Effects of pulse and press additions of salt on biofilms of nutrient-rich streams

Abstract

Chronic and pulse increments of salinity can cause different consequences on the aquatic communities, and its effects are related to factors such as the magnitude, frequency and ionic composition, as well as on the baseline salt concentrations in the water. The aim of this study was to explore the responses of the biofilms from a nutrient-rich stream to both pulse and chronic additions of salt, along with their recovery after the stressor had been removed. For this purpose, a microcosm study was conducted exposing biofilms to water enriched with sodium chloride in two treatments (press and pulse), and comparing the changes in the biofilm with control microcosms without salt additions. The experiment lasted 72h, and the variables measured included bacterial density, chlorophyll-a concentration, community composition, total carbohydrate content, oxygen consumption and the percentage of nuclear alterations in diatoms. Both treatments resulted in a decrease in the bacterial density of the biofilm and in oxygen consumption; the chronic treatment in particular also caused an increased percentage of nuclear abnormalities in the diatom assemblage. The biofilm recovered to control levels after the treatments had been discontinued for 72h. We concluded that the biofilms can be altered significantly under both chronic and pulse additions of salt even after a short-term exposure, and that the community can recover if the stressor is withdrawn.

Biofilm early stage development in two nutrient‐rich streams with different urban impacts

“…The first reach, with a lower urban impact (hereafter “LI,” 34°58′26.58″S/58°3′13.13″W), runs through a peri‐urban area with a moderate agricultural impact, mainly run‐off from greenhouses; the second stream reach with a higher urban impact (hereafter “HI,” 34°53′24.85″S/58°2′56.07″W) runs through a dense urban area, located downstream from a gated community and the discharges of a meat packing industry. Both reaches have similar geomorphology and hydrological characteristics, low velocity streams (2–3 cm/s), similar turbidity, do not have riparian vegetation, and are rich in nutrients, particularly phosphorous and nitrogen (Cochero, Licursi, & Gómez, , ; Feijoó & Lombardo, ; Giorgi, Feijoó, & Tell, ). A significantly lower water quality, due to higher concentrations of nutrients, organic matter, and heavy metals (such as Zn, Pb, Cu, and Cd), have been reported at the HI when compared with the LI site in previous studies (Armendáriz, Cortese, Rodriguez, & Rodrigues Capítulo, ; Cochero et al, ; López van Oosterom, Ocon, Armendariz, & Rodrigues Capitulo, ; Ronco, Camilión, & Manassero, ; Sierra, Gómez, Marano, & Siervi, ).…”

A review of the species, community, and ecosystem impacts of road salt salinisation in fresh waters

“…In a microcosm study of stream microbial communities using NaCl, Cochero, Licursi, and Gomez (2017) uncontaminated control conditions. In a microcosm study of stream microbial communities using NaCl, Cochero, Licursi, and Gomez (2017) uncontaminated control conditions.…”

“…Although bacterial densities can recover quickly (Cochero et al, 2017), most freshwater sys- et al, 2005). Although bacterial densities can recover quickly (Cochero et al, 2017), most freshwater sys- et al, 2005).…”

“…Few studies have investigated the effects of road salt salinisation on basal trophic levels. In a microcosm study of stream microbial communities using NaCl, Cochero, Licursi, and Gomez (2017) found bacterial densities were diminished at conductivities around 1,500 μS/ cm during a 72-hr exposure. The NaCl treatment was discontinued and after 144 hr, bacterial densities returned to similar densities as F I G U R E 1 Total number of publications (a) and citations (b) from 1970 to 2017 generated from a search of Thomson Reuters' Web of Science using the search term road salt, deicing, and deicing chemical alone and in combination with the following search terms as topics among all databases: amphibian, algae, aquatic insect, biogeochemistry, ecosystem function, fish, macroinvertebrate, microcrustacean, mollusk, phytoplankton, and zooplankton.…”

“…This is critically important because if bacterial function is reduced due to changes in species composition, trophic transfer of energy and ecosystem functions may be altered. Although bacterial densities can recover quickly (Cochero et al, 2017), most freshwater systems exhibit sustained, elevated concentrations of road salt. Thus, it is probable that changes in the number and type of bacterial species have occurred over several decades.…”