Contamination of groundwater is a pervasive and serious problem in many developed coastal areas1–3, but potential interactions of groundwaters with, and their impact on, adjoining coastal waters have generally not been considered. Although submarine ground-water discharge could be an important source of nitrogen to coastal marine environments4, there has been no direct evidence for this. Recently, subsurface discharge has been shown to account for about 10–20% of the freshwater input to Great South Bay, New York5. The upper aquifer is the presumed source of this discharge and, because it is heavily contaminated with nitrate6, we suggest that groundwater is an important source of nitrate to the bay. Our determinations of the interstitial nutrient chemistry of freshly collected cores from nearshore sediments support this hypothesis. Although highly variable in time, cores taken after substantial rainfall showed increasing nitrate concentrations and decreasing salinities with depth. We conclude that submarine groundwater discharge is indeed a source of nitrate which should be considered in estimates of nitrogen influx to coastal marine ecosystems.

A groundwater source of nitrate in nearshore marine sediments

Lake eutrophication is a large and growing problem in many parts of the world, commonly due to anthropogenic sources of nutrients. Improved quantification of nutrient inputs is required to address this problem, including better determination of exchanges between groundwater and lakes. This first of a two-part review provides a brief history of the evolution of the study of groundwater exchange with lakes, followed by a listing of the most commonly used methods for quantifying this exchange. Rates of exchange between lakes and groundwater compiled from the literature are statistically summarized for both exfiltration (flow from groundwater to a lake) and infiltration (flow from a lake to groundwater), including per cent contribution of groundwater to lake-water budgets. Reported rates of exchange between groundwater and lakes span more than five orders of magnitude. Median exfiltration is 0.74 cm/day, and median infiltration is 0.60 cm/day. Exfiltration ranges from near 0% to 94% of input terms in lake-water budgets, and infiltration ranges from near 0% to 91% of loss terms. Median values for exfiltration and infiltration as percentages of input and loss terms of lake-water budgets are 25% and 35%, respectively. Quantification of the groundwater term is somewhat method dependent, indicating that calculating the groundwater component with multiple methods can provide a better understanding of the accuracy of estimates. The importance of exfiltration to a lake budget ranges widely for lakes less than about 100 ha in area but generally decreases with increasing lake area, particularly for lakes that exceed 100 ha in area. No such relation is evident for lakes where infiltration occurs, perhaps because of the smaller sample size. Copyright © 2014 John Wiley & Sons, Ltd.

Groundwater ‐ the disregarded component in lake water and nutrient budgets. Part 1: effects of groundwater on hydrology

Phosphorus in groundwater discharge – A potential source for lake eutrophication

Direct groundwater inputs are receiving increasingattention as a potential source of nutrients and otherdissolved constituents to the coastal ocean Seepageinto St George Sound, Florida was measuredextensively from 1992 to 1994 using seepage meters Spatial and temporal variations were documented alonga 7-km stretch of coastline and up to 1 km from shore Measurements were made at 3 transects perpendicular toshore and 1 transect parallel to shore The generalresults indicated that seepage decreased with distancefrom shore (2 of 3 transects), and substantialtemporal and spatial variability was observed inseepage flow from nearshore sediments In addition,trends in mean monthly integrated seepage rates weresimilar to precipitation patterns measured at a nearbycoastal weather station Based on these measurements, weestimate that the magnitude of groundwater seepage intothe study area is substantial, representing from 023 to44 m3 ⋅ sec-1of flow through the sediments, approximately equivalentto a first magnitude spring Although it is unknown howrepresentative this region is with respect to globalgroundwater discharge, it demonstrates thatgroundwater flow can be as important as riverine andspring discharge in some cases Our subsurfacedischarge rates suggest groundwater is an importanthydrologic source term for this region and may beimportant to the coastal biogeochemistry as well

Magnitude and variations of groundwater seepage along a Florida marine shoreline

[1] The simplicity of a pan-and-bag seepage meter makes it an attractive tool for a variety of hydrologic investigations, but the performance of this device is far from simple. Laboratory experiments show that the hydraulic head required to fill collection bags can range from 0.5 mm to several millimeters at flow rates typical of seepage meters, and this additional head will divert water away from the pan. A theoretical analysis gives a semianalytical expression for the flux captured by a seepage meter using a collection bag. The analysis shows that bag conductance, radius of the pan, and hydraulic conductivity of the stream bed can be combined to give a dimensionless term that characterizes seepage meter performance. Field experiments in a sandy streambed show that conventional seepage meters can resolve spatial differences in ground water flux but only when using a highly conductive collection system that is isolated from the current.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002WR001347

David Winek

Papers

Groundwater seepage as a nutrient source to a drainage lake; Lake Mendota, Wisconsin