After a long hiatus generated by the collapse of the economy during the past 6-9 months, the project staff is ready again to begin updating everyone on our progress on the project. In the next few weeks and months, we'll be adding posts that describe our results to date and the field and laboratory work that will likely be undertaken over the winter months. We apologize for this long hiatus; making making a living took time away from the project in various unexpected ways.
The first bit of news is that Brian gave a review presentation about the project on August 2nd to about 60 people who attended the program as a part of the Town of Madison's Old Home Week activities. Most of the folks there had not heard about the project before, and so there were lots of great questions and discussions about how citizen science projects like ours can get started up, about local/regional climate change, and about the geologic and natural histories of Big PPP. Of particular interest was the possibility that folks on Silver Lake may be interested in a project like ours. We'll keep you posted on any such developments.
Meantime and for now, that's it - back soon with more "good stuff".
Monday, August 24, 2009
Monday, December 22, 2008
Scientific Information Posting No. 23
LATEST PROJECT NEWS
First, the MPEP Team has been invited, both formally and informally, to present papers regarding its work to date at the Annual Meeting of the Northeastern Section of the Geological Society of America this coming March in Portland, Maine. These invitations are the result of the scientific interest our project is generating in the post-glacial geologic and paleolimnological communities of the northeastern U.S. and adjacent Canada during the past year. This is an important opportunity for us to present and discuss our current findings with others active in the same scientific fields, and we're excited to be a part of such a process. The abstracts for each presentation can be found by clicking on the following link icon:
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| Abstracts |
As you already know, we obtained a new basal carbon-14 date for the bottom of the Pond that shows when the influences of the last glacial ice left the basin (~14,000 calendar years ago; see earlier Post). Since that time, we've analyzed the bottom 6 core samples (6 more to go), and have established that while the temperature of the Pond's water varied somewhat from time to time, the organic content of the sediments increased fairly steadily after the Pond was de-iced up to about 9,660 calendar years ago. At that point, something unusual occurred here, and right now we don't know precisely what.
Near the top of core sample T-7, we found two +/- 1 inch-thick light tan to yellow colored bands about 2 inches apart within the otherwise dark greenish brown to black sediment. These were the first such variations we found up to that point in the otherwise consistent sedimentation shown in the cores, and we immediately determined that they must represent some significant change in the environment around the point in time. We initially thought, based on what we estimated the likely rate of sedimentation in the Pond basin to be, that these bands might be the local representation of an important global cooling event that occurred 8,200 calendar years ago. If it did, it would be a very significant finding.
Accordingly, we carefully sampled each band to check their organic content, the relative temperature of the water at the time (from the species of chironomids present in the band's sediment), and their age via a sample for carbon-14 (AMS) dating taken from the regular sediment in the area between the two bands. The date came out at ~ 9,660 calendar years - too old for the bands to be related to the 8,200-year cooling event, but the organic content and the relative temperature of the water both drop significantly within each band. Thus, the bands do represent two significant cooling events of perhaps 100-years each with a break of maybe 150-200 years in between. We've tried to specifically relate the date of these bands with other known climatic cooling events, but have so far been unsuccessful.
Microscopic observation of the contents of the sediment within the bands after all organic material has been removed show they are composed of a combination of millions of siliceous diatom remains intermixed with a generally light-tan to yellow, but in some places orangey and pinkish residue that survived the high heat of the organic removal process with its various colors intact. We don't yet know what this residue is composed of, but we've sent samples out for geochemical analysis. When we get the results and combine them with the pollen analyses that are to begin soon on all the cores, we should be able to determine what these unusual sediments indicate about climate changes in the Pond basin back about 9,600 years ago.
We, of course, will keep you posted here on the blog in the next few weeks. Meantime, if you have comments or questions, please contact us by commenting here on the blog (instruction for doing so on the homepage). So far, very few folks have chosen to comment, but please do. It's easy, and it will be great to hear what you think the bands may represent about our Pond "back in "The 96-Hundreds".
