J. Prygiel

Can diatom-based pollution indices be used for biomonitoring in South Africa? A case study of the Crocodile West and Marico water management area

The inclusion of diatoms into the current suite of biomonitoring tools in use in South Africa, as well as the use of European and other diatom indices in South Africa, and in particular the Crocodile and West Marico water management area, is discussed. The indices, when compared to chemical analyses, proved useful in providing an indication of the quality of the investigated waters. Several widely distributed diatom species were shown to have similar ecological tolerances in South Africa when compared to Europe. Although most of the diatoms encountered in the study were cosmopolitan, several possibly endemic species were recorded. The occurrence of endemic species, not included in existing diatom indices may lead to miscalculations of diatom indices. It is concluded that although diatom indices developed in Europe and elsewhere are useful at the present to indicate water quality, a diatom index unique to South Africa including endemic species will have to be formulated.

Comparison of POCIS passive samplers vs. composite water sampling: A case study

The relevance of Polar Organic Chemical Integrative Samplers (POCIS) was evaluated for the assessment of concentrations of 46 pesticides and 19 pharmaceuticals in a small, peri-urban river with multi-origin inputs. Throughout the period of POCIS deployment, 24h-average water samples were collected automatically, and showed the rapid temporal evolution of concentrations of several micropollutants, as well as permitting the calculation of average concentrations in the water phase for comparison with those estimated from POCIS passive samplers. In the daily water samples, cyproconazol, epoxyconazol and imidacloprid showed high temporal variations with concentrations ranging from under the limit of detection up to several hundreds of ngL-1. Erythromycin, cyprofloxacin and iopromide also increased rapidly up to tens of ngL-1 within a few days. Conversely, atrazine, caffeine, diclofenac, and to a lesser extent carbamazepine and sucralose, were systematically present in the water samples and showed limited variation in concentrations. For most of the substances studied here, the passive samplers gave reliable average concentrations between the minimal and maximal daily concentrations during the time of deployment. For pesticides, a relatively good correlation was clearly established (R2=0.89) between the concentrations obtained by POCIS and those gained from average water samples. A slight underestimation of the concentration by POCIS can be attributed to inappropriate sampling rates extracted from the literature and for our system, and new values are proposed. Considering the all data set, 75% of the results indicate a relatively good agreement between the POCIS and the average water samples concentration (values of the ratio ranging between 0,33 and 3). Note further that this agreement between these concentrations remains valid considering different sampling rates extracted from the literature.

Evidence of highly dynamic geochemical behaviour of zinc in the Deûle river (northern France)

The monitoring of dissolved zinc in the Deûle river was undertaken at three different periods of the years 2008 and 2009. Electrolabile concentrations of Zn were estimated every 2 hours for several weeks by using an ATMS (Automatic Trace metal Monitoring System) based on voltammetric measurements using a solid Ag-Hg rotating disc working electrode. Complementary measurements were carried out with DGT (Diffusive Gradient in Thin films) pistons deployed directly in the river for 24 hours. Water samples filtrated at 0.45 μm were also analysed by HR-ICP-MS to estimate the total dissolved concentrations of zinc and other trace metals. High frequency monitoring of zinc over several weeks in the Deûle river indicated that the concentration could change significantly over short time periods. Resuspension of polluted sediment and biological activities are two main factors that control the behaviour of zinc in the Deûle river. Furthermore, in May 2009, daily cycles of the electrolabile zinc fraction have been observed at relatively constant total dissolved concentration. It is assumed that this particular behaviour of zinc is based on an exchange between colloids and/or nonelectrolabile forms and free cation and inorganic complexes at a daily time scale.

Efficiency evaluation of an algistatic treatment based on barley straw in a hypertrophic pond

AbstractEutrophication processes were closely examined in a hypertrophic pond that was subjected to a barley straw treatment to inhibit cyanobacteria blooms. A phytoplankton activity was present from February to November 2010 with Chlorophyll a concentrations that ranged between 8 and 83 µg L−1. The good oxygenation of the pond provided by primary production all along the year seems to maintain an oxic layer at the top of the sedimentary column. A high-frequency monitoring of algal development pointed out the end of the diatom bloom at the end of April and the growth of green algae from beginning of May. One month later, the development of cyanobacteria supplanted other algae several times. The implementation of barley straw does not seem to hinder the growth of cyanobacteria in June, August and September and do not promote the development of other algae potentially favoured by such a treatment. As a consequence, a barley straw treatment does not seem to be really appropriate for this kind of ponds in Nor...

Test of some ecological concepts on the longitudinal distribution of zooplankton along a lowland water course

The distribution of zooplankton communities from the source to the mouth of a lowland water course, the Scheldt, was used to test some concepts on the longitudinal distribution of organisms along both estuarine (Remane’s diversity concept) and riverine reaches (River Continuum Concept (RCC), Riverine Ecosystem Synthesis (RES)). Substantial zooplankton densities were found in both April and June samples all along the water course, and not only in the lower reaches as suggested by the RCC. Based on the zooplankton communities, and using hierarchical classifications and Generalized Linear Model, several successive zones influenced by different physical and chemical variables and trophic conditions could be distinguished along the Scheldt, in agreement with the RES model: the non-tidal riverine, the tidal freshwater, the tidal salinity gradient, and the marine zones. Over the entire freshwater reach, rotifers were numerically dominant during both samplings; crustaceans became more abundant in June than in April, specifically in the downstream reaches. Highest total zooplankton abundance and diversity were found in the tidal freshwater reach, lowest in the brackish water reach, in accordance with Remane’s concept. An influence of the tributaries on zooplankton communities is suggested, directly by import or dilution of zooplankton communities or through changing environmental conditions.

Diel cycles of reduced manganese and their seasonal variability in the Marque River (northern France)

Electrolabile reduced manganese (II) has been monitored by voltammetry during two periods of one month in summer 2014 and at the end of winter 2015 in a small river (the Marque River) located in northern France and going through a suburban area with agricultural activities. Diel variations, evolution within the one-month periods and seasonal differences have been observed. Taking into consideration the multiple physical, biological and chemical reactions regulating manganese speciation in aquatic systems, it has been demonstrated that manganese speciation is probably controlled by the competition of two antagonist reactions: the photoreduction of manganese oxides (in broad sense and represented thereafter by MnOx) and the biotic oxidation of Mn(II). Depending on the season, the biological activity in the river and the amount of luminosity reaching the MnOx, either the production of reduced labile Mn(II) or the precipitation of MnOx can become the dominant process. Other punctual events such as the drop of oxygen concentration due to large inputs of biodegradable organic matter and eutrophication phenomena, rainy events and high luminosity periods can also affect the behaviour of dissolved Mn(II) in the Marque River and so, of other contaminants.