Behavior of the groundwater in a riverine-type mangrove forest

Abstract

The behavior of groundwater and physical properties of bottom sediment in a riverine-type mangrove forest which is composed of a tidal creek and fringing mangrove swamps were investigated through field observations at Iriomote Island, Japan. After the tidal water ebbed from the swamp surface to the creek, groundwater levels at swamp sites near the creek fell by up to 15 cm by the next flood tide, although the fall was negligible at sites far from the creek and at the open coast outside the mangrove forest. The amount of groundwater discharged to the creek from the swamp depended strongly both on the tidal range and the presence of the steep bank which separates the tidal creek from the fringing mangrove swamp. Based on the fall of groundwater level, the bulk hydraulic conductivity of the swamp was estimated to be 1.5Â10 )2 cm/s. This value is two to three orders of magnitude larger than that measured in a laboratory using small scale sediment core samples collected in the swamp. These results suggest that the presence of crowded, intricate and large animal burrows as well as sediment layers rich in mangrove humus increases permeability in the mangrove swamp. Further, it is suggested that the mangrove topography with the steep bank of the tidal creek plays an important role which enhances material exchanges through groundwater between the mangrove swamp and the adjacent offshore waters.

Groundwater‐derived dissolved inorganic and organic carbon exports from a mangrove tidal creek: The missing mangrove carbon sink?

“…It has been hypothesized that this tidal variation is driven by the input of groundwater enriched in DIC and DOC during the ebb tide (Dittmar and Lara 2001; Bouillon et al 2007b), with connectivity between groundwater and surface water enhanced in mangroves because of the mosaic of macrofauna burrows and organic-rich sediment layers (Ridd 1996;Mazda and Ikeda 2006). We build on these studies by using 222 Rn to quantitatively demonstrate the groundwater input.…”

Uncoupled surface and below-ground soil respiration in mangroves: implications for estimates of dissolved inorganic carbon export

“…The data encompass oxygen measurements taken at all seven forests Ikeda 2006). Seepage of groundwater through the forest floor is controlled by a number of physical forces (Mazda et al 1990;Susilo et al 2005;Mazda and Ikeda 2006) that result in interstitial water oozing out through the bottom soil, most clearly seen as water moving through seepage channels between the forest and adjacent creek bank. In this study, we sampled water in drainage channels from all seven sites and found that DIC concentrations in the seepage were equivalent to those measured in the interstitial water (with both greater than overlying DIC water concentrations) showing that mineralized carbon is being drained advectively from these forests.…”

“…At higher tidal levels closer to land, a greater volume of the forest floor experiences tidal oscillations and faster lateral transport of drainage than flood waters, due to factors such as tidal asymmetry, number and complexity of burrows and other openings, soil texture, the extent of groundwater (if any), and slope of the forest floor (Ridd 1996;Heron and Ridd 2008). This subsurface flow is complex (Mazda and Ikeda 2006), but how it affects microbial metabolism within the forest floor is unknown.…”

Importance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)

“…The rate of porewater migration depends on the sediment permeability and the pressure gradient. Crab burrows have been found to dramatically enhance the hydraulic conductivity, and given their abundance in mangrove systems, these could be important mediators for subsurface flow of porewater to tidal creeks (Ridd, 1996;Mazda and Ikeda, 2006).…”