| ||
| Diatoms are the major autotrophic communities in the euphotic zone in most regions of the world oceans. One of the most essential nutrients for frustule formation (cell wall or, theca) in the diatoms is silicate (SiO3). Higher the availability of SiO3 faster and better is the growth of diatoms. While emphasizing on the pivotal role of Si in the biology of diatoms and radiolarians in the oceanic realms, Dr Ittekkot, in his seminar at NIO, cautioned that anthropogenic activities, in particular construction of dams on major rivers in the world, are causing reduced Si discharges into the oceans and affecting the growth and abundance of diatoms over there. Based on the available literature on diatom composition, abundance and pre- and post-obstructions of the reverine discharges he indicated that the diatoms are adversely affected and giving alarming signals of depleting phytoplankton assemblages post-obstruction. Evidences point to catastrophic effects at least in the ocean-margins on diatoms, the major, innocuous autotrophs in the oceans. With Si depletion but nitrate and phosphate in abundance, the dinoflagellates - many species of which are toxic to many marine and terrestrial life forms - bloom and bring in unwanted changes in the marine ecosystem including mass mortalities of aquatic fauna and reduced fish harvests. He also highlighted the role of Si in regulating C fluxes [higher C fluxes when Si is adequately available for phytoplankton] and suggested that a great deal of new science needs to be done to address the consequences of reduced Si reaching the oceans due to dam constructions world over. Dr Ittekkot also brought out that 2 micromoles of SiO3 in the euphotic zone is adequate for the normal growth and activities of diatoms. While the deep-sea SiO3 concentrations are much higher, the time taken to reach up in the surface layers is very long and, often may not make it to the surface layers owing to physical barriers such as upper layer stratification. He summed up the seminar by appealing scientific community to address the Si issue from both the proposed river basin connectivity and the long term consequences of ocean productivity and biogeochemistry in an altered Si cycling scenario. Dr Venu Ittekkot works at ZMT, Bremen, Germany. (Reported by: N. Ramaiah) |
Showing posts with label silica. Show all posts
Showing posts with label silica. Show all posts
Thursday, December 1, 2011
Biogeochemical significance of silicon in the world oceans
http://www.nio.org/index/option/com_newsdisplay/task/view/tid/4/sid/23/nid/33
Thursday, March 31, 2011
Decline in Diatoms in Great Lakes
Algal productivity in the Great Lakes, the fixation of atmospheric carbon by algae, is largely a result of the size of the springtime bloom of diatoms. Diatoms are algae that pull silica out of the water column to encase themselves in intricate glass coatings, Evans explains. "The amount of silica removed by the bloom has long been used as an indicator of algal production in the Great Lakes," she says.
Mining data on silica concentrations collected over the past 30 years, Evans and her colleagues determined that algal production was about 80% lower in 2008 than in the 1980s and 1990s. The decline began in the mid-1990s after zebra and quagga mussels invaded the lakes. The study estimates that mussels consume up to 74% of new spring algae. When the foundation of a food web is depleted, Evans says, populations of the fish at the top of the web can suffer.
Published paper - http://pubs.acs.org/doi/abs/10.1021/es103892w
Phytoplankton production is an important factor in determining both ecosystem stability and the provision of ecosystem goods and services. The expansive and economically important North American Great Lakes are subjected to multiple stressors and understanding their responses to those stresses is important for understanding system-wide ecological controls. Here we show gradual increases in spring silica concentration (an indicator of decreasing growth of the dominant diatoms) in all basins of Lakes Michigan and Huron (USA and Canadian waters) between 1983 and 2008. These changes indicate the lakes have undergone gradual oligotrophication coincident with and anticipated by nutrient management implementation. Slow declines in seasonal drawdown of silica (proxy for seasonal phytoplankton production) also occurred, until recent years, when lake-wide responses were punctuated by abrupt decreases, putting them in the range of oligotrophic Lake Superior. The timing of these dramatic production drops is coincident with expansion of populations of invasive dreissenid mussels, particularly quagga mussels, in each basin. The combined effect of nutrient mitigation and invasive species expansion demonstrates the challenges facing large-scale ecosystems and suggest the need for new management regimes for large ecosystems.
