Maurizio Pinna

Effect of nutrients on decomposition of Ruppia cirrhosa in a shallow coastal lagoon

Here we study the pattern of disappearance of Ruppia cirrhosa Petagna (Grande) litter in the field and evaluate several variables that determine the loss rate: external nitrogen and phosphorus availability and activity of detritivores. The study was performed in Cesine coastal lagoon (mean depth 80 cm) in the South East of Italy. Recently abscised dead R. cirrhosa was collected and 25 g of fresh weight was placed in 100 μm and 1 mm mesh size litter bags. These bags were fertilized by adding a mixture of nitrogen, nitrogen plus phosphorus and phosphorus. Macroinvertebrates were retrieved from the bags and the dry weight, carbon and nitrogen contents of the remaining plant material were measured after 0, 4, 10, 20, 40 and 60 days. Litter decomposition rates, k, were estimated using a simple exponential model. Differences in plant litter processing between the treatments were more evident after 20 days, and were faster in the treatments with nitrogen (k=0.059 day−1) and phosphorus (k=0.060 day−1) alone than in control (k=0.040 day−1) and in nitrogen plus phosphorus (k=0.039 day−1) experiments. After 40 days significant differences were obtained only between the control and enriched treatments. On the basis of our results, we conclude that the effect of nutrients on the processing of R. cirrhosa litter in Cesine lagoon was greater during the initial phases of decomposition.

Inter- and intra-habitat variability of plant detritus decomposition in a transitional environment (Lake Alimini, Adriatic Sea)

A comparative analysis of inter- and intra-habitat variations of detritus decay rates across ecosystem types was carried out in the Lake Alimini complex (Italy) to assess the relevance of major structural ecosystem features on detritus processing rates. Reed (Phragmites australis) detritus decomposition was studied in a stream, a freshwater lake and a salt marsh on a seasonal basis at a total of 20 sampling stations using the leaf pack technique. Overall, the spatial variability of leaf decomposition rates was more pronounced than the temporal variability, decomposition rates in the stream being 3.6 and 5.2 times faster than in the freshwater lake and salt marsh, respectively. The intra-habitat spatial variability of leaf decay rates in the stream was also higher than in the other systems. Environmental features were relevant factors affecting intra- and inter-habitat variation of reed decay rates, and their relevance to leaf detritus decomposition showed a strong seasonal variation.

Influence of Drought and Abiotic Factors on Phragmites australis Leaf Decomposition in the River Pula, Sardinia, Italy

ABSTRACT Temporal and spatial patterns of Phragmites australis leaf decomposition and the relative influence of summer droughts and abiotic features were studied in a Mediterranean-type river basin, the River Pula. Reed processing rates varied among seasons and sites, being on average significantly faster in the cold seasons (i.e., winter-spring) than in the warm seasons (i. e., summer-fall) and in low rather than in high stream order reaches. On the other hand, at sites protected from summer drought events (i.e., wet sites), decay rates were faster in the warm than in the cold season. Along stream order, leaf decay rates were significantly faster at wet sites than at sites suffering from summer droughts. Summer drought events explained 44% of reed decay rate spatial variability, and major water abiotic parameters explained an additional 8%.

Influence of aperiodic summer droughts on leaf litter breakdown and macroinvertebrate assemblages: testing the drying memory in a Central Apennines River (Aterno River, Italy)

Climate changes, geomorphologic modifications and the rise in water demand for human uses contribute to “aperiodic summer drought” (ASD) events in Mediterranean-type rivers. ASD results in a reach that flows in one summer, dries in next or more summers, and then flowing again. The ecological structure and function of streams affected by ASD are understudied, especially with respect to permanent and regular intermittent streams. We tested the drying memory in a reach of Aterno River (Italy) disturbed by ASD. Leaf litter breakdown of Phragmites australis and macroinvertebrate assemblages were studied. Discharge was monitored since 2006. The experiment was performed during summer 2010 using the litterbag technique, and was replicated four times. The disturbed site was affected by drought in the three previous summers while the control was always flowing. Taxonomic diversity indices, abundance and structure of macroinvertebrate assemblages varied significantly between sites. Instead, leaf litter breakdown wasn’t influenced by ASD. Therefore ASD events seem to affect the structure of macroinvertebrate assemblages, confirming the role of drying memory of the systems. The resilience of leaf litter breakdown in reach affected by ASD seems to be high, probably depending on the activity of selected microbial communities and macroinvertebrate features like metabolism and biomass.