Wednesday, October 8, 2008
Scientific Posting #22
The Chironomids
Among the sources of evidence of past climate conditions that lie buried in the layered sediments of lake bottoms are the remains of midge larvae. Today, non-biting midges (of the insect order Diptera, family Chironomidae) are abundant almost everywhere. You may have encountered tiny adult midges lying dead beneath the nightlight in the bathroom in the morning. They lay eggs in water and their larvae go through a series of molts before they metamorphose into pupae and ultimately into flying adults. The larvae (1/16th to 1/8th inch or so in length) are cumulatively so abundant that they typically form the largest single source of animal biomass in lake-bottom sediments. As such, they contribute an important food chain link between the detrital organic matter and algae that they eat and larger benthic (i.e., bottom dwelling) invertebrates or bottom-feeding fishes.
Because of their ecological importance, this group of insects has been well studied with regard to their identity (>5000 species worldwide so far), their distribution and the conditions required for their well-being. As arthropods, their construction includes a non-living exoskeleton covering that remains more or less intact long after the decomposable organic parts of the animal are lost over time. The head capsule of these animals are particularly thick and resilient and can be found identifiably preserved in the sediments into which they settled even thousands of years ago. Features of their heads – especially the appearance of their teeth, their dentition – are used by biologists to identify them at least to the genus level.
To study the chironomids present in the distant past, 3 cubic centimeter subsamples of sediment are removed from various levels within a sediment core. Each sample is immersed in hot 5% potassium hydroxide solution for 20 minutes, which disaggregates clumped sediment particles. The resulting mixture is passed through sieves with mesh sizes of 118 μm (micrometers) and 53 μm and rinsed with distilled water. Particles larger than 118 μm and 53 μm respectively, including the head capsules of chironomids, are retained in the sieves, while the bulk of the material, including most of the disaggregated sediment particles, pass through the 53 μm mesh. The material caught by each sieve is back-washed into a Petri dish and examined using 40X power of a dissecting microscope (see Figure 1).
Figure 1
Watch-makers forceps are used to transfer each head capsule present within the resulting debris to a drop of CMC-10 mounting medium on glass slides. A coverslip is added and the slide is observed using 100-430X power of a phase contrast compound microscope. Identifications are made with reference to several helpful publications (especially, Brooks, SJ, Langdon, PG, and Heiri, O. The Identification and Use of Palaearctic Chironomidae Larvae in Palaeoecology. Quaternary Research Association Technical Guide No. 10. 2007). A minimum of 50 chironomid heads must be located and identified to provide sufficient data to characterize the community of these animals found at a particular depth (= age) within a sediment core. It requires 3-5 hours of painstaking work to complete the analysis of each subsample.
The composition of the chironomid community that settles into surface bottom sediments today would be very different from that found towards the deepest segments of our core sample. The climatic conditions that favor today's community are presumably quite different (e.g., much warmer) than conditions here would have been 10,000 years ago. While many of the chironomid types found in the deepest parts of our core are no longer found locally, they do occur alive and well in today's cold climate areas such as Baffin Island or Labrador or in high elevation alpine tarns. Biologists studying these high latitude or elevation types have been able to determine the environmental conditions that these living representatives require. Distribution of chironomids is particularly highly correlated with mid-summer, surface-water temperatures of the lakes where they are found. We assume that the same critters living here years ago had similar requirements to their currently living representatives that over time followed the cold water conditions they prefer polewardly as the glaciers retreated and the climate here warmed. Species that have narrow preferences for cold water conditions are especially useful as indicator species, i.e., their presence in the past suggests that this narrow range of cold conditions existed then. Such species are referred to as stenothermal (steno – (Greek) narrow + thermal – (Greek) temperature) and they can be used as "proxy" clues to reveal temperature conditions wherever or whenever they are found.
Predictive models have been constructed based on documented requirements of each of these stenothermal species. Each species' optimal mid-summer, surface-water temperature requirement contributes in proportion to that species' abundance within a chironomid community from the past (i.e., from a particular sediment level) to produce a best-guess inferred mid-summer, surface-water temperature present at the time when that layer of sediment settled out.