Friday, August 13, 2010
Grand Lake, Ohio - Update
Sand to be used as a silica source in Grand Lake, Ohio
| Marysville company to begin Grand Lake project |
| Written by NANCY ALLEN, Celina Daily Standard |
| Wednesday, 11 August 2010 19:39 |
GRAND LAKE — A Marysville-based company will conduct a test this month in a 21 D2-acre part of Grand Lake to see if a beneficial algae species can be encouraged to grow and replace the toxic blue-green algae now dominant. Ross Youngs, CEO of Algaeventure Systems Inc., explained the test during Saturday’s meeting of the nonprofit Lake Improvement Association (LIA). The test site will be between the Celina Rotary lighthouse and a rock jetty. The process, called species flipping, is one of the solutions to help restore the lake Gov. Strickland and state leaders announced during a local news conference July 30. The test will involve adding silica (sand) to the lake to encourage the growth of diatom algae that need silica to make their glass cell walls. |
In nature sand is the source of silica for diatoms.
however merely putting sand will not be useful, a small bloom of Diatoms will take place but this is unpredictable.
Diatoms require very fine particles of silica, that can enter through the pores in their shells.
That is why dissolved silica or nano silica is required.
Tuesday, August 10, 2010
Grand Lake, Ohio - Update
http://www.theeveningleader.com/content/view/228083/1/
| LIA Briefed On Pilot Project |  |  |
| Monday, 09 August 2010 | |
| By MIKE BURKHOLDER Managing Editor CELINA — A standing-room only crowd packed the Celina Moose Saturday morning to hear about a pilot project that if successful, could help rid the lake of harmful algae. Ross Youngs, CEO of Algaeventure, briefed members of the Lake Improvement Association regarding the company’s pilot project to turn harmful cyanobacteria that is found in the lake into a nonthreatening species. Youngs said the plan is to turn the cyanobacteria into diatoms, which do not produce harmful toxins. The harmless algae would then be harvested for use in biofuels and other products. “What we are talking about ultimately is flipping the toxic algae to beneficial algae,” Youngs said. “The beneficial algae are diatoms.” Youngs said if the environment is conducive, diatoms will out-compete cyanobacteria in a given body of water. In order to thrive, diatoms need silica for food. “They are a major contributor to the food web,” Youngs said of diatoms. “Cyanobacteria are on the other end. They produce toxins to stop from being eaten. Diatoms survive because they are prolific.” Youngs said as the lake’s temperature increased, the cyanobacteria started to thrive. Once the water temperature cools, the diatoms and harmless green algae will dominate. The presence of its food sources, Youngs said, also will help diatoms return to dominance. “When you have silica present in the water that is available for the diatoms, they will dominate any culture,” Youngs said. “That’s our focus. The toxic blooms themselves come from cyanobacteria. There are no fresh water toxic blooms of diatoms.” Youngs said each type of algae will thrive depending upon which conditions are present. For cyanobacteria, the present conditions of the lake are feeding its growth. “Cyanobacteria love the high nutrients, they love the warm weather and they love stagnant water,” Youngs said. “So essentially we’ve got a great growth situation out there. Diatoms love silica. They will grow in the warmer temperatures, they will grow with nutrients and grow with fairly low nutrients. There are so many species of diatoms, that they go through succession.” As part of their program, Algaeventure plans to partition off a 2.5 acre portion of the lake to test the feasibility of flipping the algae to diatoms via the introduction of silica or sand. Youngs said if silica is in the water column and available, diatoms will dominate. “The reality is what we are trying to do hasn’t been done anywhere near this scale and that’s the challenge,” Youngs said. By the end of August, Youngs said officials plan to treat a portion of the lake near Celina in an effort to flip it. Adding silica to the lake, Youngs said, would pose little risk to the health of Grand Lake St. Marys. “The risks are minimal,” Youngs said. “People don’t realize this but silica is the No. 2 most abundant element in the Earth’s crust. It’s everywhere.” During the next few months, Youngs said he plans to look at strategies regarding what it would take to treat the entire lake. Youngs said adding silica to the lake would not fuel the growth of cyanobacteria. “Silica is only a nutrient essential for diatoms,” Youngs said. “It’s not like phosphorous or nitrogen, which will allow other organisms to have growth from it. It’s pretty much a benign material. It’s sand. It will not assist cyanobacteria or any other blue-green algae to grow.” LIA members and visitors peppered Youngs with questions regarding the project. One question had to do with where the silica would go if introduced into the lake. “We did a brief calculation, kind of back of the envelop, and if we silica treated the lake for 100 years, we’d add less than a quarter inch of sediment,” Youngs said. “We are talking microscopic amounts. When you have the right kind of silica in there and diatom dominance, it can be somewhat of a self-perpetuating system but you’ve got to keep treating it.” Grand Lake Restoration Commission member Brian Miller briefed the group about some of the other program going on around the lake. Miller said the data from the AiryGators has been forwarded to a consulting firm and should be returned in the “very near future.” A sediment collector in the Big Chickasaw is running and pumping material in to a holding tube. The collector helps remove nutrients and sediment from the stream before it dumps into the lake. Miller said a second collector is scheduled to be placed in Beaver Creek late this week or early next week. Officials also plan to use alum dosing in Big Chickasaw Creek as well so more nutrients can be collected. St. Marys Township recently was awarded a grant for a third sediment collection, Miller said. The grant, through the Ohio EPA, is for $89,000 to help cover costs of the $140,000 project. The next meeting of the LIA is scheduled for 10 a.m. Sept. 4 at the Celina Moose Lodge. For more information, visit LakeImprovement.com. |
Wednesday, June 23, 2010
Nutrient controls contributing to Karenia Brevis blooms in the Gulf of Mexico.
