Open Water Zone Research Articles

The Impact of Water Chemistry on Zooplankton Occurrence in Two Types (Field versus Forest) of Small Water Bodies

AbstractWe examined the influence of water chemistry on zooplankton community structure in the unvegetated zone (open water) and among different types of macrophytes (helophytes and elodeids) in 12 ponds located in two types of catchment area (mid‐forest and mid‐field).An equal occurrence of rotifers and crustaceans was found in mid‐field ponds, while rotifers prevailed over crustaceans in mid‐forest ponds which may have been due to phytoflagellate prevalence, contributing to diminishing the diversity index.We found variation in physical‐chemical features between both types of ponds with higher trophic status, confirmed by eutrophy indicators (K. quadrata or B. longirwostris) frequent occurrence, in the case of mid‐field ponds. The type of water body (forest vs. field) was the best predictor of zooplankton species distribution using DCA analysis. Two groups of zooplankton species were distinguished: (1) related to the mid‐forest ponds (representatives of genera: Cephalodella, Lepadella, Lecane, Trichocerca), where zooplankton densities positively correlated with chlorophyll a and CDOC and (2) related to the mid‐field ponds (representatives of genera: Keratella, Bosmina or Ceriodaphnia).Spatial differentiation of zooplankton community structure was also recorded with lower species diversity attributed to the open water zone compared to vegetated areas. Crustacean densities rose along the heterogeneity gradient of a habitat (from the open water to the zone of elodeids), which indicates the best refuge conditions in the most complex habitat during the daylight‐hours in the ponds with fish presence. Rotifers (especially those equipped with morphological adaptations againt predators) remained in the open water despite the presence of fish. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spatial variations in the composition and abundance of zooplankton in the Bahir Dar Gulf of Lake Tana, Ethiopia

AbstractThe zooplankton in the littoral and open water zones of Bahir Dar Gulf, Lake Tana, collected in June and July 2007, were investigated using basic statistical measurement of diversity indices and one way analysis of variance to characterize the zooplankton fauna, with respect to its composition, abundance and spatial distribution patterns. The zooplankton composition was typical of a tropical freshwater lake, with a total of 44 species made up of sixteen rotifers, sixteen c1adocerans and twelve copepods and their developing stages in the following order of dominance; Rotifera > Cladocera > Cylopoida > Calanoida. Variation in spatial distribution was noticeable, the abundance of zooplankton was significantly higher (P < 0.05) at the littoral zone (Stations 2 and 3) than the open water (Station 1) as a result of the preponderance of the small‐bodied nauplii stages, small rotifers and c1adocerans particularly Bosmina longirostris. Species richness, evenness, and diversity also increased as abundance increased in the littoral zones of the lake. The rotifers, particularly the brachionids Keratella and Brachionus spp., which are considered good indicators of lake trophic status constituted the dominant zooplankton group in terms of abundance and diversity, thus indicating that the lake has a high fisheries potential.

The Impact of the Macrophyte Substratum and Season on Crustacean Zooplankton Communities of Three Shallow and Macrophyte-Dominated Lakes

ABSTRACT I conducted a three-season study on three lakes in three different habitats (Chara tomentosa bed, Typha angustifolia stand, and the open water) in order to determine the best predictors of microcrustacean distribution. The seasonal composition and abundance of crustacean zooplankters were typical of the pelagic zone in temperate lakes, and there was no appreciable difference in the zooplankton communities among the lakes. The lowest species richness and total abundance were in the open water zone, while the highest richness and abundance were within the C. tomentosa stand. Moreover, two cladoceran species (Acroperus harpae and Chydorus sphaericus) were uniquely associated with C. tomentosa. Canonical correspondence analysis identified density of plant stems and oxygen and total organic carbon concentrations in the water as the most important factors structuring the distribution of the microcrustacean community. Stepwise multiple forward regression confirmed that plant stem length and biomass were biometric parameters that influenced crustacean density. Total nitrogen concentration and pH were implicated in the density of Ceriodaphnia pulchella, while temperature and conductivity influenced A. harpae abundance.

