Recent groundwater and lake-stage trends in Cape Cod National Seashore: relationships with sea level rise, precipitation, and air temperature

Abstract

Hydrological features on Cape Cod, Massachusetts, USA, include groundwater, freshwater lakes, permanent and seasonal ponds, streams, and estuaries. Rainfall and evaporation/evapotranspiration have long been considered the dominant factors influencing both lake and groundwater levels in this sole-source, unconfined aquifer. However, increases in sea level may also have an effect, especially on this narrow peninsula with a sandy substrate of high permeability. In this study, we analyzed trends between 2000 and 2017 in eleven groundwater wells and nine kettle ponds situated with Cape Cod National Seashore (CCNS). We further explored relationships of these hydrologic variables with local precipitation, temperature and sea level during this period. The results suggest that while precipitation patterns influence seasonal and inter-annual variability, it appears that sea level rise (SLR) may be partially responsible for driving the longer-term trend of rising groundwater levels in several wells. Pond stages did not exhibit any statistically significant trends, and responded more to precipitation during this period of time. Notwithstanding, further acceleration of SLR, along with potential changes in precipitation patterns, can alter the freshwater hydrology of CCNS that may subsequently have biological, chemical, and physical effects throughout these systems.

Groundwater Rise and Associated Flooding in Coastal Settlements Due To Sea‐Level Rise: A Review of Processes and Methods

“…Surprisingly, there are very few monitoring sites globally indicating a groundwater rise with SLR (Barlow, 2003). Where observed, long‐term increases in water table elevation of the freshwater aquifer match the measured rate of SLR (such as at the Massachusetts Cape Cod USGS observation well and Boston Harbor, United States of America (USA); NOAA, 2003); this supports the hypothesis that water levels will rise with SLR (Masterson, 2004; McCobb & Weiskel, 2003; Smith & Medeiros, 2019). Recently, Sukop et al.…”

Tracing the sources and depositional history of mercury to coastal northeastern U.S. lakes

“…The CCNS kettle ponds are situated in low relief landscapes, where precipitation and groundwater are the only sources of freshwater; Long Pond is situated between the high and low point of the groundwater lens, which encompasses several other ponds. 98 Precipitation may therefore be delivered to the lake both directly and via groundwater recharge. The clear water in these lakes may also promote aqueous Hg photoreduction post-deposition, which is associated with an increase in Δ 199 Hg.…”

“…36,50 It is also noted that d 202 Hg and D 199 Hg values at Long Pond are similar to those reported in seawater (d 202 Hg ¼ À0.45&, D 199 Hg ¼ 0.09&), 99 indicating that intrusion of deep, saline groundwater is another potential source of Hg to these sites, though recent monitoring found no evidence of water table draw down. 98 Despite Hg isotope values characteristic of precipitation, Hg and Pb ux proles, as well as radionuclide inventories, indicate that watershed inputs and lateral redistribution have historically dominated metal uxes, which based on anthropogenic pressures in the region are likely caused by shoreline erosion. Similar Hg deposition proles to Long Pond, where ux increased substantially in recent years, were observed in a subset of lakes across the western United States, and attributed to decreased Hg retention in watersheds with landscape disturbances.…”