Re: dead zones and water nutrients
Sorry, I should have referred specifically to shellfish farming. Shellfish are not fed, they consume plankton in the water. Thus they remove nutrients. Bill Silvert - Original Message - From: James Crants [EMAIL PROTECTED] To: ECOLOG-L@LISTSERV.UMD.EDU Sent: Sunday, February 17, 2008 3:05 AM Subject: Re: dead zones and water nutrients Regarding fish farms to solve the problem, I'm skeptical that they would work. Fish farms usually add to nutrient loads because the operators feed the fish rather than counting on the river to bring enough food in.
Re: dead zones and water nutrients
I don't have the material at hand, but I believe that these calculations have been done for the Baltic. There is a large and growing anoxic zone which is attributed to agricultural runoff, and I am almost certain that the connection has been established through quantitative models. And I see no reason why these effects should be localised. Bill Silvert - Original Message - From: Esat Atikkan [EMAIL PROTECTED] To: ECOLOG-L@LISTSERV.UMD.EDU Sent: Wednesday, February 13, 2008 7:04 PM Subject: Re: Let's talk about the Gulf dead zone and water nutrients The 'bacteria decomposing dead algae' thus depleting O2 model could possibly explain local hypoxia/anoxia. However when the O2 depleted area becomes as broad as that seen in the Gulf of Mexico or in the Pacific Ocean, off Oregon, that model may be lacking. One approach would be to estimate the actual amount of such algae reaching the bottom, and the quantity of O2 it would take to decompose (via bacteria). Is anyone aware of such a quantification? Esat Atikkan William Silvert [EMAIL PROTECTED] wrote: Just to hit the first point, the reason why hypereutrophic waters tend to have benthic dead zones is because they produce too much algae, which sink rather than being eaten and accumulates on the bottom. There it is degraded by bacteria, and this is the process that sucks up the oxygen. Bill Silvert
Re: dead zones and water nutrients
In case anyone is teaching a class on this topic, please consider directing your students to this news brief we prepared in November, 2006. http://sciencebulletins.amnh.org/?sid=b.s.dead_zones.20061113src=l --- William Silvert [EMAIL PROTECTED] wrote: I don't have the material at hand, but I believe that these calculations have been done for the Baltic. There is a large and growing anoxic zone which is attributed to agricultural runoff, and I am almost certain that the connection has been established through quantitative models. And I see no reason why these effects should be localised. Bill Silvert - Original Message - From: Esat Atikkan [EMAIL PROTECTED] To: ECOLOG-L@LISTSERV.UMD.EDU Sent: Wednesday, February 13, 2008 7:04 PM Subject: Re: Let's talk about the Gulf dead zone and water nutrients The 'bacteria decomposing dead algae' thus depleting O2 model could possibly explain local hypoxia/anoxia. However when the O2 depleted area becomes as broad as that seen in the Gulf of Mexico or in the Pacific Ocean, off Oregon, that model may be lacking. One approach would be to estimate the actual amount of such algae reaching the bottom, and the quantity of O2 it would take to decompose (via bacteria). Is anyone aware of such a quantification? Esat Atikkan William Silvert [EMAIL PROTECTED] wrote: Just to hit the first point, the reason why hypereutrophic waters tend to have benthic dead zones is because they produce too much algae, which sink rather than being eaten and accumulates on the bottom. There it is degraded by bacteria, and this is the process that sucks up the oxygen. Bill Silvert Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs
Re: dead zones and water nutrients
Nice presentation. I am not disputing the appearance of dead zones. We have been seeing them in the mainstem of the Chesapeake during the last few years. The 'excessive' algae growth model is probably appropriate in the Chesapeake Bay, possibly the Baltic, as they tend to enclosed relatively small areas, where nutrient concentrations can escalate rapidly. My question is that model sufficient to explain dead zones encountered in well cleanesed open sea/ocean areas, where the nutrient conc would not escalate that much. SO the question is there another/other factors acting outside of the dead algae model, or such factors acting synergistically. The more concrete answer is: are there studies that quantify the nutrient levels, the expected algae that would generate, and the O2 needed to decompose that biomass of algae. Esat Atikkan Ned Gardiner [EMAIL PROTECTED] wrote: In case anyone is teaching a class on this topic, please consider directing your students to this news brief we prepared in November, 2006. http://sciencebulletins.amnh.org/?sid=b.s.dead_zones.20061113src=l --- William Silvert wrote: I don't have the material at hand, but I believe that these calculations have been done for the Baltic. There is a large and growing anoxic zone which is attributed to agricultural runoff, and I am almost certain that the connection has been established through quantitative models. And I see no reason why these effects should be localised. Bill Silvert - Original Message - From: Esat Atikkan To: Sent: Wednesday, February 13, 2008 7:04 PM Subject: Re: Let's talk about the Gulf dead zone and water nutrients The 'bacteria decomposing dead algae' thus depleting O2 model could possibly explain local hypoxia/anoxia. However when the O2 depleted area becomes as broad as that seen in the Gulf of Mexico or in the Pacific Ocean, off Oregon, that model may be lacking. One approach would be to estimate the actual amount of such algae reaching the bottom, and the quantity of O2 it would take to decompose (via bacteria). Is anyone aware of such a quantification? Esat Atikkan William Silvert wrote: Just to hit the first point, the reason why hypereutrophic waters tend to have benthic dead zones is because they produce too much algae, which sink rather than being eaten and accumulates on the bottom. There it is degraded by bacteria, and this is the process that sucks up the oxygen. Bill Silvert Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs - Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.