Zooplankton community structure within various macrophyte stands of a small water body in relation to seasonal changes in water level

Zooplankton community structure within various macrophyte stands of a small water body in relation to seasonal changes in water level Different morphological features of particular water bodies, physical and chemical factors of their waters and sediments will have an impact on the development of specific aquatic vegetation types, which in turn will affect the creation of specific communities of plankton organisms. Therefore the aim of this study was to analyse the quantity and quality changes of macrophyte structure in relation to the lowering of the water level. Furthermore, the relationship between zooplankton community densities and environmental parameters was studied. Another aspect of the study was to investigate the similarity of the zooplankton communities of particular sampling stations in the three examined seasons. The study was carried out on Dąbrówka water body, a shallow and macrophyte-dominated pond, situated 10 km west of Poznań, Wielkopolska region, western Poland. The examination was conducted in the three seasons: spring, summer and autumn. The results revealed that during one vegetative period, including three seasons — spring, summer and autumn, three different layouts of aquatic vegetation were obtained, which reflected a significant transformation in the macrophyte cover. Along with the lowering of the water level the structural changes, especially in the case of submerged vegetation were recorded, which in each season was represented by different dominating species. Only three significant correlations between zooplankton densities and environmental factors observed. Negative relationship concerned total nitrogen and two positive related to biometric parameters of the macrophyte habitat (plant biomass plant stem volume). The plant biomass was a predictor of cladoceran abundance and plant stem volume referred to rotifers, which may reflect the complexity of the aquatic plant habitat, indirectly relating to the effectiveness of the macrophyte stand as anti-predator refuge. The analysis of the similarity of the zooplankton communities of particular sampling stations in the three examined seasons did not reveal any clear relationship, either in relation to a particular season or a sampling station. The participation of eutrophic species was highest in the spring and lowest during the autumn season. The open water zone possessed the highest participation of these species compared to the macrophyte zones.

Lake–peat bog transformation recorded in the sediments of the Stare Biele mire (Northeastern Poland)

The history of Stare Biele paleolake (northeast Poland) has been reconstructed using subfossil Cladocera remains and pollen and spores of aquatic and mire plants from a sediment core. Sediment accumulation began approximately 12,000 years ago during the Older Dryas chronozone. Throughout the entire Late Glacial period, the basin was a small, low-trophic state lake with a developed open-water zone. A well-recorded increase in the trophic state started at the beginning of Holocene. The lake reached its highest trophic level during the early and middle Atlantic chronozone. The first human activity in the lake catchment area occurred at this time, as recorded by fern spores and numerous charcoal grains. Repeated rises in lake water level are documented at the beginning and throughout the early part of the Younger Dryas. Two clear events of decreasing lake water levels are recorded, first during the middle part of the Younger Dryas and second in the Preboreal. Terrestrialization processes first intensified at the end of Atlantic period, which appears to correspond to a decrease in pH.

The diurnal distribution of cladocerans in a bed of Myriophyllum verticillatum in Lake Wielkowiejskie

Abstract The main aim of the study was to analyze diurnal changes in the composition and dynamics of the cladoceran community among three stations located along a horizontal transect that included the central part of a Myriophyllum verticillatum bed at the perimeter of a macrophyte stand and the open water zone of neighboring vegetated stations. Typically littoral species distinctly dominated the material examined. Ceriodaphnia quadrangula significantly influenced the total crustacean community. The maximum abundance of littoral species was noted in the middle part of the plant stand while the minimum was in the open water. These species revealed a similar pattern of diurnal distribution, irrespective of the station, with the highest numbers at night and the lowest during the day and morning. A similar pattern of diurnal distribution was also observed for pelagic species that exhibited significant differences in the open water zone between the day (the lowest numbers) and night (the highest) samplings. It was suggested that the diurnal distribution of cladoceran representatives between the macrophyte bed and the open water zone of Lake Wielkowiejskie might have been influenced by young fish predation (pelagic species) and by typical adaptations of particular species to living within the heterogeneous habitat of a macrophyte stand (littoral species).

