Thomas M. Burton

Salamander populations and biomass in the Hubbard Brook Experimental Forest, New Hampshire

There were about 2950 salamanders per ha (1770 g/ha wet wt) in the Hubbard Brook Experimental Forest in New Hampshire. The terrestrial species, Plethodon cinereus, accounted for about 93.5% of the total biomass while the streamside species, Desmognathus fuscus, Eurycea bislineata and Gyrinophilus porphyriticus, accounted for the remaining 6.5%. Notophthalmus viridescens was present, but was rare and insignificant in the biomass calculations. The population size of salamanders at Hubbard Brook appears to be stable. The biomass of salamanders is about twice that of birds during the birds peak (breeding) season and is about equal to the biomass of small mammals.

Can't See the Forest for the Stream? In-stream Processing and Terrestrial Nitrogen Exports

Abstract There has been a long-term decline in nitrate (NO3−) concentration and export from several long-term monitoring watersheds in New England that cannot be explained by current terrestrial ecosystem models. A number of potential causes for this nitrogen (N) decline have been suggested, including changes in atmospheric chemistry, insect outbreaks, soil frost, and interannual climate fluctuations. In-stream removal of NO3− has not been included in current attempts to explain this regional decline in watershed NO3− export, yet streams may have high removal rates of NO3−. We make use of 40 years of data on watershed N export and stream N biogeochemistry from the Hubbard Brook Experimental Forest (HBEF) to determine (a) whether there have been changes in HBEF stream N cycling over the last four decades and (b) whether these changes are of sufficient magnitude to help explain a substantial proportion of the unexplained regional decline in NO3− export. Examining how the tempos and modes of change are distinct for upland forest and stream ecosystems is a necessary step for improving predictions of watershed exports.

Fish Habitat Use Within and Across Wetland Classes in Coastal Wetlands of the Five Great Lakes: Development of a Fish-based Index of Biotic Integrity

The relative importance of Great Lake, ecoregion, wetland type, and plant zonation in structuring fish community composition was determined for 61 Great Lakes coastal wetlands sampled in 2002. These wetlands, from all five Great Lakes, spanned nine ecoregions and four wetland types (open lacustrine, protected lacustrine, barrier-beach, and drowned river mouth). Fish were sampled with fyke nets, and physical and chemical parameters were determined for inundated plant zones in each wetland. Land use/cover was calculated for 1- and 20-km buffers from digitized imagery. Fish community composition within and among wetlands was compared using correspondence analyses, detrended correspondence analyses, and non-metric multidimensional scaling. Within-site plant zonation was the single most important variable structuring fish communities regardless of lake, ecoregion, or wetland type. Fish community composition correlated with chemical/physical and land use/cover variables. Fish community composition shifted with nutrients and adjacent agriculture within vegetation zone. Fish community composition was ordinated from Scirpus, Eleocharis, and Zizania, to Nuphar/Nymphaea, and Pontederia/Sagittaria/Peltandra to Spargainium to Typha. Once the underlying driver in fish community composition was determined to be plant zonation, data were stratified by vegetation type and an IBI was developed for coastal wetlands of the entire Great Lakes basin.

DEVELOPMENT OF A PRELIMINARY INVERTEBRATE INDEX OF BIOTIC INTEGRITY FOR LAKE HURON COASTAL WETLANDS

The biota of aquatic systems are integrators of overall habitat quality, revealing both episodic as well as cumulative disturbance, and therefore are able to serve as natural monitors of the systems they inhabit. Invertebrate communities from three relatively pristine coastal wetlands located along the northern shore of Lake Huron were compared to those from three relatively impacted Saginaw Bay coastal wetlands in Lake Huron to identify components of the community that could ordinate wetlands according to anthropogenic disturbance. A total of 24 potential metrics were examined for each of four vegetation zones at the study sites. Of these, 14 successfully discriminated between sites and were used to generate a preliminary index of biotic integrity (IBI) for Lake Huron coastal wetlands. This IBI was then tested by assessing coastal wetlands, including five additional sites, based on invertebrate data collected the following year. The preliminary IBI seemed to provide an accurate depiction of the wetlands used to generate the IBI as well as the five additional wetlands. We do not recommend use of the presented IBI as the definitive assessment tool for Lake Huron coastal wetlands. Instead, we suggest that it be tested further on a series of wetlands with known degrees of anthropogenic disturbance.

