Mirela Sertić Perić

Seasonal and fine-scale spatial drift patterns in a tufadepositing barrage hydrosystem

We examined seasonal patterns of drifting macroinvertebrates, and transported moss and (in)organic particulate matter at a fine spatial scale within the tufa-depositing barrage hydrosystem of Plitvice Lakes, Croatia. Samples were collected at six sites along a stream reach during autumn, winter, spring and summer. The sampling sites differed in flow velocity, depending on their position within the study reach and distance from tufa barriers and associated waterfalls. Seasonality was pronounced for most physico-chemical measurements. The highest concentrations of transported (in)organic particulate matter, being related to increased amounts of moss in transport, were observed in autumn. Drift densities were highest at tufa barriers that had higher flow velocities. Drift abundance partially followed the seasonal pattern in transported (in)organic matter. Autumn peaks in drift of Oligochaeta, Coleoptera as well as some Diptera and Trichoptera were related to increased moss and particulate matter quantities, while observed increases in drifting Nematoda, Cladocera, Copepoda, Ephemeroptera, Simuliidae and Chironomidae in spring and summer were probably due to distribution shifts of larvae or to higher seston levels originating from the upstream lake. Although we found that faster flowing stream sites generally had higher drift densities, there typically was no significant correlation between flow velocity and the amount of drift. Therefore, our expectation that fine-scale spatial drift patterns primarily depend on flow differences between lotic habitats was not supported for this system. The positive correlation between transported moss and other measured drift parameters, both at the seasonal and fine spatial scale, suggests that drift patterns were influenced by trapping/refuge efficiency of moss-covered tufa substrate and respective seasonal changes in instream vegetation (moss) as linked to hydrochemistry and water temperature.

Spatio-temporal shifts of macroinvertebrate drift and benthos in headwaters of a retreating glacier

Abstract Recent alpine stream studies have aimed to predict biotic responses to changing environmental conditions, hydrological regime and climate, but there is little information on macroinvertebrate drift shifts in this context and most research was largely restricted to snow-free period. We compared seasonal drift–benthos patterns in proglacial streams of Val Roseg (Switzerland) between 2008/2009 and 1997/1998. Samples were collected monthly (including winter) in a glacial lake outlet stream, a proglacial stream, and their post-confluence stream (main channel) in both periods. Measured physical and chemical parameters indicated the largest glacial meltwater influence in the proglacial stream and its lower inflow in 2008/2009 compared to 1997/1998. Drift largely coincided with benthic structure at each site, although drift–benthos patterns were at times asynchronous, depending on site and flow conditions. Our results indicate that the initial stages of hydrological “freeze-melt” events and the period of snow cover are most favorable for macroinvertebrates in glacial streams. Drift density was significantly lower in 2008/2009 than in 1997/1998. In 2008/2009, we observed lower chironomid, but higher ephemeropteran and plecopteran drift densities. The drift–benthos changes between periods likely reflect behavioral and life-history responses of proglacial stream macroinvertebrates to seasonal shifts in environmental conditions in response to glacial retreat.

Assessment of metal exposure, ecological status and required water quality monitoring strategies in small- to medium-size temperate rivers

ABSTRACT The present study was undertaken to obtain a better understanding of the seasonal variability of total dissolved metal/metalloid levels and physicochemical parameters within small- to medium-size freshwater ecosystems in temperate climate region. The research was conducted in four seasons in the Sutla River, medium-size polluted, and the Črnomerec Stream, small-size unpolluted watercourse in Croatia. In the Sutla River, characterized by the rural/industrial catchment, physicochemical parameters and total dissolved metal concentrations of 21 trace and 4 macro elements were analysed downstream of the point source of pollution, the glass production facility, indicating for the first time their variability across four seasons. Based on dissolved oxygen, total dissolved solids, nutrient concentrations, conductivity and total chemical oxygen demand, quality status of the Sutla River was good, but moderate to poor during summer, what was additionally confirmed by the highest levels of the most of 25 measured metals/metalloids in summer. Comparison with the reference small-size watercourse, the Črnomerec Stream, indicated significant anthropogenic impact on the Sutla River, most evident for Fe, Mn, Mo, Ni, Pb, Rb and Tl levels (3-70-fold higher in the Sutla River across all seasons). Generally, presented results indicated significant decrease of the water quality in the anthropogenically impacted small- to medium-size watercourses in summer, regarding physicochemical water parameters and total dissolved metal/metalloid concentrations, and pointed to significant seasonality of these parameters. Confirmed seasonality of river ecological status indicates that seasonal assessment represents a prerequisite for proper classification of the water quality in small- to medium-size temperate rivers.

