Search

We describe development anthropogenic stress indices for coastal margins of the Laurentian Great Lakes basin. Indices were derived based on the response of species assemblages to watershed-scale stress from agriculture and urbanization. Metrics were calculated for five groups of wetland biota: diatoms, wetland vegetation, aquatic invertebrates, fishes, and birds. Previously published community change points of these assemblages were used to classify each watershed as ‘least-disturbed’, ‘at-risk’, or ‘degraded’ based on community response to these stressors. The end products of this work are an on-line map utility and downloadable data that characterize the degree of agricultural land use and development in all watersheds of the US and Canadian Great Lakes basin. Discrepancies between the observed biological condition and putative anthropogenic stress can be used to determine if a site is more degraded than predicted based on watershed characteristics, or if remediation efforts are having beneficial impacts on site condition. This study provides a landscape-scale evaluation of wetland condition that is a critical first step for multi-scale assessments to help prioritize conservation or restoration efforts.

The St. Louis River drains an area of 9412 km 2 into the western arm of Lake Superior. The river's lower section, including a 48.5 km 2 estuary, was designated as a Great Lakes Area of Concern due to degradation from industrial activities. Part of the estuary is occupied by the largest port in the Great Lakes. A GIS-based stressor index was previously developed to characterize anthropogenic stress within the watershed. The components of the stressor index were road density, point-source pollution permit density, population density, and percent agricultural and developed land. Water quality sampling was conducted at 27 sites in the estuary in tributaries and associated nearshore areas during multiple flow regimes in 2010–2011. Additional data were analyzed from 34 upper watershed sites sampled in 2009–2010. Stressor scores were significantly (p 2 − /NO 3 − -N, dissolved oxygen saturation, pH, specific electrical conductivity, chloride, sulfate, and E. coli in the upper watershed. In the estuary, the index was significantly and positively correlated with NO 2 − /NO 3 − -N, NH 4 + -N, and chloride at multiple flow regime and location combinations. Soil K factor (an erosivity index from recent NRCS SSURGO soil surveys) was found to have stronger relationships with sediment related parameters than the stressor gradient. Although originally designed to help stratify sampling across a gradient of landscape stress and identify reference areas for restoration projects, the stressor index was shown to have substantial predictive power for multiple water quality parameters.

Context Green infrastructure may improve water quality and mitigate flooding in forest-urban watersheds, but reliably quantifying all benefits is challenging because most land cover maps depend on moderate- to low-resolution data. Complex and spatially heterogeneous landscapes that typify forest-urban watersheds are not fully represented with these types of data. Hence important questions concerning how green infrastructure influences water quality and quantity at different spatial scales remain unanswered. Objectives Demonstrate the feasibility of creating novel high-resolution land cover maps across entire watersheds and highlight deficiencies of standard land cover products. Methods We used object-based image analysis (OBIA) to create high-resolution (0.5 m) land cover maps and detect tree canopy overlapping impervious surfaces for a representative forest-urban watershed in Duluth, MN, USA. Unbiased estimates of accuracy and area were calculated and compared with similar metrics for the 30-m National Land Cover Database (NLCD). Results Mapping accuracies for the high-resolution land cover and canopy overlap maps were ~90 %. Error-adjusted estimates of area indicated that impervious surfaces comprised ~21 % of the watershed, tree canopy overlapped ~10 % of impervious surfaces, and that three high-resolution land cover classes differed significantly from similar NLCD classes. Conclusions OBIA can efficiently generate high-resolution land cover products of entire watersheds that are appropriate for research and inclusion in the decision-making process of managers. Metrics derived from these products will likely differ from standard land cover maps and may produce new insights, especially when considering the unprecedented opportunity to evaluate fine-scale spatial heterogeneity across watersheds.

