Urban pocket-beach morphodynamics along the wave-dominated southwest coast of Lake Michigan: An analysis of shoreline and sand volumetric changes

Many of the world’s beaches are embayed, but while a large body of work addresses the geomorphology of pocket beaches in oceanic settings, little is known about urban analogs, especially within the Great Lakes of North America. Groins and jetties shelter these systems from direct interaction with littoral processes, which elsewhere can influence how changes in lake level, winter-ice cover, and wave climate impact beach evolution. We address the direct controls of these forcing parameters on beach morphodynamics over a 33-yr period at North Point Beach, which is confined to an engineered ‘container’ along Lake Michigan’s wave-dominated SW margin. Analysis of near-annual beach change suggests lake-level change is the dominant geomorphic driver over inter-annual to decadal timeframes, with winter ice playing a secondary role. Pocket-beach shoreline positions were found to be unreliable indicators of sand volumetric changes. Lake-level rise facilitated shoreline retreat and overwash-induced beach accretion while high lake levels created the accommodation for additional sands to enter the embayment. This is important for coastal managers to consider when developing mitigation strategies for ongoing lake-level fluctuations and anticipated regional climate impacts. This foundational assessment has implications for embayed beaches of the greater Chicago coastal margin (n > 20), where many other site-specific variables (e.g., groin orientations and shoreline aspect) may factor into nearshore and onshore beach morphodynamics. Continued research into urban pocket beaches of the Great Lakes stands to offer useful information on the impacts of littoral fragmentation on coastal sediment routing during different lake-level phases and degrees of littoral interconnectivity.     

Great lakes urban pocket-beach dynamics: A GIS-based analysis of infrastructure-design influences on geomorphic development

Chicago’s lakefront beaches experienced inundation and coastal erosion when Lake Michigan’s mean annual water level rose by >1.5 m between 2013 and 2019. Understanding beach geomorphic response to this type of lake-level event is important, as future climate predictions call for a continuation of decadal oscillatory patterns. A GIS-based study of beach change was conducted along the city’s urban lakefront, where sand is embayed by groins, jetties, and revetments. Morphologic changes associated with the most recent decadal lake-level rise were evaluated in context of the surrounding infrastructure. Beach morphometrics, derived from historical aerial images and available LiDAR products, were compared against the characteristics of the fixed urban infrastructure. Overwash volumes associated with an ～1 m-rise in lake level scaled well with beach size (R² = 0.88), suggesting that the creation of new sediment accommodation and its spatial distribution along the urban lakefront during lake-level rise is an important control on beach morphodynamic behavior. Overwash patterns were influenced by embayment orientation and groin characteristics. Counterclockwise beach rotation of up to 21° occurred in places where shorelines were exposed to the open lake. More tightly enclosed beaches retreated more uniformly along strike due to passive inundation of terrain with lake-level rise. Our insights provide managers with useful information on key beach behavioral patterns and how they are influenced by infrastructure design, allowing for the possibility of mitigation strategies to be emplaced in anticipation of future lake-level oscillations.     

Dynamics of beach-ridge formation along a migrating strandplain with implications for paleo-environmental assessment,Illinois Beach State Park,southwestern Lake Michigan

This paper provides insights into shoreline morphodynamics and ridge-plain physiographic compartmentalization along the migrating Zion Beach-ridge Plain, a mainland-attached strand along the high-energy, wave-dominated SW coast of Lake Michigan. Results of UAS-based topographic monitoring during the recent decadal lake-level high (2018–2020) captured the earliest phase of the ridge-formation process along several beach sites. This process-based study of net-erosional (i.e., littoral updrift) and net-accretionary (i.e., littoral downdrift) parts of the system offers much-needed context for assessing relict strand architectures. Embayed beach-ridge plains of the Laurentian Great Lakes have long served as paleo-environmental archives. They form from water-level changes and can be used to interpret isostacy. The preservation of beach ridges here is facilitated by unidirectional infilling. Much less is known about how nearshore littoral processes impact unconfined strand systems and whether useful paleoenvironmental information absent within embayed system analogs might be elucidated from their complex architecture. We herewith promote a model of punctuated development. Major episodes of shoreline transgression are manifested as continuous ridgelines of topographic prominence that, along the northern, erosive strand, truncate older ridges and are onlapped by younger ones. These major discontinuities reflect environmental changes greater in magnitude than decadal water-level oscillations observed to have formed ridgelines in recent decades. The temporal offset across the most lakeward of these major erosional strandlines is on the order of 1 kyrs and it formed between 1.8 ka and 0.9 ka, based on available C-14 ages, coincidental with a regional shift in dominant storm-wind pattern to one promoting higher-energy littoral dynamics.     