Figure 2
(For example, Heterotrissocladius, shown in Figure 2, has an optimal temperature of 11.1 C, while Sergentia, shown in Figure 3, is optimal at 9.8 C). Doing this repeatedly at intervals through the sediment core permits the reconstruction of the most-likely temperature history of the pond over time.
Figure 3
We extracted a first-round of 15 sediment samples at 20 cm intervals from the deepest part of our core. Preliminary results demonstrate that we need to add intervening samples, resulting in 10 cm intervals, to improve the resolution of our model-generated temperature curve. We intend to gather these additional samples (and more) when we return to the core sampling on October 25th. It will be some time before the more refined results will be available. For now, we can say that in comparison to the mid-summer, surface-water temperature of 24.5 C (76 F) at Big Pea Porridge Pond in 2008 (see Scientific Posting # 20), comparable model-generated temperatures from the earliest portions of our core are, appropriately, in the 12-18 C (53.5-64.5 F) range.
Lee Pollock
Among the sources of evidence of past climate conditions that lie buried in the layered sediments of lake bottoms are the remains of midge larvae. Today, non-biting midges (of the insect order Diptera, family Chironomidae) are abundant almost everywhere. You may have encountered tiny adult midges lying dead beneath the nightlight in the bathroom in the morning. They lay eggs in water and their larvae go through a series of molts before they metamorphose into pupae and ultimately into flying adults. The larvae (1/16th to 1/8th inch or so in length) are cumulatively so abundant that they typically form the largest single source of animal biomass in lake-bottom sediments. As such, they contribute an important food chain link between the detrital organic matter and algae that they eat and larger benthic (i.e., bottom dwelling) invertebrates or bottom-feeding fishes.
Because of their ecological importance, this group of insects has been well studied with regard to their identity (>5000 species worldwide so far), their distribution and the conditions required for their well-being. As arthropods, their construction includes a non-living exoskeleton covering that remains more or less intact long after the decomposable organic parts of the animal are lost over time. The head capsule of these animals are particularly thick and resilient and can be found identifiably preserved in the sediments into which they settled even thousands of years ago. Features of their heads – especially the appearance of their teeth, their dentition – are used by biologists to identify them at least to the genus level.
To study the chironomids present in the distant past, 3 cubic centimeter subsamples of sediment are removed from various levels within a sediment core. Each sample is immersed in hot 5% potassium hydroxide solution for 20 minutes, which disaggregates clumped sediment particles. The resulting mixture is passed through sieves with mesh sizes of 118 μm (micrometers) and 53 μm and rinsed with distilled water. Particles larger than 118 μm and 53 μm respectively, including the head capsules of chironomids, are retained in the sieves, while the bulk of the material, including most of the disaggregated sediment particles, pass through the 53 μm mesh. The material caught by each sieve is back-washed into a Petri dish and examined using 40X power of a dissecting microscope (see Figure 1).
Figure 1The composition of the chironomid community that settles into surface bottom sediments today would be very different from that found towards the deepest segments of our core sample. The climatic conditions that favor today's community are presumably quite different (e.g., much warmer) than conditions here would have been 10,000 years ago. While many of the chironomid types found in the deepest parts of our core are no longer found locally, they do occur alive and well in today's cold climate areas such as Baffin Island or Labrador or in high elevation alpine tarns. Biologists studying these high latitude or elevation types have been able to determine the environmental conditions that these living representatives require. Distribution of chironomids is particularly highly correlated with mid-summer, surface-water temperatures of the lakes where they are found. We assume that the same critters living here years ago had similar requirements to their currently living representatives that over time followed the cold water conditions they prefer polewardly as the glaciers retreated and the climate here warmed. Species that have narrow preferences for cold water conditions are especially useful as indicator species, i.e., their presence in the past suggests that this narrow range of cold conditions existed then. Such species are referred to as stenothermal (steno – (Greek) narrow + thermal – (Greek) temperature) and they can be used as "proxy" clues to reveal temperature conditions wherever or whenever they are found.
