Appendix A. Supporting material including a detailed description of methods; one table summarizing relevant variables used to calculate metabolism and nutrient uptake; and five figures showing location of Ivishak Spring; ER and GPP vs. day of the year; summary of daily PAR, air temperature, and water temperature; GPP, ER, NEP vs. water temperature; and seasonal patterns of organic matter biomass and DOC concentration.

Supporting material including a detailed description of methods; one table summarizing relevant variables used to calculate metabolism and nutrient uptake; and five figures showing location of Ivishak Spring; ER and GPP vs. day of the year; summary of daily PAR, air temperature, and water temperature; GPP, ER, NEP vs. water temperature; and seasonal patterns of organic matter biomass and DOC concentration

Landscape heterogeneity and the biodiversity of Arctic stream communities : a habitat template analysis

Author Posting. © National Research Council Canada, 2005. This article is posted here by permission of National Research Council Canada for personal use, not for redistribution. The definitive version was published in Canadian Journal of Fisheries and Aquatic Sciences 62 (2005): 1905-1919, doi:10.1139/F05-100.We predicted that substratum freezing and instability are major determinants of the variability of stream community structure in Arctic Alaska. Their effects were conceptualized as a two-dimensional habitat template that was assessed using a natural experiment based on five stream types (mountain-spring, tundra-spring, tundra, mountain, glacier). Detrended correspondence analysis (DCA) indicated distinct macroinvertebrate assemblages for each stream type. The contribution of functional feeding groups to assemblage biomass varied systematically among stream types, indicating that structure and function are linked. Assemblage position within a DCA biplot was used to assess factors controlling its structure. Springs separated from other stream types along a gradient of nutrient concentration and freezing probability. Glacier and mountain streams separated from springs and tundra streams along a gradient of substratum instability and freezing probability. Owing to differences in sources of discharge to streams, the effects of nutrients and substratum stability could not be separated from freezing. Although many factors likely contribute to the variability of Arctic stream communities, the major determinants may be conceptualized as a template structured by gradients in (i) nutrient supply and substratum freezing and (ii) substratum instability and substratum freezing. This template provides a basis for predicting the response of Arctic stream communities to climate change.Funding was provided by grants from the National Science Foundation (NSF DEB-9810222 and NSF OPP-9911278)

The influence of energy availability on population-, community-, and ecosystem-level processes in cave stream ecosystems

Detritus from surface environments supplies the energy that shapes community structure and fuels productivity in most cave ecosystems. However, only qualitative descriptions of cave energy dynamics are available, hindering development of quantitative models describing how energy availability influences cave ecosystem processes. In contrast, the importance of detritus for surface ecosystem processes has been appreciated for decades. This dissertation begins to close this knowledge gap by exploring how energy availability shapes cave stream ecosystem processes at multiple organizational levels (ecosystem-, community-, population-level) and time scales (evolutionary vs. ecological). Chapter Two examined potential correlations between litter breakdown rates and detrital storage, but found no such relationships among four cave streams. However, surface-adapted species dominated macroinvertebrate biomass, suggesting that surface-adapted taxa can have a significant influence on cave ecosystem processes. In Chapter Three, a whole-reach litter amendment was conducted to explore the influence of enhanced detrital inputs on cave community structure and energy flow. While the litter amendment significantly increased total consumer biomass via assimilation of amended corn-litter, the response was dictated by evolutionary history. Biomass of surface-adapted taxa increased significantly following the amendment, while biomass of obligate cave species remained unchanged. As in Chapter Two, consumer biomass was dominated by surface-adapted taxa, reinforcing their role in cave ecosystem processes relative to cave-adapted taxa, the traditional focus of cave studies. Chapters Four and Five utilized a 5+-year mark-recapture data set on the cave-adapted crayfish Orconectes australis to explore how energy availability has shaped its evolutionary history and population dynamics. Time-to-maturity, age-at-first-reproduction, and longevity of O. australis were substantially longer than those estimated for most crayfish species, indicating evolution of a K-selected life history. Chapter Five found that biomass and secondary production of O. australis were positively related to resource availability. Energetic models indicated resource deficits were not present, but that nearly all prey production is necessary to support each O. australis population. Thus, inter- and intra-specific competition for resources within caves is likely high. Collectively, Chapters Four and Five provide the first quantitative explanation of why K-selected life histories are an evolutionary advantage to obligate cave taxa like O. australis. (Published By University of Alabama Libraries

