Showing 11 - 17 of 17 Items

Date: 2014-08-01

Creator: Schuyler Nardelli

Access: Open access

Phytoplankton are the simple single-celled photosynthesizers that live in the ocean and form the base of the food chain. Cell size is a basic proxy for physiological rates as well as ecosystem structure. Thus, cell size can be used in a model framework to track changing environmental conditions that could potentially lead to harmful algal blooms (HABs, aka “red tides”)—events that can be detrimental to human health, marine life, and fisheries. HABs occur when a single algae (phytoplankton) species either grows unconstrained to a concentration such that it becomes toxic or causes low oxygen concentration in the water. In typical estuaries, less dense freshwater flows towards the ocean, and denser salty seawater flows into the estuary in the subsurface. However, Harpswell Sound is a reverse estuary that receives its freshwater input at its mouth from the upstream Kennebec River. This yields upstream surface low salinity flow and downstream deep high salinity flow. This rare dynamic allows phytoplankton located in the surface of seawater to be retained in the sound in conditions conducive to high growth and HABs, and can be used as a warning for conditions throughout the Gulf of Maine. To study the temporal and spatial dynamics of phytoplankton in the sound, we used the LISST-100, which uses light scattering properties to collect continuous in-situ water column observations of particle concentrations and size distributions. Although the LISST-100 was built to measure sediment size with a spherical shape, studies have been conducted that show it can accurately describe a diverse range of phytoplankton shapes and sizes, provided the population has sufficient size differences and is fairly concentrated, conditions found in Harpswell Sound. Weekly profiles of the water column were collected at the Bowdoin Buoy from 5/21/14-6/18/14, as well as a 20-day continuous time series collected at Bowdoin’s Coastal Studies Center dock from 5/30/14-6/18/14 along with supplementary oceanographic data. We determined that semi-diurnal tidal fluctuations are sufficient to move water masses past the buoy and dock with each tide, thereby connecting them. Phytoplankton were found to be in the 3-50 micron size range, with a peak diameter of approximately 7 microns. Additionally, three independent phytoplankton blooms were observed over the course of the 20-day time series as different water masses flowed through the sound. They were sourced in the oceanic water masses found under the freshened surface layer. Over the five-week period the populations gradually surfaced with their water mass as the overlying freshwater dissipated in the absence of rainfall. The LISST-100 served as a useful tool for determining phytoplankton distribution and dynamics within Harpswell Sound, and with further research there is great potential to continue to increase proficiency with the instrument in order to better understand phytoplankton dynamics and harmful algal blooms. Final Report of research funded by the Rusack Coastal Studies Fellowship.

Date: 2014-08-01

Creator: Sabine Y Berzins

Access: Open access

Eelgrass (Zostera marina) is a perennial seagrass that is widely distributed among the shallow subtidal and intertidal Atlantic coastline of the United States and Canada. A highly productive keystone species, eelgrass helps maintain healthy estuarine and ecosystem functions by stabilizing sediments, regulating water flow, absorbing nutrients, and providing critical habitat for animals including commercially important species like soft-shell clams, blue mussels, and migrating waterfowl. Loss of eelgrass beds can therefore result in degraded water quality, shoreline erosion, and reduced fish and wildlife populations. Historically, the Maine coast supported extensive eelgrass beds. However, between 2010 and 2013, eelgrass distribution in Casco Bay declined in area by over 55%. This decline in eelgrass distribution coincides with a regional population explosion of green crabs (Carcinus maenas), an invasive species that physically disturbs eelgrass while foraging for prey. This summer, I collaborated with several Casco Bay Eelgrass Partners including individuals from the Fish and Wildlife Service, Maine Department of Environmental Protection, and the Friends of Casco Bay. Led by U.S. Geological Survey biologist Dr. Hilary Neckles, this project identifies factors that make eelgrass more or less resilient to invasion by green crabs. In June, we established permanent eelgrass survey transects at five locations spanning eastern Casco Bay. Where possible, two transects were established in different types of sediment (fine or coarse/sandy). Most of the eelgrass loss observed over the past decade has been in fine sediments. The question remains; is eelgrass in coarse sediments prone to similar levels of damage? In addition to differences in substrate type, each site also exhibited varying degrees of eelgrass density, shoot height, green crab density and population structure, and other environmental stressors including light availability, temperature, nutrient availability, and natural physical disturbance. I made biweekly measurements of green crab densities at one site, Widgeon Cove in Harpswell. Crap trapping indicated few green crabs occurred near the Widgeon Cove transect, but traps at the other four Casco Bay sites collected as many as 300 crabs within a 24-hour period. Final measurements in the eelgrass transects will be taken in September and data collection will be completed in October. Data gathered this summer will provide information to help move forward with a plan to protect and potentially restore eelgrass in Casco Bay. Additionally, I identified patches of eelgrass in the Kennebec Estuary that might be viable sites for replanting next summer. I hope to continue working on this project next year, thinking about ways to restore eelgrass to the system while identifying ways to increase trapping pressure on green crabs such that their numbers might be reduced. Final Report of research funded by the Rusack Coastal Studies fellowship.