Wetland use and feeding by lesser scaup during spring migration across the upper Midwest, USA

Low food availability and forage quality and concomitant decreased lipid reserves of lesser scaup (Aythya affinis; hereafter scaup) during spring migration in the upper Midwest may partially explain reductions in the continental population of scaup. In springs 2004–2005, we examined wetland use and feeding activity of scaup on 356 randomly-selected wetlands within 6 regions in Iowa, Minnesota, and North Dakota. We examined wetland characteristics that favor high scaup use in 286 of these wetlands. We found that probabilities of wetland use and feeding by scaup increased with turbidity up to 45 and 30 NTU, respectively, but then declined at higher turbidity levels. Wetland use was positively correlated with size of open-water zone and amphipod densities, but was not correlated with chironomid densities. Feeding increased with amphipod density up to 26 m−3 and then declined at higher amphipod densities; scaup seemingly forage most efficiently at amphipod densities above 26 m−3. Wetland use was higher in North Dakota than in southern Minnesota and Iowa. Our results indicate that effective wetland restoration efforts to benefit scaup require maintaining abundant populations of amphipods (generally near 26 m−3 landscape geometric mean) in wetlands with large (> 500 m diameter) open-water zones throughout the upper Midwest, but especially within Iowa and southern Minnesota.

Influence of Emergent and Submerged Macrophytes on the Structure of Planktonic Ciliate Communities in Shallow Freshwater Lakes (Eastern Poland)

AbstractData from two shallow macrophyte‐dominated lakes (Eastern Poland) sampled with standardized methods, were evaluated in order to examine the effects of various stands of macrophytes in predicting protozooplankton community structure. Differences in macrophyte structure led to two distinct groups of habitats having different patterns of ciliate distribution. The first group consists of two vegetated habitats of sparse stem density and of the open water zone, and the second of submerged macrophyte species, which were more dense and complex. The number of significant correlations was different in the studied habitats. In central zones of macrophyte habitats the number of ciliates had the strongest correlation with concentrations of total organic carbon and Ptot. On the other side in the border zone a significant correlation between the number of ciliates and the chlorophyll a concentration was found. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Observations of short‐circuiting flow paths within a free‐surface wetland in Augusta, Georgia, U.S.A.

Velocity heterogeneity is characteristic of wetland systems and results in some influent water remaining in the wetland for less than the expected residence time on the basis of volume and flow rate. This phenomenon, known as short‐circuiting, alters the distribution of the chemical and biological transformations that occur within the wetland. Field observations in a 1.5‐km2 constructed treatment wetland in Augusta, Georgia were used to quantify the size, distribution, velocity, and transport potential of fast flow paths, which cause short‐circuiting within wetlands. The flow paths were identified by a tracer study and velocity measurements. In each of the three cells examined, between three and six fast flow paths were found, most less than 4 m wide. These flow paths had an area‐averaged velocity on the order of 1 cm s‐1, at least 10 times the velocity observed where water passed through vegetation. Within different cells in this wetland, 20‐70% of the flow had a residence time less than one‐eighth of the nominal residence time. With this degree of short‐circuiting, uniform flow is a poor approximation for the flow through the wetland. In addition, tracer studies were used to make direct measurements of mixing within open‐water deep zones. Lateral mixing was sensitive to the direction of the wind. The average daily maximum temperature in the densely vegetated slow‐flow zones was 2.0°C cooler than that at the surface of the open water zones and 0.9uC cooler than that of the fast‐flow zones. The importance of short‐circuiting flow paths in this relatively simple wetland suggests that this phenomenon is likely of even greater significance in natural wetlands because they are typically much more complex.

