Update

It's been a while since news has been posted here, so I thought it time to do so. In fact, it's way past time; the last post was in 2009 (!). Sorry...

Our project is still underway with work being complete in the labs at Plymouth State and in the labs of Beta Analytical, where our last 3 carbon-14 dates are being processed for us. We hope to have these results by months end (1/12), and I promise that I'll get them posted asap aftr I receive them. Thereafter, and after the rest of the lab work is complete, work will begin on another professional publication of our results. Portions of that will appear here as they become available.

Meantime, longtime Pond-resident Connie Brown is publishing a book about the history of the Pond in the next couple of months. That book will include the first layman's summary of climatic information for the Pond basin. So, keep an eye out for its availability, and we'll be "back here on the blog" soon.

Scientific Posting No. 24

Results at Last!

Here is one of the long overdue RESULTS reports that Brian mentioned recently. This one addresses our efforts to use subfossil remains of midge larvae to investigate Late Glacial temperatures at Big Pea Porridge Pond. As you will see, it is a work-in-progress. But this report will bring you up to date at least.

If you are interest in investigating a particular phenomenon in nature, you search the landscape for a setting that makes viewing that feature clear. To study distribution patterns of animals, for example, you don’t start out with the bewildering complexity of a tropical rainforest. On the other hand, if you are primarily interested in unraveling the story of a particular location, you must apply available procedures and make the best of the results you get. I’ll use our studies using chironomid (non-biting midge) larvae as a proxy (an indicator) of past climate temperatures to illustrate this point. Today, these insect larvae are abundant and diverse in lake bottom sediments. The same was true in the past.

To study past temperature changes, paleoecologists have selected small, shallow water bodies because they are sensitive to overlying atmospheric conditions. These water bodies mix easily and frequently with any modest wind. While in any water body, direct heating by the sun may be limited to surface waters, wind-driven mixing in shallow pools circulates warmed water throughout the water body and in the process heats up bottom sediments throughout the pond as well. When climate-sensitive adult midges reproduce and lay their eggs in such ponds, the eggs sink to the bottom where they hatch into tiny larvae that feed on organic debris, unicellular plants, and in some cases on each other. As benthic (i.e., bottom dwelling) creatures, they pass through 4 successive molts before eventually becoming pupae and finally adults. Figure 1 shows examples of these larvae.

Long after the soft parts of such larvae rot and disappear, their hard head capsules remain intact. For every egg laid or adult hatched, there are 4 hardened, exoskeleton head capsules (inset in Figure 1) left behind in the bottom sediments. Each year, debris from the plankton community, leaf litter, pollen grains, etc. sinks to form the next layer of bottom sediments, trapping beneath them sediment layers from previous years. Each year these settled sediments include midge head capsules representing the variety of these creatures alive at that time.

As waters circulate within a pond, in a fashion similar to that seen when you gently swirl a bowl of water containing small particles, there is a tendency for small items such as the heads of midge larvae to be swept from the shallows around the perimeter towards its center, where they eventually sink through the water and join that year’s layer of bottom sediments. Since there is no corresponding mechanism to sweep such midge remains from the deeper bottom toward the shallow shoreward regions, bottom samples taken toward the pond’s deep center are most apt to include the full array of chironomid types available at that time – both the shallow (often warmer-water tolerating ones) and the deeper (more cold tolerant types). Also in the deep center, the delicate annual layering of bottom sediments is far less apt to become disrupted by water movements or by biological activity (burrowing mussels, wading moose, or human boating or swimming traffic). It is conventional wisdom that coring “the deep spot” provides the least disturbed, most representative chironomid samples.

From our sediment core, I took 3 cc subsamples at 10 cm intervals starting at the bottom of the core and progressing towards the surface. Refer back to Scientific Posting 22 for a description of subsampling techniques. For each subsample examined, we determined the “species composition” of the community of chironomids alive at that location and at that period in time.

