Erick A. Bestland

Soil Organic Matter Decomposition and Turnover in a Tropical Ultisol: Evidence from δ13C, δ15N and Geochemistry

Soil organic matter (SOM), leaf litter, and root material of an Ultisol from the tropical rainforest of Kakamega, Kenya, were analyzed for stable carbon (delta (super 13) C) and nitrogen (delta (super 15) N) isotopic values as well as total organic carbon (TOC) and total nitrogen (TN) contents in order to determine trends in SOM decomposition within a very well-developed soil under tropical conditions. In addition, we quantified mineralogy and chemistry of the inorganic soil fraction. Clay mineralogical variation with depth was small and the abundance of kaolin indicates intense weathering and pedoturbation under humid tropical conditions. The soil chemistry was dominated by silica, aluminium, and iron with calcium, potassium, and magnesium as minor constituents. The relative depletion of base cations compared with silica and aluminium is an indicator for intense weathering and leaching conditions over long periods of time. Depth profiles of Delta (super 13) C and Delta (super 15) N showed a distinct enrichment trend down profile with a large (average (super 13) C = 5.0 per mil average (super 15) Delta N = 6.3 per mil) and abrupt offset within the uppermost 10-20 cm of the soil. Isotopic enrichment with depth is commonly observed in soil profiles and has been attributed to fractionation during decomposition. However, isotopic offsets within soil profiles that exceed 3 per mil are usually interpreted as a recent change from C (sub 4) to C (sub 3) dominated vegetation. We argue that the observed isotopic depth profiles along with data from mineralogy and chemistry of the inorganic fraction from the Kakamega Forest soil are a result of intense weathering and high organic matter turnover rates under humid tropical conditions.

Eocene and Oligocene Paleosols of Central Oregon

Scenic red color-banded claystones of the Clarno and Painted Hills areas of central Oregon are successions of fossil soils that preserve a record of Eocene-Oligocene paleoclimatic change. Conglomerates of the middle Eocene Clarno Formation near Clarno contain largely weakly developed paleosols compatible with an environment of volcanic lahars around a large stratovolcano. Deeply weathered paleosols (Ultisols) around a volcanic dome and overlying these conglomerates indicate a climate that was subtropical (mean annual temperature or MAT 23-25° C) and humid (mean annual precipitation or MAP of 900-2,000 mm). Comparable paleoclimates are indicated by fossil floras from the conglomerates, which show diversity and adaptive features similar to modern vegetation of Volcan San Martin, Mexico. An erosional disconformity in the Clarno area separates these older beds from less deeply weathered red paleosols (Alfisols) in the middle Eocene upper Clarno Formation. The change in paleosols may represent a decline in both temperature (MAT 19-23° C) and rainfall (MAP 900-1,350 mm), with dry seasons. Strongly developed lateritic paleosols (Oxisols and Ultisols) in the uppermost Clarno and lowermost John Day Formations in the Painted Hills record return to more humid conditions during the late Eocene. These paleosols are similar to soils of southern Mexico and Central America in climates that are subtropical (MAT 23-25° C) and humid (MAP 900-2,000 mm). Kaolinitic and iron-rich, red paleosols (Ultisols) of the lower Big Basin Member of the John Day Formation near Clarno and the Painted Hills are erosionally truncated and abruptly overlain by smectitic and tuffaceous paleosols (Inceptisols and Alfisols) of the middle Big Basin Member. This truncation surface can be correlated with the local Eocene-Oligocene boundary. Paleosols of the middle Big Basin Member are most like those of the Central Transmexican Volcanic Belt and indicate an early Oligocene paleoclimate appreciably cooler (MAT 16-18° C) and drier (MAP 600-1,200 mm) than during the late Eocene. Root traces and clay accumulations in the paleosols indicate forest vegetation, also evident from fossil leaves of the lake-margin Bridge Creek flora. The mid-Oligocene upper Big Basin Member of the John Day Formation includes distinctive brown as well as red paleosols (Alfisols). Its paleosols indicate a paleoclimate drier (MAP 500-700 mm) than before, and more grasses in the forest understory. Another erosional truncation marks the base of the late Oligocene (early Arikareean), olive-brown lower Turtle Cove Member of the John Day Formation. Calcareous paleosols with near-granular soil structure (Inceptisols and Aridisols) indicate an even drier (MAP 400-600 mm) climate, more open grassy woodland vegetation than previously, and local wooded grassland of seasonally wet bottomlands. The Clarno-John Day sequence preserves a long-term paleoclimatic record that complements the geological record of global change from deep sea cores and fossil plants. Similarly, it reveals stepwise climatic cooling and drying, with a particularly dramatic climatic deterioration at the Eocene-Oligocene boundary.

