Waxing and waning slacks: The changing ecohydrology of interdunal wetlands/slacks in a Lake Michigan coastal dune complex during rising Lake Michigan-Huron levels

Since 2016 we have studied the largest interdunal wetlands/slack lying within a deflated parabolic dune east of Lake Michigan. Geologic cross-sections show ∼ 15 m of sand and gravel beneath the dunes, creating an aquifer hydraulically connecting Lake Michigan-Huron (MH) with the water table/shallow groundwater influencing the slack. Lake Michigan-Huron (MH) water levels have risen ∼ 1 m from 2016 to 2020, increasing water levels within and around the slack ∼ 1 m. Color-infrared images and vegetation quadrat sampling show water appearing, then significantly expanding with the main slack and upland/dune vegetation transitioning to wetland vegetation in response to this rise. Monitoring well data show slack water levels rise in spring as Lake MH rises. Levels drop as the growing season begins while Lake MH continues to rise through summer. Short-term slack water level increases occur due to local rain events, but significant water level declines follow due to evapotranspiration. Slack water levels begin to rise again in late summer and into fall as the end of the growing season arrives, evapotranspiration decreases, and heavier, more frequent rain events occur. Together, these factors push slack water levels to their highest point of the year while Lake MH levels are decreasing. In late fall–winter, slack water levels drop in concert with Lake MH levels. Climate change effects, increased transpiration from higher temperatures, summer drought, and greater variability in lake level fluctuations, may make it more difficult to maintain wet growing conditions for hydrophytic vegetation. Hence, climate change poses risks to the existence of this imperiled ecosystem.     

Assessing surface water–groundwater interactions in a complex river‐floodplain wetland‐isolated lake system

Floodplain systems are most often hydrologically complex settings characterized by highly variable surface water–groundwater interactions that are subjected to wide‐ranging wetting and drying over seasonal timeframes. This study used field methods, statistical analysis, and the Darcy's law approach to explore surface water–groundwater dynamics, interactions, and fluxes in a geographically complex river‐floodplain wetland‐isolated lake system (Poyang Lake, China). The floodplain system of Poyang Lake is affected by strongly seasonal shifts between dry and wet processes that cause marked changes in surface water and groundwater flow regimes. Results indicate that wetland groundwater is more sensitive to variations in river levels than the seasonal isolated lakes. In general, groundwater levels are lower than those of the isolated lakes but slightly higher than river levels. Statistical analysis indicates that the river hydrology plays a more significant role than the isolated lakes in controlling floodplain groundwater dynamics. Overall, the river shows gaining conditions and occasionally losing conditions with highly variable Darcy fluxes of up to +0.4 and ?0.2 m/day, respectively, whereas the isolated lakes are more likely to show slightly losing conditions (less than ?0.1 m/day). Although seasonal flux rates range from 7.5 to 48.2 m/day for surface water–groundwater interactions in the floodplain, the flux rates for river–groundwater interactions were around four to seven times higher than that of the isolated lake–groundwater interactions. The outcomes of this study have important implications for improving the understanding of the water resources, water quality, and ecosystem functioning for both the river and the lake.     

An Evaluation of Effects of Groundwater Exchange on Nearshore Habitats and Water Quality of Western Lake Erie

Historically, the high potentiometric surface of groundwater in the Silurian/Devonian carbonate aquifer in Monroe County, MI resulted in discharge of highly mineralized, SO₄-rich groundwater to the Lake Erie shoreline near both Erie State Game Area (ESGA) and Pointe Mouillee State Game Area (PMSGA). Recently, regional groundwater levels near PMSGA have been drawn down as much as 45 m below lake level in apparent response to quarry dewatering. From August to November of 2003, we conducted preliminary studies of groundwater flow dynamics and chemistry, shallow lake water chemistry, and fish and invertebrate communities at both sites. Consistent with regional observations, groundwater flow direction in the nearshore at ESGA was upward, or toward Lake Erie, and shallow nearshore groundwater chemistry was influenced by regional groundwater chemistry. In contrast, at PMSGA, the groundwater flow potential was downward and lake water, influenced by quarry discharge seeping downward into nearshore sediments, produced a different lake and shallow groundwater chemistry than at ESGA. Although the invertebrate and young fish community was similar at the two sites, taxonomic groups tolerant of degraded water quality were more prevalent at PMSGA. Sensitive taxa were more prevalent at ESGA. We propose a conceptual model, based on well-described models of groundwater/seawater interaction along coastal margins, to describe the interconnection among geologic, hydrologic, chemical, and biological processes in the different nearshore habitats of Lake Erie, and we identify processes that warrant further detailed study in the Great Lakes.     

