Phytoplankton Fluctuations during an Annual Cycle in the Coastal Lagoon of Cullera (Spain)

The seasonal variation and the vertical distribution of the phytoplanktonic population of the lagoon of Cullera, an elongated coastal lagoon with estuarine circulation of water, has been studied in three sampling stations: mouth, centre and source. Seasonal variation is determined by a marine-freshwater interaction. In winter, the sea influence is important, a marine water wedge of anoxic water arrives at the sampling station located at the source and marine and brackish water species dominate the phytoplankton. Also marine species of zooplankton and fish enter the system, which may then be considered as exploited by the sea. In spring the marine wedge retreats from the source but remains in the centre and mouth, salinity diminishes, vertical mixing persists and phytoplankton is dominated by Cyclotella species. From late spring to autumn the freshwater influence prevails and a sharp stratification of the water is produced in the stations at the mouth and the centre, by means of a steep halocline coincident with an oxycline. The phytoplankton in this period follows a typical succession like those described in freshwater eutrophic lakes. Vertical distribution of phytoplankton is determined by the presence of the oxycline, originated by the marine water wedge, whose depth varies seasonally but which is always present in the mouth and centre of the lagoon; only few species of algae can be found below its level.     

The limits of phosphorus removal in wetlands

The phosphorus concentrations exported from wetlands are explored via data and a first order model. The graph of outlet concentration versus areal phosphorus loading is used to display these data and the model. For a given wetland, data and models show that P concentrations show an S curve response to increasing P loadings. The lower plateau is the background concentration and the upper plateau is the inlet concentration. The position of the ascending limb between the two plateaus is positioned differently for different wetlands. Phosphorus (P) removal in wetlands is often typified by a stable decreasing gradient of P concentrations from inlet to outlet, and an accompanying stable decreasing gradient in P assimilation. Limits to removal are inherent in the physical, chemical and biological processes. A lower outlet concentration limit exists because of the P cycle in the un-impacted wetland. The loading at which the outlet concentration departs from background, the lower knee in the loading curve, varies from wetland to wetland. An upper outlet concentration limit is imposed by the source concentration for extremely high inflows. The first order mass balance equation interpolates between these limits. The model gives further insights about performance within an overall envelope. The water carrying capacity of the wetland precludes flows in excess of the hydraulic conveyance capacity, thus limiting the possible P loadings to the system. Conversely, extremely low hydraulic loadings cause the wetland to be dominated by atmospheric additions and losses. The central tendency of inter-system data in the North American Database is shown to be inadequate to draw generalized conclusions about ecosystem processes in an individual wetland. The proposed one gram rule of Richardson, et al. (1997) is shown to be an over-simplification.     

Changes in sediment phosphate composition of seasonal ponds during filling

Most ponds from the Doñana National Park are shallow temporary freshwater bodies on eolian sands. The total phosphate concentration and the fractional P-composition of the sediments from two small ponds were studied before and inmediately after they were filled (autumn, 1996). Total phosphorus concentration was measured in 2 different size fractions: 2–0.1 mm (coarse) and <0.1 mm (fine). In both ponds, the total phosphorus concentration of the fine sediment increased by 20% at the beginning of the filling period, whereas 5 weeks later it did not increase further. The percentage of organic matter of the fine sediment was relatively high (between 13–18%) and did not change significantly during filling. The concentration of sediment total iron and Fe(OOH) increased significantly in both ponds during filling. The sequential P fractionation of the fine sediment included, besides the determination of two inorganic fractions (Ca-bound P and Fe-bound P), an organic-P fraction extracted with acid, another extracted with alkali, two organic-P fractios from the Ca-EDTA/dithionite and the Na₂-EDTA extracts which contained high concentrations of humic substances. The pond sediments were rich in organic P compounds as the sum of all organic-P fractions ranged between 267 and 320 g g^-1 (68% and 79% of the sum of all fractions). Significant changes (P<0.01) in the fractional P-composition of sediments were found after filling. Acid soluble organic phosphate increased about 30% in both ponds. Iron-bound phosphate increased significantly (about 40%) only in the pond where a higher concentration of Fe(OOH) was measured after filling. An adsorption experiment was carried out for each sediment to simulate P input during filling. Both the iron-bound phosphate and Ca-bound P increased significantly (P<0.01) suggesting that these two fractions were involved in the P-adsorption during the laboratory experiment.     