Nutrient controls contributing to Karenia Brevis blooms in the Gulf of Mexico.
by Jason Lenes, et. al.
Slides 13, 14 and 15 discuss the results of a case study in 2001.
Increase in Si resulted in a 50% fall in K. brevis biomass.
Sunday, June 20, 2010
Red Tides - Florida
Red Tide Control and Mitigation Program
Pg 25
Biological control of Karenia brevi s toxicity
Georgia Institute of Technology, Julia Kubanek
PROJECT SNAPSHOT
Can other organisms break down red tide toxins? This study demonstrated that native Gulf
of Mexico phytoplankton species are capable of detoxifying waters containing red tide. The phytoplankton do not kill Karenia brevis cells, but they remove brevetoxin from the water column.
Introduction
Growing concern over Florida red tide impacts has motivated researchers to understand how blooms work and how to lessen their effects. There are several forms of brevetoxin (PbTx) produced by Karenia brevis. Researchers at Georgia Institute of Technology have shown the amount of the most reduced 50-90% when competitive phytoplankton species are present. Further understanding how this process occurs is an important step towards developing a biological control for red tide toxicity.
Project goals
The main goals were to identify which phytoplankton competitors can degrade waterborne brevetoxins and to understand how this degradation occurs. Researchers aimed to determine whether adding live phytoplankton could be a natural biological control of Karenia brevis toxicity and whether this method could also benefit marine life.
Findings and accomplishments
Researchers learned that many phytoplankton competitors (across taxonomic groups, including
diatoms, cryptophytes, and dinoflagellates) can remove waterborne PbTx-2 (see Figure 1). Testing for removal of other brevetoxins by the diatom Skeletonema costatum showed that the detoxifying effect depends on the specific form of brevetoxin (for example, PbTx-2 and -1 were removed, but PbTx-3, -6, and -9 were not removed), suggesting that enzymes play a role in the removal of brevetoxins by competitors.
By adding brevetoxins to killed cultures of Skeletonema costatum and finding no loss of toxin,
researchers learned that live cells are required to remove brevetoxins from the water column, and that the toxin does not simply stick to cellular debris associated with the competitors. However, compounds (probably proteins) exuded by competitors are responsible for some toxin breakdown or removal.
Tests of how much Skeletonema costatum is needed to remove brevetoxins from the water showed that the quantity of competitor cells present has only a small impact on toxin removal. What is most important is the presence of competitor cells.
Experiments with marine invertebrates were also done to learn whether the effects of toxins on
marine life could also be reduced. Tests with brine shrimp (Artemia salina) showed that Skeletonema costatum reduced brevetoxins and removed all toxic effects on the brine shrimp at environmentally realistic concentrations. Tests with the sea anemone Aiptasia pallida included observing physical and behavioral responses as well as toxin levels. Results showed that Skeletonema costatum reduced, and in some cases completely protected against, the physiological damages of brevetoxin exposure.
Pg 26
The finding that Skeletonema costatum can reduce the toxic effects of brevetoxins on marine invertebrates supports using competitor phytoplankton species as control agents for Karenia brevis -- a mitigation strategy that not only will reduce waterborne brevetoxin levels but also could reduce negative impacts on ecosystems and marine wildlife.