Predictive models have been constructed based on documented requirements of each of these stenothermal species. Each species' optimal mid-summer, surface-water temperature requirement contributes in proportion to that species' abundance within a chironomid community from the past (i.e., from a particular sediment level) to produce a best-guess inferred mid-summer, surface-water temperature present at the time when that layer of sediment settled out.
Figure 2
Figure 3We extracted a first-round of 15 sediment samples at 20 cm intervals from the deepest part of our core. Preliminary results demonstrate that we need to add intervening samples, resulting in 10 cm intervals, to improve the resolution of our model-generated temperature curve. We intend to gather these additional samples (and more) when we return to the core sampling on October 25th. It will be some time before the more refined results will be available. For now, we can say that in comparison to the mid-summer, surface-water temperature of 24.5 C (76 F) at Big Pea Porridge Pond in 2008 (see Scientific Posting # 20), comparable model-generated temperatures from the earliest portions of our core are, appropriately, in the 12-18 C (53.5-64.5 F) range.
Lee Pollock
Monday, October 6, 2008
Scientific Posting #21
Follow-up Plankton Tow in Big Pea Porridge Pond, August 26, 2008
To explore the composition of the plankton community responsible for the "positive heterograde" dissolved oxygen curve (see Scientific Posting No. 20), a 10 minute plankton tow was taken along a mid-lake transect with the net weighted to tow at a depth of ca 10 feet. Here is an annotated listing of some members of the plankton community at Big Pea Porridge Pond in Madison, NH, August, 2008
PHYTOPLANKTON = the microscopic, unicellular or colonial PLANT (or in one case bacterial) component of the plankton community.
Division: Cyanobacteria – blue-green bacteria
Anabaena : Chain of beads, including an occasional, larger "bead" known as a heterocyst. This is the site of nitrogen-fixation. This genus can become overly productive blooms and cause water quality problems. The neat thing about Anabaena in Big PPP is that it was not at all abundant. However, it formed some tiny ball-like masses to which a form of stalked ciliate protozoa, Vorticella-like, was attached. The beating of the cilia to create feeding currents by the Vorticella also propelled the entire colony around through the water – presumably an asset to Anabaena by bringing it to fresh nutrients and reducing its sinking rate in the water column.
Division: Crysophyta – golden-brown algae
Dinobryon: Colonial. Vase-shaped case or lorica, each with two flagella to provide some mobility to the colony. When abundant, Dinobryon sertularia gives a fishy taste to the water.
Diatoma: Colonial diatom.
Division: Chlorophyta – green algae
Asterionella – star shaped colonies. Individuals are glued to one another at one end by mucilage.
Micractinium – small spherical cells with projecting spines to aid with floatation.
Division: Pyrrhophyta – dinoflagellates
Ceratium – armor plated cell with 3 long projecting spines that assist in floatation. They are "mixotrophic", i.e., they both photosynthesize like a plant and phagocytize, eating other organisms, like an animal.
ZOOPLANKTON = the microscopic, unicellular ANIMAL component of the plankton community.
Phylum: Rotifera
Asplanchna – large sac-like rotifer. Feeds on algae and bacteria. Its presence here suggests productivity is more towards the oligotrophic side. It also suggests that pH of Big PPP is usually at or above 7 (neutrality).
Keratella feed on algae and microorganisms. They tend to have two population maxima – one in the spring and a second in the summer. They live for about 3 weeks – longer than many rotifers whose lifespan in measured in days. They tend to be associated with oligotrophic waters.
Kellicotia longispina – with 4 long spines that assist with buoyancy – slowing its sinking rate. They are typically in oligotrophic waters and have a single mid-summer population maximum.
Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca
Order: Cladocera ("water fleas")
There are illustrations and descriptions of each of these water flea species at: http://ilmbwww.gov.bc.ca/risc/pubs/aquatic/crustacea/
Bosmina longirostrus A small, substrate-dwelling type with antennae modified to form an "elephant trunk"-like projection. The remains of exoskeletons of this type of water flea are the most common objects of animal origin found in our deep core samples from the past.