Growth and nutrient dynamics of soft-stem bulrush in constructed wetlands treating nutrient-rich wastewaters

The growth characteristics and nutritional status ofSchoenoplectus tabernaemontani (C.C. Gmelin)Palla (soft-stem bulrush or lake clubrush) wereinvestigated during the second and third growthseasons in four equivalent subsurface-flow, gravel-bedconstructed treatment wetlands. Each wetland wassupplied with a different hydraulic loading rate ofagricultural wastewater, covering the range commonlyapplied to such systems. Harvest and demographictechniques were combined to determine seasonalpatterns and gradients of growth and nutrientallocation, and net annual primary productivity(NAPP). Marked seasonal patterns of early springemergence, summer growth and autumn senescence wereobserved, with little over-wintering of liveabove-ground biomass. Starch, the dominant long-termstorage substance, comprised 20% of rhizome dryweight (DW) in autumn. Mobilization during springreduced concentrations by around half, with a trend ofincreasing depletion in the higher loaded wetlands.NAPP, including above-ground mortality, during thesecond growth season ranged between 2.5 and 3.5 kg DWm^-2, with 10-23% allocated to below-groundgrowth. Mean above-ground live and dead biomass rangedbetween 1.75 and 2.65 kg DW m^-2 by mid-summer,with below to above-ground biomass ratios similar inall wetlands at between 0.6 and 0.7. Rhizomes, whichcomprised around 80% of the below-ground biomass,were generally restricted to the upper 10 cm of thesubstratum and over half the root biomass alsooccurred in this zone, with very few roots penetratingbelow 30 cm depth. High culm concentrations of N,P, Mg and Zn in spring declined markedly over thegrowth season, while S and Ca showed generalincreases, and K, Fe and Cu remained relativelystable. Gradients of decreasing tissue concentrationof most macronutrients were noted with increasingdistance from wastewater inflows. Plant accumulationof N rose by 20-35 g m^-2 and P by 4-9 g m^-2with seasonal re-growth of above-ground shoots. Netplant N and P uptake rates rose to maximum values of0.3 g N m^-2 d^-1 and 0.1 g P m^-2d^-1 in early summer, declining markedly duringlate summer and autumn. Mass balance assessments of Nand P accumulation in plants at near maximum seasonalbiomass, after three growth seasons, showed that only6 to 11% of the N removal and 6 to 13% of the Premoval recorded from wastewaters applied to thewetlands could be ascribed to plant uptake andaccumulation.     

Filling of a wetland (Seine estuary,France): natural eutrophication or anthropogenic process? A sedimentological and geochemical study of wetland organic sediments

Hydrobiologia - For over a century the Seine estuary has been highly affected by human activities, resulting in a reduction of the surface of wetland habitat. Several ponds of the Vernier Marsh,...     

Evaluation of biotracers to monitor effluent retention time in constructed wetlands

AIMS: With concern surrounding the environmental impact of chemical tracers on the aquatic environment, this paper presents the initial evaluation of biotracers used to determine the effluent retention time, an important performance indicator, in a Free Water Surface Constructed Wetland. METHODS AND RESULTS: Production of the biotracers, coliphage MS2, and the bacteriophage of Enterobacter cloacae and antibiotic resistant endospores of Bacillus globigii is described in detail. Their subsequent use in three separate tracer experiments - January, March and June (2000) - revealed the variability of retention time with respect to effluent flow. The biotracer MS2 showed the constructed wetland had a retention time of 8-9 h at a mean discharge of 0.9 l s-1, increasing to 10-12 h at a mean discharge 0.3 l s-1. A similar retention of 9-10 h at a mean discharge of 0.3 l s-1 was calculated for the Ent. cloacae phage. In contrast, use of endospores revealed considerably longer retention times at these mean discharge rates; 12-24 h and 36-48 h, respectively. CONCLUSION: Biotracers could provide a useful and environmentally friendly technique to monitor effluent retention in constructed wetlands. At this stage the phage tracers appear particularly promising due to ease of isolation and recovery. SIGNIFICANCE AND IMPACT OF THE STUDY: Initial results are encouraging and have highlighted the potential of biotracers as alternatives to chemical tracers, even in microbially-rich waters.     

