Carbon dynamics at the river-estuarine transition: a comparison among tributaries of Chesapeake Bay

Sources and transformation of C were quantified using mass balance and ecosystem metabolism data for the upper segments of the James, Pamunkey and Mattaponi Estuaries. The goal was to assess the role of external (river inputs & tidal exchange) vs. internal (metabolism) drivers in influencing the forms and fluxes of C. C forms and their response to river discharge differed among the estuaries based on their physiographic setting. The James, which receives the bulk of inputs from upland areas (Piedmont and Mountain), exhibited a higher ratio of inorganic to organic C, and larger inputs of POC. The Pamunkey and Mattaponi receive a greater proportion of inputs from lowland (Coastal Plain) areas, which were characterized by low DIC and POC, and elevated DOC. We anticipated that transport processes would dominate during colder months when discharge is elevated and metabolism is low, and that biological processes would predominate in summer, leading to attenuation of C through-puts via de-gassing of CO2. Contrary to expectations, highest retention of OC occurred during periods of high through-put, as elevated discharge resulted in greater loading and retention of POC. In summer, internal cycling of C via production and respiration was large in comparison to external forcing despite the large riverine influence in these upper estuarine segments. The estuaries were found to be net heterotrophic based on retention of OC, export of DIC, low GPP relative to ER, and a net flux of CO2 to the atmosphere. In the James, greater contributions from phytoplankton production resulted in a closer balance between GPP and ER, with autochthonous production exceeding allochthonous inputs. Combining the mass balance and metabolism data with bioenergetics provided a basis for estimating the proportion of C inputs utilized by the dominant metazoan. The findings suggest that invasive catfish utilize 15 % of total OM inputs and up to 40 % of allochthonous inputs to the James.

The interplay between regeneration and scavenging fluxes drives ocean iron cycling

Despite recent advances in observational data coverage, quantitative constraints on how different physical and biogeochemical processes shape dissolved iron distributions remain elusive, lowering confidence in future projections for iron-limited regions. Here we show that dissolved iron is cycled rapidly in Pacific mode and intermediate water and accumulates at a rate controlled by the strongly opposing fluxes of regeneration and scavenging. Combining new data sets within a watermass framework shows that the multidecadal dissolved iron accumulation is much lower than expected from a meta-analysis of iron regeneration fluxes. This mismatch can only be reconciled by invoking significant rates of iron removal to balance iron regeneration, which imply generation of authigenic particulate iron pools. Consequently, rapid internal cycling of iron, rather than its physical transport, is the main control on observed iron stocks within intermediate waters globally and upper ocean iron limitation will be strongly sensitive to subtle changes to the internal cycling balance.

Ecological Principles and Metrics for Improving Material Cycling Structures in Manufacturing Networks

A key element for achieving sustainable manufacturing systems is efficient and effective resource use. This potentially can be achieved by encouraging symbiotic thinking among multiple manufacturers and industrial actors and establish resource flow structures that are analogous to material flows in natural ecosystems. In this paper, ecological principles used by ecologists for understanding food web (FW) structures are discussed which can provide new insight for improving closed-loop manufacturing networks. Quantitative ecological metrics for measuring the performance of natural ecosystems are employed. Specifically, cyclicity, which is used by ecologists to measure the presence and strength of the internal cycling of materials and energy in a system, is discussed. To test applicability, groupings of symbiotic eco-industrial parks (EIP) were made in terms of the level of internal cycling in the network structure (high, medium, basic, and none) based on the metric cyclicity. None of the industrial systems analyzed matched the average values and amounts of cycling seen in biological ecosystems. Having detritus actors, i.e., active recyclers, is a key element for achieving more complex cycling behavior. Higher cyclicity values also correspond to higher amounts of indirect cycling and pathway proliferation rate, i.e., the rate that the number of paths increases as path length increases. In FWs, when significant cycling is present, indirect flows dominate direct flows. The application of these principles has the potential for novel insights in the context of closed-loop manufacturing systems and sustainable manufacturing.