Regression and Weighted Averaging Models Relating Surficial Sedimentary Diatom Assemblages to Water Depth in Lake Ontario

Diatom assemblages in surface sediment samples in depth profiles from Lake Ontario and from East Lake, a shoreline lake, were analyzed for the purpose of describing the relationship between species distribution and water depth. At both sites species composition varied markedly with sample depth. In East Lake a multiple regression of four habitat groups: benthic, epiphytic, tychoplanktonic, and euplanktonic, against water depth (30 cm–8 m) produced a relationship with a standard error (SE) of 1.5 m. An analysis of the ratio of euplanktonic diatoms to periphytic diatoms over a transect from 3 m to 150 m in Lake Ontario produced a multiple regression with an SE of 11.8 m. In another approach, water depth optima for 91 diatom taxa were developed using a weighted averaging (WA) technique. A good correlation (r² > 0.9) was found between measured and inferred water depth over the range 3 m to 30 m using a unimodal WA regression model. The transfer functions offer the possibility of inferring Holocene water level changes in Lake Ontario from fossil diatom assemblages in sediment cores.     

Late Quaternary Fluvial History of the Lower Cuyahoga River in Northeastern Ohio

Over 200 drill-holes and excavations associated with the expansion of a waste treatment plant situated on an abandoned meander of the Cuyahoga River near Cuyahoga Heights, Ohio, record three sedimentary units and two cycles of fluvial scouring. With the present 175 m above mean sea level water level in Lake Erie as a datum, these events in chronologic order are: (1) deposition of glaciolacustrine and glaciofluvial gray silty clay, with traces of sand and gravel, from at least 123 m up to 227 m; (2) fluvial scouring down to at least 165 m about 12,500 yr BP; (3) fluvial deposition from 12,500 yr BP to between 8,750 and 8,540 yr BP of gray, fossiliferous (with molluscs, an elk antler, wood, and degraded plant material) fine to medium sand, with traces of silt and gravel, to an elevation of 181 m, (well above the present average surface elevation of the Cuyahoga River near the study area, suggesting that local base level may have been controlled by a log-jam triggered by a landslide); (4) the river scoured to an elevation of 170 m prior to 8,540 yr BP; (5) fluvial deposition of gray-brown silty clay overbank sediments with abundant wood and degraded plant material, starting about 8,540 yr BP and continuing as Lake Erie has risen to its present level. The elevations at the base of the two scouring events suggest that the Cuyahoga River was graded to lower water levels in the Erie basin. The radio-carbon dates indicate that these events occurred when the water was rising from Early Lake Erie level.     

Lake Balkhash (Kazakhstan): Recent human impact and natural variability in the last 2900 years

Lake Balkhash is a large and relatively shallow closed-basin lake in the arid part of Central Asia. The lake experienced an ecological crisis in the 1970s and 1980s when the filling of the Kapchagay Reservoir in the middle reaches of its main tributary caused a significant lake-level decline and salinity rise, and resulting biodiversity loss. A sediment core representing 2900 years of lake history was obtained to assess man-made alterations of the lake in the last decades in comparison to the natural status of Lake Balkhash. Analyses of sediments and of ostracod (micro-crustacean) species assemblages and shell chemistry revealed that the lake was probably relatively shallow and more brackish ca. 2900–2200 calibrated years before present (cal a BP) in comparison to the period when the Kapchagay Reservoir was filled. A relatively high lake level and lower salinity prevail since ca. 2200 cal a BP.The uppermost sediments of the obtained core and nearby surface-sediment samples provide evidence for the establishment of hypoxic conditions in Lake Balkhash since the middle of the 1970s. The lake-level decline during the filling of the Kapchagay Reservoir probably caused the redistribution of organic-matter rich littoral sediments to greater depth in the lake where dissolved oxygen became consumed due to the decomposition of organic remains. The spatial and temporal distribution of hypoxia in Lake Balkhash is not known, and systematic studies are required to assess the status of the benthic life and potential impacts of future lake-level, nutrient influx and temperature changes.     

