Phosphate supply to the eutrophic lake Eichbaumsee (Germany): Sedimentary versus groundwater sources

<p>The eutrophic lake Eichbaumsee, a ~ 1 km long and 280m wide (maximum water depth 16m) dredging lake southeast of Hamburg (Germany), has been treated for water quality improvements using various techniques (i.e. aeration plants, removal of dissolved phosphate by aluminium phosphate precipitation and by Benthophos adsorption) during the past ~ 15 years. Despite these treatments no long-term improvement of the water quality was observed and the lake water phosphate content continued to increase by e.g. ~ 350 kg phosphate per year between March 2016 and February 2019. As no creeks or rivers drain into the lake and hydrological groundwater models do not suggest any major groundwater discharge into the lake, sources of phosphate (and other nutrients) are unknown.</p><p>We investigated the phosphate fluxes from sediment pore water and groundwater into the water body of the lake. Sediment pore water was extracted from sediment cores recovered by divers in August 2018 and February 2019. Diffusive phosphate fluxes from pore water were calculated based on phosphate gradients using first Fick`s law. Stable water isotopes (δ<sup>2</sup>H, δ<sup>18</sup>O) were measured in the lake water, sediment pore water, interstitial waters in the banks surrounding the lake, the Elbe river and in three groundwater wells close to lake. Stable isotope (δ<sup>2</sup>H, δ<sup>18</sup>O) water mass balance models were used to compute water inflow/outflow to/from the lake.</p><p>Our results revealed pore-water borne phosphate fluxes between – 0.07 mg/m²/d (i.e. slight phosphate uptake by the sediments) and 2.6 mg/m²/d (i.e. phosphate release to the lake). Assuming that the measured phosphate fluxes are temporarily and spatially representative for the whole lake, about 100 kg/a to 220 kg/a of phosphate is released from sediments. This amount is slightly lower than the observed phosphate increase of the lake water. Stable isotope signatures indicate a water exchange between the aquifer and the lake water. Based on stable isotope mass balances (δ<sup>2</sup>H, δ<sup>18</sup>O) we estimate an inflow of phosphate from the aquifer to the lake between 190 kg/a and 1400 kg/a. This inflow indicates that groundwater-born phosphate is as or even more important than phosphate supply via sediment pore-water. Our study suggests that groundwater may have an important impact on lake nutrient budgets.</p>

A Proposed Budgeting Planning Model for Bimodal Transportation in a Phosphate Supply Chain

To better understand supply chain behavior and to evaluate its performance, it is necessary to start a modeling process. For this purpose, various tools and approaches are used. Among these tools, the analytical models can be used. With this background, the purpose of this study is proposition of a generic model for the transportation budgeting planning problems in multi-sites, multi-products, multi-depots and multi-periods context. The main contribution of this paper is to develop an integrated budgeting planning model (Mixed Integer Programming) applied in a phosphate supply chain. The purpose of the developed model is to define the optimum transportation budget of products routed in the various entities of the studied supply chain, considering various constraints (Capacity of facilities, availability of product and transportation vehicles, customers demand…) in order to plan and define the optimum products quantities and the optimize the costs to feed stocks and satisfy customers.

Mechanisms of northern North Atlantic biomass variability

In the North Atlantic Ocean north of 40∘ N, intense biological productivity occurs to form the base of a highly productive marine food web. SeaWiFS satellite observations indicate trends of biomass in this region over 1998–2007. Significant biomass increases occur in the northwest subpolar gyre and there are simultaneous significant declines to the east of 30–35∘ W. These short-term changes, attributable to internal variability, offer an opportunity to explore the mechanisms of the coupled physical–biogeochemical system. We use a regional biogeochemical model that captures the observed changes for this exploration. Biomass increases in the northwest are due to a weakening of the subpolar gyre and associated shoaling of mixed layers that relieves light limitation. Biomass declines to the east of 30–35∘ W are due to reduced horizontal convergence of phosphate. This reduced convergence is attributable to declines in vertical phosphate supply in the regions of deepest winter mixing that lie to the west of 30–35∘ W. Over the full time frame of the model experiment, 1949–2009, variability of both horizontal and vertical phosphate supply drive variability in biomass on the northeastern flank of the subtropical gyre. In the northeast subpolar gyre horizontal fluxes drive biomass variability for both time frames. Though physically driven changes in nutrient supply or light availability are the ultimate drivers of biomass changes, clear mechanistic links between biomass and standard physical variables or climate indices remain largely elusive.