Historical ecology of a central California estuary: 150 years of habitat change

We investigated the historical ecology of Elkhorn Slough, a 1,200 ha tidal wetland system in central California. The goal of this study was to identify patterns of change in the extent and distribution of wetland habitats during a 150-yr period and to investigate the causes of these changes. Using a geographic information system (GIS), we interpreted historic maps, charts, and aerial photographs. We created a series of summary maps to illustrate and quantify changes in tidal flow and habitat types at six representative historical periods. With the aid of custom software tools, we performed semi-automated spatial analysis of historic aerial photographs to quantify changes in marsh cover at fixed quadrats and tidal creek width at fixed cross sections. Our multiscale analysis documents dramatic shifts in the distribution of habitat types resulting from anthropogenic modifications to the hydrology of the slough. More than half of the marshlands were diked, and more than two thirds have either degraded or been converted to other habitat types. The construction of an artificial mouth abruptly transformed the wetland system from depositional to highly erosional, enlarging channels, widening creeks, and converting marsh to intertidal mudflat or open water. Increased tidal amplitude and velocity are the likely causes. In recent decades, levee failure and intentional breaching have restored the acreage under tidal influence to nearly historic levels, but recolonization of former wetlands by salt marsh vegetation has been minimal. Degraded former marshland and unvegetated mudflat are now the dominant habitat types at Elkhorn Slough. The rate of habitat change remains high, suggesting that a new equilibrium may not be reached for many decades. This study can help tidal wetland managers identify patterns and mechanisms of habitat change and set appropriate conservation and restoration goals.     

Bidirectional reflectance distribution function measurements of the Winchcombe meteorite using the Visible Oxford Space Environment Goniometer

A laboratory study was performed using the Visible Oxford Space Environment Goniometer in which the broadband (350–1250 nm) bidirectional reflectance distribution function (BRDF) of the Winchcombe meteorite was measured, across a range of viewing angles—reflectance: 0°–70°, in steps of 5°; incidence: 15°, 30°, 45°, and 60°; and azimuthal: 0°, 90°, and 180°. The BRDF dataset was fitted using the Hapke BRDF model to (1) provide a method of comparison to other meteorites and asteroids, and (2) to produce Hapke parameter values that can be used to extrapolate the BRDF to all angles. The study deduced the following Hapke parameters for Winchcombe: w = 0.152 ± 0.030, b = 0.633 ± 0.064, and h_S = 0.016 ± 0.008, demonstrating that it has a similar w value to Tagish Lake (0.157 ± 0.020) and a similar b value to Orgueil (0.671 ± 0.090). Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument, allowing two of the free parameters within the Hapke model φ and $\overline{\theta }$, which represent porosity and surface roughness, respectively, to be constrained as φ = 0.649 ± 0.023 and $\overline{\theta }$ = 16.113° (at 500 μm size scale). This work serves as part of the characterization process for Winchcombe and provides a reference photometry dataset for current and future asteroid missions.