Groundwater conditions beneath beaches of Lake Huron, Ontario, Canada

Abstract

Groundwater flow conditions below beaches of Lake Huron have been examined at eight sites. Groundwater below beaches flows towards the lake throughout the year. However, water table conditions vary between beaches with a shallow water table (< 1 m) and beaches with a deep water table (> 2 m). Where the water table is deep, the water table across a beach will rise and fall proportionally to fluctuations in lake levels. The hydraulic gradient is essentially linear across a beach. Beaches with a shallow water table exhibit very little change in the elevation of the water table over time, do not fluctuate proportionally with lake level changes, and have a break in the hydraulic gradient at ∼ 20 m from shore. Long term and season fluctuations in the surface of Lake Huron will change the elevation and location of the groundwater discharge area, resulting in the water table beneath the entire beach where the water table is deep to rise and fall proportionally and maintaining essentially the same hydraulic gradient. However, fluctuations in the lake levels have little impact on water table conditions at beaches where the water table is shallow.

Differential occurrence of Escherichia coli and human Bacteroidales at two Great Lakes beaches

“…Beach sands can therefore serve as reservoirs for FIB with later resuspension, either through human interaction or wave action, releasing stored FIB and elevating concentrations in shallow waters (Edge and Hill, 2007;Ge et al, 2012;Philip et al, 2009;Whitman et al, 2014). Groundwater discharge may also act as a source of FIB to shallow waters (Bitton et al, 2006;Boehm et al, 2004); however, the relative contribution of groundwater to E. coli contamination at Great Lakes beaches is uncertain (Crowe and Meek, 2009). The ecology of different FIB at the beach sand-water interface needs to be better understood because they might have significantly different persistence or transport characteristics associated with beach sand that would confound their ability to predict health risks.…”

Regional Similarities and Consistent Patterns of Local Variation in Beach Sand Bacterial Communities throughout the Northern Hemisphere

“…The last two saturated zones interact with a deep saltwater wedge located below the subtidal sands, resulting in complex chemical gradients and the potential exchange of nutrients and bacteria (3,6). Similarly, in the Great Lakes, seiche dynamics (a tide-like standing wave found in enclosed bodies of water) play a role similar to that played by the tidal cycles of marine beaches (7), and there is also frequently a continual discharge of groundwater to many lakes (8).…”

Application of a glyphosate-based herbicide to Phragmites australis: Impact on groundwater and near-shore lake water at a beach on Georgian Bay

“…The rate of dissipation of glyphosate from the groundwater will not be the same as calculated here at all beaches throughout the Great Lakes because physical and hydrogeological conditions vary among beaches (Crowe and Meek, 2009). However, the basic processes that affect the transport, persistence and fate of glyphosate will be the same at every beach: (1) infiltration moves the herbicide downward into the sand; (2) glyphosate is adsorbed to the Feminerals in the sand; (3) degradation above the water table is the main factor reducing levels of glyphosate; (4) infiltration transports some glyphosate and AMPA to the water table; (5) groundwater flow transports glyphosate and AMPA toward the lake; (6) concentrations are reduced through dilution as glyphosate and AMPA are transported to the water table and through the groundwater flow regime; (7) groundwater discharges at the shoreline, and hence glyphosate and AMPA is also discharged at the shoreline; and (8) glyphosate and AMPA entering the lake water will be further diluted.…”

“…Groundwater samples were obtained at five sites randomly selected below the Phragmites area where the herbicide was applied. Groundwater below beaches of the Great Lakes flows toward the lake and discharges at the seepage face at the shore (Crowe and Meek, 2009). Hence, groundwater samples were collected at five sites 3 to 4 m apart, parallel to, and within 0.5 m of the shoreline, on the narrow strip of sand adjacent to the Phragmites; this area was not sprayed with Roundup®.…”

“…However, the benefits of saving a beach that has been overgrown by Phragmites through the application of an herbicide must be balanced by the potential risks incurred by the application of an herbicide at the shoreline. The herbicide could reach the lake via groundwater flow because the water table below a beach is shallow, infiltration is rapid through beach sand, and groundwater discharges into the lake at the shoreline (Crowe and Meek, 2009;Horn, 2002). Hence, there is a potential for glyphosate to present a risk to aquatic life.…”