Watershed-Estuary Coupling in Pacific Panama: Isotopic Evidence of Forest and Pasture Land Covers on Watersheds and Marine Contributions to Suspended Particulate Matter in Mangrove Estuaries

Tropical estuaries are increasingly altered by inputs from watersheds subject to widespread deforestation, as well as by globally driven hydrodynamic changes in adjoining seas. To assess contributions of C4 and C3 plants (from pasture and forest vegetation cover, respectively) to particulates exported from Pacific Panama watersheds, we measured δ¹³C and δ¹⁵N in suspended particulate matter (SPM) within eight mangrove estuaries whose watersheds differed in degree of conversion from forest to pasture land cover. These measurements also allowed evaluation of down-estuary transformations and the relative marine influence on transport and exchanges of particles between land, estuary, and sea. Imprint of watershed mosaic was detectable in δ¹³C of SPM within upper reaches of estuaries but disappeared down-estuary. Detectably heavier δ¹³C suggested that C4 plants contributed to SPM in upper reaches of estuaries. δ¹³C signatures were sufficiently sensitive to reveal presence of a small, but still detectable, contribution by C4 grasses to SPM. Influence of heavier marine-derived sources increased down-estuary, erasing terrestrial imprints. δ¹³C and δ¹⁵N in SPM, and in mangrove species present, became enriched down-estuary, likely from increased inputs of particulates bearing heavier signatures from upwelled waters. In this tropical Pacific region, estuarine particulates are subject to increasing shifts in land cover as deforestation increases, and to global-scale changes in hydrodynamic forcing of upwelled waters.     

Exploring new methods to analyse spatial impact distributions on debris-flow fans using data from south-western British Columbia

Predicting the spatial impact of debris flows on fans is challenging due to complex runout behaviour. Debris flow mobility is highly variable and flows can sporadically avulse the channel. For hazard and risk assessments, practitioners typically base the probability of spatial impact or avulsion on their experience and expert judgement. To support decision-making with empirical observations, we studied spatial impact distributions on 30 active debris-flow fans in south-western British Columbia, Canada. We mapped 146 debris-flow impact areas over an average observation period of 74 years using orthorectified airphotos, satellite imagery, topographic base maps, LiDAR data, orthophotos, and field observations. We devised a graphical method to convert our geospatial mapping into spatial impact heat maps normalized by fan boundaries, enabling comparison of runout distributions across different fans. About 90% of the mapped debris flows reached beyond the mid-points of fans, while less than 10% avulsed more than half-way across the fan relative to the previous flow path. Most avulsions initiated at distances of 20% to 40% of the maximum fan length from the fan apex and upstream of the fan intersection point. Large volume events tend to be more mobile in the down-fan direction, but the relation between volume and cross-fan runout (e.g., avulsions) is more complex. Differences in spatial impact distributions can be explained, in part, by the degree of fan incision and whether a fan is truncated at its toe by a river or lake. There were no significant differences in spatial impact distributions based on the geology of the source area, sediment supply condition, or hydrogeomorphic process classification.     

Seismic reflection imaging of active offshore faults in the Gulf of Corinth: their seismotectonic significance

High resolution seismic reflection surveys over one of the most active and rapidly extending regions in the world, the Gulf of Corinth, have revealed that the gulf is a complex asymmetric graben whose geometry varies significantly along its length. A detailed map of the offshore faults in the gulf shows that a major fault system of nine distinct faults limits the basin to the south. The northern Gulf appears to be undergoing regional subsidence and is affected by an antithetic major fault system consisting of eight faults. All these major faults have been active during the Quaternary. Uplifted coastlines along their footwalls, growth fault patterns and thickening of sediment strata toward the fault planes indicate that some of these offshore faults on both sides of the graben are active up to present. Our data ground‐truth recent models and provides actual observations of the distribution of variable deformation rates in the Gulf of Corinth. Furthermore they suggest that the offshore faults should be taken into consideration in explaining the high extension rates and the uplift scenarios of the northern Peloponnesos coast. The observed coastal uplift appears to be the result of the cumulative effect of deformation accommodated by more than one fault and therefore, average uplift rates deduced from raised fossil shorelines, should be treated with caution when used to infer individual fault slip rates. Seismic reflection profiling is a vital tool in assessing seismic hazard and basin‐formation in areas of active extension.     

Macrophyte Abundance in Waquoit Bay: Effects of Land-Derived Nitrogen Loads on Seasonal and Multi-Year Biomass Patterns

Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems. To examine the response of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for 6 years in three estuaries subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen loads over the broad range of 12 to 601 kg N ha⁻¹ year⁻¹. Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries but remained abundant in the estuary with the lowest load. Seasonal changes in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass over the 6 years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy. The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses. The influence of watershed land uses largely overwhelmed seasonal and inter-annual differences in standing stock of macrophytes in these temperate estuaries.     

