Benthic fluxes of oxygen and nutrients in sublittoral fine sands in a north-western Mediterranean coastal area

[EN] Traditionally, benthic metabolism in sublittoral permeable sands have not been widely studied, although these sands can have a direct and transcendental impact in coastal ecosystems. This study aims to determine oxygen and nutrient fluxes at the sediment-water interface and the study of possible interactions among environmental variables and the benthic metabolism in well-sorted fine sands. Eight sampling campaigns were carried out over the annual cycle in the eastern coast of Spain (NW Mediterranean) at 9 m depth station with permeable bottoms. Water column and sediment samples were collected in order to determine physico-chemical and biological variables. Moreover, in situ incubations were performed to estimate the exchange of dissolved solutes in the sediment-water interface using dark and light benthic chambers. Biochemical compounds at the sediment surface ranged between 160 and 744 mu g g(-1) for proteins, 296 and 702 mu g g(-1) for carbohydrates, and between 327 and 1224 [mu g C g(-1) for biopolymeric carbon. Chloroplastic pigment equivalents in sediments were mainly composed by chlorophyll a (1.81-2.89 mu g g(-1)). These sedimentary organic descriptors indicated oligotrophic conditions according to the biochemical approach used. In this sense, the most abundant species in the macrobenthic community were sensitive to organic enrichment. In dark conditions, benthic fluxes behaved as a sink of oxygen and a source of nutrients. Oxygen fluxes (between -26,610 and -10,635 mu mol m(-2) d(-1)) were related with labile organic fraction (r= -0.86, p < 0.01 with biopolymeric carbon; r= -0.91, p < 0.01 with chloroplastic pigment equivalents). Daily fluxes of dissolved oxygen, that were obtained by adding light and dark fluxes, were only positive in spring campaigns (6966 mu mol m(-2) d(-1)) owing to the highest incident irradiance levels (r=0.98, p < 0.01) that stimulate microphytobenthic primary production. Microphytobenthos played an important role on benthic metabolism and was the main primary producer in this coastal ecosystem. However, an average annual uptake of 31 mmol m-2 d(-1) of oxygen and a release of DIN and Si(OH)(4) (329 and 68 mmol m(-2) d(-1) respectively) were estimated in these bottoms, which means heterotrophic conditions. (C) 2015 Elsevier Ltd. All rights reserved.We are grateful for the valuable comments of anonymous reviewers on previous version of the manuscript. This research was supported by the Conselleria d'Educacio (Generalitat Valenciana).Sospedra, J.; Falco, S.; Morata, T.; Gadea, I.; Rodilla, M. (2015). Benthic fluxes of oxygen and nutrients in sublittoral fine sands in a north-western Mediterranean coastal area. Continental Shelf Research. 97:32-42. doi:10.1016/j.csr.2015.02.002S32429

Incidental nutrient transfers: Assessing critical times in agricultural catchments using high-resolution data

AbstractManaging incidental losses associated with liquid slurry applications during closed periods has significant cost and policy implications and the environmental data required to review such a measure are difficult to capture due to storm dependencies. Over four years (2010–2014) in five intensive agricultural catchments, this study used high-resolution total and total reactive phosphorus (TP and TRP), total oxidised nitrogen (TON) and suspended sediment (SS) concentrations with river discharge data to investigate the magnitude and timing of nutrient losses. A large dataset of storm events (defined as 90th percentile discharges), and associated flow-weighted mean (FWM) nutrient concentrations and TP/SS ratios, was used to indicate when losses were indicative of residual or incidental nutrient transfers. The beginning of the slurry closed period was reflective of incidental and residual transfers with high storm FWM P (TP and TRP) concentrations, with some catchments also showing elevated storm TP:SS ratios. This pattern diminished at the end of the closed period in all catchments. Total oxidised N behaved similarly to P during storms in the poorly drained catchments and revealed a long lag time in other catchments. Low storm FWM P concentrations and TP:SS ratios during the weeks following the closed period suggests that nutrients either weren't applied during this time (best times chosen) or that they were applied to less risky areas (best places chosen). For other periods such as late autumn and during wet summers, where storm FWM P concentrations and TP:SS ratios were high, it is recommended that an augmentation of farmer knowledge of soil drainage characteristics with local and detailed current and forecast soil moisture conditions will help to strengthen existing regulatory frameworks to avoid storm driven incidental nutrient transfers