Many of the chironomids found in deeper sections of the sediment core (i.e., from several 1000 years ago when local conditions were much colder) represent species no longer active in today’s warmer climate at PPP. However, these very same species are alive today in more poleward, colder localities such as ponds of northern Canada, Labrador, etc. Scientists have visited these locations and studied the environmental conditions in which these representatives of these species thrive today. Doing so has permitted them to determine that the mid-summer surface water temperature is the environmental variable that most accurately determines which species are present in bottom sediments and which are not. They have determined the optimal mid-summer surface water temperature required by each species. Using this information one can use a mathematical model (a partial least squares weighted average (PLS-WA) model) to blend the optimal temperatures for each species found in a given subsample, weighted by proportional abundance of that species in the subsample’s community, to produce the “best guess” inferred mid-summer surface water temperature that would fit a chironomid community composition matching that observed. For each subsample, a temperature point so generated is placed on a graph. Repeating this at 10 cm intervals up the sediment core generates a temperature profile for the period.

Studies of this sort in water bodies throughout northeastern North America have generated profiles similar to that shown in Figure 2. Starting to the right, at the retreat of glacial ice, temperatures rise steeply, but then shelve off, usually with a modest mid-shelf dip. This period is referred to as the “Killarney Oscillation” and in most cases occurs just older (i.e., deeper in the core) than 11,000 radiocarbon years before the present. Following the Killarney period, temperatures plummet to near glacial conditions (9-10 C) and they stay low for approximately 1000 years – from ca 11,000 – 10,000 radiocarbon years before the present). This period is known as the Younger Dryas period and may correspond to the time when glacial retreat was enough to permit meltwaters to, for the first time, flow out through the St Lawrence system, flooding the North Atlantic. This surge of frigid freshwaters may have been sufficient to block the Gulf Stream from delivering its included heat to northern North America and Europe. The Younger Dryas ends in a steep temperature build-back to something resembling today’s climate.

The top of Figure 3 shows an example of such a profile – this one generated from sediments taken at Splan Pond in New Brunswick. The Killarney Oscillation and Younger Dryas periods are obvious. The temperature profile generated from our analysis of the core taken at Big Pea Porridge Pond in New Hampshire may be seen in the bottom of Figure 3.

Comparing these two graphs, some overall similarities are seen, such as something generally similar to the Killarney Oscillation followed by a period of much lower temperatures. But there are also clear differences. 1) There is a spike in temperature late in what “should be” the cold Younger Dryas (marked as “4” on the Pea Porridge Pond figure). 2) There is a more modest overall temperature range observed (10-16 C at Big Pea Porridge Pond vs 0-18 C at Splan Pond). So how do we explain these differences?

Table 1 compares features at Big Pea Porridge Pond to those at 14 other locations where chironomid-based temperature estimates have been made.

Big Pea Porridge Pond lies furtherest to the south of all these sites, but not so much so as to account for the differences we found. Big Pea Porridge Pond is both the deepest of any of the sites (only Splan Pond at 10.4 m comes close) and by far the greatest in surface area of all (48 ha vs. a mean value of just 4 ha for the others). Although, Big Pea Porridge Pond is small compared to other New Hampshire lakes, it is large enough so that nearly all the input source of radiant heat from the sun is absorbed in its surface waters only. Looking progressively deeper In summer, this creates a layer of warm surface water and then a “thermocline” region of sharply falling temperatures overlying otherwise much colder deep waters. Such lakes are referred to as “thermally stratified”, and as such, resist vertical mixing. The creators of the PLS-WA model were clear that their model is designed for use on small, shallow water bodies that are not large enough to thermally stratify. Their model is designed for use in small, shallow, frequently mixed water bodies. But we were trying to learn about past conditions in our particular lake which doesn’t match this description. We are in fact applying a mathematical model to a circumstance beyond the model’s limits. But nonetheless, what can we learn about the past at Big Pea Porridge Pond?