Mid Holocene lake level and shoreline behavior during the Nipissing phase of the upper Great Lakes at Alpena, Michigan, USA

The Nipissing phase was the last pre-modern high-water stage of the upper Great Lakes. Represented as either a one- or two-peak highstand, the Nipissing occurred following a long-term lake-level rise. This transgression was primarily an erosional event with only the final stage of the transgression preserved as barriers, spits, and strandplains of beach ridges. South of Alpena, Michigan, mid to late Holocene coastal deposits occur as a strandplain between Devils Lake and Lake Huron. The landward part of this strandplain is a higher elevation platform that formed during the final stage of lake-level rise to the Nipissing peak. The pre-Nipissing shoreline transgressed over Devils Lake lagoonal deposits from 6.4 to 6.1 ka. The first beach ridge formed ~ 6 ka, and then the shoreline advanced toward Lake Huron, producing beach ridges about every 70 years. This depositional regression produced a slightly thickening wedge of sediment during a lake-level rise that formed 20 beach ridges. The rise ended at 4.5 ka at the Nipissing peak. This peak was short-lived, as lake level fell > 4 m during the following 500 years. During this lake-level rise and subsequent fall, the shoreline underwent several forms of shoreline behavior, including erosional transgression, aggradation, depositional transgression, depositional regression, and forced regression. Other upper Great Lakes Nipissing platforms indicate that the lake-level change observed at Alpena of a rapid pre-Nipissing lake-level rise followed by a slower rise to the Nipissing peak, and a post-Nipissing rapid lake-level fall is representative of mid Holocene lake level in the upper Great Lakes.     

Reduced sediment export to the Pennsylvania Lake Erie littoral zone during an era of average lake levels

This paper analyzes high-resolution lidar data to estimate sediment export to the Pennsylvania Lake Erie littoral zone from lakefront bluff retreat under relatively unique lake-level conditions: approximately a decade of average lake level transitioning into a mild transgression. Analysis identifies bluff-failure patterns important to coastal hazard planning, possible feeder-bluff conservation areas to preserve sediment supply, and data pertinent to sand management in the western Erie County littoral cell (WECLC) and at Presque Isle State Park in the next-downdrift cell.Based on 2007–2015 bluff-face mapping, there were net losses of 318,250 m³ of total-sediment and 105,700 m³ of sand+ (sand-boulders) to the littoral zone. On an average annual basis, bluffs thus exported 39,800 m³ of total-sediment and 13,300 m³ of sand+ to the WECLC. Exports of sand+ by six HUC-12 watersheds ranged from ~0 to 4600 m³/yr, with ~ 30% supplied by Crooked Creek watershed bluffs that occupy only 18% of the coast. Sand+ export volumes reported here were ~65% lower than prior research covering different lake-level phases. Understanding sediment export during periods of average lake level is important because such lake-level phases occur in the record and will likely recur. Incorporating a decade-scale low sediment-supply scenario for sand management in the Presque Isle littoral cell would permit fine-tuning of estimates of sand nourishment needed to mitigate ongoing beach erosion. Uncertainty in bluff-face change can be minimized by expanding data-comparison windows; future tracking of sediment export from Pennsylvania bluffs may not need lidar surveys any more frequently than once every 10–15 years.     

