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Burghart S.E.,University of South Florida | Jones D.L.,University of South Florida | Peebles E.B.,Water Institute of the Gulf
Estuaries and Coasts | Year: 2013

A eutrophication gradient was assembled from four spring-fed estuaries and four surface-fed estuaries to determine whether changes in zooplankton and hyperbenthos abundance along the gradient were gradual or abrupt. For 1 year in each estuary, monthly faunal surveys were conducted during nighttime flood tides using oblique plankton-net tows, producing abundance data for 316 taxa. Indicator taxa for the spring-fed and surface-fed groups were identified from a combination of abundance and encounter frequencies. Seventeen of the 20 strong indicator taxa for the spring-fed group (85 %) were benthic, whereas 10 of the 13 strong indicators for the surface-fed group (77 %) were plankton-oriented. The eight communities were ordinated by canonical analysis of principal coordinates (CAP); the estuarine faunas were found to be uniquely distributed along the principal CAP axis. Success of blind reclassification of plankton samples to their respective estuaries of origin ranged from 75 to 100 % (mean, 91 %). Given the assembled gradient was composed of distinctive communities that were distributed across a broad range of trophic states, the transition between benthic and plankton-oriented indicators was investigated and found to be abrupt, with strong shifts occurring nearer the oligotrophic end of the gradient. The CAP ordination agreed with trends in light attenuation, but not dissolved oxygen. We conclude that the abrupt faunal shifts were likely related to differences in basal resource (primary producer) availability brought about by differences in light environment. Abrupt loss of benthic basal resources will affect benthic consumers and those plankton-oriented consumers that intermittently depend on benthic biomass pathways whenever plankton-based pathways are unproductive. © 2013 Coastal and Estuarine Research Federation. Source

Li X.,Texas A&M University | Bianchi T.S.,Texas A&M University | Bianchi T.S.,University of Florida | Allison M.A.,University of Texas at Austin | And 3 more authors.
Journal of Geophysical Research: Biogeosciences | Year: 2013

Sediment cores were collected from the East China Sea inner shelf in 2010 to study the decay and preservation of organic carbon (OC). The highest sediment mass accumulation rate (0.61 ± 0.20 g cm-2 yr-1), derived from 210Pb, was found near the river mouth and decreased alongshore to the south (0.17 ± 0.004 g cm-2 yr-1), and in an offshore direction (0.31 ± 0.08 g cm-2 yr -1). Average total OC content was higher at inner shelf stations (0.52%) than those offshore (0.38%). The δ13C was more depleted at nearshore (-23.49‰ to -21.97‰) than offshore (-22.49‰ to -21.60‰) stations. Principal component analysis indicated that terrestrial OC, as indicated by lignin-phenols (Λ8) values, was preserved in sediment closer to the coast (0.22-0.44), while offshore sediment was more composed of lignin-poor (0.12-0.24) degraded OC that was likely hydrodynamically sorted. Marine-derived OC, as indicated by plant pigments, was significantly more abundant in the sediment mixed layer than the underlying accumulation layer. Historical flooding events were detected in Λ8 profiles in two of the six cores located at midshelf stations. Despite the magnitude of the 2010 flood in East China, we did not see any signature of this event with the chemical biomarker in these two cores. This may suggest that reduced sediment loading due to recent dam construction may have greatly decoupled river inputs with sediment loading to shelf sediment. The total OC standing stock since 1900 was approximately 1.62 ± 1.15 kg C m-2, about one tenth of all the middle and lower lakes in the Changjiang catchment basin. This work further supports the need for more research to better understand how the reduced inputs of fluvial input of sediments from Chinese rivers (due to river diversions and dams) affect carbon cycling in the East China Sea. © 2013. American Geophysical Union. All Rights Reserved. Source

Habib E.,University of Louisiana at Lafayette | Reed D.,Water Institute of the Gulf
Journal of Coastal Research | Year: 2013