Variation in performance of surfactant loading and resulting nitrate removal among four selected natural zeolites

Surfactant modified zeolites (SMZs) have the capacity to target various types of water contaminants at relatively low cost and thus are being increasingly considered for use in improving water quality. It is important to know the surfactant loading performance of a zeolite before it is put into application. In this work we compare the loading capacity of a surfactant, hexadecyltrimethylammonium bromide (HDTMA-Br), onto four natural zeolites obtained from specific locations in the USA, Croatia, China, and Australia. The surfactant loading is examined using thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, and Raman spectroscopy. We then compare the resulting SMZs performance in removing nitrate from water. Results show that TGA is useful to determine the HDTMA loading capacity on natural zeolites. It is also useful to distinguish between a HDTMA bi-layer and a HDTMA mono-layer on the SMZ surface, which has not been previously reported in the literature. TGA results infer that HDTMA (bi-layer) loading decreases in the order of US zeolite>Croatian zeolite>Chinese zeolite>Australian zeolite. This order of loading explains variation in performance of nitrate removal between the four SMZs. The SMZs remove 8-18 times more nitrate than the raw zeolites. SMZs prepared from the selected US and Croatian zeolites were more efficient in nitrate removal than the two zeolites commercially obtained from Australia and China.

Age and origin of Terra Rossa soils in the Coonawarra area of South Australia

Abstract The famous Terra Rossa soil in the Coonawarra area, South Australia, is dominated by locally derived aeolian detritus, which probably accumulated over the last 120–130 ka. Four soil profiles and associated limestone and lunette deposits were investigated using the following methods: mass balance geochemistry of bulk soil samples (major and trace elements), quantitative X-ray diffraction (XRD) mineralogy, strontium isotopes (87/86), as well as grain-size analysis and cation exchange capacity. These data show that the Terra Rossa soil from the Coonawarra has a thick, clayey B-horizon which is geochemically homogeneous and dominated by smectite and kaolinite. Mass-balance calculations show unrealistic weathering scenarios when plotted using silicate residuum from the underlying limestone as parent. Realistic weathering scenarios are produced with fine-grained silicate material from local lunette deposits as parent. Strontium isotopes of silicate residuum from Gambier Limestone (0.78) contrast strongly with the clayey B-horizon (0.726). Strontium isotope ratios of silicate material from a local lunette (0.725) are similar to the B-horizon soil values. Strontium isotope ratios from regional geological units indicate that the strontium signature in the lunette and soil B-horizon is dominated by weathering products from the Palaeozoic Kanmantoo shales, extensively exposed upwind to the west on Kangaroo Island and the Fleurieu Peninsula. Optical (optically stimulated luminescence, OSL) dating of 61 individual quartz grains (single aliquot) from three samples in the Coonawarra soil profile (one from the A-horizon and two from the B-horizon) shows that most of the quartz sand grains have been buried for only a few thousand years. Many of the grains, however, have been buried for tens of thousands of years with three grains having exposure ages of between 105 and 109 ka. The large population of young exposure dates represents quartz sands recently exposed in the A-horizon and which have been translocated down to the B-horizon. The older exposure dates are interpreted as representing grains that were buried during or soon after the accumulation of wind-blown silt and clay. Our current model concerning the timing and conditions of aeolian deposition of the Coonawarra soil is that much of it accumulated during the relatively wet, last interglacial period around 120–130 ka. During that time span, it is thought that the playa–lunette systems in the low-lying areas to the west were particularly active and generated a significant local dust flux.

Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems.

In this study the effect of soil type, level of pre-treatment, ponding depth, temperature and sunlight on clogging of soil aquifer treatment (SAT) systems was evaluated over an eight week duration in constant temperature and glasshouse environments. Of the two soil types tested, the more permeable sand media clogged more than the loam, but still retained an order of magnitude higher absolute permeability. A 6- to 8-fold difference in hydraulic loading rates was observed between the four source water types tested (one potable water and three recycled waters), with improved water quality resulting in significantly higher infiltration. Infiltration rates for ponding depths of 30 cm and 50 cm were higher than 10 cm, although for 50 cm clogging rates were higher due to greater compaction of the clogging layer. Overall, physical clogging was more significant than other forms of clogging. Microbial clogging becomes increasingly important when the particulate concentrations in the source waters are reduced through pre-treatment and for finer textured soils due to the higher specific surface area of the media. Clogging by gas binding took place in the glasshouse but not in the lab, and mechanical clogging associated with particle rearrangement was evident in the sand media but not in the loam. These results offer insight into the soil, water quality and operating conditions needed to achieve viable SAT systems.

Stepwise Climate Change Recorded in Eocene‐Oligocene Paleosol Sequences From Central Oregon

Successions of paleosols bounded by erosional surfaces in fluvial sediments of the Eocene‐Oligocene strata of Central Oregon can be interpreted as terrestrial equivalents of the unconformity‐bound units of sequence stratigraphy. In the upper part of the upper Eocene Clarno Formation and in the lower part of the lower Eocene‐lower Miocene John Day Formation, truncation surfaces separate otherwise conformable alluvial deposits and allow for stratigraphic subdivision into informal members (lower and upper “Red Hill” claystones in the Clarno Formation and lower, middle, and upper Big Basin Members and lower Turtle Cove Member in the John Day Formation). Paleosols in each member show a stepwise change in the degree of weathering of the most strongly developed paleosols: kaolinite‐rich, Ultisollike paleosols in lower “Red Hill” claystones (late Eocene, 42‐43 Ma), smectite‐rich Alfisol‐like paleosols in the upper “Red Hill” claystones (late Eocene, 41‐42 Ma), Alfisols and Ultisol‐like paleosols in the lower Big Basin Member (late Eocene, 34–40 Ma), Alfisol and Inceptisol‐like paleosols in the middle and upper Big Basin Members (early Oligocene, 30–34 Ma), and calcic Inceptisol‐like paleosols in the lower Turtle Cove Member (middle Oligocene, 28–30 Ma). These changes across the Eocene‐Oligocene transition are interpreted as representing global cooling and drying of the midlatitudes from Eocene subtropical, humid conditions to Oligocene temperate, subhumid conditions. In central Oregon, these changes appear to be stepwise with climatically stable periods, represented by packages of similar paleosols, of approximately 2‐4 m.y. in duration. Our interpretation of these paleosol packages as non‐marine sequences is not based on correlation with sea‐level changes but on correlation with global climate change events. Geomorphic processes influenced by climate and vegetation, and not base‐level change, basin subsidence, or volcanic supply are thought to have controlled sedimentation rates. Thus, the stepwise increase in sedimentation rates across the Eocene‐Oligocene transition in the central Oregon alluvial strata reflect increased sediment yields due to drying climatic conditions. High‐precision 40Ar/39Ar age determinations of tuffs allow for the correlation of these sequences with the record of global climate change from deep sea cores. Three major paleoclimatic changes stand out. The change from Ultisol‐like paleosols formed in near‐tropical climate to AAlfisol‐like paleosols formed in subtropical climate between 42.8 and 43 Ma) corresponds to a global cooling trend after the mid‐Eocene climatic optimum. The Eocene‐Oligocene boundary (∼34 Ma) is marked by the change from subtropical Ultisol‐like paleosols to Alfisol‐like paleosols formed in temperate humid climate. Global cooling during the mid‐Oligocene (∼30 Ma) is reflected in a change from non‐calcareous, Alfisol‐like paleosols to calcareous Andisol‐like paleosols formed in sub‐humid temperate conditions. These mid‐Tertiary paleosol sequences are evidence of stepwise terrestrial climate change that was strongly coupled with marine events.