Factors influencing microplastic abundances in nearshore,tributary and beach sediments along the Ontario shoreline of Lake Erie

Sediment samples were collected from nearshore, tributary and beach environments within and surrounding the northern part of Lake Erie, Ontario to determine the concentrations and distribution of microplastics. Following density separation and microscopic analysis of 29 samples, a total of 1178 microplastic particles were identified. Thirteen nearshore samples contained 0–391 microplastic particles per kg dry weight sediment (kg^?1), whereas 4 tributary samples contained 10–462?kg^?1 and 12 beach samples contained 50–146?kg^?1. The highest concentrations of nearshore microplastics were from near the mouths of the Detroit River in the western basin and the Grand River in the eastern basin, reflecting an urban influence. The highest microplastic concentrations in beach samples were determined from Rondeau Beach in the central basin where geomorphology affects plastics concentration. The Welland Canal sample in the eastern basin contained the greatest concentration of microplastics of the tributary samples, which is consistent with high population density and shipping traffic. The overall abundance of microplastic in northern Lake Erie nearshore, tributary and beach samples is 6 times lower than in sediment sampled from northern Lake Ontario. The nearshore and beach sample results potentially reflect the transport patterns of floating plastics modeled for Lake Erie, which predict that the majority of plastic particles entering the lake are transported to southern shoreline regions rather than northern areas.     

A field study of nearshore environmental changes in response to newly-built coastal structures in Lake Michigan

In this study, we monitored changes of cohesive nearshore environment including bluff and lake bottom/bed response to newly-built coastal structures with a thousand-meter-long revetment in Lake Michigan shoreline over a six-year study period. Sequential aerial photos showed that excessive slumping occurred only on the south bluffs and no bluff recession in the middle areas with coastal structures. Field measurements using our recently developed integrated geophysical techniques provided information on bathymetry, sand layer thickness, and lakebed downcutting over the nearshore reach of Concordia University in Lake Michigan. During the study period, the bathymetry profiles at the study site fluctuated dynamically, especially in the regions outside the shoreline structures, suggesting continuous and ongoing sediment erosion and deposition. The lakebed downcutting in front of the newly-built coastal structures is correlated with CWIH (cumulative wave impact height). Significant differences of lakebed downcutting in the north and south natural beach regions were revealed and may be associated with the nearshore sediment budget. The southwardly dominant longshore current maintains the equilibrium state of beach profiles in the north region, but the coastal structures prevent sediment supply from the well-protected bluffs in the middle region to the south region. The possible source of sediment supply in the south region is therefore from lakebed or bluff materials, supported by excessive bluff failures and lakebed downcutting. Overall the newly-built coastal structures seem to pose negative impacts on bluff stability at the south shore of the coastal structures.     

Measuring and modelling nearshore recovery of an eroded beach in Lake Michigan,USA

Erosion by storms and high-water levels impacts large enclosed basins; however there have been few attempts to numerically model cumulative impacts in large lakes. Antecedent morphology is a large determinant of coastal sensitivity to storms, so capturing the beach recovery is important for overall vulnerability assessment. To study beach recovery, we apply the numerical model XBeach to simulate a period of low to moderate wave energy when beach recovery typically occurs. Surveys were conducted one month apart during summer of 2020 on the west coast of Lake Michigan and used to initiate model runs and evaluate model performance. XBeach was used to propagate offshore wave conditions from a Great Lakes Coastal Forecasting System (GLCFS) node ～1 km offshore into the nearshore, and results were compared to measurements from a nearshore pressure sensor. We tested for the optimal value of the asymmetry/skewness parameter (facua) for model-data convergence. We evaluated model skill using a Mean Square Error Skill Score (MSESS) and a decomposition. In our repeat surveys we observed slight landward migration of longshore bars and the initiation of bar welding to the shoreline but, overall, changes in bathymetry were small. We found that XBeach transforms offshore waves well and sediment transport volume was accurately predicted by the model. However, XBeach did not capture the morphologic evolution under low energy conditions, preventing simulation of beach recovery. Overall, higher values of facua resulted in improved skill scores and modeled nearshore morphology that was more similar to the morphology measured in our surveys.     

