Suchergebnisse

Intro -- Series Editor's Preface -- Contents -- 1 An Introduction to Biogeochemistry of the Critical Zone -- References -- 2 Hot Spots and Hot Moments in the Critical Zone: Identification of and Incorporation into Reactive Transport Models -- 2.1 Introduction -- 2.1.1 Definition of Terms -- 2.1.2 Scope and Overall Impact -- 2.2 Capturing Scales and Complexity Using Models -- 2.2.1 Hot Spots Within the Hyporheic Zone-The Redox Microzone Concept -- 2.2.2 HSHMs at the Floodplain Scale -- 2.2.3 HSHMs Along River Corridors -- 2.3 Current Understanding and the Path Forward -- 2.3.1 A Conceptual Take on HSHMs Using a Trait-Based Framework -- 2.3.2 Improvements in Field-Scale Characterization of Hyporheic Zones -- 2.3.3 Recent Developments in Observation and Modeling of Hot Spots Featuring the Sediment Water Interface -- 2.4 How Can Models Contribute? -- 2.4.1 Scale Aware Modeling/Parameterization -- 2.4.2 A Preemptive Prioritization of HSHMs -- 2.5 Concluding Remarks -- References -- 3 Constraints of Climate and Age on Soil Development in Hawai'i -- 3.1 Understanding Critical Zone Functioning Through State Factor Analysis -- 3.2 Physiographic Setting -- 3.3 Analytical Approach -- 3.4 Development of Critical Zone Properties Across the Hawaiian Islands -- 3.4.1 Weathering Depth and Chemical Denudation -- 3.4.2 Conditioning Lava Flows for Critical Zone Development -- 3.5 Biogeochemical Properties of Hawaiian Critical Zone -- 3.5.1 Weathering and Soil Properties -- 3.6 Soil Process Domains and Pedogenic Thresholds in Hawai'i -- 3.6.1 Process Domains -- 3.6.2 Transitions Among Process Domains -- 3.7 Conclusions -- References -- 4 Biofilms in the Critical Zone: Distribution and Mediation of Processes -- 4.1 Introduction -- 4.2 Documenting Environmental Biofilms Using the Scanning Electron Microscope -- 4.3 Biofilms in the Critical Zone.

A comprehensive cross-biome assessment of major nitrogen (N) species that includes dissolved organic N (DON) is central to understanding interactions between inorganic nutrients and organic matter in running waters. Here, we synthesize stream water N chemistry across biomes and find that the composition of the dissolved N pool shifts from highly heterogeneous to primarily comprised of inorganic N, in tandem with dissolved organic matter (DOM) becoming more N-rich, in response to nutrient enrichment from human disturbances. We identify two critical thresholds of total dissolved N (TDN) concentrations where the proportions of organic and inorganic N shift. With low TDN concentrations (0-1.3 mg/L N), the dominant form of N is highly variable, and DON ranges from 0% to 100% of TDN. At TDN concentrations above 2.8 mg/L, inorganic N dominates the N pool and DON rarely exceeds 25% of TDN. This transition to inorganic N dominance coincides with a shift in the stoichiometry of the DOM pool, where DOM becomes progressively enriched in N and DON concentrations are less tightly associated with concentrations of dissolved organic carbon (DOC). This shift in DOM stoichiometry (defined as DOC:DON ratios) suggests that fundamental changes in the biogeochemical cycles of C and N in freshwater ecosystems are occurring across the globe as human activity alters inorganic N and DOM sources and availability. Alterations to DOM stoichiometry are likely to have important implications for both the fate of DOM and its role as a source of N as it is transported downstream to the coastal ocean. ; National Science Foundation (NSF) through the Long-Term Ecological Research Network Office (LNO), National Center for Ecological Analysis and Synthesis (NCEAS), University of California-Santa Barbara [1545288]; NSFNational Science Foundation (NSF) [1556603]; New Hampshire Agricultural Experiment Station; USDA National Institute of Food and Agriculture McIntire-Stennis Project [1006760, 1016163]; Natural Environment Research Council, UK Large Grant [NE/K010689/1] ; Published version ; This work was conducted as a part of the Stream Elemental Cycling Synthesis Group funded by the National Science Foundation (NSF) under grant DEB#1545288, through the Long-Term Ecological Research Network Office (LNO), National Center for Ecological Analysis and Synthesis (NCEAS), University of California-Santa Barbara. The authors acknowledge the efforts of Julien Brun for assistance with data synthesis and the efforts of multiple individuals who collected and analyzed samples. Partial support for ASW during data synthesis and manuscript preparation was provided by NSF grant DEB#1556603 (Deciphering Dissolved Organic Nitrogen). Partial funding was provided by the New Hampshire Agricultural Experiment Station. This is Scientific Contribution 2880. This work was supported by the USDA National Institute of Food and Agriculture McIntire-Stennis Project 1006760. Support for AA was provided by the USDA National Institute of Food and Agriculture McIntire-Stennis Project 1016163. Partial support for PJJ and CAY was provided by Natural Environment Research Council, UK Large Grant NE/K010689/1 (DOMAINE: Characterizing the Nature, Origins and Ecological Significance of DOM in Freshwater Ecosystems). The authors are also grateful for feedback from two anonymous reviewers whose comments significantly improved this manuscript. This paper is dedicated to the memory of Dr. John Schade, a friend, colleague, and mentor to many of us. John studied ecological stoichiometry in freshwater ecosystems and led the Long-Term Ecological Research (LTER) group at the US National Science Foundation. ; Public domain authored by a U.S. government employee