Working in a larger, deeper, stratified pond means that only the shallow perimeter and the bottom sediments underlying its edges are significantly warmed by the sun, leaving the bulk of the lake’s interior and its underlying sediments much cooler and less variable in temperature. The published information on chironomids reveals that some larval types are associated with deeper, colder sediments (i.e., “profundal” sediments), while other species are limited to shallow, warmer sediments (i.e., “littoral” sediments). In Figure 4, we have calculated the percentage of each of the communities we observed at 10 cm intervals comprised of colder, profundal types. Sixty to eightly percent of our communities met this criterion. In previously published studies using chironomid larvae in this way, more than half the chironomids are warm littoral types. By studying communities from a deeper colder lake, we have observed communities more dominated by colder larval forms than is the case in ponds upon which the model is based. Therefore, our data matches low temperature patterns observed elsewhere, but it underestimates the higher temperature portion of the temperature profile, i.e., our smaller temperature range.

But the most obvious departure of the PPP temperature profile and that of Splan Pond is the late-Younger Dryas temperature spike. No one anywhere in the northeast has reported a similar late-YD thermal event at that time period. It makes you stop and think about the temperature conditions larvae living in the depths of thermally stratified PPP may have encountered. Eggs laid in PPP are the product of adults flying around in and totally dependent on the ambient climate conditions, including temperature. But in fact, once eggs have been laid in PPP and have sunk through the warm surface water layer followed by the thermocline, they enter cold deep water that, in a thermally stratified pond like this, shows very little temperature change year-round. Survival of larvae in all but the very shallow bottom sediments in this larger, deeper lake has little to do with temperature. Temperature is simply not much of a variable in their larval lives. What other conditions might influence which larvae survive and which do not in such lakes?

Frequently, in thermally stratified, non-circulating lakes, access to oxygen at depth is an issue. Oxygen is replenished in aquatic systems largely through diffusion into surface waters from the overlying atmosphere or as a by-product of light-driven plant photosynthesis – also a surface phenomenon. In small, shallow ponds with good mixing, frequent wind-driven circulation continually replenishes bottom sediments with oxygen. In deeper, non-circulating lakes, access to oxygen replenishment in deep sediments is a serious problem.

Once again, the published chironomid literature proved useful in providing information on which larval types are limited to conditions high in oxygen and which types are adapted to cope with reduced oxygen levels in bottom sediments. An example of an adaptation found in some species in the latter group would be the presence in body fluids of some species of hemoglobin which significantly improves oxygen uptake when it is scarce. Another low-oxygen adaptation is seen in species that build cylindrical burrows in bottom mud and use undulations to circulate water past their body. Comparison between species demanding high oxygen conditions vs those able to tolerate low oxygen levels vs those not distinguished by either characteristic, applied to communities observed from PPP, results in Figure 5.


One particularly striking change in proportions of these types can be found surrounding a depth of 790 cm within the core – exactly where the anomalous “temperature” spike occurred during the mid-Younger Dryas.

Our working hypothesis is that as the YD progressed, bottom oxygen in PPP declined. This resulted in a decline in high oxygen demanding species and a rise in those tolerant of lower oxygen. This represented an alteration in the community composition – in this case due to an oxygen crisis. But data reflecting this oxygen-related change was inserted into a mathematical model that only “understands” temperature. Consequently, the temperature model interpreted such a change in species present as necessarily being a result of a sudden temperature spike. Here is clear example of the problem in applying a model designed for use in environmental circumstances in which temperature change is the only or at least the primary controlling variable (e.g., small, shallow water bodies) to non-target circumstances in which two or more variables (in this case, both temperature & dissolved oxygen) are important.

It is possible that as the cold Younger Dryas period wore on, surface water temperatures may have dropped below 4 C. This is important because water is densest at 4 C. If less dense cold water (i.e., 1, 2, or 3 C) forms above deeper, denser, 4 C water, it will prevent the deep water from mixing with surface water. As a result of stagnation, dissolved oxygen used in bottom sediments would not be replenished. Oxygen levels would fall. Although year-round ice cover would also lead to stagnation, it would also block the input of chironomid eggs into the lake, and we noted no decline in chironomid larvae during this period.

