I was recently assigned a research paper in Environmental Biology. I chose the topic in the subject of this post. It was interesting research, although we were limited to around a thousand words. Since we all love fish, I'd like to hear your take on the damming of rivers.
The Effects of Damming on the Biodiversity of River Fish
Even if it is not readily apparent, the diversity of our freshwater fish is of utmost importance to the biological community. Fish are found in practically every river and stream system that can sustainably support them. They occupy several biological niches. Large predatory fish can be a keystone species in a river system which regulates the food cycle and other aquatic populations. The loss of biodiversity and genetic diversity caused by the damming of our river systems is a threat to the ecosystem both in and out of the water. This paper will examine the impacts of damming on fish populations and attempt to clarify steps that may be taken to mitigate the harm caused by dams.
There are several motivating factors in the decision to place dams on a river system. In modern society the production of hydroelectric power is frequently the main goal. Other goals might include the creation of a reservoir to preserve fresh water stock, to create a recreational fishery, or to prevent flooding downstream. While these goals do have socio-economic benefits, they also have external costs that are frequently ignored. Dams generate 19% of the world electrical capacity and supply (Lopez-Pujol et. al: 2009) and supply water to 30-40% of irrigated croplands amounting to 800,000 small dams and 45,000 large ones worldwide. Of course, dammed water used upstream is no longer available downstream, for fish or their human neighbors.
How might biodiversity of fish be affected in rivers after the construction of a dam? There are several factors that logically lead to a loss in biodiversity in fish. The first one that I will comment on is the environmental upheaval faced both by fish and every other organism above and below the dam. The rate of water flow is likely to be slower upstream. The reservoir is likely to be deep and sediment rich. The biochemical profile both upstream and downstream will likely be altered. Since the dam traps sediments upstream the nutrient level can be expected to be elevated in the reservoir and lower in the spill way. The temperature profile will likely also be altered as a deeper reservoir is likely to have variable temperature zones. The average temperature upstream may be considerably lower due to average depth being lower, and the opposite is true for fish downstream. The problem lies in the fact that a dam can take an environment in which the fish population has filled biological niches and change completely the environment in which they thrived. The temperature, nutrient concentration, sediment profile and water chemistry will all likely be altered by the installation of a dam. This environmental upheaval not only alters fish environment and can change the likelihood of their survival, but it also alters the environment of their predators and their prey. The vast alteration of the food web can have effects far downstream, even in estuaries and marine environments (Lopez-Pujol: 2009).
The second major problem with dams as it pertains to river fish biodiversity is the segmentation of the population. Dams frequently are an insurmountable barricade to migration upstream. For some fish, this leads to an inability to reach their original spawning grounds. This may lead to a major decline or extinction of species that have very specific spawning conditions (such as salmon). This generates separate populations with less genetic diversity. The installation of fish passage facilities (fish ladders) may abate some of the potential harm but there is significant evidence that suggests that most of the movement is upstream and that the fish are moving into an area that is not suitable habitat (as discussed before, there are major differences between a reservoir and a river environment.)(Pelicice, Aghostino : 2008). The region of Sao Paulo, brazil has mandated that every hydro-electric dam have a fish ladder installed or operate a fish hatchery to improve fish stocks that have declined as a result of the dam (Agosthino and Gomes: date unspec.). The decline of migratory fish due to dams is documented in the case of the Columbia River salmon population (Dudgeon: 2000).
The third problem encountered by the damming of rivers is the economic loss due to the decline of fisheries post-construction of dams. As in the case of the Columbia River salmon above, it seems that large, highly specialized fish frequently decline in number or even face extinction as a result. Lopez-Pujol and Ren also mention the decline of the Russian Sturgeon Acipenser gueldenstaedii, probarbus jullieni, Tenualosa ilisha, due to the construction of dams in their native regions. The construction of the Aswan High Dam resulted in the extinction of 30 of the 47 commercially exploited fish in the delta region of the Nile River just a decade after its construction. The economic loss of biodiversity is just as important as the ecological loss and is not at all limited to fish populations.
Another problem with the damming of rivers is the effects on endemic species. In the case of the Three Gorges dam on the Yangtze River, there are 44 species endemic to the area. These are species that represent the greatest threat to biodiversity if they are lost, as they are found nowhere else. Economic policy continuously outweighs environmental policy in the decision making of governments even when biodiversity is directly tied to economic output.
