Jan J.H. Ciborowski

Joint analysis of stressors and ecosystem services to enhance restoration effectiveness

With increasing pressure placed on natural systems by growing human populations, both scientists and resource managers need a better understanding of the relationships between cumulative stress from human activities and valued ecosystem services. Societies often seek to mitigate threats to these services through large-scale, costly restoration projects, such as the over one billion dollar Great Lakes Restoration Initiative currently underway. To help inform these efforts, we merged high-resolution spatial analyses of environmental stressors with mapping of ecosystem services for all five Great Lakes. Cumulative ecosystem stress is highest in near-shore habitats, but also extends offshore in Lakes Erie, Ontario, and Michigan. Variation in cumulative stress is driven largely by spatial concordance among multiple stressors, indicating the importance of considering all stressors when planning restoration activities. In addition, highly stressed areas reflect numerous different combinations of stressors rather than a single suite of problems, suggesting that a detailed understanding of the stressors needing alleviation could improve restoration planning. We also find that many important areas for fisheries and recreation are subject to high stress, indicating that ecosystem degradation could be threatening key services. Current restoration efforts have targeted high-stress sites almost exclusively, but generally without knowledge of the full range of stressors affecting these locations or differences among sites in service provisioning. Our results demonstrate that joint spatial analysis of stressors and ecosystem services can provide a critical foundation for maximizing social and ecological benefits from restoration investments.

Trends in Temperature, Secchi Depth, and Dissolved Oxygen Depletion Rates in the Central Basin of Lake Erie, 1983–2002

We examined temperature trends in a 20-year set of monitoring records collected at multiple deep-water stations in the central basin of Lake Erie. Data collected were statistically corrected (“deseasonalized”) to remove biases resulting from irregular sampling intervals within years. Depthintegrated summer temperature has increased by an average (±SE) of 0.037 ± 0.01°C per year. An observed reduction of Secchi depth (SD) by 7 ± 3 cm/y seems to be unrelated to variation in either total phosphorus (TP) or chlorophyll a concentrations. Midsummer midbasin SD values varied widely between 4 and 10 m, possibly depending on whether phytoplankton were concentrated in the epilimnion (giving shallow SD), or whether phytoplankton had settled out of the epilimnion into the lower layers, giving deeper SD values. Hypolimnetic volume-corrected oxygen depletion (HVOD) rates have also been highly variable, ranging from 2.68 to 4.72 mg/L/mo. These rates are sensitive to production of oxygen in the thermocline and hypolimnion by photosynthetically active phytoplankton that have settled from the epilimnion. The HVOD rate in any year was correlated with the previous years TP loading into Lake Erie. Since TP loading trends largely reflect the consequences of improving water treatment through the 1980s and increasing contributions from tributary run-off sediments through the 1990s, there is little direct evidence to suggest that the appearance of dreissenids has directly influenced hypolimnial oxygen depletion rates in the central basin. The observation that central-basin HVOD tracked the reductions in TP loadings through the 1980s may be the first affirmation that central basin hypolimnetic oxygen dynamics can be regulated by phosphorus inputs. This implies that TP loads must continue to be regulated if we wish to minimize oxygen depletion rates as a strategy to reduce the frequency of episodic central basin anoxia.

FUZZY COGNITIVE MAPPING AS A TOOL TO DEFINE MANAGEMENT OBJECTIVES FOR COMPLEX ECOSYSTEMS

Defining objectives for ecological rehabilitation requires consideration of how an ecosystem responds to management. Validated quantitative models of physical, chemical, and biological processes are the best way to project such impacts; however, time, data, and model limitations often make these approaches impractical. An alternative is to encode expert knowledge about interactions among ecosystem components in a fuzzy cognitive map (FCM), which then translates that subjective, qualitative information into predictions of the effects of management on an ecosystem. Herein, we present the steps involved in constructing an FCM of an ecosystem, interpreting FCM output using multivariate statistics, and portraying the information in an easily communicated fashion. To illustrate these ideas, we rely on a complex (>160 variables) ecosystem model built for the Lake Erie watershed under the auspices of the Lake Erie Lakewide Management Plan (LaMP). Based on our experiences in building this model, we also offer recommendations for increasing the efficiency of the model-development and interpretation process. Use of the FCM method in this case promoted constructive interaction among dozens of scientists, managers, and the public, as well as providing insights concerning the potential effects of broad classes of management actions upon the Lake Erie ecosystem. The analysis focused the attention of participants on four broad alternatives for the Lake. One represents present conditions, and another results from a decrease in nutrient inputs but an increase in stresses from land use and human disturbance. The two others involve reduced stress from nutrients and land use, with one having relatively more nutrients and less human disturbance and fishing. The latter ecosystem alternative was tentatively endorsed by LaMP management, and all four alternatives will be reviewed by the public.

