By Holly Mehl
Last month I introduced Big Blue Thread readers to EPA Region 7’s Conservation Focus Area analysis developed in cooperation with the Missouri Resource Assessment Partnership (MoRAP). In three separate blog entries I summarized how we looked at ecological significance, threats and irreplaceability across terrestrially based ecological sections in order to arrive at conservation focus areas on land. Since stressors operate on aquatic ecosystems differently than terrestrial, and because watershed boundaries need to be used as aquatic planning regions, an analysis for riverine ecosystems was done separately.
Aquatic Conservation Focus areas for EPA Region 7’s four states (Iowa, Kansas, Missouri and Nebraska) were defined at two resolutions based on data availability (a finer resolution assessment was possible for the state of Missouri because of robust aquatic species distribution modeling). Today I’ll cover the more refined data analysis for Missouri and carry on with describing the courser methods we used for the other three states in a future blog entry.
Above is the final map showing freshwater Conservation Focus Areas in Missouri. The idea behind this analysis is that taking measures to conserve all of these locations represents an efficient approach to conserving the distinct species, stream types, and watershed types that exist within the state. As both an ecologist and a Missourian, I find it comforting to know that our state resource managers now have this very exhaustive published research at their fingertips.
How did we do it? Resource managers and biologists with detailed and extensive knowledge of the stream resources participated in conservation planning sessions in 2004. Our goal for the aquatic assessment was to “ensure the long-term persistence of native aquatic plant and animal communities, by conserving the conditions and processes that sustain them…” and then more specifically to “identify and map a set of aquatic conservation focus areas that holistically represent the full breadth of distinct riverine ecosystems and multiple populations of all native aquatic species.” Using data from the Missouri Aquatic GAP Project and other geospatial data, MoRAP identified and mapped riverine ecosystems that are relatively distinct with regard to ecosystem structure, function, and evolutionary history. To accomplish this, a classification hierarchy was developed and used, shown below.
The Aquatic Subregions shown at the top are physiographic areas that account for differences in the ecological composition of riverine assemblages of organisms. Each Subregion (i.e., Central Plains, Ozarks, and Mississippi Alluvial Basin) contains streams with relatively distinct structural features, functional processes, and aquatic assemblages in terms of both taxonomic and ecological composition.
Embedded within Aquatic Subregions are Ecological Drainage Units (EDUs) which account for the geographic variations in taxonomic composition of fish, crayfish, mussels and snails. MoRAP found that the EDUs have assemblages of organisms with relatively similar ecological composition within a given Aquatic Subregion, such as reproductive and foraging strategies and also physiological tolerances. They also found that taxonomic composition of assemblages in any given EDU is relatively distinct due to evolutionary processes such as differences in colonization history.
MoRAP used multivariate cluster analysis of quantitative landscape data to group watersheds into distinct Aquatic Ecological System Types (AES-Types), the next level of the classification hierarchy. The AES-Types represent finer resolution variations in climatic, geologic, soil, landform, and stream character. Missouri’s AES-Types comprise 38 smaller subdrainages, which can be thought of as riverine “habitat types.” Each individual AES is a spatially distinct macrohabitat, however all individual AESs that are structurally and functionally similar fall under the same AES-Type.
Finally, each individual segment of stream from the National Hydrography Dataset is a spatially distinct habitat, but valley segments of the same size, temperature, flow, gradient and geology (through which they flow) all fall under the same Valley Segment Types (VST), the final level shown above. They account for the linear variation in ecosystem structure and function that is prevalent in riverine environments. Each distinct combination of variable attributes represents a distinct VST and have been consistently shown to be associated with geographic variation in assemblage (of species) composition.
I know I threw a lot at you and in my next blog I’ll continue explaining the methods behind our development of the Aquatic Conservation Focus Areas. Stay tuned next month, but in the meantime, visit MoRAP’s website for a more detailed description of everything that went into creating the classification hierarchy that was so inherent in doing the aquatic assessment.
About the Author: Holly Mehl is an ecologist for EPA Region 7 who helps with water monitoring in the field and performs mapping for EPA Region 7’s program offices when in the office.