Eutrophic Ecosystems Research Articles

Organic nitrogen in precipitation at the mid-Atlantic U.S. Coast—methods evaluation and preliminary measurements

Recent studies have documented the importance of inorganic nitrogen deposited from the atmosphere to coastal waters. However, due to the limited number of field measurements and concerns about the reliability of measurement techniques, the aeolian flux of organic N is very uncertain. In this study we evaluate commonly employed collection and analytical techniques for dissolved organic nitrogen (DON) in precipitation, and provide preliminary estimates of organic-N wet fluxes at the mid-Atlantic U.S. Coast (Lewes, DE). Precipitation was sampled on a daily basis using an automated wet-only collector. Compared with UV photo-oxidation, persulfate wet chemical oxidation was more efficient at converting organic-N compounds to NO - 3. Side-by-side comparisons of white polyethylene buckets (typically employed in “acid rain” studies) with stainless steel buckets suggest that DON is lost in varying amounts to the plastic surfaces. Stability tests reveal that organic-N in precipitation can be quite labile under field conditions, with significant losses observed within a few hours in some samples. Based on analysis of 37 events collected from October 1993 through December 1994, the volume-weighted average concentration of DON in precipitation at the mid-Atlantic coast is ≥9.1 μmol ℓ -1. On an annual basis, organic-N comprises at least 20% of the total dissolved nitrogen in precipitation; on an event basis, it comprises as much as 64%. From the perspective of coastal ecosystem eutrophication, the atmospheric loading of DON would appear to represent an important exogenous source of N to local coastal waters such as the Delaware and Chesapeake Bays.

Binding constants of chlorobenzenes and polychlorobiphenyls for algal exudates

In eutrophic ecosystems, primary production may significantly affect the behaviour of toxicants or the accumulation in the aquatic food chain. Little is known about the potential of extracellular carbon, e.g., exudates, to scavenge hydrophobic chemicals. In a laboratory Selenastrum capricornutum culture with 30% extracellular carbon, phytoplankton-water bioconcentration factors (BCF) and exudate-water association factors (KDOC) were measured for two chlorobenzenes and 4 PCBs (total log Kow range 4.6-7.4). The apparent logBCFs were measured after 3 day batch equilibration and varied linearly with logKow with a slope of 0.63. The KDOC values for exudates from the same batch were measured using a gas purge method and were very high and more or less equal to Kow: logKDOC=logKow −0.057 (r2=0.926, n=6). The strong association with exudates limits the bioavailability of PCBs in laboratory cultures and natural aquatic systems.

Trophic coupling between bacterial and phytoplanktonic compartments in shallow tropical reservoirs (Ivory Coast, West Africa)

Biomass and production of bacterial and phytoplanktonic communities were measured during diurnal cycles at different stations in 3 shallow tropical reservoirs (Ivory Coast). Investigations were conducted in 1995 during 2 typical hydrological seasons (dry season in March and following rainy season in December). Bacterial production in the plankton ranged from 1.2 to 26.2 pg C 1-1 h-I and bac- terial biomass ranged from 11 to 163 pg C 1-'. A slope of 0.625 (n = 93) for the regression of log-trans- formed bacterial biomass versus log-transformed production suggests that the bacteria were strongly controlled by bottom-up processes. Ratios between net primary production and bacterial production averaged 67% (range 38 to 140%), indicating that the reservoirs studied can be considered as meso- eutrophic ecosystems. Average bacterial carbon demand corresponded to 97 % of the net primary pro- duction, suggesting that the biological systems studied are based on autotrophic metabolism. These relationships are the result of a close metabolic coupling between bacterioplankton and phytoplankton, with a large fraction of primary production routed through heterotrophic bacteria and the microbial loop.

Binding constants of chlorobenzenes and polychlorobiphenyls for algal exudates

In eutrophic ecosystems, primary production may significantly affect the behaviour of toxicants or the accumulation in the aquatic food chain. Little is known about the potential of extracellular carbon, e.g., exudates, to scavenge hydrophobic chemicals. In a laboratory Selenastrum capricornutum culture with 30% extracellular carbon, phytoplankton-water bioconcentration factors ( BCF ) and exudate-water association factors ( K DOC ) were measured for two chlorobenzenes and 4 PCBs (total log K ow range 4.6-7.4). The apparent log BCF s were measured after 3 day batch equilibration and varied linearly with log K ow with a slope of 0.63. The K DOC values for exudates from the same batch were measured using a gas purge method and were very high and more or less equal to K ow : log K DOC =log K ow −0.057 (r2=0.926, n=6). The strong association with exudates limits the bioavailability of PCBs in laboratory cultures and natural aquatic systems.