Total suspended solids (TSS) and total phosphorus (TP) have been shown to be strongly correlated with turbidity in watersheds. High-frequency in situ turbidity can provide estimates of these potential pollutants over a wide range of hydrologic conditions. Concentrations and loads were estimated in four western Lake Superior trout streams from 2005 to 2010 using regression models relating continuous turbidity data to grab sample measures of TSS and TP during differing flow regimes. TSS loads estimated using the turbidity surrogate were compared with those made using FLUX software, a standard assessment technique based on discharge and grab sampling for TSS. More traditional rating curve methodology was not suitable because of the high variability in the particulates vs. discharge relationship. Stream-specific turbidity and TSS data were strongly correlated (r2 = 0.5 to 0.8; p

Many streams along the Minnesota coast of Lake Superior have been listed as impaired from either high turbidity or high fish mercury concentrations or both. Both turbidity and total mercury have been shown to be strongly correlated to total suspended sediment in many disturbed watersheds. Turbidity and total mercury concentrations and loads were estimated in four western Lake Superior watersheds from 2005–2006 using automated in-stream turbidity measurements. Regression models were developed relating this near-continuous turbidity data to grab sample measures of mercury during differing flow regimes. Total mercury values ranged from 1 to 28 ng l−1 throughout the open water season and showed a close relationship to total suspended sediment (r2 = 0.85, n = 23; p < 0.001) and a less robust but still significant relationship with turbidity (r2 = 0.40, n = 34; p < 0.001) for all four streams. Mercury loads to Lake Superior were estimated to range from 8 to 97 g yr−1 with watershed yields ranging from 0.5 to 4.3 μg m−2 yr−1. Continuous turbidity monitoring appears to be a reasonable surrogate for both suspended sediment and total mercury concentration, providing information when manual sample collection is cost-prohibitive or logistically difficult, and across a wide range of flows.

Biological indicators can be used both to estimate ecological condition and to suggest plausible causes of ecosystem degradation across the U.S. Great Lakes coastal region. Here we use data on breeding bird, diatom, fish, invertebrate, and wetland plant communities to develop robust indicators of ecological condition of the U.S. Lake Superior coastal zone. Sites were selected as part of a larger, stratified random design for the entire U.S. Great Lakes coastal region, covering gradients of anthropogenic stress defined by over 200 stressor variables (e.g. agriculture, altered land cover, human populations, and point source pollution). A total of 89 locations in Lake Superior were sampled between 2001 and 2004 including 31 sites for stable isotope analysis of benthic macroinvertebrates, 62 sites for birds, 35 for diatoms, 32 for fish and macroinvertebrates, and 26 for wetland vegetation. A relationship between watershed disturbance metrics and 15N levels in coastal macroinvertebrates confirmed that watershed-based stressor gradients are expressed across Lake Superior's coastal ecosystems, increasing confidence in ascribing causes of biological responses to some landscape activities. Several landscape metrics in particular—agriculture, urbanization, human population density, and road density—strongly influenced the responses of indicator species assemblages. Conditions were generally good in Lake Superior, but in some areas watershed stressors produced degraded conditions that were similar to those in the southern and eastern U.S. Great Lakes. The following indicators were developed based on biotic responses to stress in Lake Superior in the context of all the Great Lakes: (1) an index of ecological condition for breeding bird communities, (2) diatom-based nutrient and solids indicators, (3) fish and macroinvertebrate indicators for coastal wetlands, and (4) a non-metric multidimensional scaling for wetland plants corresponding to a cumulative stress index. These biotic measures serve as useful indicators of the ecological condition of the Lake Superior coast; collectively, they provide a baseline assessment of selected biological conditions for the U.S. Lake Superior coastal region and prescribe a means to detect change over time.

Quantifying gradients of anthropogenic stress can inform the development of sample designs, provide an important covariate in modeling relationships of response variables, identify reference and highly-disturbed sites, and provide a baseline and guidance to restoration and remediation efforts. We describe development of SumRel, a composite index of anthropogenic stress, for the U.S. and Canadian Lake Superior basin. Key elements of the project include development of high-resolution watersheds throughout the basin, summarization of the major point and non-point stressors within these watersheds, and creation of tools for scaling the watersheds and stressor summaries. SumRel was calculated at two spatial scales: for high resolution subcatchments within the Lake Superior basin (mean watershed area = 93 ha) and for coastal watersheds of Lake Superior. An assessment of subcatchments within Minnesota's St. Louis River watershed showed a correlation between the degree of disturbance, as indicated by SumRel, and impaired water quality, as evidenced by in-stream conductivity. These data and tools allow identification and visualization of reference and highly-disturbed sites at multiple spatial scales, providing decision support for individual agency and binational monitoring, assessment and restoration initiatives across the Lake Superior basin.

