Ecosystem Component Interactions

Many factors have a direct relationship to other environ mental components while others are more complex and can complicate restoration actions. Direct and indirect

Flood/acute pollution

Disturbance

K

r

V —

Time

Figure 1 Examples of benthic algal succession from acute and chronic disturbances. (a) Disturbances such as floods or chemical spills can quickly remove viable algae from the stream. Once normal environmental conditions return, fast-growing r-strategist species flourish in a low-competition environment. Over time slower growing but more competitive K-strategist species accumulate and eventually dominate late successional assemblages. (b) Chronic pollution leads to a dominance of pollution-tolerant species with few to no sensitive species present. Reduction or alleviation of the pollution source allows a more natural assemblage to gradually return. These general patterns can be applied to organisms at all trophic levels; however, population susceptibility to the disturbance and recovery time will vary among organisms.

Figure 1 Examples of benthic algal succession from acute and chronic disturbances. (a) Disturbances such as floods or chemical spills can quickly remove viable algae from the stream. Once normal environmental conditions return, fast-growing r-strategist species flourish in a low-competition environment. Over time slower growing but more competitive K-strategist species accumulate and eventually dominate late successional assemblages. (b) Chronic pollution leads to a dominance of pollution-tolerant species with few to no sensitive species present. Reduction or alleviation of the pollution source allows a more natural assemblage to gradually return. These general patterns can be applied to organisms at all trophic levels; however, population susceptibility to the disturbance and recovery time will vary among organisms.

interactions can vary temporally and spatially as environ mental conditions in the ecosystem change. Alterations of a particular component, whether by pollution or by restoration actions, often have both positive and negative affects on other ecosystem components.

Understanding how organisms respond to their environment (i.e., the ecology of streams) is critical to implementing a successful restoration project. It should be clear that specific restoration goals, cannot be addressed solely by a direct attack on the observable problem.

Some of the challenges in ecological restoration can be illustrated by data from Carter Creek in central Texas, USA. This is an urban stream heavily influenced by wastewater effluent. A continuous source of nutrients and clear water from multiple municipal wastewater outfalls increases instream primary production and light penetration which greatly increases benthic algal biomass and diurnal oxygen fluctuations throughout the year. The Carter Creek watershed is highly developed with approximately 70% covered by impervious surfaces and urban drainage systems that greatly increase watershed runoff. This scenario, along with a sandy streambed, results in a high frequency of algal scouring events that severely limits algal biomass standing stock (Figure 2). This also keeps algal assemblages in an early successional and more edible form for grazers. Ecological restoration of streams is based on component

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