http://environmentalresearchweb.org/cws/article/news/48649
“No time to waste” on transition to green energy
Meanwhile, hydropower would produce such large emissions that it could add to global warming more than coal power alone for a good 60 years or so. “Hydropower is often associated with high methane emissions [due to] the decay of organic matter in the flooded land surface,” explained Caldeira. "There may be some niche locations where additional hydropower could be environmentally desirable, but more often environmental considerations weigh in favour of removing dams, not building them."
Showing posts with label dams. Show all posts
Showing posts with label dams. Show all posts
Saturday, February 18, 2012
Sunday, March 7, 2010
The Global Biogeochemical Silicon Cycle
The Global Biogeochemical Silicon Cycle
Eric Struyf & Adriaan Smis & Stefan Van Damme &
Patrick Meire & Daniel J. Conley
http://www.springerlink.com/content/f40058279411v057/fulltext.pdf
Consequently, transport of continental DSi to the oceans is an important component
in oceanic primary production, a large part of which consists of diatoms [11]. Forty percent of all oceanic C sequestration (∼1.5–2.8 Gton C yr−1) can be attributed to the growth and sedimentation of diatoms [12, 13]. Although primary production through different groups of marine phytoplankton also results in a net CO2 flux towards the sea bottom (the “biological carbon pump”) [14], a crucial difference exists between diatoms and coccolithophores, an important subgroup of non-siliceous phytoplankton. Coccolithophores are characterized by calcite shells (=coccoliths); CO2 is produced
when calcium reacts with hydrogen carbonate during calcite formation (the “carbonate counter pump”) [15].
Therefore, an increased dominance of coccolithophores decreases the net sequestration of CO2 and consequently the flux of CO2 from the atmosphere towards the ocean floor
[11]. The biological carbon pump in the ocean is often referred to as the “biological Si pump” [7]. Changes in Si inputs to marine ecosystems, especially in the coastal ocean, can significantly influence the species composition of oceanic primary producers, especially the balance of production between diatoms and non-siliceous
phytoplankton [16]. It has been hypothesized that a higher contribution of diatoms to total oceanic phytoplankton biomass occurred during the Last Glacial Maximum (79%
vs. 54% today) as the result of increased eolian inputs of Si [11]. This demonstrates that a link exists between Si transport from terrestrial to oceanic systems, atmospheric CO2 concentrations and variations in global climate.
2.2 Silicon and Eutrophication of Coastal and Lake
Ecosystems Silicon plays an important role in the current eutrophication problems of numerous lacustrine, estuarine and coastal ecosystems [17, 18]. In most major rivers worldwide, concentrations of N and P have at least doubled as the result of anthropogenic inputs [19]. Whereas total algal growth is primarily regulated by the availability of N and P, the relative availability of Si and the availability of Si
relative to N and P, e.g. the Si:N and Si:P ratios, can influence the composition of the phytoplankton community [18]. The lack of Si can change aquatic ecosystems from
those dominated by diatoms to non-diatom based aquatic ecosystems usually dominated by flagellates [20]. Based on an evaluation of long-term algal blooms and nutrient
conditions in different regions, it can be concluded that decreased Si:N and Si:P ratios can give rise to Si limitation of diatoms and the reduction of diatoms in the phytoplankton community. In addition, subsequent non-diatom blooms can contain harmful algal species such as Phaeocystis sp., Gonyaulax sp., Chrysochromulina sp. [21].
Diatoms are the primary energetic source for estuarine and coastal food chains [22]. Transfer of energy to higher trophic levels is enhanced by diatoms through their higher nutritional value [23] and the limited amount of trophic steps between diatoms and higher trophic levels [24]. Nondiatom species are known to be less available to higher trophic levels [21, 25] and some non-diatom based food webs are economically undesirable [20]. Therefore, the proportion of diatoms in the phytoplankton community is of primary importance for many fisheries globally [20].
