Browsing by Autor "Michael E. McClain"

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Monitoring Oxbow Lakes with Remote Sensing: Insights into Turbidity, Connectivity, and Fish Habitat
(Multidisciplinary Digital Publishing Institute, 2026) Lina G. Terrazas-Villarroel; Jochen Wenninger; Marcelo Heredia-Gómez; Nick van de Giesen; Michael E. McClain
In meandering river floodplain systems, remote sensing is a valuable tool for assessing connectivity processes relevant to fish ecological functions. This study used the Google Earth Engine platform and multispectral Landsat 7 imagery. A random forest classifier was used to evaluate water types and area changes in oxbow lakes of the Beni River in Bolivia. Water type dynamics were mainly associated with lake age and distance from the main channel. Seasonal variations highlighted the role of wind-driven sediment resuspension and overflow during high discharge conditions. Long-term lake area changes reflected typical oxbow lake evolution as well as alterations caused by the main channel. Multiannual changes showed a notable area decrease during years of low discharge. Relationships between discharge and lake area dynamics allowed the classification of three lake groups with different levels of connectivity and overbank flow influence. The ecological relevance of these groups was evaluated based on fish habitat preferences and migration patterns. Results emphasize the importance of preserving natural hydrologic variability, with flooding associated with increased habitat availability. Overall, this study demonstrates the usefulness of satellite remote sensing for detecting ecohydrological processes and offers insights to preserve ecological functions in data-scarce regions.
Organic matter in Bolivian tributaries of the Amazon River: A comparison to the lower mainstream
(Wiley, 2000) John I. Hedges; Emilio Mayorga; Elizabeth Tsamakis; Michael E. McClain; A. K. Aufdenkampe; Paul D. Quay; Jeffrey E. Richey; Ronald Benner; Steve Opsahl; Brenda Black
We determined the concentrations and compositions of coarse particulate (>63 µm), fine particulate (0.1–63 µm), and dissolved (0.001–0.1 µm) organic matter collected along a river reach extending from a first‐order stream in the Bolivian Andes, through the Beni River system, to the lower Madeira and Amazon Rivers. Dissolved organic carbon (DOC) concentrations increased down the total reach from ~80 to 350 µM. The percentage of total DOC with a molecular weight greater than ~1,000 atomic mass units that could be isolated by ultrafiltration also increased downstream from 40 to 80%. Weight percentages of organic carbon in the ultrafiltered isolates also grew downstream from 5% at the uppermost station to 37% in the Amazon mainstem. Organic carbon composed only 0.4–1.2 weight percentage of the total mass of the fine particulate fraction, which accounted for 70–80% of the total organic carbon (TOC) in transport through the highly turbid (~600–2000 mg L −1 ) Beni sequence. Observed compositional differences were related primarily to the size fractions in which the organic matter occurred. On average, coarse particulate organic material exhibited an atomic C:N of 24, whereas ultrafiltered DOM was nitrogen poor, (C:N)a = 34, and fine particulate material was nitrogen rich, (C:N)a = 15. The lignin and stable‐carbon isotopic compositions of these fractions indicate tree leaves and other nonwoody tissues from C3 land plants as predominant sources. Three molecular parameters demonstrate that the coarse, fine, and dissolved fractions of individual water samples are increasingly degraded downstream. Elemental nitrogen, amino acids, and basic amino acids are all preferentially associated with fine minerals. Observed geographical patterns included more positive δ 13 C values in particulate organic matter from high altitude sites and an increase in the abundance and degradation of ultrafiltered dissolved organic matter down the drainage system. Many of these compositional patterns are imprinted within materials carried by low‐order, high‐altitude tributaries and appear to reflect processes occurring on the landscape.