Productivity of Sargassum linearifolium in potassium fortified inland saline water under laboratory conditions

Growing aquatic species in inland saline water (ISW) is one way to reduce the adverse impact of ISW to agriculture farms. This 84‐day laboratory‐trial was conducted to study the growth of Sargassum linearifolium cultured in ocean water (OW), ISW, ISW fortified with potassium equivalent to 100% (ISW100), 66% (ISW66) and 33% (ISW33) of potassium in OW at 35 g/L. The biomass and cumulative specific growth rate (SGR) of S. linearifolium increased significantly (p < .05) with increased potassium in ISW until 56 days and then declined. The ISW100 and OW resulted in similar growth patterns and yielded peak biomass at day 42, proving static biomass for the next 28 days before declining. The biomass of S. linearifolium cultured in ISW and ISW33 significantly (p < .05) decreased and was lower than in ISW100 and died after day 56. The SGR of S. linearifolium in OW, ISW100 and ISW66 levelled off and showed no difference during the first 56 days. The S. linearifolium biomass and SGR negatively and significantly (p < .05) correlated with the concentrations of nitrate, phosphate in all waters. The increased potassium concentration in ISW similar to its concentration in SW brought the growth of S. linearifolium cultured to a level that was similar in OW.     

Role of soil properties in sewage sludge toxicity to soil collembolans

Soil properties are one of the most important factors explaining the different toxicity results found in different soils. Although there is knowledge about the role of soil properties on the toxicity of individual chemicals, not much is known about its relevance for sewage sludge amendments. In particular little is known about the effect of soil properties on the toxicity modulation of these complex wastes. In addition, in most studies on sewage sludges the identity of the main substances linked to the toxicity and the influence of soil properties on their bioavailability remains unknown.In this study, the toxicity of a sewage sludge to the soil collembolan Folsomia candida was assessed in nine natural soils from agricultural, grassland and woodland sites, together with the OECD soil. Correlations between the relative toxicity of sludge for collembolans in the different soils and their physical and chemical soil properties were assessed in order to identify the main compounds responsible for the effects observed. Furthermore, the relationships between the toxic effects to collembolans and water-soluble ions released by sludge, pH and electric conductivity were also assessed, together with the modulating effects of soil properties.Sludge toxicity was directly linked to the water extractable ammonium, which explained most of the mortality of the collembolans, and part of the inhibition of reproduction. For the last endpoint, nitrite also contributed significantly to the inhibition observed. The varied levels in water extractable ammonium in the different soils at equal dosages seem to be, in turn, modulated by some soil properties. Higher organic carbon contents were associated with lower toxicity of sludge, both for survival and reproduction, probably related to its higher ammonium sorption capacity. In addition, for reproduction, increasing the C/N ratio and pH appeared to increase the toxicity, probably due to both the greater difficultly in nitrification and the known unsuitability of alkaline soils for this species.