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Über dieses Buch

This textbook presents a comprehensive process-oriented approach to biogeochemistry that is intended to appeal to readers who want to go beyond a general exposure to topics in biogeochemistry, and instead are seeking a holistic understanding of the interplay of biotic and environmental drivers in the cycling of elements in forested watersheds. The book is organized around a core set of ecosystem processes and attributes that collectively help to generate the whole-system structure and function of a terrestrial ecosystem. In the first nine chapters, a conceptual framework is developed based on distinct soil, microbial, plant, atmospheric, hydrologic, and geochemical processes that are integrated in the element cycling behavior of watershed ecosystems. With that conceptual foundation in place, students then proceed to the final three chapters where they are challenged to think critically about integrated element cycling patterns; roles for biogeochemical models; the likely impacts of disturbance, stress, and management on watershed biogeochemistry; and linkages among patterns and processes in watersheds experiencing novel environmental changes.

Included with the text are figures, tables of comparative data, extensive literature citations, a glossary of terms, an index, and a set of 24 biogeochemical problems with answers. The problems are intended to support chapter concepts and to demonstrate how critical thinking skills, simple algebra, and thoughtful human logic can be used to solve applied problems in biogeochemistry that might be encountered by a research scientist or a resource manager.

Using this book as an introduction to biogeochemistry, students will achieve a level of subject mastery and disciplinary perspective that will permit them to see and to interpret the individual components, interactions, and synergies that are represented in the dynamic element cycling patterns of watershed ecosystems.

Inhaltsverzeichnis

Frontmatter

1. General Chemical Concepts

This introductory chapter presents a brief overview of basic chemical concepts that are important in the study of biogeochemistry. Chemical bonding mechanisms are examined, with particular emphasis on complexation reactions that influence the solubility and bioavailability of metals. The chemical behaviors of different elements and compounds are discussed in relation to oxidation-reduction, polarity of molecules, equilibrium reactions, and rate-limited processes. Examples are provided for transforming molar or mass-based concentrations into units of equivalent charges for ionic charge balance analysis. Finally, stable isotopes are introduced as a tool for tracing biogeochemical patterns and processes.
Christopher S. Cronan

2. Soil Biogeochemistry

Soils are a primary determinant of site quality and environmental conditions in terrestrial ecosystems, providing water, nutrients, acid neutralizing capacity, shelter, and anchorage for terrestrial life forms. Beyond these essential functions in terrestrial ecosystems, soils also exert a strong influence on aquatic systems through effects on the chemistry and hydrologic routing of drainage water inputs to lakes and streams. In this chapter, the physical and chemical characteristics of soils are examined, along with key soil biogeochemical processes that influence the belowground cycling of elements in watershed ecosystems. Comparative data are used to illustrate the ranges of soil properties observed across the forest landscape. Results illustrate that soils provide a remarkable system of nutrient supply and storage based on integrated contributions from geologic and organic source materials.
Christopher S. Cronan

3. Microbial Biogeochemistry

The biogeochemical cycles of carbon, nitrogen, and sulfur are characterized by important gaseous pathways, biochemical transformations, immobilization processes, and mineralization reactions associated with microbial metabolism. Microbial organisms are thus important regulators of the source-sink behavior and cycling rates of these key elements in terrestrial and aquatic ecosystems. In addition, numerous other elements such as mercury, iron, and even phosphorus are affected directly or indirectly by microbial exudation, respiration, assimilation, oxidation-reduction, methylation, and acidification processes. Taken as a whole, microscopic bacteria and fungi have critical roles in controlling element cycles in the biosphere. The primary focus of this chapter is to explore the major microbial processes and associated environmental conditions influencing the biogeochemical behavior of nitrogen, sulfur, and carbon in the forest landscape.
Christopher S. Cronan

4. Plant Biogeochemistry

Terrestrial plant communities exist at the interface between the atmosphere and the underlying soil and geologic substrate, acting as major regulators of biogeochemical and hydrologic cycling patterns in the biosphere. In a forest ecosystem, the plant canopy represents the “power station” for energy flow, the major end-user for water, a massive gas exchange system, a primary sink for nutrients, and a multi-dimensional surface exposed to continuous atmospheric interactions. The belowground root system, on the other hand, contains large structural woody roots that anchor a prolific branching system of fine roots that acts as a sink for photosynthate, a nutrient absorption network, a hydrologic connection between the shoot and the soil, and a source of fresh organic matter for the surrounding subsoil environment. This chapter explores a range of plant metabolic and nutrient cycling processes and structural-functional relationships that are integral to the biogeochemical role of plants in forested watersheds.
Christopher S. Cronan

5. Cycling of Organic Matter

One of the useful ways of integrating concepts of energy flow and nutrient cycling in a terrestrial ecosystem is to focus on the cycling of organic matter. The chemical energy and nutrients sequestered in terrestrial plant biomass or within a forest soil are part of a larger ecosystem cycle of organic matter characterized by (i) multiple storage pools with different residence times and (ii) multiple component processes, including trophic transfers among consumer organisms, production of detritus or necromass from senescent or dead life forms, release of elements from organic matter via decomposition and mineralization processes, evolution of gaseous CO2 from respiration, and recycling of nutrients into new growth of organisms. This chapter examines how organic matter pools are distributed in the landscape, what processes control organic matter cycling, and how organic matter cycling is influenced by environmental and ecological conditions.
Christopher S. Cronan

