The influence of watershed run‐off on the hydrology, forest floor litter and soil carbon of headwater wetlands

Abstract

The effects of land use and land cover (LULC) on aquatic systems have been extensively studied however less research has focused on headwater wetlands. This study was conducted to evaluate the effects of watershed land conversion and associated run-off on the hydrology and carbon cycling of headwater wetlands in coastal Alabama, USA. A total of 15 headwater wetlands were selected to reflect a range of surrounding LULC across coastal Alabama. Land use and soil data were utilized to estimate watershed run-off curve numbers (CN) that were used with precipitation data to calculate surface run-off (Q). Within each wetland, water level recorders were installed to monitor ground water levels for 1 year and data were used to generate hydrological metrics related to stage and flashiness. Data varied among sites, but wetlands with higher watershed CN tended to have a greater tendency for water level measurements to exceed the normal fluctuation range (outliers). Carbon dynamics associated with leaf litter and soil storage were also measured during this time period. Leaf litter traps were installed to determine litter fall carbon input (C LF ). Bimonthly monitoring of forest floor carbon (C FF ) was conducted to evaluate its relationship to watershed run-off. Soil carbon content was quantified in each wetland by collecting 40-cm cores analysed at 10 cm sections. Watershed run-off characteristics (CN and Q) were significantly related to mean C FF and C FF : C LF (C FF adjusted for the amount of C LF ) suggesting that hydrologic export and possibly decomposition increased with run-off. Surface soil (0-10 cm) carbon content was related to median groundwater level; however, no relationship was detected between soil carbon and CN or Q.

Setting a reference for wetland carbon: the importance of accounting for hydrology, topography, and natural variability

“…Measures of duration and average water level are commonly used in wetland restoration to set performance standards and evaluate success [116,117]. Although these metrics have been linked to wetland processes [118,119], our results indicate that the most relevant aspects of the hydrologic regime may depend on the system and process of interest [54].…”

Evaluating the Effects of Land Use on Headwater Wetland Amphibian Assemblages in Coastal Alabama

“…They are known to be transported in greenhouse materials and can be associated with the horticultural trade (Kraus et al 1999). In this study, this species was found on sites with sedimentation with little microtopography and standing water, conditions common in urban headwater wetlands (Barksdale et al 2014). E. planirostris were also found in sites that had other commonly occurring frog species (A. gryllus, A. terrestris, H. cinerea, H. chrysoscelis, L. clamitans, and P. crucifer).…”

Native plant turnover and limited exotic spread explain swamp biotic differentiation with urbanization

“…With urbanization, wetlands usually experience important changes in hydrological conditions due to the proliferation of impervious surfaces that modify surface water and groundwater flows (Azous and Horner, 1997). In general, urban wetlands are characterized by higher water level fluctuations, shorter periods of water retention, and decreased recharge from groundwater (in the case of groundwater‐fed wetlands; Kentula et al, 2004; Barksdale et al, 2014), but these hydrological changes are often highly unpredictable (Ehrenfeld, 2003; Bhaskar et al, 2016). Depending on the specific local context, road development, grading alterations and the presence of rain collectors can disrupt flow patterns at the inlets or outlets of wetlands, thereby leading to increased flooding or drought (Ehrenfeld, 2000; Barksdale et al, 2014).…”

“…In general, urban wetlands are characterized by higher water level fluctuations, shorter periods of water retention, and decreased recharge from groundwater (in the case of groundwater‐fed wetlands; Kentula et al, 2004; Barksdale et al, 2014), but these hydrological changes are often highly unpredictable (Ehrenfeld, 2003; Bhaskar et al, 2016). Depending on the specific local context, road development, grading alterations and the presence of rain collectors can disrupt flow patterns at the inlets or outlets of wetlands, thereby leading to increased flooding or drought (Ehrenfeld, 2000; Barksdale et al, 2014). By releasing or intensifying anoxia stress in particular, drier or wetter wetland conditions often create new ecological plant niches (MacDougall and Turkington, 2005; Mayfield et al, 2010), which may contribute to their high beta diversity.…”