Journal of Great Lakes Research最新文献

Caves in coastal cliffs in the Apostle Islands were analyzed for factors controlling their origin and evolution. Even though the Bayfield Group quartz sandstones were found to be of relatively low tensile strength, the traditional explanation attributing speleogenesis to localized zones of lithological and tectonic weakness does not adequately explain all geomorphic features of the caves. The caves were found to be formed by coalescence of smaller arcade-shaped cavities serially developed along subhorizontal discontinuities. In concordance with the previously formulated “arcade principle”, positions and shapes of the cavities are defined by areas of reduced stress within the gravity-induced stress field. Evacuation of material from the rock massif can be attributed to wave action including the effect of water-pressurized air, and frost action. Compound cavities above the discontinuities tend to form “higher-order” arcade-like cavities/caves while those beneath more resistant strata rather develop into elongated overhangs similar to ordinary coastal notches. Propagation of the largest cavities, formed along steeply dipping joints and faults, is attributed to mass wasting and roof collapses. Similar examples of discontinuity-related cavities in coastal settings, suspectedly also controlled by gravity-induced stress distribution, can be found worldwide, being mostly concentrated to areas covered by ice sheets in the Pleistocene. The interplay between post-glacial isostatic uplift and Holocene lake-level rise is responsible for the development of mature forms of coastal caves in the Apostle Islands where present cliffs are estimated to have been exposed to the effects of wave action for the last 3–5 ky.

Food web responses to invasion can be context-dependent and therefore difficult to predict based only on invasion histories. Alewives (Alosa pseudoharengus) had generally negative impacts on the native fish communities of the Laurentian Great Lakes after they invaded in the 19th century and were thus expected to negatively impact the Lake Champlain food web after entering the lake in 2003. We evaluated the impact of alewives on the Lake Champlain food web by compiling 25 years of biomass, abundance, and diet data and constructing an Ecopath with Ecosim model of the coldwater food web. Model projections indicated that, contrary to the Great Lakes experience, biomass of native predators increased, mortality rates decreased, and overall trophic level of the pelagic fish community decreased after alewife entered the system. Consequently, the amount of primary production supporting predator biomass increased in response to the addition of prey fish production. The model suggests that alewife invasion in Lake Champlain could have altered food web structure by transferring more energy to tertiary consumers via pelagic pathways at the expense of other energy pathways and “jump started” wild lake trout recruitment by expanding the forage base. In contrast to the Great Lakes response to alewife invasion, Lake Champlain may represent an alternate trajectory for alewife invasion and demonstrates that alewife impacts are context-dependent.

Migratory fish can influence the stream ecosystems where they spawn by depositing large amounts of energy rich eggs, carcasses, and excrement which can increase primary and secondary productivity. Past research in the Great Lakes has focused on individual tributaries; accordingly, there is a poor understanding of how wide-spread resource subsidies are amongst tributaries. To determine which Great Lake tributaries received subsidies, we compared carbon stable isotope values (δ¹³C) of resident stream fishes above and below 54 barriers (e.g., low-head lamprey weirs, natural waterfalls) in 31 tributaries. Subsidies, as indicated by the difference in δ¹³C values above and below barriers, were common. The magnitude of the subsidy varied among Great Lakes with Lake Superior having significantly larger subsidies than the other three lakes. Barrier type (complete, partial) was not related to subsidy magnitude; however, the classification of barrier type was imperfect. Correspondence analysis of regional and local environmental factors showed that large subsidies were associated with oligotrophic streams with steep channels on the Canadian Shield with little agricultural land. The association between subsidies and canopy cover and substrate size were poor. Migratory fish supply resource subsidies to rivers across the Great Lakes basin, though their magnitude is contextually dependent. The presence of barriers are likely limiting the production of migratory fishes that depend on streams for juvenile production. The importance of resource subsidies should be considered when decisions are made about the fate of existing, and the construction of new, barriers that may reduce stream productive capacity.