Daphnia longiremis Their egg cases or ephippia are among the items that remain well preserved in the sediments thousands of years old in our core samples. An indicator species for cold, oligotrophic waters.
Holopedium – has an inflated body covering encased in a large gelatinous coating. Uniquely among water fleas, it swims ventral side up. It tends to be associated with lakes tending toward the acid side of the pH scale, so it's presence in Big PPP clashes a bit with the rotifer Asplanchna. An indicator species for cold, oligotrophic waters.
Leptodora – a large (up to 18 mm) and bizarre water flea with enlarged, wing-like second antennae and legs adapted for capturing rotifers and other plankton.
Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca
Order: Copepoda
Cyclopoid copepods: club-shaped body with curved antennae or moderate length. Some are predatory, others are grazers. Undoubtedly several species.
Calanoid copepods: torpedo-shaped body with long straight antennae. Algal filter-feeders. At least two species – including one bearing conspicuous orange droplets of oil-storage reserved. This species is often associated with acidified waters.
Nauplius larva: only three-pairs of appendages. Undergo six growth stages or moults. Life cycle lasts 5-6 months.
As a rough indication of the relative abundance of these members of the plankton community at Big Pea Porridge Pond in late August, 2008, the following lists numbers observed in a 5 cc sample from a 10 minute plankton tow at 10 foot depth.
Phytoplankton (# of colonies)
300 Dinobryon slender
10 Dinobryon sertularia
600 Micractinium
60 Asterionella
80 Diatoma
10 Ceratium (individuals)
2 Anabaena
Rotifera
1 Dichoerca
24 Keratella
2 Asplanchna
4 Kellicottia
Cladocera
1 Leptodora kindtii
8 Holopedium gibberum
19 Diaphanosoma brachyurum
4 Daphnia pulcaria?
3 Bosmina longirostrus
17 Ceriodaphnia reticulata
Copepoda
61 Calanoid copepods
49 Cyclopoid copepods
(Click on the image below to be linked to a slideshow of more images of community members)
Lee Pollock
To explore the composition of the plankton community responsible for the "positive heterograde" dissolved oxygen curve (see Scientific Posting No. 20), a 10 minute plankton tow was taken along a mid-lake transect with the net weighted to tow at a depth of ca 10 feet. Here is an annotated listing of some members of the plankton community at Big Pea Porridge Pond in Madison, NH, August, 2008
PHYTOPLANKTON = the microscopic, unicellular or colonial PLANT (or in one case bacterial) component of the plankton community.
Division: Cyanobacteria – blue-green bacteria
Anabaena : Chain of beads, including an occasional, larger "bead" known as a heterocyst. This is the site of nitrogen-fixation. This genus can become overly productive blooms and cause water quality problems. The neat thing about Anabaena in Big PPP is that it was not at all abundant. However, it formed some tiny ball-like masses to which a form of stalked ciliate protozoa, Vorticella-like, was attached. The beating of the cilia to create feeding currents by the Vorticella also propelled the entire colony around through the water – presumably an asset to Anabaena by bringing it to fresh nutrients and reducing its sinking rate in the water column.
Division: Crysophyta – golden-brown algae
Dinobryon: Colonial. Vase-shaped case or lorica, each with two flagella to provide some mobility to the colony. When abundant, Dinobryon sertularia gives a fishy taste to the water.
Diatoma: Colonial diatom.
Division: Chlorophyta – green algae
Asterionella – star shaped colonies. Individuals are glued to one another at one end by mucilage.
Micractinium – small spherical cells with projecting spines to aid with floatation.
Division: Pyrrhophyta – dinoflagellates
Ceratium – armor plated cell with 3 long projecting spines that assist in floatation. They are "mixotrophic", i.e., they both photosynthesize like a plant and phagocytize, eating other organisms, like an animal.
ZOOPLANKTON = the microscopic, unicellular ANIMAL component of the plankton community.
Phylum: Rotifera
Asplanchna – large sac-like rotifer. Feeds on algae and bacteria. Its presence here suggests productivity is more towards the oligotrophic side. It also suggests that pH of Big PPP is usually at or above 7 (neutrality).
