Showing papers by "Stephen R. Carpenter published in 2005"

Global Consequences of Land Use

Abstract: Land use has generally been considered a local environmental issue, but it is becoming a force of global importance. Worldwide changes to forests, farmlands, waterways, and air are being driven by the need to provide food, fiber, water, and shelter to more than six billion people. Global croplands, pastures, plantations, and urban areas have expanded in recent decades, accompanied by large increases in energy, water, and fertilizer consumption, along with considerable losses of biodiversity. Such changes in land use have enabled humans to appropriate an increasing share of the planet’s resources, but they also potentially undermine the capacity of ecosystems to sustain food production, maintain freshwater and forest resources, regulate climate and air quality, and ameliorate infectious diseases. We face the challenge of managing trade-offs between immediate human needs and maintaining the capacity of the biosphere to provide goods and services in the long term.

Social-Ecological Resilience to Coastal Disasters

Abstract: Social and ecological vulnerability to disasters and outcomes of any particular extreme event are influenced by buildup or erosion of resilience both before and after disasters occur. Resilient social-ecological systems incorporate diverse mechanisms for living with, and learning from, change and unexpected shocks. Disaster management requires multilevel governance systems that can enhance the capacity to cope with uncertainty and surprise by mobilizing diverse sources of resilience.

Eutrophication of aquatic ecosystems: Bistability and soil phosphorus

Abstract: Eutrophication (the overenrichment of aquatic ecosystems with nutrients leading to algal blooms and anoxic events) is a persistent condition of surface waters and a widespread environmental problem. Some lakes have recovered after sources of nutrients were reduced. In others, recycling of phosphorus from sediments enriched by years of high nutrient inputs causes lakes to remain eutrophic even after external inputs of phosphorus are decreased. Slow flux of phosphorus from overfertilized soils may be even more important for maintaining eutrophication of lakes in agricultural regions. This type of eutrophication is not reversible unless there are substantial changes in soil management. Technologies for rapidly reducing phosphorus content of overenriched soils, or reducing erosion rates, are needed to improve water quality.

Ecosystem subsidies: terrestrial support of aquatic food webs from 13c addition to contrasting lakes

Abstract: Whole-lake additions of dissolved inorganic C-13 were used to measure allochthony (the terrestrial contribution of organic carbon to aquatic consumers) in two unproductive lakes (Paul and Peter Lakes in 2001), a nutrient-enriched lake (Peter Lake in 2002), and a dystrophic lake (Tuesday Lake in 2002). Three kinds of dynamic models were used to estimate allochthony: a process-rich, dual-isotope flow model based on mass balances of two carbon isotopes in 12 carbon pools; simple univariate time-series models driven by observed time courses of delta(13)CO(2); and multivariate autoregression models that combined information from time series of delta(13)C in several interacting carbon pools. All three models gave similar estimates of allochthony. In the three experiments without nutrient enrichment, flows of terrestrial carbon to dissolved and particulate organic carbon, zooplankton, Chaoborus, and fishes were substantial. For example, terrestrial sources accounted for more than half the carbon flow to juvenile and adult largemouth bass, pumpkinseed sunfish, golden shiners, brook sticklebacks, and fathead minnows in the unenriched experiments. Allochthony was highest in the dystrophic lake and lowest in the nutrient-enriched lake. Nutrient enrichment of Peter Lake decreased allochthony of zooplankton from 0.34-0.48 to 0-0.12, and of fishes from 0.51-0.80 to 0.25-0.55. These experiments show that lake ecosystem carbon cycles, including carbon flows to consumers, are heavily subsidized by organic carbon from the surrounding landscape.

Surrogates for Resilience of Social–Ecological Systems

Abstract: From its roots in ecology, resilience (Holling 1973) has more recently been applied to social-ecological systems, or SES. Theories of changing resilience explicitly address the persistence or breakdown of diverse states of complex systems (Gunderson and Holling 2002). These ideas have attracted interest from interdisciplinary research groups interested in change, conservation or restoration of SES (Berkes and others 2003; Scheffer and others 2003). From a practical standpoint, resilience theory provides a conceptual foundation for sustainable development (Folke and others 2002). The transition from the ory to practice, however, requires assessment or estimation of resilience (Carpenter and others 2001). So far, there is little experience with esti mating resilience of SES, and little understanding of the sensitivity of resilience measures to changes in SES. This shortage of practical field experience is a barrier to building understanding through empirical study of resilience in SES. Direct measurement of resilience is difficult be cause it requires measuring the thresholds or boundaries that separate alternate domains of dynamics for SES. The only sure way to detect a threshold in a complex system is to cross it (Carpenter 2003). Yet threshold-crossings do not occur very often. In the natural sciences, much understanding of thresholds has come from delib erate manipulations of ecosystems, or before/after studies of large disturbances (Turner and Dale

