James M. Omernik

Regional reference sites: a method for assessing stream potentials

Field assessments of impacted streams require a control or at least an unbiased estimate of attainable conditions. Control sites, such as upstream/downstream or wilderness sites, have proven inadequate for assessing attainable ecological conditions where the control streams differ naturally from the impacted streams to a considerable degree or where different disturbances exist than those being studied. Relatively undisturbed reference sites with watersheds in areas having the same land-surface form, soil, potential natural vegetation, and land use as are predominant in large, relatively homogeneous regions are suggested as alternative control sites. These areas are considered typical of the region and therefore the sites also are considered typical of the region because their watersheds exhibit all the terrestrial variables that make that region a region. The logical basis for developing regional reference sites lies in the ability to group watersheds and common stream types into regions by integrating available maps of terrestrial variables that influence streams. Relatively undisturbed reference sites can be selected from typical areas of the regions and from transition zones where one or two of the terrestrial variables are not the predominant one(s) of the region. These reference sites are useful for estimating attainable conditions, for evaluating temporal and spatial changes in ecological integrity, for classifying attainable uses of streams, and for setting biological and environmental criteria.

Correspondence between spatial patterns in fish assemblages in ohio streams and aquatic ecoregions

Land classification systems can be useful for assessing aquatic ecosystems if relationships among them exist. Because the character of an aquatic ecosystem depends to a large extent upon the character of the landscape it drains, spatial patterns in aquatic ecosystems should correspond to patterns in the landscape. To test this hypothesis, the US state of Ohio was divided into four aquatic ecoregions based on an analysis of spatial patterns in the combination of land-surface form, land use, potential natural vegetation, and soil parent material. During the period July–October 1983, fish assemblages were sampled in 46 streams that were representative of the ecoregions, and that had watersheds relatively undisturbed by human activities. Spatial patterns of the fish assemblages were examined relative to the ecoregions; distinct regional differences were identified. The assemblages differed most between the Huron/Erie Lake Plain region and the Western Allegheny Plateau region; assemblages in the Eastern Corn Belt Plains and the Erie/Ontario Lake Plain-Interior Plateau regions were intermediate. This pattern also reflects the gradient in landscape character as one moves from the northwest to the southeast of Ohio.

Environmental Review: Ecoregions: A Geographic Framework to Guide Risk Characterization and Ecosystem Management

Two central tenets of the ecosystem management paradigm are integrity and sustainability. Recognizing, maintaining, and/or restoring ecosystem integrity and sustainability present a major challenge...

Summer total phosphorus in lakes: A map of Minnesota, Wisconsin, and Michigan, USA

A map of summer total phosphorus in lakes has been compiled for Minnesota, Wisconsin, and Michigan to clarify regional patterns in attainable lake trophic state. Total phosphorus was used as a measure of lake trophic state because: (1) phosphorus plays a central role in controlling the overall fertility of most lakes, (2) total phosphorus values are available for a great number of lakes, and (3) phosphorus is measured in a consistent manner. The maps were compiled using patterns of total phosphorus data and observed associations between these data and geographic characteristics including physiography, land use, geology, and soils. Regions depicted on the map represent areas of similarity in phosphorus concentrations in lakes, or similarity in the mosaic of values, as compared to adjacent areas. Within each region, differences in total phosphorus can be compared to natural and anthropogenic factors to determine the types of lakes representative of each region, the factors associated with differences in quality, and the realistically attainable phosphorus levels for each type of lake.

Usefulness of natural regions for lake management : analysis of variation among lakes in northwestern Wisconsin, USA

A map of summer total phosphorus in lakes was compiled recently for a three-state area of the upper Midwest for purposes of identifying regional patterns of total phosphorus in lakes and attainable lake trophic state. Spatial patterns in total phosphorus from approximately 3000 lakes were studied in conjunction with maps of geographic characteristics that tend to affect phosphorus balance in lakes to identify regions of similarity in phosphorus concentrations in lakes or similarity in the mosaic of values as compared to adjacent areas. While degrees of relative homogeneity are apparent at many scales, the map was designed at a scale that would yield regions with sufficient homogeneity to be useful for lake management throughout the area. In this study, data from 210 lakes in a 1560-mi2 area in northwestern Wisconsin, sampled by the Wisconsin Department of Natural Resources in the spring of 1988 (subsequent to the compilation of the phosphorus map), were examined to: (1) substantiate the existence of the regions depicted on the map in northwest Wisconsin, (2) determine the nature and relative precision of the regional boundaries, (3) determine the relative importance of natural and anthropogenic watershed characteristics, lake types, lake area, and lake depth in explaining within-region differences in lake phosphorus, and (4) demonstrate how the regions might be used by local lake managers.

