Patterns of Nutrient Loss from Unpolluted, Old‐Growth Temperate Forests: Evaluation of Biogeochemical Theory
TL;DR: In this article, the authors report on patterns of hydrologic nutrient loss from old-growth temperate forest ecosystems in southern Chile based on chemical analyses of small streams draining 31 watersheds.
Abstract: Atmospheric pollution and other human activities have altered natural ele- ment cycles over large regions of the world. Much current understanding of nutrient dy- namics in temperate region ecosystems has been derived from such biogeochemically altered areas. While it is increasingly difficult to find regions of temperate forest that can be classified as free from human influences, studies of unpolluted and undisturbed areas can (1) provide important "baseline" information about natural patterns of element cycling, against which disturbed cycles can be compared; (2) provide insights into the biogeochem- ical conditions that acted as evolutionary and selective constraints on biotic communities before the advent of regional-scale human impacts; and (3) provide an opportunity to evaluate the general nature of biogeochemical theories that have been developed in areas subject to strong human influences. We here report on patterns of hydrologic nutrient loss from old-growth temperate forest ecosystems in southern Chile based on chemical analyses of small streams draining 31 watersheds. These forests have not been subject to air pollution inputs and have remained floristically stable throughout the Holocene. For major elements our results support pre- dictions from current biogeochemical theory (the "nutrient retention hypothesis") that net biotic retention of elements should be minimal in old-growth forest ecosystems. Despite the dilute nature of watershed streams, the overall patterns of loss of most elements could be explained almost exclusively by atmospheric inputs of marine aerosols. In contrast, patterns of nitrogen loss were more complex than predicted by current conceptual models. Hydrologic N losses occurred nearly exclusively (95% of total N) as dissolved organic forms of nitrogen (DON), rather than as the inorganic forms NO3- (0.2% of total N) and NH4+ (4.8% of total N). The strong dominance of organic over inorganic losses of N indicates that losses of N from old-growth forest ecosystems are not exclusively subject to traditional mechanisms of direct biotic control (i.e., mineralization supply or biotic uptake), but are also subject to indirect biotic control associated with the long-term ac- cumulation, humification, and leaching of soil organic N during ecosystem succession. The view of unpolluted old-growth forests as "leaky" vs. "non-leaky" with respect to N depends on whether ecosystem budgets or models consider dissolved organic, as well as inorganic, forms of N. High- and mid-elevation forests in our study area showed the lowest efflux concentrations of N as NO3- reported from any old-growth temperate forest ecosystem (0.10 vs. 0.30 pg/L, respectively). Comparisons against other old-growth forests, subject to varying levels of N deposition, indicated that levels of NO3- and the relative abundance of NO3- vs. NH4+ in Northern Hemisphere forests may be strongly influenced by atmospheric N inputs. Our analyses suggest that patterns of N cycling, as well as evolutionary selective pressures on plant and microbial species, may have changed as a function of regional-scale increases in atmospheric N deposition to European and North American temperate forests. We hypothesize that, because they inherently are more poor than aggrading forests at retaining added nutrients, old-growth forest ecosystems are particularly sensitive indicators of N deposition.
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TL;DR: In this article, a review of available scientific evidence shows that human alterations of the nitrogen cycle have approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; increased concentrations of the potent greenhouse gas N 2O globally, and increased concentration of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth.
Abstract: Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many terrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered the global cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their influence spreads regionally and even globally. Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needs such as agricultural production, their environmental conse- quences are serious and long term. Based on our review of available scientific evidence, we are certain that human alterations of the nitrogen cycle have: 1) approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; 2) increased concentrations of the potent greenhouse gas N 2O globally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; 3) caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility; 4) contributed substantially to the acidification of soils, streams, and lakes in several regions; and 5) greatly increased the transfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientific evidence we are confident that human alterations of the nitrogen cycle have: 6) increased the quantity of organic carbon stored within terrestrial ecosystems; 7) accelerated losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen, and losses of the animals and microorganisms that depend on them; and 8) caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.
5,729 citations
Cites background from "Patterns of Nutrient Loss from Unpo..."
...…of interacting factors that correlate with a system’s capacity to retain N (prior to becoming N saturated) have been identified, including the C:N ratio of soil organic matter, soil texture and degree of chemical weathering, fire history, rate of biomass accumulation, and past human land use....
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...Rather, it presents an overview of the current state of scientific understanding of this human-caused global change....
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...…unevenly over Earth’s surface—some areas (e.g., northern Europe) are profoundly altered (Berendse et al. 1993, Wright and van Breeman 1995), while others (e.g., remote south-temperate regions) receive little direct input (Galloway et al. 1982, Hedin et al. 1995)—but no place on Earth is unaffected....
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...Nevertheless, studies in remote southern hemisphere temperate regions (Galloway et al. 1982, Hedin et al. 1995) illustrate that valuable information on areas that have been minimally altered by humans remains to be gathered....
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...Analyses of recent data suggest that N in streams and rivers draining relatively undisturbed forests is largely organic N (Schindler et al. 1980, Hedin et al. 1995); with increasing human disturbance, total N fluxes in rivers increase and a higher proportion is composed of nitrate (Howarth et al…...
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TL;DR: In this paper, the authors compared the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr) and found that human activities increasingly dominate the N budget at the global and at most regional scales, and the terrestrial and open ocean N budgets are essentially dis-connected.
