Stream hydrograph separation using naturally occurring geochemical tracers holds great potential for elucidating mineral weathering and solute transport. This study addresses a critical need to characterize catchment runoff generation in the humid tropics using multiple natural tracers for hydrograph separation and concentration/discharge (C/Q) hysteresis analysis. We use hydrometric and geochemical data collected at the start of the wet season from three small, steep catchments located in the humid seasonal tropics of central Panama that differ primarily in land cover. We apply a dual source hydrograph separation model between two end-members: new event water precipitation and pre-event water stored in the catchment. We compare the effectiveness of electrical conductivity (EC) and stable water isotopes (δD and δ 18 O) tracers for identifying precipitation event water in stream runoff using across forested (1.43km 2), mixed land use 'mosaic' (1.82km 2) and pasture (0.42 km 2) catchments. Hysteretic C/Q loops are analyzed for flowpath interpretation using δD, Ca 2+ , Mg 2+ , Na + , K + , Cl-, and SO 4 2-. During a medium-large magnitude event on May 23, 2013, forest and mosaic stream δD, Ca 2+ , Mg 2+ , and Na + exhibited clockwise hysteresis, SO 4 2exhibited anticlockwise hysteresis, and K + and Cleach showed no hysteresis. EC as a surrogate for total dissolved solids agrees acceptably with stable water isotope hydrograph separations during small peak runoff events (<3 mm/hr). However, isotope and conductivity tracers strongly disagree during a large runoff event (>10 mm/hr) in the mosaic catchment. Early wet-season events indicate lower event water fractions than events farther into the wet season. Despite previous work showing land cover strongly controls storm runoff efficiencies, hydrograph separation and hysteresis analyses only indicate weak event water delivery differences between the paired forest and mosaic catchments.

Understanding land use/land cover (LULC) effects on tropical soil infiltration is crucial for maximizing watershed scale hydro-ecosystem services and informing land managers. This paper reports results from a multiyear investigation of LULC effects on soil bulk infiltration in steep, humid tropical, and lowland catchments. A rainfall simulator applied water at measured rates on 2 × 6 m plots producing infiltration through structured, granulated, and macroporous Ferralsols in Panama's central lowlands. Time-lapse electrical resistivity tomography (ERT) helped to visualize infiltration depth and bulk velocity.

In humid tropical watersheds, the hydrologic flow paths taken by rain event waters and how they interact with groundwater and soil matrix water to form streamflow are poorly understood. Preferential flow paths (PFPs) confound storm infiltration processes, especially in the humid tropics where PFPs are common. This work applies germanium (Ge) and silicon (Si) as natural flow path tracers in conjunction with water stable isotopes and electrical conductivity to examine the rapid delivery of shallow soil water, the activation of PFPs, and event water partitioning in an experimental catchment in central Panama. We employed a three‐component mixing model for hydrograph separation using the following end‐member waters: (i) base flow (high [Si], low [Ge], and low Ge/Si ratio), (ii) dilute canopy throughfall (low [Si] and low [Ge]), and (iii) shallow (<15 cm) soil matrix water (low [Si], high [Ge], and high Ge/Si ratio). These three end‐members bounded all observed Ge/Si streamflow ratios. During small rain events (<∼24 mm), base flow and dilute canopy throughfall components dominated stormflow. During larger precipitation events (>∼35 mm), we detected the third shallow soil water component with an elevated [Ge] and Ge/Si ratio. This component reached its maximum during the hydrograph's receding limb coincident with the maximum event fraction, and increased proportionally to the total storm rainfall exceeding ∼35 mm. Only shallow (<15 cm) soil matrix water exhibited elevated Ge concentrations and high Ge/Si ratios. This third component represents rapidly delivered soil matrix water combined with shallow lateral PFP activation through which event waters interact with soil minerals.

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The design of infrastructure used for deploying water quality sensors can potentially impact data quality. Despite this, sensor infrastructure design has not been well discussed in the peer-reviewed literature. Here, we present side-by-side measurements from two contrasting designs; a "monopod" consisting of a strut driven into the streambed and a downrigger suspended from an "overhead cable." We collected measurements over an approximately 6-month period from two wadeable stream monitoring sites within the National Ecological Observatory Network. In general, we observed minimal differences between measurements, suggesting both designs to be viable options from a data quality perspective under normal operating conditions. However, the monopod design was more susceptible to coming out of the water during low stage and burial by sedimentation. While more expensive and logistically complex to install, the overhead cable design exhibited greater survivability, adjustability, and serviceability. We discuss additional design considerations and potential modifications that we hope will prove useful to other researchers in instrumenting their own sites.