-----------------------------------------
Pg 31
Nutrient controls contributing to Karenia brevi s blooms in the Gulf of Mexico
University of South Florida, Jason Lenes
PROJECT SNAPSHOT
This project addresses one piece of the nutrient puzzle related to red tide. Researchers used computer models and experiments to show that increasing the amount of the nutrient silica in an ecosystem may favor the growth of more beneficial phytoplankton species rather than Karenia brevis.
Introduction
Understanding how Florida red tide blooms start, grow, and maintain themselves is key to finding ways to stop or reduce their impacts. Trichodesmium, a nitrogen-fixing marine microorganism, and rotting fish killed by brevetoxins are primary food sources for Karenia brevis in the eastern Gulf of Mexico. These nutrient sources provide nitrogen and phosphorus but not silica. Large amounts of silica continually enter the Gulf from Florida’s rivers.
Although Karenia brevis does not need silica to grow, competitive and faster-growing organisms in the Gulf do. In the early stages of a bloom, organisms that are close to sources of silica may be able to compete more effectively for nutrients. This competition may help slow the growth of Karenia brevis and its potential prey.
Project goals
The project used laboratory and field experiments and computer simulation models to test the role of silica in Karenia brevis growth. Researchers wanted to know how different types and amounts of nutrients available to Karenia brevis may favor growth of more beneficial species. This information can help explain how Karenia brevis blooms grow and maintain themselves in the Gulf, and possibly how altering types and amounts of nutrients might be used to control blooms.
Pg 32
...
To see whether the presence of silica resulted in competition for food sources, two test cases were run: (1) normal initial silica concentrations and (2) elevated initial silica concentrations.
In case 1, a Karenia brevis bloom began in June (see Figure 1a) in response to the “new” nitrogen provided by Trichodesmium. In late July, the bloom reached levels that would kill fish, which gave it nutrients from the rotting fish. The maximum Karenia brevis level predicted by HABSIM in early October was similar to what was seen in the 2001 bloom. Case 2 showed a similar pattern, but the higher concentrations of silica led to an increase in diatoms, which decreased the predicted overall Karenia brevis concentration by about 50 percent (see Figure 1b).
Potential applications
The project results and HABSIM are great starting points for bloom prediction. Future experiments will test how nutrients with and without silica can alter natural shore samples and will help show competition and dominance among co-occurring Gulf of Mexico phytoplankton species. These results will be used to further test HABSIM as a prediction tool. If models continue to show that increases in silica reduce Karenia brevis concentrations, then ways of changing the nutrient regime to treat and reduce blooms can be considered.
Sunday, March 14, 2010
Glacial / interglacial variations in atmospheric carbon dioxide
http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf
Glacial/interglacial variations in atmospheric carbon dioxide
Daniel M. Sigman* & Edward A. Boyle²
* Department of Geosciences, Guyot Hall, Princeton University, Princeton, New Jersey 08544, USA
² Department of Earth, Atmospheric, and Planetary Sciences, Room E34-258, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Massachusetts 02139,
USA
Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's `biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involving both the biology and physics of that region.
Pg 8 -
In the subantarctic, planktonic foraminiferal Cd/Ca and the 13C/12C of diatom-bound organic matter both show changes that are consistent with an ice age state of higher nutrient utilization62,82.
Fig 6 on page 9 gives a very clear depiction of the Dissolved Oxygen levels of surface water in present day oceans and during the last glacial period.
Glacial/interglacial variations in atmospheric carbon dioxide
Daniel M. Sigman* & Edward A. Boyle²
* Department of Geosciences, Guyot Hall, Princeton University, Princeton, New Jersey 08544, USA
² Department of Earth, Atmospheric, and Planetary Sciences, Room E34-258, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Massachusetts 02139,
USA
Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's `biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involving both the biology and physics of that region.
Pg 8 -
In the subantarctic, planktonic foraminiferal Cd/Ca and the 13C/12C of diatom-bound organic matter both show changes that are consistent with an ice age state of higher nutrient utilization62,82.
Fig 6 on page 9 gives a very clear depiction of the Dissolved Oxygen levels of surface water in present day oceans and during the last glacial period.