We developed ecological indicators of stream macroinvertebrates in two regions of the Midwestern USA dominated by row-crop agriculture. Indicators were identified in a hierarchical fashion. Reach-scale variables related to macroinvertebrate attributes were first identified, and then catchment-scale variables related to those reach-scale variables were identified. Reach-scale indicators common to both regions were % fine sediments, number of habitats, and width:depth ratio. SD of elevation and % commercial land use were selected as catchment-scale indicators in both regions. Our analyses revealed a multi-scale mechanistic relationship between macroinvertebrate attributes associated with degraded conditions (i.e., fewer taxa of Plecoptera and Trichoptera, and a higher proportion of chironomids, burrowers, and depositional taxa) and % fine sediments in stream reaches, which, in turn, was negatively related to catchment characteristics (i.e., SD of elevation) in one region. Understanding how natural variables such as topography influence channel shape and within-channel structure can help guide management options and expectations for different regions. We suggest that developing multi-scale indicators in a mechanistic fashion will be more effective than developing indicators at only one spatial scale for protecting and restoring stream structure and function.

Developing indicators of ecosystem condition is a priority in the Great Lakes, but little is known about appropriate spatial scales to characterize disturbance or response for most indicators. We surveyed birds, fish, amphibians, aquatic macroinvertebrates, wetland vegetation, and diatoms at 276 coastal wetland locations throughout the U.S. Great Lakes coastal region during 2002-2004. We assessed the responsiveness of 66 candidate indicators to human disturbance (agriculture, urban devel- opment, and point source contaminants) characterized at multiple spatial scales (100, 500, 1,000, and 5,000 m buffers and whole watersheds) using classification and regression tree analysis (CART). Non- stressor covariables (lake, ecosection, watershed, and wetland area) accounted for a greater proportion of variance than disturbance variables. Row-crop agriculture and urban development, especially at

Identification of reference conditions for ecological assessments of coastal ecosystems poses a challenging problem in highly modified landscapes. A method is described for characterizing disturbance in coastal ecosystems using remotely sensed land classification and other publicly available GIS data. Within ecoregions bordering the US Great Lakes coast, aquatic habitats bordering the shoreline were classified into five ecological types: high‐energy shoreline, embayments, open‐coast, river‐influenced and protected wetlands. Degree of anthropogenic disturbance in contributing areas to these ecosystems was assessed using a watershed approach for wetland types or a moving window approach for high‐energy shorelines. Anthropogenic stress variables included proportions of agricultural or residential land use, information on population and road density, and distance from the nearest point source. Polygons (wetlands) or pixels (high‐energy shoreline) were categorized as ‘reference’ if the magnitude of the most se...

Land use and geology are two important extrinsic factors regulating the structure and function of stream ecosystems. The interactions among these two landscape-scale factors on streams are, however, poorly understood. To determine the effects of these factors on stream flow, sediment, and nutrients, we analyzed 72 ungaged, agricultural watersheds in Minnesota and Michigan using the hydrologic model SWAT (the Soil Water Assessment Tool). The watersheds differed in surficial geology (landform) and land use, but were of similar size, with streams ranging from 2nd to 3rd order. SWAT was developed for use on ungaged basins, but to improve the outputs we used US Geological Survey discharge data from sites near our study watersheds for calibration. We found seasonal and annual differences in flow and nutrient and sediment loading across different land forms and land use types. Watersheds with greater amounts of row-crop agriculture and watersheds dominated by morainal landforms were associated with more sediment and nutrients and greater flow volumes and flashiness. Multivariate analyses identified at least nine landscape variables which were related to nutrients, sediment, and flow, although the responses varied between Minnesota and Michigan. Results also indicated the possibility of a threshold effect for row crop agricultural. Increases in this land use had little additional effect on nutrients or flow when percent row crop exceeds the threshold value. At moderate to high levels of row crop agriculture, watersheds appeared to show greater sensitivity to differences in landform.

Understanding the relationship between human disturbance and ecological response is essential to the process of indicator development. For large-scale observational studies, sites should be selected across gradients of anthropogenic stress, but such gradients are often unknown for a population of sites prior to site selection. Stress data available from public sources can be used in a geographic information system (GIS) to partially characterize environmental conditions for large geographic areas without visiting the sites. We divided the U.S. Great Lakes coastal region into 762 units consisting of a shoreline reach and drainage-shed and then summarized over 200 environmental variables in seven categories for the units using a GIS. Redundancy within the categories of environmental variables was reduced using principal components analysis. Environmental strata were generated from cluster analysis using principal component scores as input. To protect against site selection bias, sites were selected in random order from clusters. The site selection process allowed us to exclude sites that were inaccessible and was shown to successfully distribute sites across the range of environmental variation in our GIS data. This design has broad applicability when the goal is to develop ecological indicators using observational data from large-scale surveys.