We are currently exploring techniques for trying to distinguish between the roles of these two variables at PPP. If we are able to quantify changes in PPP’s chironomid community due to oxygen variations, perhaps we can “subtract” the oxygen influence to produce a clearer picture of temperature changes during this Late Glacial period.

Lee Pollock

Overdue Updates

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".

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:

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".

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

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)

From Scientific Posting #21

Lee Pollock

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.

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

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.

Scientific Information Posting No. 18

LARGER PHOTOGRAPHS AVAILABLE

Several folks have asked if there are larger versions of the photographs included in Scientific Post No. 17 available(?). Yes, there are.

Bob Christiansen emplaced a link near the bottom of Post No. 17 which, if you click on it as instructed, will lead you to a selection of enlarged images for easier viewing.

Scientific Information Posting No. 17

Splitting the Cores

Sorry to offer this posting a little out of order. With all the flurry of follow-up investigation of material sampled from the core, we neglected to offer a glimpse of the core splitting session itself.

A group of us met at Plymouth State University on Saturday, May 3 to begin the process. To start with, we retrieved the deeper core segments from the 4 C coldroom where they had been stored since the original sampling date. The foil and cling wrap covering of the core segment was carefully unwrapped and details regarding its appearance and texture were noted.




Then the segment was split longitudinally into halves to reveal the interior material.
Having laid a tape measure along side it, we photo-documented the segment and, using a standard soil color chart, we noted its appearance before subtle color tones could change as these sediments were exposed to air for the first time in thousands of years.



Most core segments (such as the one below) have a brownish-gray appearance produced by the remains of biologically produced organic materials (plant, animal, and microorganismal remains) mixed with inorganic mineral materials. Brownish organic deposits in lake bottoms is known as "gyttja" (a Swedish word, pronounced "yit-yah").



Then at specific depth intervals along the core, subsamples of sediment were extracted for detailed analysis. All subsamples were removed from one side of the split core so that the opposite side could be stored intact for archival purposes. Subsamples taken






will be examined for the remains of midge larvae (or chironomids – useful in reconstructing past temperatures), pollen (useful in reconstructing a picture of changes in the surrounding landscape), the degree of sediment compaction (useful in analyzing the impact of overlying geological forces) and organic content (using a "loss on ignition" or LOI technique – useful in characterizing changes in overall biological productivity over time). The significance of each of these studies will be presented as results become available in the months ahead.

As we had seen in the field, in the 11th segment we collected, a dramatic change in appearance was noted between the brownish (gyttja) sediments and the gray mineral silts that apparently lack such organics. The illustration below shows that transition point between 23 and 24 meters below the Pond surface. A subsample of sediment from this transition point was used for dating purposes (described in Scientific Posting 16).

Click on this image for short slideshow of larger images!

Lee Pollock

WHERE ARE THE PICTURES?

Several people have recently asked where/how to find the pictures and slide show taken during the actual drilling out on the ice last March. It's easy.

Simply scroll all the way down to the last the postings on the blog as it exists today and then click on "Older Postings" in the lower right-hand corner. Once you're into these older postings, scroll down until you reach the post that includes the photos/slide show.

Scientific Information Posting No. 16

WHEN DID THE GLACIER LEAVE THE BIG PEA PORRIDGE POND BASIN?

Well folks, sorry for the long delay in getting information to you here on the blog. Since we finished the first round of sample splitting and sampling in early May, we've been awaiting laboratory results to report and to use to plan the next steps in our investigation. Now, the first of these results is "in", and here it is - the one you've all been waiting for.

The Carbon-14 (AMS) age of the likely oldest organic material at the bottom of the Pond is 12,150 +/- 50 years. If you correct this to calender years, it lies between 13,910 and 14,100 years, or just about 14,000 years.