Investigation of the soluble metals in tissue as biological response pattern to environmental pollutants (Gammarus fossarum example).

In the present study, Gammarus fossarum was used to investigate the bioaccumulation and toxic effects of aquatic pollutants in the real environmental conditions. The novelty of the study is the evaluation of soluble tissue metal concentrations in gammarids as indicators in early assessment of metal exposure. In the Sutla River, industrially/rurally/agriculturally influenced catchment in North-Western Croatia, physico-chemical water properties pointed to disturbed ecological status, which was reflected on population scale as more than 50 times lower gammarid density compared to the reference location, Črnomerec Stream. Significantly higher levels of soluble toxic metals (Al, As, Cd, Pb, Sb, Sn, Sr) were observed in gammarids from the Sutla River compared to the reference site and reflected the data on higher total dissolved metal levels in the river water at that site. The soluble metal estimates were supplemented with the common multibiomarker approach, which showed significant biological responses for decreased acetylcholinesterase activity and increased total soluble protein concentrations, confirming stressed environmental conditions for biota in the Sutla River. Biomarker of metal exposure, metallothionein, was not induced and therefore, toxic effect of metals was not confirmed on molecular level. Comparable between-site pattern of soluble toxic metals in gammarids and total dissolved metal levels in water suggests that prior to biomarker response and observed toxic impact, soluble metals in tissue might be used as early warning signs of metal impact in the aquatic environment and improve the assessment of water quality.

Meiofauna constitute a considerable portion of invertebrate drift among moss-rich patches within a karst hydrosystem

Aiming to establish the most frequent invertebrate taxa in drift at the small spatial scale within a moss-rich karst tufa-precipitating hydrosystem, we sampled drift among microhabitats differing in substratum type and flow conditions along a tufa barrier-cascading lotic reach. Additionally, we addressed the question of the contribution and the potential significance of meiofauna within the overall invertebrate drift at the small spatial scale. During the study period, a total of 60 invertebrate taxa were recorded in the drift. Six of these taxa belonged to the annelid/arthropod meiofauna and they represented 35% of total drift density. Macroinvertebrates found in drift were represented mainly by larval insects. The composition of the most abundant taxa in total drift was as follows: Alona spp. (Cladocera 26.7%), Riolus spp. (Coleoptera: Elmidae 13.2%), Simulium spp. (Diptera: Simuliidae 12.2%), Enchytraeidae (Oligochaeta 10.4%), Hydrachnidia (6.3%), Orthocladinae (Diptera: Chironomidae 3.9%) and Naididae (Oligochaeta 3.6%). Faunal drift densities and amounts of transported particulate matter (PM) were highest at the fast-flowing sites located at the barriers and lowest at the slow-flowing sites within pools. Similarly to the seasonal amounts of transported PM, faunal drift was lowest in winter, and peaked in autumn and in late spring/early summer. Correlation between flow velocity and PM-faunal drift densities suggested a significant effect of the dislodged PM, though a minor influence of discharge and flow velocity on faunal drift. We suggest that the small-scale habitat heterogeneity and the respective feeding and refugial strategies of the fauna, as well as faunal passive dislodgement initiated by the shear forces of the flow were the most important drivers of observed drift patterns.