Furthermore, DSi limitation of diatoms and resultant blooms dominated by non-diatom species can result in anoxic conditions, increased water turbidity and excessive
production of toxic components [26].
Increases in diatom biomass as a result of higher N and P inputs results in increased diatom sinking rates and increased diatom burial in bottom sediments [27]. Consequently, in anthropogenically eutrophied systems that have experienced increases in N and P loading from human activities with sufficiently long hydrodynamic residence times, the aquatic DSi stock decreases and eutrophication problems are worsened [18]. A similar effect has been described for dams, e.g. the artificial lake effect [28]. Dams increase the residence time of water in river ecosystems, which stimulates phytoplankton productivity [29]. This results in the increased trapping of biogenic Si in lake sediments, and decreased transport of DSi downstream. This effect has been described for major dams worldwide, and is an important component of changed N:P:Si ratio’s in coastal ecosystems.
Eric Struyf & Adriaan Smis & Stefan Van Damme &
Patrick Meire & Daniel J. Conley
http://www.springerlink.com/content/f40058279411v057/fulltext.pdf
Consequently, transport of continental DSi to the oceans is an important component
in oceanic primary production, a large part of which consists of diatoms [11]. Forty percent of all oceanic C sequestration (∼1.5–2.8 Gton C yr−1) can be attributed to the growth and sedimentation of diatoms [12, 13]. Although primary production through different groups of marine phytoplankton also results in a net CO2 flux towards the sea bottom (the “biological carbon pump”) [14], a crucial difference exists between diatoms and coccolithophores, an important subgroup of non-siliceous phytoplankton. Coccolithophores are characterized by calcite shells (=coccoliths); CO2 is produced
when calcium reacts with hydrogen carbonate during calcite formation (the “carbonate counter pump”) [15].
Therefore, an increased dominance of coccolithophores decreases the net sequestration of CO2 and consequently the flux of CO2 from the atmosphere towards the ocean floor
[11]. The biological carbon pump in the ocean is often referred to as the “biological Si pump” [7]. Changes in Si inputs to marine ecosystems, especially in the coastal ocean, can significantly influence the species composition of oceanic primary producers, especially the balance of production between diatoms and non-siliceous
phytoplankton [16]. It has been hypothesized that a higher contribution of diatoms to total oceanic phytoplankton biomass occurred during the Last Glacial Maximum (79%
vs. 54% today) as the result of increased eolian inputs of Si [11]. This demonstrates that a link exists between Si transport from terrestrial to oceanic systems, atmospheric CO2 concentrations and variations in global climate.
2.2 Silicon and Eutrophication of Coastal and Lake
Ecosystems Silicon plays an important role in the current eutrophication problems of numerous lacustrine, estuarine and coastal ecosystems [17, 18]. In most major rivers worldwide, concentrations of N and P have at least doubled as the result of anthropogenic inputs [19]. Whereas total algal growth is primarily regulated by the availability of N and P, the relative availability of Si and the availability of Si
relative to N and P, e.g. the Si:N and Si:P ratios, can influence the composition of the phytoplankton community [18]. The lack of Si can change aquatic ecosystems from
those dominated by diatoms to non-diatom based aquatic ecosystems usually dominated by flagellates [20]. Based on an evaluation of long-term algal blooms and nutrient
conditions in different regions, it can be concluded that decreased Si:N and Si:P ratios can give rise to Si limitation of diatoms and the reduction of diatoms in the phytoplankton community. In addition, subsequent non-diatom blooms can contain harmful algal species such as Phaeocystis sp., Gonyaulax sp., Chrysochromulina sp. [21].
Diatoms are the primary energetic source for estuarine and coastal food chains [22]. Transfer of energy to higher trophic levels is enhanced by diatoms through their higher nutritional value [23] and the limited amount of trophic steps between diatoms and higher trophic levels [24]. Nondiatom species are known to be less available to higher trophic levels [21, 25] and some non-diatom based food webs are economically undesirable [20]. Therefore, the proportion of diatoms in the phytoplankton community is of primary importance for many fisheries globally [20].