Lake Tanganyika is recognized for its unique rich fish biodiversity of high socio-ecological value, exceptional beauty, and the fact that it sustains one of the most important African inland fisheries. Most cichlid fishes are targeted by the inshore fisheries and have habitat preferences in the nearshore environment within different habitats along the coastline. Many human threats challenge these critical habitats and freshwater biodiversity could be on the decline. Here we document the extent of the fisheries pressures on the inshore fish communities in northwestern Lake Tanganyika, a highly changing area with respect to human population and protein needs. From field data and communities-based fisheries consultations, we noted the following: 1) there are very limited data available on the inshore fish diversity and the current status of fish stocks, 2) there are data deficiencies on the spatial distribution and current levels of exploitation for a significant proportion of fish species (78%), though there is enough data to indicate that they are overexploited and caught while still immature, 3) resource users’ awareness and alternatives remain low, and many fish species are constantly threatened with local declines and habitat-loss due to unsustainable fishing practices, and 4) conservation actions of fishery resources are diminished due to the lack of long-lasting policy and updated fisheries legislation. Our findings suggest that fishing activities are widely destructive and no longer sustainable for the fishing communities. Therefore, we should initiate conservation programs and fisheries-related decision making based on scientific data that is contextual with communities and their fisheries awareness. We describe potential paths forward, and we give an overview of the inshore fisheries activities and species richness to encourage sustainable management measures at Lake Tanganyika to prevent this tragedy of the commons.

At 1270 km², Lake Champlain, is the 13th largest lake in the United States. Lake Champlain experiences annual blooms of cyanobacteria, particularly in Missisquoi Bay. Here the Cyanobacteria Index, a previously published algorithm, was applied to satellite imagery from OLCI (available from 2016 through the present) and MODIS (available from 2000-present). The remotely sensed timeseries of the CI was derived and described from each sensor, along with cross-calibration among OLCI and MODIS. The resultant timeseries described when and where cyanobacteria blooms generally occur. Five distinct regions of Lake Champlain were considered for analysis: Malletts Bay, the Northeast Arm, Saint Albans Bay, Missisquoi Bay, and the Main Lake. Saint Albans and Missisquoi Bay were the only basins shown to have consistent cyanobacteria blooms. Saint Albans Bay, due to its small size was not an ideal fit for the methods used here, and the focus of this manuscript was Missisquoi Bay. The objective of this study is to explore the interannual variability of blooms in Missisquoi Bay and compare the variability to cyanobacteria blooms in Lake Erie, Saginaw Bay, and Green Bay. The blooms in Missisquoi Bay showed interannual variability in size, intensity, and start and end date. Observed data from the Burlington International Airport and modeled data from NASA’s Giovanni program were used in an effort to explain this bloom variability. A 2-parameter multiple regression model fit the cyanobacterial data well and showed that the interannual variability of blooms in Missisquoi Bay are a function of atmospheric instability and temperature.

Eutrophication is a global environmental problem in aquatic ecosystems, mainly caused by increased nutrient loads (nitrogen and phosphorus). Phytoplankton and periphyton responses to the nutrients increase and temporal variation may be related to mutual seeding and/or variable environmental constraints. Each of these communities may be useful for characterizing and monitoring eutrophication processes. However, little information exists about the simultaneous responses or interactions between such communities during eutrophication, even less in high-altitude tropical lakes such as Lake Titicaca. Here, we first established a eutrophication gradient with stable isotopes (δ¹⁵N and δ¹³C) and physicochemical variables in a shallow bay of Lake Titicaca. Later, we analyzed the shifts in taxonomic and morphological forms of phytoplankton and periphyton colonizing the underwater stems of totora (Schoenoplectus californicus ssp. tatora), an emergent aquatic macrophyte, along the eutrophication gradient. There is a clear turnover (groups, genera, and morphological forms) in phytoplankton and periphyton and decreased biodiversity along the eutrophication gradient. Gomphonema genus relative abundance increase with eutrophication in both communities, while Achnanthidium abundance decreases. However, other genera behave differently in each community, allowing for the identification of specific bioindicators of eutrophication for phytoplankton (Oscillatoria, Spirogyra, and Euglena) and periphyton (Oedogonium, Stigeoclonium, and Characium). They share genus composition with some taxa showing similar behaviors, thus interactions between phytoplankton and periphyton may exist. We also believe that each compartment can act as a seeding reservoir for the other, though remaining independent to some extent.

