Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Benthos of southern Green Bay, Lake Michigan have not been comprehensively examined since 1978. Since then, invasive species appeared, urbanization intensified, and restoration efforts were implemented, which likely altered the benthic macroinvertebrate community. Further, current benthos are subjected to dynamic factors including eutrophication, sedimentation, and periodic hypoxia. Understanding community responses to these anthropogenic stressors and natural habitat gradients is imperative to preserving biological integrity within Green Bay. Therefore, the objectives of this project were to describe the current macroinvertebrate community, examine changes since 1978, and assess the roles of productivity, substrate type, water depth, and hypoxia in structuring macroinvertebrate communities. Benthos were sampled at 197 stations, including 97 also sampled in 1978 by Markert (1982) and 100 that were added to increase spatial resolution. We collected 93 macroinvertebrate taxa in southern Green Bay with the community dominated by Chironomus and immature tubificid worms. Nonmetric multidimensional scaling (NMDS) ordination distinguished present and historical communities. Although oligochaete worms and chironomids remained dominant over time, Chironomus abundance increased and characterized the present community, whereas benthos were historically more diverse. The magnitude of temporal change varied spatially among zones of Green Bay, with larger differences concentrated in the Middle Bay and the Inner Bay remaining comparable to 1978. Present-day assemblages were most associated with the trophic gradient driven by Green Bay’s southernmost tributary, the Fox River, but also differed with substrate type and had similar structures in areas subjected to frequent hypoxia. Routine monitoring should continue to track changes while accounting for spatial effects.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Eutrophication alters the trophic dynamics in lakes and may result in biotic homogenization. How nutrient enrichment drives patterns of taxonomic and functional (i.e., trait‐based) homogenization of macroinvertebrate assemblages at within‐lake (local) and among‐lake (regional) scales is, however, not well understood. Taxonomic and functional compositions of macroinvertebrate assemblages in 41 lakes of the middle and lower reaches of the Yangtze River and Huaihe River were analyzed at within‐lake and among‐lake scales. Our results indicated that there was a significant difference in macroinvertebrate assemblages among lakes under different trophic status, and that total phosphorus was the major environmental factor that regulated both taxonomic and functional beta diversity of macroinvertebrate assemblages. That the abundances of pollution‐tolerant species (e.g., Limnodrilus hoffmeisteri and Microchironomus tabarui) increased with trophic state contributed the most to among‐lake dissimilarity. Functional beta diversity was significantly positively correlated with taxonomic beta diversity, while functional beta diversity was on average lower than taxonomic beta diversity. A combination of univariate and multivariate techniques revealed that nutrient enrichment homogenized taxonomic and functional diversity of benthic macroinvertebrate assemblages in shallow lakes at within‐lake and among‐lake scales, and that there was an overall trend toward taxonomic homogenization that exceeded the trend of functional homogenization. Thus, taxonomic and functional compositions should be considered simultaneously to improve understanding of the response of aquatic communities to anthropogenic disturbance, as the loss and gain of species may be influenced by species‐specific features, and functional composition may exhibit a relatively high correspondence with changes in environmental conditions.
Article
Full-text available
The Green Bay watershed, draining a total area of approximately 40,468 km², comprises about a third of the Lake Michigan drainage. In the early years, fur trade was the dominant economic activity within the watershed. Later, when timber harvesting, papermaking, and agriculture came on the scene in the 19th and early 20th centuries, major environmental changes occurred in a relatively short period of time. Nutrient and sediment loadings, accompanied by organic wastes from sawmills and paper mills, resulted in a pollutant overload in the Fox River and in the eutrophication of the waters of lower Green Bay. Citizen complaints about these severely degraded conditions initiated a period of scientific investigation. Starting slowly with a few studies and surveys in the first half of the 20th century, serious investigatory work began at mid-century with support from the University of Wisconsin Sea Grant Institute. Examples of topics that have been investigated since then with support from numerous sources are: biological oxygen demand (BOD), phosphorus and total suspended solids loads, trophic status and food chain efficiencies, coastal wetland characterization, dynamics of the benthic layer, algae and abiotic solids, phosphorus cycling and mass balance, PCBs, seasonal hypoxia, and climate change impacts. These studies have provided the scientific foundation for government-led programs such as the Green Bay Remedial Action Program, the PCB clean-up program, and the TMDL program. Progress has been made—reduction in BOD is an example—but a fuller rehabilitation of this large-scale ecosystem remains an elusive goal. The saga goes on.
Article
Full-text available
We present water column thermal structure for two climatically different years: 2012, which experienced abnormally warm spring and summer air temperatures preceded by a relatively low ice winter and 2013, which experienced cooler than average spring and average summer air temperatures and preceded by average ice conditions. Mean bottom water temperatures for the season and during cold water intrusions were significantly warmer in 2012 than 2013 leading to a significantly reduced stratified season in 2012. Cold water intrusions were driven into southern Green Bay by southerly winds while intrusions were terminated when winds switched to persistent northerly winds. 2012 observed a significant increase in northerly winds relative to 2013, decreasing cold water intrusion presence and duration but winds did not fully explain the difference in thermal conditions for southern Green Bay. These cold bottom waters drive stratification in polymictic southern Green Bay while dimictic waters were found to have significantly warmer bottom temperatures during 2012 and a deeper mixed layer. Our observations suggest that relatively shallow (<20 m), seasonally stratified systems may not increase in stratification strength and duration under a warming climate; rather, changing wind climatology and surface heat flux can inform the degree to which the mixing regime can be expected to change and impact stratification and thermal structure of coastal systems. We discuss the biogeochemical implications of different thermal regimes, particularly within the context of multiple drivers of physical water column structure in eutrophic, stratified coastal systems.
