Biogeoscience

The Biogeographic History of Iceland - The North Atlantic Land Bridge Revisited

by Fridgeir Grimsson

2011
Thomas Denk, Fridgeir Grimsson, Reinhard Zetter, Leifur A Simonarson
Springer
Chapter 12

Effects of urbanization on nutrient biogeochemistry of aridland streams

by David Lewis

Nancy B. Grimm, J. Ramón Arrowsmith, Chris Eisinger, James Heffernan, Amanda MacLeod, David B. Lewis, Lela Prashad, Tyler Rychener, W. John Roach, and Richard W. Sheibley
Pp. 129-146 in "Ecosystems and Land Use Change," Geophysical Monograph 153, editors R. DeFries, G. Asner, and R. Houghton. American Geophysical Union, Washington (2004)

Land-use and land-cover change affect the biogeochemistry of stream ecosystems in numerous ways, both direct and... more Land-use and land-cover change affect the biogeochemistry of stream ecosystems in numerous ways, both direct and indirect. Changes result from hydrologic modifications, including direct alterations of flow regimes and hydrologic flowpaths and indirect changes in hydrologic patterns via increased impervious cover in contributing areas of watersheds. Direct changes to channel morphology (i.e., reduced complexity) and to floodplains of streams and rivers also influence biogeochemistry, for example, by eliminating surface water–groundwater exchange. The nature of and strength of connections between the stream and its watershed may be altered by large-scale changes such as those brought about by urban and suburban development. Finally, in urban and agricultural areas, elevated nutrient loading is exacerbated by land-cover changes that increase the potential for erosion or overland flow, and decrease the opportunities for nutrient retention. Using comparative analysis based on published work, mined public data, and new research, we evaluate urbanization effects on stream ecosystems in the Sonoran Desert region of central Arizona. Five key characteristics of non-urban desert streams—nitrogen limitation, a flashy hydrologic regime that initiates succession, extensive groundwater–surface water interaction, episodic terrestrial–aquatic interactions, and high capacity for nutrient retention—are both dramatically altered and scarcely affected by urbanization. The similarities exhibited by aridland streams and their urban counterparts arise from large-scale constraints (e.g., episodic terrestrial–aquatic interaction is imposed by the climatic regime in both stream types), whereas the differences, like interrupted flowpath continuity in the urban landscape, likely result from the myriad direct modifications of streams and catchment land cover in cities.

Agrarian legacy in soil nutrient pools of urbanizing arid lands

by David Lewis

David Bruce Lewis, Jason P. Kaye, Corinna Gries, Ann P. Kinzig, and Charles L. Redman
Global Change Biology (2006) 12:703–709

Today's worldwide expansion of dry land cities consumes cultivated and native ecosystems, providing laboratories for... more Today's worldwide expansion of dry land cities consumes cultivated and native ecosystems, providing laboratories for investigating imprints of former land use in places where people now live. Around Phoenix, USA, we compared soil nutrient pools in residential yards converted from farms with nutrient pools in yards developed on native desert. Organic matter, carbon (C), nitrogen (N), and soluble ions were >2-fold greater in yards that were previously agrarian than in yards that were not. These pools remain elevated 40 years after land conversion to residential use. Present N accumulation (1.5 g per m2 per yr) is not affected by prior land use, suggesting that rates of residential fertilizer application and retention are not affected by antecedent soil fertility. Bioavailable, inorganic phosphorus (Pav) is elevated in soil with a recent agrarian past, but this signal disappears after 10–30 years of residential use owing to an accumulation of Pav in never-farmed yards. Our results indicate a ‘direct agrarian legacy,’ wherein agrarian amendment of nutrient pools endures urbanization, more so than an ‘indirect legacy,’ wherein present land management is molded by former land use. Agriculture in dry lands thus sequesters material in soils, and—as we also found higher material contents in residential soils than in contemporary agrarian soils—residential land use simply adds to the agrarian legacy these soils already bear. Intense human use of arid lands may cause increases in material pools in soils, a condition with potential global consequence.