Food Webs, Body Size, and Species Abundance in Ecological Community Description

Abstract: I. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 A. Trivariate Relationships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 B. Bivariate Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 C. Univariate Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 D. EVect of Food Web Perturbation . . . . . . . . . . . . . . . . . . . . . . . . 4 I

Eutrophication due to phosphorus recycling in relation to lake morphometry, temperature, and macrophytes

Abstract: Lakes may have alternative states due to excessive phosphorus (P) input: a clear-water state and turbid one with high chlorophyll concentrations. Because shifts between these states have large ecosystem effects, and restoration after the shifts is costly or sometimes impossible, precise evaluation of the possibility of alternative states is needed for lake management. Yet the shifts are quite variable and seem to depend on many factors, including lake morphometry, temperature, and dominance of macrophytes. Here we evaluated the role of these factors using an empirically based model that included more mechanistic detail than earlier models of regime shifts in trophic state. Mean depth and temperature strongly influenced the susceptibility of lakes to regime shifts and lake restoration. The macrophyte effect of preventing P recycling from sediments was critical to the susceptibility of shallow lakes to regime shift. With warmer temperatures, eutrophication was more likely and restoration was less successful due to increased internal P recycling from the sediment. Lakes with intermediate depths were most susceptible to regime shifts and were least restorable. These lakes were too deep to be protected by macrophytes in their littoral zones and were too shallow to mitigate P recycling through hypolimnetic dilution. Our results illustrated the interplay of multiple physical, chemical, and biotic mechanisms in regime shifts, a complex type of causality that may arise in regime shifts of other types of ecosystems.

Body sizes of consumers and their resources

Abstract: Trophic information—who eats whom—and species' body sizes are two of the most basic descriptions necessary to understand community structure as well as ecological and evolutionary dynamics. Consumer–resource body size ratios between predators and their prey, and parasitoids and their hosts, have recently gained increasing attention due to their important implications for species' interaction strengths and dynamical population stability. This data set documents body sizes of consumers and their resources. We gathered body size data for the food webs of Skipwith Pond, a parasitoid community of grass-feeding chalcid wasps in British grasslands; the pelagic community of the Benguela system, a source web based on broom in the United Kingdom; Broadstone Stream, UK; the Grand Caricaie marsh at Lake Neuchtel, Switzerland; Tuesday Lake, USA; alpine lakes in the Sierra Nevada of California; Mill Stream, UK; and the eastern Weddell Sea Shelf, Antarctica. Further consumer–resource body size data are included for planktonic predators, predatory nematodes, parasitoids, marine fish predators, freshwater invertebrates, Australian terrestrial consumers, and aphid parasitoids. Containing 16 807 records, this is the largest data set ever compiled for body sizes of consumers and their resources. In addition to body sizes, the data set includes information on consumer and resource taxonomy, the geographic location of the study, the habitat studied, the type of the feeding interaction (e.g., predacious, parasitic) and the metabolic categories of the species (e.g., invertebrate, ectotherm vertebrate). The present data set was gathered with the intent to stimulate research on effects of consumer–resource body size patterns on food-web structure, interaction-strength distributions, population dynamics, and community stability. The use of a common data set may facilitate cross-study comparisons and understanding of the relationships between different scientific approaches and models.

Do dams and levees impact nitrogen cycling? Simulating the effects of flood alterations on floodplain denitrification

