ISSN:
1573-5117
Keywords:
dispersion
;
dissolved oxygen
;
gas tracer
;
macrophytes
;
reaeration coefficient
;
hydraulic variables
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
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, K 2(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 K 2(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 K 2(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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1003837231848
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