The spatial structure of variability in a semi-arid, fluvial ecosystem

by David Lewis

David Bruce Lewis, John D. Schade, Anne K. Huth and Nancy B. Grimm
Ecosystems (2006) 9:386-397

The arrangement and composition of flowpath types within a given network are thought to govern its functioning. This... more The arrangement and composition of flowpath types within a given network are thought to govern its functioning. This concept assumes that different flowpath types are functionally distinct. We investigated this assumption in a fluvial ecosystem by comparing the riparian zone, parafluvial zone (in-channel gravel bars), and surface stream. We hypothesized that differences in advection, uptake, and sorption would render material cycles more (a) open and (b) mutable in the surface stream, whereas the converse would occur in the riparian zone, and an intermediate state would be seen in the intervening parafluvial zone. To test our first hypothesis, we predicted that spatial heterogeneity in solute concentrations would be least in the surface stream, greater in the parafluvial zone, and greatest in the riparian zone. Using a null model, we ascertained that this pattern was shown by all solute species we examined (nitrate, ammonium, total dissolved inorganic nitrogen [DIN], dissolved organic N, total dissolved N, soluble reactive phosphorus, dissolved organic carbon, and chloride). To test our second hypothesis, we predicted that temporal change in spatial heterogeneity would be greatest in the surface stream, less in the parafluvial zone, and least in the riparian zone. Nitrate, DIN, and chloride showed this pattern. In particular, surface stream inorganic N was less spatially variable following months of high rainfall. According to an extant hypothesis, these results suggest that inorganic N processing may be a stable function in this ecosystem. Other solute species did not support our second prediction, perhaps because their retention and release dynamics are influenced principally by geochemistry. Generally, our findings indicate that a geomorphic template can generate spatial patterns in ecosystem function, warranting an expansion of the spiraling framework to a variety of flowpath types.

N2 fixation and cycling in Alnus glutinosa, Betula pendula and Fagus sylvatica woodland exposed to free air CO2 enrichment.

by Jonathan Millett

Millett J, Godbold D, Smith AR and Grant H (2012). Oecologia. DOI: 10.1007/s00442-011-2197-4

We measured the effect of elevated atmospheric CO2 on atmospheric nitrogen (N2) fixation for the tree species Alnus... more We measured the effect of elevated atmospheric CO2 on atmospheric nitrogen (N2) fixation for the tree species Alnus glutinosa growing in monoculture or in mixture with the non-N2-fixing tree species Betula pendula and Fagus sylvatica. We addressed the hypotheses that 1: N2 fixation in A. glutinosa will increase in response to increased atmospheric CO2 concentrations, when growing in monoculture, 2: the impact of elevated CO2 on N2 fixation in A. glutinosa is the same in mixture and in monoculture and 3: the impacts of elevated CO2 on N cycling will be evident in a decrease in leaf δ15N and in the soil-leaf enrichment factor (EF), and that these impacts will not differ between mixed and single species stands. Trees were grown in a forest plantation on former agricultural fields for 4 growing seasons, after which the trees were on average 3.8 m tall and canopy closure had occurred. Atmospheric CO2 concentrations were maintained at either ambient or elevated (by 200 ppm) concentrations using a free-air CO2 enrichment (FACE) system. Leaf δ15N was measured and used to estimate the amount (Ndfa) and proportion (%Ndfa) of N derived from atmospheric fixation. On average 62% of the N in A. glutinosa leaves was from fixation. %Ndfa and Ndfa for A. glutinosa trees in monoculture did not increase under elevated CO2, despite higher growth rates. However, N2 fixation did increase for trees growing in mixture, despite the absence of significant growth stimulation. There was evidence that fixed N2 was transferred from A. glutinosa to F. sylvatica and B. pendula, but no evidence that this affected their CO2 response. This study shows that N2 fixation in A. glutinosa may be higher in a future elevated CO2 world, but that this effect will only occur where the trees are growing in mixed species stands.

Evidence for bias in C/N, δ13C and δ15N values of bulk organic matter, and on environmental interpretation, from a lake sedimentary sequence by pre-analysis acid treatment methods.

by Chris Brodie

In Press - Quaternary Science Reviews

Lead Author: Dr. Chris Brodie (Hong Kong University, Hong Kong)

Co-Authors: Dr. James Casford (Durham University); Dr. Jeremy Lloyd (Durham University, UK); Prof. Melanie Leng (NIGL, UK); Dr. Timothy Heaton (NIGL, UK); Christopher Kendrick (NIGL, UK); Dr. Zong Yongqiang (Hong Kong University, Hong Kong).

ABSTRACT:
There is a known bias in C/N, d13C and d15N values of organic matter (OM) due to pre-analysis acid... more ABSTRACT:
There is a known bias in C/N, d13C and d15N values of organic matter (OM) due to pre-analysis acid treatment methods. We report here, for the first time, the results of a pre-analysis acid treatment method comparison of measured C/N, d13C and d15N values in bulk OM from a sedimentary sequence of samples to illustrate this bias. Here we show that acid treatment significantly reduces the accuracy (between method biases) and precision (within method bias) of C/N, d13C and d15N values of OM, suggesting a differential response of sample OM between methods and sample horizons, and in some cases inefficient removal of inorganic carbon. We show that different methods can significantly influence environmental interpretation in some of our sample horizons (i.e. interpretation of aquatic vs. terrestrial OM source; C3 vs. C4 vegetation). Specifically, there are unpredictable and non-linear differences between methods for C/N values in the range of ~ 1 – 100; d13C values in the range of 0.2 – 6.8 ‰ and; d15Nvalues in the range of 0.3 – 0.7 ‰. Importantly, these ranges are mostly much greater than the instrument precision (defined as the standard deviation of replicate analysis of standard reference materials; for this study, ± 0.5 for C/N values, ± 0.1 ‰ for d13C values and; ± 0.1 ‰ for d15N). The accuracy and precision of measured C/N, d13C and d15N values of bulk OM is not just dependent upon environmental variability, but on acid pre-treatment, residual inorganic carbon and organic matter state and composition. Collectively, this makes the correlation between samples prepared in different ways, including those from down core reconstructions, highly questionable.

