Estuary Processes and Managment - River Dynamics and Integrated River Management - page 468

Female rivers provide stable habitats for both terrestrial and aquatic bio-communities and therefore
have a higher biodiversity than that of male rivers. Benthic invertebrates and fish are main elements of
aquatic ecology. Streambed sediment is one of the main factors affecting the biodiversity of benthic
invertebrates (Duan et al., 2009). Samples of fish were taken from the lower reaches and samples of
macro-invertebrates were taken from the beds of the lower reaches of the Yellow, Yangtze and Pearl
rivers (Yi et al., 2008). Benthic macro-invertebrates were taken with a kick-net with holes of 420 ȝm and
a weighted Petersen grab (1/16 m 2 ) and then sieved with a 420-ȝm sieve. Several sites were chosen for
sampling for each river. Specimens were manually sorted out from sediment on a white porcelain plate
and preserved in 75% ethanol. All species were identified under microscopes by experienced biologists.
Fish samples were taken from the lower reaches of the Yangtze and Pearl rivers by hiring fishermen and
using seine. For each river, four fishermen captured fish species for 3 days.
Table 8.2 lists the species of invertebrates and fish sampled from the lower reaches of the Yellow,
Yangtze and Pearl rivers. The Yellow River is a male river and its channels are unstable. Erosion and
sedimentation occurred occasionally. Samples of macro-invertebrates were taken from 6 sites selected
from the lower reaches of the Yellow River. Only one species Palaemonidae (shrimp) was found from
the river channels. Another eight species of invertebrates were sampled from a riparian wetland in the
Yellow River delta. The extremely low biodiversity was caused by erosion, sedimentation of the river
bed, and migration of the channel. There are only a few fish species in the lower Yellow River and the
abundance of fish is low. Therefore, the Yellow River has no fisheries and no fisherman can be hired for
fish sampling.
Female rivers have stable habitats and low sediment load, therefore, they have high biodiversity. The
taxa richness and abundance of invertebrates and fish were much higher in the Yangtze and Pearl rivers
than in the Yellow River. The results support the conclusion that habitat stability is the most important
factor for high biodiversity (Wang and Xu, 2010). Fish samples were taken from six sites in the lower
reaches of the Yangtze River. 43 species belonging to 11 families of fish were found from the 6 sampling
sites. In the Pearl River, 70 species belonging to 29 families of macro-invertebrates were found from 18
sampling sites and 68 species belonging to 25 families of fish were found from 9 sampling sites.
The biodiversity in the female rivers are much higher than that of male rivers. In general, if a river
changes its gender from male to female the biodiversity increases. Nevertheless, the causes of gender
change (dam construction and water and sediment diversion) and the gender change itself are stresses on
the bio-communities. Therefore, the ecology may be impaired during the gender change.
8.1.4 Parasitizing Rivers
Male rivers carry heavy sediment load to the lower reaches and deltas. Humans made continuous effort
to control floods by constructing and enhancing grand levees. Overtime, the male rivers become perched
rivers in their lower reaches and deltas. Over the course of time avulsions occurred and thus created
many abandoned channels. Some abandoned channels have combined with other rivers and formed new
river systems. Some abandoned channels have been cut into several depressions or wetlands, or totally
disappeared due to human reclamation. Other abandoned channels still exist and rely on their father river.
Moreover, male rivers have no tributaries in the perched reaches; instead, rainwater falling on the
surrounding land of the river flows in new drainage channels parallel to the levees. These abandoned
channels and new drainage channels are not tributary or distributary rivers, but their location and stability
depend on their father rivers. These channels are parasitizing rivers of the male river.
The lower Yellow River is a perched river with its riverbed more than 10 m higher than the surrounding
ground. The rain water can not flow into the river and water diversion from the river affects the fluvial
process (Wang et al., 2008). Many drainage channels have developed on the levees and flow parallel with