Article
Full-text available
We used the results of seventeen years of Great Lakes benthic monitoring conducted by the U.S. EPA's Great Lakes National Program Office to describe the spatial and temporal patterns of benthic communities, assess their status, trends, and main drivers, and to infer the potential impact of these community changes on ecosystem functioning. Benthic abundance and diversity were higher at shallow (<70 m in depth) stations with chlorophyll concentrations above 3 μg/L than at deeper sites (<1 μg/L). We infer that lake productivity, measured by chlorophyll was likely the major driver of benthic abundance and diversity across lakes. Consequently, benthic diversity and abundance were the highest in the most productive Lake Erie, followed by lakes Ontario, Michigan, Huron, and Superior. Multivariate analysis distinguished three major communities shared among lakes (littoral, sublittoral, and profundal) that differed in species composition and abundance, functional group diversity, and tolerance to organic pollution. Analysis of temporal trends revealed that the largest changes occurred in profundal communities, apparent in significant shifts in dominant taxa across all lakes except Lake Superior. In lakes Michigan, Huron, and Ontario, the former dominant Diporeia was replaced with Dreissena and Oligochaeta. Profundal species, with the exception of dreissenids, became less abundant, and their depth distribution has shifted. In contrast, density and diversity of native littoral and sublittoral communities increased. The invasion of dreissenids was among the most important drivers of changes in benthic communities. Continued monitoring is critical for tracking unprecedented changes occurring in the Great Lakes ecosystem.
Article
Full-text available
Benthic invertebrate biomonitoring has long been a tool of choice for assessing the impacts of anthropogenic stress in aquatic systems. The Oligochaete Trophic Index (OTI) is used by the U.S. EPA Great Lakes National Program Office to assess Great Lakes trophic status for State of the Great Lakes reporting under the Great Lakes Water Quality Agreement. OTI scores are based on pollution tolerances of ubiquitous profundal oligochaetes. OTI limitations include the fact that the index is based on a limited number of species belonging to a single oligochaete class, species assignment to trophic groups in the index were determined by best professional judgment and cannot be tested independently, and the index's correlation with lake productivity has not been evaluated. To address these concerns, we developed two new indices of Great Lakes water quality based on the OTI equation by: (1) expanding the number of oligochaete species included in the index and reassigning previous classifications of oligochaete species to trophic groups (improved OTI, or iOTI); and (2) adding non-oligochaete species to the OTI (modified Trophic Index, or mTI). Finally, we tested a modeling approach using Modern Analogue Technique (MAT) transfer functions based on species responses to a surface chlorophyll gradient to derive assessment of site trophic status and an independent assignment of species to trophic categories. We found that both iOTI and mTI had a stronger relationship with surface remote-sensed spring chlorophyll than did OTI, but MAT models had stronger correlations with chlorophyll than did any of the indices.
Article
Full-text available
Phosphorus load estimates have been updated for all of the Great Lakes with an emphasis on lakes Superior, Michigan, Huron and Ontario for 1994–2008. Lake Erie phosphorus loads have been kept current with previous work and for completeness are reported here. A combination of modeling and data analysis is employed to evaluate whether target loads established by the Great Lakes Water Quality Agreement (GLWQA, 1978, Annex 3) have been and are currently being met. Data from federal, state, and provincial agencies were assembled and processed to yield annual estimates for all lakes and sources. A mass-balance model was used to check the consistency of loads and to estimate interlake transport. The analysis suggests that the GLWQA target loads have been consistently met for the main bodies of lakes Superior, Michigan and Huron. However, exceedances still persist for Saginaw Bay. For lakes Erie and Ontario, loadings are currently estimated to be at or just under the target (with some notable exceptions). Because interannual variability is high, the target loads have not been met consistently for the lower Great Lakes. The analysis also indicates that, because of decreasing TP concentrations in the lakes, interlake transport of TP has declined significantly since the mid-1970s. Thus, it is important that these changes be included in future assessments of compliance with TP load targets. Finally, detailed tables of the yearly (1994–2008) estimates are provided, as well as annual summaries by lake tributary basin (in Supplementary Information).
Article
Full-text available
The Cat Island Chain of Islands, located within Green Bay, Lake Michigan, was severely eroded due to high water levels and extreme wave attack in the early 1970s. It is believed that the loss of the above water part of the islands was responsible for the loss of almost 700 acres of emergent and submerged aquatic vegetation in the lee of the islands. In addition to these indirect impacts, the terrestrial habitat on the islands themselves was also directly lost. The Lower Green Bay and Fox River Remedial Action Plan (RAP) recommended restoration of these habitats as a high priority for improving fish and wildlife populations. Brown County and the US Army Corps of Engineers in partnership with the US Fish & Wildlife Service, Wisconsin Department of Natural Resources, and UW Sea Grant Institute plan to restore the islands through beneficial use of clean dredged sediment from the Green Bay Federal Navigation Channel. The results from a detailed investigation have shown that significant regions of aquatic vegetation that previously existed on the lee side of the Cat Island chain have been prevented from recovering due, in part, to two processes that impair water clarity; 1) the advection and dispersion of sediment plumes discharged from Duck Creek and the Fox River, and 2) re-suspension of lakebed sediment induced by wave action. Further analyses have concluded that re-suspension of lakebed sediment as a result of wave action could be reduced to levels conducive to the recovery and survival of aquatic vegetation with the construction of the islands. The water clarity impairment associated with the plumes discharged from the two rivers will not significantly improve with the construction of the islands, however, a reduction in the sediment delivery from both watersheds must be addressed in order aid in the recovery of aquatic vegetation in lower Green Bay.
