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Ephemeral tributaries functionally connected to a Central Appalachian stream through asynchronicity of flow and particulate organic matter input
Citation:
Fritz, K., G. Pond, B. Johnson, AND C. Barton. Ephemeral tributaries functionally connected to a Central Appalachian stream through asynchronicity of flow and particulate organic matter input. 2018 Universities Council on Water Resources, Pittsburgh, PA, June 26 - 28, 2018.
Impact/Purpose:
The purpose of our study was to measure and examine relationships that describe the extent and timing of coarse particulate organic matter deposition and transport from ephemeral tributaries to a downstream perennial stream. This study informs the understanding about the ecological connections between ephemeral tributaries and downstream waters in forested river networks. This presentation was invited to be part of special session entitled Functions of Vulnerable Waters across a Continuum of Connectivity.
Description:
Headwater ephemeral tributaries are key external interfaces between uplands and downstream waters. Terrestrial coarse particulate organic matter (CPOM) is vital in fueling aquatic ecosystems, but the extent to which ephemeral tributaries are functionally connected to downstream waters through fluvial transport of CPOM has been little studied. We measured hydrology and deposition of leaf and wood, and surrogate transport (Ginkgo biloba leaves and wood dowels) over month-long intervals through the winter and spring seasons (6 months) in 10 ephemeral tributaries (1.3 – 5.4 ha) of Clemons Fork in Robinson Forest, Kentucky. The onset of flow in ephemeral tributaries coincided with precipitation, but often, not all tributaries were flowing simultaneously. The number of recorded flow events and percent of record with flow in the tributaries was positively related to drainage area. Leaf deposition and surrogate transport varied across 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. Maximum daily rainfall within periods was positively correlated with mean amounts of deposited leaves within periods. Ephemeral tributaries within the stream network were estimated to annually contribute 110.6 kg AFDM km-1 y-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. We find strong evidence that the ephemeral tributaries are functionally connected to downstream waters through a delayed CPOM subsidy (lag function) maintained by the asynchrony of autumnal leaf input and late-winter and early-spring pulsed flows.