Expansion of dreissenid mussel populations and decreased nutrient loading have led to a decrease in seston concentration and an increase in water clarity documented by Secchi depth and photosynthetically active radiation (PAR) in Lakes Michigan, Huron and Ontario. We hypothesized that the increase in water clarity also led to increased penetration of ultraviolet (UV) wavelengths that may affect diurnal vertical migrations and survival of zooplankton and larval fish. To predict UV penetration from standard limnological variables and how they may vary across habitats, we measured penetration of ultraviolet wavelengths and PAR across seasons in nearshore and offshore areas of Lakes Michigan and Huron from 2012 to 2021. Offshore and nearshore areas of Lake Huron showed little difference in UV and PAR penetration among sites; however, UV and PAR penetration in Lake Michigan increased with distance from shore owing to dilution of high concentrations of chromophoric dissolved organic matter (CDOM), total suspended solids, and high chlorophyll a associated with loading from major rivers. A comparison with data from the mid-1980s in Lake Michigan indicated that UV-A and PAR penetration has increased in spring before and immediately after stratification, likely related to removal of particulate material by dreissenid mussel grazing when they are connected with the total water column during isothermal periods. In contrast, UV-B penetration, because of its strong association with CDOM, has remained unchanged or even decreased during summer. Nearshore areas near major rivers may serve as refuges for UV-sensitive organisms. Potential impacts on plankton and larval fishes are discussed.

Rotifers are among the most abundant zooplankters in lakes yet are often overlooked, and limited information is available on their seasonal and spatial distribution within the Laurentian Great Lakes. Herein, we present data on the seasonal succession of the Lake Ontario rotifer community, with samples collected from April to October 2018 as part of the bi-national inter-agency Cooperative Science and Monitoring Initiative. All sites had epilimnetic samples, but several sites included meta- and hypolimnetic samples. Prior to and during stratification, rotifers were most abundant in the epilimnion and differences in community composition with depth were minor. Mean epilimnetic rotifer density peaked in August (average 330 L⁻¹) when surface water temperature was highest. Seasonal succession included a spring dominated by Synchaeta to the co-dominance of Conochilus and Keratella in early summer and the eventual dominance of Keratella during late summer through fall. Model selection found temperature and Bythotrephes to be key factors influencing overall rotifer abundance as well as genera-specific abundances. The best models for specific genera varied and included Secchi depth, chlorophyll, Cercopagis, Diacyclops, and Daphnia. Rotifers reached their highest proportion of total zooplankton epilimnetic biomass in early summer at 11 %. Analysis of seasonal patterns in 2018 suggest rotifer data collected by the Great Lakes biological monitoring program in April and August represents spring and summer through fall communities but not the June community which was different from other seasons.

Beaches within the Laurentian Great Lakes Basin are frequently contaminated with fecal bacteria such as Escherichia coli (E. coli), leading to beach closures due to potential health risks. Although climatic drivers and landscape sources of E. coli to nearshore areas are well established, the role of coastal wetlands as sources of coliform bacteria remains a knowledge gap. We investigated E. coli abundance and dynamics in four coastal wetlands (3 drowned river mouths and 1 barrier beach lagoon) on the north-shore of Lake Ontario for over a decade (2009–2018). Applying a general additive model revealed significant seasonal, interannual, spatial, inter-seasonal, and interannual spatial trends for E. coli across the study area. Additionally, we observed celled sites (i.e., natural ponds in wetlands) to have a higher partial effect on E. coli concentrations across the study period, indicating these wetland features may be an important reservoir for endogenously sourced E. coli. To determine whether increased wave activity, indicative of seiche events, influenced E. coli concentrations in the wetland and the nearshore of Lake Ontario, we developed a local structural equation model to represent the entire study area. Seiche events were identified to significantly increase suspended solid loadings, which in turn resulted in significantly (p-value < 0.05) elevated E. coli concentrations in both coastal wetlands and Lake Ontario. In addition to watershed inputs, results demonstrated that coastal wetlands significantly (p-value < 0.05) influence E. coli concentrations in the nearshore of Lake Ontario, and should be considered in nearshore water quality assessments and mitigation efforts.