While the data definitely suggests that biodiversity and fish stocks are negatively impacted by dams, there is evidence that some species do increase in number after the damming of a river. While many fish suffer a decline in number, there are instances where a species may increase in number after the construction of a dam (***ushima, et. al.:2007). This may be the result of a decline in predators of that species, or an impact of the increased water volume upstream of the species that were not inhibited from their spawning grounds.
In conclusion, it should be very obvious that the damming of rivers negatively impacts biodiversity of fish species both upstream and downstream. A fragmented population, a major change in habitat, alteration of the food web, loss of traditional spawning grounds, the inhibition of migratory spawning grounds and a change in biochemical properties of habitat all contribute to a negative effect on biodiversity of fish populations in the regions where dams are built. There are several techniques such as fish ladders and restocking programs designed to improve the plight of affected species. These techniques have been shown to be ineffective as fish passages act as ecological traps and stocking programs do not alter the survivability of the habitat into which the fish are stocked. The most effective way to preserve fish biodiversity is to forego the building of dams, especially large dams that drastically alter habitat. The removal of dams to restore biodiversity among fish populations and aquatic environments may be the only way to rescue threatened species although the socio-economic costs are high. The secondary and tertiary effects of having these dams may be even higher when external costs are included. While fish face threats from dams, these are compounded by the threats from climate change, pollution, and commercial extraction. The biodiversity of fish cannot be preserved in the face of a growing amount of dams, pollution, and over-utilization.
1. Aghostinho, Angelo Antonio and Luiz Carlos Gomez. Biodiversity and Fisheries Management in the Parana River Basin: Success and Failures. Maringa-PR Brazil: Universidade Estadual de Maringá – Nupelia, date unspecified. PDF.
2. Cyril C. Ajuzie. Aspects of Biodiversity Studies in a Small Rural Tropical Reservoir (Lamingo Reservoir) in Jos, Nigeria. World Rural Observations 2012;4(1):23-33]. ISSN: 1944-6543 (Print); ISSN: 1944-6551 (Online).
3. Lopez-Pujol, Jordi and Ming-Xun Ren. Biodiversity and the Three Gorges Reservoir: a troubled marriage. Spain, China: Journal of Natural History Vol. 43, Nos. 43-44 (2009):2765-2786. PDF.
4. Pelicice, Fernando Mayer and Angelo Antonio Agosthino. Fish-Passage Facilities as Ecological Traps in Large Neotropical Rivers. Maringa, Parana, Brazil: Conservation Biology 2008: Vol. 22 No. 1
5. McAllister, Don E., John F. Craig, Nick Davidson, Simon Delany and Mary Seddon. Biodiversity Impacts of Large Dams. IUCN: Background Paper No. 1, 2001.
6. Waples, Robin S., Richard W. Zabel, Mark D. Scheurell, and Beth L. Sanderson. Evolutionary responses by native species to major anthropogenic changes to their ecosystems: Pacific salmon in the Columbia River hydropower system. Seattle: Molecular Ecology 2007: 17, 84-96.
de Merona, Bernard, Regis Vigoroux and Fransisco Leonardo Tejerina-Garro. Alteration of fish diversity from Petit-Saum Dam in French Guiana. Implication of ecological strategies of fish species. France, Brazil: Hydrobiologia (2005) 551:33-47
7. Halls, A.S., A.I. Payne, S.S. Alam, ans S.K. Barman. Impacts of flood control schemes on inland fisheries in Bangladesh: guidelines for migration. Wiltshire, London, UK; Dhaka Bangladesh: Hydrobiologia (2008) 609:45-58
8. ***ushima, Michio, Satoshi Kameyama, Masami Kaneko, Katsuya Nakao, and Ashley Steel. Modeling the effects of dams on freshwater fish distributions in Hokkaido, Japan. Ibaraki and Hokkaido, Japan; Seattle, WA: Freshwater Biology (2007): 52, 1511-1524
9. Dudgeon, David et al. Freshwater diversity: importance, threats, status and conservation challenges. Cambridge, UK: Biology Review (2006): 81,163-182.