Palaeoenvironments of Early Miocene Kisingiri volcano Proconsul sites: evidence from carbon isotopes, palaeosols and hydromagmatic deposits

Early Miocene (c. 18 Ma) hominoid sites (Proconsul) from Rusinga Island, Lake Victoria occur in palaeosols and volcaniclastic strata deposited in a semi-arid, seasonal climate on the flanks of the active, low-relief edifice of the Kisingiri volcano. Palaeosols interbedded with sequences of primary pyroclastic deposits have stable carbon isotope values indicative of C3 vegetation from semi-arid environments. Isotopic values of palaeosol organic matter and pedogenic carbonate from the Rusinga Group have average δ13C of – 23.8 ± 0.8 and – 7.7 ± l.l‰, respectively, considerably heavier than average C3 vegetation. These isotopic values were most likely caused by reduced photosynthetic fractionation under water-stressed conditions. Prolonged dry seasons and semi-arid precipitation levels for Rusinga Group fossil soils are also supported by the profile depth of calcareous horizons and vertic clay structures. The principal fossil-bearing units of the Rusinga Group (Kiahera and Hiwegi formations) are dominated by sandy strata which are interbedded with palaeosols and have features indicative of hydromagmatic pyroclastic deposition. Pyroclastic surge features include very low-angle cross-bedding, low amplitude and long-wavelength dune bedforms, moderate to poorly sorted layers of tuffaceous and pebbly sandstones, and common, isolated cobbles and boulder clasts of Precambrian basement rocks with associated impact sags. These features are interpreted as the deposits of pyroclastic surge dune bedforms and ballistically implaced volcanic ejecta, both produced by powerful hydromagmatic explosions from the Kisingiri volcano. According to this interpretation, the initial stages of this carbonatite-nephelinite volcano had repeated episodes of hydromagmatic eruptions which built a large (15–20 km radius), low-relief tuff ring or maar volcano. The palaeosol sequences interbedded with the primary pyroclastic deposits represent periods of volcanic quiescence lasting hundreds to thousands of years. Thus, Proconsul and associated fauna and flora inhabited a frequently disturbed landscape that experienced repeated catastrophic volcanic deposition in an overall semi-arid seasonal climate.

Palaeoenvironmental reconstruction of the Late Pleistocene to Early Holocene Robertson Cave sedimentary deposit, Naracoorte, South Australia

