HR: 10:30h
AN: NB22B-01    [Abstracts]
TI: Hydrochemistry and Periphyton in the Perennial, Intermittent, and Ephemeral Selwyn River, South Island, New Zealand.
AU: * Larned, S T
EM: s.larned@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, P. O. Box 8602, Riccarton, Christchurch, New Zealand
AU: Kilroy, C
EM: c.kilroy@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, P. O. Box 8602, Riccarton, Christchurch, New Zealand
AU: Fenwick, G
EM: g.fenwick@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, P. O. Box 8602, Riccarton, Christchurch, New Zealand
AU: Kelly, D
EM: d.kelly@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, P. O. Box 8602, Riccarton, Christchurch, New Zealand
AU: Scarsbrook, M
EM: m.scarsbrook@niwa.co.nz
AF: National Institute of Water and Atmospheric Research, P. O. Box 11115, Hamilton, New Zealand
AB: The Selwyn River flows from the Southern Alps across an alluvial plain to the South Island's east coast. The mainstem loses water to an unconfined aquifer for 40 river kms, then gains water from a confined aquifer for 20 kms. The presence and magnitude of flow at any point is controlled by upstream discharge and/or local groundwater level. Flow permanence ranges from 100% at the furthest upstream (run-off dominated) and downstream (groundwater-dominated) reaches to 10% in the central reach. Flow permanence also varies among small-scale habitats: backwaters and remnant channels have greater permanence than riffles and runs. In the gaining reach, conductivity and sodium, nitrate, and inorganic phosphorus concentrations are 2-7 times higher than in the losing reach. A subreach within the losing reach is dominated chemically by tributary inflows. Differences between gaining and losing reaches diminish when they are hydrologically-connected, but connection only occurs about 60 d/yr. Between-reach differences are primarily due to solute-enriched influent groundwater. Flow permanence is a poor predictor of water chemistry, in part because tributaries alter flow permanence and chemistry simultaneously. In contrast, periphyton biomass is closely related to flow permanence, suggesting that emersion in intermittent reaches limits periphyton growth more than nutrient availability.
DE: 1845 Limnology
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly