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.
Megan Fork's paper on the effects of DOC on denitrification in Florida rivers came out today in the year's first issue of Ecosystems. Congrats again Megan!
We've just heard from NSF that our proposal to study the wetlands of Big Cypress National Preserve will be funded! The Big Cypress landscape is a mosaic of isolated wetlands, grasslands, and pine forests. The core observation that motivates our proposal is that the Cypress wetlands appear to be regularly spaced. This sort of regular pattern occurs in dryland vegetation, in peatlands (including the nearby Everglades) and elsewhere, and is thought to arise from feedbacks that are spatially-dependent. Basically, organisms improve the environment in their immediate vicinity, but that has the effect of making more distant locations unsuitable. In Big Cypress, we think that cypress trees essentially capture water from the surrounding landscape by dissolving the limestone bedrock and creating wetland depressions. Pretty smart! Testing this core hypothesis, and all of its pieces, requires an interdisciplinary team. My colleagues at UF, who are going to do most of the field work, include ecohydrologists, soil scientists, and organic and inorganic geochemists. Brad Murray and I are in charge of developing a model of this landscape. It's gonna be fun.
Meredith Steele's paper (with a long list of co-authors) on the surface water characteristics of US cities has been accepted at Ecosystems! Congratulations Meredith!
Abstract: Earth’s surface is rapidly urbanizing, resulting in dramatic changes in the abundance, distribution and character of surface water features in urban landscapes. However, the scope and consequences of surface water redistribution at broad spatial scales are not well understood. We hypothesized that urbanization will lead to convergent surface water abundance and distribution: in other words, cities will gain or lose water such that they become more similar to each other than are their surrounding natural landscapes. Using a database of more than 1 million water bodies and 1 million km of streams, we compared the surface water of 100 US cities with their surrounding undeveloped land. We evaluated differences in areal (AWB) and numeric densities (NWB) of water bodies (lakes, wetlands, etc.), the morphological characteristics of water bodies (size), and the density (DC ) of surface flow channels (i.e. streams and rivers). The variance of urban AWB, NWB, and DC across the 100 MSAs decreased, by 89%, 25%, and 71% respectively, compared to undeveloped land. These data show that many cities are surface-water poor relative to undeveloped land; however, in drier landscapes urbanization increases the occurrence of surface water. This convergence pattern strengthened with development intensity, such that high intensity urban development had an areal water body density 98% less than undeveloped lands. Urbanization appears to drive the convergence of hydrological features across the US, such that surface water distributions of cities are more similar to each other than to their surrounding landscapes.
An unformatted version of Meredith Steele's paper on the morphological characteristics of urban lakes is now available online.
Understanding and managing urban aquatic ecosystems has to begin with good information about their distribution and about characteristics like size and shape (hydrography). We've just received word that our paper on this topic, led by post-doc Meredith Steele, has been accepted for publication in Ecological Applications! One simple thing that makes this paper significant is the spatial extent of Meredith's analysis (100 cities across the whole US). A second simple thing about this paper is what the data show: urban water bodies (lakes, ponds, wetlands) are of moderate size. That is, in comparison to undeveloped land outside cities, there are fewer very large and fewer very small water bodies. The more complicated thing we want to know is how these differences arise. One possibility is that cities are located near particular types of water bodies. A second possibility is that, during urban development, we remove small (and large?) water bodies, and build medium-sized ones. We use some subtler patterns in our data to distinguish among these processes, and ask how their importance might change over time. This paper is the first of several papers Meredith has in review or in prep that will deal with other scales and other aspects of urban hydrographic change. Very exciting! And congratulations Meredith!
Congratulations are due to Ewan Isherwood, who successfully defended his MS thesis this morning at FIU! Ewan's research addresses the distinctness of vegetation communities (ridges and sloughs) in the Florida Everglades, with a particular focus on how these these distinct communities become more blended as a result of hydrologic modification and microtopographic flattening. To do this, Ewan developed statistical proxies of distinctness using multivariate techniques, and applied them across our Everglades-wide sampling regime.
A few weeks ago, Dr. Todd Kana delivered a new instrument to the River Center. The Membrane Inlet Mass Spectrometer, which Todd designs and builds, measures dissolved gases directly from water samples. We had one of these instruments in our lab at FIU, and used it to study denitrification in the Floridan Aquifer and in spring-fed and blackwater rivers.
Yesterday, Todd returned to us to train about 8 people from the River Center and other labs on the use of the new instrument, which is a slightly different model than the old MIMS. We also had lunch with about a dozen people where we discussed the different applications of the MIMS, including the different gases it can measure and the different kinds of samples it can measure (air, water; field samples, in line experiments, etc.). We are very excited to have this new capability in the lab, and look forward to all of the neat things we will learn with it!
|The Heffernan Lab at Duke University||