This is the age of the first organic material to be deposited on the surface of the very compact silt and clay basin left by the glacier when it departed, and it represents the starting date for the rest of the paleoecological history of the Pond our investigation will gradually reveal over the coming months. This date represents the point in time when the local climate had warmed sufficiently from very cold glacial conditions so that the first types of pond vegetation and critters could sustain themselves in and around the Pond. Our investigation from here will document just what these life forms were and how they changed over time to the present. Suffice to say for now, though, you can rely on the fact that we are all part of a history here on the Pond that started 14,000 years ago.

Bear in mind that this date is just the first in what we expect will be a long line of such information (along with more professional analyses) that will come out of our investigations over the next several months. Please feel free to send us your comments and questions via the Commenting Feature here on the blog. We'd enjoy the chance to talk with you about these exciting developments.

Also, keep on eye here for "social postings" about the one or more of information meetings we hope to conduct this summer on the Pond to describe what we're finding and discuss what it all means about the paleoclimate and past ecology of the Pond's basin. As things proceed along with our work and we learn more and more about what went on here in the past 14,000 years, "the Pond will never be the same" to any of us.

More later and as it becomes available...

Scientific Information Posting No. 15

Follow-up DO-Temperature Profile

Earlier, we posted a temperature-dissolved oxygen profile for Big Pea Porridge Pond taken March 30, 2008. Its purpose was to show:

1) the winter temperature profile, with densest (4 C) water filling the lake bottom and underlying colder (therefore less dense) water beneath the ice-covered surface. With less dense water "capping off" more dense deep water, the water column is stabilized, i.e., little vertical mixing or replenishment of deep waters occurs in winter. Also, ice cover prevents wind (the major force behind lake water mixing) from accessing the water surface. Winter stagnation of the column results.

2) the dissolved oxygen curve dropping off with depth. Loss of oxygen in deeper waters is primarily the result of the bacterial/fungal decomposition of organic (i.e., biologically derived) matter that has sunk to accumulate on the bottom. Without circulation to replenish lost oxygen, the extent of oxygen loss is a rough measure of how much organic matter is produced in the lake – in other words, its level of productivity.

As warmth returns in spring and the ice melts, the < 4 C surface waters heat up to match the 4 C deep waters. At that point, temperatures and therefore density of waters within the entire water column are equal. As a result, the water column loses its "stability". As the wind blows across surface waters, pushing them toward the leeward side of the lake, surface waters are driven downward, while elsewhere in matching volume, the lake deep waters are forced to the surface. This creates a "turnover" during which the water column becomes uniformly mixed. Temperatures and dissolved oxygen levels (replenished as oxygen-stripped deeper waters mix to the surface and make atmospheric contact) are equal top to bottom.

This process is the "spring turnover". Full lake vertical mixing like this returns to sun-lit surface waters the nutrients that were freed during the winter as decomposers worked over the organic matter there. These vital nutrients were trapped until the turnover by the stagnant winter water column. With sunlight and nutrients finally available in surface waters, the single-celled and colonial phytoplankton (the plant component of the plankton community – algae, diatoms, dinoflagellates, bluegreen bacteria, etc.) – can surge into photosynthetic action, producing a peak in lake's annual productivity known as the "spring bloom".

The graph below shows the temperature-dissolved oxygen profile observed on May 9, 2008 at the "deep spot" in Big Pea Porridge Pond. If you tip your head 90 degrees to the left, you can see the results from top (left) to bottom. As you will see, we missed catching the turn-over period exactly. While the water column is still pretty uniform with regard to dissolved oxygen levels, the temperature profile is no longer uniform. Understandably, the top 3 meters of surface waters are capturing more heat than deeper waters. By doing that, the warming surface waters, referred to as the "epilimnion", are also becoming progressive less dense than the deeper, cold waters of the "hypolimnion". (There is an inverse relationship between temperature and density – the higher the temperature, the lower the density of water). The intermediate zone including the steep temperature gradient separating these two layers, e.g., between 2-3 meters on this graph, forms the "metalimnion" or "thermocline". As the temperature-density contrast builds between epilimnion and hypolimnion waters, the stability of the water column builds. Deeper, colder, denser waters resist wind-driven vertical mixing of warmed surface waters. The whole lake is no longer involved in mixing – just the wind-driven, warmer epilimnion waters continue to circulate. As the vertical depth of mixing becomes more limited, lower-density, surface epilimnion waters become warmer and warmer, and the stability of the water column increases. This leads to a summer-time stratification/stagnation of the water column that isolates deep, darker, colder hypolimnion from the sunny, warm low density epilimnion. The buildup of the summer temperature stratification will be the subject of our next temperature-dissolved oxygen profile later on in the season.



