An Aircraft Wetland Inundation Experiment Using GNSS Reflectometry

In early May of 2017, a flight campaign was conducted over Caddo Lake, Texas, to test the ability of Global Navigation Satellite System-Reflectometry (GNSS-R) to detect water underlying vegetation canopies. This paper presents data from that campaign and compares them to Sentinel-1 data collected during the same week. The low-altitude measurement allows for a more detailed assessment of the forward-scattering GNSS-R technique, and at a much higher spatial resolution, than is possible using currently available space-based GNSS-R data. Assumptions about the scattering model are verified, as is the assumption that the surface spot size is approximately the Fresnel zone. The results of this experiment indicate GNSS signals reflected from inundated short, thick vegetation, such as the giant Salvinia observed here, results in only a 2.15 dB loss compared to an open water reflection. GNSS reflections off inundated cypress forests show a 9.4 dB loss, but still 4.25 dB above that observed over dry regions. Sentinel-1 data show a 6-dB loss over the inundated giant Salvinia, relative to open water, and are insensitive to standing water beneath the cypress forests, as there is no difference between the signal over inundated cypress forests and that over dry land. These results indicate that, at aircraft altitudes, forward-scattered GNSS signals are able to map inundated regions even in the presence of dense overlying vegetation, whether that vegetation consists of short plants or tall trees.

Multispecies and Watershed Approaches to Freshwater Fish Conservation

<em>Abstract</em>.—Caddo Lake, along with its swamps and tributary bayous, supports a diversity of aquatic ecosystems and has been designated a wetland of global significance by the Ramsar Convention. The life blood of Caddo Lake is the network of tributary creeks and bayous that drain into the wetland complex of the lake’s upper reaches. The ecology of the main tributary, Big Cypress Bayou, however, has been altered by flow regulation by Lake O’ the Pines dam. Additional threats from giant salvinia <em>Salvinia molesta </em>and other invasive plants, water quality impacts, and land uses have added stress to the ecosystem. Several conservation organizations, led by the Caddo Lake Institute, have formed partnerships to address these threats to the watershed. The Sustainable Rivers Program, a partnership of The Nature Conservancy and the U.S. Army Corps of Engineers (Corps), has managed dam operations to enhance the natural ecology of Big Cypress Bayou and Caddo Lake downstream. The Corps has been releasing recommended flows to allow researchers to gather more information to evaluate the success of restoration efforts. Early monitoring results indicate a potential positive response of the fish community to these flow releases. We present results of flow restoration work and associated ecological monitoring. We also summarize floodplain vegetation monitoring, paddlefish restoration and invasive species management projects in Caddo Lake and the Cypress River basin.

Black Bass Diversity: Multidisciplinary Science for Conservation

<em>Abstract</em>.—Virginia is at the edge of the range of <em>Micropterus dolomieu dolomieu</em>, and it is uncertain whether they are native to particular watersheds. Patterns of population genetic variation could inform knowledge of natural history and provide the scientific basis for management of the species. Three-hundred fifteen individuals representing 13 populations were screened at 10 microsatellite DNA loci. Numbers of alleles per locus ranged from 2 to 10. Collections from native Tennessee River drainage populations were more variable (4.5 alleles/locus) than the New River collection (4.3) and those for introduced populations (3.8), although numbers of alleles for the respective groups overlapped. More genetic variation was found within (82.7%) than between (17.3%) populations. Geographic structuring of genetic variation was weak, but tended to show divergence of Caddo Lake, Arkansas (the <em>M. d. velox</em> outgroup) from the Clinch and Powell, Holston, and New River and Atlantic slope collections. Analysis of our results in the context of existing knowledge suggests that the New and James River populations may be admixtures of native and introduced gene pools. Our findings suggest that the Clinch–Powell and Holston River populations should be regarded as two management units, New River populations as another, and introduced populations as yet another. Because native stocks are likely to be locally adapted, we recommend assessment of potential adaptive variation and no stocking from outside of each management unit.