1. LINKAGES: Integrating linkages among aquatic and terrestrial landscape elements. Ecosystem Studies Program, National Science Foundation. 2000-2003. Stuart Fisher, PI/PD; Jianguo Wu and Beth Boyer, Senior Associates; Wanli Wu, Post-Doctoral Associate; Jill Welter and Julia Henry, Graduate RAs.

This research project concerns changes in nitrogen transport, transformation, and retention along flowpaths linking sites of atmospheric deposition in terrestrial desert uplands to permanent streams supporting rich riparian forests. In arid lands of southwestern U.S.A., including the study area, atmospheric deposition of nitrogen (N) exceeds export by streams and rivers. This suggests a large annual storage increment, yet both terrestrial and aquatic primary production are N-limited. The research objective is to identify the hot spots (in space and time) for N transformation and retention (input-output) in an aridland catchment and to thereby account for the loss of N between precipitation input and streamflow output.

 We are attacking this puzzle from the perspective of running water ecology by using a flowpath approach. The flowpath approach is a natural outgrowth of research in streams where flow, connection, and longitudinal change are essential elements of theory (i.e., material spiraling and river continuum concepts). Flowpath and nutrient retention studies are being conducted in three connected landscape elements: the upland, an intermediate tributary system, and the stream riparian corridor.

 This research will contribute to understanding of the mechanisms of N retention in arid landscapes, but it also is relevant to more global questions of how increased N deposition affects ecosystems, how aquatic and terrestrial components of landscapes are linked, the effect of variable climatic regimes on ecosystem-level processes, and what aspects of spatial configuration in landscapes are associated with maximal nutrient retention. For stream ecology, it will include an explicit investigation of the effects of branching pattern, a characteristic of streams that heretofore has been neglected.

2. LTREB: Short-Term Climate Change and Variable Response to Disturbance in an Arid Land Watershed-Stream Ecosystem (National Science Foundation, 1997-2002) Nancy Grimm, PI/PD; Stuart Fisher, Co-PI; all others, participants and collaborators.

Funded by NSF's Long-Term Research in Environmental Biology (LTREB) program, this project is a long-term investigation of the capacity of various components of a desert stream ecosystem to respond to a disturbance, which itself varies with interannual variation in climate. Climate interacts with this ecosystem by providing, through runoff, both water and nutrients to the stream channel. In particular, nitrogen, a key element in desert ecosystems, varies in stream water as a function of extended (several years) dry or wet periods. Nitrogen availability has a strong influence on both algal succession and the capacity of invertebrates to recover after disturbance. Climatic forcers affecting precipitation and runoff provide the predominant form of disturbance in this ecosystem, flash floods and drought. Therefore, climate, by influencing precipitation, evapotranspiration, and resulting runoff, both alters inputs of essential materials to the ecosystem and is a major disrupter of biotic structure.

We have investigated both the mechanisms of terrestrial-aquatic linkage and interannual patterns of disturbance response in Sycamore Creek, Arizona, using a combination of manipulative and experimental approaches. This research relies heavily upon an existing long-term database describing structure and functioning of this ecosystem. The project is in its final synthesis stage.

3. CAP LTER: Central Arizona - Phoenix Long - Term Ecological Research Project. Nancy Grimm, PI/PD; Stuart Fisher, Co-PI and IGERT PI/PD; David Lewis and Wanli Wu, post-doctoral associates; Jennifer Edmonds, John Roach, Darrel Jenerette, Matt Luck, and Aisha Coppola, graduate RAs and IGERT fellows or associates.

This long-term study of the urban area of central Arizona focuses on the Phoenix metropolis. The overall question being addressed in this study is: How does the pattern of the city alter ecological conditions of the city and its surrounding environment, and how do changes in ecological conditions feed back to the human social system? Please see the CAP LTER web page for further information. An Integrated Graduate Education and Research Training (IGERT) Program in urban ecology supports graduate students in Biology, Plant Biology, Sociology, Anthropology, Geology, and Geography.

4. SAHRA: Science and Technology Center: Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA). Nancy B. Grimm, Senior Associate by sub-contract from the University of Arizona (Soroosh Sorooshian, University of Arizona, PI/PD); U of A collaborators: Martha Conklin, Roger Bales; USGS collaborator: Judson Harvey; ASU participants: John Schade and David Lewis, post-doctoral associates; John Roach, graduate RA (spring 2000).

The goal of this research is to understand the coupling between nutrient cycles (nitrogen and carbon) and the hydrologic cycle in semi-arid riparian systems. Initially, we plan to focus on the nitrogen cycle. The workplan includes the development of innovative methods to characterize the amount of nitrogen  (nitrate, ammonia, organic nitrogen) and the rate of nitrogen retention (e.g., plant uptake and denitrification) in semi-arid riparian systems. We will use these techniques to characterize nitrogen cycling in the San Pedro River and then apply them to other stream systems (e.g., Rio Grande and Owens River).  Specific aims include determining nitrogen retention along different flowpaths in the riparian system, developing a nitrate/chloride (in collaboration with others) balance for the watershed, and to develop a model that links stream and hyporheic zone processes for nitrogen cycling. Please see the SAHRA web page for further information.