Re: dead zones and water nutrients
The 'excessive' algae growth model is probably appropriate in the Chesapeake Bay, possibly the Baltic, as they tend to enclosed relatively small areas, where nutrient concentrations can escalate rapidly. I wonder if the Arabian Sea, hypoxic below 100 m, might qualify. Along the coast of Oman both high primary productivity and periodic fish kills are attributed to seasonal upwellings of high nutrient, low oxygen deep waters - produced by high primary productivity death and sinking. I wonder too if fish kills in Maldives in late 2007 may have a similar explanation. Bill On Feb 16, 2008 12:37 PM, Esat Atikkan [EMAIL PROTECTED] wrote: Nice presentation. I am not disputing the appearance of dead zones. We have been seeing them in the mainstem of the Chesapeake during the last few years. The 'excessive' algae growth model is probably appropriate in the Chesapeake Bay, possibly the Baltic, as they tend to enclosed relatively small areas, where nutrient concentrations can escalate rapidly. My question is that model sufficient to explain dead zones encountered in well cleanesed open sea/ocean areas, where the nutrient conc would not escalate that much. SO the question is there another/other factors acting outside of the dead algae model, or such factors acting synergistically. The more concrete answer is: are there studies that quantify the nutrient levels, the expected algae that would generate, and the O2 needed to decompose that biomass of algae. Esat Atikkan Ned Gardiner [EMAIL PROTECTED] wrote: In case anyone is teaching a class on this topic, please consider directing your students to this news brief we prepared in November, 2006. http://sciencebulletins.amnh.org/?sid=b.s.dead_zones.20061113src=l --- William Silvert wrote: I don't have the material at hand, but I believe that these calculations have been done for the Baltic. There is a large and growing anoxic zone which is attributed to agricultural runoff, and I am almost certain that the connection has been established through quantitative models. And I see no reason why these effects should be localised. Bill Silvert - Original Message - From: Esat Atikkan To: Sent: Wednesday, February 13, 2008 7:04 PM Subject: Re: Let's talk about the Gulf dead zone and water nutrients The 'bacteria decomposing dead algae' thus depleting O2 model could possibly explain local hypoxia/anoxia. However when the O2 depleted area becomes as broad as that seen in the Gulf of Mexico or in the Pacific Ocean, off Oregon, that model may be lacking. One approach would be to estimate the actual amount of such algae reaching the bottom, and the quantity of O2 it would take to decompose (via bacteria). Is anyone aware of such a quantification? Esat Atikkan William Silvert wrote: Just to hit the first point, the reason why hypereutrophic waters tend to have benthic dead zones is because they produce too much algae, which sink rather than being eaten and accumulates on the bottom. There it is degraded by bacteria, and this is the process that sucks up the oxygen. Bill Silvert Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs - Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.
Re: dead zones and water nutrients
I don't see why an excessive algal growth model would fail to predict a large hypoxic zone around the mouth of the Mississippi. In fact, the models apparently do predict it, though I can't say if they get the right answer for the wrong reason. The Mississippi watershed is vast, and an enormous portion of that watershed is dedicated to intensive agriculture with heavy fertilizer use. Also, the algae are presumably dispersed beyond where they grow and die, and the hypoxic water presumably disperses beyond where decomposition occurs, so the hypoxic zone need not be restricted to locations with enough nutrients to support algal blooms. Given that the hypoxic zone is pretty much on the continental shelf and away from the Gulf's major currents (based on maps you cna find at http://oceancurrents.rsmas.miami.edu/caribbean/caribbean-cs.html and http://www.epa.gov/gmpo/nutrient/hypoxia_pressrelease.html), it seems plausible that the Gulf in the vicinity of the mouth of the Mississippi is stagnant enough to allow the hypoxic zone to grow quite large. Regarding fish farms to solve the problem, I'm skeptical that they would work. Fish farms usually add to nutrient loads because the operators feed the fish rather than counting on the river to bring enough food in. Also, you mentioned keeping the fish in lakes connected to the river, I believe. It seems to me that, every growing season, these lakes would sprout algal blooms, go hypoxic, and kill off the fish. But then, I'm a terrestrial biologist. I don't know quite enough about aquatic ecology to answer the original question satisfactorally, but I don't think I've yet heard of a miracle cure for everything that actually worked. Jim