Abstract: This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.
4,555 citations
Book•
01 Sep 2011
TL;DR: In this paper, the Ecosystem Concept is used to describe the Earth's Climate System and Geology and Soils, and the ecosystem concept is used for managing and sustaining ecosystems.
Abstract: I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References
3,086 citations
TL;DR: It is suggested that depletion, soil barriers, and low-P parent material often cause ultimate limitation because they control the ecosystem mass balance of P and cause it to be an ultimate limiting nutrient.
Abstract: Nutrient limitation to primary productivity and other biological processes is widespread in terrestrial ecosystems, and nitrogen (N) and phosphorus (P) are the most common limiting elements, both individually and in combination. Mechanisms that drive P limitation, and their interactions with the N cycle, have received less attention than mechanisms causing N limitation. We identify and discuss six mechanisms that could drive P limitation in terrestrial ecosystems. The best known of these is depletion-driven limitation, in which accumulated P losses during long-term soil and ecosystem development contribute to what Walker and Syers termed a "terminal steady state" of profound P depletion and limitation. The other mechanisms are soil barriers that prevent access to P; transactional limitation, in which weathering of P-containing minerals does not keep pace with the supply of other resources; low-P parent materials; P sinks; and anthropogenic changes that increase the supply of other resources (often N) relative to P. We distinguish proximate nutrient limitation (which occurs where additions of a nutrient stimulate biological processes, especially productivity) from ultimate nutrient limitation (where additions of a nutrient can transform ecosystems). Of the mechanisms that drive P limitation, we suggest that depletion, soil barriers, and low-P parent material often cause ultimate limitation because they control the ecosystem mass balance of P. Similarly, demand-independent losses and constraints to N fixation can control the ecosystem-level mass balance of N and cause it to be an ultimate limiting nutrient.
1,922 citations
Cites background from "Patterns of Nutrient Loss from Unpo..."
...Persistent losses of dissolved organic N from undisturbed ecosystems can satisfy this condition (Hedin et al. 1995, Perakis and PLATE 1....
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TL;DR: In the US, nitrogen deposition remains relatively constant in the northeastern United States and is increasing in the Southeast and the West (Fenn et al. as mentioned in this paper, 2003), while acid acid deposition is increasing.
Abstract: N itrogen emissions to the atmosphere due to human activity remain elevated in industrialized regions of the world and are accelerating in many developing regions (Galloway 1995). Although the deposition of sulfur has been reduced over much of the United States and Europe by aggressive environmental protection policies, current nitrogen deposition reduction targets in the US are modest. Nitrogen deposition remains relatively constant in the northeastern United States and is increasing in the Southeast and the West (Fenn et al. in press). The US acid deposition effects
1,734 citations
References
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TL;DR: The principles of ecological succession bear importantly on the relationships between man and nature and needs to be examined as a basis for resolving man’s present environmental crisis.
Abstract: The principles of ecological succession bear importantly on the relationships between man and nature. The framework of successional theory needs to be examined as a basis for resolving man’s present environmental crisis. Most ideas pertaining to the development of ecological systems are based on descriptive data obtained by observing changes in biotic communities over long periods, or on highly theoretical assumptions; very few of the generally accepted hypotheses have been tested experimentally. Some of the confusion, vagueness, and lack of experimental work in this area stems from the tendency of ecologists to regard “succession” as a single straightforward idea; in actual fact, it entails an interacting complex of processes, some of which counteract one another.
4,419 citations
TL;DR: On the basis of analytical chemical data for numerous rain, river, lake, and ocean samples, the three major mechanisms controlling world surface water chemistry can be defined as atmospheric precipitation, rock dominance, and the evaporation-crystallization process.
Abstract: On the basis of analytical chemical data for numerous rain, river, lake, and ocean samples, the three major mechanisms controlling world surface water chemistry can be defined as atmospheric precipitation, rock dominance, and the evaporation-crystallization process.
2,885 citations
TL;DR: In this article, the authors describe ways in which excess nitrogen from fossil fuel combustion may stress the biosphere, and the complexity of these effects on water quality and on forest nutrition is discussed.
Abstract: This article describes ways in which excess nitrogen from fossil fuel combustion may stress the biosphere. Nitrogen emissions can have a direct effect on air quality through both the oxidizing potential of nitrogen oxides and the role these compounds play in the formation of ozone. The complexity of these effects on water quality and on forest nutrition is discussed.
2,333 citations
Book•
29 Oct 1999
TL;DR: In this paper, the authors present the bulk composition, structure, and dynamics of the atmosphere and discuss the chemistry of the Troposphere: the Methane Oxidation Cycle, ozone, and sulfur compounds.
Abstract: Bulk Composition, Structure, and Dynamics of the Atmosphere. Photochemical Processes and Elementary Reactions. Chemistry of the Stratosphere. Chemistry of the Troposphere: The Methane Oxidation Cycle. Ozone in the Troposphere. Hydrocarbons, Halocarbons, and Other Volatile Organic Compounds. The Atmospheric Aerosol. Chemistry of Clouds and Precipitation. Nitrogen Compounds in the Troposphere. Sulfur Compounds in the Atmosphere. Geochemistry of Carbon Dioxide. The Evolution of the Atmosphere. References. Appendix: Supplementary Tables.
1,528 citations