Article
Full-text available
Green Bay, while representing only ,7% of the surface area and ,1.4% of the volume of Lake Michigan, contains one-third of the watershed of the lake, and receives approximately one-third of the total nutrient loading to the Lake Michigan basin, largely from the Fox River at the southern end of the bay. With a history of eutrophic conditions dating back nearly a century, the southern portion of the bay behaves as an efficient nutrient and sediment trap, sequestering much of the annual carbon and nitrogen input within sediments accumulating at up to 1 cm per year. Depositional fluxes of organic matter varied from ,0.1 mol C m22 yr21 to .10 mol C m22 yr21 and were both fairly uniform in stoichiometric composition and relatively labile. Estimates of benthic recycling derived from pore-water concentration gradients, whole-sediment incubation experiments, and deposition-burial models of early diagenesis yielded an estimated 40% of the carbon and 50% of the nitrogen recycled back into the overlying water. Remineralization was relatively rapid with ,50% of the carbon remineralized within ,15 yr of deposition, and a mean residence time for metabolizable carbon and nitrogen in the sediments of 20 yr. On average, organic carbon regeneration occurred a s7 5 % CO2 ,1 5 % CH4, and 10% dissolved organic carbon (DOC). Carbon and nitrogen budgets for the southern bay were based upon direct measurements of inputs and burial and upon estimates of export and production derived stoichiometrically from a coupled phosphorus budget. Loadings of organic carbon from rivers were ,3.7 mol m22 yr21 ,8 0% in the form of DOC and 20% as particulate organic carbon. These inputs were lost through export to northern Green Bay and Lake Michigan (39%), through sediment burial (26%), and net CO2 release to the atmosphere (35%). Total carbon input, including new production, was 4.54 mol m22 Cy r 21, equivalent to ,10% of the gross annual primary production. Nitrogen budget terms were less well quantified, with nitrogen export ,54% of total inputs and burial ,24%, leaving an unquantified residual loss term in the nitrogen budget of ,22%.
Article
Full-text available
The U.S. Environmental Protection Agency and Environment Canada are supporting the development of indicators of ecosystem health that can be used to report on progress in restoring and maintaining the Great Lakes ecosystem, as called for in the Great Lakes Water Quality Agreement between the United States and Canada. One indicator under development is based on burrowing mayflies (Hexagenia: Ephemeroptera: Ephemeridae). We sampled in western Lake Erie, Saginaw Bay (Lake Huron), and Green Bay (Lake Michigan) in spring 2001 at 117 stations covering about 1,870 km of lake bed, to determine the status of nymphal populations of Hexagenia, and to provide information that would further the technical development of an indicator of ecosystem health based on Hexagenia. In western Lake Erie, density and biomass of nymphs were generally highest on fine-grained substrate in offshore waters and were lower on coarser substrates in near shore waters. Nymphs were virtually absent from Saginaw Bay, where only one nymph was collected at 28 stations. Nymphs were collected at only 6 of 48 stations in Green Bay, and density and biomass were highest at the northern end of the bay. Polluted sediments are likely responsible for the absence or low density and biomass of nymphs observed on fine-grained substrates in western Lake Erie, Saginaw Bay, and Green Bay, all of which historically supported abundant populations.
Article
Full-text available
The tributaries of Green Bay have long been recognized as major sources of phosphorus in the Lake Michigan basin. The status of Green Bay as a sink or source of phosphorus for Lake Michigan proper has been less well defined. The bay receives nearly 70% of its annual load of phosphorus ( 700 metric tons (t) · year-1) from a single source: the Fox River. Most of this phosphorus is deposited in sediments accumulating at rates that reach 160 mg · cm-2 · year-1 with an average of 20 mg · cm-2 · year-1. The phosphorus content of these sediments varies from <5 to >70 µmol · g-1. Deposition is highly focused, with ~70% of the total sediment accumulation and at least 80% of the phosphorus burial occurring within 20% of the surface area of the bay. Diagenetic and stoichiometric models of phosphorus cycling imply that >80% of the phosphorus deposited is permanently buried. External phosphorus loading to the bay is combined with sediment fluxes of phophorus to arrive at a simple phosphorus budget. Green Bay acts as an efficient nutrient trap, with the sediments retaining an estimated 70-90% of the external phosphorus inputs before flowing into Lake Michigan.
Article
Full-text available
In this review the effects of hypoxia on benthic fauna are summarized and detailed information is given on (1) the impact on community structure and function in fjords, estuaries, coastal and offshore areas (2) behavioural changes (3) recovery processes (4) ecosystem energy flow implications, and (5) tolerance in experimental studies. There is no other environmental variable of such ecological importance to coastal marine ecosystems that has changed so drastically in such a short period as dissolved oxygen. While hypoxia and anoxic environments have existed through geological time, their occurrence in shallow coastal and estuarine areas appears to be increasing, most likely accelerated by human activities. Ecological problems associated with the occurrence of low oxygen are increasing on a global scale. The oxygen budgets of most major estuarine and coastal ecosystems have been adversely affected mainly through the process of eutrophication, which acts as an accelerant or enhancing factor to hypoxia and anoxia, and when coupled with adverse meteorological and hydrodynamic events, hypoxia increases in frequency and severity. The area of hypoxic and anoxic bottom water is even increasing within systems that historically are considered oxygen stressed. Many ecosystems that are now severely stressed by hypoxia appear to be near or at a threshold. Should oxygen concentrations become slightly lower, catastrophic events may overcome the systems and alter the productivity base that leads to fisheries species. Examples of such events are becoming increasingly common. At what point permanent damage will result is difficult to say. To date there is no large system that has recovered after development of persistent hypoxia or anoxia. The only exception may be small systems where pollution inputs have ceased and recovery initiated from surrounding non-affected areas. The expanding occurrence of hypoxia and anoxia continues to bring about significant structural changes in benthic communities and to affect benthic-pelagic coupling. Restoring ecosystem balance and reversing the trend of increasing hypoxia and anoxia will require dealing with the global problem of coastal eutrophication and determining how to reduce the production of organic matter in sensitive estuarine and coastal areas.