Cumulative Habitat Impacts of Nearshore Engineering

A multi-disciplinary, multi-institutional research team evaluated a broad range of physical and biological characteristics at six Great Lakes nearshore sites in order to develop and test a conceptual modeling framework to assess linkages between bluff erosion, sediment supply, coastal processes, and biological utilization of nearshore and coastal habitats. The sites were chosen to represent a broad range of hydrogeomorphic conditions, with the objective of assessing the response of these nearshore systems to anthropogenic modifications and coastal change. As a result of this 2-year field effort, new methods and integrated approaches were developed to characterize, map, and assess the dynamic nature of the nearshore zone (area generally less than 10 m water depth). Thus, these data provide an initial quantitative assessment of nearshore change. In addition, our data indicate that shoreline modifications have led to cumulative impacts that have irreversibly modified Great Lakes nearshore coastal habitats and the processes that create and maintain them. Of special note is our observation that altered nearshore substrate dynamics resulting from shoreline modifications may enhance the colonization success of lithophilic aquatic invasive species in nearshore areas of the Great Lakes. Continued development of the shoreline may exacerbate changes in Great Lakes nearshore food-web structures and ecosystem services. Further study and monitoring of these phenomena are needed, and our work suggests that a holistic, multidisciplinary approach is necessary to develop effective management strategies to address these and other issues affecting nearshore areas of the Great Lakes.     

Delineating spatial distribution and thickness of unconsolidated sand along the southwest Lake Michigan shoreline using TEM and ERT geophysical methods

Erosion and accretion of various magnitudes occur along the southwest Lake Michigan shoreline. These processes are triggered by natural events and human activities, which affect the distribution and thickness of sand on the nearshore lake bottom. Significant erosion along the Illinois coastline has highlighted the need for a large-scale means of acquiring spatially rich data to build models of sand distribution along the entire shoreline. Thus, we implemented a high-resolution airborne transient electromagnetic (TEM) method, coupled with a ground-based electrical resistivity tomography (ERT) method to determine the sand distribution and thickness along the shore from the beach to ~1 km into the lake. From Kenosha, Wisconsin, to Chicago, Illinois, we acquired 1049 line-km of TEM data, and 13.43 line-km of ERT data. Our results indicated a distinct, uneven distribution and thickness of the unconsolidated sand unit covering the southwestern Lake Michigan shoreline. The unconsolidated sand unit was found to range in thickness from 0 to ~12 m. This unconsolidated sand unit was shown to be thickest (4.5 to ~10 m) in the northern part of the study site. In southern Wisconsin and Chicago, the sand layer beneath the water column was found to be very thin, ≤1 m. We propose, based on our analysis, that lake-bed conditions and wind direction are the main factors that limit southward littoral transport. Our data suggest that the current state of the shoreline is relatively analogous to how it has always behaved; however, anthropogenic disturbance has exacerbated the natural patterns of erosion and accretion.     

Coastal geomorphic response to seasonal water-level rise in the Laurentian Great Lakes: An example from Illinois Beach State Park,USA

Hydrodynamic processes, such as fluctuating water levels, waves, and currents, shape coastlines across timescales ranging from minutes to millennia. In large lacustrine systems, such as the Laurentian Great Lakes, the role of water level in driving long-term (centuries to millennia) coastal evolution is well understood. However, additional research is needed to explore short-term (weeks to months) beach geomorphic response to fluctuating water level. Developing a process-focused understanding of how water level fluctuations shape coastal response across these shorter time scales is imperative for coastal management. Here, we present measurements of geomorphic response along a lacustrine beach ridge plain to seasonal water level fluctuations during a decadal high-stand in Lake Michigan water level. Frequent topographic change measurements revealed high spatial and temporal variability in geomorphic response to rising lake level. Sites immediately downdrift of shore protection began to erode immediately as lake level increased. The co-occurrence of peak seasonal lake levels and a modest increase in wave energy resulted in erosion and overwash at sites that resisted erosion during the initial seasonal rise in lake level. None of the sites in this study returned to their initial morphology following seasonal lake level rise. Given that peak water levels were nearly identical in 2017 and 2018, yet the majority of erosion at our sites occurred in 2017, we postulate that erosion associated with seasonal lake level rise is primarily a function of the change in annual maximum water level from year to year, rather than solely the elevation of the water level.     

