NO3 application) of a 10-year experiment in Watkinsville, Georgia, at different times and soil depths. Air-dried soil samples were extracted by deionized water followed by filtration (G0.45 Km), and soluble C and N, absorptivity at 254 nm, and fluorescence excitation/emission matrix in the extract were determined. Results showed that poultry litter application accumulated higher amounts of water-extractable organic C and N than NH4NO3 application. But no significant difference was found between tillage and no-tillage for both water-extractable C and N. Absorptivity at 254 nm decreased during cropping years for conventional tillage and NH4NO3 application, indicating accumulation of aliphatic organic compounds in WEOM, but the fluorescence-measured humification index showed an opposite trend. For no-tillage and poultry litter application treatments, there was no difference in absorptivity over the sampling time. Parallel factor analysis of excitation/emission matrix data showed that WEOM consisted of three fluorophore components: humic-, fulvic-, and tyrosine- like ''compounds,'' and relative distribution of these components differed among treatments and changed over soil depths. The tyrosine-like com- ponent tended to accumulate in the lower sampling depth (915 cm). Overall, the quantity and spectral properties of WEOM responded to the types of nutrient application and tillage practices.

Soil test P (STP) methods were developed for fertilizer P recommendation in crop production. As soil P content of arable land increases due to manure application, the suitability of these STP methods for assessing P runoff potential from a field needs to be evaluated. The objective of this research was to evaluate various P extraction and determination methods using manured soils for their potential use as environmental P testing methods. Eighty one soil samples were taken in 1998 from various manured fields and research plots across Alberta. Phosphorus in the samples was extracted using deionized water, Miller-Axley (0.03 M NH4F + 0.015 M H2SO4), modified Kelowna (0.015 M NH4F + 0.25 M NH4OAc), and Mehlich 3 (M3) (1.5 M NH4F + 0.1 M EDTA) procedures. Phosphorus concentration in all extraction solutions was determined by the molybdenum blue colorimetric method in a Technicon II autoanalyzer. In addition, P content of the deionized water and M3 extractions was determined by an inductively coupled plasma emission spectroscopy (ICP) method. Soluble organic carbon content was measured in the deionized water extraction. The extractable P concentration increased as the acidity of the extraction solution increased in the order: M3 > modified Kelowna > Miller-Alxey > deionized water. The P extracted by Miller-Axley and M3 was strongly related to the deionized water extractable P, suggesting that both methods may be useful in assessing potential P runoff from arable land. The P concentration by the ICP determination was much higher than with the colorimetric method in M3 and the deionized water. The P concentration difference between the two determination methods was largely correlated to the soluble organic carbon in the deionized water extraction (r = 0.828***), suggesting that the undetected P by the molybdenum blue colorimetric method may exist in organic forms. To asses P runoff risk from arable land, both soluble inorganic and organic P need to be considered, and the ICP method can determine the total P, which includes both. In developing a STP for environmental soil P management, both P extraction and P determination methods should be standardized, and our results suggest that M3 and Miller-Axley extraction, and ICP determination are suitable methods for assessing P runoff. Key words: Soil test P, colorimetric P, ICP-P, dissolved organic carbon, soluble organic P, manure application rate

Since the early 1970's, soil nitrate nitrogen (NO3-N) levels have been used as a basis for N fertilizer recommendations in western Canada. However, soil nitrate N does not represent the supplying power of soil N for plant uptake. Furthermore, the nitrate concentration in soil changes depending on the time and ambient conditions at sampling. Researchers in the past have used mineralization potential to predict N supply power for plant growth. There are two methods to estimate the potential mineralizable N: a laboratory incubation and a chemical extraction method. The laboratory incubation method requires a long time to obtain a measurement. By comparison the chemical extraction method (e.g., hot KCl extraction) provides a quick estimation of potential mineralizable N, but the method requires calibration with laboratory incubation results. Alberta Agriculture, Food and Rural Development has established benchmark sites to monitor soil property changes from agricultural practices. Hot KCl extractable N and so...

Water-extractable organic matter (WEOM) contains labile organic carbon (C) and nitrogen (N) and is sensitive to soil management. However, knowledge about quantitative changes of water soluble organic C (WSOC) and N (WSON) impacted by land use conversion is still limited. In this chapter, the level and degradability of WSOC and WSON in soils sampled from subarctic Alaska under three different land use managements (i.e. forest, agriculture; and grassland converted from agricultural use and under a Conservation Reserve Program-CRP) were examined. There was no statistical difference of WSOC and WSON among three land uses. Furthermore, WSOC was dominated by large (>0.45 μm) and small (