Date: 2014-08-01

Creator: Bailey Moritz

Access: Open access

With increased CO2 in the atmosphere from the burning of fossil fuels, more is absorbed into the surface ocean, causing a reaction that leads to lower pH. This process is known as ocean acidification, which has raised global concern. Over the past decade, the clam flat near Head Beach in Phippsburg has been reduced to approximately a sixth of its former productive area. The town of Phippsburg allots money every spring to seed the clam flat with juvenile soft-shell clams (Mya arenaria) in order to support the local clamming economy, but the clams are no longer growing in much of the mud flat. A possible explanation for this loss is acidification. In order to understand if ocean acidification is the cause, I collected water samples from the mud to test for alkalinity along a transect of 5 sites spanning productive and non-productive areas of the flat. Alkalinity is a measurement of the waters ability to buffer pH changes. Lower alkalinity could mean that clams would have more difficulty forming their calcium carbonate shells due to dissolution in low pH waters. Combined with the pH measurements gathered by my peer, Lloyd Anderson ‘16, we were able to calculate aragonite saturation state. Water with a saturation state below 1 is capable of dissolving calcium carbonate (aragonite) shells. A large portion of this research project was figuring out the best methodology to use for collecting data on the clam flat. The tested water needs to represent that which the clams are actually using while they are embedded in the mud. Additionally, juvenile clams only live in the upper centimeter or so of sediment. We followed methodologies used in past studies in Maine (Green et al 2013). Three pore water samples from each site were extracted and brought back to the lab to be filtered on 7 separate days throughout July. We began sampling 2 hours prior to low tide. I determined alkalinity using an automated titration system. Average alkalinity ranged from 2200-2500 μeq/kg. The results indicated that there was not a significant difference or pattern in alkalinity or saturation state between productive and unproductive areas of the clam flat (Fig. 1). Error bars in the figure represent variability at each site over the entire study period, while analytical reproducibility was ± 9.04 μeq/L. Large changes were observed merely from one day to another. Coastal ecosystems are complex and variations such as time of day, temperature, or productivity may have influences on the porewater characteristics (Duarte 2013). While ocean acidification does not appear to be the primary driving force behind the clams’ decline at this location, the saturation state was consistently quite low ( Final Report of research funded by the Rusack Coastal Studies Fellowship.

