Hydrobiologia

, Volume 416, Issue 0, pp 203–214 | Cite as

The influence of aquatic macrophytes on the hydraulic and physico-chemical properties of a New Zealand lowland stream

  • Robert J. Wilcock
  • Paul D. Champion
  • John W. Nagels
  • Glenys F. Croker

Abstract

The effects of macrophytes on hydraulic and physico-chemical variables were examined by conducting tracer experiments with SF6, CH3Cl and rhodamine WT in a stream before and after complete removal of plants from a 180 m reach. Whakapipi Stream has high average biomasses (up to 370 g dw m-2) of macrophytes (predominantly Egeria densa) that, on average, cause summer velocities to be lowered by 30% and depths increased by 40%, compared to a plant-free channel. Manning's roughness coefficent was consistently higher by 0.13 and longitudinal dispersion coefficients were more variable (CV = 52%, cf. 20% when plants removed), when macrophytes were present. Stream dissolved oxygen (DO) and temperatures were unevenly distributed, possibly as a result of transient storage zones attributable to plant biomass. Surface water in macrophyte patches was 1-5 °C warmer than water in channels or beneath the plants near the bed of the stream, and DO was 2-28% of saturation higher at the top of the plants than in channel water and up to 7% higher than in bottom water. Effects of increased small-scale turbulence on the reaeration coefficient, K2(20), were cancelled by increased stream depth and reduced velocity so that it varied little with flow. Application of a single-station diurnal curve model, DOFLO (Dissolved Oxygen at Low Flow), to continuous monitoring data gave values of K2(20) in broad agreement with those measured by the gas tracer method and showed that rates of gross photosynthetic production in daylight (10-27 g m-2 d-1) and respiration at 20 °C (19-37 g m3 d-1) were high by comparison with other rural streams. Streams with smaller K2(20) values than Whakapipi Stream but with similar levels of productivity and community respiration would show more pronounced diurnal variations in DO and even be anoxic at times.

dispersion dissolved oxygen gas tracer macrophytes reaeration coefficient hydraulic variables 

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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Robert J. Wilcock
    • 1
  • Paul D. Champion
    • 1
  • John W. Nagels
    • 1
  • Glenys F. Croker
    • 1
  1. 1.National Institute of Water and Atmospheric Research Ltd.HamiltonNew Zealand Author for correspondence

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