Geology topics

Bryan L. Brown

Publications and source records attributed to Bryan L. Brown.

3 recordsLinked to original sources

USGS2026

Stream health shows indirect and threshold responses to implementation of agricultural conservation practices

Many agricultural conservation practices (hereafter conservation practices) are intended to protect streams from the deleterious effects of agriculture, but desired effects of their implementation are not always realized. Understanding the pathways through which conservation practices influence stream health can guide future implementation. Our goal was to quantify how conservation practices influence stream health in pastureland watersheds. We asked 4 research questions: R1) What are the effects of land use and conservation practices on instream conditions? R2) What are the effects of instream conditions on biota? R3) What are the relative effects of land use, conservation practices, and instream conditions on biota? R4) How do conservation practice density (no./ha) and agricultural land use interact to influence stream health? We collected data on water quality (total suspended solids, total N, total P, and Escherichia coli bacteria), instream habitat (substrate embeddedness and bank stability), and macroinvertebrate communities from 31 sites in the upper Tennessee River basin of southwest Virginia, USA. The sites collectively represented spatial analytical gradients of agricultural land use and density of conservation practices, with the dominant practices including prescribed grazing, brush management, and fencing. We found that conservation practice implementation was indirectly related to biotic assemblages through changes in water quality and habitat, but practice density in the study area was not associated with instream conditions that supported biotic communities representative of reference conditions. Further improving instream habitat conditions may require innovative conservation practices, targeted placement of practices in critical source areas of pollutants, or higher densities of practices.

Virginia↗

USGS2022

Multiple dimensions of functional diversity affect stream fish β-diversity

When investigating metacommunity dynamics, functional differences among species are often assumed to be as important as environmental differences between sites in determining β-diversity. However, few studies have examined the influence of functional diversity on β-diversity. We examine the relative importance of regional functional diversity partitioned by niche dimensions and environmental variation in structuring taxonomic β-diversity of stream fishes using a large dataset of stream fish assemblages (hereafter, simply β-diversity). We predicted that both functional diversity and environmental variation play a role in determining β-diversity. We tested this prediction by modelling the patterns of stream fish β-diversity as a function of environmental variation, functional diversity and γ-richness across 10,220 sites for 329 fish species using a series of conceptual path models. Environmental variation consistently affected β-diversity across all models, whereas functional diversity and γ-richness influenced β-diversity only in some models. We show that including relevant trait differences among species in path models can improve their ability to explain β-diversity, suggesting that functional traits influence β-diversity. The ability of path models to explain β-diversity varied depending on the trait grouping included in the model, demonstrating that specific path models representing different niche dimensions can improve the ability of a model to explain β-diversity. In addition, parsing traits into different niche dimensions revealed alternative patterns of functional diversity–β-diversity relationships that otherwise would have been missed. The selection of relevant traits and linked niche dimensions is critical for detecting relationships between functional diversity and β-diversity. Using traits associated with different niche dimensions allows for the identification of niche dimensions most strongly associated with species sorting and the detection of patterns missed by focusing on a single niche dimension. Determining the niche dimensions that influence β-diversity could provide insights into the processes driving biodiversity and metacommunity dynamics, improving our ability to conserve or restore aquatic communities.

Eastern United States↗

USGS2021

A new composite abundance metric detects stream fish declines and community homogenization during six decades of invasions

Aim We developed a new technique, utilizing species-specific counts of individuals from historical fish community samples, to examine landscape-level, spatio-temporal trends in relative abundance distributions. Abundance-based historical distribution analyses are often plagued by data comparability issues, but provide critical information about community composition trends inaccessible to those using analyses based only on species presence–absence. We established trends in native and non-native fish abundance and community homogenization, uniqueness and diversity to help local conservation managers prioritize targets and motivate similar studies globally to support fish conservation. Location Upper and middle New River (UMNR) basin, Appalachian Mountains, USA. Methods We compiled catch data from 61 years of fish community surveys (1958–2019) and tested for community homogenization by comparing data from repeatedly sampled sites (1900s versus 2000s samples) using dispersion analyses. We measured community uniqueness (site contributions to beta diversity) and species diversity (Shannon index) at sampled streams to identify potential conservation hotspots. We then used regression analyses and Wilcoxon signed-rank tests to examine species-specific basin-wide and local abundance trends and identify species of potential conservation concern. Results Dispersion of sites in species abundance space was significantly greater in the 1900s compared with the 2000s, indicating homogenization had occurred. Of 36 native species analysed, 44.4% (16) showed basin-wide declines. Non-native species exhibited mixed patterns; site-level abundance increased in 2 of 15 species analysed (13%). Main conclusions Our results indicate basin-wide community homogenization has occurred within the UMNR, but many unique and diverse communities persist. If conserved, these could help maintain regional fish diversity. We found basin-wide declines in four endemic species, as well as spread patterns of non-native and native species that were not detected by a presence–absence analysis applied within the same study area. This finding illustrates the importance of considering both species’ abundance and occurrence patterns as separate dimensions of biodiversity to inform conservation planning.

North Carolina, Virginia, West Virginia↗