The effects of population size limitation on fecundity in mosaic populations of the clonal macrophyte Scirpus maritimus (Cyperaceae)

The clonal macrophyte Scirpus maritimus (Cyperaceae) propagates locally by rhizomes and reproduces sexually by achenes. The purpose of this paper was to examine whether in size-limited habitats in patchy and discrete marshes in two Mediterranean wetlands in southern France natural populations may suffer from a reduced maternal fecundity due to a deficit in outcross pollen. We first verified that S. maritimus suffers from a reduced fecundity when self-pollinated. At a site in the Camargue, mean fecundity (mean number of achenes per centimetre of spikelet) measured in 1995 and 1996 in seven and nine populations, respectively (surface area from 50 to 4500 m) increased significantly with population surface area in 1995 but not in 1996. In the second wetland at Roquehaute, which is composed of small ponds, fecundity was very low in all 12 local populations studied in 1996 (1.1 achenes per spikelet, SD = 1.2) and was not correlated with the population surface area (from 10 to 400 m). We performed a pollen supplementation experiment in five local populations at Roquehaute to determine whether this low fecundity may be due to a pollen limitation. A significant increase in fecundity after among-pond pollinations compared to within-pond pollinations indicated that local populations suffer from a deficit in outcross pollen, since each pond appears to contain one or a few number of clones (or incompatibility types). In S. maritimus, clonal spread may have a cost in terms of reduced fecundity in small habitats because each habitat is colonized by very few clones.     

The large Branchiopoda (Crustacea) from temporary habitats of the Drakensberg region,South Africa

The Drakensberg forms part of the Escarpment which separates the coastal plain from the inland plateau in southern Africa. This mountain range runs for about 400 km along the KwaZulu-Natal/Lesotho border and into the Eastern Cape province of South Africa. Altitude ranges from 1500 to 3000 masl. Rock pools and tarns are the main type of temporary pool habitat in the Drakensberg. 90 different habitats were sampled over a four-year period and various physical and chemical characteristics of these pools are presented. Large branchiopods occurred in 26 of these habitats. Five Branchipodopsis and two Streptocephalus species composed the anostracan fauna, while Triops granarius was collected only from the summit of the Escarpment at one locality. Four genera of Spinicaudata are represented in the Drakensberg but the current state of the taxonomy of this group does not allow identification to species level. Absence of large branchiopods from a high percentage of temporary habitats could be attributed to predation or many pools may not be sufficiently ephemeral. Most pools were inhabited by a single species of large branchiopod. This could be a result of low levels of food resources in pools, as indicated by extremely low conductivities. Restricted food resources could also be the limiting factor in the distribution of Streptocephalus and Triops which are only found in pools with higher conductivities. Four of the five Branchipodopsis species are endemic to the Drakensberg pools. These habitats are also inhabited by a high diversity of ostracods and other micro-crustaceans. Most of the KwaZulu-Natal Drakensberg falls within conservation areas but the Lesotho and Free State localities could be threatened by future development.     

Lakes Hula and Agmon: destruction and creation of wetland ecosystems in northern Israel

A portion of the former Lake Hula wetland (northern Israel) was re-flooded in spring 1994 and the physical, chemical and biological developments within the resulting new lake and wetland complex (Agmon) was followed closely by a multi-disciplinary scientific team. The first three years of study relating to Lake Agmon are reported in this issue of Wetlands Ecology & Management. We provide in this paper a general background on the Lake Hula Draining Project in the 1950s and the recent re-flooding and creation of the Agmon wetland.