Research Theme II:  HES - Hydrologic,Ecologic, and Socio-economic systems

Ecosystem impacts and, Socio-economic impacts, policy-making and adaptation

Research theme leaders: J. Ramirez, L. Poff, and N. Grigg

Student programs in this theme area will equip scientists to explain and respond to impacts of water management actions on economic and ecologic systems.  Given the need to open minds of the public and policy makers about long-term ecosystem damage from natural and human-caused drivers, this area of research is directed at an urgent national need.  For example, use changes such as in the Everglades can alter water flows and have large impacts on ecosystems; or climate change and imbalances of demand between agricultural and urban uses present challenges to develop sustainable management of rivers and human wellbeing, especially in the semi-arid and arid west.

  1. Non-native species invasion and extinction of native species
  2. Processes governing conversion of grasslands to shrubland
  3. Balancing economic and ecosystem needs for water in heavily-modified river basins

Non-native Species Invasion and Extinction of Native Species


Climate change has the likely consequence of altering the spatial and temporal distribution of runoff in river networks.  Hydrologically-driven fluvial processes sustain the habitat and ecological conditions required by many aquatic and riparian species in river ecosystems (Poff et al. 1997).   Human-alteration of fluvial dynamics has contributed to the diminishment of many native species and has allowed the establishment and expansion of many non-indigenous ones, some of them being noxious or nuisance.  For example, Eurasian saltcedar (Tamarix spp.) is a nonnative riparian shrub in the Southwest that has been replacing native cottonwood (Populus) in rivers having dams that truncate peak flows needed for cottonwood seedling establishment (Friedman et al. 2005).  The relationships between runoff and the relative success of saltcedarare now reasonably well understood (Stromberg et al. 2007, Merritt and Poff, in press), as are its ecological consequences (Shafroth et al. 2005).  Future climate change will do two things: 1) allow saltcedar to spread northward as temperatures warm, and 2) alter precipitation and modify timing and magnitude of runoff, which will alter fluvial disturbance dynamics that modulate the relative success of these two dominant riparian species.  A key question is: given the projected range of climate change in a region, what is the range of alteration in the timing and magnitude of river runoff, and how will this influence the risk of spread of invasive saltcedar and its competitive outcomes with already-established cottonwood species?  How might dams in the region be managed “adaptively” to reduce projected saltcedar spread and maintain cottonwood coexistence? And how would new dams interact with a changing climate to moderate the rate and extent of spread of saltcedar? 
Similar kinds of questions could be asked for many other species of concern, both native (e.g., endangered species such as salmonids in the Interior West) or invasive pest species (such as the New Zealand mud snail).  The physical alteration of the landscape and hydrologic cycle by humans has already extensively modified the hydrologic and sediment flux at the global scale (Vörösmarty et al. 2004, Syvitski et al. 2005) and has broad regional and continental scale implications for maintaining regional biodiversity and ecosystem function (Poff et al. 2007).
WATER-IGERT students would be involved in developing conceptual frameworks that span the ecological, hydrological and economic foundations of sustainability and build models that capture these complexities and feedbacks to support pro-actively both the interrelationships between water resources management and ecosystem sustainability.
By integrating climatological, hydrological, and ecological processes (and uncertainties), an optimization framework could be developed for a given social context and goals or a decision-support system that could allow for proactive multi-objective planning and management for climate change.

Processes Governing Grasslands to Shrubland Conversions


Climate change will change organismic, community, and ecosystem processes.  Variability in weather and economic conditions has enhanced uncertainty in the characteristics and land use decisions of rangelands in the Great Plains.  The production of forage is highly vulnerable to changes in precipitation.  Increases in the frequency of extreme events, trends and variability in precipitation and temperatures enhance the uncertainty in the rangeland systems and the social well being of the region. Today, there is a growing need to develop and implement a regional integrated assessment methodology in order to evaluate the impacts of climate change on these rangeland ecosystems and the human systems that depend on them (Mangan et al. 2003). 
Our research will develop a regional integrated modeling and assessment system by combining numerical modeling, simulations and field studies of short and long-term effects on biogeochemical cycles and their feedbacks to climate and the consequences of floods and droughts for land managers (Mangan et al. 2003).  As part of our integration between the natural and human systems will use many of the integration and dissemination tools used by the CSU Cooperative Extension Service.  An important product of our project will be the development of a set of written and digital information packages that can be disseminated to resource managers.
This research theme will test the following hypotheses: (a) The complexity of climate change impacts on ecosystem processes and associated societal demands can be effectively analyzed using empirical models that will provide ecological and managerial insight.  (b) Reductions in snow melt water inputs in combination with reductions in spring and or in summer rain, will favor the growth and development of shrubs compared to grasses. This increase in shrub abundance will result in only slight decreases in leaf carbon gain, slight decreases in leaf transpiration, use of deep as opposed to shallow water sources and reductions in the net CO2 flux of these systems in combination with reductions in soil and plant N cycling. (c) Drought conditions will shift the extent of carbon and water coupling at the plant and at the ecosystem scale.
The overall objectives of this research theme are thus:

  • Develop a modeling system that combines both rangeland-level decision-making about production choices and market-level processes that determine net profitability based on an ecosystem model of rangeland ecosystems.  We will evaluate use of water, soil fertility, and livestock yields and climate information based on observations, forecasts, and historical scenarios of precipitation.
  • Examine the combined effects of climate and vegetation changes on ecosystem processes of rangeland systems in the region.
  • Quantify how in situ manipulations of winter and summer precipitation will affect organismic, community and ecosystem processes including carbon and water vapor flux.
  • Quantify the coupling of carbon and water at the leaf and ecosystem scale and identify the mechanisms that allow shrubs to flourish under drought at the expense of the growth and development of grasses.
  • Provide estimates of water vapor flux that can be integrated with atmospheric modeling of precipitation.

Integrative modeling: Our ecosystem modeling will consist of using the CENTURY (DAYCENT version-Del Grosso et al. 2002) ecosystem model to evaluate how changes in precipitation regimes affect water, carbon and N fluxes and their feedbacks to atmospheric processes (Del Grosso et al. 2002).  CENTURY is a general model of the plant-soil ecosystem capable of simulating C and nutrient dynamics for grasslands, forests, croplands, and combined forest-herbaceous systems (e.g., Sanford et al.1991, Del Grosso et al. 2002, Mangan et al. 2003). Under different scenarios of precipitation conditions and associated weather patterns we will use CENTURY to estimate the magnitude of changes water vapor flux, carbon exchange and nitrogen processes.  These simulations will be accomplished using existing information plus the findings from our experimental studies and the output will be used to assist land managers in evaluating land use consequences under a range of precipitation regimes.
Field Studies: We will conduct our study at the Central Plains Experimental Range located in the shortgrass steppe of northeastern Colorado.  The vegetation of the area is characterized by a mixture of shrubs, Atriplex canescans (four wing salt bush) and a herbaceous understory dominated by the C4 perennial bunchgrass Bouteloua gracilis (blue grama). We will chose two sites for our field studies, one that is dominated by grasses and the other that is dominated by shrubs.  The shrub-dominated site represents a community that reflects the vegetation change that is often associated by prolonged droughts (Archer et al. 1995) while the grass dominated community represents a system that is accustomed to low precipitation but one that could undergo significant changes under drought scenarios.  This design will allow us to accurately portray what are the magnitudes of water, carbon and nitrogen processes under short-term drought in a existing grassland and what the magnitudes of biogeochemical fluxes will be like when droughts have been extensive and caused significant vegetation changes.  We are thus substituting community-type for temporal changes expected under prolonged drier conditions.

Balancing Economic and Ecosystem Needs for Water in Heavily-modified River Basins


The economies of many communities in the western United States (and elsewhere) depend greatly on the alteration of the natural hydrologic cycle.  Along the Front Range of Colorado, rivers have been fundamental to economic development, both through irrigated agriculture and municipal drinking water supplies.  Climate change and projected population growth are introducing new uncertainties into water resources management, and the ecological integrity and water quality of rivers in the region are vulnerable to continued over-allocation of available runoff.  Running from the Continental Divide, through Ft. Collins and the Great Plains, the Poudre is such a river. 
Many interests and administrative authorities are in the basin, including the Northern Colorado Water Conservancy District, the US Corps of Engineers, and various municipalities.  The river has value both as a direct economic asset but also from a recreational perspective, and the continued health of this “working” river is dependent on finding some balance among the multiple competing interests.  Scientists are challenged with translating their understanding of the river ecosystem into a language that can be appreciated by the broader public and governmental entities to effectively incorporate that understanding into public policy.  A whole basin approach is critical to include not only all political and socio-economic interests but to consider the spatially-distributed sources and causes of water quality impairment and ecological resilience.
This research theme will address the following questions: How are the range of ecosystem goods and services quantitatively related to the river hydrograph?  How sensitive are these to inter-annual variability in runoff?  What are the magnitudes of uncertainty in spatial and temporal components of ecosystem provision of goods and services?  And how do these ecological uncertainties scale relative to those derived from economic analysis?  How can these be combined into whole-basin models of the water cycle and its social-ecological dependencies?  Are there “limits” of development that create unacceptable risk of collapse of the river corridor?  Are these spatially distributed and how do they interact with projected climate change and population growth?  Can a “model” framework be developed to transfer to other basins in the West or globally to ‘balance’ human and ecosystem needs in water-limited settings?  Can lessons be learned from this system that are transferrable to other arid-land rivers facing similar pressure.

Organizing Concept

The primary mission of I-WATER is to prepare Ph.D. students to work in an interdisciplinary team-based activity. Our research themes involve interacting teams of hydrologists, meteorologists, ecologists, and management experts. I-WATER features problem-focused research to bridge basic and applied science by combining fundamental research on scientific problems with application of scientific knowledge to actual resource issues.

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