Keratella feed on algae and microorganisms. They tend to have two population maxima – one in the spring and a second in the summer. They live for about 3 weeks – longer than many rotifers whose lifespan in measured in days. They tend to be associated with oligotrophic waters.
Kellicotia longispina – with 4 long spines that assist with buoyancy – slowing its sinking rate. They are typically in oligotrophic waters and have a single mid-summer population maximum.
Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca
Order: Cladocera ("water fleas")
There are illustrations and descriptions of each of these water flea species at: http://ilmbwww.gov.bc.ca/risc/pubs/aquatic/crustacea/
Bosmina longirostrus A small, substrate-dwelling type with antennae modified to form an "elephant trunk"-like projection. The remains of exoskeletons of this type of water flea are the most common objects of animal origin found in our deep core samples from the past.
Daphnia longiremis Their egg cases or ephippia are among the items that remain well preserved in the sediments thousands of years old in our core samples. An indicator species for cold, oligotrophic waters.
Holopedium – has an inflated body covering encased in a large gelatinous coating. Uniquely among water fleas, it swims ventral side up. It tends to be associated with lakes tending toward the acid side of the pH scale, so it's presence in Big PPP clashes a bit with the rotifer Asplanchna. An indicator species for cold, oligotrophic waters.
Leptodora – a large (up to 18 mm) and bizarre water flea with enlarged, wing-like second antennae and legs adapted for capturing rotifers and other plankton.
Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca
Order: Copepoda
Cyclopoid copepods: club-shaped body with curved antennae or moderate length. Some are predatory, others are grazers. Undoubtedly several species.
Calanoid copepods: torpedo-shaped body with long straight antennae. Algal filter-feeders. At least two species – including one bearing conspicuous orange droplets of oil-storage reserved. This species is often associated with acidified waters.
Nauplius larva: only three-pairs of appendages. Undergo six growth stages or moults. Life cycle lasts 5-6 months.
As a rough indication of the relative abundance of these members of the plankton community at Big Pea Porridge Pond in late August, 2008, the following lists numbers observed in a 5 cc sample from a 10 minute plankton tow at 10 foot depth.
Phytoplankton (# of colonies)
300 Dinobryon slender
10 Dinobryon sertularia
600 Micractinium
60 Asterionella
80 Diatoma
10 Ceratium (individuals)
2 Anabaena
Rotifera
1 Dichoerca
24 Keratella
2 Asplanchna
4 Kellicottia
Cladocera
1 Leptodora kindtii
8 Holopedium gibberum
19 Diaphanosoma brachyurum
4 Daphnia pulcaria?
3 Bosmina longirostrus
17 Ceriodaphnia reticulata
Copepoda
61 Calanoid copepods
49 Cyclopoid copepods
(Click on the image below to be linked to a slideshow of more images of community members)
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| From Scientific Posting #21 |
Lee Pollock
Monday, September 29, 2008
NEWS
LATEST NEWS
Now that the summer's activities and travels, along with two weddings(!), are out of the way, work is scheduled to restart on the project. The splitting, sampling, and logging of the remaining core samples is scheduled to be completed over the weekend of October 25-26, and thereafter, the remaining laboratory work (C-14, pollen analyses, Loss-On-Ignition, magnetic susceptibility, etc.) will be completed as soon as practical by the various labs services. Meantime, scheduling discussions will begin soon for the completion of the pond bottom-surface ground penetrating radar survey (GPR) that had to be postponed last winter because of slushy ice surface conditions on the pond.
So, as all this gets retarted, the blog will begin to become more active as this Autumn and Winter progress. For now, sorry for the long silence. We didn't quit the project - just had lots of professional and family obligations.
Tuesday, August 26, 2008
Scientific Posting #20
Mid-Summer Temperature-DO Profiles
Earlier, we posted results from winter and spring water column surveys of temperature and dissolved oxygen (a posting from April 4, 2008 and Scientific Posting Numbers 15 respectively). Accompanying those results are discussions of how this information can help us understand the circulation and productivity of Big Pea Porridge Pond.