Keywords: C/N ratios, δ13C, δ15N, organic matter; pre-analysis acid treatment methods, environmental interpretation, palaeoclimate.

N2O Concentration and Isotope Signature Along Profiles Provide Deeper Insight Into the Fate of N2O In Soils

by Klaus-Holger Knorr

Dynamics of Redox Processes In a Minerotrophic Fen Exposed to a Water Table Manipulation

by Klaus-Holger Knorr

Impact of Experimental Drought and Rewetting on Redox Transformations and Methanogenesis In Mesocosms of a Northern Fen Soil

by Klaus-Holger Knorr

Fluxes and 13C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

by Klaus-Holger Knorr

Dynamics of redox processes in a minerotrophic fen exposed to a water table manipulation

by Klaus-Holger Knorr

Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation techniques

by Chris Brodie

Chemical Geology. 282, 67 - 83.

Lead Author: Dr. Chris Brodie (Durham University, UK; Hong Kong University, Hong Kong)

Co-Authors: Prof. Melanie Leng (NIGL, UK), Dr. James Casford (Durham University, UK), Christopher Kendrick (NIGL, UK), Dr. Jeremy Lloyd (Durham University, UK), Dr. Zong Yongqiang (Hong Kong University, Hong Kong), Prof. Michael Bird (James Cook University, Australia).

ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the... more ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the reliability of organic carbon [C] and nitrogen [N], and carbon isotope (δ13C) values on a range of terrestrial and aquatic, modern and geological environmental materials. We investigated the 3 most common methods; (i) acidification followed by sequential deionised water rinses (“rinse method”); (ii) acidification in silver capsules (“capsule method”); and (iii) acidification by exposure to an acid vapour (“fumigation method”). We also investigated the effect of sample size and capsule type (silver and tin) on C/N ratio and δ13C values. We find (i) %C, %N, C/N and δ13C showed significant within and between method variability; (ii) disproportionate and non-linear offsets of %C, %N and C/N values after acidification within and between methods and within and between sample materials; (iii) that alterations in %C did not necessarily manifest themselves in shifts in δ13C, and vice-versa; (iv) small (~ 90 μg C) sample sizes showed consistent overestimations and inaccuracies after acidification; (v) The effect of capsule type was not significant on most samples, but did show a notable effect on our aquatic materials, generally increasing %C and %N, and producing depleted δ13C values. These findings raise cause for concern on the interpretative nature of C/N ratios and their support for carbon isotope values. The comparability between laboratories (different preparation methods) and environmental settings (amount, type and nature of OM) are also likely to be problematic. We conclude that the response of C and N concentrations in organic matter to acid treatment in environmental materials is neither negligible nor systematic.

Keywords: δ13C; C/N ratio; Method comparison; Rinse method; Capsule method; Fumigation method; environmental reconstruction

A snapshot of CO2 and CH4 evolution in a thermokarst pond near Igarka, northern Siberia

by Klaus-Holger Knorr

Isotopic Evidence for Condensed Aromatics From Non-Pyrogenic Sources In Soils-Implications for Current Methods for Quantifying Soil Black Carbon

by Klaus-Holger Knorr

Experimental Drought Alters Rates of Soil Respiration and Methanogenesis but Not Carbon Exchange In Soil of a Temperate Fen

by Klaus-Holger Knorr

Dynamics of Belowground Redox Processes In a Minerotrophic Fen Exposed to a Water Table Manipulation

by Klaus-Holger Knorr

Arsenic Speciation and Turnover In Intact Organic Soil Mesocosms During Experimental Drought and Rewetting

by Klaus-Holger Knorr

Effects of short-term drying and irrigation on CO2 and CH4 production and emission from mesocosms of a northern bog and an alpine fen

by Klaus-Holger Knorr

Impact of Altering the Water Table Height of An Acidic Fen on N2O and NO Fluxes and Soil Concentrations

by Klaus-Holger Knorr