Assessing habitat for lake sturgeon (Acipenser fulvescens) reintroduction to the Maumee River,Ohio using habitat suitability index models

Lake sturgeon (Acipenser fulvescens) were a candidate for reintroduction in the Maumee River, Ohio, where they were historically abundant, but are now functionally extirpated. Our objective was to determine if current habitat quality and quantity could support reintroduction efforts. We developed a spatially explicit habitat suitability index model for two lake sturgeon life stages: spawning adult and age-0 fish. To estimate habitat quality, substrate, water depth, and water velocity were assessed and integrated into suitability index values to delineate good, moderate, and poor areas for each life stage. Each habitat characteristic was mapped and combined to provide an overall assessment of habitat suitability, quantity, and location. Model results indicated 208 ha (10.2% of all habitat) of good adult spawning habitat (e.g., coarse substrates, depths between 0.3 and 8 m, and velocity between 0.5 and 1 m/s) and 529 ha (28.2% of all habitat) of good age-0 habitat (e.g., fine substrates, depths between 0.2 and 6 m, and velocity between 0.1 and 0.7 m/s). Good age-0 habitat was located mostly downstream of good spawning habitat, which will provide nursery areas for age-0 fish after hatch. Our models suggested habitat is not limiting for lake sturgeon and efforts to reintroduce this species into the Maumee River, and for the first time in the Lake Erie basin, were supported. The results of this work supported reintroduction efforts that began in 2018.     

Submerged macrophyte communities and the controlling factors in large,shallow Lake Taihu (China): Sediment distribution and water depth

Lake Taihu, the third largest lake in China, is subjected to severe eutrophication and cyanobacterial blooms as a result of development and urbanization. In order to restore the degraded lake ecosystem, it is important to identify which environmental factors control the submerged macrophytes which declined during eutrophication. To characterize community structure of submerged macrophytes and to assess the plant–environmental relationships in Lake Taihu, a monthly investigation was conducted from May to October in 2010. A total of six species were recorded, dominated by Potamogeton malaianus and Vallisneria natans. Multivariate analysis showed that water depth, depth of soft sediments and nutrient variables (orthophosphate of water, organic matter of sediment, total nitrogen and total phosphorus of sediment) were the major factors determining growth and community composition of submerged macrophytes in the lake. A strong predictive association of soft-sediment depth and plant biomass indicated preference of submerged macrophytes for firm bottoms along the eastern shore and approximately 0.2 m could be regarded as an optimum depth for the growth of plants. The biomass of plants responded proportionately to water depth, and approximately 1.8 m could be regarded as the optimum depth for the growth of submerged macrophyte in Lake Taihu. Our results indicated that improvement of habitat and the selection of appropriate submerged macrophytes species are very important for ecological restoration in large eutrophic lakes. This study could provide useful information for managers and policy makers to evaluate and modify restoration practices in large, shallow lakes.     

Cattail Invasion of Sedge/Grass Meadows in Lake Ontario: Photointerpretation Analysis of Sixteen Wetlands over Five Decades

