Journal of Great Lakes Research最新文献

This landscape investigation is focused on finding the most suitable Wetlaculture^TM (wetland + agriculture) restoration sites within the former 6700 km² Great Black Swamp in the western basin of Lake Erie, the shallowest of the Laurentian Great Lakes in North America. The western basin of Lake Erie is now plagued by harmful algal blooms annually due to nutrient discharges primarily from this basin, and water quality was impacted so significantly with toxic cyanobacteria in 2014 that the city of Toledo’s water supply was shut off, affecting hundreds of thousands of residents. This study is aimed to estimate the area of suitable Wetlaculture^TM zones using multi-criteria decision-making GIS model with Analytical Hierarchy Process analysis, especially in agricultural and historic wetland area, with high suitability for flipping farmland to wetlands. A potential indicator GIS model was developed, with various layers of hydrology, soils, and prime farmlands combined, to identify and classify suitable Wetlaculture^TM areas in the now-drained Great Black Swamp region that could mitigate nutrient inflows to Lake Erie. Overall, the estimated area of highly suitable potential Wetlaculture^TM restoration areas in the Western Lake Erie Basin and in the Great Black Swamp area is approximately 1000 km² (4 %) and 800 km² (13 %), respectively, much larger than the 400 km² of wetlands that have been suggested as necessary to control the algal blooms in Lake Erie.

Lake Erie algal bloom discussions have historically focused on cyanobacteria, with foundational “blooms like it hot” and “high nutrient” paradigms considered as primary drivers behind cyanobacterial bloom success. Yet, recent surveys have rediscovered winter-spring diatom blooms, introducing another key player in the Lake Erie eutrophication and algal bloom story which has been historically overlooked. These blooms (summer vs. winter) have been treated as solitary events separated by spatial and temporal gradients. However, new evidence suggests they may not be so isolated, linked in a manner that manifests as an algal bloom cycle. Equally notable are the emerging reports of cyanobacterial blooms in cold and/or oligotrophic freshwaters, which have been interpreted by some as shifts in classical bloom paradigms. These emerging bloom reports have led many to ask “what is a bloom?”. Furthermore, questioning classic paradigms has caused others to wonder if we are overlooking additional factors which constrain bloom success. In light of emerging data and ideas, we revisited foundational concepts within the context of Lake Erie algal blooms and derived five key take-aways: 1) Additional bloom-formers (diatoms) need to be included in Lake Erie algal discussions, 2) The term “bloom” must be reinforced with a clear definition and quantitative metrics for each event, 3) Algal blooms should not be studied solitarily, 4) Shifts in physiochemical conditions serve as an alternative interpretation to potential shifts in ecological paradigms, 5) Additional factors which constrain bloom success and succession (i.e., pH and light) require consideration.

Cyanobacterial blooms in the western basin of Lake Erie have been well studied with a focus on planktonic Microcystis and the cyanotoxin microcystin, but recent research has shown that blooms are not entirely Microcystis. Previous studies have documented other taxa in blooms capable of producing other cyanotoxins. Furthermore, benthic cyanobacteria have historically been overlooked in Lake Erie. Saxitoxin is a cyanotoxin of emerging concern in freshwater, and the sxtA gene which encodes its production has been found in the Maumee River and central basin of Lake Erie. Collectively, these points indicated that saxitoxin-producing cyanobacteria may also occur in the western basin. We utilized three sources of data to determine the spatial and temporal distribution of potential saxitoxin-producing cyanobacteria in the water column (years 2018–2022) and deployed nutrient diffusing substrata (NDS) to determine the impact of nutrients, depth, and season on potential-STX producing benthic cyanobacteria (years 2018 & 2019). The water column datasets showed that “hotspots” of sxtA lasted only a few weeks. sxtA gene copies per mL did not correlate with Dolichospermum or Aphanizomenon biovolume, which have been associated with sxtA elsewhere. In the NDS, saxitoxin (ng/cm²) and cyanobacteria chlorophyll were inversely correlated with the highest saxitoxin in September and at the deeper depth, whereas cyanobacteria chlorophyll was highest during June and at the shallower depth. This research suggests continued monitoring is needed to determine drivers of saxitoxin in the western basin, and we recommend that future Lake Erie cyanobacteria research should not solely focus on microcystins and planktonic blooms.

This study investigated variability in ecosystem metabolism in the meromictic, oligotrophic, and deep Lake Tanganyika. A large buoy equipped with a weather station, oxygen and temperature sensors for every 10 m down to 102 m depth and an irradiance sensor at 0 and 22 m depth, provided a three-month data with one-minute frequency. These data enabled us to derive detailed description of water column mixing and light conditions along with daily depth specific rates of gross primary production, ecosystem respiration and net production over a 3-month period. We applied a mass balance approach which included dissolved oxygen exchange between depth layers driven by mixed-layer deepening and eddy diffusivity from a one-dimensional hydrodynamic model. The vertical extent of the upper mixed layer varied between 21–40 m and the extent of the metalimnion varied between 48–75 m, with the euphotic zone (20–38 m) extending into the metalimnion on several days, providing enough light for primary production to occur below the upper mixed layer. Vertical profiles of metabolism showed several periods with elevated primary production in the metalimnion around the deep chlorophyll maximum. This deep productivity may compensate for the decreasing primary production in the epilimnion caused by climate change induced reductions in nutrient inputs from deeper waters.