Recovery of burrowing mayflies (Ephemeroptera: Ephemeridae: Hexagenia) in western Lake Erie

Burrowing mayflies (Hexagenia spp.) are native to western Lake Erie and were abundant until the 1950s, when they disappeared due to degraded water and sediment quality. Nymphs were absent from the sediments of most of western Lake Erie after the 1950s, although small, widely disjunct populations apparently persisted near shore. Sediment samples collected in 1993 revealed several small populations near the western and southern shores and beyond the mouths of the Detroit and Maumee rivers. A larger population was found in the southern island area, but nymphs were absent in the middle of the basin. By 1995, nymphs had spread throughout the western half and eastern end of the basin but remained absent from the middle of the basin. These data indicate that Hexagenia began recolonizing nearshore areas before offshore areas. Increasingly large swarms of winged Hexagenia on shore and over the lake between 1992 and 1994 further indicate that mayflies are recolonizing the basin. Factors that have permitted Hexagenia recovery in western Lake Erie probably include improved sediment and water quality attributed to pollution abatement programs implemented after the early 1970s, and perhaps environmental changes in the early 1990s attributed to effects of the exotic zebra mussel (Dreissena polymorpha)

Responsiveness of Great Lakes Wetland Indicators to Human Disturbances at Multiple Spatial Scales: A Multi-Assemblage Assessment

ABSTRACT 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 development, 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 larger spatial scales, were about equally influential and were more explanatory than a contaminant stress index (CSI). The CSI was an important predictor for diatom indicators only. Stephanodiscoid diatoms and nest-guarding fish were identified as two of the most promising indicators of row-crop agriculture, while Ambloplites rupestris (fish) and Aeshna (dragonflies) were two of the strongest indicators of urban development. Across all groups of taxa and spatial scales, fish indicators were most responsive to the combined influence of row-crop and urban development. Our results suggest it will be critical to account for the influence of potentially important non-stressor covariables before assessing the strength of indicator responses to disturbance. Moreover, identifying the appropriate scale to characterize disturbance will be necessary for many indicators, especially when urban development is the primary disturbance.

Recolonization and possible recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia spp.) in Lake Erie of the Laurentian Great Lakes

Burrowing mayflies of the genus Hexagenia spp. were widely distributed (ca. 80% of sites) and abundant (ca. 160 nymphs/m2) in the western basin of Lake Erie of the Laurentian Great Lakes in 1929–1930, prior to a period of anoxia in the mid 1950s. Nymphs were absent or rare in the basin between 1961 and 1973–1975. In 1979–1991, nymphs were infrequently found (13–46% of sites) in low abundance (3–40 nymphs/m2) near shore (<7.5 km from shore), but were absent or rare offshore (0–7% of sites at 0–1 nymphs/m2). Increased abundance occurred offshore between 1991 (0% of sites) and 1993 (52% of sites at 7/m2). Annual sampling, beginning in 1995, indicates that nymphs increased in both nearshore and offshore waters. By 1997, nymphs were found throughout the lake (88% of sites) at a mean density 40-fold greater (392/m2) than that observed in 1993 (11/m2). In 1998, the distribution of nymphs remained the same as 1997 (88% of sites) but density declined 3-fold (392 to 134/m2). These data indicate that mayflies have recolonized sediments of western Lake Erie and that their abundance may be similar to levels observed before their disappearance in the mid 1950s. However, prior to the mid 1950s, densities were greater in offshore than nearshore waters, but between 1979 and 1998 greater densities occurred near shore than offshore. In addition, there were two areas in the 1990s where low densities consistently occurred. Therefore, recovery of nymphs in western Lake Erie may not have been complete in 1998. At present we do not know the cause for the sudden recolonization of nymphs in large portions of western Lake Erie. Undoubtedly, pollution-abatement programs contributed to improved conditions that would have ultimately led to mayfly recovery in the future. However, the explosive growth of the exotic zebra mussel, Dreissena polymorpha, undoubtedly diverted plankton foods to bottom substrates which could have increased the speed at which Hexagenia spp. nymphs recolonized sediments in western Lake Erie in the 1990s.