The future of biotic indices in the ecogenomic era: Integrating (e)DNA metabarcoding in biological assessment of aquatic ecosystems

The bioassessment of aquatic ecosystems is currently based on various biotic indices that use the occurrence and/or abundance of selected taxonomic groups to define ecological status. These conventional indices have some limitations, often related to difficulties in morphological identification of bioindicator taxa. Recent development of DNA barcoding and metabarcoding could potentially alleviate some of these limitations, by using DNA sequences instead of morphology to identify organisms and to characterize a given ecosystem. In this paper, we review the structure of conventional biotic indices, and we present the results of pilot metabarcoding studies using environmental DNA to infer biotic indices. We discuss the main advantages and pitfalls of metabarcoding approaches to assess parameters such as richness, abundance, taxonomic composition and species ecological values, to be used for calculation of biotic indices. We present some future developments to fully exploit the potential of metabarcoding data and improve the accuracy and precision of their analysis. We also propose some recommendations for the future integration of DNA metabarcoding to routine biomonitoring programs.

Do Mining Activities Significantly Affect Feeding Behavior of Freshwater Benthic Macroinvertebrates? A Case Study in South Sardinia (Italy)

We investigated the cascading effects of chemical contaminants on alder leaf detritus quality and the exploitation of this feeding resource by benthic macroinvertebrates (isopods, gastropods, and mayfly nymphs). Trophic behavior and energetics of benthic macroinvertebrates were used to evaluate the effects of contaminants on detritus exploitation. A two-way factorial nested experimental design was used to statistically quantify how leaf detritus origin (polluted and unpolluted streams) and the pollution level of the site selected for microbial conditioning of the detritus could affect the feeding resource quality for aquatic benthic macroinvertebrates, as measured by their trophic behavior (i.e. food selection) and exploitation (i.e. food ingestion). Alder leaves collected from a polluted stream in a former mining area (South-Sardinia, Italy) had Cd, Pb, and Zn concentrations up to 10 times that of leaves collected from an unpolluted stream. When benthic macroinvertebrates were given the option to choose, they all selected leaves from the unpolluted stream and/or those conditioned in the unpolluted stream. Ingestion rates were also significantly affected by both considered factors: leaf origin and conditioning. In addition, synergistic effects strongly increased the chemical contaminant stress on the leaf detritus quality. These results show that the terrestrial component of land–water ecotones affected by mining can be a relevant indirect pathway of chemical stress to benthic macroinvertebrate species.ZusammenfassungWir untersuchten den Kaskadeneffekt chemischer Kontaminanten auf die Qualität von Erlenlaubdetritus und auf die Nutzung dieser Nahrungsresource durch benthische Makroinvertebraten (Isopoda, Gastropoda und Nymphen von Ephemeroptera). Das trophische Verhalten und die Energetik benthischer Makroinvertebraten wurden verwendet, um die Effekte von Kontaminanten auf die Nutzung von Detritus zu bewerten. Ein experimenteller