January 2019 - Present
Kharbush, J.J., D.J. Smith, M. Powers, H.A. VANDERPLOEG, D.L. FANSLOW, R.S. ROBINSON, G.J. Dick, and A. Pearson. Chlorophyll nitrogen isotope values track shifts between cyanobacteria and eukaryotic algae in a natural phytoplankton community in Lake Erie. Organic Geochemistry 128:71-77 (DOI:10.1016/j.orggeochem.2018.12.006) (2019).
Chlorophylls are produced by all photosynthetic organisms and are ideal targets for compound-specific isotopic studies of phytoplankton. In laboratory cultures, the difference between the nitrogen (N) isotope ratio (δ15N value) of chlorophyll and the δ15N value of biomass, known as εpor, varies taxonomically, yielding potential applications for studying productivity in modern and ancient environments. Here we take advantage of the annual cyanobacterial bloom in Lake Erie, USA, to demonstrate εpor patterns in a natural community. The resulting time series shows that environmental observations are similar to laboratory cultures: predicted εpor endmember values range from 4.6‰ to 7.4‰ for eukaryotic algae, and −18‰ to −21‰ for cyanobacteria. Because the range and sensitivity of εpor is similar between laboratory and natural settings, the data support the use of εpor as a reliable tracer of the relative contributions of cyanobacteria and eukaryotic algae to nutrient utilization and primary production in lacustrine environments.
Lee, C.-M., C.-Y. Kuo, J. Sun, T.-P. Tseng, K.-H. Chen, W.-H. Lan, C.K. Shum, T. Ali, P. CHU, and Y. Jia. Evaluation and improvement of coastal GNSS reflectometry sea level variations from existing GNSS stations in Taiwan. Advances in Space Research 63(3):1280-1288 (DOI:10.1016/j.asr.2018.10.039) (2019).
Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1 m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10 cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7 cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.
Marino, J.A., S.D. Peacor, D.B. Bunnell, H.A. VANDERPLOEG, S.A. POTHOVEN, A.K. ELGIN, J.R. Bence, J. Jiao, and E.L. Ionides. Evaluating consumptive and nonconsumptive predator effects on prey density using field times series data. Ecology (DOI:10.1002/ecy.2583) (2019). (IN PRESS)
Determining the degree to which predation affects prey abundance in natural communities constitutes a key goal of ecological research. Predators can affect prey through both consumptive effects (CEs) and nonconsumptive effects (NCEs), although the contributions of each mechanism to the density of prey populations remain largely hypothetical in most systems. Common statistical methods applied to time series data cannot elucidate the mechanisms responsible for hypothesized predator effects on prey density (e.g., differentiate CEs from NCEs), nor provide parameters for predictive models. State space models (SSMs) applied to time series data offer a way to meet these goals. Here, we employ SSMs to assess effects of an invasive predatory zooplankter, Bythotrephes longimanus, on an important prey species, Daphnia mendotae, in Lake Michigan. We fit mechanistic models in a SSM framework to seasonal time series (1994‐2012) using a recently developed, maximum likelihood‐based optimization method, iterated filtering, which can overcome challenges in ecological data (e.g. nonlinearities, measurement error, and irregular sampling intervals). Our results indicate that B. longimanus strongly influences D. mendotae dynamics, with mean annual peak densities of B. longimanus observed in Lake Michigan estimated to cause a 61% reduction in D. mendotae population growth rate and a 59% reduction in peak biomass density. Further, the observed B. longimanus effect is most consistent with an NCE via reduced birth rates. The SSM approach also provided estimates for key biological parameters (e.g., demographic rates) and the contribution of dynamic stochasticity and measurement error. Our study therefore provides evidence derived directly from survey data that the invasive zooplankter B. longimanus is affecting zooplankton demographics and offer parameter estimates needed to inform predictive models that explore the effect of B. longimanus under different scenarios such as climate change.
