Nutrient limitation happens when nutrient supply is insufficient to meet demand by biota, but most assessments of nutrient limitation are based only on concentration. In streams, where metabolism is highly variable and streamflow continuously replenishes nutrient supply, concentration has been a poor predictor of nutrient limitation and autotroph biomass. We have a paper out in Freshwater Science that explores new predictors of nutrient limitation, based on nutrient spiraling theory and empirical measurements of metabolism and nutrient flux. The paper was led by Sean King, who finished his PhD at the University of Florida a few years ago, and is now at the Southwest Florida Water Management District (SWFWMD). Congratulations Sean!
Meredith Steele's paper on convergent surface water distributions in US cities is now available online (and open accesss) at Ecosystems. In this paper, meredith showed that the abundance and distribution of surface water (hydrography) is largely a function of land use, and relatively insensitive to climatic and geologic controls, within the boundaries of 100 US cities. In essence, we add lakes, ponds, and canals to dry places, and remove them from wet places; the end result is that cities have very similar hydrography whether they are situated in a desert, a subtropical wetland, or a temperate forest. Check it out!
We have two new papers that just came out as part of a special issue of Frontiers in Ecology and the Environment on continental scale ecology.
The first paper (Heffernan et al. 2014; Macrosystems Ecology: Understanding Ecological Pattern and Processes at Continental Scales) proposes a framework for incorporating a systems perspective more completely into the study of broad-scale ecological phenomena. This means thinking about processes like feedbacks between vegetation and climate, long-distance connections between ecosystems, and ways in which broad- and fine-scale phenomena influence one another. We think that this broad scale systems perspective ('Macrosystems Ecology') is going to be essential for predicting the effects of many different anthropogenic changes that have causes and consequences at the scale of whole regions and continents. One challenge in writing this paper is that ecologists and others have been thinking about regions and continents for a long time, in sub-disciplines like biogeography and related fields like climate science. We argue that two things are changing - 1) across these fields, we are incorporating more and more process into that understanding (which is made easier through data sets that have a fine resolution but cover broad extents); and 2) that we are able to make more and more connections across different types of phenomena (e.g., linking climate change, population genetics, and habitat loss; or understanding the diverse ecological consequences of bark beetle outbreaks). We also deal with the question of 'What is distinct about macrosystems?' Again, part of the challenge is that many ecological theories are supposed to apply to all scales, so lots of characteristics of macrosystems are likely to fit within such theory. One the other hand, some may not; one way (the only way?) to figure out whether macrosystems are distinct is to study regions and continents as systems through the lens of such theory. There is already some neat work that tries to do this, and hopefully lots more on the way!
The second paper (Groffman et al. 2014; Ecological homogenization of urban USA) is an overview of our 'Urban Homogenization' project, and presents some of the preliminary data that led us to this work in the first place. This is the project that includes Meredith Steele's work on surface water features in cities.
This is the homepage of the Heffernan Lab at Duke University. Here you can find all sorts of information about our research, teaching, and outreach. If you have any questions, contact Dr. Heffernan.
Dr. Jim Heffernan
I am an Assistant Professor in the Nicholas School of the Environment at Duke University. My research is focused on the causes and consequences of major changes in ecosystem structure, mostly in streams and wetlands.
|The Heffernan Lab at Duke University||