Date: 2014-08-01

Creator: Anna Hall

Access: Open access

High-latitude peatlands store a large stock of carbon in accumulated belowground biomass, estimated at 500 ± 100 Gt C (Yu 2012). For comparison, the atmospheric C pool is estimated at about 775 Gt (IPCC 2007) making the peatland carbon pool a potentially significant player in the global carbon cycle. Peatland carbon storage is controlled by a balance between plant productivity and decomposition, with plant matter produced during the summer months accumulating from year to year rather than fully decomposing. Peatlands are sensitive to changes in climatic regime and have the potential to shift from a net sink of atmospheric C to a net source of C with future disturbance by climate warming (Yu 2012).There are two major predictions as to how climate change could affect peatland C accumulation. Warmer temperatures could cause faster decomposition of plant biomass and lead to C release to the atmosphere and a positive feedback effect on climate change (Schuur et al. 2008). If this is the case, current warming trends suggest that peatlands could release up to 100 Gt C to the atmosphere by the year 2100 (Davidson and Janssens 2006). Alternatively, warmer summer temperatures and a longer growing season could lead to faster peat production and therefore CO2 drawdown from the atmosphere, somewhat mitigating the effects of climate change (Schuur et al. 2008). A detailed study of past C accumulation rates over a known historical warm period gives insight into how peatlands may respond to future climate warming. This project focuses on C accumulation in peatlands in Labrador, Canada, over the past 8,000 years. Because Canadian peatlands store approximately 150 Gt C, approximately 1/3 of the global peatland carbon pool, it is important to understand how the dynamics of these peatlands could be affected by present and future climate warming (Tarnocai 2006). However, the majority of research has focused on central Canada, leaving significant knowledge gaps surrounding coastal Eastern Canada (vanBellen et al. 2012). Particular emphasis in this study was given to the Holocene Thermal Maximum (HTM) which occurred from 4-6 thousand years ago in Labrador, when summer temperatures were 0.5 – 1°C warmer than at present (Kerwin et al. 2004). This study also attempts to determine the effect of fires on rates of C storage in these peatlands. Lightning-ignited peat fires have the potential to consume stored biomass and release significant CO2 to the atmosphere (Tarnocai 2006). Six peat cores (out of a total of 14 collected in Labrador in 2013) were used for this study. Throughout the following year, calibrated radiocarbon dates, bulk density, and percent carbon were used to calculate carbon accumulation rates. This summer, areal charcoal concentration (a measure of macroscopic charcoal used as a proxy for fire severity) was used to determine the influence of fires in this region. From 8,000 years ago to the present, rates of C accumulation averaged 23.1 ± 6.7 gC m-2 yr-1. Accumulation rates were highest during the HTM, averaging 29.6 ± 2.4 g C m-2 yr-1. Samples containing macroscopic charcoal had an average concentration of 0.62 mm2 cm-3 with a maximum concentration found of 3.51 mm2 cm-3. These consistently low charcoal concentrations indicate that fire was neither common nor severe in Labrador peatlands. While Kuhry (1994) and Payette et al. (2012) found that fires in Canada occurred twice as frequently during the HTM than at present, no trends in fire severity were found in these cores, and there was no evidence that fires had a significant influence on C accumulation. Therefore, the C accumulation trend we see in Labrador is not controlled by fire and is likely either a direct result of temperature variation or of vegetational and hydrological shifts caused by changes in climate. This work supports a growing body of evidence from high latitude peatlands suggesting that future warming conditions could lead to increased soil C sequestration. Final Report of research funded by the Freedman Coastal Studies Fellowship.