We investigated impacts of harvesting on soil disturbance and vegetation in the aspen cover type of northern Minnesota, United States. The soil disturbance (resistance to penetration) and understory vegetation were characterized for 19 sites on five 60-m 2 plots placed along a disturbance gradient: landings (high harvesting traffic), skid trails (inter- mediate harvesting traffic), and areas off skid trails (low to no harvesting traffic). Penetration levels were quite variable, but they still indicated that within-site responses to disturbance patterns created by clear-cut harvesting were not uniform. In general, soil disturbance and understory species composition within landings were similar to those with skid trails. The soil disturbance and vegetation composition of these two levels differed from those of the low-disturbance plots (off skid trails), indicating that removing trees alone did not affect vegetation composition as much as creating an es- tablished skid trail, regardless of harvest timing. However, sites with more variable species composition (win- ter-harvested sites) and lower disturbance levels were less altered than sites with likely lower initial diversity (summer-harvested sites). The results suggest that it is important for recovery of understory plant communities to not only limit the amount and level of disturbances but also consider the spatial layout of harvesting, thus maintaining a spatially connected network of remnant forest patches large enough to contain interior forest species. Resume : Les auteurs etudie l'impact des activites de recolte sur la perturbation du sol et la vegetation dans les forets de peuplier faux-tremble du nord du Minnesota aux Etats-Unis. La perturbation du sol (resistance a la penetration) et la vegetation de sous-bois ont ete caracterisees pour 19 sites dans cinq places-echantillons de 60 m 2 etablies de long d'un

ECOPHYS, an individual-based process model for poplar, requires a three-dimensional soil water redistribution model to simulate soil water dynamics, plant uptake, and root growth. SOILPSI is a potential-driven water redistribution model based on the RHIZOS rhizosphere simulator. It expands on RHIZOS by calculating water flux based on water potential, and has a macropore flow mode to allow rapid drainage of the soil. SOILPSI simulates water flux in three dimensions and accounts for slope. SOILPSI was evaluated by comparing model output to soil moisture data collected under bare soil conditions. AMMI analysis of a date × depth matrix of differences between simulated and observed soil moisture content showed that excluding the two shallowest soil layers resulted in a difference matrix that conformed to an additive model. The grand mean predicted values were within 2% of the observed values, and 50 of 56 predicted values were within 5% of the observed values. Better agreements between simulated and observed soil moisture content were observed deeper in the soil profile and later in the season. Agreement between SOILPSI and field conditions was consistently more accurate than RHIZOS. Improving simulation of evaporative flux at the soil surface would improve simulation accuracy in the upper horizons.  2002 Elsevier Science Ltd. All rights reserved.

Predicting ozone-induced reduction of carbon sequestration of forests under elevated tropospheric ozone concentrations requires robust mechanistic leaf-level models, scaled up to whole tree and stand level. As ozone effects depend on genotype, the ability to predict these effects on forest carbon cycling via competitive response between genotypes will also be required. This study tests a process-based model that predicts the relative effects of ozone on the photosynthetic rate and growth of an ozone-sensitive aspen clone, as a first step in simulating the competitive response of genotypes to atmospheric and climate change. The resulting composite model simulated the relative above ground growth response of ozone-sensitive aspen clone 259 exposed to square wave variation in ozone concentration. This included a greater effect on stem diameter than on stem height, earlier leaf abscission, and reduced stem and leaf dry matter production at the end of the growing season. Further development of the model to reduce predictive uncertainty is discussed.