Dissolved Oxygen Downstream of an Effluent Outfall in an Ice-Covered River: Natural and Artificial Aeration

In ice-covered rivers, dissolved oxygen (DO) might fall below critical levels for aquatic biota in the absence of surface aeration, combined with low winter flow conditions and reduced photosynthesis rates. Open-water zones, however, can be created downstream of a diffuser by warm effluent discharges, resulting in an increase in surface aeration. In this study, we modeled the behavior of the effluent plume and the resulting open-water lead development in the Athabasca River, Alberta, Canada downstream of a pulp mill diffuser. The DO was found to increase by 0.26 mg∕L due to surface aeration of an open-water lead of 6.07 km . We also evaluated oxygen injection into the effluent pipeline to increase the DO in the river. At an injection rate of 3,500 and 5,000 lb∕day of liquid oxygen, the DO was increased by 0.16 and 0.21 mg∕L , which corresponded to an absorption efficiency of about 50%. The artificial aeration technique evaluated here appears to be an effective alternative to increase DO levels in ice-cove...

Wetland Selection by Mallard Broods in Canada's Prairie‐Parklands

ABSTRACT Although brood survival has a pronounced effect on population growth in mallards (Anas platyrhynchos), knowledge of brood ecology is more limited than for other vital rates. During 1993–1997 we collected wetland selection data from 210 radiomarked mallard broods on 15 study areas located throughout the Canadian Prairie‐Parklands. We used information‐theoretic approaches to select the best‐approximating model of habitat selection in relation to wetland characteristics. Wetland permanence, cover type, width of flooded emergent vegetation, and interactions between these variables and date, moisture level, and dominant species of emergent vegetation were all important predictors of wetland selection. Mallard broods selected deeper wetlands, especially later in the brood‐rearing season. Mallard broods also selected wetlands with large central expanses of open water and wide peripheral zones of flooded emergent cover. These habitat characteristics can most easily be met in landscapes that already contain an abundance and diversity of natural wetland habitats. Where such wetlands are unavailable, restoration or management of deeper wetlands may be necessary to meet the habitat requirements of mallard ducklings.

Habitat choice in rotifera communities of three shallow lakes: impact of macrophyte substratum and season

The distribution of rotifer communities between emergent (Typha angustifolia) and submerged (Chara tomentosa) vegetation and a comparatively open water zone were compared during the spring, summer and autumn seasons at three macrophyte-dominated lakes. This survey identified 107 rotifera species of which 58% of the taxonomical structure was common for the three examined lakes. Stoneworts with a more complicated spatial and morphological structure (having a much longer stem length than the narrow leaf cattail), supported higher rotifer densities. The stem length appeared to be the best predictor of all the macrophyte parameters and pH and chlorophyll a for the chemical variables, for explaining the variation of rotifer densities using the stepwise multiple forward regressions. The distribution of pelagic species did not differ between particular sites, which may have reflected the behavioural requirements of those rotifers. Some of them remained in the open water zone while others seeking an anti-predator refuge, gathered within macrophyte stands during the daytime. Moreover, there were nine Chara-associated species recorded and only one Typha-associated species was noted. The similarity of rotifer communities was most strongly influenced by particular habitat and season.

Size spectra and abundance of planktonic ciliates within various habitats in a macrophyte-dominated lake (Eastern Poland)

Body size, community structure, abundance and biomass of ciliates were compared in various stands of macrophytes in a macrophyte-abundant shallow lake in Eastern Poland. Samples were collected in belts of Phragmites, Typha, Ceratophyllum, Elodea, Stratiotes and Chara. Additionally, protozooplankton was collected from the open water zone surrounding the vegetation belts. Differences in numbers of ciliate taxa between micro-sites were statistically significant. The highest numbers were found in Chara and Ceratophyllum stands, lower numbers in Stratiotes and Elodea stands and the lowest in the open water, Phragmites and Typha areas. Ciliate biomass was, like density, significantly higher in submerged macrophytes than in emergent macrophytes and open water zones. Based on differences in macrophyte structure, two groups of habitats with similar patterns of size-related ciliate distribution were distinguished. The first group consisted of two vegetated zones of sparse stem structure (Phragmites and Typha) and the open water zone, the second group comprised submerged macrophyte species, which were more dense and complex. Generally, the abundance of ciliates correlated positively with total suspension solid (TSS) and total organic carbon (TOC) concentrations. In the Chara and Ceratophyllum stands, relations between ciliate numbers, TSS and TOC were stronger.

