A beginner's guide to nutritional profiling in physiology and ecology.

The nutritional history of an organism is often difficult to ascertain. Nonetheless, this information on past diet can be particularly important when explaining the role of nutrition in physiological responses and ecological dynamics. One approach to infer the past dietary history of an individual is through characterization of its nutritional phenotype, an interrelated set of molecular and physiological properties that are sensitive to dietary stress. Comparisons of nutritional phenotypes between a study organism and reference phenotypes have the potential to provide insight into the type and intensity of past dietary constraints. Here, we describe this process of nutritional profiling for ecophysiological research in which a suite of molecular and physiological responses are cataloged for animals experiencing known types and intensities of dietary stress and are quantitatively compared with those of unknown individuals. We supplement this delineation of the process of nutritional profiling with a first-order analysis of its sensitivity to the number of response variables in the reference database, their responsiveness to diet, and the size of reference populations. In doing so, we demonstrate the considerable promise this approach has to transform future studies of nutrition by its ability to provide more and better information on responses to dietary stress in animals and their populations.

Thermal stratification patterns in urban ponds and their relationships with vertical nutrient gradients.

Ponds that collect and process stormwater have become a prominent feature of urban landscapes, especially in areas recently converted to residential land use in North America. Given their increasing number and their tight hydrological connection to residential catchments, these small aquatic ecosystems could play an important role in urban biogeochemistry. However, some physicochemical aspects of urban ponds remain poorly studied. Here we assessed the frequency and strength of water column stratification, using measurements of vertical water temperature profiles at high spatial and temporal frequency, in 10 shallow urban stormwater management ponds in southern Ontario, Canada. Many of the ponds were well stratified during much of the summer of 2010 as indicated by relatively high estimates of thermal resistance to mixing (RTRM) indices. Patterns of stratification reflected local weather conditions but also varied among ponds depending on their morphometric characteristics such as maximum water depth and surface area to perimeter ratio. We found greater vertical nutrient gradients and more phosphorus accumulation in bottom waters in ponds with strong and persistent stratification, which likely results from limited particle resuspension and more dissolved phosphorus (P) release from sediments. However, subsequent mixing events in the fall diminished vertical P gradients and possibly accelerated internal loading from the sediment-water interface. Our results demonstrate that stormwater ponds can experience unexpectedly long and strong thermal stratification despite their small size and shallow water depth. Strong thermal stratification and episodic mixing in ponds likely alter the quantity and timing of internal nutrient loading, and hence affect water quality and aquatic communities in downstream receiving waters.

Release of phosphate in a wetland by changes in hydrological regime.

Phosphate can be removed from the water column in wetlands by adsorption, sedimentation, or biological uptake. However, phosphate removal efficiency in wetlands is variable because phosphate can also be re-released from wetland sediment to water body under certain conditions. This study was conducted to investigate mechanism of changes in removal efficiency of phosphate under different hydrological regime. For this, we constructed wetland microcosms, which were exposed to consecutive drying and rewetting periods. At the initial period of wetland operation, phosphate removal efficiency was high (60.1-100%) probably due to high adsorption capacity and low phosphatase activity. However, a large amount of phosphate was released in a rewetting period followed by a drying period. This result can be explained by two mechanisms. Firstly, rewetting of soil followed by drying released phosphate by desorption of previously adsorbed phosphate, which was clearly demonstrated in our supplementary isotherm experiment. Secondly, we observed a huge shift of phosphatase activity by drying of soil (1.4 nmol min(-1) g(-1) in the initial period and 12.4 nmol min(-1) g(-1) in a drying period), which lasted even in the rewetting period (14.2 nmol min(-1) g(-1)). These results suggest that repeated drying and rewetting events in wetlands can cause substantial release of phosphate by chemical changes and activation of P-mineralizing enzyme, which may last even when the water table is returned to the original level.