Grantee Research Project Results
Final Report: Development and Evaluation of Multi-Scale Mechanistic Indicators of Regional Landscapes
EPA Grant Number: R825870Title: Development and Evaluation of Multi-Scale Mechanistic Indicators of Regional Landscapes
Investigators: Richards, Carl , Host, George E. , Johnson, Lucinda
Institution: University of Minnesota - Duluth , Natural Resources Research Institute
EPA Project Officer: Packard, Benjamin H
Project Period: December 1, 1997 through November 30, 2000
Project Amount: $925,000
RFA: Ecosystem Indicators (1997) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems
Objective:
The main objectives of this research project were to: (1) develop predictive models that integrate landscape-scale factors with reach-scale physical and chemical stream attributes; (2) quantify key compositional and structural attributes of stream biota; (3) derive ecosystem indicators at multiple spatial scales; (4) evaluate the appropriate scale of terrestrial and aquatic data necessary to resolve regional and local aquatic resource questions and improve our ability to distinguish and quantify natural variation in indicators from that derived from anthropogenic stressors; and (5) assess the extent to which regional and local-scale indices (including standard indices of ecological integrity (e.g., IBI)) reflect fundamental ecosystem processes and structural properties of stream habitats and biota.
Summary/Accomplishments (Outputs/Outcomes):
Experimental Design Summary of Accomplishments. We evaluated the importance of terrestrial features that were relevant to stream ecosystems by examining stream heterogeneity among streams nested within watersheds, watersheds within subregions, and subregional watersheds within larger geographic areas. We examined 36 watersheds in the Saginaw Bay region of Michigan, and 36 watersheds in southeastern Minnesota. Both regions are dominated by agricultural land uses.
Landscape Analyses: Mapping Riparian Zones. Riparian zones are important landscape features that perform many important ecosystem services, such as the contribution of organic matter, shade and cover, and the mediation of water, nutrients and sediment inputs from the watershed. Because riparian buffer strips in agricultural regions are very narrow, they are difficult to map and characterize using datasets based on Landsat Thematic Mapper imagery. We quantified the error resulting from the use of satellite images when calculating land cover in riparian zones by conducting detailed air photo interpretations in 12 Minnesota streams. These data had a minimum of 0.5 m resolution and were classified to 21 data classes for a distance of up to 500 m lateral to stream. Data were compared with the National Land Cover Dataset (NLCD), which has a 28.5 m resolution and the same 21 data classes. Within the first 30m (one pixel) lateral to the stream, the NLCD data overestimated the amount of rowcrop agriculture by approximately 25 percent, compared to the detailed air photo interpretation. Within three pixels (~90 m), rowcrop was overestimated by approximately 18 percent.
Figure 1. Land Use Characteristics of Study Watersheds
Figure 2. Percent of Rowcrop Agriculture Overestimated by NLCD Data Compared With Aerial Photographs
Models that predict instream properties from satellite image-derived riparian data must account for this error. High-resolution satellite imagery (~5 m resolution) may be required to map riparian zone land cover accurately in agricultural landscapes.
Nutrients and Flow. Land use and geology are two of the most important factors in determining the structure and function of a stream ecosystem. To determine the interactive effects these factors have on stream flow, sediment, and nutrients, we analyzed 72 ungaged agricultural watersheds in Minnesota and Michigan, using the Soil Water Assessment Tool (SWAT) model. The basins differed in surficial geology (landform) and land use composition, but were similar in size, with streams ranging from second to third order. SWAT was developed for use on ungaged basins; however, to improve the outputs, we used U.S. Geological Survey discharge data for calibration at sites near our study watersheds. We found that both land use and landform were important for predicting flow and nutrient variables, and that there were at least nine distinct features within the watersheds that influence nutrients, sediment, and flow. Some instream variables responded most strongly to land use alone (soluble P, nitrate, constant velocity of flow), some to geology alone (NH4, organic nitrogen), and others to both land use and geology (organic P, flow, and flow predictability). However, the magnitude and relative importance of specific landscape characteristics of the two regions differed. Differences between the two regions were related to basic geological contrasts, such as underlying geology. Morainal soils in Minnesota are underlain by karst geology, which has important influences on groundwater flow. Nonetheless, contrasts in land use patterns between the two regions, particularly with respect to the extent of rowcrop agriculture, may have been the most important difference in water flow and nutrient status. Minnesota had much higher proportions and less variation in rowcrop agriculture than Michigan. A threshold in the amount of agriculture yields little additional change in flow or nutrients, and this may have been observed in Minnesota.
Wood in Low Gradient Streams. Despite the relatively low abundance of large wood in streams in Michigan and Minnesota streams, wood is an important habitat for macroinvertebrates. A substantial portion of local diversity can be attributed to the presence, but not the abundance, of wood habitats. Thus, habitat heterogeneity appears to be the major driving variable accounting for local biodiversity.
Strong interactions between land use and surficial geology occurred across the Michigan study area and influenced the standing stocks and distributions of wood. Features at the local scale (e.g., bank-full width, percent of open canopy) had a large influence on the density and distribution of accumulations, and a moderate influence on wood abundance. In contrast, riparian and catchment features including riparian vegetation type, link number, percent urban land use in the catchment, and topographic heterogeneity exerted greater control over total wood length in a reach. At a reach scale, the differences in the factors predicting wood standing stocks versus accumulation densities are probably related to the local processes that entrain wood into accumulations. Overall, standing stocks and distribution of wood in these channels reflect current and past land use practices, as well as underlying processes (i.e., hydrologic regime) controlled by landforms. As a result, wood standing stock and distribution patterns differ from those observed in high gradient and low gradient forested streams.
