An Isotopic Examination of Cave, Spring and Epigean Trophic Structures in Mammoth Cave National Park

AN ISOTOPIC EXAMINATION OF CAVE, SPRING AND EPIGEAN TROPHIC STRUCTURES IN MAMMOTH CAVE NATIONAL PARK Name: Zacchaeus Greg Compson Date: October 15, 2004 Pages: 56 Directed by: Philip Lienesch, Doug McElroy, Michael Stokes and Richard Bowker Department of Biology Western Kentucky University Abstract High-water events in the Green River result in flow-reversals which flush native and introduced fishes into Mammoth Cave, posing threats to indigenous cave fauna. However, little is known about the trophic interactions between cave and epigean aquatic systems or their connectivity via natural springs. The purpose of this study was to use stable isotopes of C and N to describe and compare the trophic structure of epigean, spring and cave aquatic systems within Mammoth Cave National Park. Fourteen sites were sampled from fall 2002 to fall 2003; four in the Green River (epigean), four in spring-heads, and three inside Mammoth Cave. Two a priori hypotheses were tested: fish and invertebrates living in spring heads should express delta 13C values intermediate to those of organisms in cave and epigean aquatic systems and overall trophic levels in cave and spring samples should be compressed, showing lower delta15N values compared to epigean sites. Though cave and spring systems were dominated by allochthonous leaf litter, characteristic of headwater streams, the epigean system was also largely dependent on detrital inputs. Primary differences in delta13C were seen at higher trophic levels, particularly in top consumers such as Lepomis species, where delta13C values decreased from epigean to spring to cave habitats. Though all three habitats supported a similar number of trophic levels (N: 5), the trophic structure was compressed in cave and spring compared to epigean habitats. This trend, however, was obfuscated by delta15N values of accidental species in caves, which tended to be enriched, even when compared to epigean signals. This was attributed to either trophic enrichment from yolk sacs or starvation and subsequent self-processing. Overall, spring trophic structure was found to be intermediate to cave and epigean trophic structures in terms of delta13C values of upper-level fish consumers, but spring trophic structure was more similar to the cave trophic structure in terms of delta15N values, excluding cave accidentals

Leaf-litter leachate is distinct in optical properties and bioavailability to stream heterotrophs

Dissolved organic C (DOC) leached from leaf litter contributes to the C pool of stream ecosystems and affects C cycling in streams. We studied how differences in leaf-litter chemistry affect the optical properties and decomposition of DOC. We used 2 species of cottonwoods (Populus) and their naturally occurring hybrids that differ in leaf-litter phytochemistry and decomposition rate. We measured DOC and nutrient concentration in leaf leachates and determined the effect of DOC quality on heterotrophic respiration in 24-h incubations with stream sediments. Differences in DOC composition and quality were characterized with fluorescence spectroscopy. Rapidly decomposing leaves with lower tannin and lignin concentrations leached ~40 to 50% more DOC and total dissolved N than did slowly decomposing leaves. Rates of heterotrophic respiration were 25 to 50% higher on leachate from rapidly decomposing leaf types. Rates of heterotrophic respiration were related to metrics of aromaticity. Specifically, rates of respiration were correlated negatively with the Fluorescence Index and positively with Specific Ultraviolet Absorbance (SUVA254) and T280 tryptophan-like fluorescence peak. These results reveal that leaf-litter DOC is distinctly different from ambient streamwater DOC. The relationships between optical characteristics of leaf leachate and bioavailability are opposite those found in streamwater DOC. Differences in phytochemistry among leaf types can influence stream ecosystems with respect to DOC quantity, composition, and rates of stream respiration. These patterns suggest that the relationship between the chemical structure of DOC and its biogeochemistry is more complex than previously recognized. These unique properties of leaf-litter DOC will be important when assessing the effects of terrestrial C on aquatic ecosystems, especially during leaf fall

Environmental filtering of macroinvertebrate traits influences ecosystem functioning in a large river floodplain

Article describes how the biodiversity–ecosystem function hypothesis postulates that higher biodiversity is correlated with faster ecosystem process rates and increased ecosystem stability in fluctuating environments. The authors examined linkages among floodplain wetland habitats, invertebrate communities and their associated traits, and ecosystem function across 60 sites within the floodplain wetlands of the lower Wolastoq, Saint John River, New Brunswick

DNA metabarcoding reveals metacommunity dynamics in a threatened boreal wetland wilderness

Too often, ecological monitoring studies are designed without understanding whether they have sufficient statistical power to detect changes beyond natural variability. The Peace–Athabasca Delta is North America’s largest inland delta, within a World Heritage area, and is currently threatened by human development. Using multispecies occupancy models we show that the wetland macroinvertebrate community is highly diverse, and spatial and temporal turnover are so high that composition is nearly random, emphasizing stochastic processes of assembly. Using DNA metabarcoding, our study detected more taxa, both overall and per sample, than traditional morphology-based sample processing, increasing our power to detect ecosystem change. Improving data quality and quantifying error are key to delivering effective monitoring and understanding the dynamic structure of the metacommunity.The complexity and natural variability of ecosystems present a challenge for reliable detection of change due to anthropogenic influences. This issue is exacerbated by necessary trade-offs that reduce the quality and resolution of survey data for assessments at large scales. The Peace–Athabasca Delta (PAD) is a large inland wetland complex in northern Alberta, Canada. Despite its geographic isolation, the PAD is threatened by encroachment of oil sands mining in the Athabasca watershed and hydroelectric dams in the Peace watershed. Methods capable of reliably detecting changes in ecosystem health are needed to evaluate and manage risks. Between 2011 and 2016, aquatic macroinvertebrates were sampled across a gradient of wetland flood frequency, applying both microscope-based morphological identification and DNA metabarcoding. By using multispecies occupancy models, we demonstrate that DNA metabarcoding detected a much broader range of taxa and more taxa per sample compared to traditional morphological identification and was essential to identifying significant responses to flood and thermal regimes. We show that family-level occupancy masks high variation among genera and quantify the bias of barcoding primers on the probability of detection in a natural community. Interestingly, patterns of community assembly were nearly random, suggesting a strong role of stochasticity in the dynamics of the metacommunity. This variability seriously compromises effective monitoring at local scales but also reflects resilience to hydrological and thermal variability. Nevertheless, simulations showed the greater efficiency of metabarcoding, particularly at a finer taxonomic resolution, provided the statistical power needed to detect change at the landscape scale

Encroachment order and spatial patterns of broad-leaf tree species in the naturalization of a Cunninghamia lanceolata plantation

Authors of the article state that the aim of this study was to understand the encroachment order, spatial patterns, interspecific associations, and species diversity of a Cunninghamia lanceolata plantation and to provide context for how to improve the spatial structure of C. lanceolata plantations. Their results show that the encroachment of broad-leaf trees into the C. lanceolata plantation followed a clear successional sequence of tree community assembly: intolerant tree species encroachment first, such as Alniphyllum fortunei and Liquidambar formosana, encroached; neutral tree species then encroachment, such as Daphniphyllum oldhamii and Schima superba, and shade-tolerant tree species encroachment last, such as Castanopsis eyrei and Castanopsis tibetana

Effects of travertine and flow on leaf retention in Fossil Creek, Arizona

Abstract Leaf retention is important in transferring energy from riparian trees to stream food webs. Retention increases with geomorphic complexity such as substrate coarseness, sinuosity, and the presence of debris dams. High discharge can reduce retention, particularly when streams lack physical trapping features. Travertine formations, caused by calcium carbonate deposition, can alter stream morphology. To date, however, we know of no study testing the effect of travertine on leaf retention. This study capitalized on a river restoration project in Fossil Creek, Arizona, where water was returned to the channel after a century of diversion. We examined how the fixed factors Flow (before and after restoration) and Morphology (travertine and rifflepool sites) affected leaf retention. Leaf retention was higher in sites where travertine forms barriers across the river, relative to sites with riffle-pool morphology. Most leaves retained in travertine reaches were concentrated at the bottom of pools formed between dams. Although flow restoration did not alter retention rates across all sites, it diminished them at travertine sites, indicating an interaction between stream flow and morphology. We conclude that stream complexity and leaf retention are enhanced by travertine deposition but that high discharge can reduce the retentive capacity of in-stream structures

Replicate DNA metabarcoding can discriminate seasonal and spatial abundance shifts in river macroinvertebrate assemblages

Metabarcoding is capable of delivering consistent and accurate fine-resolution biodiversity data, and offers great promise for improving aspects of environmental assessment and research. Even so, many ecologists are keen to make further inferences about species’ abundances and the number of sequence reads has proven to be a poor proxy for abundance. The conservative interpretation has been to treat metabarcoding data as presence/absence, and although such data are less rich, occurrence and abundance are only different expressions of the same phenomenon. Interestingly if we assume the probability of detecting individuals is constant, it should be possible to use changes in the frequency of detection to infer changes in the underlying abundance. We tested the possibility that changes in the abundance structure of benthic macroinvertebrate communities could be recovered using replicated metabarcoding.We conducted 5 monthly surveys from Jun-Nov 2019 at the Catamaran Brook, a small tributary of the Little Southwest Miramichi River in New Brunswick, Canada. Each survey collected 30 benthic samples divided between control and treatment cages that excluded predatory fish. A further 6 samples were taken for traditional microscopic identification and counting.Analysis of the metabarcoding data demonstrated that we could recover plausible changes in abundance from occurrence data, including significant responses to both seasonal dynamics and the experimental exclusion of predators. The microscopy samples merely confirmed that count data are highly stochastic, and therefore while specific estimates of expected abundance from our model are highly uncertain, they capture those differences we could validate. In summary, while we confirmed that occurrence data are more robust for routine bioassessment, it is possible to recover fine-resolution changes in abundance that can inform ecological studies using metabarcoding

Functional traits link anthropogenic impact and disturbance regimes driving ecosystem function in a floodplain wetland complex

