A stream classification system to explore the physical habitat diversity and anthropogenic impacts in riverscapes of the eastern United States

Abstract

Describing the physical habitat diversity of stream types is important for understanding stream ecosystem complexity, but also prioritizing management of stream ecosystems, especially those that are rare. We developed a stream classification system of six physical habitat layers (size, gradient, hydrology, temperature, valley confinement, and substrate) for approximately 1 million stream reaches within the Eastern United States in order to conduct an inventory of different types of streams and examine stream diversity. Additionally, we compare stream diversity to patterns of anthropogenic disturbances to evaluate associations between stream types and human disturbances, but also to prioritize rare stream types that may lack natural representation in the landscape. Based on combinations of different layers, we estimate there are anywhere from 1,521 to 5,577 different physical types of stream reaches within the Eastern US. By accounting for uncertainty in class membership, these estimates could range from 1,434 to 6,856 stream types. However, 95% of total stream distance is represented by only 30% of the total stream habitat types, which suggests that most stream types are rare. Unfortunately, as much as one third of stream physical diversity within the region has been compromised by anthropogenic disturbances. To provide an example of the stream classification’s utility in management of these ecosystems, we isolated 5% of stream length in the entire region that represented 87% of the total physical diversity of streams to prioritize streams for conservation protection, restoration, and biological monitoring. We suggest that our stream classification framework could be important for exploring the diversity of stream ecosystems and is flexible in that it can be combined with other stream classification frameworks developed at higher resolutions (meso- and micro-habitat scales). Additionally, the exploration of physical diversity helps to estimate the rarity and patchiness of riverscapes over large region and assist in conservation and management.

Modelling physical characteristics of river habitats

“…The delineation of river reach classes to whole river networks attending to differences of physical habitat attributes could assist river conservation planning. For example, conservation priorities could be set in order to account for those river classes that have reduced lengths and are subject to greater human impacts (McManamay et al, ). Moreover, if the response of fluvial biota to hydraulic changes was similar within each physical habitat class (as expected), the classification might guide the application of environmental flow rules to ungagged river reaches.…”

Biogeographic classification of streams using fish community– and trait–environment relationships

“…Mean summer temperature is a key physicochemical variable directly linked to fish community composition along gradients of stream size, elevation and latitude (Lyons et al, ; Rahel & Hubert, ). Mean summer (July–August) stream temperature from >800 monitoring sites were previously compiled and used to develop a predictive model to extrapolate summer temperatures to all NHD reaches (Figure e; McManamay et al, ). Hydrology is a putative determinant of fish community composition (Poff et al, ).…”

“…A second objective was to assign classes to the ~ 853,000 confluence‐to‐confluence stream reaches in the eastern United States, estimate the prevalence of classes, and evaluate the degree to which each class has been degraded by anthropogenic disturbance. It is our goal that public dissemination of high‐resolution (i.e., reach scale) maps will inform decision‐making in water resource policy and biodiversity conservation planning (sensu McManamay et al, ).…”

A stream classification system for the conterminous United States

“…For instance, stream classifications are often based on commonalities in hydrologic variation 2 , thermal regimes 3 , or geomorphic properties 4,5 . As such, stream classifications are fundamentally important in understanding the diversity of stream ecosystems across large regions 6 and their role in structuring biological communities 7 . However, stream classifications are also practically important to management, such as serving as conservation planning units 8 , prioritizing conservation and restoration 9 , stratifying environmental monitoring programs 10 , providing predictive variables for species distribution modeling 11 , and identifying reference sites to inform monitoring 12 .…”

“…While the approach to developing a stream classification rests upon its intended objectives for use 30 , there are several design principles of classifications that we believe maximize the application breadth for stream research and management 6 . These include developing classifications that are: 1) at the stream-reach resolution, 2) based on multiple layers of habitat components, 3) spatially contiguous and comprehensive, 4) inductive (i.e.…”