Lee

Scientific Information Posting No. 14

While not purely scientific information, this is a project follow-up note on aesthetics for residents of Big Pea Porridge Pond looking out across the melting but still nearly complete ice cover (here on April 23!). We just wanted you to know that the debris the melting ice is revealing in the general vicinity of the drilling site is NOT anything we left behind there! But it is indicative of the depth of ice & snow cover this winter that the bright red plastic milk crate and the several large blocks of wood revealed now were completely and invisibly buried there at the time of our drilling operation. Lee.

Quick update on scheduled presentations regarding the MPEP project

1. We will be included with a poster/information table display at the Climate Change Forum scheduled for 6:30-8:30 p.m. on Monday, April 28th at the Kennett High School Auditorium. At the forum, presentations from experts around the country will focus on the science as well as economic and social aspects of the climate change phenomenon, including regional and global challenges and solutions. Speakers from organizations and state agencies will provide presentations on New Hampshire’s Climate Change Action Plan, information and science related to their field of expertise, and will also answer audience questions. Call 539-1859 for more information. Hosted by the Green Mountain Conservation Group, Eagle Academy and Timberland, Inc. The public and other schools are welcome to attend this event.

2. We will also use the poster/ information table format to help represent the activities of the Tin Mountain Conservation Center at a gathering from 6:30-8:30 at Granite State College on Wednesday, May 21. We have recently formed a linkage to Tin Mountain, finding that the MPEP project has much in common with their educational mission.

3. We will present a program based on the MPEP study for the Kennett High School Environmental Club at their monthly meeting at the Tin Mountain Conservation Center on Wednesday, May 21. Contact Tin Mtn for more information: 447-6991.

4. On Tuesday, June 10, we will review the MPEP program so far, and talk about its goals as part of the Tin Mountain Conservation Center's Nature Program series. More information at Tin Mtn: 447-6991.

At each of these sessions, we hope to gather names of individuals interested in the issues raised by our project. This group will form an informal discussion "club" that will be invited to meet at the Tin Mountain Center periodically to learn about new information as analytic results become available and to help us all explore the evolving story of the post-glacial period in this area.

Lee Pollock

Scientific Information Posting No. 13

QUICK NEWS UPDATE

It's been relatively quiet on the MPEP front since we completed the drilling and sampling in early March, but things are beginning to percolate once again.

First, the project staff has now scheduled the so-called "Splitting and Sampling Party" for Saturday, May 3rd. This "party" will take place in the paleolimnology lab facilities at Plymouth State University with Dr. Lisa Doner as our gracious host. This activity will establish the next stage of the project's work tasks, primarily those that involve careful laboratory testing and documentation.

There are several specfic purposes of this activity once our samples have been retrieved from the walk-in storage cooler (maintained at 4 degrees Celcius since the field samlping) at PSU:

(a) to carefully split the samples longitudinally so we can inspect their interior where the shearing effects of the drilling and sampling process will not have disturbed them;

(b) to photograph and carefully document the nature, texture, and sedimentary structure we see on these freshly-exposed surfaces; and,

(c) to determine what type and how many specific laboratory test samples to take from these surfaces to develop the best picture of the samples' ages and fossil organic components.

