Basic Principles and Ecological Consequences of Altered Flow Regimes for Aquatic Biodiversity Stuart E. Bunn & Angela H. Arthington (2002)

In their examination of flow in rivers and their related environs, Bunn and Arthington identified the elements of flow as "flow extremes, flow regimes, hydraulics, substrate composition, and stability" (p. 494). They establish four basic principles related to flow as it applied to aquatic plants and animals. The first, "flow is a major determinant of physical habitat in streams, which in turn is a major determinant of biotic composition" (p. 492). The second principle reinforced the evolutionary influence of flow on biological development of plant and aquatic species in a river environment. The third principle, closely related to the other two, stipulated that "maintenance of natural patterns of longitudinal and lateral connectivity is essential to the viability of populations of many riverine species" (p. 492). The last principle claimed that changes in flow regimes facilitated the ability of invasive and non-native species to enter an area. Natural and human forces play a role in flow: floods, drought, dams, hydro power stations, channels, levee banks, and even weirs. Flow factors, depth, velocity, and cover, increase the diversity of river fauna.

Similarly, flow regimes impact fish diversity and the size of populations and community composition. The authors specifically mentioned the humpback chub, a threatened specie in the Colorado River. They attributed the Glen Canyon Dam and its alterations in "flow, temperature, sediment transport and vegetation dynamics" (p. 496). The chub thrives in peak flows, which trigger spawning cues. Changes in flow have caused pre-adult chub to adapt to "modified shoreline habitat provided by the exotic tamarisk than in natural habitats" (p. 496).

The authors contest the assertion that "the loss of riverine habitat associated with impoundments is balanced by the creation of lake habitat" (p. 496). They cited the differences in functioning, water levels, chemical and nutrient compositions, and temperature. The Colorado River and its hundreds of reservoirs has experienced the transformation of fish species from those native to turbid flows to "exotic fishes (over 50 species), many thriving in impoundments and regulated river reaches" (p. 496). The decline of the Colorado River cutthroat trout illustrated this point. In contrast, the Colorado River squawfish in the Yampa River spawn with rising flows of the river.

The authors concluded their article by voicing uncertainty over any definitive answer to the questions surrounding the consequences of flow changes. Land use changes complicate the discussion. They acknowledged "several interrelated causal mechanisms operating over different temporal and spatial scales, and no one characteristic of the flow is responsible" (p. 502). More confidently, they described the causation between flow regimes to fish migration, spawning, and floodplain viability. They stressed the need for flow experiments to test ecosystem response and restoration.

Bunn, S. E. & Arthington, A. H. (2002). Basic Principles and Ecological Consequences of Altered Flow Regimes for Aquatic Biodiversity. Environmental Management, 30, 4, pp. 492-507.