Ana I. Lillebø

Nutrient cycling and plant dynamics in estuaries: A brief review

Eutrophication of European estuaries due to massive nutrient loading from urban areas and diffuse runoff from extensively cultivated land areas is analysed. Consequences for the ecology of estuaries, namely changes in plant species composition, which also affects heterotrophic organisms, are approached based on examples showing that the result is often a fundamental structural change of the ecosystem, from a grazing and/or nutrient controlled stable systems to unstable detritus/mineralisation systems, where the turnover of oxygen and nutrients is much more dynamic and oscillations between aerobic and anaerobic states frequently occur. Several relevant aspects are examined, namely the influence of rooted macrophytes on nutrient dynamics, by comparing bare bottom sediments with eelgrass covered sediments, primary production and the development of organic detritus, and hydrodynamics and its relations to the spatial distribution of macrophytes in estuarine systems.

Mercury pollution in Ria de Aveiro (Portugal): a review of the system assessment

The Ria de Aveiro (Portugal) is a coast al lagoon adjacent to the Atlantic Ocean and it has an inner bay (Laranjo bay) that received a highly contaminated effluent discharged by a mercury cell chlor-alkali plant from the 1950s until 1994. The aim of this study is to review in a holistic way several research studies that have been carried out in the Ria de Aveiro, in order to evaluate the remobilization of the mercury accumulated within the system and the recovery of the lagoon. The spatial distribution of the total mercury in the surrounding terrestrial environment has also been considered. Results indicate that the main mercury contamination problems in the Ria de Aveiro are confined to the Laranjo bay. Mercury export to the coastal waters and its impact on the nearshore compartments (water column, sediment and biota) are low. No direct effects of the mercury from nearby industrial activities were detected in Aveiro’s urban soils, although historical mercury contamination is still affecting soil quality in the immediate vicinity of the chlor-alkali plant, located in Estarreja. Moreover, macrophyte harvesting for human direct or indirect use and the consumption of mussels, crabs and the sea bass from the Laranjo bay may constitute a health risk. Further studies focusing on developing skills for the restoration of the ecosystem are presently underway.

The effect of different primary producers on Hydrobia ulvae population dynamics: a case study in a temperate intertidal estuary

The effect of macroalgal blooms and the consequent disappearance of Zostera noltii meadows on Hydrobia ulvae population dynamics and production was studied in the Mondego estuary based on data obtained from January 1993 to September 1995. Sampling was carried out at a non-eutrophicated area, covered with Z. noltii, and also at an eutrophicated area, where seasonal Enteromorpha spp. blooms occur. Stable populations represented by individuals of all age classes were found only at the Z. noltii meadows throughout the study period. On the contrary, at the eutrophicated area, during most of the time, solely juveniles were present, with adults appearing only during the macroalgal bloom (>1.5 mm width). During the algal bloom (e.g. 1993), H. ulvae population density was clearly higher in the eutrophicated area due to the combined effect of stronger benthic recruitments (99% of veliger larvae newly recruited) and dispersion of juveniles proceeding from the Z. noltii meadows to this area. On the other hand, in the absence of macroalgae (spring of 1994), 98.9% of veliger larvae was recruited in the Z. noltii meadows. Therefore, H. ulvae seems to respond rapidly to macroalgal dynamics and its presence at the eutrophicated area depends on the existence of green macroalgae. H. ulvae presented the same benthic recruitment pattern at the two sampling areas, with new cohorts being produced in March, June, July and September. Depending on the time of the year in which the recruitment took place, cohorts showed different growth rhythms. However, after 12 months they reached a similar size. A three-generation life cycle involving a short-lived (16 months), fast growing spring generation, a medium growing (17–19 months) summer generation and a longer-lived (20 months) slower growing generation that overwinters is identified. As a general trend, productivity and mean population standing biomass were higher at the Z. noltii meadows, during the entire study, except for a short period, during the macroalgal bloom, when production was higher at the eutrophicated area. On the contrary, P/B ratios were higher at the eutrophicated area. According to our results, H. ulvae population structure and yearly productivity are clearly affected by eutrophication, namely by the dynamics of macroalgal blooms. In the long run, we may infer that, following the disappearance of the Z. noltii meadows, due to eutrophication, H. ulvae would also tend to disappear, since reproductive adults were almost exclusively found in this area.

