Long-Term Changes of Hypolimnetic Dissolved Oxygen and Phytoplankton Community Composition in a Large Lake, Lake Simcoe, Ontario and Revisit Dissolved Oxygen Profile Models for Lakes in Central Ontario

Long-term changes in volume-weighted hypolimnetic dissolved oxygen (VWHDO) and phytoplankton community composition were examined as important water quality indicator in Lake Simcoe, a large freshwater lake with impacts by various drivers such as dreissenid mussel (DM) invasion, reduction in phosphorus (P) loading and climatic change and oscillations. VWHDO dynamics were examined by several multiple linear regressions which revealed that VWHDOmin was positively correlated with the invasion of DM and negatively correlated with hypolimnetic water temperature; VWHDO depletion rate (DR) was positively correlated with ammonia and total phosphorus (TP) annual loading. Hence, longer period of thermal stratification (L) may have offset improvements in VWHDOmin generated by P controls and invasive species. Redundancy analysis and variation partitioning revealed that DM acted on phytoplankton composition indirectly by changing the environmental conditions because environmental variables and DM individually explained little variance in phytoplankton composition but water chemistry variables and DM collectively explained a large portion of the variation. A series of models predicting the uppermost plane of the DO-depleted zone (Zox), spring dissolved oxygen (DOi) profile and end-of-summer dissolved oxygen (DOf) profile built by Molot et al. (1992) were re-analyzed, re-calibrated with more recent data (A lakes during 1990-2013), and validated (B lakes during 1990-2013). With the current brownification trend (increased DOC), we expected to see increased DOf at all depths; however, increased reduced N species (ammonia) in the hypolimnion would offset the brownification effect

Numerical modeling of thermal bar and stratification pattern in Lake Ontario using the EFDC model

Thermal bar is an important phenomenon in large, temperate lakes like Lake Ontario. Spring thermal bar formation reduces horizontal mixing, which in turn, inhibits the exchange of nutrients. Evolution of the spring thermal bar through Lake Ontario is simulated using the 3D hydrodynamic model Environmental Fluid Dynamics Code (EFDC). The model is forced with the hourly meteorological data from weather stations around the lake, flow data for Niagara and St. Lawrence rivers, and lake bathymetry. The simulation is performed from April to July, 2011; on a 2-km grid. The numerical model has been calibrated by specifying: appropriate initial temperature and solar radiation attenuation coefficients. The existing evaporation algorithm in EFDC is updated to modified mass transfer approach to ensure correct simulation of evaporation rate and latent heatflux. Reasonable values for mixing coefficients are specified based on sensitivity analyses. The model simulates overall surface temperature profiles well (RMSEs between 1-2°C). The vertical temperature profiles during the lake mixed phase are captured well (RMSEs < 0.5°C), indicating that the model sufficiently replicates the thermal bar evolution process. An update of vertical mixing coefficients is under investigation to improve the summer thermal stratification pattern. Keywords: Hydrodynamics, Thermal BAR, Lake Ontario, GIS

Investigating summer thermal stratification in Lake Ontario

Summer thermal stratification in Lake Ontario is simulated using the 3D hydrodynamic model Environmental Fluid Dynamics Code (EFDC). Summer temperature differences establish strong vertical density gradients (thermocline) between the epilimnion and hypolimnion. Capturing the stratification and thermocline formation has been a challenge in modeling Great Lakes. Deviating from EFDC's original Mellor-Yamada (1982) vertical mixing scheme, we have implemented an unidimensional vertical model that uses different eddy diffusivity formulations above and below the thermocline (Vincon-Leite, 1991; Vincon-Leite et al., 2014). The model is forced with the hourly meteorological data from weather stations around the lake, flow data for Niagara and St. Lawrence rivers; and lake bathymetry is interpolated on a 2-km grid. The model has 20 vertical layers following sigma vertical coordinates. Sensitivity of the model to vertical layers' spacing is thoroughly investigated. The model has been calibrated for appropriate solar radiation coefficients and horizontal mixing coefficients. Overall the new implemented diffusivity algorithm shows some successes in capturing the thermal stratification with RMSE values between 2-3°C. Calibration of vertical mixing coefficients is under investigation to capture the improved thermal stratification