Newell, S.E., T.W. Davis, T.H. JOHENGEN, D.C. GOSSIAUX, A. BURTNER, D. PALLADINO, and M.J. McCarthy. Reduced forms of nitrogen are a driver of non-nitrogen-fixing harmful cyanobacterial blooms and toxicity in Lake Erie. Harmful Algae 81:86-93 (DOI:10.1016/j.hal.2018.11.003) (2019). https://www.glerl.noaa.gov/pubs/fulltext/2019/20190010.pdf
Western Lake Erie (WLE) experiences anthropogenic eutrophication and annual, toxic cyanobacterial blooms of non-nitrogen (N) fixing Microcystis. Numerous studies have shown that bloom biomass is correlated with an increased proportion of soluble reactive phosphorus loading from the Maumee River. Long term monitoring shows that the proportion of the annual Maumee River N load of non-nitrate N, or total Kjeldahl nitrogen (TKN), has also increased significantly (Spearman's ρ = 0.68, p = 0.001) over the last few decades and is also significantly correlated to cyanobacterial bloom biomass (Spearman's ρ = 0.64, p = 0.003). The ratio of chemically reduced N to oxidized N (TKN:NO3) concentrations was also compared to extracted chlorophyll and phycocyanin concentrations from all weekly sampling stations within WLE from 2009 to 2015. Both chlorophyll (Spearman's ρ = 0.657, p < 0.0001) and phycocyanin (Spearman's ρ = 0.714, p < 0.0001) were significantly correlated with TKN:NO3. This correlation between the increasing fraction of chemically reduced N from the Maumee River and increasing bloom biomass demonstrates the urgent need to control N loading, in addition to current P load reductions, to WLE and similar systems impacted by non-N-fixing, toxin-producing cyanobacteria.
POTHOVEN, S.A., and A.K. ELGIN. Dreissenid veliger dynamics along a nearshore to offshore transect in Lake Michigan. Journal of Great Lakes Research (DOI:10.1016/j.jglr.2019.01.001) (2019). (IN PRESS)
Dreissenid mussel veligers compose a substantial component of pelagic biomass in the Great Lakes, yet their dynamics are poorly understood. To evaluate seasonal, spatial, and inter-annual variation in veliger density, we used a 64-μm mesh plankton net (2008, 2013–2016) and a 153-μm mesh plankton net (2007–2016) to collect dreissenid veligers at nearshore (15–25 m depth), transitional (45 m) and offshore (93–110 m) sites in southeast Lake Michigan during March–December. We also evaluated trends in density of recently settled mussels relative to veliger abundance and the density of the standing stock of adult mussels. Veliger density peaked during both summer and fall at all sites, but peak densities in summer were generally higher nearshore, whereas peak densities in the fall were generally higher offshore. The density of veligers in the 153-μm net was overall 28% of that in the 64-μm net, but there was high variability in this comparison among months. Smaller veligers were much more abundant in the 64-μm net, but there was little difference in the size distribution and abundance between nets for the 210–300 μm size classes. Thus, the 153-μm net could still be a useful tool for assessing density trends of larger veligers just prior to their settlement. Newly settled mussels (≤2 mm) were most abundant in summer or fall at the nearshore and offshore sites but were nearly absent at the transitional site despite the high density of veligers there. Factors other than veliger density must play an important role in mussel recruitment.
POTHOVEN, S.A., and H.A. VANDERPLOEG. Variable demographics and consumption requirements of Bythotrephes longimanus (Crustacea, Cercopagididae) along a nearshore to offshore gradient in Lake Michigan. Hydrobiologia 830(1):63-75 (DOI:10.1007/s10750-018-3850-2) (2019).
Demographic differences in Bythotrephes longimanus populations are often used to infer the prevalence of different environmental conditions that regulate their population. We collected seasonal data on Bythotrephes abundance and life history at a nearshore (15 m), transitional (45 m) and offshore site (110 m) in Lake Michigan during 2007–2016. Due to higher fish predation requirements and the small size of zooplankton prey at the nearshore site, we expected life-history attributes of Bythotrephes would differ compared to the deeper sites, but body and spine length, percent of growth allocated to the spine, and brood size were similar among depths. Owing to higher abundances in the offshore, the ratio of consumption requirements: prey production (C:P) was relatively high throughout the growing season at the deepest site compared to the two shallower sites, where C:P was generally only high in the fall. However, reproductive characteristics of Bythotrephes at the offshore site did not reflect a food-limited population compared to the other two sites. Rather the proportion of barren females was higher at the nearshore site than those at the deeper sites, leading to much lower birth rates and abundance of Bythotrephes at the shallow site compared to the deeper sites.
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