Contribution of Spartina maritima to the reduction of eutrophication in estuarine systems

Salt marshes are among the most productive ecosystems in the world, performing important ecosystem functions, particularly nutrient recycling. In this study, a comparison is made between Mondego and Tagus estuaries in relation to the role of Spartina maritima in nitrogen retention capacity and cycling. Two mono-specific S. maritima stands per estuary were studied during 1yr (biomass, nitrogen (N) pools, litter production, decomposition rates). Results showed that the oldest Tagus salt marsh population presented higher annual belowground biomass and N productions, and a slower decomposition rate for litter, contributing to the higher N accumulation in the sediment, whereas S. maritima younger marshes had higher aboveground biomass production. Detritus moved by tides represented a huge amount of aboveground production, probably significant when considering the N balance of these salt marshes. Results reinforce the functions of salt marshes as contributing to a reduction of eutrophication in transitional waters, namely through sedimentation processes.

Mapping and Assessment of Ecosystems and their Services: Indicators for ecosystem assessments under Action 5 of the EU Biodiversity Strategy to 2020

Environment Europe Direct is a service to help you find answers to your questions about the European Union Summary The second MAES report presents indicators that can be used at European and Member States level to map and assess biodiversity, ecosystem condition and ecosystem services according to the Common International Classification of Ecosystem Services (CICES v4.3). This work is based on a review of data and indicators available at national and European level and is applying the MAES analytical framework adopted in 2013.

Salinity as the major factor affecting Scirpus maritimus annual dynamics: Evidence from field data and greenhouse experiment

Abstract During the life cycle of Scirpus maritimus , ramets produce photosynthetic shoots that are active for a single growing season and only the belowground parts persist into the next year. Several authors have described that the growing season of S. maritimus in Europe and North America occurs between April and September of each year. In the Mondego estuary (western coast of Portugal) the life cycle of S. maritimus showed an opposite seasonal pattern, with a growing season from January to April/May. It was hypothesised that seasonal fluctuations in salinity, connected to salinity tolerance, could explain this contrasting annual cycle. This hypothesis was tested using a greenhouse experiment. Exposure to different salinities significantly affected plant survival. During the first 10 days, the survival curves were very similar, which suggested that the plants were able to tolerate high salinity for short periods. After 2 weeks of exposure, the plants started to show differences, with increased mortality following the increase in salinity. Results show that a peculiar seasonal variation of salinity in the Mondego estuary affected the S. maritimus life cycle in this ecosystem and may explain the differences between these western Portugese populations and other European and North American populations.

Mercury cycling and sequestration in salt marshes sediments: An ecosystem service provided by Juncus maritimus and Scirpus maritimus

In this study two time scales were looked at: a yearlong study was completed, and a 180-day decay experiment was done. Juncus maritimus and Scirpus maritimus have different life cycles, and this seems to have implications in the Hg-contaminated salt marsh sediment chemical environment, namely Eh and pH. In addition, the belowground biomass decomposition rates were faster for J. maritimus, as well as the biomass turnover rates. Results show that all these species-specific factors have implications in the mercury dynamics and sequestration. Meaning that J. maritimus belowground biomass has a sequestration capacity for mercury per square metre approximately 4-5 times higher than S. maritimus, i.e., in S. maritimus colonized areas Hg is more extensively exchange between belowground biomass and the rhizosediment. In conclusion, J. maritimus seems to provide a comparatively higher ecosystem service through phytostabilization (Hg complexation in the rhizosediment) and through phytoaccumulation (Hg sequestration in the belowground biomass).

The influence of Spartina maritima on carbon retention capacity in salt marshes from warm-temperate estuaries.

