Influence of habitat conditions on macrophyte growth dynamics in croatian lowland watercourses

Utjecaj stanišnih uvjeta na dinamiku razvoja makrofita praćen je tijekom 2007., 2008. i 2009. godine na 75 lokaliteta u tri dijela nizinske Hrvatske s razvijenom mrežom vodotoka: Baranja, Lonjsko polje i sliv rijeke Bosut. Prema prikazanom sastavu makrofita i stanišnih uvjeta identificirana su područja s većom raznolikošću makrofita i većom koncentracijom nutrijenata. Na područjima s poljoprivrednom proizvodnjom i redovito održavanim plićim vodotocima utvrđen je razvoj amfibijskih i kopnenih vrsta. U slivovima s većim udjelom naselja i većom koncentracijom nutrijenata razvijene su slobodno-plivajuće vrste. U dubokim vodotocima s većom prozirnošću vode razvijene su submerzne vrste. Amfibijske i kopnene vrste dominirale su u sušnom razdoblju, a slobodno-plivajuće vrste u razdoblju veće količine oborina i visokih vodostaja. Povećana koncentracija nutrijenata, kompetitivna prednost i ostali stanišni uvjeti utjecali su na sezonsku izmjenu dominantnih vrsta.The influence of habitat conditions on macrophyte growth dynamics was monitored during 2007, 2008 and 2009 on 75 sites in watercourses of three regions in lowland Croatia: Baranja, Lonjsko polje and Bosut River Basin. The areas with higher species richness and elevated nutrient conditions were indicated according to species composition and habitat conditions. In catchments with highly agricultural land use with shallow, maintained watercourses and anthropogenic disturbance development of amphibious and terrestrial species were recorded. The spread of free-floating species were associated with higher urban land use and higher nutrient concentrations. Submerged aquatic vegetation was found in deeper watercourses with the higher transparency. Amphibious and terrestrial macrophytes have been dominated during drought conditions and free-floating species during rainy periods of high water. Seasonal changes of dominate species were controlled by nutrient enrichment, competitive advantages and other habitat conditions

Distribution and morphological variations of invasive macrophytes Elodea nuttallii (Planch.) H. St. John and Elodea canadensis Michx in Croatia

The invasive species Elodea nuttallii was recorded for the first time in the Croatian flora in 2006, in the drainage channels of Kopački rit (Baranja). After its establishment, E. nuttallii begins to spread to the eastern and northern part of the drainage channel network from 2006–2009. High water levels are responsible for the linear spreading direction of E. nuttallii, E. nuttallii and E. canadensis show a wide range of morphological variation, which is characteristic of successful invaders. To show morphological variations of two Elodea species, the most impor tant characters indicated in the literature were measured on 24 fresh collected samples from the seven sites in Croatia. In spite of some overlap in leaf length and width between the two Elodea species, the differences of all morphological traits except internode length are statistically significant. In E. nuttallii leaf width, length and internode length show a higher morphological variability as a result of the higher adaptive strategy to environmental parameters. The most reliable morphological characters distinguishing E. nuttallii and E. canadensis are leaf width 0.5 mm below the tip and the angle at the apex. E. nuttallii can be expected to spread to other areas of Croatia

Physiological and biochemical effect of silver on the aquatic plant Lemna gibba L.: Evaluation of commercially available product containing colloidal silver

This paper aims to evaluate the effects of a product containing colloidal silver in the aquatic environment, using duckweed Lemna gibba as a model plant. Therefore, growth parameters, photosynthetic pigments content and protein content as physiological indices were evaluated. Changes in the content of non-enzymatic antioxidants and activity of several antioxidant enzymes, alongside with the accumulation of hydrogen peroxide and lipid peroxidation end- products were assessed to explore the potential of colloidal silver to induce oxidative stress. The commercially available colloidal silver product contained a primary soluble form of silver. The treatment with colloidal silver resulted in significant physiological and biochemical changes in L. gibba plants and a consequent reduction of growth. Accumulation of silver caused altered nutrient balance in the plants as well as a significant decrease in photosynthetic pigments content and protein concentration. The antioxidative response of L. gibba plants to treatment with colloidal silver was inadequate to protect the plants from oxidative stress caused by metal accumulation. Silver caused concentration-dependent and time- dependent hydrogen peroxide accumulation as well as the elevation of lipid peroxidation levels in L. gibba plants. The use of commercially available products containing colloidal silver, and consequent accumulation of silver, both ionic and nanoparticle form in the environment, represents a potential source of toxicity to primary producers in the aquatic ecosystem

Consistency of impact assessment protocols for non-native species

Standardized tools are needed to identify and prioritize the most harmful non-native species (NNS). A plethora of assessment protocols have been developed to evaluate the current and potential impacts of non-native species, but consistency among them has received limited attention. To estimate the consistency across impact assessment protocols, 89 specialists in biological invasions used 11 protocols to screen 57 NNS (2614 assessments). We tested if the consistency in the impact scoring across assessors, quantified as the coefficient of variation (CV), was dependent on the characteristics of the protocol, the taxonomic group and the expertise of the assessor. Mean CV across assessors was 40%, with a maximum of 223%. CV was lower for protocols with a low number of score levels, which demanded high levels of expertise, and when the assessors had greater expertise on the assessed species. The similarity among protocols with respect to the final scores was higher when the protocols considered the same impact types. We conclude that all protocols led to considerable inconsistency among assessors. In order to improve consistency, we highlight the importance of selecting assessors with high expertise, providing clear guidelines and adequate training but also deriving final decisions collaboratively by consensus