Article
Full-text available
Morphological and molecular characters support that the former clitellate family Naididae Ehrenberg, 1828 is nested within another family, Tubificidae Vejdovský, 1876. To avoid paraphyly of the latter, it has been suggested that the two should be regarded as a single taxon. A recent decision by the International Commission of Zoological Nomenclature [2007; opinion 2167 (Case 3305)] ruled against a proposed reversal of the nomenclatural priority of Naididae over Tubificidae, with the consequence that all former tubificids should now be regarded as members of the Naididae whenever these two names are regarded as synonyms. The paper is a plea to clitellate researchers to conform to this ruling.
Article
Full-text available
The effects of low dissolved oxygen or hypoxia (<2 mg l−1) on macrobenthic infaunal community structure and composition in the lower Chesapeake Bay and its major tributaries, the Rappahannock, York, and James rivers are reported. Macrobenthic communities at hypoxia-affected stations were characterized by lower species diversity, lower biomass, a lower proportion of deep-dwelling biomass (deeper than 5 cm in the sediment), and changes in community composition. Higher dominance in density and biomass of opportunistic species (e.g., euryhaline annelids) and lower dominance of equilibrium species (e.g., long-lived bivalves and maldanid polychaetes) were observed at hypoxia-affected stations. Hypoxia-affected macrobenthic communities were found in the polyhaline deep western channel of the bay mainstem north of the Rappahannock River and in the mesohaline region of the lower Rappahannock River. No hypoxic effects on the infaunal macrobenthos were found in the York River, James River, or other deep-water channels of the lower Chesapeake Bay.
Article
Full-text available
Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O2/liter to designate waters as hypoxic is below the empirical sublethal and lethal O2 thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated. • benthic community • oxygen • coastal ecosystems • eutrophication • impacts
Article
Full-text available
The phylogenetic relationships of the Clitellata were investigated with a data set of published and new complete 18S rRNA gene sequences of 51 species representing 41 families. Sequences were aligned on the basis of a secondary structure model and analysed with maximum parsimony and maximum likelihood. In contrast to the latter method, parsimony did not recover the monophyly of Clitellata. However, a close scrutiny of the data suggested a spurious attraction between some polychaetes and clitellates. As a rule, molecular trees are closely aligned with morphology-based phylogenies. Acanthobdellida and Euhirudinea were reconciled in their traditional Hirudinea clade and were included in the Oligochaeta with the Branchiobdellida via the Lumbriculidae as a possible link between the two assemblages. While the 18S gene yielded a meaningful historical signal for determining relationships within clitellates, the exact position of Hirudinea and Branchiobdellida within oligochaetes remained unresolved. The lack of phylogenetic signal is interpreted as evidence for a rapid radiation of these taxa. The placement of Clitellata within the Polychaeta remained unresolved. The biological reality of polytomies within annelids is suggested and supports the hypothesis of an extremely ancient radiation of polychaetes and emergence of clitellates.
Article
Hypoxia in aquatic ecosystems is often a result of anthropogenic activities, such as increased nutrient loading, originating from agriculture or urbanization, as well as global warming. Aquatic invertebrates are especially important in ecosystems due to their central role in secondary production and in dynamics of food webs. To better understand impacts of oxygen availability on key physiological processes in invertebrates, we conducted a literature search and synthesized the findings of published studies. We found 55 studies that quantified impacts of hypoxia on feeding, growth, reproduction and respiration rates in 54 different aquatic invertebrate species. We applied non-linear regression models which took into account phylogenetic correlation in the data set. Fitting Michaelis-Menten models, we found that there were differences in how different processes responded to a decline in oxygen availability. Respiration rates were halved at highest oxygen concentration (6.44 mg O2/L), followed by reproductive (3.66 mg O2/L), growth (1.77 mg O2/L) and, finally, feeding rates (0.77 mg O2/L). Our findings confirm observations that reproduction is highly sensitive as organisms quickly reduce their reproductive output when exposed to stressful conditions. As long as they have sufficient reserves, organisms continue growing even under stressful conditions, and we confirmed that growth was not very sensitive to a decline in oxygen availability. We discuss potential impacts of global warming on oxygen availability and demand for aquatic macroinvertebrates. Given that oxygen availability is declining in many ecosystems, we can expect that organismal responses will be increasingly compromised with potential consequences for ecosystems and the services they deliver.
Article
Six years (2009–2015) of temperature and dissolved oxygen profile data show hypoxic conditions are common in the bottom waters of southern Green Bay, Lake Michigan during the summer. Depleted oxygen concentrations (<5 mg L⁻¹) affect nearly 70% of the 38 stations sampled representing an area of ~500–600 km². Stratification typically lasts 2+ months, from late June to early September, and some stations exhibit bottom water hypoxia (<2 mg L⁻¹) at a frequency of nearly 25% when sampled during this period. A monitoring program initiated in 1986 by the Green Bay Metropolitan Sewerage District has provided a 23 year, recreational season record (May–September) of continuous (15 min interval) in situ bottom water oxygen and temperature measurements at the Entrance Light station of the Green Bay navigational channel. The duration of the hypoxic season ranges from 2 weeks to over 3 months at this shallow 7 m offshore site. This variability likely results from a combination of thermal stratification, oxygen consumption in deeper waters of the bay, and physical forcing mechanisms that drive cool, oxygen depleted, bottom waters on a southerly trajectory across this sensor. These data suggest the duration of hypoxic conditions may have increased during the stratified season in recent years. Hypoxia in the bay would also appear to be sensitive to relatively small changes in these forces, particularly changes in organic carbon loading and the duration of stratification.
