Testing alternative conceptual models of river-aquifer connectivity and their impacts on baseflow and river recharge processes

This study characterizes the dynamics of exchange fluxes between Brazos River Alluvium Aquifer and the Brazos River, TX, USA. Seven alternative conceptual models for the connection between the river and the aquifer were simulated in HYDRUS 2D using small-scale, high-resolution transects across the river. These models assumed varying aquifer lithology and river incision depths and considered processes such as riverbed clogging and seepage face flows. The simulations were forced by observed river stage values and tested against observed hydraulic heads in two nearby monitoring wells. The nearly 1.5 years of sub-hourly measurements spanned both flood and drought periods. The best-fit conceptual model supported a hypothesized hydraulic disconnection between the subsurface near the river and the wider alluvial aquifer. In contrast to the assumptions of previous studies, these data were more consistent with the presence of an abandoned paleochannel rather than riverbed clogging or other low-permeability zones. The implications for groundwater-surface water exchanges, and their modelling, are profound. Across the range of models, the difference in average baseflow predicted was nearly 13 m3/d/m, equivalent to seven times the firm water rights allocated for river users.

Trace elements in mussel shells from the Brazos River, Texas: environmental and biological control

In sclerochronology, understanding the drivers of shell chemistry is necessary in order to use shells to reconstruct environmental conditions. We measured the Mg, Ca, Sr, Ba, and Mn contents in water samples and in the shells of two freshwater mussels (Amblema plicata and Cyrtonaias tampicoensis) from the Brazos River, Texas to test their reliability as environmental archives. Shells were analyzed along growth increments using age models established with stable and clumped isotopes. Shells were also examined with cathodoluminescence (CL) microscopy to map Mn / Ca distribution patterns. Sr / Ca correlated with Mn / Ca, while Mg / Ca and Ba / Ca showed no clear trends. Mn / Ca correlated inversely with the log of river discharge. Because dissolved and inorganic particulate sources of manganese are low during low flow, peak Mn / Ca values may come from elevated feeding or metabolic rates. Shell Mn / Ca values were used to reconstruct river discharge patterns, which, to our knowledge, has previously only been performed with shell chemistry using oxygen isotopes.

New records of the Mountain Mullet, Dajaus monticola (Bancroft, 1834), and an overview of historical records in Texas

Dajaus monticola (Bancroft, 1834) is an amphidromous species of mugilid known from South and Central America and the islands of the Caribbean but is rarely collected in Gulf coast states of the United States. Two new records of D. monticola collected from the Gulf of Mexico (Brazoria Co.) and the Brazos River (Washington Co.) are reported from Texas. The rare occurrence of D. monticola in Texas is discussed and diagnostic characters used to distinguish this species from other mugilids found in Texas are reevaluated.

The Choice of an Appropriate Information Dissimilarity Measure for Hierarchical Clustering of River Streamflow Time Series, Based on Calculated Lyapunov Exponent and Kolmogorov Measures

The purpose of this paper was to choose an appropriate information dissimilarity measure for hierarchical clustering of daily streamflow discharge data, from twelve gauging stations on the Brazos River in Texas (USA), for the period 1989–2016. For that purpose, we selected and compared the average-linkage clustering hierarchical algorithm based on the compression-based dissimilarity measure (NCD), permutation distribution dissimilarity measure (PDDM), and Kolmogorov distance (KD). The algorithm was also compared with K-means clustering based on Kolmogorov complexity (KC), the highest value of Kolmogorov complexity spectrum (KCM), and the largest Lyapunov exponent (LLE). Using a dissimilarity matrix based on NCD, PDDM, and KD for daily streamflow, the agglomerative average-linkage hierarchical algorithm was applied. The key findings of this study are that: (i) The KD clustering algorithm is the most suitable among others; (ii) ANOVA analysis shows that there exist highly significant differences between mean values of four clusters, confirming that the choice of the number of clusters was suitably done; and (iii) from the clustering we found that the predictability of streamflow data of the Brazos River given by the Lyapunov time (LT), corrected for randomness by Kolmogorov time (KT) in days, lies in the interval from two to five days.