Denitrification in created riverine wetlands: Influence of hydrology and season

Created riverine wetlands play an important role in nitrate removal from non-point source pollution. In this study, we investigated the effect of flooding frequency on seasonal denitrification rates in two created riverine wetlands in the Midwest USA receiving controlled hydrologic pulses. Denitrification was measured using the in situ acetylene block technique; sampling plots were distributed in a longitudinal gradient, i.e., along the water flow and in a transverse gradient from the edge to the center of the wetlands. Flood frequency plots in the transverse gradient were influenced by hidrological pulses as follows: low marsh and open water zones were permanently flooded, high marsh zones had permanently saturated soils, but standing water during pulses, and edge zones were normally dry with standing water during flood pulses. Denitrification was significantly correlated with soil temperature in all plots and with growing season nitrate concentrations in the inflow surface water in permanently flooded plots. Late spring denitrification rates in the high marsh zone were significantly higher under flood pulsing (778 ± 92 μg N m −2 h −1) than under steady flow (328 ± 63 μg N m −2 h −1). In the low marsh and edge zones, flood pulses did not affect denitrification. N 2O/N 2 ratios were higher in intermittently flooded (high marsh and edge) zones than in permanently flooded (low marsh) zones and ratios increased in the cold seasons. Highest mean denitrification rates were observed in the low marsh zone (800 ± 102 μg N m −2 h −1) and they were significantly higher ( P < 0.05) than in the high marsh (458 ± 87 μg N m −2 h −1) and edge (315 ± 40 μg N m −2 h −1) zones, but not significantly different from the open water zone (584 ± 101 μg N m −2 h −1). Denitrification in high marsh zones was not significantly different than in the open water and edge zones. In permanently flooded areas, denitrification rates were significantly higher near the wetland inflow than near the outflow, which was related to nitrate concentrations in the water column. Denitrification appeared to be nitrogen-limited in the low marsh, high marsh, and edge plots, but both carbon- and nitrogen-limited in open water. Flood frequency, nitrate availability, and soil temperature were important factors controlling denitrification rates in these created wetlands.

Spatial Analysis of Production by Macrophytes, Phytoplankton and Epiphyton in a Large River System under Different Water-Level Conditions

Relative contributions by macrophytes, epiphyton and phytoplankton to total primary production was estimated in a large (∼300 km2) widening of the St. Lawrence River (Canada), over a 2-year period with contrasting flows and water levels. Spatially-explicit estimates of whole-system production were obtained by combining field measurements with remotely sensed data and empirical models using GIS. Primary production and relative contributions of each producer type differed markedly between open-water and wetland habitats. Spatial differences within each habitat arose from interactions between physical factors including light, water depth, water transit times and wind stress. At the whole-system level, annual primary production represented 105 gC m−2 y−1, divided roughly equally among phytoplankton (34%), submerged macrophytes (27%), emergent macrophytes (23%) and epiphyton (16%). A 10% decrease in annual flows and 1-m decline in water levels between 2000 and 2001 resulted in a 50% loss of marsh habitat, a 60% increase in phytoplankton production in the open-water zone, and in the appearance of conspicuous filamentous algal mats. Low water levels induced substantial shifts in the spatial configuration and relative importance of primary producers although total river primary production remained stable between years.