Regional Patterns of Total Phosphorus in Lakes of the Northeastern United States

ABSTRACT A map of total phosphorus regions has been compiled for lakes in the glaciated portion of the northeastern United States. Total phosphorus data from over 2,600 of the approximately 22,000 lakes larger than 1 hectare in the study area were used for the analysis. Many of the lake regions delineated include lakes with widely differing phosphorus levels. The distinguishing feature of each region is the distribution, or mosaic, of lake phosphorus values. The pattern of values is determined by, or associated with, the particular landscape characteristics of that region and differs in comparison to patterns of lake phosphorus values in adjacent regions. Characteristics examined included: physiography, land cover/land use, vegetation (both potential and existing), soil type, and bedrock and surficial geology. For some regions, where summer lake phosphorus data were sparse, increased emphasis was placed on using combinations of landscape characteristics to refine boundaries. This method comprised using th...

Total alkalinity of surface waters: a map of the upper midwest region of the United States

This map (see the inside back cover of this issue) illustrates the regional patterns of mean annual alkalinity of surface water in the northern portions of Minnesota, Wisconsin, and Michigan, USA. It provides a qualitative graphic overview of the relative potential sensitivity of surface waters to acidic input in the upper midwest portions of the United States. The map is based on data from approximately 14,000 lakes and streams and the apparent spatial associations between these data and macroscale watershed characteristics that are thought to affect alkalinity.

How Misapplication of the Hydrologic Unit Framework Diminishes the Meaning of Watersheds

Hydrologic units provide a convenient but problematic nationwide set of geographic polygons based on subjectively determined subdivisions of land surface areas at several hierarchical levels. The problem is that it is impossible to map watersheds, basins, or catchments of relatively equal size and cover the whole country. The hydrologic unit framework is in fact composed mostly of watersheds and pieces of watersheds. The pieces include units that drain to segments of streams, remnant areas, noncontributing areas, and coastal or frontal units that can include multiple watersheds draining to an ocean or large lake. Hence, half or more of the hydrologic units are not watersheds as the name of the framework “Watershed Boundary Dataset” implies. Nonetheless, hydrologic units and watersheds are commonly treated as synonymous, and this misapplication and misunderstanding can have some serious scientific and management consequences. We discuss some of the strengths and limitations of watersheds and hydrologic units as spatial frameworks. Using examples from the Northwest and Southeast United States, we explain how the misapplication of the hydrologic unit framework has altered the meaning of watersheds and can impair understanding associations between spatial geographic characteristics and surface water conditions.

An improved technique for estimating mean depth of lakes

Abstract We describe a technique for determining mean lake depth utilizing a systematically aligned dot grid. This technique is, on average, 55% faster than the traditional planimeter methods, depending on the type of planimeter and the size and complexity of the lake. No detectable bias is associated with results from this technique compared with those of traditional planimeter methods. The relationship N D = 4 √A ; where ND = the number of dots falling within the shoreline of the lake and A = the surface area of the lake in ft2, gives a quick estimation of the number of dots that should fall within the shoreline boundary of a lake for optimum sampling.

Quantitative Soil Descriptions for Ecoregions of the United States

Researchers have defined and mapped ecological regions of the United States based on similar patterns of ecosystems such as deserts, forests, and croplands. These studies are useful in regional research, monitoring, and environmental management because data can be more readily extrapolated within the same ecoregion and to regions with similar characteristics. The description of ecoregions is largely holistic and qualitative. Conversely, quantitative information for soil are abundant and soil is an important ecosystem component related to many ecoregion properties. We used the nationwide State Soil Geographic database (STATSGO) to describe the soils of 84 Level III ecoregions in the United States. Among the 24 soil characteristics studied were texture, rock fragments, available water capacity, bulk density, and organic matter content. For each ecoregion we developed ranks to describe (i) its similarity to the U.S. average soil characteristics, (ii) the accuracy of predicting those characteristics, (iii) how well the soil map unit boundaries fit within ecoregion boundaries, (iv) the spatial relationship of soils across neighboring ecoregion boundaries, and (v) the homogeneity of texture-rock patterns. We present a national map of soil texture and rock fragments and five soil ranks for each ecoregion, and examine relationships between soils and other ecological components for selected ecoregions. Because soils relate to other ecosystem components such as vegetation, geology, and land use, the soil ranks complement and enrich the qualitative ecoregion descriptions. Similar analyses of physical or biological components of ecoregions will expand the understanding of the ecosystem patterns.