Furthermore, DSi limitation of diatoms and resultant blooms dominated by non-diatom species can result in anoxic conditions, increased water turbidity and excessive
production of toxic components [26].
Increases in diatom biomass as a result of higher N and P inputs results in increased diatom sinking rates and increased diatom burial in bottom sediments [27]. Consequently, in anthropogenically eutrophied systems that have experienced increases in N and P loading from human activities with sufficiently long hydrodynamic residence times, the aquatic DSi stock decreases and eutrophication problems are worsened [18]. A similar effect has been described for dams, e.g. the artificial lake effect [28]. Dams increase the residence time of water in river ecosystems, which stimulates phytoplankton productivity [29]. This results in the increased trapping of biogenic Si in lake sediments, and decreased transport of DSi downstream. This effect has been described for major dams worldwide, and is an important component of changed N:P:Si ratio’s in coastal ecosystems.
Saturday, January 2, 2010
Hydrological Alterations and Marine Biogeochemistry: A Silicate Issue?
Hydrological Alterations and Marine Biogeochemistry: A Silicate Issue?
Venugopalan Ittekkot, Christoph Humborg and Petra Schäfer
BioScience, Vol. 50, No. 9, Hydrological Alterations (Sep., 2000), pp. 776-782
(article consists of 7 pages)
Published by: American Institute of Biological Sciences
Stable URL: http://www.jstor.org/stable/1313953
Silicon Retention in River Basins
Silicon Retention in River Basins: Far-Reaching Effects on Biogeochemistry and Aquatic Food Webs in Coastal Marine Environments
Christoph Humborg, Daniel J. Conley, Lars Rahm, Fredrik Wulff, Adriana Cociasu and Venugopalan Ittekkot
Ambio, Vol. 29, No. 1 (Feb., 2000), pp. 45-50
(article consists of 6 pages)
Published by: Allen Press on behalf of Royal Swedish Academy of Sciences
Stable URL: http://www.jstor.org/stable/4314993
Silicon Retention in River Basins: Far-Reaching Effects on Biogeochemistry and Aquatic Food Webs in Coastal Marine Environments, by Christoph Humborg, Daniel J. Conley, Lars Rahm, Fredrik Wulff, Adriana Cociasu and Venugopalan Ittekkot © 2000 Royal Swedish Academy of Sciences.
Abstract
Regulation of rivers by damming as well as eutrophication in river basins has substantially reduced dissolved silicon (DSi) loads to the Black Sea and the Baltic Sea.
Whereas removal of N and P in lakes and reservoirs can be compensated for by anthropogenic inputs in the drainage basins, no such compensation occurs for DSi.
[ except for Nualgi ]
The resulting changes in the nutrient composition (DSi:N:P ratio) of river discharges seem to be responsible for dramatic shifts in phytoplankton species composition in the Black Sea.
In the Baltic Sea, DSi concentrations and the DSi:N ratio have been decreasing since the end of the 1960s, and there are indications that the proportion of diatoms in the spring bloom has decreased while flagellates have increased.
The effects on coastal biogeochemical cycles and food web structure observed in the Black Sea and the Baltic Sea may be far reaching, because it appears that the reductions in DSi delivery by rivers are probably occurring worldwide with the ever increasing construction of dams for flow regulation.
Christoph Humborg, Daniel J. Conley, Lars Rahm, Fredrik Wulff, Adriana Cociasu and Venugopalan Ittekkot
Ambio, Vol. 29, No. 1 (Feb., 2000), pp. 45-50
(article consists of 6 pages)
Published by: Allen Press on behalf of Royal Swedish Academy of Sciences
Stable URL: http://www.jstor.org/stable/4314993
Silicon Retention in River Basins: Far-Reaching Effects on Biogeochemistry and Aquatic Food Webs in Coastal Marine Environments, by Christoph Humborg, Daniel J. Conley, Lars Rahm, Fredrik Wulff, Adriana Cociasu and Venugopalan Ittekkot © 2000 Royal Swedish Academy of Sciences.
