UNDERGRADUATE RESEARCH (REU)
Effects of episodic drought on vegetation along an elevational gradient 
To gain exposure to ecosystem studies as an undergraduate, I worked in Hawaii as a summer research assistant (REU) for Dr. Peter Vitousek at Stanford University.  There, I assisted his former graduate student, Dr. Alan Townsend (now CU), in field and lab research determining the effects of land use change and temperature on soil organic matter turnover in tropical soils.  I also performed an independent project examining the effects of an episodic drought on the vegetation along an elevational gradient on Mauna Loa, Hawaii.  The results from this study suggested that occasional, severe droughts might play a role in shaping primary succession.  I submitted this research as my undergraduate honors thesis at Cornell under the direction of Drs. Robert Howarth and Peter Vitousek and later published these findings (Lohse, Vitousek, and Nullet, 1995).  

Lohse, K.A., D. Nullet, and P.M. Vitousek. 1995. The Effects of an Extreme Drought on the Vegetation of a Single Lava Flow on Mauna Loa, Hawaii.  Pacific Science. 49:212 - 220. 

DISSERTATION RESEARCH
Hydrologic nitrogen losses from wet tropical forests following N additions
In my dissertation research, I explored the patterns and regulation of hydrologic nutrient losses from wet tropical forests receiving first-time and long-term nitrogen (N) additions.  There is growing evidence that anthropogenically-enhanced nitrogen deposition is shifting from a temperate zone concern to a global issue with dramatic increases predicted in the tropics over the next several decades (Matson, Lohse, and Hall, 2002).  At present, there is little information on the consequences of anthropogenic N inputs for tropical ecosystems, particularly aqueous losses.  My dissertation research took the first step to fill this gap in knowledge. 

In contrast to many temperate ecosystems where N is a limiting nutrient to productivity, many tropical ecosystems grow on highly weathered soils where another nutrient such as P or Ca is thought to limit tree growth and where N appears to be already in relative excess.  Unlike many N-limited ecosystems that experience delays in losses following N additions, I hypothesized that non-N limited ecosystems would not be able to retain initial inputs of N and would respond with large and immediate nitrate solution losses.  Alternatively, I predicted that soil chemical and physical properties that vary with soil age would strongly influence nitrate solute transport and retention processes.  

 I tested these hypotheses using sites located at the extreme ends of a chronosequence of soils in the Hawaiian Islands, 300 year old soils on the Island of Hawaii where tree growth has been experimentally shown to be N-limited and 4.1 million year old soils on the Island of Kauai where N availability is high and where tree growth has been experimentally shown to be P-limited.  In contrast to my initial expectations that nutrient status would control short-term losses, I found that tropical forests growing on volcanic soils responded to first-time N additions with immediate and large NO3 losses, particularly from the N-limited tropical forest on young soils.  Detailed hydrological studies conducted as a part of this study showed that changes in hydrological processes due to soil development with time could largely explain these observed differences in losses (Lohse 2002, Lohse and Matson, 2005).  In subsequent research, I used artificial rainfall experiments with dual isotope tracers of deuterium and nitrate to determine the relative importance of biological, physical, and chemical processes in controlling transport and retention of nitrate at these two sites (Lohse and Dietrich, 2005). In the future, I plan to extend this research and examine forest responses to anthropogenic N inputs along other environmental gradients. 

Effects of soil age on hydrological properties and flow paths
As an integral component of my dissertation research, I conducted detailed hydrological studies in collaboration with Dr. William Dietrich at the University of California, Berkeley to examine the influence of soil age on soil hydrologic properties and flow paths.  While many studies have used soil chronosequences to show temporal changes in soil physical properties such as clay content, mineralogy, and soil volume, few studies have actually quantified how these changes alter hydrological processes.    Results of these studies showed systematic changes in hydrological properties and flow paths, with decreasing subsurface saturated hydraulic conductivity increasing the relative importance of lateral to vertical flow paths as soils aged.  These findings have important implications for the rate and trajectory of soil development, watershed biogeochemistry, storm runoff mechanisms, and landscape evolution (Lohse 2002, Lohse and Dietrich 2005).  In future research, I plan to explore trends in hydrological processes along climate and parent material gradients.

Matson, P.A., K.A. Lohse, and S.J. Hall. 2002. The globalization of nitrogen: consequences for terrestrial ecosystems. Ambio.3:113-119.

Lohse, K.A. 2002. Hydrological and Biogeochemical Controls on Nitrogen Losses from Tropical Forests: Responses to Anthropogenic Nitrogen Additions. Dissertation Thesis. University of California, Berkeley.

Lohse, K.A. and P.A. Matson. 2005. Consequences of nitrogen additions for soil processes and soil solution losses from wet tropical forests. Ecological Applications.15: 1629-1648.