This posting continues the sequence by adding temperature and oxygen profiles from summer (August 3, 2008), when the temperature stratification or layering of the water column is maximal. The warmed top layer or epilimnion of the lake shows temperature in the 23-25 C range (73.4-77 F) extending some 4 meters (13 ft) into the water column. The deep waters of the lake, i.e., the hypolimnion waters, are in the 7-8 C (44.5-46.5 F) range. The intervening zone, from 4-8 meters depth, in which the temperature falls by at least 1 degree/meter, is the metalimnion or thermocline.
Larger, "first class" lakes hold all of the summer-added heat in surface waters, leaving the deep hypolimnion waters constant at 4 C (39.2 F) year-round. The hypolimnion depths in smaller lakes like Big Pea Porridge Pond incorporate some "excess" surface heat defining our lake as a "second class" lake (an unfortunate term with ABSOLUTELY NO bearing on its importance to us!).
Oxygen enters freshwater lakes in one of three ways: imported -- via diffusion from the surrounding atmosphere or as dissolved oxygen in inlet streams, or in-situ -- as a by-product of photosynthesis (6 CO2 + 6 H20 → C6H12O6 (glucose) + 6 O2). The August 4th oxygen profile (circles) provides interesting results. A curve of this sort, with the oxygen maximum in the metalimnion (thermocline) is known as a "positive heterograde oxygen curve". Large, cold water inlet streams could theoretically bring higher levels of oxygen in as a colder, denser water mass at such depths. But there are no such inlet streams entering Big Pea Porridge Pond. The only other logical source for high levels of oxygen 6 meters down in the metalimnion would be productivity by single-celled or colonial phytoplankton located there. Because high light levels (including damaging UV light) found in surface waters are actually inhibitory to most phytoplankton, maximal photosynthetic activity by phytoplankton is usually found somewhat deeper. But a deep positive heterograde peak like that seen here in early August results from dominance by cold-adapted phytoplankton that do best in waters away from the sun-heated epilimnion. Often less-desirable blue-green photosynthetic bacteria such as the filamentous Oscillatoria are responsible for such curves. (Blue-greens are less desirable because they tend to produce chemical byproducts that other organisms find toxic). We need to follow up with a deep plankton tow to determine what phytoplankters are found at depth here in our pond.
Observed dissolved oxygen readings can be compared to the line in the figure with triangle symbols that represents what would have been saturation levels of dissolved oxygen based on the actual temperature reading alone (recall the inverse relationship between temperature and the solubility of all gases -- meaning that the higher the temperature, the less dissolved oxygen would be available). The supersaturation levels within the metalimnion are clear. But also note that observed dissolved oxygen falls short of saturation levels toward the bottom. Typically, loss of dissolved oxygen in deep waters results from oxygen consumption by the bacterial and fungal decomposers found in bottom sediments. The degree of their activity, and thus the degree of oxygen consumption through their respiration, is a reflection of the amount of organic (biologically produced) matter available. Little productivity (oligotrophy) would result in little decomposer activity and little oxygen depletion below saturation levels. High productivity (eutrophy) would provide enough organic fall-out to fuel extensive decomposer action and a steep depletion of deep oxygen perhaps even to producing anaerobic (oxygen-free) conditions. Our situation matches what we observed in our March profiles – about one half the available oxygen has been consumed, suggesting a mesotrophic condition in Big Pea Porridge Pond. .. Lee
Earlier, we posted results from winter and spring water column surveys of temperature and dissolved oxygen (a posting from April 4, 2008 and Scientific Posting Numbers 15 respectively). Accompanying those results are discussions of how this information can help us understand the circulation and productivity of Big Pea Porridge Pond.