Abstract: A fundamental challenge in understanding the global nitrogen cycle is the quantification of denitrification on large heterogeneous landscapes. Because floodplains are important sites for denitrification and nitrogen retention, we developed a generalized floodplain biogeochemical model to determine whether dams and flood-control levees affect floodplain denitrification by altering floodplain inundation. We combined a statistical model of floodplain topography with a model of hydrology and nitrogen biogeochemistry to simulate floods of different magnitude. The model predicted substantial decreases in NO3-N processing on floodplains whose overbank floods have been altered by levees and upstream dams. Our simulations suggest that dams may reduce nitrate processing more than setback levees. Levees increased areal floodplain denitrification rates, but this effect was offset by a reduction in the area inundated. Scenarios that involved a levee also resulted in more variability in N processing among replicate floodplains. Nitrate loss occurred rapidly and completely in our model floodplains. As a consequence, total flood volume and the initial mass of nitrate reaching a floodplain may provide reasonable estimates of total N processing on floodplains during floods. This finding suggests that quantifying the impact of dams and levees on floodplain denitrification may be possible using recent advances in remote sensing of floodplain topography and flood stage. Furthermore, when considering flooding over the long-term, the cumulative N processed by frequent smaller floods was estimated to be quite large relative to that processed by larger, less frequent floods. Our results suggest that floodplain denitrification may be greatly influenced by the pervasive anthropogenic flood-control measures that currently exist on most majors river floodplains throughout the world, and may have the potential to be impacted by future changes in flood probabilities that will likely occur as a result of climate shifts.

Soil phosphorus variability: scale-dependence in an urbanizing agricultural landscape

Abstract: We examine the hypothesis that human activity changes patterns of variance in soil P (Bray-1) concentrations across several spatial scales. We measured soil P concentrations and variability for each of four different land uses at three distinct levels of analysis. Land uses were remnant prairie, lawns, corn fields of cash grain farms, and corn fields of dairies in Dane County, Wisconsin (USA). For each land use type, levels of analysis were sites (an agricultural field, residential lawn or prairie, ranging in size from 100 m 2 to approximately 20 ha), 10-m plots within a site, and points within the 10-m diameter plot. The rank of mean soil P concentrations was cash grain > dairy > lawn > prairie. For all land use types, most of the variance was accounted for by site-to-site variation. Among-site variance was higher for human-dominated sites (0.55, 0.15, 0.14 [log (mg/kg)] 2 for cash grain, dairy, and lawn sites, respectively) than it was for prairies (0.07 [log (mg/kg)] 2 ). However, prairies had the highest among-plot variation (0.04 [log (mg/kg)] 2 ) compared to other sites (0.01, 0.002, and 0.01 [log (mg/kg)] 2 for cash grain, dairy, and lawn sites, respectively). The results indicate that in this watershed, human activity has increased the mean soil P and variance of soil P, and shifted the scale of variance to larger spatial extents. Human impacts on landscape pattern extend to soil properties that affect nutrient flow and eutrophication of surface waters. Because soil P turns over slowly, the legacy of altered soil P patterns may affect freshwaters for centuries.

Uncertainty in Discount Models and Environmental Accounting

Abstract: Cost-benefit analysis (CBA) is controversial for environmental issues, but is nevertheless employed by many governments and private organizations for making environmental decisions. Controversy centers on the practice of economic discounting in CBA for decisions that have substantial long-term consequences, as do most environmental decisions. Customarily, economic discounting has been calculated at a constant exponential rate, a practice that weights the present heavily in comparison with the future. Recent analyses of economic data show that the assumption of constant exponential discounting should be modified to take into account large uncertainties in long-term discount rates. A proper treatment of this uncertainty requires that we consider returns over a plausible range of assumptions about future discounting rates. When returns are averaged in this way, the schemes with the most severe discounting have a negligible effect on the average after a long period of time has elapsed. This re-examination of economic uncertainty provides support for policies that prevent or mitigate environmental damage. We examine these effects for three examples: a stylized renewable resource, management of a long-lived species (Atlantic Right Whales), and lake eutrophication.

State of the Art in Simulating Future Changes in Ecosystem Services

Abstract: Coordinating Lead Author: Peter Kareiva Lead Authors: John B. R. Agard, Jacqueline Alder, Elena Bennett, Colin Butler, Steve Carpenter, W. W. L. Cheung, Graeme S. Cumming, Ruth Defries, Bert de Vries, Robert E. Dickinson, Andrew Dobson, Jonathan A. Foley, Jacqueline Geoghegan, Beth Holland, Pavel Kabat, Juan Keymer, Axel Kleidon, David Lodge, Steven M. Manson, Jacquie McGlade, Hal Mooney, Ana M. Parma, Miguel A. Pascual, Henrique M. Pereira, Mark Rosegrant, Claudia Ringler, Osvaldo E. Sala, B. L. Turner II, Detlef van Vuuren, Diana H. Wall, Paul Wilkinson, Volkmar Wolters Review Editors: Robin Reid, Marten Scheffer, Antonio Alonso