Lohse, K.A. and W.E Dietrich. 2005. Contrasting effects of soil development on hydrologic properties and flow paths. Water Resources Research. 41: W12419,doi:10.1029/2004WR003403.

POSTDOCTORAL RESEARCH
In a step to extend my research into the realm of landscape ecology and watershed science, I secured an EPA STAR postdoctoral fellowship working with Adina Merenlender in the Department of Environmental Science, Policy and Management (ESPM) at the University of California, Berkeley.  This research was an interdisciplinary project in collaboration with Greg Biging in ESPM, John Landis in City and Regional Planning, and Peter Berck in Agricultural Resource Economics.  Our goal was to examine the environmental consequences of land use change for California's coastal watersheds that are experiencing rapid urban and agricultural expansion. Our approach was to incorporate economic variables into spatially explicit land use change models to predict probabilities of vineyard and residential conversion at the parcel level in Sonoma County, California. 

Effects of Land-Use Change on Sediment Loading to Streams
In collaboration with Dr. Adina Merenlender and her former graduate student, Dr. Jeff Opperman, we explored the relationship between upland land cover and land-use characteristics (LULC) and in-stream habitat characteristics across a wide range of watersheds in the Russian River basin, California.  We were particularly interested in examining the relationship between land cover and embeddedness, the proportion of spawning gravels filled with fines, because of its relevance to salmonid fish spawning and rearing habitat.  Results from our study showed a strong relationship between the percent of agriculture in watersheds and degree of embeddedness (Opperman, Lohse et al. 2005).

Recently, we built on this knowledge to understand the relative impacts of urban, rural-residential, and agriculture on in-stream processes. We used spatially explicit parcel-level data to examine the influence of land use (including urban, rural-residential, and vineyard) on salmon-spawning substrate quality in tributaries of the Russian River Basin in California. We developed a land-use change model to forecast the probability of losses in high-quality spawning habitat and to recommend priority areas for incentive-based land conservation efforts. Ordinal logistic regression results indicated that all three land-use types negatively affect spawning substrate quality, with urban development having a larger marginal impact than either rural-residential or vineyard use. For two reasons, however, forecasted rural-residential and vineyard development have much larger influences on decreasing spawning substrate quality than urban development. First, the land-use change model estimates 10 times greater land-use conversion to both rural-residential and vineyard compared to urban. Second, forecasted urban development is concentrated in the most developed watersheds, which already have poor spawning substrate quality, such that the marginal response to future urban development is less significant. Our findings suggest that conservation efforts should target within moderately and less-developed watersheds, where high-quality fish habitat is threatened, rather than the most-developed watersheds, where land prices are typically much higher and land-use development has already resulted in significant habitat degradation.We developed an ordinal logistic regression model based on the observed distributions of fine sediment in spawning gravels and coupled this with a land use change model to predict future impacts of growth on fine sediment in streams (Lohse et al. in review).

Social Resilience and Water Scarcity
As an extension of this work in the Russian River, Dr. Ruth Landridge and graduate student, Juliet Christian-Smith, and I explored the factors controlling social resilience and vulnerability to water scarcity. We recognized that resilience is a vital attribute that characterizes a system’s capacity to cope with stress. While researchers have examined the measurement of resilience in ecosystems and in social–ecological systems, and the comparative vulnerability of social groups, our paper refocused attention on the processes and relations that create social resilience. Our central proposition was that the creation of social resilience is linked to a community’s ability to access critical resources. We explore this proposition through an analysis of how community resilience to the stress of water scarcity is influenced by historically contingent mechanisms to gain, control, and maintain access to water. Access is defined broadly as the ability of a community to actually benefit from a resource, and includes a wider range of relations than those derived from property rights alone. We provide a framework for assessing the construction of social resilience and use it to examine, first, the different processes and relations that enabled four communities in northern California to acquire access to water, and second, how access contributed to their differential levels of resilience to potential water scarcity. Legal water rights are extremely difficult to alter, and given the variety of mechanisms that can generate access, our study suggests that strengthening and diversifying a range of structural and relational mechanisms to access water can enhance a community’s resilience to water scarcity (Landridge, Christian-Smith, and Lohse 2006).

Opperman, J., K. Lohse, A. Merenlender, M. Kelly, and C. Brooks. 2005. Influence of watershed-scale land use on fine sediment in salmonid spawning gravels within the Russian River basin, California. Canadian Journal of Fisheries and Aquatic Sciences. 62:2740-2751, doi:10.1139/F05-187.

Landridge, R., Christian-Smith, J., and K. Lohse. Access and Resilience: Analyzing the Construction of Social Resilience to the Stress of Water Scarcity in a Mediterranean-Climate Region. Ecology and Society. 11(2): 18. [online] URL:http://www.ecologyandsociety.org/vol11/iss2/art18/

Lohse, K.A., D. A. Newburn, J.J. Opperman, and A. M. Merenlender. In review. Forecasting the relative impacts of land use on fine sediment in anadromous fish habitat to guide development and conservation programs.