Sedimentological investigations and geochemical analyses of the Robertson Cave deposit, 7 km south of Naracoorte, South Australia, document a palaeoenvironmental record for the Late Pleistocene and Early Holocene. Three distinct depositional episodes spanning the interval 32 – 8 ka are represented by over 4 m of sediments exposed in the chamber 2 excavation pit. The oldest of the three, the lower unit (>30 ka BP) is dominated by reddish and brown sandy silts. A 20 cm band of red silt horizons that cap this unit contain enriched δ15N values (12 – 15‰), low C/N ratios, significant SO3 (20%) and CaO (18.5%) contents, a high alkyl-C component and phosphorus-rich mineralogy. These unique sediment horizons are interpreted as being derived from the accumulation of bat guano and degraded cave rock fragments. Their presence suggests a period of low sediment input into the cave, possibly reflecting the existence of a stable geomorphic environment prior to 30 ka. The time period 30 – 27 ka saw the rapid deposition of the middle unit, a sequence of coarser homogeneous sands that resulted in the entrance to chamber 2 becoming blocked. These horizon-less sediments, with clear aeolian features, are most likely representative of the drier conditions associated with the Last Glacial Maximum, which peaked at 20 – 17 ka. Deposition into the chamber recommenced at approximately 13 ka and continued until 8 ka, resulting in the accumulation of the upper unit, a sequence of silt, charcoal and organic matter rich horizons. Here, a shift to more 13C-depleted values (−25‰ to −27‰) is evident in the bulk soil organic matter and charcoal between 11 and 10 ka, possibly reflecting a shift from the dry Last Glacial Maximum to the wetter environs of the Holocene. The upper unit may also be a record of burning practices associated with Aboriginal migration to the area.

Guano-derived deposits within the sandy cave fills of Naracoorte, South Australia

Geochemical and mineralogical data suggest that bat guano has made a major contribution to the development of several separate sedimentary layers, in the predominantly clastic sand and coarse silt deposits of the Naracoorte Caves, South Australia. A 20 cm thick group of reddish fine silt sediments located in Robertson Cave contains the phosphate minerals whitlockite and apatite, significant concentrations of SO3, P2O5, and CaO, and organic matter with low C/N ratios and highly enriched δN values. These data suggest that accumulations of bat guano and weathered cave limestone contributed significantly to the red silts formation. Sedimentary deposits located in Wet and Blanche Caves also contain horizons that exhibit increased concentrations of SO3, P2O5 and CaO, relatively lower C/N ratios and enriched δN values, suggesting that bat guano may have also contributed to their formation. Physical attributes evident for both these horizons further support this interpretation. A milky-white material that appears...

Preliminary 14C dates on bulk soil organic matter from the Black Creek megafauna fossil site, Rocky River, Kangaroo Island, south Australia

Radiocarbon age determinations and stratigraphy suggest that the deposits in Black Creek Swamp on Kangaroo Island record 3 phases of deposition and associated soil development which spanned at least the last 20,000 yr. Four new (super 14) C age determinations on bulk soil organic matter and their stratigraphic context are presented in this paper. Three of these age determinations (FP6: 15,687+ or -110 BP [WK11487]; FP7: 16,326+ or -385 BP [WK11488]; and FP8: 17,618+ or -447 BP [WK11489]), are from the organic-rich fossil layer located 45-75 cm below the current floodplain surface. The fourth, a much younger date, FP5: 5589+ or -259 BP (WK11486), was obtained from the base of the overlying modern soil. The dates for the fossil layer increase systematically with depth and correlate well with 5 previous (super 14) C dates (Hope et al., unpublished), ranging between 15,040+ or -120 BP and 19,000+ or -310 BP. This suggests that the data set represents a possible minimum age of the bulk organic matter, and considering the high organic matter contents of approximately 8%, has implications for the age of the megafauna buried in this layer. The overlying modern soil, with its much younger date, contains lower levels of organic matter (3-7%) and gastropods not seen in the fossil layer. This suggests a substantial change in environmental conditions probably due to an alteration in the floodplain drainage conditions. This chronological and sedimentological discontinuity indicates that 2 distinct depositional regimes existed and were separated by up to 10,000 (super 14) C yr. A calcareous, sandy silt deposit underlying the fossil layer is a calcarenite deposit with low total organic content and is considered the base of the section; it suggests a third separate depositional episode. As such, the Black Creek Swamp in the southwest corner of Kangaroo Island formed intermittently over at least the last 20,000 yr during 3 distinct depositional phases, one of which was the formation of the fossil-laden, organic-rich floodplain surface, which has a possible minimum age of approximately 15,000 to 19,000 BP.