This latter step will probably require the longest portion of this rather "full day" at PSU. We will report to you all asap after the work is done as to what was found and what testing is proposed to be done. That report will include the best photographs of the day, descriptions of the more interesting structural findings from within the samples, and preliminary comments on the possible paleoclimate history we begin to see. We will also attempt to establish a schedule for the lab results to "come in" and when we might be able to formulate a better picture of the Pond's paleoclimatic history, likely sometime in the mid to late Summer this year.

The second item of news is that Thom Davis and Brian Fowler have been asked to present papers as part of a northern New England pond paleolimnology theme session at the annual meeting of the Northeast Section of the Geological Society of America next Spring. Word of our project "has gotten out" in the regional geological community, and people are interested in what we've done, how we've done it, and what results we may have obtained by the time of the meeting. Abstracts for these presentations will be available nationally through the Society, so word of MPEP will spread. We'll also post them here on the blog. More about this later...

So for now, things are moving more slowly but surely. We will be back in touch in several weeks with more exciting news. Please stay tuned, and please give us your comments and questions here on the blog. For those not familiar with its use, please refer back several Scientific Posts to the one that provides the simple instructions. We'd love to hear from you all!

Amount of Organic Sediments Accumulated….Reconsidered.

Thinking about a full meter of sediments settling in a millennium seems like a lot of material to accumulate. On the other hand, when you recalculate that same meter of sediments on an annual basis, 1 meter or 1000 millimeters in 1000 years, the accumulate rate is only 1 mm per year, and that seems much more plausible. This would be especially so when you consider concentrating particulate materials appearing throughout the lake's interior in the lake's deepest area (much like gently swirling a coffee cup accumulates the grounds in the bottom center).

The accumulation rate of organic materials also depends on how productive the lake is – especially the contribution by the photosynthetic members of the microscopic plankton community (i.e., the "phytoplankton" – such as algae, diatoms, or blue-green bacteria). The VLAP data for Big PPP suggests chlorophyll-a concentrations are low enough to qualify the lake as oligotrophic (see other blog posts for a discussion of both VLAP and the oligotrophic/eutrophic questions), although the levels of cholorophyll-a and total phosphorus in surface waters of the lake show a historical trend of increase. More on that during the next year since the VLAP promises a report for the lake that will include a more extensive analysis of changes they have observed in more than 10 years of sampling data.

Meantime, another way to gain a "snapshot" view of the amount of organic matter produced within a lake (often primarily the result of phytoplankton productivity), is to observe a temperature-dissolved oxygen profile through the water column, taken when there is minimal circulation of the lake's waters. There are two times of year when this condition is met. Toward mid- to late-summer, when surface waters heat up more than deeper waters (your body is warm but your feet are cold when floating upright in the water), very little mixing of the water column occurs and deep waters stagnate. Also during the winter, when surface waters are colder than deeper waters (because freshwater at about 4 C is densest and sinks to occupy deeper parts of the lake – so water both less than AND more than 4 C are less dense and sit above 4 C water) and ice prevents wind from causing water movement and circulation, again the deep waters stagnate. In either case, without circulation, oxygen in deep waters can not be replenished from the surface, so if oxygen is consumed down there, the concentration of oxygen dissolved in the surrounding deep water declines. (Oxygen replenishment to the depths occurs primarily during spring and fall period of "turnover", when the whole water column is similar in temperature and thus equal in density, and the resistance to vertical mixing is minimal).

Some deep water oxygen is lost to various chemical reactions in bottom sediments. But the major source of oxygen depletion is from fueling the biological activities of the decomposer community – the bacteria, protists, fungi, etc. that live on and in bottom sediments and use the fall-out of organic particles (plant or animal parts, undigested wastes, biological detritus rinsed in from the surrounding landscape, etc.) as their food – their energy source. Like the rest of us "consumers", most of these decomposers use aerobic (oxygen-consuming) biochemical breakdown pathways, so to the degree that decomposition is going on, oxygen is lost from stagnant deep waters – and what is lost is not replenished until the next turn-over period.