Article
The last historic Hexagenia specimen in lower Green Bay was officially recorded in 1955. Field surveys and Hexagenia viability studies were completed to determine if lower Green Bay could support Hexagenia re-ecesis and where in the bay egg stocking could best be accomplished. The invertebrate field data were compared with historical population data based on earlier published studies in the 1950s, 1970s and 1990s to determine the bay's ecological trajectory to better understand the re-ecesis success potential of Hexagenia. No native Hexagenia were observed during this study. Deep water invertebrate diversity within the upper lower bay appears to be improving, whereas the diversity along the lower mid-bay may be deteriorating. Shallower, nearshore samples indicated a better condition with Caenis mayflies sparsely present, amphipods, isopods, gilled snails, odonates, oligochaetes, chironomids, and meiofauna present. These results suggested improved conditions shoreward versus degraded conditions deeper. Hexagenia egg viability and neonate growth indicated Hexagenia could successfully inhabit in situ Green Bay nearshore (<2 m) substrates; however, deep substrates were generally inhospitable probably due to hypoxia and unstable fluid substrates. As an outcome of the field surveys and studies of Hexagenia viability in Green Bay mud, Hexagenia stocking began in 2014 with the first adults since 1955 emerging in 2016 at several lower bay nearshore locations. Improved water quality from remediation efforts in the watershed could facilitate the return of Hexagenia to deeper water.
Chapter
The physical processes that drive the circulation and the thermal regime in the bay largely control the duration and persistence of hypoxic conditions in Green Bay. A review of previous studies, existing field data, our own measurements, hydrodynamic modeling, and spectral analyses were used to investigate the effects on the circulation and the thermal regime of the bay by the momentum flux generated by wind, the heat flux across the water surface, the Earth’s rotation, thermal stratification and the topography of the basin. Stratification and circulation are intimately coupled during the summer. Field data show that continuous stratification developed at regions deeper than 15–20 m between late June and September and that surface heat flux is the main driver of stratification. Summertime conditions are initiated by a transition in the dominant wind field shifting from the NE to the SW in late June and remain in a relatively stable state until bay vertical mixing in early September. It is during this stable period that conditions conducive to hypoxia are present. Wind parallel to the axis of the bay induces greater water exchange than wind blowing across the bay. During the stratified season flows in the bottom layers bring cold water from Lake Michigan to Green Bay and surface flows carry warmer water from the bay to Lake Michigan. Knowledge of the general patterns of the circulation and the thermal structure and their variability will be essential in producing longer term projections of future water quality in response to system scale changes.
Article
Several types of indices distinguished by the sort of information they summarize are discussed and illustrated with examples from the literature. Then an index of eutrophication and pollution that is based upon the relative abundance of oligochaete species differing in their response to organic enrichment is described and the results of a trial in which this index was compared to others which, though commonly used, are deficient in information content are discussed.
Article
We conducted a high-resolution survey along the nearshore (369 km) in Green Bay using towed electronic instrumentation at approximately 15-m depth contour, with additional transects of the bay that were oriented cross-contour (49 km). Electronic sensor data provided an efficient characterization of a spatial pattern in water quality parameters. Nearshore water quality was correlated with adjacent landscape characterization. The regressions were able to explain over 80% of the alongshore variability for some parameters. The parameters with the strongest correlation were specific conductivity, beam attenuation, and chlorophyll. A clear feature of Green Bay is the loading introduced by the Fox River at the head of the bay. River loading sets up the conditions for a longitudinal gradient along the bay. Nutrient and chlorophyll gradients have persisted since first observed in monitoring surveys decades ago in spite of rapid flushing of the bay and efforts for remedial actions to restore areas of concern (AOCs). The water quality gradients were steepest in the 25-km closest to the mouth of the Fox River decreasing inversely with distance to where the bay opens to Lake Michigan. Summarized data from our 2010 tow and a concurrent National Coastal Condition Assessment (NCCA) survey compared to historical data (1971–1989) show a bay-wide rise in specific conductivity and chlorides, but only suggest highly variable total phosphorous and chlorophyll a in the inner bay. The tools employed (towed sensors, landuse characterization, and NCCA) can provide an efficient approach to a more regular and comprehensive bay-wide assessment.
Article
Benthos samples were collected from 50 stations in southwestern Lake Michigan at depths ranging from 3 to 18 m from February 1973 through April 1974. Oligochaete species made up large portions of the benthos community at each station. Early spring and late summer peaks in the abundance of a number of species were observed. Fine sand and sand with silt were the predominant substrates. The distributions of 22 taxa of Tubificidae, 10 Naididae, and one Lumbriculidae were examined in relation to depth and substrate type. Oligochaeta increased in abundance with depth. Tubificidae were most abundant at depths of 9 through 18 m in silt substrates. Naididae were most numerous in the sandy 3 and 6 m locations. Stylodrilus heringianus, the only lumbriculid present, was most abundant at depths greater than 9 m and was the most numerous oligochaete in sand substrates.
Article
The paper discusses the rationale behind the use of biological variables in environmental monitoring of lakes, as well as the principles of variable selection and the limitations of data usability. Profundal benthic communities are suggested to be an integral measure of autotrophic and heterotrophic lake processes. Measures of community structure and their relationship to morphometric and edaphic factors are presented and discussed, including indicator species/communities, diversity/species richness, oligochaete/chironomid ratio, and oligochaete abundance.
Article
Maps of climatological circulation in Lake Michigan are presented for the first time. They are based on ten years continuous modeling of lake hydrodynamics from 1998-2007 using observed meteorological data as the forcing function. Model results show a remarkably stable large-scale cyclonic circulation pattern during both stratified and unstratified conditions. Lake-averaged mean current speed is about 2 cm/s, but currents can reach 10 cm/s in some locations. The model results are confirmed by long-term current observations.
