Hillslope and wetland hydrodynamics in a tussock grassland, South Island, New Zealand

Abstract

Abstract:Previous research on two experimental catchments at the Glendhu Forest (Otago) showed that runoff dynamics from this landscape differ substantially from other areas in New Zealand. In particular, the recession curves from these catchments have two distinct phases: a rapid decline for a period of several hours, followed by a slow decline that may last many days to weeks. In the current study, soil water matric potential measurements indicated that perched saturated zones develop very rapidly in the surface (0-30 cm) soil horizons. Deep (50-250 cm) loess horizons remain moist throughout the year and may be near or at saturation at the bedrock contact, and respond only slowly to rain events. Soils in the middle horizons are often drier than the surface soil above or the deep soils below. Throughflow measurements showed that storm runoff occurs primarily as interflow through a retentive but pervious mat of mosses, litter, and roots at the soil surface. Despite the presence of abundant earthworm burrows, less water is transmitted through the soil horizon just below this surface mat. Only a small fraction of stormflow was transmitted through the deep, mineral horizons. However, baseflow could be sustained for long periods (up to 4 weeks) from unsaturated flow of soil moisture stored in the deep loess horizons. Water storage in bog peats and associated riparian soils (which are numerous in this area) is insufficient to sustain baseflow for more than a few days. The results from this study are consistent with previous hydrometric, soils, and isotopic observations and suggest that any land-use practices that disrupt the surface soil horizons are likely to change the runoff characteristics of this area.

Organic carbon efflux from a deciduous forest catchment in Korea

“…Using various tracers, the end-member mixing analysis has been used to elucidate flow paths and hydrological processes in several catchments (e.g., Hooper et al, 1990;Elsenbeer et al, 1995;Katsuyama et al, 2001). Numerous conceptual models have adopted the flow path dynamics proposed by Anderson et al (1997), i.e., both pre-event soil water and bedrock groundwater contribute to the formation of a saturated zone in the area adjacent to the stream (e.g., McGlynn et al, 1999;Bowden et al, 2001;Uchida et al, 2002).…”

Runoff generating processes in adjacent tussock grassland and pine plantation catchments as indicated by mean transit time estimation using tritium

“…The importance of interflow in producing stormflow has been demonstrated by earlier workers (Miller, 1994;Bowden et al, 2001). Bowden et al (2001) showed that lateral flow in the thin Organic and A Horizon layers was substantial and probably often emerged as flow over the wetland surface in high quickflow events, contributing to the new water inputs to the streams. They identified slow drainage from deep loess horizons (layers B and C) as the source of the extended baseflow in the catchments.…”

“…Samples were collected from two tubes permanently inserted in the central wetland of GH5 (Fahey et al, 1998;Bowden et al, 2001). One was a piezometer tube drawing from 1 m depth near the mid-bog piezometer nest, the other from an aluminium tube drawing from 1.2 m depth near the lower piezometer nest.…”

“…The young fractions (0.84±0.01 for GH1 and 0.74±0.01 for GH2) indicate that the majority of the water in the streams is young. This young water is expected to be derived from the shallow groundwater connecting the near-surface layers of the wetlands and the surrounding hillslopes with the stream (Bonell et al, 1990;Fahey et al, 1998;Bowden et al, 2001). But there is also a substantial fraction of old water in the streamflow in both catchments.…”

“…Miller (1994), however, concluded that these features may not be important sources of baseflow, but merely serve to link the surrounding hillslopes with the streams that drain them. Fahey et al (1998) and Bowden et al (2001) found that storm runoff occurs primarily as interflow, and that baseflow can be sustained for long periods from soil moisture stored in the deep loess horizons blanketing the surrounding hillslopes, but only for a few days from the water in the bog itself.…”