This study presents an assessment of uncertainty associated with the predictive models utilized in Louisiana's 2012 Coastal Master Plan. In this context, model uncertainty was defined as the deviation of model prediction from the actual ecosystem response to certain proposed projects. The focus is on parametric-related uncertainties, which are due to imperfect knowledge about parameters and relationships used within the models. Due to the large number of models used in the master plan, a reduced set of model parameters (34) was identified as the most uncertain. A limited sampling experiment was designed on the basis of stratified sampling from predefined simple probability distributions of the selected parameters. Two phases of analysis were conducted. The first phase focused on examining the impact of parameter uncertainties on model predictions and comparing such uncertainties with the predicted impacts of individual projects. The second phase focused on comparing model uncertainties in predicting the future-without-action conditions vs. a proposed draft version of the master plan. The study attempts to answer some key questions that are relevant for model development and planning and project selection aspects: How uncertain are the models in predicting changes in key ecosystem metrics? Does the uncertainty vary spatially across the coast and temporally into future years? How does parameter-induced uncertainties compare with those due to other exogenous large-scale drivers? How can the uncertainty analysis inform decisions? Finally, the paper discusses implications of uncertainties for using the models as prediction tools, and highlights critical data gaps and modeling development efforts needed for future analysis. © 2013 Coastal Education & Research Foundation. Source

Darnell K.M.,University of Texas at Austin | Darnell K.M.,Water Institute of the Gulf | Dunton K.H.,University of Texas at Austin
Marine Ecology Progress Series | Year: 2015

Seed consumption by animals can limit reproductive success and recruitment of seagrasses. Consumption of seeds by crustaceans has been reported for several temperate seagrass species, but its prevalence for sub-tropical seagrass species remains unknown. Using laboratory and field feeding experiments, we investigated consumption of seeds and seedlings of the subtropical seagrass species turtle grass Thalassia testudinum along the Texas coast. More turtle grass seedlings were removed from uncaged tethers than caged tethers and time-lapse photography captured a spider crab and pinfish near the tethered seedlings. In laboratory experiments, blue crabs and spider crabs readily consumed 35.0 ± 9.3% and 36.9 ± 6.02% (mean ± SE) of offered turtle grass seedling tissue, respectively, but hermit crabs did not consume seed or seedling tissue. Observations indicate that blue crabs broke open turtle grass fruits and ate the seeds within. Seeds contained 250 and 400% more nitrogen and phosphorus, respectively, than the fruits encasing them. The enhanced nutritional value of turtle grass seeds and seedlings relative to fruit and leaf tissue may be the major driver for the observed patterns in consumption. Seedling growth experiments indicate that consumption by blue crabs severely reduces seedling growth and survival. As in terrestrial ecosystems, propagule consumption by benthic animals could potentially limit seedling survival and recruitment of sub-tropical seagrass species, but the significance of this process is not well understood at this time. © Inter-Research 2015. Source

Kolker A.S.,Louisiana Universities Marine Consortium | Kolker A.S.,Tulane University | Cable J.E.,University of North Carolina at Chapel Hill | Johannesson K.H.,Tulane University | And 2 more authors.
Journal of Hydrology | Year: 2013

Rivers are considered to be the primary means driving hydrological and geochemical fluxes between the continents and the ocean. However, it is unclear how well surface water fluxes represent total fluxes, or whether more diffuse subterranean fluxes of river water to the coastal ocean occur. This question is important in light of research demonstrating that submarine groundwater discharge (SGD) is important for geochemical and hydrological fluxes. Here, we examine the pathways and potential magnitude of the role that SGD plays in the Mississippi River Delta (MRD), the largest delta in North America. We present multiple independent lines of evidence demonstrating a hydrological connection between the Mississippi River (MR) and the MRD. Evidence includes hydrological budgets demonstrating downstream water losses from the MR, which are unexplained and are of the same magnitude as water sources to adjacent coastal bays of the MRD; well data indicating a correlation between groundwater height and the stage of the MR; and excess 222Rn inventories exceeding that expected from in situ production, implying an advective, i.e., groundwater source, to coastal bays. SGD likely flows from the MR to its delta via paleochannels and other buried sand bodies. Seismic data indicates that such features are common, whereas resistivity data suggest the intrusion of low salinity water to coastal bays adjacent to the river. These results may be applicable to other deltas worldwide, as many of the world largest rivers have deltas with numerous abandoned distributaries that could act as conduits for groundwater. © 2013 Elsevier B.V. Source

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