Mercedes Arauzo

Short-term harmful effects of unionised ammonia on natural populations of Moina micrura and Brachionus rubens in a deep waste treatment pond.

Populations of Moina micrura and Brachionus rubens in a deep waste treatment pond were exposed to the natural short-term fluctuations of unionised ammonia (90-min intervals of monitoring) that occur in the course of a day during a summer algal bloom. Under natural conditions, three replicate experiments were conducted in which water temperature, pH, dissolved oxygen, total ammonia, unionised ammonia, phytoplankton biomass and zooplankton (number of living and dead organisms, mortality rate and instant mortality) were studied. The time-course of unionised ammonia concentration was consistent with those shown by temperature, pH, phytoplankton biomass, dissolved oxygen, Moina micrura mortality and Brachionus rubens mortality. On the other hand, temperature, pH and dissolved oxygen never exceeded the tolerance ranges described for Moina and Brachionus, which led us to attribute the cause of zooplankton mortality to unionised ammonia toxicity. Mortality rates of 63%, 27% and 34% were recorded for Moina in each replicate experiment. Brachionus was less affected, with mortalities of 7.3%, 6.2% and 6.0%. These results confirm previous field observations (Water Res. 34(14) (2000) 3666; Water Res. 37(5) (2003) 1048) that attributed a reduction in zooplankton biomass during certain periods of summer (algal blooms) to a harmful side-effect of an excessive increase in phytoplankton biomass: high photosynthetic activity during these periods of proliferation of algae gives rise to an increased pH (>/=8) and, subsequently, leads to production of unionised ammonia (toxic for aquatic organisms) from its ionised fraction.

The role of algae in a deep wastewater self-regeneration pond

Abstract The present investigation was designed to gain information on the role of algae in a deep wastewater self-regeneration pond. The experimental pond was continuously fed with secondary effluent from a municipal wastewater treatment plant. Biological, physical and chemical profiles were recorded throughout the water column during the period July 1996 to December 1997. The removal efficiencies of several chemical and sanitary indicators were calculated. The time course of species biomass was used to evaluate phytoplankton dynamics and its relationship with the performance of the deep pond. The efficiency of the system seemed to be conditioned by temperature and phytoplankton biomass. Improved performance was observed during periods of mixing. Chlorococcales and Volvocales grew extensively during stratification periods. Euglenophyceae dominated during the mixing. When the total phytoplankton biomass exceeded 15,000 mgC m −3 , the removal efficiencies of the chemical oxygen demand (COD) and the suspended solids acquired negative values. These phytoplankton blooms were associated with an intense increase in pH and, consequently, in NH 3 levels, in the epilimnion, during the stratification. When such a bloom occurred, considerable decreases in zooplankton and bacterial biomasses were observed, which temporarily destabilized the trophic structure of the pond.

Harmful effects of un-ionised ammonia on the zooplankton community in a deep waste treatment pond

The harmful effects of NH(3) on the zooplankton community in a deep waste treatment pond were evaluated under natural conditions. The pond, supplied with secondary effluent from a conventional urban wastewater treatment plant, was designed to improve water quality for agricultural reuse.The aim of the study was to verify the hypothesis suggested in Arauzo et al. (Water Environ. Res. 34(14), 3666) that during phytoplankton blooms in the stratification periods high un-ionised ammonia content values, due to an intense photosynthetic activity and high related pH, lead to a decrease in zooplankton biomass and, thus, to a collapse of the treatment process efficiency. Empirical models were developed to determine relationships between phytoplankton biomass, pH and NH(3) levels. They provided an easy and quick method of detecting when the system was liable to collapse due to the NH(3) effect on the zooplankton community and offered the possibility of adopting measures to guarantee water quality at the effluent. A significant decrease in zooplankton community biomass was observed at un-ionised ammonia levels over 2.5 mgL(-1).

Vulnerability of groundwater resources to nitrate pollution: A simple and effective procedure for delimiting Nitrate Vulnerable Zones

This research was undertaken to further our understanding of the factors involved in nonpoint-source nitrate pollution of groundwater. The shortcomings of some of the most commonly used methods for assessing groundwater vulnerability have been analysed and a new procedure that incorporates key improvements has been proposed. The new approach (LU-IV procedure) allows us to assess and map groundwater vulnerability to nitrate pollution and to accurately delimit the Nitrate Vulnerable Zones. The LU-IV procedure proved more accurate than the most widely used methods to assess groundwater vulnerability (DRASTIC, GOD), when compared with nitrate distribution in the groundwater of 46 aquifers included in the study (using the drainage basin as the unit of analysis). The proposed procedure stands out by meeting the following requirements: (1) it uses readily available parameters that provide enough data to feed the model, (2) it excludes redundant parameters, (3) it avoids the need to assign insufficiently contrasted weights to parameters, (4) it assess the whole catchment area that potentially drains N-polluted waters into the receptor aquifer, (5) it can be implemented within a GIS, and (6) it provides a multi-scale representation. As the LU-IV procedure has been demonstrated to be a reliable tool for delimiting NVZ, it could be particularly interesting to use it in countries where certain types of environmental data are either not available or have only limited availability. Based on this study (and according to the LU-IV procedure), it was concluded that an area of at least 1728km2 should be considered as NVZ. This sharply contrasts with the current 328km2 officially designated in the study area by the Spains regional administrations. These results highlight the need to redefine the current NVZ designation, which is essential for an appropriate implementation of action programmes designed to restore water quality in line with Directive 91/676/EEC.

The Rhyacophila fasciata Group in Western Europe: Confirmation of Rhyacophila denticulata McLachlan 1879 ( stat. prom. ) and Rhyacophila sociata Navás 1916 ( stat. res. ), based on morphological and molecular genetic evidence (Trichoptera: Rhyacophilidae)

In order to check the presence and distribution of Rhyacophila fasciata fasciata Hagen 1859 (species described from Austria) and R. fasciata denticulata McLachlan 1879 in the Iberian Peninsula, we studied the morphology of Spanish, French, and Austrian specimens, together with their mitochondrial cytochrome c oxidase (mtCOI). We observed that the individuals considered to date as R. fasciata denticulata are in fact two different species: R. denticulata, presently known from France and possibly in some rivers of the Basque Country (Spain), and R. sociata Navás 1916 distributed in Spain and France. These two species are also different from the reference species (R. fasciata) from Austria, so we propose a change in the taxonomic status of R. fasciata denticulata to R. denticulata (stat. prom.) and the restoration of R. sociata (stat. res.), with the designation of a neotype, due to the loss of the holotype.