Nearshore Community Characteristics Related to Shoreline Properties in the Great Lakes

Successful protection and restoration of Great Lakes nearshore ecosystems will likely rely on management of terrestrial resources along Great Lakes shorelines. However, relationships between biological communities and changing shoreline environmental properties are poorly understood. We sought to begin understanding the potential roles of shoreline geomorphological and land cover properties in structuring nearshore biological communities in the Laurentian Great Lakes. Despite high variability in densities (benthic macroinvertebrates and zooplankton) and catch per unit effort (CPUE, shallow water and nearshore fish) within and among lake areas, several biological community patterns emerged to suggest that nearshore aquatic communities respond to shoreline features via the influences of these features on nearshore substrate composition and stability. Benthic macroinvertebrate densities were not different between shoreline types, although they were generally lower at nearshore sites with less stable substrates. Shallow water fish CPUE and zooplankton densities were generally lower for nearshore areas adjacent to developed mid-bluff shorelines and sites characterized by less stable substrates. Larger fish CPUE appeared to be unresponsive to local shoreline and substrate properties of nearshore zones. The emergence of these patterns despite significant ecological differences among lake areas (e.g., productivity, community composition, etc.) suggests that shoreline development may have comparable influences on nearshore ecosystems throughout the Great Lakes, providing a terrestrialbased indicator of relative nearshore biological and ecological integrity.     

Littoral drift by alongshore flow at Visakhapatnam – East Coast of India

The littoral drift in the surf zone of Visakhapatnam has been evaluated using simulated longshore current. In this study we examined littoral processes, driven by longshore currents using a set of numerical models (Mike-21 modeling system). Deepwater waves as they approach shallow water dissipate energy and the water from the broken waves flow parallel to the shoreline known as longshore current. In order to simulate the current from wave breaking, offshore wave data for the period 1995–2004, have been collected from British Meteorological Office (BMO), UK. Waves having an annual exceedance of 20% are allowed to propagate to nearshore using a nearshore spectral wind-wave model from predominant directions. The wave-induced radiation stress obtained from wave model then formed the basis for simulating the longshore current and associated sediment transport. The results of these simulations show the pattern of longshore flow and sedimentation. The net annual discharge at selected coastal stretches is estimated and presented. It has been inferred from the study that the sediment transport for the coast is of the order of 0.4–0.6 million m³/year.     

Controls on the geomorphic response of beach-dune systems to water level rise

This paper offers a synthesis of the disparate evidence on the importance of the magnitude and duration of water level rise in both lacustrine and marine environments in relation to other long-term controls on coastal response (e.g., wind climatology, vegetation growth, geological context). A brief review of two 'equilibrium profile' models (i.e., the Bruun and RDA models) is provided as a conceptual foundation before considering a range of complicating factors that are important to determining how sandy coasts may evolve in the future under rates of relative water level rise (RWLR) similar to recent increases in sea level. Key processes controlling beach-dune interaction are reviewed, especially the rates of morphodynamic action relative to the inundation potential driven by water level increases, leading to the conclusion that transgression distances due to RWLR are small in comparison to characteristic shoreline excursions driven by storm events and subsequent reconstruction phases. Much of the available evidence suggests that the beach and foredune (together with the nearshore profile) will migrate landward intact, keeping pace with relatively slow rates of RWLR similar in magnitude to those predicted by current sea-level scenarios. However, the documented response of shorelines in the Great Lakes to several episodes of relatively rapid rates of RWLR over a period of about a decade indicates that landward migration of the foredune through aeolian processes may be too slow to keep pace with this magnitude of shoreline transgression, and therefore the foredune will be over-run by the translating beach and nearshore profile.     