Wednesday, March 10, 2010
Role of Increased Marine Silica Input on Paleo-pCO2 Levels
http://www.agu.org/journals/pa/v015/i003/1999PA000427/
PALEOCEANOGRAPHY, VOL. 15, NO. 3, PAGES 292–298, 2000
Role of Increased Marine Silica Input on Paleo-pCO2 Levels
Kevin G. Harrison
Geology and Geophysics Department, Boston College, Chestnut Hill, Massachusetts
Abstract
Changing the supply of silica to the ocean may alter pCO2 levels. The increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake. The increased silica levels shifted species composition: Diatom populations increased and coccolith populations decreased. Decreasing the population of coccoliths decreased the flux of calcite to the sediments, which, in turn, lowered pCO2 levels enough to explain the glacial-interglacial pCO2 transition. Furthermore, the contemporary increase in dust delivered to the ocean’s mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present. To set the stage, this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses.
---------------
Silica flow into oceans has decreased in 20th Century and has not increased, this is one of the causes of Dead Zones in estuaries and coastal waters and for fish kills and harmful algal blooms in lakes and rivers.
The reduction is silica is both actual and in proportion to N and P flow.
Dams reduce the amount of silt flowing down rivers and higher agricultural activity results in higher N and P flow down rivers.
Its well documented that in River Mississippi Si : N ratio was 3 : 1 fifty years ago and not its < 1 : 1. This has resulted in the Gulf of Mexico Dead Zone.
PALEOCEANOGRAPHY, VOL. 15, NO. 3, PAGES 292–298, 2000
Role of Increased Marine Silica Input on Paleo-pCO2 Levels
Kevin G. Harrison
Geology and Geophysics Department, Boston College, Chestnut Hill, Massachusetts
Abstract
Changing the supply of silica to the ocean may alter pCO2 levels. The increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake. The increased silica levels shifted species composition: Diatom populations increased and coccolith populations decreased. Decreasing the population of coccoliths decreased the flux of calcite to the sediments, which, in turn, lowered pCO2 levels enough to explain the glacial-interglacial pCO2 transition. Furthermore, the contemporary increase in dust delivered to the ocean’s mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present. To set the stage, this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses.
---------------
Silica flow into oceans has decreased in 20th Century and has not increased, this is one of the causes of Dead Zones in estuaries and coastal waters and for fish kills and harmful algal blooms in lakes and rivers.
The reduction is silica is both actual and in proportion to N and P flow.
Dams reduce the amount of silt flowing down rivers and higher agricultural activity results in higher N and P flow down rivers.
Its well documented that in River Mississippi Si : N ratio was 3 : 1 fifty years ago and not its < 1 : 1. This has resulted in the Gulf of Mexico Dead Zone.
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.
Modification of the biogeochemical cycle of silica with eutrophication
Modification of the biogeochemical cycle of silica with eutrophication
Daniel J. Conley, Claire L. schelske, Eugene F. stoermer
Vol. 101: 179-192, 1993 MARINE ECOLOGY PROGRESS SERIES Mar. Ecol. Prog. Ser.
http://www.int-res.com/articles/meps/101/m101p179.pdf
ABSTRACT- Nutrient enrichment and consequent alteration of nutrient biogeochernical cycles is a serious problem in both freshwater and marine systems. The response of aquatic systems to additions of N and P is generally to increase algal biomass. The partitioning of these nutrients into different functional groups of autotrophic organisms is dependent upon both intrinsic and extrinsic factors.
A common response to nutrient loading in northern temperate aquatic ecosystems is an increase in diatom biomass. Because nutrient enrichment generally leads to increases in water column concentrations of total N and total P (and not Si) such nutrient loading can lead to transient nutrient limitation of diatom biomass due to lack of dissolved silicate (DSi). Increased production of diatom biomass can lead to an increased accumulation of biogenic silica in sediments, ultimately resulting in a decline in the water column reservoir of DSi. Such biogeochemical changes in the silica cycle induced by eutrophication were first reported for the North American Laurentian Great Lakes. However, these changes are not a regional problem confined to the Great Lakes, but occur in many freshwater and marine systems throughout the world. Here we summarize the effects of anthropogenic modification of silica biogeochemical cycles for the North American Laurentian Great Lakes, describe some of the biogeochemical changes occurring in other systems, and discuss some of the ecological implications of a reduction in water column DSi concentrations, including changes in species composition, as DSi concentrations become limiting to diatom growth and biomass, changes in food web dynamics, and altered nutnent-recycling processes.
...
Pg 11
"Man cannot alter the inputs of DSi to aquatic ecosystems to any significant extent; they are essentially uncontrollable and result from weathering reactions in the watershed."
