Characterization of large wood and its relationship to pool formation and macroinvertebrate metrics in southeastern coastal plain streams, USA

Large wood has important structural and functional roles in streams but there is little information on large wood dynamics in the southeastern coastal plains, USA. In this study, we surveyed 35 streams in the Choctawhatchee River watershed of southeastern Alabama. These streams were broadly classified into three categories based on land use: urban, forest, and mixed (agriculture plus forest). The number, volume, and functions of large wood were quantified. Pool number, pool spacing, and drainage areas of each stream were measured along with assessment of macroinvertebrate assemblages. Large wood number and volume plus pool number and spacing were used to examine the relationship among large wood characteristics and functions, pool characteristics, drainage area, and attributes of macroinvertebrate assemblages including species richness, Shannon-Wiener diversity (H'), number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species, and the Invertebrate Community Index (ICI a multimetric index that reflects biological integrity of streams). There were significant differences in large wood number and volume among the three different stream categories, with highest large wood number and volume in forest streams. More pools and storage sites for sediment and organic matter were found in forest streams than urban and mixed streams. Large wood appeared to be positively related to macroinvertebrate assemblages, as species richness, H', EPT, and ICI were generally higher in forest streams as compared to those of urban and mixed streams. The outcome of this study suggests that large wood contributes to the physical and biological complexity of streams in the southeastern coastal plain streams of the USA.