The role of geomorphology in river biogeochemical processing

Although once treated as simple downstream transporters of material, river networks are now recognized for their role in processing, or transformation, storage, and removal, of carbon and nutrients during transport. The linkages between channel geomorphic structure, biogeochemistry, and ecology of lotic ecosystems are important to their functioning. The overarching goal of this research was to develop a better understanding of the relationships among geomorphology, ecosystem metabolism, and carbon and nutrient dynamics in a larger river. This research exploited natural changes in river form associated with broad-scale geologic transitions in the Cahaba River, AL. Spatial and temporal patterns of ecosystem metabolism along the Cahaba indicated an important effect of regional geology. In the Coastal Plain this effect was expressed through strong seasonal changes in plankton productivity, driving high rates of gross primary production and ecosystem respiration. Anthropogenic activity associated with Birmingham, AL, causes elevated water-column nutrient concentrations. However, downstream nutrient levels are comparable to upstream of Birmingham. Corresponding to the location of this decline is a broad geomorphic transition creating shoal habitat, which supports expansive crops of macrophytes. We found whole ecosystem metabolism, and the biomass of macrophytes, could significantly contribute to water column nutrient declines. Recent models of organic matter export from rivers have identified the potential significance of seasonal pulses of autochthonous production and the dearth of knowledge regarding the fate of riverine algal production. Our evaluation of phytoplankton production, in the Coastal Plain, confirmed an important role in fueling water column processing and provided evidence of phytoplankton delivery to sediments. The identity and characteristics of primary producers appears to be constrained by broad geomorphologic transitions and has widespread ecological consequences including altering the timing and character of nutrient and carbon delivery downstream and the spatially and temporally dynamic nature of the relative importance of water-column and benthic processes. Overall, this research contributes to our understanding of river biogeochemistry by highlighting the complexity and variability of interactions among factors influencing rates of carbon and nutrient processing. Expanding the spatial and temporal scales of empirical measurements of ecosystem processes is critical to accurately predicting the biogeochemical activity of river networks. (Published By University of Alabama Libraries

The effects of N and P supply on invertebrate foodwebs: an experimental test of ecological stoichiometry in detritus-based ecosystems

In the last several decades, ecological stoichiometry has emerged as a promising framework for predicting how shifts in the relative availability of N and P influence biological processes from cellular to ecosystem scales. However, explicit tests of ecological stoichiometry theory from ecosystem scale experiments remain rare. In this dissertation, I present the results of a three year experiment where five detritus-based headwater streams were continuously fertilized with N and P at different concentrations, creating a range of molar N:P ratios (from 2:1 to 128:1), for two years following one year of pre-nutrient enrichment monitoring. Nutrient enrichment of the five detritus-based streams resulted in significant shifts in the N and P content of leaf detritus, which is the primary food resource for the invertebrate communities. Patterns of invertebrate productivity among the five streams were closely related to the N:P ratio of leaf detritus, providing strong evidence of food web P-limitation. In addition to effects on overall productivity, nutrient enrichment resulted in shifts in the taxonomic composition of the resident invertebrate community, which were largely driven by increased biomass of a few common detritivores. Nutrient enrichment also had significant effects on organic matter flows within the detrital food webs, as flows of all detrital resources to consumers increased following nutrient enrichment. Increased organic matter flows were necessary to support higher rates of invertebrate production following enrichment and were significantly related to the N:P ratio of leaf detritus, which accounted for ~2/3 of total organic matter flows. Furthermore, invertebrates consumed a greater proportion of the total mass of leaf litter lost from these systems annually following enrichment, a pattern that was once again driven by the N:P ratio of leaf litter. The results of this study provide compelling support for ecological stoichiometry as a framework for predicting consequences of altered N and P dynamics. Our ability to predict how ecosystems respond to shifting N and P availability remains an important challenge in contemporary ecological research given the globally pervasive nature of anthropogenic impacts on biogeochemical N and P cycles. (Published By University of Alabama Libraries