INVESTIGATING THE EFFECTS OF WINTER DRAWDOWNS ON THE ECOLOGICAL CHARACTER OF LITTORAL ZONES IN MASSACHUSETTS LAKES

Anthropogenic alteration of water levels in lakes is a major stressor to the ecological integrity of littoral zones, which provide critical heterogenous resources that support diverse biological communities. Annual winter drawdowns have been practiced in Massachusetts (MA) for several decades; however, few studies have estimated impacts to littoral zone habitat and biological communities, particularly at relatively mild magnitudes (i.e., m) and in lakes that co-occur with other anthropogenic pressures (e.g., lakeshore development) as seen in MA lakes. My dissertation reviewed the winter drawdown literature and collected empirical data in MA lakes to characterize winter drawdown hydrological regimes and estimate responses of physical habitat (macrophytes, sediment texture, coarse wood), macroinvertebrate assemblages, and mussel assemblages to variable levels of drawdown magnitude. Through a stratified random selection approach, I selected 21 MA lakes (18 drawdown, 3 non-drawdown) based on drawdown information from an email survey to local conservation commissions and lake and pond associations. I continuously monitored water levels for 3–4 years within these lakes that represented a drawdown magnitude gradient. Drawdown regimes displayed considerable inter- and intra-lake variability in the timing and duration of annual drawdown events. The majority of winter drawdown events were incongruous to MA state issued timing guidelines, particularly for April 1st refill dates. In the same set of lakes, I found increased drawdown magnitude was correlated with coarser substrates and reduced silt, reductions in macrophyte biomass and biovolume, and proportional increases of macrophyte taxa with annual longevity strategy and amphibious growth form. During normal water levels, I found markedly lower freshwater mussel densities at drawdown-exposed depths compared to the same depths in non-drawdown lakes. I also found drawdown magnitude significantly structured macroinvertebrate taxonomic and functional composition with evidence that suggests several drawdown-sensitive taxa (e.g., Amnicola) and traits (e.g., semivoltinism). To minimize losses to lake ecological integrity, winter drawdown management should consider the extent of lakebed and littoral zone area exposed during drawdowns, incorporate depth-specific monitoring efforts for susceptible biota (e.g., mussels), and anticipate water level responses to climate change

Phytoplankton response to water quality threats in Midwest reservoirs

Harmful cyanobacterial blooms and invasive species threaten water quality. These threats are expected to worsen in the future, emphasizing the need for creative management solutions and a thorough understanding of their impacts. The objective of this dissertation is to investigate the influence of light on biomass and community composition of phytoplankton with the hypothesis that light will have an impact, regardless of nutrients and grazing. We investigate a novel geoengineering approach designed to control cyanobacteria by reducing light. We demonstrate that daily application of glacial rock flour, a fine particulate that floats on the water's surface, reduces light by half and results in up to a 78 percent decrease in cyanobacterial biovolume. We also look at the accumulation of microcystin in the tissues of bluegill and largemouth bass. Microcystin is higher in bluegill, likely because they feed from lower trophic levels. It is also higher in spring and decreases throughout the year, suggesting that time of the year might be an important consideration for microcystin fish consumption advisories. We also find that invasive zebra mussels are not causing an increase in water clarity in MO reservoirs like they are in natural, northern latitude lakes. This could be because reservoir conditions are suboptimal for zebra mussels, thus preventing them from reaching high densities. Understanding how aquatic resources have responded to stressors in the past enables us to predict how they will respond to changes in the future.Includes bibliographical references

Forecasting dispersal of nonindigenous species

A leading conceptual model of the invasion process suggests that nonindigenous species (NIS) must pass through a series of ‘filters’ when dispersing from colonized to non-colonized regions. These steps include the initial dispersal of propagules, survival of these propagules upon encountering the new physicochemical environment, and biological integration into the new community. Here, I forecast invasions for two aquatic NIS, the spiny waterflea Bythotrephes longimanus and zebra mussel Dreissena polymorpha based on the entire invasion sequence using gravity models to assess movement of propagules, data on lake morphometry and physicochemistry, and data on fish community composition. The gravity models included information on movement patterns of recreationalists and life-history characteristics of the NIS that may facilitate invasions. I also contrast the abilities of a hierarchical approach to a single ‘all-in-one’ model that considered all variables simultaneously in detecting actual invasions versus false alarms. Here, the ‘all-in-one’ model was better at predicting invasions if they had, in fact, occurred. Next, I compare predictions of Bythotrephes invasions for three types of gravity models: total-flow-, production- and doubly-constrained. These models differ in the type of information required to parameterize the model. The Production-constrained model was most likely to detect actual invasions relative to false alarms, and the total-flow-constrained model was least likely to predict false positives. I also compare backcast patterns of propagule pressure for two groups of related species: one group comprising the spiny waterflea and the fishhook waterflea Cercopagis pengoi; and the other, the zebra mussel and quagga mussel Dreissena rostriformis bugensis. Differences in species\u27 life-histories may interact with various transport mechanisms to produce highly dissimilar levels of propagule pressure to inland lakes. Species with the broadest distribution had the highest propagule pressure scores. Finally, I examine the attributes of an invasion network formed by lakes invaded by spiny waterfleas connected by recreational traffic. I was interested in whether specific lakes served as ‘hubs’, and whether the network of lakes exhibited a scale-free topology. Management implications for a scale-free invasion network include a potential decrease in the overall rate of NIS spread if propagule flow from ‘hubs’ is reduced

Plan for an Aquatic Invasive Species Web Portal

This report, prepared for NOAA, presents recommendations for an aquatic invasive species (AIS) central web portal and an analysis of existing AIS databases. We gathered data from federal agencies and private entities through interviews, questionnaires, and surveys. The information compiled from our research was used to determine and justify the details of our recommendations