1. Landscape characteristics of sixty-two subcatchments within the Saginaw Bay Catchment of central Michigan were examined to identify relationships with stream water chemistry. Land use, land cover and elevation were quantified for both entire catchments and the upland–river ecotone (100 m stream buffer strip). Catchment and ecotone data were then empirically compared with stream water chemistry using multivariate and regression analyses. Redundancy analysis was used to partition variance among land use, geology, and the shared influence of land use and geology. 2. Major catchments dominated by rowcrop agriculture had the highest alkalinity, total dissolved solids and nitrate + nitrite concentrations. 3. Strong seasonal differences were observed in total nitrogen and nitrite + nitrate, but not in total phosphorus or suspended solids. Land use and landscape structure factors such as slope and patch density (number of land use patches per km2) accounted for most of the observed variance in summer. 4. In both autumn and summer, landscape factors accounted for much of the observed variation in total dissolved solids and alkalinity. During autumn, geological factors and the shared influence of geology/landscape structure plus land use exerted more influence than did land use alone. 5. Total phosphorus and total suspended solids were much better explained by land use within the stream ecotone in summer than in other seasons. However, total nitrogen, nitrate, orthophosphate and alkalinity were equally well explained by land use within the ecotone and throughout the whole catchment. Only total dissolved solids in summer and ammonium in autumn were explained better by the whole catchment than the ecotone. 6. Our results show that relatively coarse spatial databases can provide useful descriptors of regional water quality.

A simulation model is described that grows stands of aspen of given age, site quality, and stocking from establishment to breakup. Specifying mean July air temperature allows custom application to most aspen growing regions in North America and Scandinavia. The program predicts total yields in number of trees, basal area, and biomass; and merchantable yields in cubic feet and cords for user-specified utilization standards, and in board feet, Scribner. North. J. Appl. For. 13(4):164-170.

A generic bioenergetics model for chinook salmon was modified to estimate solid wastes from a commercial net-pen aquaculture operation in a Minnesota mine-pit lake. The model was calibrated using data from the operation on growth, ration, and temperature. Multiple simulations were run to form three-dimensional response surfaces for consumption, egestion, excretion and respiration as a function of fish size and water temperature. These formed the basis for the Fish Simulation Culture (FIS-C) Model. Predictions for food consumption and solids load were compared with actual ration levels and sedimentation within the mine-pit lake from 1989 to 1992, and compared well with the general trends of the observed data. However, the actual predictive power of FIS-C was very sensitive to our initial model assumption that aquaculture operations are predicated on maximizing the growth of their stock. FIS-C currently does not account for management decisions electing sub-optimal stock growth, but under these conditions does estimate a worst case loading scenario for the system. The annual phosphorus load to the system predicted by FIS-C was not significantly different from that of the mean of 17 values of annual P-load estimated empirically from the literature. However, FIS-C's estimate of P-loading shows a pronounced seasonal pattern to the annual loading. FIS-C offers substantial benefits to users by estimating seasonal and shorter term food wastage and wasteloads to receiving waters under particular operating conditions. Then, other operational scenarios can be created to examine the effects of changing fish inventory, feeding schedule, food composition, etc., in order to examine the impacts on production, environmental and/or regulatory requirements, prior to costly implementation.

A strategy for process modelling of short-rotation Salix coppice plantations is presented. To integrate effectively both large- and small-scale processes, this model must simulate critical processes at scales ranging from the individual leaf to the plantation. This multiscale modelling strategy extrapolates the detail of mechanistic physiological models to the patch and plantation scales. To accomplish this scaling, regional climatic and soil databases are used to generate model inputs; i.e. site and climatic information is passed from the regional scale to drive models operating at the stand or tree level. Key input variables at the individual tree level include genetically determined factors such as leaf morphology and branch architecture, as well as phenological and physiological parameters. Outputs such as carbon fixation, leaf area index, biomass by component, and yields per hectare are then passed back up to address regional questions. This strategy requires a parallel programme of modelling and experimentation. While this strategy focuses on Salix , the approach should also be applicable to species with similar life history attributes, such as Betula and Populus .

In order to effectively deploy short-rotation woody crop plantations for energy and fiber production at regional scales, biologically sound-field-level models of plant growth are required. Individual tree growth process models have proven effective at predicting growth based on environmental driving variables, but in the past these models have been too complex to use at the plantation scale. In this paper we describe an object-oriented strategy for scaling ECOPHYS, an individual tree growth process model for hybrid poplar, to a plantation. Included in this strategy are methods of scaling from an individual shoot to a tree, from individual trees to a patch, and from patches to a plantation. In describing interactions among trees, both above- and below-ground processes are considered. Finally, we describe methods for integrating the plantation level ECOPHYS with EPIC, a field scale model of soil productivity and erosion used in regional assessment.