Seasonal drift-benthos trends on a moss-covered tufa barrier within a karst barrage hydrosystem (Plitvice Lakes, Croatia)

macroinvrtebrate drift and streambed material transport are very important for the redistribution of energy sources and habitat-building elements within lotic ecosystems. the objective of the present study was to examine seasonal drift-benthos trends of macroinvertebrates and organic/inorganic matter particles between barrier and pool habitats at a small spatial scale within a karst barrage hydrosystem (Plitvice lakes). benthos and drift were sampled seasonally between November 2006 and July 2007 at four sampling sampling sites representing barrier (b; fast-flow velocity) and pool (P; slow-flow velocity) habitats. During the entire study period, amounts of drifting macroinvertebrates, and organic and inorganic particles were significantly higher at barriers than in pools. In benthos, such barrier trend was found for moss only. Considering seasonal differences, benthos showed no significant trends, whereas in drift we found significantly higher loads of all measured items in autumn and winter than in other two seasons, but such trend was observed at barriers only. the quantities of organisms in benthos and drift greatly followed the respective trends of particulate organic and inorganic matter, especially moss. at both habitat types macroinvertebrate drift mostly presented a smaller proportion of total benthos faunal composition, although there were some taxa that occurred in drift or benthos only. In total (including benthos and drift samples), we found 63 taxa during the study 5 of them were found only within pools, 38 only at barriers and 20 of them were found at both habitat types. the most dominant in both benthos and drift, were Oligochaeta, cladoceran Alona spp., Copepoda, and larval stages of coleopteran Riolus spp. and dipteran Simulium spp. most of them belong to mobile, epiphytic and/or interstitial detritivores that most likely originated from the submerged aquatic vegetation (i.e., moss), floating leaf litter and/or sediments along our study reach, whereas cladoceran and copepod taxa likely originated from the upstream lake. the observed seasonality in the faunal drift-benthos composition (e.g., Cladocera increase in summer and autumn, ephemeroptera decrease/absence in winter and spring), was likely a consequence of the seasonal food sourcing for individual taxa, and their particular life history traits. Our findings suggest that within the tufa-precipitating Plitvice lakes hydrosystem: a) drift has a very important role in maintaining benthos structure and stability within the barrier and pool habitats; b) tufa barriers are highly dynamic habitats, characterized by pronounced season-specific dislodgement of the benthic organisms and particulate matter, and effective moss-mediated macroinvertebrate dispersal; c) the abundance of macroinvertebrates and the amounts of organic/inorganic particles in drift are influenced not only by flow velocity and the seasonal lake discharges/biocommunity dynamics, but also by the initial distribution of particles/organisms within benthos as well as by the life history traits of the individual benthic organisms.

Ecological determinants of rotifer vertical distribution in a coastal karst lake (Vrana Lake, Cres Island, Croatia)

Vrana Lake is a coastal karst lake on Cres Island within the eastern Adriatic coast. It appears to have formed as a cryptodepression on karstified carbonate rocks, and is filled with fresh water. It is classified as an oligotrophic hydrosystem and serves as a natural water supply reservoir (max. depth 74.5 m; surface area 5.5 km2; water volume 220 × 106 m3). The aim of this study was to assess the influence of seasonally and spatially varying ecological conditions (i.e., thermal stratification, dissolved oxygen, orthophosphate and chlorophyll a concentrations) on the vertical distribution of the rotifer plankton community in this geomorphologically and hydrologically specific coastal lake. The rotifer community was surveyed monthly over a one year period. During the study period, a total of 21 rotifer taxa were identified. Among them Ascomorpha spp. (including A. ecaudis, A. ovalis and A. saltans), Filinia terminalis, Keratella cochlearis, Synchaeta gr. tremula-oblonga and Polyarthra vulgaris prevailed, representing 92% of the total rotifer abundance. Measured seasonal and spatial patterns of the rotifer assemblage along a vertical profile of Vrana Lake were considerably affected by temperature, food availability and biotic (competition, predation) interactions in the zooplankton community.