Critical loads for nitrogen deposition and their exceedance at European scale

In Europe serious problems associated with emissions of nitrogen oxides and ammonia are related to eutrophication and acidification. Impacts of eutrophication in terrestrial ecosystems are associated with changes in floristic composition and in ecosystem function and stability. Various activities have been initiated to assess the risk posed by nitrogen deposition for negotiations concerning the UN/ECE NO x Protocol. As there are difficulties in mapping critical loads for nitrogen, two different methods are presented here at European scale. One method uses a sensitivity approach linked to data for empirically derived critical loads; the other method uses a nitrogen saturation approach which sums quantitative values for acceptable long-term removal rates of nitrogen from the ecosystem and accumulation in soil organic matter. Resulting critical load maps show significant areas across Europe that are potentially sensitive to nitrogen deposition. Generally, the spatial distribution of sensitivity shows similarities using both approaches. However, the range of empirical critical loads in the literature determined for certain vegetation types is greater than those calculated using the saturation approach. A comparison with 1990 total nitrogen deposition does reveal a similar distribution of exceedance, but only when the lower end of the empirical critical load range is used. There are uncertainties associated with both methods nevertheless they do illustrate that substantial areas across Europe may be at risk from deleterious impacts caused by nitrogen deposition.

Taxonomic characterization of pelagic and periphytic heterotrophic bacteria isolated from the tropical Ebrie lagoon, Cote d'lvoire

Activity of heterotrophic bacteria is recognized as an important process governing the biochemical functioning of many aquatic ecosystems. The aim of this study is to compare (1) bacterial isolates of pelagic heterotrophic bacteria from two sites, each with a different trophic status (4 pg/l at Kpass and 23 pg/l at Layo for chlorophyll index) located in the Ebrie lagoon, and (2) the bacteria associated with periphyton growing on an artificial reef of bamboos stuck into the sediment of the two sites. Hierarchical classifications were performed from morphological and bio- chemical tests of 343 heterotrophic bacterial strains isolated from the two sites and for each habitat. Despite differences in trophic status, numerical taxonomic analysis of the pelagic bacterial strains (n = 165) showed a dominant cluster (72% of strains) of mixed origin (close to 50 % of isolates from each site). The majority of these strains were non-fermentative rods producing neither amino-acids decarboxylases, nor acid from any carbohydrates. In the more eutrophic site (Layo), few differences of proper- ties were observed between pelagic and periphyton-associated bacteria. On the con- trary, a large part of bacteria isolated from bamboo at Kpass was characterized by specific particularities such as the degradation of arginine, tryptophan and citrate. Nu- merical taxonomic analysis allowed the distinguishing of specific characteristics of bacteria according to the habitat. Our results suggest that hydrological and biological conditions (especially photosynthetic exudates from periphyton) may induce an obvi- ous specialization of the periphytic bacteria in the less eutrophic ecosystem (Kpass) compared to the bacteria isolated from the more eutrophic environment (Layo).

Phosphorus sorption capacities and saturation of soils in two regions with different livestock densities in northwest Germany

Abstract. Soils in areas with high livestock density contribute to the eutrophication of aquatic ecosystems through loss of nutrients, especially phosphorus (P). In order to identify the potential for P loss from such soils we determined phosphorus extracted by water (H2O‐P), by double lactate (DL‐P), and P sorption capacity (PSC) and degree of P saturation (DPS) in soil samples from two counties, one with low (Harle‐catchment) and the other with very high livestock density (Vechta). Both catchments are hydrologically connected with the tidal areas of the North Sea.The mean concentrations of H2O‐P (0.4mmol/kg) and DL‐P (3.9 mmol/kg) were lower in the Harle‐catchment than in the Vechta area (1.2 mmol/kg, 6.8mmol/kg). Although oxalate‐extractable Al (Alox) and Fe (Feox) and the derived PSCs varied according to soil type and to land use, the livestock density and the resulting high concentrations of oxalate‐extractable P (Pox) were shown to be the main reason for the very high DPS of up to 179% in the county of Vechta. These values exceeded DPS reported from other intensive pig feeding areas in western Europe and indicate the potential for significant P loss. Less than 40% of the variation in Pox could be explained by the routinely determined H2O‐Por DL‐P. Geostatistical analyses indicated that the spatial variability of Pox depended on manurial history of fields and Alox, showed still smaller‐scale variability. These were the major constraints for regional assessments of P losses and eutrophication risk from agricultural soils using available soil P‐test values, digital maps and geostatistical methods.