This is no longer true.
NUALGI is a cost effective means to provide Silica to diatoms.
Daniel J. Conley, Claire L. schelske, Eugene F. stoermer
Vol. 101: 179-192, 1993 MARINE ECOLOGY PROGRESS SERIES Mar. Ecol. Prog. Ser.
http://www.int-res.com/articles/meps/101/m101p179.pdf
ABSTRACT- Nutrient enrichment and consequent alteration of nutrient biogeochernical cycles is a serious problem in both freshwater and marine systems. The response of aquatic systems to additions of N and P is generally to increase algal biomass. The partitioning of these nutrients into different functional groups of autotrophic organisms is dependent upon both intrinsic and extrinsic factors.
A common response to nutrient loading in northern temperate aquatic ecosystems is an increase in diatom biomass. Because nutrient enrichment generally leads to increases in water column concentrations of total N and total P (and not Si) such nutrient loading can lead to transient nutrient limitation of diatom biomass due to lack of dissolved silicate (DSi). Increased production of diatom biomass can lead to an increased accumulation of biogenic silica in sediments, ultimately resulting in a decline in the water column reservoir of DSi. Such biogeochemical changes in the silica cycle induced by eutrophication were first reported for the North American Laurentian Great Lakes. However, these changes are not a regional problem confined to the Great Lakes, but occur in many freshwater and marine systems throughout the world. Here we summarize the effects of anthropogenic modification of silica biogeochemical cycles for the North American Laurentian Great Lakes, describe some of the biogeochemical changes occurring in other systems, and discuss some of the ecological implications of a reduction in water column DSi concentrations, including changes in species composition, as DSi concentrations become limiting to diatom growth and biomass, changes in food web dynamics, and altered nutnent-recycling processes.
...
Pg 11
"Man cannot alter the inputs of DSi to aquatic ecosystems to any significant extent; they are essentially uncontrollable and result from weathering reactions in the watershed."
This is no longer true.
NUALGI is a cost effective means to provide Silica to diatoms.
Monday, March 1, 2010
Silicate as regulating nutrient in phytoplankton competition
http://www.int-res.com/articles/meps/83/m083p281.pdf
Vol. 83: 281-289, 1992
MARINE ECOLOGY PROGRESS SERIES
Published July 16
Silicate as regulating nutrient in phytoplankton competition
J. K. Egge, D. L. Aksnes
Department of Fisheries and Marine Biology. University of Bergen. Heyteknologisenteret, N-5020 Bergen. Norway
ABSTRACT- The development of phytoplankton communities was studied in floating enclosures. The enclosures were supplied with either surface water or water from 40 m depth. Nutrients with or without silicate were added in some of the experiments, while others received no artificial fertilization. It is shown that diatom dominance occurred irrespective of season if silicate concentration exceeded a threshold of approximately 2 PM. Flagellate dominance changed to diatom dominance within a few days after nutrient addition resulting in silicate concentrations above this threshold. Dominance of Phaeocystis sp. appeared on several occasions after the bloom of another species, but never at high silicate concentrations. The success of the diatom group seemed to be due to a high inherent growth rate at non-limiting silicate concentrations. Calculations indicated that the inherent growth rate for the diatom group had to be 5 to 50 % higher than for the flagellate group in order to explain the outcome of our experiments.
Vol. 83: 281-289, 1992
MARINE ECOLOGY PROGRESS SERIES
Published July 16
Silicate as regulating nutrient in phytoplankton competition
J. K. Egge, D. L. Aksnes
Department of Fisheries and Marine Biology. University of Bergen. Heyteknologisenteret, N-5020 Bergen. Norway
ABSTRACT- The development of phytoplankton communities was studied in floating enclosures. The enclosures were supplied with either surface water or water from 40 m depth. Nutrients with or without silicate were added in some of the experiments, while others received no artificial fertilization. It is shown that diatom dominance occurred irrespective of season if silicate concentration exceeded a threshold of approximately 2 PM. Flagellate dominance changed to diatom dominance within a few days after nutrient addition resulting in silicate concentrations above this threshold. Dominance of Phaeocystis sp. appeared on several occasions after the bloom of another species, but never at high silicate concentrations. The success of the diatom group seemed to be due to a high inherent growth rate at non-limiting silicate concentrations. Calculations indicated that the inherent growth rate for the diatom group had to be 5 to 50 % higher than for the flagellate group in order to explain the outcome of our experiments.