Repeat photography of Lake Michigan coastal dunes: Expansion of vegetation since 1900 and possible drivers

Coastal dunes are prominent features along the Lake Michigan shoreline, especially along Michigan’s Lower Peninsula. Numerous studies in recent years have reconstructed the geomorphic history of these dune systems, from their initial formation in the mid-Holocene to about 300 years ago. These studies have suggested linkages between past dune behavior and climatic variability and fluctuating lake levels. Less is known, however, about how these dune systems change on shorter-temporal scales in the modern era and the potential drivers of that change. Using repeat photography, this paper attempts to demonstrate how the coastal dunes of Lake Michigan’s eastern shore have changed since the 19th century. We collected hundreds of photographs of these dunes, taken between the years 1885 and 2018, from archives and citizen scientists. In the spring and summer of 2019, we took ∼70 new photographs replicating the original images. The changes between coastal dune conditions in the original photographs and in the 2019 photographs show a general expansion of vegetation across formerly barren and active surfaces along the entire shoreline. Although human development has also played a role in reshaping the coastal dune systems, the most pronounced difference between historical and current dune conditions where repeat photography was conducted is the expansion of vegetation – grasses, shrubs, and even trees. Here, we present the 20 photograph pairs most representative of these trends, explore these changes, and discuss the likely causes, including the increase in precipitation in Michigan in the past  ∼80 years.     

Multiscale relationships between Great Lakes nearshore fish communities and anthropogenic shoreline factors

The multi-scale nature of streams, rivers, and inland lakes is well documented, although relationships between the ecology of Great Lakes nearshore areas and shoreline processes are generally poorly described. Given the high levels of development pressure currently exerted on Great Lakes shorelines, we sought to determine whether patterns exist between measures of shoreline development quantified at multiple spatial scales and adjacent fish community measures. We expected that fish measures for nearshore areas immediately adjacent to intact versus modified shorelines would differ as a result of the greater buffering capacity of the intact shorelines. Further, we expected anthropogenic shoreline factors to act cumulatively in combination with prevailing currents to influence fish communities in downdrift nearshore areas. Our results indicated that a few shallow water and nearshore fish community measures exhibited significant patterns that may be attributable to immediately adjacent shoreline characteristics. In addition, several fish measures were related to urban-residential land uses and shore structure numbers of updrift shoreline areas, suggesting that cumulative anthropogenic factors operating over larger spatial scales also influence local fish communities. Based on these results, we argue that there is critical need for multi-scale management strategies for shorelines that address the potential for both local and cumulative, larger-scale environmental impacts relative to local nearshore biota.     

Iron cycling in a littoral freshwater beach: Implications for floc trace metal dynamics

This field-based study demonstrates that highly dynamic trace metal (Ag, Co, Cu and Pb) behavior in suspended floc and the sediment surface fine-grained lamina (SFGL) is linked specifically to Fe mineral cycling between these two compartments driven by rapidly fluctuating energy regimes in a shallow, littoral beach of Lake Ontario. Results reveal distinct, Fe mineral controls on trace metal sequestration patterns under quiescent conditions. Higher metal sequestration occurred in floc associated with amorphous Fe oxyhydroxides (FeOOH), while less reactive crystalline Fe oxides (FeOx) dominated bed metal sequestration. Spatial shifts in energy regime governing floc settling and sediment erosion controlled the mixing of FeOOH and FeOx, resulting in discernible, hydrodynamic-dependent floc and SFGL trace metal associations. Low turbulence offshore limited compartment mixing, resulting in enrichment of FeOOH and metals in floc and SFGL over bulk bed sediments. In contrast, higher turbulence nearshore increased bed erosion resulting in less distinct floc and SFGL-FeOOH/metal abundances and partitioning. Diurnal shifts in energy regime impacting floc and SFGL geochemistry were observed nearshore. Accumulation of FeOOH and trace metals occurred in the SFGL under calm morning conditions, while diurnal wind-induced waves rapidly re-cycled the SFGL back into the overlying water-column. Post mixing, re-suspended FeOOH and smaller floc particulates entrained within a higher photosynthetically-induced pH water-column increased overall floc trace metal uptake. Taken together, these findings demonstrate highly dynamic linkages between energy regime and physico-chemistry impacted Fe mineral cycling resulting in observable compartment-specific trace metal partitioning patterns for littoral floc and surficial sediments in beach environments.     