Geographic Information Systems (GIS) were used to assess the relationships between land use patterns and the physical habitat and macroinvertebrate fauna of streams within similar sized watersheds. Eleven second or third order watersheds ranging from highly urbanized to heavily forested were selected along Lake Superior's North Shore. Land use patterns within the watersheds were quantified using readily available digital land use/land cover information, with a minimum mapping resolution of 16 ha. Physical habitat features, describing substrate characteristics and stream morphology, were characterized at sample points within each stream. Principle component and correlation analyses were used to identify relationships between macroinvertebrates and stream physical habitat, and between habitat and land use patterns. Substrate characteristics and presence of coarse woody debris were found to have the strongest correlations with macreinvertebrate assemblage richness and composition. Agricultural and urban land use was correlated with substrate characteristics. Algal abundance, associated with macroinvertebrate compositional differences, was correlated with housing density and non-forest land covers. The use of readily available spatial data, even at this relatively coarse scale, provides a means to detect the primary relationships between land use and stream habitat quality; finer-resolution GIS databases are needed to assess more subtle influences, such as those due to riparian conditions.

SUMMARY 1 Patterns of macroinvertebrate community composition were examined in streams within a 40000-km2 catchment in central Michigan, U.S.A., to identify the major environmental gradients influencing community variation. Agriculture and associated clay and sandy soils predominated in much of the region. 2 Eighty macroinvertebrate taxa were collected from stream surveys conducted during May and August 1990. Community composition varied primarily by the proportions of Plecoptera and Ephemeroptera. Benthic communities from the heaviest agricultural zones were most different from those at other sites. 3 Chemical composition among the sites varied most in relation to nutrients (NH3, NO3, PO4). Other parameters were relatively similar. Physical characteristics of the sites were scored in six habitat categories: (i) substrate characteristics, (ii) instream cover, (iii) channel morphology, (iv) riparian zone and stream-bank conditions, (v) riffle/run quality, (vi) pool quality. Most physical habitat scores were lowest in the intense agriculture zones. 4 The relative importance of physical and chemical variables in explaining variation in macroinvertebrate communities was quantified using canonical correspondence analysis. Substrate characteristics were most important in both surveys. Significant correlations (P

A model of photosynthate production is the central component of a larger whole-tree ecophysiological growth process model for Populus (ECOPHYS). This photosynthesis model was validated by comparing predicted photosynthate production values for individual leaves and the total tree with hourly field measurements collected on four days spaced throughout a growing season. Simulated trees had identical numbers of leaves and leaf areas as the sample trees studied in the field, and hourly weather data collected on the plantation site were supplied as a model input. Total production for the four sample days ranged between 200 and 4900 mg CO(2) tree(-1) day(-1). Model predictions of total daily photosynthate production were within 12% of the observed rates for three of the four sampling days. Diurnal variations in stomatal conductance and ambient CO(2) concentrations and seasonal variations in area leaf weight were the primary sources of error. Total leaf area, proportion of sunlit leaf area, and photosynthetic efficiency were the most important factors influencing carbon dioxide exchange rates.

Watersheds represent spatially explicit areas within which terrestrial stressors can be quantified and linked to measures of aquatic ecosystem condition. We delineated thousands of Great Lakes watersheds using previously proven and new watershed delineation techniques. These were used to provide summaries for a variety of anthropogenic stressors within the Great Lakes. All delineation techniques proved useful, but each had applications for which they were most appropriate. A set of watershed delineations and stressor summaries was developed for sampling site identification, providing relatively coarse strata for selecting sites along the U.S. Great Lakes coastline. Subsequent watershed delineations were used for high-resolution site characterization of specific sites and characterizing the full coastal stressor gradient. For these delineations we used three general approaches: 1) segmentation of the shoreline at points midway between adjacent streams and delineation of a watershed for each segment; 2) specific watershed delineations for sampled sites; and 3) a Great Lakes basin-wide, high-resolution approach wherein sub-basins can be agglomerated into larger basins for specific portions of the coast. The third approach is unique in that it provides a nested framework based on hierarchies of catchments with associated stressor data. This hierarchical framework was used to derive additional watershed delineations, and their associated stressor summaries, at four different scales. Providing anthropogenic stressor metrics in such a format that can quickly be summarized for the entire basin at multiple scales, or specifically for particular areas, establishes a strong foundation for quantifying and understanding stressor-response relationships in these coastal environments.