AREA AND HABITAT RELATIONSHIPS OF BIRDS IN GREAT LAKES COASTAL WET MEADOWS

Although relationships of birds to patch area and habitat characteristics have been dominant themes in avian ecology over the past few decades, relatively little is known about these relationships in wetland-dominated landscapes of the Great Lakes coastline. During 1997 and 1998, we surveyed birds and measured habitat characteristics along transects in wet meadows associated with the northern Lake Huron shoreline (NLHS) in the Upper Peninsula of Michigan. Using a suite of multivariate techniques, we related abundance and presence/absence of individual species to wet meadow area and habitat characteristics. Nine species were positively associated with increasing wet meadow area, which underscores the importance of large wetlands to avian conservation in the region. Bird variables also were related to habitat characteristies. Higher values of bird variables were generally associated with a suite of characteristics: more robust and dense grass/sedge vegetation, structural diversity in the horizontal and vertical planes, and increased frequency of willow shrubs. Individual species that require particular aspects of these characteristics for nesting or foraging were associated with principal components containing those aspects. In the NLHS, large wet meadows that possess these characteristics would support the greatest diversity and benefit the majority of species. However, conservation efforts that focus only on these traits will not be sufficient for all species because habitat requirements for some species are very specific (e. g., open water for mallard), and for others, habitat preferences may change from year to year in response to lake-level changes. While our results provide important insights, continued research is needed to further the successful conservation and management of birds in Great Lakes coastal wetlands.

Validation and performance of an invertebrate index of biotic integrity for Lakes Huron and Michigan fringing wetlands during a period of lake level decline

Development of indicators of ‘ecosystem health’ for the Great Lakes was identified as a major need at the State-of-the-Lakes Ecosystem Conference in 1998, 2000, and 2002. Our goal was to develop an invertebrate-based index of biotic integrity that was robust to water level fluctuations and applied to broad classes of lacustrine wetlands across wave-exposure gradients. Our objectives were to evaluate the performance and test the robustness of our preliminary index (e.g., Burton et al., 1999) at a range of water levels, eliminate any problems with the index of biotic integrity, remove the preliminary status, test the index on similar wetlands of Lake Michigan, and establish stressor:ecological-response relationships. Twenty-two sites, both open- and protected-fringing lacustrine marshes of Lake Huron and Michigan were selected for study. Correspondence analysis and Mann-Whitney U tests were used to test the robustness of existing metrics and search for additional metrics. Wilcoxon Signed Rank tests were used to determine if metrics were responding to inter-annual water level fluctuation. Principal components analysis and Pearson correlations were used to establish stressor:ecological response relationships. Analyses confirmed the utility of most of the metrics suggested in our preliminary index, but we recommended several improvements. With improvements, the index was able to place all sites in a comparable order of disturbance that we placed them a priori based on adjacent landuse/landcover, limnological parameters and observed disturbances. The improved index worked very well from 1998 through 2001 despite the substantial decreases in lake level over this time-period. Analyses of 2001 data collected from similar fringing wetlands along the northern shore of Lake Michigan suggested that the index could also be used for fringing wetlands of northern Lake Michigan. We are confident that our index is ready for implementation as a tool for agencies to use in assessing wetland condition for Lakes Huron and Michigan fringing wetlands.

A Comparison of Macroinvertebrates of Two Great Lakes Coastal Wetlands: Testing Potential Metrics for an Index of Ecological Integrity

The macroinvertebrates of two northern Lake Huron wetlands were compared to assess water quality and test potential metrics for an Index of Ecological Integrity (IEI) for Great Lake coastal wetlands. Macroinvertebrates were collected using sediment coring and dip-net sampling monthly from June through September 1996. One wetland was impacted by domestic wastewater from a lagoon, urban storm-water runoff, and local marina traffic. A nearby wetland with a similar size drainage basin, no wastewater or urban storm-water input or marina traffic served as a reference. Greatest differences in chemistry between sites occurred during lagoon discharge in September. Compared to the reference, the impacted wetland had higher Cl, NH4-N, NO3-N, soluble reactive P, conductivity and lower dissolved oxygen levels. There were fewer insects, especially Ephemeroptera and Trichoptera in the impacted wetland than in the reference wetland. A greater proportion of macroinvertebrates in the impacted wetland were Amphipoda, Isopoda, and Naididae. Observed differences in macroinvertebrate communities were used to test 38 metrics, used in indices of biological integrity for streams, to determine their potential as metrics for an index of ecological integrity for Great Lake wetlands. Invertebrate attributes sensitive to water quality changes were identified as candidate metrics if they exhibited low within-site variability and detected differences between wetlands for each sampling period. Candidate metrics included relative abundance of Ephemeroptera, Isopoda, Trichoptera, predators, collector-filterers, and herbivore/detritivore ratio.