Article
We evaluated the abundance patterns of Gammarus fasciatus and Echinogammarus ischnus in dreissenid and macrophyte areas in Hatchery Bay, Lake Erie before (1997) and after round goby (2001, 2002) invaded the area. Total amphipod abundance was higher before round goby invasion in both habitats. In mussel beds, E. ischnus abundance was similar or significantly higher than G. fasciatus. In macrophytes, G. fasciatus was significantly more abundant than E. ischnus. In laboratory experiments, we compared amphipod survivorship and growth when fed mussel feces and pseudofeces (F+P) or macrophytes with epiphytes (M+E). Gammarus fasciatus survivorship and growth were higher when fed F+P than M+E. Echinogammarus ischnus showed similar survivorship under both diets, but significantly higher growth when fed M+E than F+P. Therefore inter-habitat differences in food resources cannot explain the abundance patterns observed in the lake. We also estimated the relative vulnerability of G. fasciatus and E. ischnus to yellow perch (Perca flavescens) and round goby (Neogobius melanostomus) predation in laboratory feeding trials using mussel colonies or macrophyte beds as substrate. Both fish strongly preferred E. ischnus in macrophytes, but consumed relatively more G. fasciatus than E. ischnus in dreissenid habitats. Our results suggest that dreissenid establishment may have facilitated the invasion of E. ischnus. However, habitat-specific differences in vulnerability to fish predation may mediate the coexistence of G. fasciatus and E. ischnus by minimizing expansion of E. ischnus to macrophyte areas. Our results also suggest that round goby invasion can alter amphipod abundance patterns in Lake Erie.
Article
To obtain updated, more accurate estimates of macroinvertebrate standing stocks in Lake Michigan, benthic biomass (ash-free dry weight) was determined at 40 stations in the southern end of the lake in 1980 and 1981. Biomass generally increased as sampling depth increased from 16 to 30 m, peaked at depths of 30–40 m, and then declined at depths greater than 40 m. Mean total biomass at the 16–30 m, 31–50 m, 51–90, and > 90 m depth intervals was 4.9, 7.8, 4.2, and 1.9 g m−2, respectively. Oligochaetes (46%) and Pontoporeia hoyi (44%) accounted for most of the biomass at depths shallower than 30 m, but P. hoyi was the dominant form (65%) at depths greater than 30 m. Differences in total biomass between years and seasons (spring, summer, fall) were not significant, but year × season interaction was significant at depths greater than 30 m. Mean biomass in the profundal of southern Lake Michigan (> 90 m) was over twice that found in the profundal of either Lakes Superior, Huron, or Ontario.
Article
In many aquatic ecosystems benthic invertebrate abundance has increased following zebra mussel (Dreissena polymorpha) invasion. We examine the impact of zebra mussel density on the abundance and distribution of benthic invertebrates and postulate refuge from predation as a mechanism for the increases we found in some taxa. Benthic invertebrates in zebra mussel druses and in adjacent sediment samples were surveyed at sites in six locations representing various trophic conditions in lower Green Bay. Mean invertebrate density and taxa richness were significantly higher in the druses than in the adjacent sediment. Species diversity in the druses was inversely correlated to turbidity over the study area. Sediment samples were dominated by oligochaetes and chironomids. Amphipods were the most abundant taxa in most, but not all, of the druse samples. Other taxa present included leeches, hydra, mayflies, and caddisflies. The effectiveness of druses as refuge from predation for amphipods was investigated under laboratory conditions with various predators (perch, round goby, and rusty crayfish). In mesocosms, predation losses averaged 75% lower where zebra mussels were present. In the absence of mussels, predation loss to perch and round goby was 100% and 66% to crayfish. We conclude that the increased abundance of other invertebrates in druses in lower Green Bay may be due to increased refugia, however the assemblage composition at any given site varies with local conditions.
Article
Trends in benthic macroinvertebrate populations were examined in inner and outer Saginaw Bay, Lake Huron, from 1987 to 1996. These years represent the time period after phosphorus abatement, but immediately before (1987 to 1990) and after (1991 to 1996) colonization of the bay by the zebra mussel, Dreissena polymorpha. In 1987 to 1990, densities of the major macroinvertebrate groups in the inner and outer bay were not significantly different from, or were greater than, densities reported just prior to abatement efforts in the early 1970s. Oligochaete densities in the deepwater/silt region of the inner bay were trending downward between 1988 and 1991, but pollution-tolerant forms dominated the community, indicating the system was eutrophic just prior to Dreissena colonization. Dreissena impacts on the macroinvertebrate community varied depending on the particular habitat. At shallow-water/sand sites in the inner bay, Gammarus increased, and sphaeriids declined after Dreissena colonization, but no changes were observed in oligochaetes and chironomids, and overall species diversity showed little change. At deepwater/silt sites in the inner bay, densities of oligochaetes and chironomids declined just after the peak in Dreissena, but then returned to levels generally similar to those found prior to Dreissena. The oligochaete trophic index at deepwater/silt sites indicated a shift from eutrophic to more oligotrophic indicator species after Dreissena became established, and species diversity increased. In the outer bay, Diporeia and sphaeriids declined after Dreissena peaked, but few other changes were observed. Total non-dreissenid macroinvertebrate biomass (AFDW) in the inner bay, and in shallow areas of the outer bay, did not change as a result of Dreissena colonization. On the other hand, biomass in the deeper regions of the outer bay decreased because of the loss of Diporeia. Changes in the inner and outer bay typify the growing dichotomy between nearshore and offshore in the Great Lakes since Dreissena became established.