Developing optimal abatement strategies for the effects of sulphur and nitrogen deposition at European scale

Integrated Assessment Models were successfully used to provide input to the negotiations for the Oslo Protocol on Further Reductions of Sulphur Emissions, finalized within the United Nations Economic Commission for Europe Convention on Long-range Transboundary Air Pollution in Oslo in June 1994. The techniques developed within this framework will be extended now to the simultaneous analysis of sulphur and nitrogen deposition. In addition to acidification, atmospheric deposition of nitrogen contributes to eutrophication of certain ecosystems, through a nutrient effect, and originates from the long-range transport of emissions of both oxidised and reduced nitrogen (NOx and NH3). Modelling reductions in nitrogen deposition thus introduces a need to establish multi-pollutant multi-effect modelling techniques. This paper investigates the development of a model set up to examine reductions of these pollutants in an economically and environmentally efficient manner. The control of nitrogen deposition encompasses action across several economic sectors, particularly the power, transport and agricultural sectors. Combining sulphur and nitrogen deposition limits on a European scale will require a flexible modelling approach and the issues governing possible approaches are presented.

Biological structure in a shallow cove (Kertinge Nor, Denmark) — Control by benthic nutrient fluxes and suspension-feeding ascidians and jellyfish

Abstract In 1991 Kertinge Nor was characterized by a high benthic autotrophic biomass dominated by the filamentous macroalga Chaetomorpha linum which reduced the flux of inorganic nitrogen and phosphorus from the sediment to the water column. A dense population of filter-feeding ascidians Ciona intestinalis (up to 270 individuals m-2) had a significant controlling impact on the phytoplankton biomass. Also, small jellyfish Aurelia aurita were present in extremely high densities (up to 300 individuals m-3) controlling the zooplankton population. During a long period of calm and warm weather in the summer of 1992 the filamentous algal mat rose from the sediment surface. High amounts of nutrients were then released to the water column causing a phytoplankton bloom (up to 120 µg chlorophyll a l-1), but the zooplankton biomass remained low due to intense predation by theA. Aurita population. It is concluded that Kertinge Nor is an unstable eutrophic ecosystem in which interactions between suspension-feeding org...

Fossil indicators of nutrient levels. 1: Eutrophication and climate change

Abstract Both phosphorus and nitrogen are elements essential to life. Availability of these biolimiting nutrients therefore exerts a major control on the carbon cycle through ocean productivity, bringing about changes in ocean-atmosphere chemistry and climate. This review begins with a brief account of the biological importance of phosphorus and nitrate to the cell, and introduces current terminology relating to the interlinked carbon-nutrient cycles in the oceans. Nitrate-limited, eutrophic ecosystems are associated with modern upwelling zones, characterized by high rates of delivery of new phosphorus, high rates of new primary production and export production. Fossil indicators include high accumulation rates of biogenic silica, apatite, baryte and organic matter, plus non-spinose, smaller planktonic foraminifera. Examples from biomineral chemistry include indications of high Ba/Ca, high Cd/Ca and increased differences between δ 13 C in planktonic and benthic foraminiferal test calcite. Such eutrophic indicators are shown to have peaked during glacial phases in the Quaternary, supporting a model in which Milankovitch-related reductions in solar isolation influenced the availability of nutrients, increasing primary productivity and lowering the levels of atmospheric carbon dioxide.

Techniques and strategies for the reduction of ammonia emission from agriculture

Agricultural production systems are recognised as a major source of atmospheric ammonia (NH3). When deposited, the NH3 may contribute to eutrophication of oligotrophic ecosystems and to acidification. Techniques for the reduction of ammonia emission are mainly focused on reducing the NH3 emitting area exposed to the air, reducing the NH3 or ammonium (NH 4 + ) concentration in solution or reducing the exchange of air above the emitting surface. In this paper we present the techniques and changes in farming practice which may reduce NH3 emission. Due to interactions between different sources on a farm, reduction in NH3 emission from individual parts of the livestock production system cannot simply be added to give the net reduction in emission from the total system. Thus a whole farm system approach is needed for devising control strategies for reducing NH3 emission.