Effects of emergence date and maternal size on egg development and sizes of eggs and first-instar nymphs of a semelparous aquatic insect

Abstract We examined whether or not sizes of eggs and offspring were related to emergence date or maternal size in a semelparous aquatic insect (the burrowing mayfly, Hexagenia) in which parental care is lacking and oviposited eggs are passively dispersed. We quantified the size of males and female imagos over the emergence span at a site on the Detroit River, Canada, and investigated relationships between emergence date and female size and (1) egg size and (2) size of first-instar nymphs. Although size of female imagos (H. limbata and H. rigida combined) declined significantly (P<0.025) over the emergence season, there was no significant relationship between body length and emergence date for males of either species. Males were significantly (P<0.001) smaller than females. H. limbata eggs, subsampled from three individuals from each of three size classes of female imagos collected on seven sampling dates, were measured using video image analysis. Eggs (n=100) oviposited by each of 63 H. limbata imagos were inspected daily for hatching. Newly hatched nymphs were removed, counted and measured. Egg size (P<0.001) and size of first-instar nymphs (P<0.001) varied significantly with emergence date, but not maternal size. The largest eggs and newly hatched nymphs occurred at peak emergence of adults. The synchronous release of larger (faster-sinking) eggs may result in reduced predation. Plasticity in egg development time and egg and nymph size may account for the ability of this taxon to recover from episodes of massive population reduction.

Lake Erie Trophic Status Collaborative Study

Lake Erie is in a stage of transition, reflecting human and environmental influences simultaneously acting on a poorly understood system. For several decades, the ecosystem has been a focus of both directed and fundamental research. As the shallowest and most heavily populated of the Great Lakes, it has been the first to reflect the consequences of both stress and of remediation efforts. Consequently, Lake Erie is a sentinel of the changes to be expected in other large, mesotrophic systems (Munawar et al. 1999a). During the 1960s, Lake Erie experienced significant cultural eutrophication resulting in huge algal blooms, low oxygen waters, and fish kills (Snodgrass 1987). Eutrophication of the western and central basins driven by years of unregulated inputs of nutrients stimulated efforts to understand the dynamics of Lake Erie’s trophic structure, and resulted in the implementation of a phosphorus reduction program (Burns 1985). Research on Lake Erie played a major role in the limiting nutrient debate and in identifying phosphorus control as the best means of controlling eutrophication. Phosphorus was being released from wastewater treatment plants, as well as non-point sources such as agricultural runoff (DePinto et al. 1986). Study of these problems led to the recognition of the relationship between nutrients and water quality and the development of an ecosystem approach (Burns 1985). Target levels for phosphorus loading were determined by binational collaborative programs, which generated models of ecosystem structure and function (reviewed in State of Lake Erie collection of papers in the Journal of Great Lakes Research) (Vollenweider 1987). The J. Great Lakes Res. 31 (Supplement 2):1–10 Internat. Assoc. Great Lakes Res., 2005

Use of alternative classifications in studying broad-scale distributional patterns of lotic invertebrates

Multivariate analyses were used to examine relationships between each of three biological classifications of mayfly (Ephemeroptera) larvae and environmental variables recorded at 95 river sites encompassing 18 degrees of latitude in northwestern North America. Biological samples, collected by kick net, were classified by family and superfamily, by size, and by morphological/behavioural group. Environmental variables included measures obtained from topographical maps and hydrological features recorded at each site. Results of canonical correlation analyses showed that all three biotic indicators were significantly associated with environmental variables. Morphological/behavioural classification yielded stronger correlations with environmental data than did taxonomic or size classifications. Multivariate curvilinear regression analyses gave equivalent results and showed that, although several relationships were curvilinear, all were monotonic. Environmental variables independently and significantly associated with mayfly relative abundance included river size, velocity, slope, latitude, and conductivity. Use of alternative classification variables can potentially reveal patterns not evident when standard taxonomic units are applied.

Organic Contaminants in Adult Aquatic Insects of the St. Clair and Detroit Rivers, Ontario, Canada

Abstract Night-flying Trichoptera and Ephemeroptera were attracted using long-wave ultraviolet light and collected from 8 Canadian sites adjacent to the St. Clair and Detroit rivers. Gas chromatographic analysis of the extracts from 40 samples of the insects revealed significant concentrations of pentachlorobenzene (QCB), hexachlorobenzene (HCB), octachlorostyrene (OCS), and 16 polychlorinated biphenyl (PCB) congeners in almost all animals collected. Principal component analysis accounted for 84% of variation in contaminant concentration among samples. The principal components (PCs) correlated highly with concentrations of 9 hexa-, hepta-, and octachlorobiphenyls (PC-I; 46% of overall variation), 4 tetra- and pentachlorobiphenyls (PC-II; 17% of variation), QCB, HCB, and OCS (PC-III; 8%), and 2 trichlorobiphenyls (PCs IV and V; each 6% of variation). Values of PC-I were significantly greater among Detroit River than among St. Clair River samples. Values of PC-II were highest for samples from upstream stations on the two rivers. Values of PC-III were higher for St. Clair River samples than for Detroit River samples. These trends are consistent with patterns observed in other biota and sediment previously collected from equivalent sites. Contaminant levels also varied among taxa collected from the same site, possibly because of different larval feeding habits or microdistribution, or adult flight ability. Collection of adults has potential as an inexpensive alternative to aquatic sampling methods in surveys of biota for organic contamination.