Figure 3. Total Number of Taxa From Michigan and Minnesota Study Streams Associated With Individual Habitats
Algal Production. Due to the importance of algal production to stream systems, we examined the influence of reach and watershed-scale features on algal growth. We conducted nutrient bioassays with nutrient diffusing substrates in Minnesota and Michigan streams to determine whether nutrients were limiting to algal growth among watersheds with different geology and land use. We sampled 36 streams in the Michigan and Minnesota study regions in summer and fall of 1998, and spring, summer, and fall of 1999. In each of these seasons, we conducted nutrient limitation experiments in each stream to determine whether nitrogen, phosphorus, or nitrogen + phosphorus limited periphyton accrual on artificial substrates. Nutrient limitation by any individual nutrient or their combination was observed only 5 times in 172 separate experiments (5 seasons x 36 streams), indicating that nutrients do not limit primary production in these highly agricultural watersheds. This corresponded with relatively high observed background nutrient concentrations in the spring, summer, and fall samples, although concentrations were highest in the spring. The influence of other reach and watershed factors on periphyton accrual was assessed with a regression model. Riparian zone width, percent open water, maximum temperature, percent benthic fines, and percent residential land use were the most important of these variables, and explained 86 percent of the total variation in periphyton accrual.
Invertebrate and Reach-Scale Physical Characteristics. To identify the relevant scales at which physical characteristics and biological communities respond in streams, we employed a two-step procedure. In step 1, we identified the reach-scale physical attributes that had the strongest influence on biota within study watersheds. We also developed regression models to compare the relative influence of various reach-scale variables on individual invertebrate metrics. In step 2, we identified the catchment-scale attributes influencing these important reach-scale factors. The models indicated considerable differences among the 20 invertebrate metrics in terms of the variables having greatest influence. For example, taxa richness was most strongly influenced by the number of habitats in a stream reach (see Figure 4), whereas the proportion of gatherers was most strongly influenced by percent fines. Important reach-scale physical variables were related to catchment variables with regression models in a similar manner to step 1. As with macroinvertebrate metrics, we noted considerable variation in the relative influence of various catchment parameters on individual reach-scale variables (see Figure 4).
Figure 4. Frequency with which reach or watershed variables were significant in regressions models.
Clear patterns emerge from the summaries of these analyses. In Minnesota, the number of habitats in a stream reach, the maximum temperature experienced by a stream reach, percent fines, and width-to-depth ratio were the reach-scale physical variables that were most frequently included as predictors in the regression models (see Figure 4). The catchment-scale factors most strongly influencing these reach-scale features were those that influenced stream size (number of stream links), indicated major differences in surface slopes and underlying geology (SD elevation), and erosiveness of the soils (k-factor). In Michigan, percent fines and percent of open canopy were the most important variables followed by dissolved inorganic nitrogen (DIN) and number of habitats. Clear patterns in catchment-scale features that had most influence on these variables were more difficult to identify. Only percent organic matter and percent residential land cover were detected in more than one model.
The behavior of some common metrics utilized in biological assessments varied between the two regions. For example, Ephemeroptera, Plecoptera, and Trichoptera taxa did not respond similarly in the two regions. In Minnesota, it was well predicted, and in Michigan, it was poorly predicted. Other metrics such as taxa richness, which was most strongly influenced by the numbers of habitats, responded similarly in both regions.
Identification of Indicators. Our study illustrates the importance of recognizing the scale dependance of individual stream parameters when developing suites of stream indicators. In addition to the watershed or landscape composition, the stream's physical, chemical, and biological attributes may respond to features at different scales. It is essential to understand the relative importance of such attributes as riparian and catchment characteristics, in addition to land use and geological configuration. The indicators' identities are ultimately driven by the stream ecosystem characteristic of interest. However, there are some common trends among the characteristics. Our study indicates that the extent and distribution rowcrop agriculture is a pervasive feature that dominates stream ecosystem function in Midwestern landscapes. Extent and distribution of rowcrop agriculture determines many aspects of nutrient, flow, and physical heterogeneity within streams. Our results hint that watersheds with 80 percent or greater rowcrop land uses may be beyond a threshold of response to land use. The strongest landscape indicators of stream variation in such homogenous agricultural regions are often structural features of the landscape, such as soil erosivity, watershed size, and underlying geology. These features dominate the flow of water and materials into streams and are separate from land use designations.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 38 publications | 1 publications in selected types | All 1 journal articles |
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Johnson LB, Breneman DH, Richards C. Macroinvertebrate community structure and function associated with large wood in low gradient streams. River Research and Applications 2003;19(3):199-218. |
R825870 (Final) |
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Supplemental Keywords:
ecological effects, nutrients, sediment, nitrogen, ecosystem, indicators, restoration, regionalization, streams, riparian, macroinvertebrates, fish, scaling, aquatic, habitat, terrestrial, conservation, biology, ecology, hydrology, landscape ecology, watersheds, modeling, satellite, landsat, remote sensing, Midwest, Great Lakes, EPA Region 5, agriculture., RFA, Scientific Discipline, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Midwest, Ecology, Hydrology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Environmental Chemistry, Chemistry, Ecological Effects - Environmental Exposure & Risk, Geology, Ecological Indicators, EPA Region, agriculturally impacted watershed, aquatic ecosystem, nutrient supply, ecological exposure, EMAP, remote sensing, landscape indicator, satellite images, stressors, watersheds, ecosystem integrity, stream ecosystems, regional scale, soil, aquatic ecosystems, water quality, ecosystem stress, multiscale assessment, spatial and temporal patterns, Region 5, land useProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.