Escherichia coli (E. coli) distribution in the Lake Malawi nearshore zone

Residents along the shoreline of Lake Malawi depend on nearshore water for drinking, cooking, and bathing. Despite the importance of clean nearshore waters to public health, we are aware of no published studies of shoreline water quality in the lake. To address this gap, we explore seasonal and temporal trends of the fecal indicator bacteria Escherichia coli (E. coli) in nearshore water and sand. E. coli concentrations in sand ranged from 0 to 17,600 colony forming units (CFU)/100?ml, and in water concentrations ranged from 0 to 21,200?CFU/100?ml. Fifty-three percent of water samples exceeded the U.S. Environmental Protection Agency Recreational Water Quality Criteria of 126?CFU/100?ml, and 90% exceeded the World Health Organization drinking water standard of 0?CFU/100?ml. Distance from shore was the variable most predictive of E. coli concentration, with the level of beach use also playing a significant role. At 15?m from the shore, E. coli concentrations dropped to between 0.3% and 17% of shoreline values. Results suggest that the collection of water at distances >15?m from the beach could substantially decrease exposure to fecal bacteria. Further studies are needed to identify sources of fecal pollution and to determine the utility of E. coli as a predictor of the potential for waterborne disease.     

Fine-scale nutrient enrichment and water quality on the rural shores of Southeast Lake Huron

Recently, there has been public concern that water quality in the nearshore of Southeast Lake Huron has been deteriorating, inferred partly from fouling of shoreline by algae. In 2010, fine-scale patterns in nutrient concentrations and other water quality features were examined to better understand the influence of the adjacent land on the nearshore environment in the region. Surveys at two areas of coastline were conducted over a seasonal cycle. Monitoring of water quality in tributaries to the study areas indicated that water of poor quality was periodically discharged to the lake as indicated by elevated levels of nutrients, fecal indicator bacteria, suspended solids and chloride. The extent of the nearshore that was directly influenced by land runoff was small, restricted to the shoreline fringe, relative to the broader nearshore. Pulse-like inputs of phosphorus from wave-induced erosional events and periods of precipitation-related runoff, both characterized by high levels of particle-bound phosphorus, contributed to highly dynamic and spatially variable levels of total phosphorus (TP), and proportions of TP in dissolved form, in the nearshore. The proportion of TP associated with particulate material was strongly correlated with lake depth. Phosphorus distributions in the nearshore indicate contrasting conditions with proximity to shoreline. Land runoff enriches nutrient levels along sections of the immediate shoreline, which contrasts sharply with the ultraoligotrophic conditions in the broader nearshore. The nearshore of Lake Huron arguably has always been highly sensitive to phosphorus pollution and it appears likely that the shoreline may be even more so today.     

Loading and lake circulation structures recurrent patterns of water quality on the Toronto – Mississauga waterfront of Lake Ontario

Urban centers line western Lake Ontario where urban rivers, wastewater treatment plants and stormwater load nutrients, major ions and suspended solids to the nearshore. In 2018, nearshore water quality and associated physical conditions bordering the cities of Toronto and Mississauga were assessed as a benchmark for future effects of urban growth and municipal infrastructure projects to improve water quality. Conductivity and UV-fluorescence were used as water quality surrogates and mapped over blocks of shoreline stratified by distance offshore. Patterns in UV-fluorescence aligned with loading points, and generally higher levels near the shoreline, were correlated with concentrations of nutrients, major ions and suspended solids. Water quality was more land-impacted over the shoreline from the Credit River to Humber Bay contrasting with the more lake-like conditions from Toronto Eastern Beaches to the Rouge River. Within Toronto Harbour, cross-harbour gradients in water quality varied with weather-related changes in river and storm water loading. Mixing areas at wastewater treatment plant outfalls and tributary mouths, frequently shaped by alongshore lake circulation, resulted in a mosaic of water quality over the shoreline. Area-wide elevation of chloride and conductivity, and poorer water quality in late spring, was linked to heightened river discharge. Thermal stratification affected how discharges were distributed in the water column, but measurements at the lake surface reflected the strongest overall land-effects on water quality. The patterns of temporal-spatial variability identified within geographically-defined areas of shoreline can be used as past footprints in future monitoring to detect change.