Fish exploit opportunities within aquatic ecosystems to increase their likelihood of survival, growth, and reproduction, ultimately to maximize fitness over the entire life cycle. Fitness is increased by moving to find abiotic and biotic conditions suitable for various life history stages. Smallmouth bass (Micropterus dolomieu) are known to spawn in lakes and flowing waters displaying high nest site fidelity in both environments. Some populations of smallmouth bass are adfluvial, living as adults in lakes and ascending rivers to spawn. However, this life history variant is poorly understood, particularly in the Great Lakes. The objective of our study was to determine if smallmouth bass migrate 13 km upstream to a barrier in the Maitland River from Lake Huron. Stable isotopes were used to make inferences about the migratory status of Maitland River smallmouth bass. We found significant separation in the isotopic space for adult bass captured downstream of a migration barrier (mean δ¹³C = −18.93 ‰; mean δ¹⁵N = 11.02 ‰) compared to bass found upstream (mean δ¹³C = −26.58 ‰; mean δ¹⁵N = 15.29 ‰) river segments. Stable isotope values for juvenile bass, forage fishes, and invertebrates all grouped in similar δ¹³C isotopic space across the lower and upper river segments. Adfluvial smallmouth bass are underappreciated, yet an important life history variant supporting population biodiversity in the Great Lakes.

Water quality trends and loads were analyzed at Wolfe Island for the years 2000 to 2019. This station captures the nutrient and contaminant concentrations leaving the Canadian Great Lakes system into the St. Lawrence River. In addition to tracking what is leaving the Great lakes system, this station provides an indication of contaminants flowing downstream where a number of sensitive areas exist such as the Thousand Island National Park as well as the St. Lawrence River Area of Concern at Cornwall. In terms of trends, trace metals and PAHs are generally decreasing at Wolfe Island while the nutrients and major ions are increasing. Organic compounds are more challenging to summarize since the number of non-detects prevented modeling of many or the frequency of analysis was too low to model. In a general sense, there is an overall decreasing trend in the organics and the large number of compounds whose concentrations are below detection levels does signify the very low concentration of these contaminants. A notable change in trend predominantly for the metals was noted around 2010 and is discussed herein. The amount of recent (5 years) exceedances of the most stringent water quality guidelines is lower than the previous study period (only PCBs and phosphorus, PFOS and most likely dieldrin). While there are many additional downstream sources of contaminants after the Wolfe Island station, the reductions observed from this study indicate a lower contribution from the Great Lakes in many cases.

Lake Tanganyika, in central Africa, contains a diverse and endemic fauna under threat from global climate change, overfishing, and nearshore sediment pollution. Previous studies of sediment pollution focused justifiably on impacts along rocky shorelines where diversity is high, but Lake Tanganyika also contains widespread shelly accumulations (shell beds) unprecedented in the modern East African lakes, but where impacts are less constrained. Here we integrate multiple datasets from three sites along the Tanzanian shoreline to explore how variation in sedimentation rates and sediment quality impacts shell-bed substrate and diversity and abundance of ostracodes and sponges across sites that exhibit varying watershed characteristics. Taphonomic overprinting of the shells are similar over the three sites, suggesting lake-wide processes control their accumulation. However, shell bed distribution and sediment volume and compositions vary. There are also differences in the abundance of studied taxa. Where organic matter is diluted by clastic mud, ostracodes are less abundant and less diverse. Where sediment is pervasive and shell density is low, fewer sponges occur. Using the fallout radionuclide ²¹⁰Pb, the two sites with discontinuous shell beds show sedimentation rates at least twice as high as the site where shell beds are more continuous. These differences are likely related to modest differences in watershed morphology, urbanization, and land cover. Our study suggests that modern sediment pollution creates sediment blankets that cover extant shell beds and likely reduce live populations of the snails that contribute to the accumulations. This has important conservation implications as planning must focus on large watersheds where agriculture and urbanization tend to be higher.

Aquatic ecosystems are deteriorating, with the most impacted species and populations having insufficient data to inform conservation and management. Monitoring aquatic biodiversity and evaluating anthropogenic impacts typically rely on time-consuming, logistically challenging, and invasive methods (e.g., seining, trawling or electrofishing). Environmental DNA (eDNA) methods have been touted as an important advancement, especially in fish biodiversity assessment. We compare eDNA metabarcoding and seining methods along a 350 km section of the Upper St. Lawrence River (Canada) for: i) mapping the distribution of invasive and threatened fish species, ii) describing species richness and fish community structure, and iii) assessing the effect of habitat type and anthropogenic degradation of riparian zones on fish community composition and richness. eDNA detected more fish species (n = 67) than seining (n = 38) and revealed higher fish diversity in samples adjacent to intact, natural riparian zones. Fish assemblages were influenced by habitat type according to analyses using eDNA, while no effect of any environmental predictor on fish community composition was found using seining. Altogether, our results support eDNA metabarcoding as a powerful, complementary tool in fish monitoring and testing for the impacts of anthropogenic disturbances.