The possible importance of silicon in marine eutrophication
http://www.int-res.com/articles/meps/3/m003p083.pdf
Officer, C B., Ryther, J H (1980).
The possible importance of silicon in marine eutrophication.
Mar. Ecol. Prog. Ser 3: 83-91
Earth Sciences Department, Dartmouth College, Hanover, New Hampshire 03755, USA
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
ABSTRACT: Diatom phytoplankton populations are the usual food for zooplankton and filter feeding fishes and contribute in a direct way to the large fishable populations in coastal zones. Flagellates, on the other hand, are frequently poor foods for most grazers and can lead to undesirable eutrophication effects. Arguments are presented that silicon is often the controlling nutrient in altering a diatom to a flagellate community. The alteration is governed by the relative magnitudes of the natural fluxes of the nutrients nitrogen, phosphorus and silicon to the receiving water body and the recycled fluxes of nitrogen and phosphorus from zooplankton grazing and phytoplankton respiration and decomposition. Examples of such alterations are presented for oceanic, estuarine and inland water bodies.
THESIS
We can delineate several phytoplankton-based ecosystems in the coastal zone which may be altered by human introduction of nutrients and other biostimulatory chemicals into the ocean. Two such systems are of particular importance. One is the ecosystem dominated by diatoms which are the usual food for filter feeding fishes and zooplankton and contribute in a direct way to the large fishable populations in coastal zones. Diatoms grow very rapidly, have short lifetimes, are grazed heavily, and are rarely a nuisance. The other is the nondiatom ecosystem usually dominated by flagellates, including dinoflagellates, chrysophytes, chlorophytes and coccolithophoridae, though it also may contain large proportions of nonmotile green and bluegreen algae, particularly in brackish and estuarine environments. For convenience, the latter will be referred to here as the 'flagellate' ecosystem.
Flagellates persist for longer periods of time, many are known to be poor foods for most grazers, and the motile species are able to concentrate to undesirable concentrations due to their ability to swim and respond to light. Certain dinoflagellate epidemics, for example, are serious pollution events that must be understood to be predicted and controlled.
To our knowledge all excessive marine phytoplankton growths which have led to undesirable eutrophication effects have been related to flagellate blooms. These eutrophication effects can take several forms. One, the excessive growth, which is not grazed, can lead to oxygen deficiencies when the organic particulate matter sinks and subsequently consumes oxygen by respiration and decay. Such anoxic conditions can lead directly to fish and shellfish kills. Two, the toxic dinoflagellates, including some red tides, can adversely effect the marine ecosystem and can poison man through the consumption of shellfish which have filtered out the toxic components. Three, the flagellate blooms can reach proportions which discolor the water and make it unsightly and malodorous, reducing its esthetic and recreational value.
Diatoms require the major nutrients nitrogen, phosphorus and silicon for their photosynthesis; diatoms use silicon in approximately a one-to-one atomic ratio with nitrogen (Redfield et al., 1963). The flagellates associated with coastal eutrophication effects need only nitrogen and phosphorus, together with the trace elements and micronutrients that all autotrophs require.
Pg 5
H. Peterson (personal communication) states that San Francisco Bay does not at present have excessive or undesirable phytoplankton concentrations or conditions that might lead to the development of predominantly nuisance species or to serious dissolved oxygen deficiencies except locally, as in tributary streams along the margins. He cautions, however, that a significant reduction in the amount of available silicate that would accompany large scale diversions of freshwater inflow could alter this situation.
Pg 6
We suggest that the silicon in the bloom area was removed during the spring diatom bloom and that the recycled nitrogen and phosphorus provided the nutrient pool for the summer algal bloom.
CONCLUSIONS
Arguments have been presented as to the importance of the nutrient silicon in altering a generally desirable, diatom phytoplankton population to a frequently undesirable, flagellate phytoplankton population and consequent eutrophication effects. If these arguments are accepted, several possible conclusions follow. We mention three. One, rather than considering treatment procedures which remove the nutrients nitrogen and phosphorus from a sewage discharge into a eutrophied region, one might consider the addition, if feasible, of silica in quantity at the discharge site to alter the receiving waters to a diatom population and a consequent fertile and productive region. Two, regions with substantial natural silica inputs can toler ate larger sewage inputs of nitrogen and phosphorus before undesirable eutrophication effects occur. Three, as in Lake Michigan silica measurements are a critical key to the determination of the onset of undesirable eutrophication effects.
