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Research Highlights

A decade of seasonal dynamics and co-occurrences within freshwater bacterioplankton communities from Lake Mendota, WI, USA

As the size and extent of biological data sets grow, scientists turn to new quantitative techniques, such as network analysis, to understand biological complexity over large scales. For network analysis of microbial datasets, topological ‘co-occurrence’ networks are generated from correlative metrics, in which nodes represent observed variables and significant correlations are represented by the edges connecting them. We used an unprecedented decade-long time series of freshwater bacterioplankton molecular community fingerprints to test the following hypotheses: (1) community co-occurrence networks from this sample set are non-random, (2) seasonality explains the organization and complexity of co-occurrence networks, and (3) community richness and diversity correlate to co-occurrence network complexity.

Relationships between boaters and lakes: Longitudinal survey data in the NHLD

Much of the recreational activity in the NHLD centers around boating on many of the 7500+ lakes in the region. NTL-LTER is now collecting longitudinal data on the relationship between this important user group and the lakes of the NTL-LTER. In the 2011 season, we intercepted 1700 boaters at 136 lakes in Vilas and Oneida counties, ultimately receiving logbooks documenting over 5900 trips taken by 834 participants.

 

Long-term Phosphorus Dynamics in the Yahara River Lake Chain

The four Yahara River chain of lakes – Mendota, Monona, Waubesa, and Kegonsa – have experienced undesirable blue-green algal blooms fueled by excessive phosphorus (P) inputs for years. Analyzing over 30 years of highly variable P loading and in-lake data, NTL-LTER scientists developed P load reduction targets needed for improving water quality in the lakes. These reduction targets were based on lower P loads measured during a 2-year drought when water quality in all four lakes was substantially better.

Management of Aquatic Invasives: Rusty Crayfish Removal in Sparkling Lake

Invasive species are a leading driver of biodiversity loss in aquatic systems.  Removing established invasive species may restore native communities and ecosystem function, and also reveal unexpected  indirect connections between invasive species and other community members.  In an attempt to restore the native littoral food web, we removed ~95,000 invasive rusty crayfish (Orconectes rusticus) from Sparkling Lake from 2001-2008 via trapping, and changed fishing regulations to increase predation of crayfish by littoral fishes. (image credit: Jeff Gunderson, Minnesota Sea Grant)

Changes in Fire-Drought Relationships With Land Use change in the Northern Highlands Lake District

Fire is a complex phenomenon that responds to climate and vegetation and may become more difficult to manage in the context of global climate and land use change (Bowman et al., 2009).  Understanding dynamics of fire over extended periods of time that incorporate climate variability and forest change could help inform management of forests in the 21st century (Whitlock et al., 2008). Our study focused on fire-drought interactions in a small landscape of northern Wisconsin over a 200-year period characterized by dramatic shifts in human settlement and forest use and management. 

Spatial and Temporal Variability of Algal Blooms in a Eutrophic Lake

Harmful algal blooms are a globally pervasive problem, and with a changing climate are expected to be an increasing concern. Because of this rising concern, scientific understanding is becoming ever more important to improve prediction and inform management decisions. Spatio-temporal dynamics of algal blooms remain poorly understood, largely due to multiple drivers, sampling limitations, and spatial variability itself. Observations of near shore blooms or scums can differ widely from pelagic areas of a lake, where most sampling occurs. With the advent of new rapid sampling technologies, sampling regimes can be augmented with rapid fluorescence sampling of algal pigments (chlorophyll and phycocyanin) that can substantially improve spatial and temporal sampling scopes.

Nitrogen uptake and hydrologic connectivity in streams and flow-through wetlands

Human alterations of nutrient cycles have jeopardized the status of many water bodies.  Currently, there is a need to understand how individual water bodies- which range widely in shape, size, and hydrology- may contribute differentially to nutrient transport and transformation through river networks.  For example, wetlands can be important sites of nutrient cycling and organic matter settling, but the role of wetlands depends partly on internal hydrologic connections between nutrient sources and sinks.

 

Lakeshore residential development and largemouth bass growth: a cross-lakes comparison

As humans develop lake shorelines, several aspects of the terrestrial and aquatic habitats are altered, and these changes have potential effects that can ripple through aquatic food webs (Engel and Pederson 1998, Francis and Schindler 2009).  Modifications to habitat structures along with direct human impacts, such as increased angling effort with lakeshore residential development (NRC 1992), may drive changes in game fish ecology.

Drivers of gas flux from temperate lakes: Partitioning the energetic contributions of wind and convection in 42 lakes

Estimating the flux of carbon dioxide (CO2) from lakes is important for understanding the role of these ecosystems in regional and global carbon budgets.  The efflux of partially soluble gasses such as CO2 is controlled by near-surface turbulence.  Lakes receive turbulent inputs across the air-water interface via two primary mechanisms: wind shear and negative buoyancy flux (convective cooling).  We examined the relative importance of wind and convection in 42 temperate lakes from multiple countries that covered gradients in latitude, size, and water clarity.

Genetic diversity of cyanobacteria in four eutrophic lakes

We explore the genetic diversity of cyanobacteria in four eutrophic NTL core study lakes (Lakes Mendota, Monona, Kegonsa, and Wingra) using a culture-independent genetic method (Miller and McMahon 2011).  The goals of this study were to 1) describe the phylogeny of cyanobacteria in each lake, and 2) examine genotype richness and evenness as the determinants of cyanobacterial diversity.

 

 

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