Date: 2014-08-01

Creator: Sasha Kramer

Access: Open access

Phytoplankton require certain essential nutrients for growth. The Redfield ratio (Redfield, 1934) dictates an ideal element proportion of 106 carbon: 16 nitrogen: 1 phosphorus in order to maintain balanced phytoplankton growth through photosynthesis (Li et al., 2008). Under typical conditions, the concentration of nutrients present in the water directly controls the attainable phytoplankton yield (i.e. one inorganic nitrogen from nitrate yields one organic nitrogen in cellular form). While plankton that are starved of nutrients tend to die off quickly, plankton that are simply nutrient limited can adjust to constant but low levels of nutrient concentration (Cullen et al., 1992), often by adjusting their Redfield ratio. As an essential nutrient, nitrogen is a limiting factor for phytoplankton growth in the ocean (Dugdale, 1967). In oceanic and coastal ecosystems, dissolved nitrate (NO3-) is the most commonly available form of nitrogen (Zielinski et al., 2011). The formation of nutrients through microbial processes such as denitrification in deep water creates a source of nitrogen in the deep ocean (Arrigo, 2005). Phytoplankton growth is limited by both light and nutrients: therefore, the transport of nitrate into the euphotic zone controls the rate of primary production. In the Gulf of Maine, nitrate concentration varies with depth and season. Water density is determined by temperature and salinity; these qualities in turn control the depth of mixing and stratification, and thus the depth of the nitracline, the depth at which the high-nutrient deep waters are found (Townsend, 1998). An instrument known as the In Situ Ultraviolet Spectrophotometer (ISUS by Satlantic, Inc.) offers the ability to quantify nitrate concentrations based on optical properties. The instrument specifically measures the magnitude of absorption of ultraviolet light by dissolved nitrate molecules in the water. The concentration is determined from the ratio of the measured absorption coefficient to the molar absorption coefficient of nitrate. The ISUS is placed directly into the water at a site of specific interest—it measures the absorption and computes the nitrate concentration at this site every hour. This method of analysis gives superior stability, precision, and accuracy in data compared to a typical water sample analysis in a laboratory setting (Johnson & Coletti, 2002). For the past 4 years, an ISUS sensor has been deployed on the Bowdoin Buoy in Harpswell Sound collecting hourly observations of nitrate concentration concurrent with hourly observations of chlorophyll fluorescence (which can be used as a proxy for phytoplankton biomass). Once per week between May 21, 2014 and June 18, 2014, measurements of the depth distribution of salinity, temperature, density, chlorophyll fluorescence, and dissolved oxygen content were taken at the Bowdoin Buoy. Water samples were collected at five discrete depths each week, and were returned to the lab for analysis of chlorophyll concentration on the Turner fluorometer and nutrient concentration on the SmartChem. These laboratory analyses were used to calibrate and validate the buoy- and boat-based optical observations. The analysis of nitrate observations was performed in two phases. First, the variability in nitrate measured on the buoy since 2007 along with co-located discrete water samples was compared to a published historical dataset in order to place Harpswell Sound in the broader context of the Gulf of Maine. Second, the timeseries buoy observations of nitrate and chlorophyll were analyzed to determine temporal covariability. The historical nutrient and water quality data for the Gulf of Maine gathered by Rebuck et al. 2009 for 1990-2009 (in addition to unpublished data from 2010-2012) provided a broader spatial and temporal range for comparison with data from the Bowdoin Buoy in Harpswell Sound, Maine from 2007-2012. The historical nutrient data for the Gulf of Maine were measured in the lab; the nutrient data for Harpswell Sound was measured by the ISUS. There are relatively few match-ups for validation, but these points did show the correlation between the two methods. However, the similarity of the distribution of measured nitrate from water samples in lab and the in situ temperature and salinity characteristics of the sampled waters were very coherent with those measured by the ISUS, providing some quantitative validation. Future analysis of the ISUS data from summer 2014, in comparison to nutrient data from the water samples taken over the course of this summer, will further justify the validity of the ISUS data. A clear relationship between nitrate concentration and water temperature and nitrate concentration and salinity for both the Gulf of Maine and Harpswell Sound emerged (Figure 1). The highest concentrations of nitrate are found in the saltiest water (between 30-34 psu) and coldest water (between 3 and 12 degrees Celsius). This pattern was observed both generally in the Gulf of Maine and more specifically in Harpswell Sound, indicating that processes observed in Harpswell Sound are connected to broader scale oceanographic processes. These results also indicate that nutrients generated by deep ocean processes are dominant and river sources are negligible, a result that is not found in most areas. For both chlorophyll data and ISUS nitrate data, 2010 proved to be a model year with a clear and thorough timeseries from early February to late November. After analysis, the relationship between nitrate and chlorophyll showed a strong preliminary correlation of chlorophyll concentration (once again, as a proxy for phytoplankton biomass) increasing as nitrate concentration decreases (Figure 2). The low levels of phytoplankton consume the high levels of nitrate and therefore, as the bloom grows, the concentration of nitrate decreases proportionally. The expected dependence of chlorophyll concentration on nitrate concentration becomes incredibly clear through these results, similar to the results presented in Li et al., 2010. The ISUS data from 2007-2012 requires further processing in order to fully explore the relationship between chlorophyll and nitrate concentration on a pertinent timescale to bloom growth dynamics. While it is possible to construct a full time-series from the newly manipulated ISUS dataset after this summer work, it would be important and interesting to further examine the relationship between chlorophyll concentration and nitrate concentration in Harpswell Sound on daily, weekly, seasonal, and yearly timescales. This next step of investigation will require more time for data processing, but the work done this summer to validate the ISUS data and show the correlation between Harpswell Sound and the Gulf of Maine is incredibly promising for future work. Final report of research funded by the Doherty Coastal Studies Research Fellowship.