Officer, C B., Ryther, J H (1980).
The possible importance of silicon in marine eutrophication.
Mar. Ecol. Prog. Ser 3: 83-91
Earth Sciences Department, Dartmouth College, Hanover, New Hampshire 03755, USA
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
ABSTRACT: Diatom phytoplankton populations are the usual food for zooplankton and filter feeding fishes and contribute in a direct way to the large fishable populations in coastal zones. Flagellates, on the other hand, are frequently poor foods for most grazers and can lead to undesirable eutrophication effects. Arguments are presented that silicon is often the controlling nutrient in altering a diatom to a flagellate community. The alteration is governed by the relative magnitudes of the natural fluxes of the nutrients nitrogen, phosphorus and silicon to the receiving water body and the recycled fluxes of nitrogen and phosphorus from zooplankton grazing and phytoplankton respiration and decomposition. Examples of such alterations are presented for oceanic, estuarine and inland water bodies.
THESIS
We can delineate several phytoplankton-based ecosystems in the coastal zone which may be altered by human introduction of nutrients and other biostimulatory chemicals into the ocean. Two such systems are of particular importance. One is the ecosystem dominated by diatoms which are the usual food for filter feeding fishes and zooplankton and contribute in a direct way to the large fishable populations in coastal zones. Diatoms grow very rapidly, have short lifetimes, are grazed heavily, and are rarely a nuisance. The other is the nondiatom ecosystem usually dominated by flagellates, including dinoflagellates, chrysophytes, chlorophytes and coccolithophoridae, though it also may contain large proportions of nonmotile green and bluegreen algae, particularly in brackish and estuarine environments. For convenience, the latter will be referred to here as the 'flagellate' ecosystem.
Flagellates persist for longer periods of time, many are known to be poor foods for most grazers, and the motile species are able to concentrate to undesirable concentrations due to their ability to swim and respond to light. Certain dinoflagellate epidemics, for example, are serious pollution events that must be understood to be predicted and controlled.
To our knowledge all excessive marine phytoplankton growths which have led to undesirable eutrophication effects have been related to flagellate blooms. These eutrophication effects can take several forms. One, the excessive growth, which is not grazed, can lead to oxygen deficiencies when the organic particulate matter sinks and subsequently consumes oxygen by respiration and decay. Such anoxic conditions can lead directly to fish and shellfish kills. Two, the toxic dinoflagellates, including some red tides, can adversely effect the marine ecosystem and can poison man through the consumption of shellfish which have filtered out the toxic components. Three, the flagellate blooms can reach proportions which discolor the water and make it unsightly and malodorous, reducing its esthetic and recreational value.
Diatoms require the major nutrients nitrogen, phosphorus and silicon for their photosynthesis; diatoms use silicon in approximately a one-to-one atomic ratio with nitrogen (Redfield et al., 1963). The flagellates associated with coastal eutrophication effects need only nitrogen and phosphorus, together with the trace elements and micronutrients that all autotrophs require.
Pg 5
H. Peterson (personal communication) states that San Francisco Bay does not at present have excessive or undesirable phytoplankton concentrations or conditions that might lead to the development of predominantly nuisance species or to serious dissolved oxygen deficiencies except locally, as in tributary streams along the margins. He cautions, however, that a significant reduction in the amount of available silicate that would accompany large scale diversions of freshwater inflow could alter this situation.
Pg 6
We suggest that the silicon in the bloom area was removed during the spring diatom bloom and that the recycled nitrogen and phosphorus provided the nutrient pool for the summer algal bloom.
CONCLUSIONS
Arguments have been presented as to the importance of the nutrient silicon in altering a generally desirable, diatom phytoplankton population to a frequently undesirable, flagellate phytoplankton population and consequent eutrophication effects. If these arguments are accepted, several possible conclusions follow. We mention three. One, rather than considering treatment procedures which remove the nutrients nitrogen and phosphorus from a sewage discharge into a eutrophied region, one might consider the addition, if feasible, of silica in quantity at the discharge site to alter the receiving waters to a diatom population and a consequent fertile and productive region. Two, regions with substantial natural silica inputs can toler ate larger sewage inputs of nitrogen and phosphorus before undesirable eutrophication effects occur. Three, as in Lake Michigan silica measurements are a critical key to the determination of the onset of undesirable eutrophication effects.
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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