15.1 INTRODUCTION Riparian zones are the ecotones or transition areas between upland and aquatic ecosystems, located at the margins of rivers, lakes, ponds and wetlands. Their boundaries are defined by changes in soil, moisture, and vegetation (Naiman 2000, Decamps 1996, Gregory et al. 1991). Although these ecosystems may be small relative to the aquatic systems they abut, they perform many important ecosystem services, including shading (thus buffering air and water temperature), retaining nutrients and/or sediments, stabilizing stream banks and littoral zones, and providing organic material (leaves, wood) and critical habitat for a diverse community of plant and animal species (Malanson 1993). Riparian zones are highly variable systems whose structure and composition are shaped by geomorphology, vegetation patterns, disturbance regimes (Decamps 1996), as well as current (Erickson and DeYoung 1993) and perhaps historic land use practices (Foster et al. 2003). Processes that operate over a large range of temporal and spatial scales control these structuring factors. At one end of the time/space continuum are processes such as tectonics, volcanism, glaciation, and climate change. At intermediate spatial and temporal scales are historic land use practices (e.g., burning regimes implemented by native peoples, permanent land cover conversion) and catastrophic flooding. At small scales, localized flooding and land management practices influence the structure and function of riparian zones. Some processes occur over multiple scales and their effects may also vary by scale. The fine-scale variation of vegetative cover resulting from moisture and soil gradients around streams and wetlands has posed a challenge to research scientists and land managers (Muller 1997, Congalton et al. 2002). One of the current

Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be valuable tools in environmental research and management. Despite the fundamental appeal of a regional approach, development of regional stress measures remains one of the most important current challenges in environmental science. Using publicly available, pre-existing spatial datasets, we developed a geographic information system database of 86 variables related to five classes of anthropogenic stress in the U.S. Great Lakes basin: agriculture, atmospheric deposition, human population, land cover, and point source pollution. The original variables were quantified by a variety of data types over a broad range of spatial and classification resolutions. We summarized the original data for 762 watershed-based units that comprise the U.S. portion of the basin and then used principal components analysis to develop overall stress measures within each stress category. We developed a cumulative stress index by combining the first principal component from each of the five stress categories. Maps of the stress measures illustrate strong spatial patterns across the basin, with the greatest amount of stress occurring on the western shore of Lake Michigan, southwest Lake Erie, and southeastern Lake Ontario. We found strong relationships between the stress measures and characteristics of bird communities, fish communities, and water chemistry measurements from the coastal region. The stress measures are taken to represent the major threats to coastal ecosystems in the U.S. Great Lakes. Such regional-scale efforts are critical for understanding relationships between human disturbance and ecosystem response, and can be used to guide environmental decision-making at both regional and local scales.

Predicting ozone-induced reduction of carbon sequestration of forests under elevated tropospheric ozone concentrations requires robust mechanistic leaf-level models, scaled up to whole tree and stand level. As ozone effects depend on genotype, the ability to predict these effects on forest carbon cycling via competitive response between genotypes will also be required. This study tests a process-based model that predicts the relative effects of ozone on the photosynthetic rate and growth of an ozone-sensitive aspen clone, as a first step in simulating the competitive response of genotypes to atmospheric and climate change. The resulting composite model simulated the relative above ground growth response of ozone-sensitive aspen clone 259 exposed to square wave variation in ozone concentration. This included a greater effect on stem diameter than on stem height, earlier leaf abscission, and reduced stem and leaf dry matter production at the end of the growing season. Further development of the model to reduce predictive uncertainty is discussed.

Reports that both forest floor removal and soil compaction significantly reduced biomass and height of 2-year-old aspen suckers in plots in northern Minnesota.

Potential nitrogen mineralization and nitrification were studied in three upland forest ecosystems to develop an understanding of nitrogen turnover on a landscape basis. The northern Michigan forests studied were an oak ecosystem primarily associated with glacial outwash features and two sugar maple ecosystems that occurred on morainal landforms but differed in the diversity and abundance of ground flora species. Four randomly chosen stands separated by at least 6 km were sampled within each of the three ecosystems. Potential net nitrogen mineralization and nitrification were determined by an aerobic laboratory incubation. Litter was collected from all ecosystems during autumn. Litter production, nitrogen returned to the forest floor, and net mineralization differed by a factor of two between the oak and sugar maple ecosystems. The species-rich sugar maple ecosystems exhibited a fourfold increase in potential nitrification compared with the species-poor sugar maple ecosystem. Nitrification was virtually absent in the oak ecosystem. The distribution of ecosystems could be used to predict differences in potential mineralization and nitrification. Areas susceptible to nitrate loss following intensive forest management practices may be related to the occurrence of plant associations. In this upland landscape, high nitrification potentials appear to be confined to species-rich sugar maple forests.