Salt marshes constitute highly productive systems playing an important role on ecosystem functions. The aim of this study is to compare the role of Spartina maritima salt marshes on carbon cycling. Thus, four salt marshes located in two mesotidal estuarine systems (Tagus and Mondego, two salt marshes per estuary) were studied. The S. maritima above- and belowground biomass, carbon production, decomposition rates (through a litterbag experiment) and carbon content in the sediment were estimated for a one year period in both systems and compared. In Corroios (located at the Tagus estuary) S. maritima salt marsh had the highest belowground production (1008 gC m(-2) y(-1)), slower decomposition rate (k=0.0024 d(-1)), and the highest carbon content in sediments (750 gC m(-2) y(-1)); and thus, the highest carbon retention capacity. The other three salt marshes had comparatively higher aboveground productions, higher decomposition rates and lower carbon retention capacity. Therefore, Corroios had the most important carbon cycling characteristics. As a whole, results show that differences in carbon cycling in salt marshes depend mostly on its own characteristics and maturity, rather than the system itself. The intrinsic characteristics of the salt marshes, namely the physicochemical conditions determined by the maturity of the system, are more important factors affecting the role of warm-temperate mesotidal salt marshes as carbon sinks.

The Effect of Zostera noltii, Spartina maritima and Scirpus maritimus on sediment pore-water profiles in a temperate intertidal estuary

The objective of the present work was to study the effect of plants common in temperate latitudes (Zostera noltii, Spartina maritima and Scirpus maritimus) on sediment nutrient profiles, and to compare it to sand- and mud-flats without vegetation. The study focused on the organic matter contents, the concentration of dissolved inorganic nutrients (PO4–P, NH3–N, NO3–N), an on the estimation of the total amount of these nutrients during day and night conditions and their potential net-fluxes. It was also hypothesised that in an estuarine system, different plants may have specific effects, and consequently different contributions to the system nutrient dynamics as a whole. Sediment profiles of loss on ignition (LOI) showed an increase of the organic matter contents from sand-flat, to Zostera, Spartina, mud-flat and Scirpus. Statistically, there were significant differences between sediment profiles of phosphate, ammonia and nitrate (Mann-Whitney test, p<0.05), during day and night periods. These results suggest that there is an intense mobility of nutrients in the sediment, showing a day-night variation of nutrient concentrations in the pore-water. In the plants’ rhizosphere, the day-night variation of nutrients seemed dependent on plant biomass and penetration of the roots. Additionally, coupling between plant and sediment seems to be a species-specific process. In spring, Scirpus salt marsh reaches the maximum density and biomass, and despite the higher organic matter contents in the plant covered sediment, Scirpus acts as a sink of nutrients. In contrast, the top 10 cm of the sediment in the Spartina salt marsh and in the Zostera beds may contribute to the efflux of nutrients during the night period, especially phosphate.

Determination of Total Nitrogen and Phosphorus in Leaf Litter

In many freshwater and coastal marine environments plant litter is abundant and an important source of energy for the aquatic food webs. Nitrogen (N) and phosphorus (P) are important nutrients determining the quality of plant litter, and consequently their decomposition rates (Enriquez et al. 1993). Most phosphorus is used for the synthesis of ATP, RNA, DNA, and phospholipids (e.g. Sterner & Elser 2002), while nitrogen is mainly associated with proteins (see Chapter 9, Flindt et al. 1999). Generally, fast growing plants have low C:N and C:P ratios (high N and P content) and low fibre content, and decompose fast, whereas plants with slow growth rates exhibit slower litter decomposition rates (Enriquez et al. 1993, Flindt et al. 1999, Hill & Perrot 1995, Wrubleski et al. 1997). Table 8.1 summarizes nitrogen and phosphorus contents and C:N and C:P ratios of leaf litter of selected plant species. A large fraction of the phosphorus is rapidly leached from dead leaf tissue, although P may be retained when autumn-shed leaves enter the aquatic environment before they dry out (Gessner 1991). Nitrogen is not generally leached upon senescence and death, although initially decreasing concentrations have been observed in some studies (Meyer & Johnson 1983). During decomposition,N and P concentrations of leaves usually increase (Webster & Benfield 1986, Gessner 1991). This increase is attributed to microbial colonization, which enhances the nutritional quality of leaf litter for detritivores (Webster & Benfield 1986). The easiest way to quantify total N concentrations of leaves is with a CHN analyser. However, this equipment is expensive and not readily available in many laboratories. The method described here is a modification of the standard Kjeldahl-N method for plant samples (Ferskvandsbiologisk Laboratorium University of Copenhagen 1992). Samples of plant material are dried, homogenized and digested