[1] Source waters and flow paths of streamflow draining high-elevation catchments of the Colorado Rocky Mountains were determined using isotopic and geochemical tracers during the 1996 snowmelt runoff season at two subcatchments of the Green Lakes Valley, Colorado Front Range. A two-component hydrograph separation using d18 O indicates that new water dominated (82 ± 6%) streamflow at the 8-ha Martinelli catchment and old water dominated (64 ± 2%) at the 225-ha Green Lake 4 (GL4) catchment. Snowmelt became isotopically enriched as the melt season progressed, complicating the interpretation of source water models. Thus old water may be underestimated if the temporal variation in d 18O of snowmelt is ignored or extrapolated from point measurements to the catchment. Two-component hydrograph separations for unreacted and reacted waters using a single geochemical tracer were not always meaningful. Three-component hydrograph separations using end-member mixing analysis indicated that subsurface flow contributed more than two thirds to the streamflow at both catchments. Talus fields contributed more than 40% of the total discharge during summer at the GL4 catchment. A conceptual model was established for flow generation based on these results. It is suggested that surface water and groundwater interactions are much more important to the quantity and quality of surface water in high-elevation catchments than previously thought.

[1] Spatial and temporal trends in stream chemistry were investigated in a large (1600 km 2 ) alpine watershed in the southern Rocky Mountains of Colorado to help understand mechanisms of streamflow generation. We observed linear increases of concentrations of chemical constituents in streamflow as accumulated drainage area increased along the main channel of Saguache Creek. We tested two conceptual models of streamflow generation against our stream chemistry observations. One model is essentially two-dimensional and treats streamflow generation at the large watershed scale as the aggregation of runoff responses from individual hillslopes, primarily surface and shallow subsurface flow paths. Alternatively, a fully three-dimensional conceptual model treats streamflow generation as being controlled by a distribution of large-scale groundwater flow paths as well as surface and shallow subsurface flow paths. The structure and magnitude of groundwater contributions in streamflow as a function of increasing scale provided a key distinction between these two conceptual models. End-member mixing analysis and measurements of hydraulic head gradients in streambeds were used to quantify basin-scale groundwater contributions to streamflow with increasing spatial scale in the Saguache Creek watershed. Our data show that groundwater contributions are important in streamflow generation at all scales and, more importantly, that groundwater contributions to streamflow do increase with increasing watershed scale. These results favor the three-dimensional conceptual model in which long groundwater flow paths provide a streamflow generation process at large scales that is not operative at smaller scales. This finding indicates that large watersheds may be more than simply the aggregation of hillslopes and small catchments.

Streamflow generation in the semiarid, seasonally snow‐covered, and forested mountain catchments of the Valles Caldera, New Mexico, was investigated using chemical tracers. Samples were collected from snow, subsurface flow from hillslopes, and streamflow at Redondo and La Jara Creeks from December 2004 to July 2005. A new modeling procedure was developed by combining diagnostic tools of mixing models and end‐member mixing analysis to evaluate the assumptions of mixing models. This procedure was successfully used to determine conservative chemical tracers, identify the number of end‐members that contribute to streamflow, and evaluate eligibility of end‐members. The results show that streamflow at Redondo Creek was generated from two end‐members: lateral subsurface flow (∼80%) and thermal meteoric water (∼20%). Streamflow at La Jara Creek was primarily from lateral subsurface flow alone. Overland flow of snowmelt was not a significant contributor to streamflow in either catchment. Lateral subsurface flow is an important process of streamflow generation in semiarid environments in the southwest United States and should play a critical role in regulating biogeochemical cycles.

breakthrough in power conversion efficiency of 22.1%, [19] comparable to conventional silicon based solar cell. Wavelength tunable LEDs and optically pumped lasers have been achieved by simply changing the ration of halide anions. However, there are still challenges in electroluminescence with high efficiency and electrically pumped lasers. [20] One intrinsic limitation in perovskite is relatively low exciton binding energy that cannot suppress the exciton ionization in the working condition devices. [21] For example, microwave photoconductance and photoluminescence (PL) study revealed exciton binding energy of 18-32 meV [22,23] in MAPbI 3 , comparable to room temperature thermal energies of K B T ≈ 25 meV. By substitution doping of Cl, larger exciton binding energy of 62.3 ± 8.9 meV can be obtained in perovskite thin film. [24] In MAPbBr 3 quantum dots, exciton binding energy can be as large as 375 meV in comparison to their bulk counterpart of 65 meV. [25] In this regard, low dimensional perovskite single crystals with optical or size confinement are becoming promising in complementing their bulk counterparts. With reduced dimensionality, lead halide perovskite provides a platform where exciton behavior, such as exciton-photon interaction [26,27] and exciton binding energy, [28] can be well modulated, giving the pathway to obtain highly efficient optoelectronic devices.