A comparison of nutrient uptake efficiency and growth rate between different macrophyte growth forms.

Aquatic macrophytes grow abundantly in many lowland streams and play a key role in ecosystem functioning, such as nutrient retention. In this study, we performed a microcosm experiment to quantify and compare the contribution of two freshwater macrophyte growth forms to nutrient cycling. We measured and compared inorganic nitrogen (NH4-N and NO3-N) and phosphorus (PO4-P) uptake kinetic parameters (Vmax and Cmin) in 12 submerged and seven amphibious plant species. We tested whether relative growth rate (RGR) was related to high Vmax and low Cmin, and quantified changes in nutrient uptake kinetic in a subset of six out of 19 plants species during the growth season. Uptake rates of NH4-N were higher in submerged compared to amphibious plants, whereas uptake rates of NO3-N were significantly higher in amphibious species; PO4-P uptake kinetics were not significantly different between the two growth forms. There were also significant seasonal differences in Vmax NH4-N rate among both submerged and amphibious species and in Vmax NO3-N among amphibious species. Highest uptake rates were observed in summer for both submerged and amphibious species. Overall, we found that nutrient uptake kinetics differed between the two growth forms within and between seasons. Consequently, the presence of both growth forms should extend the period of nutrient uptake across the year and enhance nutrient uptake within seasons. We conclude that higher functional diversity enhances annual nutrient uptake in streams and that stream restoration efforts should consider increasing the niche space available for both submerged and amphibious species.

Comparability of river quality assessment using macrophytes: a multi-step procedure to overcome biogeographical differences.

This paper exposes a new methodological approach to solve the problem of intercalibrating river quality national methods when a common metric is lacking and most of the countries share the same Water Framework Directive (WFD) assessment method. We provide recommendations for similar works in future concerning the assessment of ecological accuracy and highlight the importance of a good common ground to make feasible the scientific work beyond the intercalibration. The approach herein presented was applied to highly seasonal rivers of the Mediterranean Geographical Intercalibration Group for the Biological Quality Element Macrophytes. The Mediterranean Group of river macrophytes involved seven countries and two assessment methods with similar acquisition data and assessment concept: the Macrophyte Biological Index for Rivers (IBMR) for Cyprus, France, Greece, Italy, Portugal and Spain, and the River Macrophyte Index (RMI) for Slovenia. Database included 318 sites of which 78 were considered as benchmarks. The boundary harmonization was performed for common WFD-assessment methods (all countries except Slovenia) using the median of the Good/Moderate and High/Good boundaries of all countries. Then, whenever possible, the Slovenian method, RMI was computed for the entire database. The IBMR was also computed for the Slovenian sites and was regressed against RMI in order to check the relatedness of methods (R(2)=0.45; p<0.00001) and to convert RMI boundaries into the IBMR scale. The boundary bias of RMI was computed using direct comparison of classification and the median boundary values following boundary harmonization. The average absolute class differences after harmonization is 26% and the percentage of classifications differing by half of a quality class is also small (16.4%). This multi-step approach to the intercalibration was endorsed by the WFD Regulatory Committee.

Least Disturbed Condition for European Mediterranean rivers.

The present report describes a three-step approach that was used to characterize and define thresholds for the Least Disturbed Condition in Mediterranean streams of four different types, regarding organic pollution and nutrients, hydrological and morphological alterations, and land use. For this purpose, a common database composed of national reference sites (929 records) from seven countries, sampled for invertebrates, diatoms and macrophytes was used. The analyses of reference sites showed that small (catchment <100 km(2)) siliceous and non-siliceous streams were mainly affected by channelization, bank alteration and hydropeaking. Medium-sized siliceous rivers were the most affected by stressors: 25-43% of the samples showed at least slight alterations regarding channelization, connectivity, upstream dam influence, hydropeaking and degradation of riparian vegetation. Temporary streams were the least affected by hydromorphological changes, but they were nevertheless affected by alterations in riparian vegetation. There were no major differences between all permanent stream types regarding water quality, but temporary streams showed lower values for oxygenation (DO) and wider ranges for other variables, such as nitrates. A lower threshold value for DO (60%) was determined for this stream type and can be attributed to the streams' natural characteristics. For all other river types, common limits were found for the remaining variables (ammonium, nitrate, phosphate, total P, % of artificial areas, % of intensive and extensive agriculture, % of semi-natural areas in the catchment). These values were then used to select the list of reference sites. The biological communities were characterized, revealing the existence of nine groups of Mediterranean invertebrate communities, six for diatoms and five for macrophytes: each group was characterized by specific indicator taxa that highlighted the differences between groups.