Ecosystems flows 87

In a temperate forest ecosystem on Isle Royale, Michigan, ecologists found that it takes 762 pounds (346 kg) of plant food to support every 59 pounds (27 kg) of moose, and that 59 pounds of moose are required to support every one pound (0.45 kg) of wolf. The basic point is that massive amounts of energy do not flow from one trophic level to the next energy is lost at each stage of the food chain, so there are more plants than herbivores and more herbivores than carnivores. 

The energy flow through an ecosystem is the most important factor determining the numbers, the types, and the interactions of the plants and animals in that ecosystem. 

Figure 5. Paradigm of energy flow within the Antarctic marine ecosystem. (Reproduced with permission from reference 33 by the Scientific Committee on Antarctic Research of the International Council of Scientific Unions. Copyright 1987.)...

Fig. 3-9 Trophic levels in ecosystems. Thin arrows show flow of energy up the food chain (through living biomass) and the broad arrows show the complementary flow of dead organic matter (detritus) back down. R indicates respiration.

Abstract In most of the world s watercourses, dramatic modifications have occurred as a consequence of intensive use by human societies. The simplification of the channel network and the alteration of water fluxes have an impact upon the capacity of fluvial systems to recover from disturbances, because of their irreversible consequences. However, human impacts on river hydrology, such as those that derive from regulating their flow or by affecting their channel geomorphology, affect the functional organisation of streams, as well as the ecosystem services that derive from them, and lead to the simplification and impoverishment of these ecosystems. 

Alterations of water flow, independent of the cause, impact the stmcture and function of aquatic ecosystems. Extended drought produces the loss of hydrologic connectivity between stream compartments, and affects the biota. Therefore, flow cessation triggers a chain of cascading effects, eventually affecting community structure and ecosystem functioning. 

Arthington AH, Bunn SE, LeRoy Poff N et al (2006) The challenge of providing environmental flow rules to sustain river ecosystems. Ecol Appl 16 1311-1318... 

Overall the results reported in this review indicate that water scarcity might increase metal exposure (due to low dilution), metal uptake (due to higher retention under low flow), and metal toxicity and/or accumulation (depending on the dose and time of exposure), but also might cause opposite effects depending on the source of pollution. In addition, water scarcity will influence nutrient loads and will also modulate the fate and effects of metals. Thus, future studies addressing the role of environmental stress on the effects of toxicants at community scale are key to predict the impact of toxicants in the aquatic ecosystems. 

The water supply to the Delta comes predominantly from the Sacramento River ( 80%) with lesser amounts from the San Joaquin River ( 15%) and rivers on the east side of the Delta ( 5%). Year-to-year variability in water supply is large. Combined average annual unimpaired runoff (an estimate of flows without upstream dams or diversions) for the Sacramento and San Joaquin rivers for the past century ranges from 6.2 km in 1977 to 68 km in 1983 [2]. The percentage of freshwater flows that go to San Francisco Bay are estimated to be 87% in wet years, 69% in average years, and 51% in dry years. Climate variability associated with the Mediterranean chmate of the region is an essential component of the Delta ecosystem. 

Terrestrial ecosystems (plants and animals) under water scarcity suffer from water stress, and aquatic ecosystems of intermittency in water flow. Water scarcity has implications on hydrologic resources and systems coimectivity, as well as negative side-effects on biodiversity, water quality, and river ecosystem functioning. Finally, water scarcity has also direct impacts on citizens and economic sectors that use and depend on water, such as agriculture, tourism, industry, energy and transport. 

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