Date: 2014-08-01

Creator: Sophie Janes

Access: Open access

The central pattern generator (CPG) is a neural network that controls the rhythmic patterned outputs, which generate locomotion as needed. The lobster provides a good model to study CPGs because it has a relatively simple CPG. The lobster CPG, or cardiac ganglion accommodates for a range of activities and changes in the environment (Cooke, 2002).The small lobster CG is made up of nine neurons that control the neurogenic heart. The lobster CG is located on the inner dorsal wall of the heart and forms long neurites that branch onto the heart muscle. The CG, through an intrinsic mechanism, generates patterned and rhythmic bursts to the heart (Cooke 2002).The H. americanus CG sends information to the heart muscle to regulate the heart beat. The patterned bursts from the CG need to be adjusted in response to changing demands, for example, activity level or blood volume. Two general mechanisms, intrinsic feedback and extrinsic neuromodulation, have been identified to facilitate this adjustment. Through an intrinsic feedback mechanism, the muscle sends information back to the CG via a positive pathway and a negative pathway. In the positive pathway, stretch-sensitive dendrites of cardiac neurons increase the frequency of heart contractions when stretched (Cooke 2002). In the negative pathway, nitric oxide (NO), produced by the cardiac muscle, slows the frequency (Mahadevan et al. 2004). The interplay between the negative and positive feedback pathways regulates the output of the CG. An extrinsic mechanism has also been identified to regulate the CG output. Chemical neuromodulators that are released either locally or as hormones signal to the heart or CG to modulate ganglion activity. The intrinsic and extrinsic mechanisms affect the contraction amplitude and frequency of the heart.Within this simple invertebrate organism, a complex layering of control exists. Studies of the effects of various extrinsic modulators suggest that these modulators may alter how the feedback pathways operate. I examined what effect the neuromodulator GYSDRNLRFamide (GYS), a peptide found in the lobster nervous system, has on the balance between the positive and negative pathways (Ma et al., 2008). Recent experiments have demonstrated that when GYS was applied at high concentrations in the whole heart, the frequency decreased. This suggests that GYS may play a role in the intrinsic feedback pathways, and likely enhances the negative pathway.I looked at if nitric oxide altered the modulation of the heartbeat frequency when enhanced by the extrinsic modulator, GYS. Based on previous experiments, I hypothesized that GYS allows the NO, or negative pathway to predominate. In order to test my hypothesis, I examined the effects of GYS when I removed nitric oxide, which allows the negative pathway to exist. I compared the characteristics of the heartbeat when saline was run through the heart to when GYS was run through the heart. I also compared the characteristics of the heartbeat when the NO inhibitor, L-NA, was applied to when GYS was applied in the presence of L-NA. I finally compared the changes in frequency between these two comparisons. I found a significant difference between the change in frequency of the heart perfused with GYS in saline as opposed to perfused with GYS in L-NA. GYS had a greater negative effect without L-NA. These results demonstrate that NO is likely the cause of the observed decrease in frequency. Final Report of research funded by the Doherty Coastal Studies Research Fellowship.

Date: 2014-08-01

Creator: Anna Bearman

Access: Open access

There are numerous anthropogenic pollutants present in both marine and terrestrial waters.1 Though many of these chemicals do not absorb light and therefore cannot undergo photolyic degradation on their own, dissolved organic matter (DOM), found alongside pollutants in natural aquatic waters, can act as a catalyst in the attenuating process of contaminants. DOM is a complex mixture of organic compounds derived from decaying plants, animals and microorganisms. Since DOM can absorb light, it can transfer energy to contaminants, allowing them to break into smaller and often less hazardous molecules. The behavior of DOM is largely determined by its functional chemical components, and the character of DOM is constantly changing with the environment. For example, two International Humic Substances Society standards Pony Lake DOM from Antarctica and Suwannee River DOM from Georgia demonstrate very different compositions and characteristics2. More important than simply identifying varying functional groups in DOM these standards, however, may be understanding how our local water in the Androscoggin River and Gulf of Maine behaves and attenuates contaminants. The goal for this project was to first isolate DOM from the Androscoggin River and the Gulf of Maine. DOM was extracted using the Thurman and Malcolm procedure,3 beginning with collection and filtration of water from the Androscoggin River boat launch and Simpson’s Point. The water was then run through a chromatography column, through the method of absorption chromatography the dissolved organic matter sticks to the resin within the column. DOM was then eluted from the column, concentrated, and protonated with an ion exchange column. The resulting concentrated DOM solution was then freeze-dried to obtain the final powdered DOM fraction. Because the quantity of DOM isolated from the Gulf of Maine was too small for characterization, we determined that a new collection method using equipment suited for sampling larger volumes of water will be necessary for future DOM characterization. Instead we focused on collecting samples from the Androscoggin on a weekly basis. Following isolation, the Androscoggin River DOM was dissolved in Type I water to make 3mg/L DOM samples and then characterized through UV-Vis absorption and 3D fluorescence Excitation-Emission Matrix (EEM) spectroscopy techniques. The data was then processed using the parallel factor analysis (PARAFAC) method.4 PARAFAC deconvolutes the fluorescence spectra into the distinct fluorescent components present in the complex DOM mixture (Figure 1). This preliminary analysis indicates that Androscoggin River DOM is made up of at least six specific fluorophores. In the future, I will identify the types of molecules responsible for each component signature and attempt to ascertain the relative concentration of each photoactive constituent in the DOM samples. This information will have significant implications for the photochemistry of natural and anthropogenic chemicals in natural waters. Funded by the Henry L. Grace Doherty Coastal Studies Research Fellowship and James Stacy Coles Summer Research Fellowship in Chemistry.