This posting continues the sequence by adding temperature and oxygen profiles from summer (August 3, 2008), when the temperature stratification or layering of the water column is maximal. The warmed top layer or epilimnion of the lake shows temperature in the 23-25 C range (73.4-77 F) extending some 4 meters (13 ft) into the water column. The deep waters of the lake, i.e., the hypolimnion waters, are in the 7-8 C (44.5-46.5 F) range. The intervening zone, from 4-8 meters depth, in which the temperature falls by at least 1 degree/meter, is the metalimnion or thermocline.
Larger, "first class" lakes hold all of the summer-added heat in surface waters, leaving the deep hypolimnion waters constant at 4 C (39.2 F) year-round. The hypolimnion depths in smaller lakes like Big Pea Porridge Pond incorporate some "excess" surface heat defining our lake as a "second class" lake (an unfortunate term with ABSOLUTELY NO bearing on its importance to us!).
Oxygen enters freshwater lakes in one of three ways: imported -- via diffusion from the surrounding atmosphere or as dissolved oxygen in inlet streams, or in-situ -- as a by-product of photosynthesis (6 CO2 + 6 H20 → C6H12O6 (glucose) + 6 O2). The August 4th oxygen profile (circles) provides interesting results. A curve of this sort, with the oxygen maximum in the metalimnion (thermocline) is known as a "positive heterograde oxygen curve". Large, cold water inlet streams could theoretically bring higher levels of oxygen in as a colder, denser water mass at such depths. But there are no such inlet streams entering Big Pea Porridge Pond. The only other logical source for high levels of oxygen 6 meters down in the metalimnion would be productivity by single-celled or colonial phytoplankton located there. Because high light levels (including damaging UV light) found in surface waters are actually inhibitory to most phytoplankton, maximal photosynthetic activity by phytoplankton is usually found somewhat deeper. But a deep positive heterograde peak like that seen here in early August results from dominance by cold-adapted phytoplankton that do best in waters away from the sun-heated epilimnion. Often less-desirable blue-green photosynthetic bacteria such as the filamentous Oscillatoria are responsible for such curves. (Blue-greens are less desirable because they tend to produce chemical byproducts that other organisms find toxic). We need to follow up with a deep plankton tow to determine what phytoplankters are found at depth here in our pond.
Observed dissolved oxygen readings can be compared to the line in the figure with triangle symbols that represents what would have been saturation levels of dissolved oxygen based on the actual temperature reading alone (recall the inverse relationship between temperature and the solubility of all gases -- meaning that the higher the temperature, the less dissolved oxygen would be available). The supersaturation levels within the metalimnion are clear. But also note that observed dissolved oxygen falls short of saturation levels toward the bottom. Typically, loss of dissolved oxygen in deep waters results from oxygen consumption by the bacterial and fungal decomposers found in bottom sediments. The degree of their activity, and thus the degree of oxygen consumption through their respiration, is a reflection of the amount of organic (biologically produced) matter available. Little productivity (oligotrophy) would result in little decomposer activity and little oxygen depletion below saturation levels. High productivity (eutrophy) would provide enough organic fall-out to fuel extensive decomposer action and a steep depletion of deep oxygen perhaps even to producing anaerobic (oxygen-free) conditions. Our situation matches what we observed in our March profiles – about one half the available oxygen has been consumed, suggesting a mesotrophic condition in Big Pea Porridge Pond. .. Lee
Wednesday, August 6, 2008
Scientific Information Posting No. 19
NOTICE
UPCOMING PROJECT INFORMATION PROGRAMS
There are 2 informational programs concerning the project scheduled in the next several days for those interested who want to get caught up on latest research developments and plans.
The first is a slide and video illustrated presentation at 7:00 PM, on Thursday, August 7th, at the Tin Mountain Conservation Center's Headquarters, on Bald Hill Road, in Albany, NH. Specific program details can be obtained by contacting the TMCC at 447-6991.
The second is an informal "Display and Q & A Session" to be held in conjunction with the Green Mountain Conservation Group's Annual Celebratory Evening & Fundraising Dinner, beginning at 4:30 PM, on Saturday, August 9th, at the Province Lake Golf Club, in Parsonfield, Maine. Event information can be obtained by contacting the GMCG at 539-1859.
We look forward to seeing you.
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