Article
The history of Great Lakes benthic research from 1870 to the present is briefly reviewed. An examination of the status of taxonomic work on benthic components, and a consideration of the zoogeographical history of the benthos leads to a discussion of bottom communities and macroinvertebrate production in the five major lakes.Profundal communities throughout the lakes are dominated by the glaciomarine relict amphipod Pontoporeia affinis and various species of Oligochaeta, Sphaeriidae, and Chironomidae. The specific composition of these components, and natural and recently imposed changes in their proportions within communities are examined. Population densities and standing stocks, and the proportion of oligochaetes in communities, all tend to increase in response to a natural gradient in productivity inferred from increasing concentrations of parameters such as organic matter and water hardness. Man's influence on water quality anywhere along this gradient compounds the effects of natural factors towards tubificid communities of predictable species composition: Limnodrilus hoffmeisteri, L. claparedeianus, L. cervix, L. maumeensis, Peloscolex multisetosus, and often Tubifex tubifex. The ameliorating influence of water depth is shown in Lake Erie where the change in community composition reflects improving profundal water quality from west to east — a reversed model of the Great Lakes system as a whole.
Article
Eggs of Chironomus plumosus (L.) are laid on the lake surface in masses averaging 1676 eggs. These masses absorb water, swell, and sink to the lake bottom, where the eggs hatch in 3-14 days. Larval stages range from 1.4-mm, colorless, first instars to 30-mm, dark red, fourth instars. The newly hatched first instars are free-swimming and positively phototrophic. All instars, except perhaps the first, construct U-shaped tubes in the bottom mud and, at temperatures above 5°C, feed indiscriminately by “filter feeding.“ There is evidence that larvae may occasionally become limnetic, but normally they remain in their tubes and eventually pupate there. Female larvae must weigh 60 mg or more to pupate, but male larvae will pupate when they weigh 48-56 mg. Emergence may occur at any hour, day or night, but is most prevalent just before sunset. Newly emerged flies fly weakly with the wind, eventually accumulating on the lee shore. Swarms of males form about 1 hr before sunrise and disperse about 1 hr after sunset in response to light. The swarms, typically containing several thousand flies, orient over objects that contrast with the background. Females fly into the swarms for mating, which occurs most commonly in the early morning. Mated females, after a preoviposition period of 1½-5 days, fly out over the lake to oviposit, extruding their egg masses onto their hind legs while in flight; oviposition occurs commonly at all hours of day or night. In the laboratory, adults lived 3-11 days, longest at cool temperatures and 100% RII. The larvae are eaten by many fish and by 1 species of leech, are parasitized by a microsporidian, and are occasionally killed by unknown diseases. There are normally 2 generations a year in Lake Winnebago. Overwintering fourth-instar larvae pupate and emerge during mid-May; their progeny emerge from mid-July to early September. Rate of development and time of emergence are dependent on mud temperatures. If unknown stimuli necessary for pupation are absent, a generation may be delayed or entirely missed.
Article
Dreissenid mussels (the zebra mussel Dreissena polymorpha and the quagga mussel Dreissena bugensis) have invaded lakes and rivers throughout North America and Europe, where they have been linked to dramatic changes in benthic invertebrate community diversity and abundance. Through a meta-analysis of published data from 47 sites, we developed statistical models of Dreissena impact on benthic macroinvertebrates across a broad range of habitats and environmental conditions. The introduction of Dreissena was generally associated with increased benthic macroinvertebrate density and taxonomic richness, and with decreased community evenness (of taxa excluding Dreissena). However, the strength of these effects varied with sediment particle size across sites. The effects of Dreissena differed among taxonomic and functional groups of macroinvertebrates, with positive effects on the densities of scrapers and predators, particularly leeches (Hirudinea), flatworms (Turbellaria), and mayflies (Ephemeroptera). Gastropod densities increased in the presence of Dreissena, but large-bodied snail taxa tended to decline. Dreissena was associated with declines in the densities sphaeriid clams and other large filter-feeding taxa, as well as burrowing amphipods (Diporeia spp.), but had strong positive effects on gammarid amphipods. These patterns are robust to variation in the methodology of primary studies. The effects of Dreissena are remarkably concordant with those of ecologically similar species, suggesting universality in the interactions between introduced byssally attached mussels and other macroinvertebrates.
Article
Hypothesis-testing methods for multivariate data are needed to make rigorous probability statements about the effects of factors and their interactions in experiments. Analysis of variance is particularly powerful for the analysis of univariate data. The traditional multivariate analogues, however, are too stringent in their assumptions for most ecological multivariate data sets. Non-parametric methods, based on permutation tests, are preferable. This paper describes a new non-parametric method for multivariate analysis of variance, after McArdle and Anderson (in press). It is given here, with several applications in ecology, to provide an alternative and perhaps more intuitive formulation for ANOVA (based on sums of squared distances) to complement the description provided by McArdle and Anderson (in press) for the analysis of any linear model. It is an improvement on previous non-parametric methods because it allows a direct additive partitioning of variation for complex models. It does this while maintaining the flexibility and lack of formal assumptions of other non-parametric methods. The test-statistic is a multivariate analogue to Fisher’s F-ratio and is calculated directly from any symmetric distance or dissimilarity matrix. P-values are then obtained using permutations. Some examples of the method are given for tests involving several factors, including factorial and hierarchical (nested) designs and tests of interactions.
Article
Howmiller & Scott (1977) presented an ‘Environmental Index’ based on thorough knowledge of the ecological demands of species of freshwater oligochaetes frequently found in North American waters. These authors emphasized the fact that common diversity measures do not utilize information about the ecological attributes of the constituent species but rather about community structure. A modification of the ‘Environmental Index’ is here presented with the aim of increasing its sensitivity in Europe and possibly also in North America. Four ecological groups are here preferred to the original three, and the ecological valence of the ‘key-species’ Tubifex tubifex is discussed at some length. Whereas most environmental and diversity indices remain little affected by changes in the total abundance of oligochaetes, the modified index is sensitive to such changes. Comparisons are made with two of the most popular diversity indices applied to specific situations, i.e. the Shannon-Weaver index and Simpson's index. In spite of recommendation in pollution manuals, indices of diversity may be inadequate in correctly characterizing situations of nutrient enrichment of freshwater environments. In the present study it is stressed that low diversity is usually found at both ends of the trophic scale and high diversity, which is supposed to characterize a clean and unstressed environment, is generally obtained in zones of transit between oligotrophic and eutrophic conditions — a likely result of the ‘nonequilibrium state’ described by Connell (1978) from coral reefs and rain forests in the tropics.