A string of large and deep gas-induced depressions (pockmarks) offshore Killini peninsula, western Greece

A string of five large depressions (pockmarks) has been discovered offshore Killini peninsula in western Greece. They can be considered as some of the deepest (61-m maximum detected depth), if not the deepest observed on the seafloor world-wide. The pockmarks erode deeply buried compacted sediments and are modified by sliding. Their formation is attributed to gases which were detected in the subbottom sedimentary layers. Gas origin is considered to be both biogenic and thermogenic as gas was detected geochemically in exploratory wells in the neighbouring Katakolon area. Although uncertainties concerning their mode of formation, age and activity still remain, it is believed that the high seismicity and salt tectonics of the region contributed to the violent eruption and escape of large quantities of gases through small faults or joints which enabled erosion deep into the seafloor.     

Verification of a One-Dimensional Model of $$\hbox {CO}_{2}$$ Atmospheric Transport Inside and Above a Forest Canopy Using Observations at the Norunda Research Station

A model of \(\hbox {CO}_{2}\) atmospheric transport in vegetated canopies is tested against measurements of the flow, as well as \(\hbox {CO}_{2}\) concentrations at the Norunda research station located inside a mixed pine–spruce forest. We present the results of simulations of wind-speed profiles and \(\hbox {CO}_{2}\) concentrations inside and above the forest canopy with a one-dimensional model of profiles of the turbulent diffusion coefficient above the canopy accounting for the influence of the roughness sub-layer on turbulent mixing according to Harman and Finnigan (Boundary-Layer Meteorol 129:323–351, 2008; hereafter HF08). Different modelling approaches are used to define the turbulent exchange coefficients for momentum and concentration inside the canopy: (1) the modified HF08 theory—numerical solution of the momentum and concentration equations with a non-constant distribution of leaf area per unit volume; (2) empirical parametrization of the turbulent diffusion coefficient using empirical data concerning the vertical profiles of the Lagrangian time scale and root-mean-square deviation of the vertical velocity component. For neutral, daytime conditions, the second-order turbulence model is also used. The flexibility of the empirical model enables the best fit of the simulated \(\hbox {CO}_{2}\) concentrations inside the canopy to the observations, with the results of simulations for daytime conditions inside the canopy layer only successful provided the respiration fluxes are properly considered. The application of the developed model for radiocarbon atmospheric transport released in the form of \(^{14}\hbox {CO}_{2}\) is presented and discussed.     

Groundwater flow in an ‘underfit’ carbonate aquifer in a semiarid climate: application of environmental tracers to the Salt Basin,New Mexico (USA)

The Salt Basin is a semiarid hydrologically closed drainage basin in southern New Mexico, USA. The aquifers in the basin consist largely of Permian limestone and dolomite. Groundwater flows from the high elevations (～2,500 m) of the Sacramento Mountains south into the Salt Lakes, which are saline playas. The aquifer is ‘underfit’ in the sense that depths to groundwater are great (～300 m), implying that the aquifer could transmit much more water than it does. In this study, it is speculated that this characteristic is a result of a geologically recent reduction in recharge due to warming and drying at the end of the last glacial period. Water use is currently limited, but the basin has been proposed for large-scale groundwater extraction and export projects. Wells in the basin are of limited utility for hydraulic testing; therefore, the study focused on environmental tracers (major-ion geochemistry, stable isotopes of O, H, and C, and ¹⁴C dating) for basin analysis. The groundwater evolves from a Ca–HCO₃ type water into a Ca–Mg (Na) – HCO₃–Mg (Cl) water as it flows toward the center of the basin due to dedolomitization driven by gypsum dissolution. Carbon-14 ages corrected for dedolomitization ranged from less than 1,000 years in the recharge area to 19,000 years near the basin center. Stable isotopes are consistent with the presence of glacial-period recharge that is much less evaporated than modern. This supports the hypothesis that the underfit nature of the aquifer is a result of a geologically recent reduction in recharge.     

Post-mortem transport of freshwater mollusc shells in the northern Caspian Sea: A cautionary note on the implications for palaeoecological reconstructions

Fossils of stenohaline taxa are frequently used in palaeoecological and archaeological investigations to indicate the former position of deltas or the occurrence of freshwater conditions. However, the post-mortem transport of freshwater mollusc shells from deltaic and other areas can complicate interpretation of fossil assemblages. We present an example from the north Caspian Sea that shows that failure to consider these taphonomic processes can lead to erroneous conclusions.