Doppelwegeinflussversuchsansatz wurde gewählt, um statistisch zu quantifizieren, wie Blattdetritus aus kontaminierten und nicht-kontaminierten Bächen und das Niveau der Kontamination am ausgewählten Ort der Probe, an welchem die mikrobielle Konditionierung des Detritus stattfand, die Qualität der Nahrungsressource für aquatische benthische Makroinvertebraten beeinflussen könnte, gemessen an ihrem trophischen Verhalten (d.h. Nahrungsselektion) und Nutzung (Nahrungsaufnahme). Erlenblätter, aufgesammelt in einem kontaminierten Bach in einem Altbergbaugebiet (Sardinien, Italien), hatten Cd, Pb und Zn-Konzentrationen bis zum Zehnfachen von Blättern aus einem nicht-kontaminierten Bach. Wenn sie die Wahl hatten, bevorzugten die Makroinvertebraten Blätter aus dem nicht-kontaminierten Bach bzw. solche, die in dem nicht-kontaminierten Bach konditioniert worden waren. Die Aufnahmeraten waren durch beide Faktoren signifikant beeinflusst: Blattherkunft und Konditionierung. Zusätzlich erhöhten synergistische Effekte stark die Belastung der Blattqualität durch chemische Kontaminanten. Diese Ergebnisse zeigen, daß die terrestrische Komponente der bergbaubeeinflussten Land-Wasser Ökotone ein erheblicher indirekter Pfad chemischer Belastung auf Arten benthischer Makroinvertebraten sein kann.ResumenHemos investigado los efectos en cascada de los contaminantes químicos sobre la calidad del detrito de las hojas del aliso y la explotación de este recurso alimentario por los macroinvertebrados bentónicos (isópodos, gasterópodos y ninfas de las moscas). También se evaluaron los efectos de los contaminantes sobre la explotación de detritos a través de la energética y el comportamiento trófico de los macroinvertebrados. Se utilizó un diseño experimental factorial de dos vías para cuantificar estadísticamente cómo el origen del detrito de hoja (contaminadas y no contaminadas) y el nivel de contaminación del sitio seleccionado para el acondicionamiento microbiano de los detritos podría afectar la calidad de los recursos de alimentación de los macroinvertebrados bentónicos acuáticos, medidos por su comportamiento trófico (i.e., selección de alimento) y explotación (i.e., ingestión de alimento). Las hojas colectadas en una zona contaminada en un área minera (Cerdeña, Italia) tenían Cd, Pb y Zn en concentraciones 10 veces superiores a las de las hojas colectadas en zonas no contaminadas. Mientras los macroinvertebrados bentónicos tuvieron opción, ellos seleccionaron hojas de zonas no contaminadas y/o aquellos acondicionadas en una zona no contaminada. Las velocidades de ingestión fueron también significativamente por el orígen de la hoja y su acondicionamiento. Además, los efectos sinérgicos incrementaron fuertemente el estrés provocado por la contaminación química sobre la calidad del detrito de hoja. Estos resultados muestran que el componente terrestre de los ecotones terrestres afectados por la minería puede ser una vía indirecta relevante de estrés químico para las especies de macroinvertebrados bentónicos.摘 要研究了化学污染物对赤杨落叶碎屑的影响及赤杨落叶碎屑作为食物对底栖大型无脊椎动物(等足目、腹足纲和蜉蝣稚虫)进食行为的级联影响。以底栖大型无脊椎动物营养行为和力能特征来判断污染物对落叶碎屑利用率的影响。采用两阶巢试验设计定量评价了落叶碎屑来源(污染河流和非污染河流)和场地污染水平(经微生物处理的碎叶)如何影响水生底栖大型无脊椎动物的食物质量,表现为底栖大型无脊椎动力的营养行为(例如食物选择)和食物利用率(例如食物摄入)特征。从意大利撒丁岛老采矿区采集的赤杨叶的镉、铅和锌污染物浓度是非污染河流赤杨叶的10倍。当用两种落叶碎屑喂食大型底栖无脊椎动物时,它们选择未污染河流的碎叶或经微生物处理的碎叶。碎叶摄入率明显受碎叶来源和是否微生物处理两种因素影响。同时,协同作用明显增强了化学污染物对落叶碎屑质量的压力。研究结果表明,在受采矿影响的陆-水群落交错区,受采矿影响的陆生群落成为底栖大型无脊椎动物种群间接遭受化学污染压力的通道