It is generally held that surface runoff in heavily forested ecosystems is minimal and therefore nutrient fluxes via runoff are unimportant. This is based in large measure on the absence of direct observation or remnant physical evidence. It is further held that protected forests with heavy understory and litter serve as a nutrient sink due to maximum uptake and interception. Our Sierran studies have detected the presence of surface runoff at several sites in the form of both overland and litter interflow with concentrations of NH 4 -N as high as 87.2 mg L −1 , NO 3 -N as high as 95.4 mg L −1 , and PO 4 -P as high as 24.4 mg L −1 . Data suggest that nutrients are derived from the mature O-horizons, and that there has been little contact with the mineral soil or root zone where strong retention and/or uptake of these ions would be expected. Such contributions from overland/interflow could be particularly important in areas where ultra-oligotrophic lakes (e.g., Lake Tahoe) are now trending towards meso-oligotrophic status. We believe that fire exclusion in these systems may have exacerbated N and P inputs to Lake Tahoe and elsewhere by allowing unnatural buildups of O-horizons that are apparently a source of nutrients to surface runoff.

Large planetary impacts are believed to cause significant deformation on the opposite hemisphere of the target body as a consequence of focusing of the seismic waves produced from impact to the basin's antipode. Near-surface pressure gradients can produce significant deformation and surface disruption, resulting in antipodal terrains (

Mimas is the innermost, and smallest (r = 198.2 km), regular moon of Saturn. Mimas' surface is heavily cratered, and it is easily identified by the large Herschel impact basin (Figure 1). As summarized in Schenk et al. (2018) and Castillo-Rogez et al. (2018), tectonic activity on Mimas is sparse, and there is no evidence of past or present volcanism. Within the resolution limit of the data, Mimas' craters appear unrelaxed, suggesting limited heat flows over time (Schenk et al., 2018). This lack of activity is surprising because Mimas is currently in a close (less than 3 Saturn radii), high eccentricity (e = 0.0197) orbit, which ought to stimulate intense tidal activity. Other moons in similar orbits display global geologic activity and high tidal heat flows as a result of tidal deformation (e.g., de Pater et al., 2021;Nimmo et al., 2018;. At Io, Europa, and Enceladus, mean motion resonances maintain the moons' orbital eccentricities despite their high dissipation, whereas Mimas is not currently in an eccentricity resonance (Peale, 1976). Hence, the lack of geologic activity or high heat flows, while retaining a high eccentricity in the absence of a resonance, suggests that tidal dissipation has not been significant in the evolution of Mimas (Matson et al., 2009). Rather, Mimas has likely remained cold since its final assembly, with the expectation that it is a homogenous mixture of ice and rock.Our understanding of Mimas drastically changed when the Cassini spacecraft measured its librations, and model fits ruled out a homogeneous interior structure. The initial study (Tajeddine et al., 2014) found that Mimas must be differentiated, and that either the rocky core must be elongated (i.e., non-hydrostatic) or Mimas' outer layer is composed of an ice shell over a liquid water ocean (Figure 1). In the ocean model, the ice shell must be 24-31 km thick, depending on the viscosity structure of the shell (Tajeddine et al., 2014). Further analysis of libration phases supports the ocean interpretation, whether or not the core is elongated (Caudal, 2017;Noyelles, 2017).

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