Biomonitoring of metals under the water framework directive: detecting temporal trends and abrupt changes, in relation to the removal of pollution sources

Temporal trends in metal concentrations, i.e. Ag, Cd, Cu, Cr, Hg, Ni, Pb and Zn, measured in soft tissues of Mytilus galloprovincialis mussels and Crassostrea gigas oysters collected from estuarine waters within the Basque Country (Bay of Biscay), have been investigated to determine if actions undertaken have improved the environmental quality of rivers and estuaries. Data compiled between 1990 and 2010 have been analysed statistically, applying the Mann-Kendall and the Mann-Whitney-Wilcoxon tests. Moreover, in those cases with significant trends, the Kolmogorov-Zurbenko Adaptive (KZA) filter was applied to detect abrupt changes. Results showed significant decreasing trends for some metals, i.e. Ni, Cu, Pb and Zn, and differences between medians. Trend lines showed abrupt changes occurring between 1998 and 2002. Therefore, observed downward trends were related to increased wastewater treatment and diversions of discharges to ocean, implemented mainly during 2000-2002.

Intertidal macrofaunal communities in an intensely polluted estuary

The Bilbao estuary (northern Spain) has suffered a serious environmental deterioration due to industrial and domestic discharges during decades. A total of 21 sampling stations were selected in order to: (1) study the intertidal fauna distribution on both hard and soft bottoms; (2) link this information with the prevalence of certain environmental variables at the sampling sites; and (3) define distinct biological zones with all the information gathered. Up to 50 taxa were identified mainly in the outer estuary with an abrupt decrease upstream. In general, fauna on hard substrates was more diverse, while soft bottom communities exhibited a more consistent structure. Sporadic hypoxic events were recorded in the water column of all the sites studied, which affects the distribution of species. Three major biotic zones are proposed in the estuary. This provides a reliable biomonitoring tool for assessing the effectiveness of a sewerage and remediation scheme ongoing on the river and evaluating the future use of each area in the urban development of the city of Bilbao and conurbation.

Concordance degrees in macrozoobenthic monitoring programmes using different sampling methods and taxonomic resolution levels

In summer 1997, an intensive survey on the hard bottoms of the 'Abra de Bilbao' (N. Iberian Peninsula) was carried out in the context of the macrozoobenthic monitoring programmes developed to assess the biological recovery of the area. Three types of measurements (abundance, biomass and cover) were used to describe and compare the structure and composition of the communities at three littoral zones: subtidal, lower intertidal and upper intertidal. In addition, several taxonomic aggregation levels of data were successfully applied. The main objective of this paper is to explore the relative effect caused on the results of such programmes by earlier decisions concerning the type of measurement and the taxonomic resolution level to be applied. A 'second stage' multivariate procedure of analysis has been perforrmed based on the previously obtained sampling site ordinations. The measurement type chosen has been found to have a greater effect on the results than the taxonomic resolution used. Moreover, it is suggested that analyses based on abundance data usually lose more information when taxonomic resolution decreases than those based on biomass or cover estimates. The highest concordance among the different analyses has been found in the subtidal zone, which is considered the most appropriate habitat for the development of benthic monitoring programmes.

Extreme variation in the concentration of trace metals in sediments and bivalves from the Bilbao estuary (Spain) caused by the 1989-90 drought

Intertidal sediments and bivalves Scrobicularia plana from Bilbao estuary (Spain) were repeatedly sampled during and after the 1989-90 drought. The organic content (OC) and the concentration of most of the 10 metals analysed in sediments were extremely variable (e.g. Cd ranged from 4 to 112 micrograms g-1, ppm dry wt), and they were strongly related to an index applied to estimate the magnitude of the drought (namely the deficit flow of the main river). After OC normalisation, the correlation versus deficit was lost for some elements (Cr, Fe, Ni) but not for others (Cd, Co, Cu, Pb, Zn). This leads to the conclusion that both a natural and a man-induced process account for the observed rise and fall of the contamination pattern: the reduced river flow raised the metal-binding capacity of sediments, and restrictions in the water supply increased the corrosion of sewers and their leaching of some elements. The concentration of trace metals in local bivalves (Cd reached 100 and 458 ppm dry wt, respectively, for whole tissues and digestive gland) mirrored the sediment contamination dynamics, but at a slower pace. The means by which S. plana is able to tolerate such high Cd tissue levels remain unknown. These results constitute some prime field evidence of drought effects that should be born in mind when pollution and risk from climate change are assessed in estuaries.

ENVIRONMENTAL AUDITING: Measuring Redundancy in Data from Pollution Impact Studies

/ Time and money could be saved and better invested on environmental monitoring and assessment programs if redundant elements in biological communities were identified. Either aggregation of species into higher taxonomic groupings or selection of indicator taxa are known procedures to eliminate redundancy in large faunal data sets. One further step, the analysis of data without reference to a taxonomic scale, is proposed here. A nondestructive method to just count burrows on sediment surfaces proved adequately suitable to relate faunal responses to water dissolved-oxygen deficiencies along a severely polluted estuary. Consequently, not only taxonomic activities but also the classical destructive approaches separating biota from sediments could be deemed redundant when applied to this case study. Finally, we obtained an extensive benchmark of the situation before the impact is mitigated through the implementation of a sewerage plan promoted by the local water authority. This will serve to: (1) measure the potential recovery of defaunated sediments and (2) evaluate the efficacy of the vast engineering civil work in abating pollution in the near future.KEY WORDS: Redundancy; Faunal surveys; Burrow counts; Hypoxia; Cost effectivenesshttp://link.springer-ny.com/link/service/journals/00267/bibs/24n3p415.html