Comparative Effects of Global Climate on
Ecosystem Nitrogen and Soil Biogeochemistry in the U.S. National Parks

Duration: June 1999 - June 2005

Many National Parks and other lands under the stewardship of the U.S. Department of Interior are being subjected to three overlapping global stressors:

1. Life zone or biogeographic change, such as desertification.
2. Biogeochemical and biotic change from acid rain, elevated levels of carbon dioxide () in the atmosphere, altered carbon (C) and nitrogen (N) cycles, and human-introduced trace elements.
3. Climate change, including the effects of changing temperatures on life zones, depth to permafrost, melting snow fields and glaciers; and change in precipitation patterns.
   

Increases or decreases in precipitation amount can raise or lower surface and groundwater levels and thereby change mineralization rates and the quantities of minerals and organic matter entering streams and lakes.Precipitation change also impacts soil nutrient dynamics and hydrologic characteristics that can alter microbial relationships and ecosystem stability.Research in representative, relatively undisturbed, "natural" watersheds containing protected ecosystems can provide a basis for understanding such changes.

Our research addresses multi-regional issues of nitrogen (N) and carbon (C) dynamics affecting the integrity of "natural" ecosystems.Our results will shed light on how the effects of changing biogeochemical cycles, particularly inorganic N, coupled with shifts in temperature and/or moisture can affect species invasions and biodiversity. Nitrogen is one of the building blocks of life and the most common limiting nutrient in terrestrial ecosystems.There is a high potential for present atmospheric inputs of N to be significantly augmented by by the release of mineral N from soil organic matter with only a slight increase in temperature and/or moisture.

Forest ecosystems, in particular, have large organic N and C reservoirs.Changes in the availability of N and C could, in time, switch these ecosystems from C sinks (accumulators) to C sources (exporters). A change in terrestrial N availability could also alter the quantity and quality of dissolved organic carbon (DOC) and nitrogen (DON) released from the forest floor and soil. Continuous nitrate addition, as from atmospheric inputs, could also increase DOC and DON export below the rooting zone and into aquatic ecosystems.

Once these processes are initiated, they will eventually lead to marked changes in ecosystem biodiversity, both above- and below-ground. Such ecosystem stress will be chronic, subtle, and very widespread, making tactical mitigation, as through local management, nearly impossible.

Approach:

During 1980 to 1982, the U.S. National Park Service embarked upon a program of long-term watershed research and monitoring. The purpose was to better understand how "natural" watersheds function. Current watershed study sites range from the hot Chihuahuan Desert in the Southwest, to the moist boreal forests, to eastern deciduous forests, and to the alpine and taiga-tundra. This system of watersheds in National Parks is a natural choice for comparative studies of the N cycle.

Continued integrated monitoring of atmospheric inputs, climate, surface water chemistry, soil, vegetation, hydrology, and aquatic resources at five of these watershed study sites will provide the backdrop for our analyses of both existing data and new data to be collected beginning in summer of 2000. New data will include: above- and below-ground C, cycling and fluxes (including growth, litterfall, microbial C, and dissolved C); dissolved N fluxes and below-ground N transformations (N release and uptake, N mineralization, dissolved inorganic N and dissolved organic nitrogen [DON] fluxes); and linkages between N and C fluxes and forest dynamics, climate, and hydrology.

Intensive plot studies will be conducted in the dominant vegetation types of each watershed. We will measure vegetation quality and quantity, air and soil temperature, soil moisture, precipitation, and soil water ions and DOC and DON in this network of small plots.Net N mineralization rates and climate will be monitored at all sites. Soil water flow direction and quality will be monitored on these gradients.Forest floor and soil bacterial functional diversity will be used to assess below ground biological relations with soil organic matter, temperature, and moisture.Mycorrhizal biomass will be quantified seasonally using the small core method. Gross N mineralization and immobilization will be measured on a subset of plots in each vegetation type.This study will be conducted for two years.