10. Dudgeon, David. The Ecology of Tropical Asian Rivers and Streams in Relation to Biodiversity Conservation. Hong Kong: Annual Review of Ecological Systems (2000) 31:239-263
11. Tordoff, Andrew et. al. Indo-Burma Biodiversity Hotspot. Asia: Critical Ecosystem Partnership Fund (2007)
12. Araujuo, Francisco Gerson et. al. Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology. Brazil: Hydrobiologia (2009) 618:89-107
The Effects of Damming on the Biodiversity of River Fish
Even if it is not readily apparent, the diversity of our freshwater fish is of utmost importance to the biological community. Fish are found in practically every river and stream system that can sustainably support them. They occupy several biological niches. Large predatory fish can be a keystone species in a river system which regulates the food cycle and other aquatic populations. The loss of biodiversity and genetic diversity caused by the damming of our river systems is a threat to the ecosystem both in and out of the water. This paper will examine the impacts of damming on fish populations and attempt to clarify steps that may be taken to mitigate the harm caused by dams.
There are several motivating factors in the decision to place dams on a river system. In modern society the production of hydroelectric power is frequently the main goal. Other goals might include the creation of a reservoir to preserve fresh water stock, to create a recreational fishery, or to prevent flooding downstream. While these goals do have socio-economic benefits, they also have external costs that are frequently ignored. Dams generate 19% of the world electrical capacity and supply (Lopez-Pujol et. al: 2009) and supply water to 30-40% of irrigated croplands amounting to 800,000 small dams and 45,000 large ones worldwide. Of course, dammed water used upstream is no longer available downstream, for fish or their human neighbors.
How might biodiversity of fish be affected in rivers after the construction of a dam? There are several factors that logically lead to a loss in biodiversity in fish. The first one that I will comment on is the environmental upheaval faced both by fish and every other organism above and below the dam. The rate of water flow is likely to be slower upstream. The reservoir is likely to be deep and sediment rich. The biochemical profile both upstream and downstream will likely be altered. Since the dam traps sediments upstream the nutrient level can be expected to be elevated in the reservoir and lower in the spill way. The temperature profile will likely also be altered as a deeper reservoir is likely to have variable temperature zones. The average temperature upstream may be considerably lower due to average depth being lower, and the opposite is true for fish downstream. The problem lies in the fact that a dam can take an environment in which the fish population has filled biological niches and change completely the environment in which they thrived. The temperature, nutrient concentration, sediment profile and water chemistry will all likely be altered by the installation of a dam. This environmental upheaval not only alters fish environment and can change the likelihood of their survival, but it also alters the environment of their predators and their prey. The vast alteration of the food web can have effects far downstream, even in estuaries and marine environments (Lopez-Pujol: 2009).
The second major problem with dams as it pertains to river fish biodiversity is the segmentation of the population. Dams frequently are an insurmountable barricade to migration upstream. For some fish, this leads to an inability to reach their original spawning grounds. This may lead to a major decline or extinction of species that have very specific spawning conditions (such as salmon). This generates separate populations with less genetic diversity. The installation of fish passage facilities (fish ladders) may abate some of the potential harm but there is significant evidence that suggests that most of the movement is upstream and that the fish are moving into an area that is not suitable habitat (as discussed before, there are major differences between a reservoir and a river environment.)(Pelicice, Aghostino : 2008). The region of Sao Paulo, brazil has mandated that every hydro-electric dam have a fish ladder installed or operate a fish hatchery to improve fish stocks that have declined as a result of the dam (Agosthino and Gomes: date unspec.). The decline of migratory fish due to dams is documented in the case of the Columbia River salmon population (Dudgeon: 2000).
The third problem encountered by the damming of rivers is the economic loss due to the decline of fisheries post-construction of dams. As in the case of the Columbia River salmon above, it seems that large, highly specialized fish frequently decline in number or even face extinction as a result. Lopez-Pujol and Ren also mention the decline of the Russian Sturgeon Acipenser gueldenstaedii, probarbus jullieni, Tenualosa ilisha, due to the construction of dams in their native regions. The construction of the Aswan High Dam resulted in the extinction of 30 of the 47 commercially exploited fish in the delta region of the Nile River just a decade after its construction. The economic loss of biodiversity is just as important as the ecological loss and is not at all limited to fish populations.
Another problem with the damming of rivers is the effects on endemic species. In the case of the Three Gorges dam on the Yangtze River, there are 44 species endemic to the area. These are species that represent the greatest threat to biodiversity if they are lost, as they are found nowhere else. Economic policy continuously outweighs environmental policy in the decision making of governments even when biodiversity is directly tied to economic output.
