Rg. Young et Ad. Huryn, LONGITUDINAL PATTERNS OF ORGANIC-MATTER TRANSPORT AND TURNOVER ALONG A NEW-ZEALAND GRASSLAND RIVER, Freshwater Biology, 38(1), 1997, pp. 93-107
1. We determined the longitudinal pattern of organic matter concentrat
ion, quality, size composition and spiralling length along a 310-km gr
assland river system (Taieri River, New Zealand). 2. Organic seston co
ncentration (0.24-4.05 mg ash-free dry mass (AFDM) l(-1)) and dissolve
d organic carbon (DOC) concentration (2.3-5.7 mg C l(-1)) showed no ob
vious longitudinal patterns. In contrast, there was a significant down
stream increase in inorganic seston concentration (0.13-13.73 mg ash l
(-1)), presumably because of a downstream increase in the proportion o
f the catchment developed for agriculture. 3. Although there was a tre
nd toward increasing particle size in the first 25 km of the river con
tinuum, organic seston was primarily composed of ultrafine particles (
0.6-30 mu m) at all study sites. The ratio of coarse (> 250 mu m) to u
ltrafine organic seston decreased logarithmically down the continuum.
Organic content generally decreased with particle size. Ultrafine part
icles, however, had significantly higher organic fractions than fine (
60-100 mu m) and very fine (30-60 mu m) particles. 4. Daily organic ca
rbon turnover length ranged from 10 to 98 km and increased downstream.
This is consistent with other studies along river continua and sugges
ts that organic carbon turnover length is largely controlled by the re
lationship between channel dimensions and discharge, rather than the p
resence of specific retention devices. 5. Concentrations and nutrition
al quality of organic seston and concentrations of DOC were highest in
an unconstrained floodplain reach in the upper river. These data sugg
est that new material enters the river channel in this reach, potentia
lly providing an important energy source for the river community downs
tream. The effect of this reach on the longitudinal pattern of organic
matter concentration and quality emphasizes how changes in channel fo
rm can alter river ecosystem structure and function.