Tracking Barrier Island Response to Early Holocene Sea-level Rise: High Resolution Study of Estuarine Sediments in the Trinity River Paleovalley

Understanding how barrier islands respond to factors such as variations in sediment supply, relative sea-level rise, and accommodation is valuable for preparing coastal communities for future impacts of climate change. Increasingly, the underlying antecedent topography has been observed to have a significant control on the evolution of the barrier island system by providing increased elevation, decreased accommodation, and sediment supply for the barrier to rework and anchor upon. However, less attention has been focused on how back barrier sediments respond to this decreased accommodation, and how this may affect barrier island evolution. Additionally, the control in which the geometry of the underlying valley itself has on the initiation of barrier islands is poorly understood. Here we examine the stratigraphic framework of the Trinity River incised valley, offshore Galveston, Texas in order to investigate the role of antecedent topography in the evolution of an ancient barrier island system. We present high-resolution imaging of the Trinity incised valley fill using over 1200 km2 of 3D seismic, <700 km of 2D envelope and full waveform chirp data, along with 2 piston cores, 4 gravity cores, 1 platform boring, with associated grain size, foraminiferal, and radiocarbon data. We find that the geometry and elevation of the underlying antecedent topography plays a central role in the evolution of the barrier island system, promoting both initiation and stabilization. This study provides a methodology to investigate the evolution of a relict barrier island system where little to none of the barrier is preserved. With this methodology, we revise the established Holocene paleoshoreline model for the Trinity incised valley.

Implications of taxonomic and numerical resolution on DNA metabarcoding-based inference of benthic macroinvertebrate responses to river restoration

Exploring and clearly defining the level of taxonomic identification and quantification approaches for diversity and biomonitoring studies are essential, given its potential influence on the assessment and interpretation of ecological outcomes. In this study, we evaluated the response of benthic macroinvertebrate communities to the restoration or construction of gravel bars conducted in the dam-impacted Trinity River, with the non-dam influenced tributaries serving as the reference sites. We aim to evaluate the performance of different taxonomic and numerical (i.e., abundance vs. presence/absence data) resolutions of DNA metabarcoding with consequent comparison to morphology-based identification and how it affects assessment outcomes. DNA metabarcoding detected 93% of the morphologically identified individuals and provided finer taxonomic resolution. We also detected significant correlations between morphological sample abundance, biomass, and DNA metabarcoding read abundance. We observed a relatively high and significant congruence in macroinvertebrate community structure and composition between different taxonomic and numerical resolutions of both methods, indicating a satisfactory surrogacy between the two approaches and their varying identification levels and data transformation. Additionally, the community-environmental association were significant for all datasets but showed varying significant associations against the physicochemical parameters. Furthermore, both methods identified Simulium spp. as significant indicators of the dam-impacted gravel bars. Still, only DNA metabarcoding showed significant false discovery rate proving the method’s robustness compared to morphology-based identification. Our observations imply that coarser taxonomic resolution could be highly advantageous to DNA metabarcoding-based applications in situations where the lack of taxonomic information, e.g., poor reference database, might severely affect the quality of biological assessments.

A multi-proxy assessment of terrace formation in the lower Trinity River valley, Texas

A proposed null hypothesis for fluvial terrace formation is that internally generated or autogenic processes such as lateral migration and river-bend cutoff produce variabilities in channel incision that lead to the abandonment of floodplain segments as terraces. Alternatively, fluvial terraces have the potential to record past environmental changes from external forcings that include temporal changes in sea-level and hydroclimate. Terraces in the Trinity River valley have been previously characterized as Deweyville groups and interpreted to record episodic cut and fill during late Pleistocene sea-level variations. Our study uses high-resolution topography of a bare-earth digital elevation model derived from airborne lidar surveys along ~88 linear km of the modern river valley. We measure both differences in terrace elevations and widths of paleo-channels preserved on these terraces in order to have two independent constraints on terrace formation mechanisms. For 52 distinct terraces, we quantify whether there is a clustering of terrace elevations – expected for allogenic terrace formation tied to punctuated sea-level and/or hydroclimate change – by comparing variability in a chosen set of terrace elevations against variability associated with randomly selected terrace sets. Results show Deweyville groups record an initial valley floor abandoning driven by allogenic forcing, which transitions into autogenic forcing for the formation of younger terraces. For 79 paleo-channel segments preserved on these terraces, we connected observed changes in paleo-channel widths to estimates for river paleo-hydrology over time. Our measurements suggest the discharge of the Trinity River has changed systematically by a factor of ~2 during the late Pleistocene. Methods introduced here combine river-reach scale observations of terrace sets and paleohydrology with local observations of adjacent terrace-elevation change and paleo-channel bend number to show how interpretations of allogenic versus autogenic terrace formation can be evaluated within a single river system.

Using Hybrid Wavelet-Exponential Smoothing Approach for Streamflow Modeling

Considering the three intrinsic components (of autoregressive, seasonality, and error) of streamflow time series, the overall performance of the streamflow modeling tool is associated with the correct estimation of these components. In this study, a new hybrid method based on the wavelet transform (WT) as a multiresolution forecasting tool and exponential smoothing (ES) method, with two presented scenarios (WES1 and WES2), was introduced. To this end, the performance of the proposed method was investigated versus four conventional methods of the autoregressive integrated moving average (ARIMA), ES ad-hoc, artificial neural network (ANN), and wavelet-ANN (WANN) for daily and monthly streamflow modeling of West Nishnabotna and Trinity River watersheds with different hydro-geomorphological conditions. In the presented WES technique, firstly, WT is employed for decomposing the observed signal to one approximation (deterministic trend) and more diverse components of subseries (each at a specific frequency). Then, for the first scenario (WES1), only two subseries are introduced to the model as input parameters; however, for the second scenario (WES2), decomposed subseries are separately used as the inputs of ES models. The obtained results indicated that combining WT with the ES method and ANN led to more accurate modeling. The proposed methodology (WES2) that used all decomposed subseries separately improved the efficiency of models up to 30% and 10% for the daily dataset and up to 88% and 57% for the monthly dataset, respectively, for the West Nishnabotna and Trinity Rivers.