6. Atmospheric Deposition

Biogeochemical processes in watershed ecosystems are closely coupled with dynamic and complex cycling processes and source-sink relationships involving the atmosphere. In some cases, terrestrial systems act as important emission sources contributing to atmospheric chemistry; in other cases, watersheds serve as major sinks or receptors for elements and compounds cycling through the atmosphere. This chapter focuses on the role of atmospheric deposition in ecosystem element budgets and the factors that determine the chemistry and amounts of atmospheric deposition found in different regions and watersheds. Comparative field data are presented in an effort to illustrate patterns of atmospheric deposition observed at various watershed study sites.
Christopher S. Cronan

7. Mineral Weathering

Mineral weathering is a process characterized by chemical and physical breakdown of geologic materials, accompanied by the generation of dissolved solutes plus relatively stable new mineral phases. Weathering is important as a (i) source of nutrients such as calcium, magnesium, potassium, sodium, iron, silica, and a variety of trace metals; (ii) source of acid neutralizing capacity or alkalinity; (iii) source of phosphorus and sulfur in certain types of geologic formations; and (iv) vital process contributing to formation of clay colloids or secondary minerals. In watershed ecosystems, mineral weathering represents a crucial process of replenishment that helps to offset cation losses resulting from leaching and forest harvesting, and it restores alkalinity consumed by acidic deposition and soil acidification processes. This chapter examines weathering processes, controls on weathering rates, methods for estimating weathering contributions to element budgets, and comparative field data illustrating weathering estimates from different watershed ecosystems.
Christopher S. Cronan

8. Watershed Hydrology

Watershed hydrology and the influences of hydrologic patterns and processes on element cycling are an integral part of the study of ecosystem biogeochemistry. One of the fundamental challenges in watershed hydrology is to understand the flow paths of water movement within catchments, patterns of streamflow generation that result from moisture inputs to a given watershed, and the interplay of biogeochemical and hydrologic processes within a watershed ecosystem. If water chemistry is sampled along a drainage gradient from precipitation inputs, through soils and surficial deposits, and into a stream channel, it is apparent that the chemistry of water is dynamic and changes dramatically in response to various biogeochemical transformation processes during drainage through the catchment. These spatial changes and seasonal differences in soil and stream water chemistry are determined by interactions between hydrologic flow paths and spatially distributed biogeochemical processes within a drainage basin. Because of this, it is important to understand the hydrologic source compartments and drainage pathways that control runoff patterns and processes in watershed ecosystems.
Christopher S. Cronan

9. Aqueous Chemistry

Many of the important inputs, outputs, and internal transfers of elements in watershed ecosystems occur through the medium of water. As water moves through the drainage gradient in a watershed, solution chemistry evolves and changes in response to the differential influences of biogeochemical processes. By tracking changes in aqueous chemistry, it is possible to infer how ions and solutes are influenced by biogeochemical processes that are otherwise invisible and difficult to detect. The intent of this chapter is to examine patterns of solution chemistry in watershed ecosystems and to discuss the major physical, biological, and chemical factors and processes controlling the chemistry and fluxes of elements in natural waters. We shall explore how and why aqueous chemistry varies in space and over time in a watershed. It will become evident that elements do not simply “flush down the drainage pipe” via mass flow and gravity in a watershed ecosystem. Our ultimate goal is to develop a conceptual framework for understanding the individual behavior of different types of ions and solutes in natural waters.
Christopher S. Cronan

10. Integrated Element Cycling

Element cycling is a simple concept that describes a vast and complex set of interacting processes that govern the distribution and movement of elements in the biosphere. For any given nutrient or element, it is possible to describe pools where the element is stored or accumulated and fluxes or transfers of the element between storage compartments or pools. Element pools include living biomass, geologic substrates, soil organic matter, and the soil exchange complex. Element fluxes include transfers in leaf litter, canopy leaching, soil leaching, stream export, and atmospheric deposition. This chapter integrates processes from previous chapters to examine system-level cycling of nutrients and other elements at scales ranging from local forest stands to regional drainage basins, and includes a final section on global-scale cycling. Examples from a range of studies illustrate the different ways in which elements accumulate and cycle under varying environmental conditions.
Christopher S. Cronan

11. Biogeochemical Models

Although some natural systems are relatively simple, many others are complex and contain intricate relationships and feedbacks. Whatever the level of complexity, it can be very useful to have a framework or a model for integrating current understanding about a particular system of interest. A model can be defined as a qualitative conceptual or quantitative numerical representation of a process, pattern, or system. Biogeochemical models range in scale and complexity from rudimentary exponential decay equations describing the loss of leaf mass in decomposing litter to large integrated ecosystem models capable of simulating the dynamic patterns of energy flow, nutrient cycling, and hydrologic routing in a watershed. This chapter examines how biogeochemical models provide valuable tools for integrating knowledge and synthesizing new insights regarding element cycling patterns and processes.
Christopher S. Cronan

12. Ecosystem Disturbance and Stress

Forest ecosystems are influenced by a wide variety of persistent or acute forcing factors, including stochastic disturbances, cyclic or chronic environmental stresses, and human management activities. A disturbance is an event that removes or damages organisms, generates openings in a community, or abruptly alters environmental conditions, leading to changes in ecosystem structure or function. By comparison, a stress can be viewed as any biotic (e.g., pathogen) or abiotic (e.g., drought) constraint or influence that adversely affects critical life processes for organisms. When ecosystems are exposed to disturbance events, stresses, or other forcing factors, there may be dynamic changes in multiple interrelated processes and system properties. One of the intriguing challenges in biogeochemistry is to be able to predict ecosystem responses to diverse anthropogenic or natural forcing factors.
Christopher S. Cronan

Backmatter

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