Strictly "oligotrophic" lakes, with few nutrients and very limited phytoplankton productivity as a result, produce very little organic fall-out for the bottom-dwelling decomposers to use. As a result, not much oxygen is consumed in deep waters – even during periods of water column stagnation. Conversely, "eutrophic" lakes, loaded with nutrients and supporting dense phytoplankton growth, produce lots of organic fall-out, offering an on-going feast to the decomposers, who oblige by stripping the deep waters of their oxygen content. Comparing the actual levels of dissolved oxygen present throughout the water column with the maximal amount of dissolved oxygen possible, given the water temperature and no sources of consumption (i.e., the "saturation" level of dissolved oxygen), gives you a valuable piece of evidence about how much decomposition, and thus how much productivity, has occurred in a given lake. Little departure from saturation levels – ultra-oligotrophic, very low productivity lake. Oxygen levels falling to very low levels or perhaps to zero (= anaerobic conditions) – strongly eutrophic, very productive lake.

On Sunday, March 30, 2008, I performed such a temperature-dissolved oxygen profile on Big PPP. Since it's later in the season, I worked my way cautiously out toward the drilling site – stopping 4 times to auger my way through the snow & ice cover to be sure I was safe. In each case, there was 32-34" of consolidated, frozen snow & underlying ice present – including 10" of pretty solid ice at the base. In no case did I even begin to penetrate through the overlying consolidated snow layers, and knowing there was 10" of ice beneath, I felt okay proceeding. (Thanks to Bob Denoncourt for sharing his DO meter for this).



The graph below shows the results of this survey. You'll need to tip your head 90 degrees to the left to see the graph with data lines proceeding from the surface to the deepest spot at this particular site – about 33 ft. The temperature line (square-symbol line) is to the left and shows the less than 4 deg C (i.e., less dense waters) sitting on top of the 4 C layer toward the bottom. (If it weren't for this so-called "density anomaly" of water – being densest at 4 C (cold, but above freezing) – freshwater bodies would freeze top to bottom, and probably do in most of the creatures therein in the process). The actual dissolved oxygen curve (circle-symbol line) ranges from about 15 mg/L near the surface down to ca 5.7 mg/L at the bottom. The triangle-symbol line to the right shows what saturation dissolved oxygen levels (based solely on temperatures) would look like at each depth.

Clearly, the observed DO line doesn't closely follow the saturation curve, so we aren't as oligotrophic as would be possible. But it doesn't fall off to really low numbers or zero at the bottom, so we aren't strongly eutrophic. Using this one estimate of productivity, we might surmise that Big PPP is somewhere in between – tending toward the oligotrophic side of being "mesotrophic", since the 50% loss of saturation oxygen we see still leaves a fair bit of dissolved oxygen in the deep water to stimulate decomposition. But this does suggest to us that there is fair phytoplankton productivity in the surface waters, and that surely phytoplankton joined by zooplankton (the animal members of the plankton community) remains will have made a significant contribution to the buildup of organic-rich sediments at least in recent years.

.. Lee Pollock

Blog-meister does it tough!

Spare a thought as your fearless Madison Hills Paleoecology project blog-meister (wearing the appropriate protective gear) battles significant environmental hardship (distraction?) down-under to update the blog with the latest scientific data (and ruminations) just in from the arctic tundra field team on BPPP - fourteen times zones and two seasons away!

Social Posting #7

With the success of our latest drilling day behind us I want to extend a heartfelt thank you to those who helped before, during and after the project on the behind-the-scenes activities. Firstly, and very importantly, a huge thanks go to Lee and Sylvia Pollock for their enthusiasm, encouragement, and support in so many ways I can't begin to describe. One way was in allowing us to use their house for the initial January introductory meeting where so many of you came to find out what this was all about. They have supplied food and drink for that first meeting and countless other informal meetings about the project. They put their heads together with us and came up with the "patch" design and it's name. And, they've been a constant source of project energy and creativity-intellectual, physical and psychological. I'm not sure we could have pulled this off without them.