Importance of aquatic macrophyte for invertebrate diversity in large subtropical reservoir

The abundance and preferences of individual invertebrate populations (including zooplankton) closely associated with the substrates provided by aquatic plant structures and open-water areas of Lake Nasser were quantified in this study in order to gain understanding of the importance of submerged macrophyte for invertebrate diversity, and their relation to water properties. The following water parameters were measured: temperature, pH, dissolved oxygen (DO), total dissolved salts, electrical conductivity, turbidity, total suspended solids, carbonate, bicarbonate, nitrate, nitrite, phosphate, sulphate, silica, potassium, total hardness, calcium and magnesium. Five macrophyte species were recorded: Myriopyllum spicatum, Najas horrida, Potamogeton schweinfurthii, Potamogeton pectinatus and Vallisneria spiralis. In total 67 invertebrate species were recorded, comprising 39 Rotifera, 12 Cladocera, 4 Copepoda, 4 Insecta, 2 Protozoa, 2 Ostracoda and one species of Turbellaria, Tardigrada, Annelida and Nematoda. Thirty-seven species were exclusively epiphytic, 11 species were collectively planktonic and 19 species were found in both habitats. The greatest abundance of epiphytic invertebrates occurred in association with N. horrida– P. schweinfurthii community. The results indicated that total suspended solids (TSS), TH and NO 2 are the most influential water variables on the distribution of the aquatic macrophyte samples and their invertebrate communities. Also, the study indicates that water variables have a higher impact on the aquatic macrophytes than on the associated invertebrate populations. P, NO 3, K, Na, Mg, Cl and DO were the most influential water variables that dictate the distribution of invertebrate groups recorded in the open-water zone. Water temperature, electric conductivity, pH, NO 2, SO 4 −−, SiO 3 −, CO 3 −− and turbidity have a lesser influence of the distribution of the invertebrates recorded in this zone.

Seasonal variation in primary production of a large high altitude tropical lake (Lake Tana, Ethiopia): effects of nutrient availability and water transparency

Primary production rates, chlorophyll and phytoplankton biovolume were measured monthly from April 2003 to November 2004 in Lake Tana, a large tropical lake in the highlands of Ethiopia. The lake is characterised by low nutrient concentrations, and a low water transparency due to high silt load of the inflowing rivers during the rainy seasons (May–November) and daily resuspension of sediments in the inshore zone. The mean chlorophyll-a concentrations varied seasonally and ranged from 2.6 mg m−3 to 8.5 mg m−3 (mean: 4.5 mg m−3) in the offshore zone. Primary production was measured using the light–dark bottles technique. We incubated only at three depths, i.e. 0.6, 1.2 and 1.8 m. Therefore, we may have missed a substantial part of the depth production profile and probably also frequently missed Pmax. Gross primary production in the openwater averaged 2.43 g O2 m−2 d−1 and ranged between 0.03 g O2 m−2 d−1 and 10.2 g O2 m−2 d−1; production was significantly higher in the inshore zone. The highest production rates were observed in the post-rainy season (Oct–Nov), which coincided with a bloom of Microcystis and higher chlorophyll levels. This seasonal high production is probably caused by a relatively high nutrient availability in combination with favourable light conditions. The gross primary production rates of L. Tana are among the lowest compared with other tropical lakes. This will be partly the result of our underestimation of gross primary production by often missing Pmax. Another cause is the oligotrophic nature of the lake in combination with its relatively low water transparency. The gross primary production per unit chlorophyll in the openwater zone was in the same range as in 30 other tropical lakes and reservoirs. The higher primary production in the inshore zone is probably the result of the daily water column mixing (Zmix ≥ Zt) in this area, enhancing nutrient recycling. A large proportion of the annual primary production is realised in one of the four seasons only. This productive post-rainy season is relatively short (2 months) and therefore efficiency of transfer of matter between the first and second trophic level of the Lake ecosystem will be poor.