Article
Asexual reproduction is employed by species of Naididae during favorable environmental conditions. In species characteristic of aquatic habitats subject to rapid fluctuations in water levels and temperatures most individuals in a population become sexually mature, and there is degeneration of the alimentary tract, a shortened breeding season, and aclitellar formation of cocoons. Cocoon deposition allows a population to survive periods of environmental stress. Sexual reproduction predominates near the edges of ranges where stress conditions are more prevalent. Species that reproduce sexually in spring are intolerant of summer conditions, while those that breed in autumn are intolerant of winter. Species typical of environmentally stable bodies of water usually have a minority of the population mature at any time, an extended breeding season, and the ability to continue feeding while mature; thus, adaptations for survival in unstable habitats are lacking.
Article
Hypoxia occurs during summer in the southeastern region of Corpus Christi Bay, Texas. The objectives of this study were to identify potential causes of recurrent hypoxic events, to determine hypoxic effects on benthic macroinfauna, and to develop models of benthic response. Long-term and short-term hydrographic surveys were performed, and macroinfaunal samples were collected from normoxic and hypoxic regions of the bay. Hypoxia occurred in seven of the nine summers sampled (1988 to 1996). In 1994, the hypoxic event persisted for approximately 3 wk. Hypoxic events were associated with water column stratification where the difference between bottom and surface salinity was as high as 7.2‰ and averaged 4.1‰ The salinity difference is surprising because water column stratification is not expected in shallow (< 4 m), windy (average 18.5 km h−1) bays. Stratification did occur—hypersaline bottom water in a relatively stagnant portion of the bay—in spite of mixing forces (i.e., high winds), giving rise to hypoxia. Benthic biomass decreased 12-fold, and abundance and diversity decreased 5-fold under hypoxic conditions. In addition, dominance patterns shifted as oxygen levels declined from 5 mg O2 1−1 to <1 mg O2 1−1. The polychaete Streblospio benedicti and oligochaetes tolerated low oxygen better than other infauna. Community response to hypoxic disturbance was fit to a nonparametric categorical model and a parametric logistic model. Biomass, abundance, and diversity exhibited a lag response at <3 mg l−1, and increased exponentially from 3 mg 1−1 to 6 mg 1−1. Based on both models, 3 mg 1−1 appears to define the breakpoint between normoxic and hypoxic benthic communities in Corpus Christi Bay. This value is higher than traditional definitions of hypoxia, <2 mg 1−1 or <2 ml 1−1 (ca. 2.8 mg 1−1). *** DIRECT SUPPORT *** A01BY085 00002
Article
Moorings with current meters and temperature recorders were deployed along a mid-bay transect on either side of Chambers Island in Green Bay from September 1988 to October 1989. Daily transport estimates calculated from the current, temperature, and wind data, show temporal and spatial variability. Net summer transport during stratification west of Chambers Island was out of the lower bay (350 m3s−1) in the epilimnion, into the lower bay (900 m3s−l) in the hypolimnion, and out of the lower bay (320 m3s−1) through the passage east of the island. The residence time for the lower bay is reduced to less than 1 year using the above transport compared to a water balance estimate of over 3 years. During the mid-September to May isothermal period, a horizontal transport gradient existed. Under the solid ice cover of winter, transport variability was significantly reduced and was uniformly out of the lower bay (500 m3s−1). Fluctuations in daily transport were often large (up to 2 × 104 m3s−1). The temporal and spatial variability of the water volume transport suggests that material mass fluxes between lower and upper Green Bay will be similarly dependent.
Article
Short-term (24 h) effects of four stressors (hypoxia, hyperoxia, potassium dichromate, fenitrothion) on the activity of the electron transport system (ETS) and total lipid, glycogen and protein contents were assessed in 4th instar larvae of Chironomus riparius. Hypoxia and hyperoxia caused an increase in ETS activity and protein content. Glycogen content decreased when larvae were placed under hypoxic conditions. ETS activity increased following exposure to 2 microg x l(-1) of fenitrothion. It decreased in larvae exposed to 20 microg x l(-1) of this insecticide. A decrease in lipid and glycogen contents was observed in larvae exposed to potassium dichromate or fenitrothion. Changes in ETS activity and lipid and glycogen contents may be related to the activation of the respiratory chain due to an increase in energy cost associated with homeostatic phenomena, such as detoxification processes. These results suggest that some parameters related to energy metabolism, such as ETS activity and lipid and glycogen contents, may be used as biomarkers of environmental disturbance in Chironomus riparius larvae.
Biological studies of the Fox River and Green Bay, 1955-1956
  • Balch
Sedimentary phosphorus cycling and a phosphorus mass balance for the Green Bay (Lake Michigan) ecosystem
  • Klump
Chironomidae of the Holarctic Region
  • T Anderson
  • P S Cranston
  • J H Epler
Anderson, T., Cranston, P.S., Epler, J.H., 2013. Chironomidae of the Holarctic Region. Media-Tryck, Lund, Sweden.
Biological studies of the Fox River and Green Bay
  • R F Balch
  • K M Mackenthum
  • W M Vanhorn
  • T F Wisniewski
Balch, R.F., MacKenthum, K.M., VanHorn, W.M., Wisniewski, T.F., 1956. Biological studies of the Fox River and Green Bay, 1955-1956. Wis. State Comm. Water Pollut. Bull. WP. 102, 74.