Abstract
Regulation of rivers by damming as well as eutrophication in river basins has substantially reduced dissolved silicon (DSi) loads to the Black Sea and the Baltic Sea.
Whereas removal of N and P in lakes and reservoirs can be compensated for by anthropogenic inputs in the drainage basins, no such compensation occurs for DSi.
[ except for Nualgi ]
The resulting changes in the nutrient composition (DSi:N:P ratio) of river discharges seem to be responsible for dramatic shifts in phytoplankton species composition in the Black Sea.
In the Baltic Sea, DSi concentrations and the DSi:N ratio have been decreasing since the end of the 1960s, and there are indications that the proportion of diatoms in the spring bloom has decreased while flagellates have increased.
The effects on coastal biogeochemical cycles and food web structure observed in the Black Sea and the Baltic Sea may be far reaching, because it appears that the reductions in DSi delivery by rivers are probably occurring worldwide with the ever increasing construction of dams for flow regulation.
Sunday, December 20, 2009
Silica Depletion and Lake Regulation
Mr. Roger Wheeler's blog Friends of Sebago Lake has a few interesting comments about role of dams, silica and diatoms on water quality and red tides.
Very few people are making this connection that decline in silica in water reduces diatom population and this causes a bloom of Cyanobacteria and Dinoflagellates.
http://friendsofsebago.blogspot.com/2009/12/silica-depletion-and-lake-regulation.html
SATURDAY, DECEMBER 19, 2009
Silica Depletion and Lake Regulation
Everything in Nature is Connected
It turns out that one key factor associated with harmful algal blooms is dissolved silica; intense red tides tend to occur in coastal waters where dissolved silica is low. We are all familiar with nitrogen and phosphorus as nutrients fueling algae growth, but silica is also an essential nutrient for one of the most abundant algae called diatoms. Without adequate dissolved silica, diatoms can't grow and reproduce. Much of the dissolved silica found in our State's coastal waters can be traced back to weathering processes of Maine rocks and soils. Silica, along with other minerals, slowly dissolves and is then carried from the watersheds by rivers to the ocean. With the continuous input of silica from rivers, along with other nutrients, diatoms grow in sufficient numbers and serve to suppress harmful algae that cause “red tides”. Healthy diatom populations in the Gulf of Maine also supply the nutrient foundation for one of the historically richest fisheries in the world.
...
I suggest that our current management strategies of Maine dam hydrology may be an unwitting, but important factor, contributing to silica depletion, increased harmful algal blooms and the present coastal ecosystem decline.
Very few people are making this connection that decline in silica in water reduces diatom population and this causes a bloom of Cyanobacteria and Dinoflagellates.
http://friendsofsebago.blogspot.com/2009/12/silica-depletion-and-lake-regulation.html
SATURDAY, DECEMBER 19, 2009
Silica Depletion and Lake Regulation
Everything in Nature is Connected
It turns out that one key factor associated with harmful algal blooms is dissolved silica; intense red tides tend to occur in coastal waters where dissolved silica is low. We are all familiar with nitrogen and phosphorus as nutrients fueling algae growth, but silica is also an essential nutrient for one of the most abundant algae called diatoms. Without adequate dissolved silica, diatoms can't grow and reproduce. Much of the dissolved silica found in our State's coastal waters can be traced back to weathering processes of Maine rocks and soils. Silica, along with other minerals, slowly dissolves and is then carried from the watersheds by rivers to the ocean. With the continuous input of silica from rivers, along with other nutrients, diatoms grow in sufficient numbers and serve to suppress harmful algae that cause “red tides”. Healthy diatom populations in the Gulf of Maine also supply the nutrient foundation for one of the historically richest fisheries in the world.
...
I suggest that our current management strategies of Maine dam hydrology may be an unwitting, but important factor, contributing to silica depletion, increased harmful algal blooms and the present coastal ecosystem decline.
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