During this same two-year period, we will experiment with increasing the forest floor temperature on a subset of net N mineralization plots.This study will give us an indication of the change in net and gross N mineralization rates in response to temperature change.Field measurements of CO2 efflux will serve as an index of below-ground respiration during the study. Field studies of N mineralization and CO2 evolution rates will be repeated under controlled laboratory conditions for varying moisture and temperature levels.

Goals and Objectives:

The two overall goals of our research are: 1) to provide a basic understanding the structure and processes of aquatic and terrestrial ecosystems, and 2) to generate timely scientific input to assist in developing mitigation strategies to address major threats to the ecological integrity of the public lands, specifically protected lands such as the National Parks (NP's).Greater resolution of the structure and function of forested ecosystems, their ecotones, and their response to global change will result from our analyses of the N-cycle in watersheds having long-term monitoring and biogeochemical cycling data.

Specific short-term (5 year) objectives are to: 1) quantify long-term change in hydrologic, nutrient, and C budgets on a gradient of watershed ecosystem biota; 2) monitor long-term trends in soil N status; 3) examine spatial and temporal change in subsurface soil water chemistry and flow to quantify N export and response to change in soil temperature and moisture; 4) examine how changes in soil N availability alters forest floor and soil production of dissolved organic carbon (DOC) and DON; 5) quantify change in labile C and N compounds from microbial biomass in response to soil temperature and N availability; 6) evaluate long-term trends in forest floor and soil microbial activity, soil microbial biomass and functional diversity, and provide biological parameters for measuring ecosystem stability and response to disturbance; 7) assess spatial and temporal patterns in decomposition rates, as decomposition of plant litter is a key ecosystem process linking the below-ground microbial component with primary ecosystem production; 8) assess impact of changes in forest structure alone and in combination with environmental changes (atmospheric inputs, global climate) on the function of forested watersheds (biogeochemistry and nutrient retention); and, 9) provide management recommendations concerning human impacts on Park watersheds.

We will test the following 5 hypotheses:

1. Nitrogen outputs can equal or exceed inputs in unpolluted late successional ecosystems.
2. Nitrate (NO3-) concentrations in streams at low flow will reflect watershed N saturation.
3. Watershed conditions, precipitation and temperature will affect the size of the NO3- (and maybe DON) pulse in stream water.
4. Temperature, precipitation and N input gradients will affect soil microbial communities.
5. Soil microbial biomass and functional diversity will decline as soil NO3- levels increase.
   

Applications of Results:

The development of mitigation strategies for natural ecosystems requires research coupled with inventory and monitoring to maximize the probability that: 1) changes in response to stress will be detected, 2) the magnitude of change will be quantified, and 3) the sources of stress, human or non-human, will be separable and quantifiable before important ecosystem values and services are irreplaceably lost. Long-term, ecosystem-level perspectives are essential for understanding ecosystem structure, function, and response to stress.

After almost 20 years of integrated biogeochemical data collection and analyses we are now able to draw a few management and policy conclusions and provide some management alternatives. We are generating scientific inputs and long-term data bases to assist in developing mitigation strategies to address threats to the ecological integrity of the public lands, specifically the NP's.

Anticipated Products:

Products of our work will include:

• Annual reports summarizing accomplishments, major research results, publications, and research plans for the following fiscal year.
• Updates of the long-term data for stream and precipitation chemistry. climate, litterfall, and biomass information.
• Characterizations of physical and biological parameters in forested sites.
• Papers for journal and symposia publication.

Presentations of findings at scientific conferences.
We will also continue to provide management and policy recommendations concerning human impacts on NP watersheds.
Collaborators and Cooperators:

This research is being conducted in cooperation with Michigan Tech University, Utah State University, University of Washington, Texas Tech University, University of Maine, University of Alaska, Colorado State University, and Sul Ross University.

Binkley, Dr. Robert L. Edmonds, Steve Moore,
Georgia Murray, David Toczydlowski, Dr.
Kevin Urbanczyk, Dr. Helga van Miegroet, Dr.
Keith Yarborough and Dr. John C. Zak.

	Primary Contacts: Ray Herrmann and Bob Stottlemyer, USGS Fort Collins Science Center (FORT) [formerly Midcontinent Ecological Science Center (MESC)]