Comparison of Hydrology of Two Atlantic Coastal Plain Forests

Abstract

Abstract. This article compares the short-term and long-term hydrology of two typical forests in the humid Atlantic Coastal Plain, including a relatively undisturbed forest with natural drainage in South Carolina (SC) and a drained pine plantation in North Carolina (NC), using monitoring and modeling approaches. Highly dynamic outflow (O) from both of these systems is driven by the water table (WT) position, as influenced by rainfall (R) and evapotranspiration (ET). The annual runoff coefficient (ROC) varied from 5% in dry years to 56% in wet years, depending on the soil water storage (SWS), with a significantly higher average value for the NC site despite its deeper WT, on average, than the SC site. Although both sites behaved similarly in extreme climate conditions, the change in SWS above the WT influenced the annual RO, ROC, and ET. The 17-year average annual ET of 1114 mm (R – O, assuming annual balanced SWS) for the SC site was significantly higher (p = 0.014) than the ET of the drained NC site (997 mm) despite the SC site’s lower mean annual R of 1370 mm, compared to 1520 mm for the NC site. This may be due to both the higher potential ET (PET) and soil water-holding capacity of the SC site. The SC site had higher frequency and duration of WT near the surface during winter, deeper summer WT, and higher correlation of annual ET to annual R (r2 = 0.90 vs. 0.15), suggesting that the SC site was often moisture-limited, particularly during the growing season. Most of the streamflow in these systems occurred during winter, with low ET demands. However, summer periods with tropical storms also resulted in large RO events, generally with higher frequency and longer durations at the drained NC site. These results are similar to an earlier short-term comparison with an unstable behavior period at the SC site after Hurricane Hugo (1989). This study highlighted (1) the differences in hydrology between coastal forests drained for silvicultural production and undrained natural forests managed only for restoration, (2) the importance of long-term monitoring and the effects of regeneration as well as vegetation management on flow regime, and (3) the application and limitations of two widely used models (MIKESHE and DRAINMOD) in describing the hydrology of these forests. Long-term studies can be a basis for testing new hypotheses on water yield, stormwater management, wetland hydrology, vegetation restoration, bioenergy production, and climate change, in addition to applications of proper models for assessing the eco-hydrologic impacts of land use and climate change on freshwater coastal forests linked with downstream riparian rivers and estuaries affected by tidal fluxes and sea level rise.HighlightsOutflow, driven by water table position on these forest systems, is highly variable, depending on its soil water storage.The hydrologic responses of both forest sites were similar during extreme climatic events or disturbances.Effect of forestry drainage on runoff was obscured by its large interannual differences.Long-term monitoring provides better insights on climate and vegetation management effects on flow regime and model validation Keywords: Drainage, Evapotranspiration, Hydrologic models, Pine forest, Poorly drained soils, Runoff coefficient, Water table.

Evaluation of Paired Watershed Runoff Relationships since Recovery from a Major Hurricane on a Coastal Forest—A Basis for Examining Effects of Pinus palustris Restoration on Water Yield

“…Runoff generation in coastal watersheds with shallow water table (WT) (<2-3 m deep) soils with variable permeability and infiltration rates is dominated by saturation excess flow [3][4][5][6]. The runoff process is complicated by interactions of forest management and extreme events [7][8][9][10][11]. The near-surface or shallow WT, a surrogate of soil water storage regulated by ET [12][13][14], drives most streamflow (as shallow surface runoff and drainage) in these shallow coastal systems [15].…”

“…The near-surface or shallow WT, a surrogate of soil water storage regulated by ET [12][13][14], drives most streamflow (as shallow surface runoff and drainage) in these shallow coastal systems [15]. Furthermore, microtopography influencing both surface and subsurface storage [16][17][18][19][20], (dis)connectivity [21], and drainage network pathways [7,22] have been shown to be important factors affecting runoff and its timing. Thus, a careful examination of such spatial catchment characteristics, including the abovecanopy and below-canopy leaf areas that regulate soil moisture and ET, is fundamental for an accurate interpretation of water yield [23].…”

Hydrologic Relationships of a Paired Coastal Watershed on the Santee Experimental Forest for Evaluating Watershed-scale Effects of Longleaf Pine Restoration on Water Yield

“…Also, the difference in percent time of zero runoff days between the watersheds was found smaller (3.3%) for the current period compared to 8.2% for the 1969-1978 period although the two periods covered different number of days. Runoff exceeded 115 mm day -1 , as extreme events, for less than only 0.1% of time with a steeper slope on both, which is an indicative of flooding regime on these poorly drained watersheds consistent with (Amatya et al, 2019).…”

“…The runoff generation processes on coastal watersheds with shallow WT (< 2-3 m) soils with variable permeability and infiltration rates has been shown to be dominated by saturation excess flow (Eshleman, Pollard, & O'Brien, 1994;Griffin, Callahan, Vulava, & Williams, 2014;Slattery, Gares, & Phillips, 2006;Williams, 2007). The runoff process is complicated by interactions of both forest management and extreme events (Amatya, Williams, Nettles, Skaggs, & Trettin, 2019;Hornbeck, Adams, Corbett, Verry, & Lynch, 1993;Kelly, McGuire, Miniat, & Vose, 2016;Shelby, Chescheir, Skaggs, & Amatya, 2005). The near-surface or shallow WT, a surrogate of soil water storage regulated by ET (Acharya, Jawitz, & Mylavarapu, 2012;Amatya, Skaggs, & Gregory, 1996;Loheide, Butler, & Gorelick, 2005) drives most streamflow (as shallow surface runoff and drainage) in these shallow coastal systems (Harder, Amatya, Callahan, Trettin, & Hakkila, 2007).…”

“…Evaristo and McDonnell (2019)'s finding based on their global analysis that the amount of water stored in a landscape and increased loss of water through ET are the most important factors in predicting streamflow response to forest removal and planting, respectively, is possibly applicable in the coastal systems also. Furthermore, microtopography influencing both surface and subsurface storage (Amoah, Amatya, & Nnaji, 2013;Hu, Bao, Shi, Wang, & Lu, 2020;Walega, Amatya, Caldwell, Marion, & Panda, 2020;Wu & A. Johnston, 2008), role of dis(connectivity) (Ares, Varni, & Chagas, 2020) and drainage network pathways (Amatya et al, 2019;Todd, Buttle, & Taylor, 2006) have been shown to be important factors affecting runoff and its timing. Thus, a careful examination of such spatial catchment characteristics, including the above and below canopy vegetation leaf area that regulate soil moisture and ET influencing the runoff from the watersheds is fundamental for an accurate interpretation of the water yield, as part of the LLP restoration evaluation study (Trettin et al, 2019).…”