Photointerpretation studies were conducted to evaluate vegetation changes in wetlands of Lake Ontario and the upper St. Lawrence River associated with regulation of water levels since about 1960. The studies used photographs from 16 sites (four each from drowned river mouth, barrier beach, open embayment, and protected embayment wetlands) and spanned a period from the 1950s to 2001 at roughly decadal intervals. Meadow marsh was the most prominent vegetation type in most wetlands in the late 1950s when water levels had declined following high lake levels in the early 1950s. Meadow marsh increased at some sites in the mid-1960s in response to low lake levels and decreased at all sites in the late 1970s following a period of high lake levels. Typha increased at nearly all sites, except waveexposed open embayments, in the 1970s. Meadow marsh continued to decrease and Typha to increase at most sites during sustained higher lake levels through the 1980s, 1990s, and into 2001. Most vegetation changes could be correlated with lake-level changes and with life-history strategies and physiological tolerances to water depth of prominent taxa. Analyses of GIS coverages demonstrated that much of the Typha invasion was landward into meadow marsh, largely by Typha × glauca. Lesser expansion toward open water included both T. × glauca and T. angustifolia. Although many models focus on the seed bank as a key component of vegetative change in wetlands, our results suggest that canopy-dominating, moisture-requiring Typha was able to invade meadow marsh at higher elevations because sustained higher lake levels allowed it to survive and overtake sedges and grasses that can tolerate periods of drier soil conditions.     

Satellite based lake bed elevation model of Lake Urmia using time series of Landsat imagery

This study presents a lake bed elevation model of Lake Urmia. In the course of model generation, a time series of the extent of the lake surface was derived from 129 satellite images with different acquisition dates based on the Landsat sensors Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), and Operational Land Imager (OLI). Due to the rapid shrinking of the lake during the last two decades, lake surface areas ranging from 890 km² to 6125 km² could be covered. The water edge of the various lake extents was then linked to the observed water level on the day of the satellite image acquisition. The resulting contour lines, covering water levels between 1270.04 m and 1278.42 m a.s.l. and thus representing the lakebed morphology in its shallow parts, were merged with existing data (deeper parts) and interpolated to generate a lake bed elevation model. Finally, Lake Urmia’s Level-Area-Volume relationships were derived from the lake bed elevation model and compared to bathymetric data previously published.     

A comparison of mercury cycling in Lakes Michigan and Superior

Mercury cycling in Lake Superior and Lake Michigan was evaluated based on measurements of mercury levels, modeling of evasional fluxes, and development of first-order mass balance models. Total mercury, methylmercury, and dissolved gaseous mercury were measured on sampling cruises in Lake Michigan (2005) and Lake Superior (2006). Average total mercury concentrations in unfiltered surface water were higher in Lake Michigan (420 ± 40 pg/L) compared to Lake Superior (210 ± 20 pg/L). Methylmercury levels were below the detection limit in Lake Michigan. Larger sample volumes were collected to lower detection limits in Lake Superior in 2006 and methylmercury levels averaged 7 ± 6 pg/L. Dissolved gaseous mercury concentrations were also higher in Lake Michigan (27 ± 7 pg/L) compared to Lake Superior (14 ± 8 pg/L). Evasional fluxes were estimated using a two-film model for air–water exchange. The annual evasional flux in Lake Michigan was determined to be ~ 380 kg/yr from Lake Michigan and ~ 160 kg/yr from Lake Superior. Total mercury burdens in each lake were estimated to be ~ 2500 kg in Superior and ~ 2100 kg in Lake Michigan demonstrating that evasional fluxes play an important role in the mass balance of each lake, particularly Lake Michigan. A simple first-order mass balance model demonstrates the importance of air–water exchange and sedimentation as primary removal processes for Hg in each lake. Uncertainties in the mass balance model are highlighted due to lack of key data, particularly in Lake Superior.     

