Abstract
Headwater ephemeral tributaries are interfaces between uplands and downstream waters. Terrestrial coarse particulate organic matter (CPOM) is important in fueling aquatic ecosystems; however, the extent to which ephemeral tributaries are functionally connected to downstream waters through fluvial transport of CPOM has been little studied. Hydrology and deposition of leaf and wood, and surrogate transport (Ginkgo biloba leaves and wood dowels) were measured over month-long intervals through the winter and spring seasons (6 months) in 10 ephemeral tributaries (1.3–5.4 ha) in eastern Kentucky. Leaf deposition and surrogate transport varied over time, reflecting the seasonality of litterfall and runoff. Leaf deposition was higher in December than February and May but did not differ from January, March, and April. Mean percent of surrogate leaf transport from the ephemeral tributaries was highest in April (3.6% per day) and lowest in February (2.5%) and May (2%). Wood deposition and transport had similar patterns. No CPOM measures were related to flow frequency. Ephemeral tributaries were estimated to annually contribute 110.6 kg AFDM·km−1·yr−1 of leaves to the downstream mainstem. Ephemeral tributaries are functionally connected to downstream waters through CPOM storage and subsequent release that is timed when CPOM is often limited in downstream waters.
Highlights
Landscapes are comprised of freshwater and terrestrial ecosystems, wet and dry ecosystems are largely studied in isolation (Soininen et al 2015)
A key exchange across the land–water interface that affects community structure and ecosystem function in temperate forested streams is the seasonal input of terrestrial coarse particulate organic matter (CPOM) as deciduous leaves and wood (Fisher and Likens 1973, Richardson 1991, Wallace et al 1999)
We find strong evidence that the ephemeral tributaries in a temperate forest are functionally connected to a downstream water through a delayed CPOM subsidy maintained by the asynchrony of autumnal leaf input and late-winter and early-spring pulsed flows
Summary
Landscapes are comprised of freshwater and terrestrial ecosystems, wet and dry ecosystems are largely studied in isolation (Soininen et al 2015). Despite the widespread abundance of ephemeral tributaries—those that flow in direct response to precipitation and snowmelt—their connections to downstream waters have been less studied than their intermittent and seasonally flowing counterparts (Boulton 2015). This pattern applies to CPOM dynamics within temporary tributaries (reviewed by von Schiller et al 2017) where ephemeral tributaries have been less studied (but see Jacobson et al 2000, Hutmacher et al 2015). Like ephemeral tributaries, that alternate from dry to wet function as ecosystem interfaces will foster research that spans the historical boundaries separating terrestrial and aquatic research (Soininen et al 2015)
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