Research Highlights

Although water cycles across North America have fluctuated in response to climate throughout geological time, recent climatic impacts and near-term forecasts are uncertain due largely to short and sparse hydrological records that are also often confounded by land-use or direct human influences, such as impoundment and diversion. To overcome these shortcomings and investigate long-term regional hydrologic dynamics, a collaborative effort among researchers and water resource managers across Wisconsin assembled a unique hydrologic data set of water levels and meteorology in northern Wisconsin and the Laurentian Great Lakes region.


stream C iconAlthough streams are now recognized as important components of regional and global carbon budgets, patterns and controls of stream CO2 and CH4 budgets are poorly documented for most landscapes. One major question is: Do streams support their CO2 and CH4 emissions through internal processing or do terrestrial sources and groundwater provide most of the gas supply?


Rapid transitions in ecosystem structure, or regime shifts, are a hallmark of alternative stable states. However, regime shifts can occur even when feedbacks are not strong enough to cause alternative stable states. Despite the theoretical and practical importance of distinguishing between different types of threshold responses, empirical evaluations of alternative stable states on management-relevant scales are rare. NTL-LTER researchers have observed rapid transitions between invasive rusty crayfish (Orconectes rusticus) and native sunfishes (Lepomis spp.) in two LTER lakes.

 


Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, and these measures may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role in shaping cyanobacterial communities on daily time scales based on function because declining N has been shown to select for N2 fixers.


graph iconPrimary production is perhaps one of the most fundamental processes in ecosystems and is a foundation of understanding long-term ecosystem dynamics among LTER sites.  There is a long history of estimating primary production in both freshwater and marine ecosystems using 14carbon (14C) incubations. An advantage of the 14C approach is the ability to quantify production in systems with low production.  On the other hand, due to logistical challenges of 14C incubations, obtaining high temporal resolution estimates (e.g., daily production) is difficult and cost prohibitive. Thus, whole ecosystem estimates of ecosystem production at daily to annual time scales often necessitate interpolating between infrequent measurements.


Understanding the conditions that enable or constrain success in environmental governance is crucial for developing effective interventions and adapting approaches. Efforts to achieve and assess success in environmental quality improvement are often impeded by changes in conditions that drive outcomes but lie outside the scope of intervention and monitoring. Through historical trend analysis, GIS mapping, and policy analyses of the Yahara River watershed (YRW; the watershed for NTL study lakes Mendota, Monona, and Wingra), we documented how long-term changes in land use, agriculture, and climate act as non-stationary drivers of change that combine to render water quality management interventions less effective and increasingly difficult to assess.


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.


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.

 


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.


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)