Silica Depletion in Lake Victoria: Sedimentary Signals at Offshore Stations

Six short sediment cores from offshore stations in Lake Victoria (East Africa) were analyzed for evidence of recent change in the lake's pelagic ecosystem. Three stations were located on a NW-SE transect between 48 m water depth, near the present upper limit of seasonal hypolimnetic oxygen depletion, and the deepest point of Lake Victoria at 68 m. Four stations formed a NE-SW transect across the east-central zone of maximum Holocene sediment accumulation below 64 m water depth. ^2I0Pb dating of two cores from deepwater stations established average recent sediment-accumulation rates of 0.032 ± 0.001 g/cm²/yr and 0.028 ± 0.001 g/cm²/yr. Although the deepest part of the basin has been subject to an event of possibly widespread sediment erosion dated to the mid-1920s, core correlation based on the stratigraphy of biogenic Si above this unconformity indicates that deepwater stations have accumulated representative high-resolution archives of lake history over the past 70 years. The sedimentary record of biogenic-Si accumulation in deepwater cores reflects a sequence of events in which progressive enrichment of Lake Victoria with essential nutrients other than Si first led to increased diatom production, until the combination of excess Si demand and greater burial losses of diatom-Si resulted in depletion of the dissolved-Si reservoir and a transition to Si-limited diatom growth. Available sediment chronologies infer that increased diatom production in offshore areas started between the 1930s and early 1950s, and that the recently documented phytoplankton transition to year-round dominance by cyanobacteria started in the late 1980s. Excess diatom production over the past half century has led to significantly higher burial losses of biogenic Si only in the depositional center of the basin at water depths below 60 m.     

Mapping the spatial changes in Lake Volta using multitemporal remote sensing approach

Lake Volta is the world's largest man‐made lake by surface area, and the fourth largest by water volume. Located completely within Ghana, it has a surface area of about 8502 km² (3283 square miles). Like many other lakes on the African continent, Lake Volta is a major natural resource for Ghana, storing water for the operation of the hydroelectric dam, water supply for domestic, agricultural and industrial purposes, habitat for diverse aquatic species, an avenue for recreational activities, means of navigation between the north and south parts of the country, and a climate modulator for the tropical region. The lake has experienced variable water level and surface area changes attributable to climate change and excessive water abstractions. Using histogram thresholding techniques, this study produced binary images and vector maps of the lake. Spatial extent mapping of the lake using Landsat TM 1990, ETM + 2000 and ETM + 2007 images indicated the lake experienced both increased and decreased surface area changes during the study period. The lake's surface area varied by about 197 km² between 1990 and 2007, with the water level fluctuating between ±7 m. Factors thought to be contributing to these changes include human factors (regulated flows, deforestation, increased water abstractions and pollution) as well as natural phenomenon (climate change, water run‐off and subsequent sediment transport).     

Depth and temperature selection of lake charr (Salvelinus namaycush) ecotypes in Lake Superior revealed by popup satellite archival tags

Lake charr exhibit morphological diversity in large North American lakes, largely attributed to habitat partitioning. Bathythermal habitats of lean lake charr have been assessed but remain largely unknown for other lake charr ecotypes. Popup satellite archival tags (PSATs) were used to determine depth and temperature profiles of lean (n = 15), siscowet (n = 16) and redfin (n = 3) lake charr ecotypes in Lake Superior during segments of the year. Monthly median depths of leans were < 20 m throughout the year while the median depth of redfins was 24–32 m (June-September). Monthly median depth of siscowets ranged from 103 to 204 m but they exhibited four distinctive patterns: deep (>80 m), shallow (<10 m), extreme vertical movements (>80–0 m), and high frequency vertical movements between 100 and 125 m. Siscowets were the most stenothermal with habitat temperatures generally 4–5 °C but not exceeding 12 °C. Leans were found as low as 0 °C (January-March) and up to 15 °C (July-September). Median monthly habitat temperatures for redfins were 1–3 °C colder than leans during July-September. PSATs confirmed that siscowets exhibit extreme vertical movements and may feed near the surface. The timing and duration of the extreme vertical movements exhibited by siscowets did not appear to be associated with time of day (i.e., not diel vertical movements) and may be described as opportunistic movements presumably related to foraging. Data obtained from the PSATs reinforces the view that lake charr are highly adaptive and can thrive in cold, oligotrophic lakes by optimizing the use of the entire water column.     