Sediment phosphorus fractions and profile distribution at different vegetation growth zones in a macrophyte dominated shallow Wuliangsuhai Lake, China

Sediment phosphorus (P) fractions and profile distribution at submerged macrophyte growth zone, emergent macrophyte growth zone and open-water zone were studied in Wuliangsuhai Lake, China, as well as the correlations among water content, grain size, and organic matter and P fractions. Among the three surveyed zones, the highest concentrations of most P forms occurred in the surface sediment and the lowest between a depth of 12 and 22 cm, except HCl-P and NaOH-P. Sediment phosphorus was mainly associated to inorganic forms (>50%) in three surveyed areas, and the highest value of inorganic phosphorus (IP) in the surface sediment was obtained from submerged macrophyte growth zone. Submerged and emergent macrophytes increased the IP content by 107 and 44 μg/g, respectively, in the surface sediment compared with open-water zone. Vertical profiles of IP in the three surveyed zones showed that the concentrations decreased from surface to 12 cm depth and then increased. There was a similar trend in the sediment profiles of organic phosphorus (OP) and total phosphorus (TP), but the highest concentration of OP and TP in surface sediment was obtained from the emergent macrophyte growth zone. Compared with open-water zone, the emergent macrophyte increased TP content in surface sediment by 1.73 times to 1,320 μg/g, while submerged macrophyte enhanced TP content in the surface sediment by 1.13 times to 865 μg/g. It was observed that in macrophyte growth zones, a strong linear correlation existed between organic matter and OP (r > 0.98), and the maximum concentrations of OP were present in the areas with maximum concentrations of organic matter. Results show that, although rooted macrophyte could uptake directly P from sediments, it is responsible for increasing the internal P loading especially OP by reducing current velocities, attenuating wave energy and generating organic residue in Wuliangsuhai Lake.

Spatial patterns in dissolved oxygen and methane concentrations in a prairie pothole wetland in Iowa, USA

The presence of live and dead emergent vegetation alters the microbial metabolism of communities within the water column of prairie pothole wetlands. To demonstrate the effects, dissolved CH4, dissolved O2, plant densities, and litter densities were measured in transects from emergent vegetation to open water zones. O2 concentrations were consistently lower and CH4 concentrations consistently higher in emergent zones. Plant surface cover most likely interferes with gas flux across the air-water interface in the emergent zone, impeding O2 transport into the water column and impeding CH4 transport out of the water column. Either directly or indirectly, the presence of emergent vegetation may alter aerobic and anaerobic metabolism; since wet and dry cycles can result in emergent plant cover from nearly absent to nearly 100%, understanding these dynamics over the long-term will require studies over a range of wetland stages.

Zooplankton of two arms in the Morava River floodplain in Slovakia

The species composition, seasonal dynamic of biomass and density of zooplankton were studied in two arms with a different hydrological regime. The samples were collected in two hydrologically different years — extremely wet in 2002 and extremely dry in 2003. In the first arm the mean annual chlorophyll-a concentration was 31.6 µg L−1 (2002) and relatively high 64.7 µg L−1 during 2003. Mean seasonal zooplankton wet biomass was low and varied: 11.6 g m−3 (2002) and 2.93 g m−3 (2003). Total zooplankton density was high (7,370 N L−1) in 2002, when rotifers predominated in an open water zone and contributed up to 81% of the total zooplankton biomass and 83% of the total zooplankton density. In medial and littoral zone, in total, 22 cladoceran and 15 copepod species were identified. In the second arm the mean annual concentration of chlorophyll-a was high: 74.8 µg L−1 (2002) and 61.4 µg L−1 (2003). Mean seasonal zooplankton wet biomass varied from 92.5 g m−3 (2002) and 44.10 g m−3 (2003). In 2002 the planktonic crustaceans predominated; their mean biomass was 87.1 g m−3 and B. longirostris formed more than 91% of this value. In 2003, the zooplankton density was high (15,687 N L−1), when rotifers contributed up to 94% of this value. The boom of rotifers (58,740 N L−1) was recorded in June 2003. In total, 45 cladoceran and 14 copepod species were recorded in the medial and littoral zones. During observation we concluded that the structure of zooplankton, particularly species composition, abundance, biomass and seasonal dynamics are affected by the fluctuation of water levels in the arms of the rivers’ inundation areas. This unstable hydrological regime prevented the development of planktonic crustaceans.