E. L. Gallo

The University of Arizona | UA · Department of Hydrology and Water Resources

Streamflow in arid and semi-arid regions is predominantly temporary, an integral part of mountain block hydrology and of significant importance for groundwater recharge and biogeochemical processes. However, temporary streamflow regimes, especially ephemeral flow, remain poorly quantified. We use electrical resistance sensors and USGS stream gauge...

Ephemeral and intermittent streams are increasing with climate and land use changes, and alteration in stream water presence or flow duration will likely affect litter decomposition and nutrient dynamics in channel and riparian zones more than uplands. To investigate the influence of varying climate and streamflow regimes on rates of decomposition...

Mountains are vital to ecosystems and human society given their influence on global carbon and water cycles. Yet the extent to which topography regulates montane forest carbon uptake and storage remains poorly understood. To address this knowledge gap, we compared forest aboveground carbon loading to topographic metrics describing energy balance an...

Ephemeral streams are abundant in drylands, yet we know little about how their vegetation differs from surrounding terrestrial zones and about their projected response to regional warming and drying. We assessed plant communities at seven ephemeral streams (and terrestrial zones) distributed among three climatic settings in Arizona. Compared to ter...

Nitrogen (N) loading is a global stressor to fresh and salt water systems with cascading effects on ecosystem processes. However, it is unclear if generalized global response patterns exist between discharge and N sourcing and retention with respect to land cover and precipitation. Using data compiled from 78 catchments from across the world, we id...

Forest soil respiration is a major carbon (C) flux that is characterized by significant variability in space and time. We quantified growing season soil respiration during both a drought year and a non-drought year across a complex landscape to identify how landscape and climate interact to control soil respiration. We asked the following questions...

The influx of atmospheric nitrogen to soils and surfaces in arid environments is of growing concern due to increased N emissions and N usage associated with urbanization. Atmospheric nitrogen inputs to the critical zone can occur as wet (rain or snow) or dry (dust or aerosols) deposition, and can lead to eutrophication, soil acidification, and grou...

Background/Question/Methods Ephemeral streams are an important but little studied resource in the American Southwest. Many streams in arid and semi-arid regions are ephemeral (e.g. 89% of western US), only flowing in response to rainfall, and the distribution of these streams is likely to increase in a changing climate. Given the hydrologic varia...

Rapid increases in human population and land transformation in arid and semi-arid regions are altering water, carbon (C) and nitrogen (N) cycles, yet little is known about how urban ephemeral stream channels in these regions affect biogeochemistry and trace gas fluxes. To address these knowledge gaps, we measured carbon dioxide (CO2), nitrous oxide...

Recent work suggests that a coupled effective energy and mass transfer (EEMT) term, which includes the energy associated with effective precipitation and primary production, may serve as a robust prediction parameter of critical zone structure and function. However, the models used to estimate EEMT have been solely based on long-term climatological...

Recharge of urban runoff to groundwater as a stormwater management practice has gained importance in semi-arid regions where water resources are scarce and urban centers are growing. Despite this trend, the importance of land cover in controlling semi-arid catchment runoff quantity and quality remains unclear. Here we address the question; How do l...

Urban expansion and the scarcity of water supplies in arid and semiarid regions have increased the importance of urban runoff to localized water resources. However, urban catchment responses to precipitation are poorly understood in semiarid regions where intense rainfall often results in large runoff events during the short summer monsoon season....

Recent work suggests that a coupled effective energy and mass transfer (EEMT) term, which includes the energy associated with effective precipitation and primary production, may serve as a robust prediction parameter of critical zone structure and function. However, the models used to estimate EEMT have been solely based on long-term climatological...

Stormwater drainage systems can have a large effect on urban runoff quality, but it is unclear how ephemeral urban streams alter runoff hydrochemistry. This problem is particularly relevant in semi-arid regions, where urban storm runoff is considered a renewable water resource. Here we address the question: how do stream channels alter urban runoff...

Human activities such as urban development and intensification of agriculture change landscape profoundly and pervasively. Recognition of the strong association between land use and water quality, and between human health and clean water, has increasingly focused attention on the relationships between catchment characteristics and water quality. Wh...

Urbanization has increased anthropogenic non-point sourcing of inorganic nitrogen (N). Elevated inorganic N inputs can alter stream channel biogeochemistry and degrade the quality of downstream waters, particularly in N-limited regions such as the semi-arid southwest. However, it is unclear how N cycling in ephemeral urban waterways respond to epis...