Floodplains are disturbance-driven ecosystems with high spatial and temporal habitat diversity, making them both highly productive and hosts to high biodiversity. The unpredictable timing of flood and drought years creates a mosaic of habitat patches at different stages of succession, while water level fluctuation directly influences macrophyte community dynamics, and thus habitat structure. This habitat complexity and diversity of disturbance regimes makes floodplains an ideal ecosystem in which to examine the links between biodiversity, traits and ecosystem function. With up to 90% of floodplains in North America and Europe altered to the point of functional extinction, it is particularly imperative to study and conserve those that remain intact, such as the Lower Saint John River and its associated floodplain, including the Grand Lake Meadows and Portobello Creek wetland complex. Despite the rise in trait-based science, taxonomic resolution has imposed limitations, especially in wetland and floodplain ecosystems where communities are vastly understudied compared to their riverine counterparts. Compared to traditional biomonitoring, DNA-based biomonitoring from high-throughput genomics sequencing methods is powerful in that it can reliably characterize community composition in unprecedented detail, allowing us to assess how disturbance and environmental filters interact with invertebrate traits and ecosystem function. Using structural equation analysis, we take a whole ecosystem approach to examine ecosystem health across a floodplain disturbance gradient. We focus chiefly on how anthropogenic alteration within watersheds affects downstream floodplain wetlands, how the resulting patch diversity shapes communities and, finally, how those communities influence ecosystem function through trait diversity metrics. We also examine and compare which traits are associated with crucial ecosystem gradients

Stream carbon and nitrogen supplements during leaf litter decomposition: contrasting patterns for two foundation species

11 páginas, 3 figuras, 2 tablasLeaf litter decomposition plays a major role in nutrient dynamics in forested streams. The chemical composition of litter affects its processing by microorganisms, which obtain nutrients from litter and from the water column. The balance of these fluxes is not well known, because they occur simultaneously and thus are difficult to quantify separately. Here, we examined C and N flow from streamwater and leaf litter to microbial biofilms during decomposition. We used isotopically enriched leaves (13C and 15N) from two riparian foundation tree species: fast-decomposing Populus fremontii and slow-decomposing Populus angustifolia, which differed in their concentration of recalcitrant compounds. We adapted the isotope pool dilution method to estimate gross elemental fluxes into litter microbes. Three key findings emerged: litter type strongly affected biomass and stoichiometry of microbial assemblages growing on litter; the proportion of C and N in microorganisms derived from the streamwater, as opposed to the litter, did not differ between litter types, but increased throughout decomposition; gross immobilization of N from the streamwater was higher for P. fremontii compared to P. angustifolia, probably as a consequence of the higher microbial biomass on P. fremontii. In contrast, gross immobilization of C from the streamwater was higher for P. angustifolia, suggesting that dissolved organic C in streamwater was used as an additional energy source by microbial assemblages growing on slow-decomposing litter. These results indicate that biofilms on decomposing litter have specific element requirements driven by litter characteristics, which might have implications for whole-stream nutrient retention.The National Science Foundation provided funding through the Frontiers in Integrative Biological Research (DEB-0425908), Integrative Graduate Education and Research Traineeship (DGE-0549505), and Ecosystem Studies (DEB-1120343) research programs. Funding was also provided by the MED-FORESTSTREAMS (CGL2011-30590-C02-01) project. A. P. was supported by a Formación de Personal Investigador Ph.D. fellowship from the Spanish Ministry of Science and Innovation within the context of ISONEF (CGL2008-05504-C02-01).Peer reviewe

Studying Ecosystems With DNA Metabarcoding:Lessons From Biomonitoring of Aquatic Macroinvertebrates

An ongoing challenge for ecological studies has been the collection of data with high precision and accuracy at a suitable scale to detect and manage critical global change processes. A major hurdle has been the time-consuming and challenging process of sorting and identification of organisms, but the rapid development of DNA metabarcoding as a biodiversity observation tool provides a potential solution. As high-throughput sequencing becomes more rapid and cost-effective, a “big data” revolution is anticipated, based on higher and more accurate taxonomic resolution, more efficient detection, and greater sample processing capacity. These advances have the potential to amplify the power of ecological studies to detect change and diagnose its cause, through a methodology termed “Biomonitoring 2.0.” Despite its promise, the unfamiliar terminology and pace of development in high-throughput sequencing technologies has contributed to a growing concern that an unproven technology is supplanting tried and tested approaches, lowering trust among potential users, and reducing uptake by ecologists and environmental management practitioners. While it is reasonable to exercise caution, we argue that any criticism of new methods must also acknowledge the shortcomings and lower capacity of current observation methods. Broader understanding of the statistical properties of metabarcoding data will help ecologists to design, test and review evidence for new hypotheses. We highlight the uncertainties and challenges underlying DNA metabarcoding and traditional methods for compositional analysis, specifically comparing the interpretation of otherwise identical bulk-community samples of freshwater benthic invertebrates. We explore how taxonomic resolution, sample similarity, taxon misidentification, and taxon abundance affect the statistical properties of these samples, but recognize these issues are relevant to applications across all ecosystem types. In conclusion, metabarcoding has the capacity to improve the quality and utility of ecological data, and consequently the quality of new research and efficacy of management responses