Impact of Lake Michigan water level rise on complex bidirectional flow in the Chicago Area Waterway System (CAWS)

In the past decade, continuously rising water levels in Lake Michigan have been threatening lakefront areas, especially in metropolitan regions like the Greater Chicago area. This provides the motivation to analyze the impact that high lake levels have on the Chicago Area Waterway System (CAWS). As the only primary free connection between the CAWS and Lake Michigan, the Calumet Area waterway subsystem plays a key and unique role. In this work, a numerical model covering the Calumet subsystem and having Lake Michigan as a boundary condition, is set up, calibrated, and validated using limited field observations. It is found that the Calumet subsystem has become bidirectional, where both discharge and flow directions are controlled by lake levels. When lake levels are below −0.15 m (-0.5 ft, Chicago City Datum, CCD), the discharge in the Grand Calumet River is around zero, with water flowing along its east branch towards Indiana. When lake levels are above +0.46 m (+1.5 ft, CCD), the flow reverses direction and drains west into Illinois. In 2020, the mean lake-level was at +1.07 m (+3.5 ft, CCD), and the base discharge in the Grand Calumet River was approximately 8.5 m³/s (300 ft³/s). The higher Lake Michigan’s level is, the larger the discharge would be into Illinois. Potential impact of this extra discharge on Lake Michigan Diversion Accounting (LMDA) of the State of Illinois and flood management in the Chicago Sanitary and Ship Canal (CSSC), is analyzed; while the nature of the bidirectional flows is characterized with the intent of shedding light on this complex phenomenon.     

Assessment of lake–groundwater interactions and anthropogenic stresses,using numerical groundwater flow model,for a Rift lake catchment in central Ethiopia

A steady-state groundwater flow model (MODFLOW) was used to study lake and groundwater interactions in a complex rift volcanic catchment. It also was used to assess the effects of water pumping from wells, and of variable recharge rates associated with climate and lake level changes, on the dynamics of the volcanic aquifers surrounding Lake Awassa. The model simulations were made after first developing a reasonable conceptual model, on the basis of conventional hydrogeological mapping, pumping test and hydrometeorological data analyses, and from ancillary information obtained from hydrochemical and isotope techniques. The model results indicated that the lakes and Rift aquifers are fed by large groundwater inputs that originate in the highlands. The lakes and rivers have important roles in recharging the aquifers in some locations. Lake Awassa receives a major groundwater inflow from its southern and eastern shorelines, while substantial water leakage from the lake occurs along the northern shoreline. The annual groundwater outflow from the catchment is estimated to 52.5 × 10⁶ m³. Scenario analyses revealed that increasing the current pumping rate from wells by fourfold will substantially reduce the groundwater level substantially, although the regional flow pattern would remain the same. There appears to be no immediate danger to the Rift aquatic environment from the current water pumping rate. Drying the small Lake Shalo and associated swamps, however, will cause a large change in the water balance of the larger Lake Awassa. Slight changes in groundwater recharge can cause large differences in groundwater levels for most of the Rift caldera floor far from the lake shores. This study provides a reasonable foundation for developing detailed transient predictive models, which can then readily be used as a decision support tool for development and implementation of sustainable water resources practices.     

Barrier beaches and breaches: Historical changes on the Point Pelee foreland

The Great Lakes are non-tidal, but experience significant water level fluctuations at hourly, seasonal, and decadal scales. A rise of 0.83 m was observed between 2013 and 2020 on Lake Erie with the annual water level near the previous record high of 174.89 m set in 1986. In response to elevated water levels, barrier beach-ridges located on the eastern shore of the Point Pelee foreland, in the Lake Erie’s central basin, experienced accelerated erosion including overwash and breaching, removal or burial of vegetation, and damage to infrastructure and sensitive habitat. Historical aerial imagery between 1931 and 2020 and annual average lake levels between 1920 and 2020 were examined to characterize barrier retreat and breach initiation, expansion, and closure. Results indicate that the barriers have transgressed at a rate of >1 m y⁻¹, but the rate of transgression and progradation, overwash, and breaching are dependent on decadal-scale variations in water level. Ephemeral breaches and delta deposits were found to be a significant source of landward sediment transport if breaches remained open for multiple years. This may represent a self-reinforcing cycle that promotes breach fill-in processes, even during high lake levels, and increases the barrier width and resiliency in response to further lake level fluctuations. While common patterns of barrier dynamics were found throughout the time series, human impacts may modify historic barrier transgression rates and breach and recovery processes.     