Semi-arid regions are experiencing disproportionate increases in human population and land transformation worldwide, taxing limited water resources and altering nitrogen (N) biogeochemistry. How the redistribution of water and N by urbanization affects semi-arid ecosystems and downstream water quality (e.g. drinking water) is unclear. Understanding...

Primary productivity and vegetation cover are strongly related to how precipitation is partitioned into surface discharge, storage, and evapotranspiration (ET). Thus, quantifying feedbacks between changes in precipitation and vegetation at regional scales is a critical step toward predicting both carbon balance and water resources as climate and la...

Urbanization alters ecosystem function and subsequently impacts quantity and quality of stormwater runoff. In arid and semi-arid urban ecosystems, solutes may accumulate in upland environments for several months between rainfall events, which flush these potential pollutants to stream channels. Although this decline in water quality is well documen...

Storm water infiltration and recharge is a key component of sustainable water resource management in rapidly expanding urban areas of arid and semi-arid regions. Near surface streambed permeability affects the partitioning of stream flows to infiltration and subsequent groundwater recharge, or increasing runoff to be conveyed downstream. Therefore,...

Atmospheric nitrogen input to soils and surfaces in arid environments is of growing concern due to increased urbanization. Atmospheric nitrogen can be deposited as wet (rain or snow) or dry (dust or aerosols) deposition, and can lead to water eutrophication, soil acidification, and groundwater contamination through leaching of excess nitrate. Urban...

Stream channel biogeochemical processes may significantly alter the quality of downstream urban steam flows. Specifically, carbon and nitrogen gaseous losses following a rainfall pulse may reduce the magnitude of the solute reservoirs readily available for transport during subsequent stream flow. However, there is little information on how gaseous...

The amount and timing of plant available water influence ecosystem structure, carbon source-sink relationships, and human water resources, yet there is no consensus on how changes in precipitation will affect these basic ecosystem services of hydrologic partitioning and productivity. Ongoing changes in both climate and vegetation are resulting in c...

Utilization of recharged urban runoff to complement municipal water supply has gained importance in arid regions where populations and their urban footprint continue to grow, and where water resources are scarce. However, our understanding of how runoff quantity and quality respond to urbanization in arid landscapes is largely incomplete and poses...

Background/Question/Methods A key function of terrestrial ecosystems is maintaining water quality by attenuating pollutants introduced from local land use and regional atmospheric deposition. This ecosystem service is critical in arid and semi-arid regions where urban runoff is managed to recharge groundwater for municipal supply. However, little...

Background/Question/Methods Rapid population growth and development of urban centers in arid to semi-arid regions of the world are increasing stress on already limited water resources. In these regions, and particularly in the Southwest US, urban runoff is a water resource that can potentially offset groundwater mining and recharge local aquifers....

Urban storm runoff in arid and semiarid areas is used as a potential groundwater recharge resource, but knowledge gaps remain in our understanding on the underlying hydrologic and biogeochemical processes that control the water quality of urban runoff. This study addresses this gap by evaluating how hydrologic and biogeochemical processes interact...

The impact of non-point source pollution on urban storm runoff is of major concern in the Southwest where water resources are scarce, episodic rainfall is intense and runoff recharge is a water management strategy. The objectives of this study are to 1) determine the extent to which specific types of urban land use impact the quality of monsoonal r...

Although floodplains are known to be tightly controlled by the flood cycle, we know comparatively little about how flooding influences predators and their consumption of secondary production, particularly in highly seasonal floodplains typical of Mediterranean climates. In this study, we investigate how the seasonal dynamics of a central California...

High resolution spatial monitoring of floodwaters across an experimental floodplain in Central California has revealed patterns in dissolved organic carbon, chlorophyll-a, and nutrients which may have ramifications for local biota and future floodplain restorations. In 2004, seven sites across a 40 ha restored floodplain were monitored before and a...

Previous weekly monitoring of a floodplain in the California Central Valley confirmed the dynamic spatiotemporal nature of biogeochemical floodplain processes, but did not resolve short-term (

The lower San Joaquin River in California's Central Valley experiences periods of hypoxia during the late summer and fall that is detrimental to aquatic organisms and migration of fall-run chinook salmon and steelhead trout. Hypoxia is attributable, in part, to excess nutrients from urban waste water and agricultural runoff, which contribute to gro...

Nutrient spiraling and cycling are critical processes for floodplain systems, but these have not been well studied in western North America. Floodplain production and function relies on the integrity of river-floodplain interactions, particularly during periods of hydrologic connectivity. The purpose of this study was to: (1) determine the importan...