Variation in overstory biomass and mean annual biomass increment (MABI) of upland forest stands was studied at two spatial scales: glacial landforms (1: 250 000–1: 000 000) and ecological land units (1: 10 000–1: 80 000). Ecological land units were defined based on combinations of ground-flora vegetation, soil, and physiography. Biomass estimates were based on allometric regression equations developed in the Lake States area. Analyses of covariance were used to study the patterns of total biomass and biomass increment among glacial landforms and among ecological land units; stand age was used as the covariate. Overstory biomass ranged from 105 t/ha (MABI = 1.5 t ha−1 year−1) on glacial outwash landforms to 208 t/ha (MABI = 3.2 t ha−1 year−1) on morainal landforms; 37% of the total variation in biomass was accounted for by landform. Analysis at the ecological land unit scale accounted for a higher proportion of variation, approximately 60% of the total. Overstory biomass among ecological land units ranged from 85 t/ha (MABI = 1.3 t ha−1 year−1) for oak-dominated forests occurring on xeric sandy outwash sediments to almost 250 t/ha (MABI = 3.6 t ha−1 year−1) for sugar maple–red oak forests occurring in mesic morainal positions. Variation in biomass appeared to be strongly related to differences in species composition and variation in soil moisture availability, as evidenced by differences in soil texture and the presence or absence of deep-lying textural bands. Since ground-flora composition often reflects variation in soil properties, we examined the relationship between ground-flora composition and biomass increment. Detrended correspondence analysis was used to ordinate stands along a floristic gradient. Regression of stand ordination scores against MABI was significant (r2 = 0.65), indicating a relatively strong association between ground-flora composition and productivity. One advantage of understanding spatial variation in site productivity is that ecological land units can be readily mapped, whereas traditional estimates of site potential, such as site index, are point specific.

Potential net nitrogen (N) mineralization, potential net nitrification, and overstory (boles and branches) biomass were measured in nine forest ecosystems commonly found within the well-drained uplands of northern Lower Michigan. The ecosystem types ranged from oak-dominated forests on coarse-textured outwash sands to mesic northern hardwood forests on sandy glacial till. Overstory biomass was calculated using species-specific allometric equations developed for Lake States hardwood species. Potential net N mineralization and potential net nitrification were measured by a 30-day aerobic laboratory soil incubation. Analyses of (co)variance were used to determine differences in potential N mineralization, net nitrification, overstory biomass, and biomass increment among the nine ecosystem types. Linear and nonlinear regression analyses were used to predict overstory biomass and biomass increment using potential net N mineralization as the independent variable. Overstory biomass ranged from 92 t•ha−1 in a xeric oak ecosystem to 243 t•ha−1 in a northern hardwood ecosystem; annual biomass production ranged from 1.3 to 3.5 t•ha−1 year−1, respectively. Potential net N mineralization was lowest in the xeric oak ecosystem (52.0 μg N•g−1) and greatest in the mesic northern hardwood ecosystem (127.8 μg N•g−1). Potential net nitrification was 45.5 μg NO3−-N•g−1 in the northern hardwood ecosystem; 10 to 230 times greater than in other ecosystems. A saturating exponential model (y = a(1–e−kx) + c) produced the smallest residual mean squares in predicting overstory biomass (R2 = 0.822) and annual biomass increment (R2 = 0.847) from potential net N mineralization. Maximum overstory biomass and biomass increment predicted from this equation were 247 t•ha−1 and 3.7 t•ha−1, respectively. In addition, laboratory net N mineralization potentials were highly correlated with annual rates of N mineralization determined by insitu incubation (r2 = 0.849). Overstory biomass and woody biomass increment were poorly correlated with potential net nitrification. The exponential function used to predict biomass increment from N mineralization suggests that the productivity of some northern hardwood forests in northern Lower Michigan is not limited by N availability.