ONGOING PROJECTS
Effects of hydrological flow paths on rates and forms of N loss in a Meditterrean watershed
In collaboration with graduate student, Jonathan Sanderman and Professor Ronald Amundson at UC Berkeley (Jan 2005-present), I have been examining the influence of variations in precipitation and hydrological pathways on the rate and form of N export along toposequences in two well-characterized Mediterranean catchments in northern California.  Patterns of precipitation and runoff in California are changing and likely to influence the structure and functioning of watersheds.  While several studies have demonstrated that hydrologic flushing during seasonal transitions in Mediterranean ecosystems can exert a strong control on nitrogen (N) export, few studies have examined the influence of different hydrological flow paths on rates and forms of nitrogen (N) losses.  Over the course of one water year, I analyzed seasonal patterns of dissolved organic nitrogen (DON), nitrate and ammonium concentrations in rainfall, throughfall, matrix and preferential flow, and stream samples.  I also analyzed seasonal soil N dynamics along this toposequence. Preliminary results show that during the transition to the winter rain season, but prior to any soil water displacement to the stream, DON and nitrate moved through near-surface soils as preferential flow.  Once hillslope soils became saturated, saturated subsurface flow flushed nitrate from the hollow resulting in high stream nitrate/DON concentrations. During the transition to the wet season, rates of soil nitrate production were high in the hollow relative to the hillslope soils.  In the spring, these rates systematically declined as soil moisture decreased.  Findings from our suggest seasonal fluctuations in soil moisture control soil N cycling, and seasonal changes in the hydrological connection between hillslope soils and streams control the seasonal production and export of hydrologic N (Lohse, Sanderman, Amundson 2005, Sanderman, Lohse, Amundson 2005).

Indirect effects of short- and long-term N additions on soil properties and soil solution losses
A current extension of my Hawaii research includes examining the indirect effects of long-term N loading on soil properties and solution losses.  In temperate ecosystems, base cation reactions often buffer soils from anthropogenic N inputs.  In highly weathered tropical soils that are already depleted in base cations, aluminum reactions may play a more important role and result in immediate increases in aluminum mobility.  Data from this project are still being evaluated, but to date, my results support these hypotheses, showing significantly elevated losses of aluminum from the tropical forest on highly weathered soils following first-time N additions and significantly elevated aluminum and base cations following long-term N additions (Lohse 2004).
As a piece of a larger puzzle, I have also been examining the effects of long-term N additions on soil anion exchange capacity.   Tropical soils with significant quantities of variable charge minerals and subsequently high anion exchange capacity (AEC) can adsorb nitrate.  Because these chemical reactions are highly dependent on pH, chronic N inputs that acidify soils may increase anion exchange capacity and potentially reduce NO3- solution losses.  Consistent with these expectations, I found that long-term N additions resulted in significant declines in pH and increased AEC.  These results suggest that AEC may serve as a long-term mechanism delaying nitrate losses in tropical forests experiencing chronic anthropogenic N inputs.  Papers on these findings are works in progress (Lohse, 2004). 

Atmospheric deposition across a desert city
For the past year, I have been working with Dr. Nancy Grimm at ASU evaluating the effects of urbanization on atmospheric deposition. Atmospheric deposition is an important source of nutrient inputs to many ecosystems, particularly in arid environments.  Urbanization is significantly enhancing atmospheric deposition of both nutrients and pollutants in cities as well as in downwind recipient ecosystems on regional scales. Despite this trend, there are relatively few studies of the spatial patterns in atmospheric deposition of nutrients and major ions across urban areas. We examined spatial patterns in wet and dry deposition chemistry over a four to six year period across the Central Arizona-Phoenix (CAP) region,the site of one of the two urban programs within the National Science Foundation’s Long Term Ecological Research network. While annual mean fluxes of wet and dry nitrogen deposition were relatively low and did not differ significantly across sites, wet and dry deposition of dissolved organic carbon (DOC) were significantly elevated in the urban and downwind desert compared to the upwind sites. Dry loads of phosphorus and potassium and wet loads of calcium were significantly elevated in the core urban sites. Measured loads of DOC to the urban core (14.9 kg C/yr) were half those predicted by atmospheric models (37 kg C/yr).  Lower than predicted dry deposition of nitrogen to the urban core maybe explained by the dominance of gaseous-phase N in hot, arid environments and volatilization of dry deposition from surrogate surfaces.These possibilities are being further explored with detailed measurement of deposition velocities and aerosol and gas concentrations in the atmosphere (Lohse et al. in prep).