Landscape Evolution and Deglaciation of the Upper Peninsula,Michigan: An Examination of Chronology and Stratigraphy in Kettle Lake Cores

We propose a radiometric chronology bracket for the last glacial advance/retreat, called the Marquette readvance, in the Upper Peninsula of Michigan (Upper Peninsula) using organic material from kettle lakes and previously published age determinations on wood buried by glaciofluvial sediments. The lakes are located both inside and outside the ice-contact margin of the Marquette readvance. Wood buried in glaciofluvial sediments from the Marquette readvance was previously dated at 10,025 ± 100 ¹⁴C yr BP (Hughes and Merry 1978, Lowell et al. 1999, and Pregitzer et al. 2000). Ackerman Lake, a kettle lake located inside the ice-contact margin, yielded a basal radiocarbon date of 9,495 ± 70 ¹⁴C yr BP representing the time of organic accumulation after ice retreat. These dates above and below the glacial deposit bracket the age of the Marquette readvance/retreat to 360–700 ¹⁴C yr, or the midpoint of 530 ¹⁴C yr. Ackerman Lake yielded multiple radiocarbon dates, including an average date of 8,811 ± 11 ¹⁴C yr BP (9,736–9,913 cal yr BP) at a change in stratigraphy from red clay to gray silt. This transition along the northern Upper Peninsula is interpreted to represent ice sheet retreat into Lake Superior and the reworking of older glacial sediments by ∼8,500 ¹⁴C yr BP. Organic material from the kettle lake sediments spanning multiple geomorphic locations (both inside and outside of the ice-contact margin) and previous radiocarbon dates from the entire Upper Peninsula yielded dates concentrating around 9,500 ¹⁴C yr BP. We attribute this synchronous organic accumulation in the Upper Peninsula to be a result of climatic signature corresponding with the Preboreal Oscillation, so the duration of the Marquette glacial cover may have been less then implied by the Ackerman Lake basal age.     

The Effects of Groundwater and Surface Water Use on Total Water Availability and Implications for Water Management: The Case of Lake Naivasha, Kenya

This study discusses the effects of water abstractions from two alternative sources on the available water volume around Lake Naivasha, Kenya: the lake itself and a connected aquifer. An estimation of the water abstraction pattern for the period 1999–2010 is made and its effect on the available water volume in Lake Naivasha and its connected aquifer is evaluated using a simple water balance modeling approach. This study shows that accurate estimates of annual volume changes of Lake Naivasha can be made using a simple monthly water balance approach that takes into account the exchange of water between the lake and its connected aquifer. The amount of water that is used for irrigation in the area around Lake Naivasha has a substantial adverse effect on the availability of water. Simulation results of our simple water balance model suggests that abstractions from groundwater affect the lake volume less than direct abstractions from the lake. Groundwater volumes, in contrast, are much more affected by groundwater abstractions and therefore lead to much lower groundwater levels. Moreover, when groundwater is used instead of surface water, evaporation losses from the lake are potentially higher due to a larger lake surface area. If that would be the case then the overall water availability in the area is more strongly affected by the abstraction of groundwater than by the abstraction of surface water. Therefore water managers should be cautious when using lake levels as the only indicator of water availability for restricting water abstractions.     

Density and habitat use by the round goby (Apollonia melanostoma) in the Bay of Quinte,Lake Ontario

We assessed round goby (Apollonia melanostoma) density and size structure in two sections of the Bay of Quinte (Lake Ontario) that had been invaded by this species two years apart. Round goby density was assessed with 50 m linear transects, recorded with an underwater video recording apparatus developed for this study that included a depth sounder for maintaining a fixed distance above the substrate. The highest mean round goby densities were observed in the shallowest depth zone (1.5–3 m) at both sites, but there were differences between the sites in the habitat types where the highest densities occurred and there were no significant density differences among habitat types at either site (rock with sparse vegetation, mud with sparse vegetation, sand/mud with moderate vegetation cover). In the upper bay, mean body length of round gobies declined with depth, whereas in the lower bay, mean round goby length was greatest in the deepest zone. Mean body length of round gobies did not differ significantly by habitat type in either section of the bay.