Effects of Multiple Stressors in Aquatic Ecosystems

Elizabeth Fleming – Source and photodegradation of dissolved organic matter as factors of fluoranthene phototoxicity to Daphnia magna.  Mentors: Dr. Jim Oris and Dr. Craig Williamson, Zoology

Dissolved organic matter (DOM) has been shown to greatly reduce the phototoxicity of fluoranthene to aquatic organisms both by decreasing its bioavailability and by absorbing and scattering solar ultraviolet radiation (UVR).  Recent studies have suggested that photodegradation of DOM decreases its ability to bind to phototoxic chemicals similar to fluoranthene.  Acute toxicity tests were performed under artificial sunlight with both photodegraded and non-photodegraded treatments of DOM from autochthonous and allochthonous sources utilizing 5 fluoranthene concentrations.  A bioaccumulation test provided 12 hour body accumulation data for each treatment (µg/g).  12 hour median lethal concentrations (LC50s) were compared to UV-A (340 nm) specific absorption and 12 h body burden for all treatments; individual treatments were compared using parametric analysis.  Only non-photodegraded, allochthonous DOM significantly decreased Daphnia mortality.  LC50s were directly correlated with specific absorbance and, in contrast to previous research, body burden.  UVR absorption and scattering were determined to be the cause of decreased mortality for non-photodegraded, allochthonous DOM treatments; however, further research is required in order to determine why mortality and body burdening were inversely correlated.   
      

Mark Mackey – Single and Interactive Effects of Overwintered Green Frog Tadpoles, an Insecticide, and Cyanobacteria on Gray Treefrog Tadpoles.  Mentor: Dr. Michelle Boone, Zoology

Amphibians are exposed to a number of stressors throughout their life cycles, especially during their aquatic larval period.  During this developmental stage the effects of these variables can have life-long impacts.  Human impact has increased the amount of stressors that many amphibians experience.  With world-wide amphibian population declines it is becoming increasingly critical to gain a better understanding of how amphibian communities affected by anthropogenic factors.  This study examined how overwintered green frog tadpoles, an insecticide, and a species of cyanobacteria singly and interactively affected gray treefrog tadpoles. We reared tadpoles in outdoor mesocosm through metamorphosis and measured the effects of factors on time, mass, and survival to metamorphosis.  We found malathion increased survival to metamorphosis, increased mass at metamorphosis, and decreased the larval period of gray treefrogs.  Our results indicated that some factors can interact in ways not predicted by single factors alone. 

Elizabeth Cable – Land use and seasonal effects on inorganic carbon cycling in Ohio streams and reservoirs.  Mentor: Dr. Mike Vanni, Zoology

Recent global and regional carbon budgets have largely ignored freshwater systems, but current research shows that these systems are significant in sequestering organic carbon and venting CO2. In response to this new research, these systems should be examined more closely to determine their importance as carbon sinks or sources. Dissolved inorganic carbon (DIC) plays a significant role as part of the overall carbon budget and should be investigated in depth. For this study, we looked primarily at two Ohio reservoirs to determine how land use and storm events may influence DIC concentrations in these freshwater systems, as well as how partial pressure CO2 (pCO2) changes between lakes and over time. One reservoir in the study, Acton Lake, has a watershed dominated by agriculture (89% agricultural), while the other, Burr Oak, has a watershed of only 14% agricultural use and 81% forest. We found that DIC concentrations in Acton were at least two times higher than Burr Oak concentrations (~30 versus 15 mgC/L). A comparison of DIC levels in twenty Ohio reservoirs during mid-August showed a positive correlation between percent watershed agriculture and DIC. pCO2 did not vary significantly between Acton and Burr Oak, but decreased in late summer when primary production is the highest. We also examined the effects of stream discharge at the two study sites and found that as discharge increased, such as during a storm event, the DIC concentrations decreased. When considering load, we found that as stream discharge increased, dissolved inorganic carbon loading increased as well. We found that in both the streams and reservoirs DIC comprised the largest fraction of carbon during baseflow and minor storm events. Particulate organic carbon became relatively more important during larger storms.

Sonii Kollie – Long Term Trends in the Burial of Carbon and Nutrients in a Eutrophic Lake in Relation to Changing Agricultural Practices.  Mentor: Dr. Bill Renwick, Geography

Eroded sediments from agricultural fields, buries carbon (C) and nutrients and causes tremendous water quality problems downstream. In the last few decades the amount of crop lands practicing sustainable farming methods are on the rise, and this is leading to a reduction in erosion rates in agricultural areas (Renwick et al., 2005), and hence a reduction in all of the nutrients and carbon trapped in these sediments. Sediment cores were collected from Acton Lake, the final drainage basin of the predominately agricultural Upper Four Mile Creek Watershed (UFMC).  Cores were collected from 1994-2007, at the dam sites, the inflow (river), and at the midpoint between the river and dam sites. The organic carbon (OC), nitrogen (N) and phosphorus (P) contents of the cores were examined. There was a general increase in nutrient content as one moved from the river, where there is a high input of allochthonous OC, N, and P, to the dam sites, where the nutrients and OC are primarily autochthonous. We expected to find a seasonal gradient in nutrient content, with nutrient being highest in the spring, when precipitation is highest and hence the discharge into Acton is also high, but there was no such relationship. When annual trends were examined there was a steady increase in nutrient content at both the middle and river sites until 1998, and has since remained at the same level or has even started to decrease at the river site. The OC content of the sediments followed patterns similar to that of the nutrients.

Kelsey Friese – The Potential Relationship between Daphnia Diel Vertical Distribution and their Food Resources (Food Quantity and Food Quality). Mentor: Dr. Maria Gonzalez, Zoology

Zooplankton can vary in their daily vertical distributions in the water column.  These variations are influenced by temperature, fish predation, and food resources.  All of these pressures are influenced by light. My project analyzed the potential relationship between Daphnia daily vertical distribution and their food quantity and food quality.  I hypothesized that food quality would have more significant relationship with Daphnia vertical distribution than food quantity. Sampling was done in Acton Lake, an artificial reservoir in southwestern Ohio. Depth profiles of zooplankton and seston were taken every week throughout the spring and summer months.  Daphnia mean depth, abundance, and clutch sizes were recorded and seston samples were filtered for chlorophyll-a, carbon, nitrogen, and phosphorus ratios.  Daphnia mean depth in the water column was consistently below the euphotic zone depth throughout the spring and summer seasons and Daphnia mean depth did not correspond with the depth of the lake with the highest amount of chlorophyll-a.  Carbon: Phosphorus ratios decreased with depth in the lake and C:P ratios at Daphnia mean depth were lower than in the euphotic zone.  These results suggest that Daphnia seek depths of the water column where food quality is greatest and not necessarily where there is the greatest quantity of food.  Because Daphnia are common prey for larval fish, this depth distribution could have a significant influence on the type of fish that make up a reservoir/lake.  Larval fish unable to descend to the depths where Daphnia food quality is greater will be out competed with the larval fish that can successfully hunt at those depths.