A method for estimating pore water drainage from marsh soils using rainfall and well records

Abstract

Rainfall events during low tide exposure cause the water table in marshes to rise.If one has long time series of both rain events and water levels in wells along transects from creek bank to marsh interior, one can correlate well response with rain amount. In cases examined so far the well response is found to be a linear function of rain amount.As it is reasonable to assume that the amount of tidal infiltration required to restore the water table to the elevation of the marsh surface is equal to the amount of rain that would be required to do so, one can estimate the annual drainage of pore water from a well site by dividing the mean drawdown of the water table at low tide by the slope of the response-versus-rain regression and then multiplying the result by the number of tidal drawdowns in a year. Integration of such results along the transect then gives an estimate of the total annual drainage. An example of the use of this method is given for two well transects in a Typha and a Spartina marsh at the Plum Island Estuary Long Term Ecological Research (PIE-LTER) site in Massachusetts, USA. Both transects yielded pore water drainage rates of about 160 m 3 yr -1 per meter of channel length. Although the annual volume of pore water drainage is small compared to the annual volume of the tidal prism its impact on nutrient budgets in the estuary could be large because of the high concentrations of nutrients in marsh pore waters. We also discuss the possible effects of the capillary fringe, air entrapment and tidal forcing during rain events on these results.

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

“…Other processes that might be included in the water budget were the freshwater budget (Ganju et al 2012), storage in marshtop ponds , and porewater absorption to sediments (swelling), infiltration, and drainage over daily to biweekly tidal cycles (Nuttle and Hemond 1988;Gardner and Gaines 2008). I distinguish low salinity groundwater from brackish porewater in this discussion, in that groundwater refers specifically to the freshwater component entering the system, while porewater refers to water in the sediments derived from the mixture of creekwater, rain, and groundwater inputs.…”

“…Pond and marsh porewater infiltration and drainage over the spring-neap tidal cycle could be important fluxes relative to the water cycling in the marsh platform, but drainage tends to be protracted such that instantaneous fluxes are low compared to creek advection except during overtopping spring tides. For example, marsh porewater drainage at a similar site on the Parker River (~5 km north along Plum Island Sound) was estimated to be ~0.1 m 3 tide −1 per meter of creek (Gardner and Gaines 2008). This would be equivalent to 10 m 3 per tide at each creek, or less than 1% of the tidal volume (roughly 1000 m 3 , with roughly 50 m 3 remaining at low tide), though long-term drainage is likely to be more heterogeneous at our site because of the artificial ditches draining the marsh platform.…”

Wetland‐estuarine‐shelf interactions in the Plum Island Sound and Merrimack River in the Massachusetts coast

“…Outflows from the other six ungauged rivers were specified as a proportion of the Parker River discharge based on their watershed area relative to that of the Parker River [Vallino and Hopkinson, 1998], but with updated watershed area obtained from MassGIS (http:// www.mass.gov/mgis/) ( Table 1). Annual seepage from salt marshes into tidal creeks in PIS is estimated at ∼ 4 × 10 8 m 3 /yr [Gardner and Gaines, 2008], but it is unknown what fraction of this seepage represents new groundwater addition, so we assume it to be 100%. Since tidal creeks are very narrow and tidal excursion is larger than PIS geometric scale [Vallino and Hopkinson, 1998], the estimated freshwater input due to groundwater was simply added to the river discharge.…”

Nutrient dynamics in pore water of tidal marshes near the Yangtze Estuary and Hangzhou Bay, China

“…On the other hand, seeping by percolation, diffusion or bioirrigation of pore water are extremely important in controlling the nutrient levels, and can even enhance the degree of eutrophication (Deborde et al 2008). The impact of pore water drainage on nutrient budgets in estuaries could be significant because of its high nutrient concentrations and the very large area covered (Gardner and Gaines 2008;Burnett et al 2003). In addition, the export of reduced nutrient also affects the structure and composition of coastal systems (Valiela and Teal 1979;Burnett et al 2003).…”