Diatom colonization dynamics in a lotic system

A series of three overlapping sets of slides were exposed in riffle and pool habitats in a fourth order river in the Upper Peninsula of Michigan. Each set was exposed for 6–8 weeks and overlapped the preceeding set by 2 weeks. Diatom cell densities and community structure were determined after daily or weekly exposure periods for each set. The first set was placed on August 4, 1982, and the third set removed on October 16, 1982. Species diversity and evenness peaked quickly during colonization. Both indices decreased as the length of exposure increased. Early colonizing diatom species that occasionally accounted for large proportions of the total diatom community were soon replaced by other diatom species that tended to persist through time. Major dominant species were well established by day 28. Severe net cell losses (up to 17% of the total density) were recorded after only an 8–9 day exposure in both pools and riffles. Pool slides showed greater cell densities during the first few days exposure than did slides exposed in riffle zones. After this brief conditioning period, however, the riffle slides showed more rapid cell growth and/or accumulation rates. Mean cell densities were similar between pool and riffle slides after 6–8 week exposures.Seasonal changes appeared to strongly influence diatom species succession. Seasonal changes in water velocity, temperature, or light may have the same effect as the more dramatic flood events which reset periphyton to earlier successional stages, resulting in increased major changes in species composition of the periphyton diatom community.

Birds in North American Great Lakes coastal wet meadows: is landscape context important?

Landscape context can influence species richness, abundance, or probability of patch-use by birds. Little is known, however, about the effects of landscape context on birds in wetland-dominated landscapes. This lack of knowledge is alarming because many wetlands are threatened by development and other human impacts, while serving critical functions as migratory, breeding and foraging habitat. To address this lack of knowledge, we censused birds in North American Great Lakes coastal wet meadows located along the northern Lake Huron shoreline in Michigan (USA) during 1997 and 1998. Using a suite of multivariate techniques, we first accounted for effects of area and within-patch habitat characteristics before testing for effects of landscape context. Most bird variables were significantly related to landscape context, and two major patterns were apparent. First, avian species richness, abundance, and probability of patch-use by some species were higher for wet meadows located in complex contexts (adjacent to many patch types) compared to simpler contexts (adjacent to only one patch type). Second, these variables were higher for wet meadows located in wetland contexts compared to contexts that were terrestrial and road-impacted, dominated by open water habitats, or dominated by forested wetland habitats. Conservation plans for wetlands have focused on saving large wetlands and creating the vegetative habitat structure required by birds, but they should go further and explicitly consider the landscape context of wetlands as well. Specifically, wetlands located in complex and/or wetland contexts should have a higher conservation value than similar wetlands located in simpler, more terrestrial contexts.

Changes in the abundance and diversity of coastal wetland fauna from the open water/macrophyte edge towards shore

Great Lakes coastal wetlands are widely recognized as areas of concentrated biodiversity and productivity, but the factors that influence diversity and productivity within these systems are largely unknown. Several recent studies have suggested that the abundance and diversity of flora and fauna in coastal wetlands may be related to distance from the open water/macrophyte edge. We examined this possibility for three faunal groups inhabiting a coastal wetland in Saginaw Bay, Lake Huron. We sampled crustacean zooplankton and benthic macro-invertebrates at five distances from open water in the summer 1994, and fish at three distances from open water in 1994 and 1995. We found significant spatial trends in the total abundance and diversity of zooplankton and fish, as well as the diversity of benthic macro-invertebrates. Zooplankton abundance and taxa richness were highest at intermediate distances from open water in a transition zone between the well-mixed bayward portion of the wetland, and the non-circulating nearshore area. Benthic macro-invertebrate taxa richness increased linearly with distance from open water. In contrast, fish abundance and species richness declined linearly and substantially (abundance by 78%, species richness by 40%) with distance from open water. Of the 40 taxa examined in this study, 21 had significant horizontal trends in abundance. This led to notable differences in community composition throughout the wetland. Our results suggest that distance from open water may be a primary determinant of the spatial distributions of numerous organismal groups inhabiting this coastal wetland. Several possible reasons for these distributions are discussed.