While the data definitely suggests that biodiversity and fish stocks are negatively impacted by dams, there is evidence that some species do increase in number after the damming of a river. While many fish suffer a decline in number, there are instances where a species may increase in number after the construction of a dam (***ushima, et. al.:2007). This may be the result of a decline in predators of that species, or an impact of the increased water volume upstream of the species that were not inhibited from their spawning grounds.
In conclusion, it should be very obvious that the damming of rivers negatively impacts biodiversity of fish species both upstream and downstream. A fragmented population, a major change in habitat, alteration of the food web, loss of traditional spawning grounds, the inhibition of migratory spawning grounds and a change in biochemical properties of habitat all contribute to a negative effect on biodiversity of fish populations in the regions where dams are built. There are several techniques such as fish ladders and restocking programs designed to improve the plight of affected species. These techniques have been shown to be ineffective as fish passages act as ecological traps and stocking programs do not alter the survivability of the habitat into which the fish are stocked. The most effective way to preserve fish biodiversity is to forego the building of dams, especially large dams that drastically alter habitat. The removal of dams to restore biodiversity among fish populations and aquatic environments may be the only way to rescue threatened species although the socio-economic costs are high. The secondary and tertiary effects of having these dams may be even higher when external costs are included. While fish face threats from dams, these are compounded by the threats from climate change, pollution, and commercial extraction. The biodiversity of fish cannot be preserved in the face of a growing amount of dams, pollution, and over-utilization.
1. Aghostinho, Angelo Antonio and Luiz Carlos Gomez. Biodiversity and Fisheries Management in the Parana River Basin: Success and Failures. Maringa-PR Brazil: Universidade Estadual de Maringá – Nupelia, date unspecified. PDF.
2. Cyril C. Ajuzie. Aspects of Biodiversity Studies in a Small Rural Tropical Reservoir (Lamingo Reservoir) in Jos, Nigeria. World Rural Observations 2012;4(1):23-33]. ISSN: 1944-6543 (Print); ISSN: 1944-6551 (Online).
3. Lopez-Pujol, Jordi and Ming-Xun Ren. Biodiversity and the Three Gorges Reservoir: a troubled marriage. Spain, China: Journal of Natural History Vol. 43, Nos. 43-44 (2009):2765-2786. PDF.
4. Pelicice, Fernando Mayer and Angelo Antonio Agosthino. Fish-Passage Facilities as Ecological Traps in Large Neotropical Rivers. Maringa, Parana, Brazil: Conservation Biology 2008: Vol. 22 No. 1
5. McAllister, Don E., John F. Craig, Nick Davidson, Simon Delany and Mary Seddon. Biodiversity Impacts of Large Dams. IUCN: Background Paper No. 1, 2001.
6. Waples, Robin S., Richard W. Zabel, Mark D. Scheurell, and Beth L. Sanderson. Evolutionary responses by native species to major anthropogenic changes to their ecosystems: Pacific salmon in the Columbia River hydropower system. Seattle: Molecular Ecology 2007: 17, 84-96.
de Merona, Bernard, Regis Vigoroux and Fransisco Leonardo Tejerina-Garro. Alteration of fish diversity from Petit-Saum Dam in French Guiana. Implication of ecological strategies of fish species. France, Brazil: Hydrobiologia (2005) 551:33-47
7. Halls, A.S., A.I. Payne, S.S. Alam, ans S.K. Barman. Impacts of flood control schemes on inland fisheries in Bangladesh: guidelines for migration. Wiltshire, London, UK; Dhaka Bangladesh: Hydrobiologia (2008) 609:45-58
8. ***ushima, Michio, Satoshi Kameyama, Masami Kaneko, Katsuya Nakao, and Ashley Steel. Modeling the effects of dams on freshwater fish distributions in Hokkaido, Japan. Ibaraki and Hokkaido, Japan; Seattle, WA: Freshwater Biology (2007): 52, 1511-1524
9. Dudgeon, David et al. Freshwater diversity: importance, threats, status and conservation challenges. Cambridge, UK: Biology Review (2006): 81,163-182.
10. Dudgeon, David. The Ecology of Tropical Asian Rivers and Streams in Relation to Biodiversity Conservation. Hong Kong: Annual Review of Ecological Systems (2000) 31:239-263
11. Tordoff, Andrew et. al. Indo-Burma Biodiversity Hotspot. Asia: Critical Ecosystem Partnership Fund (2007)
12. Araujuo, Francisco Gerson et. al. Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology. Brazil: Hydrobiologia (2009) 618:89-107