Internal eutrophication of aquatic ecosystems: mechanisms and possible remedies

Summary Eutrophication is an important problem in aquatic environments in Europe. In the Netherlands, many aquatic macrophytes have strongly declined while, at present their former habitats are characterized by non-rooting species such as Lemna species, Spirodela polyrhiza (L.) Schleiden and Azollla filiculoides Lamark. The experiments reveal that processes that cause eutrophication without the external input of nutrients (i.e. internal eutrophication) play an important role in the eutrophication of semi-aquatic habitats. The alkaline nature and high sulphate content of the river Rhine water which is allowed into large parts of the peaty lowlands of the Netherlands is suggested to be responsible for this internal eutrophication. Internal eutrophication appears to be caused by increased mineralisation of organic matter in semi aquatic and aquatic habitats due to the alkalinisation of sediments. Alkalinisation is caused by the production of bicarbonate owing to the reduction of sulphate and the alkaline nature of the inlet water. Next, free iron levels in the sediment have decreased due to increased iron sulphide precipitation and decreased iron inputs by seepage. Finally, sulphide and phosphorus levels have increased after the exhaustion of mobile iron in the sediment. The results also show that the mobilisation of phosphorus from the sediment is prevented by the addition of iron to iron depleted-sediments. Some possible remedies that can prevent or diminish internal eutrophication are discussed.

Effects of atmospheric ammonia on vegetation—A review

Atmospheric ammonia does not only cause acute injuries at vegetation close to the source, but significantly contributes to large scale nitrogen eutrophication and acidification of ecosystems because the amount of sources is high and after conversion to ammonium it can reach remote areas by long-range atmospheric transport. Besides having acute toxic potential, NH 3 and NH 4 + (= NH y) may disturb vegetation by secondary metabolic changes due to increased NH y uptake and assimilation leading to higher susceptibility to abiotic (drought, frost) and biotic (pests) stress. Prevention of damage to natural and semi-natural ecosystems will only be achieved if NH 3 emissions are drastically reduced. In this paper, the current knowledge on NH y emission, deposition, and its effects on vegetation and ecosystems are reviewed. Critical levels and critical loads for nitrogen deposition are discussed.

Sulphate-mediated iron limitation and eutrophication in aquatic ecosystems

In large parts of the peaty lowlands of The Netherlands, alkaline, sulphate-enriched river water poor in iron is let in to compensate for decreased ground water levels. As a result, iron input rates decrease while sulphate reduction rates in the anaerobic sediment increase. Iron sulphide precipitatio and decreased iron input result in iron exhaustion, sulphide accumulation and increased phosphate mobilization in the anaerobic sediments. Futhermore, iron shortage and sulphide toxicity can occur in aquatic species while disturbance of the iron cycle results in increased phosphate levels in the water layer.

Fertilizers and eutrophication in southwestern Australia: Setting the scene

An excess of plant nutrients has caused serious eutrophication in aquatic ecosystems of southwestern Australia manifested by excessive growth and accumulation of green and bluegreen algae. Phosphorus is generally the limiting nutrient for algal growth and phosphatic fertilizers applied to nutrient-deficient, leaching, sandy soils are the main source of P, supplemented by rural industry point sources. Nitrogen is the limiting nutrient in marine embayments with little drainage from the land. Measures to reduce the load of P delivered to drainage include basing fertilizer application rates on soil testing for P and the use of less soluble P fertilizers. Catchment management plans are being implemented with community involvement to reduce P loads and maintain agricultural production. This introductory paper reviews the history of eutrophication in southwestern Australia and of studies into its causes, principally in the large Peel-Harvey estuary. It briefly summarises other papers in this special issue concerned with different aspects of the problem: how to fertilize the land without causing eutrophication.

A carbon budget for a eutrophic marine ecosystem and the role of sulfur metabolism in sedimentary carbon, oxygen and energy dynamics

A carbon budget for a eutrophic marine ecosystem and the role of sulfur metabolism in sedimentary carbon, oxygen and energy dynamics

Estimating bacterial DNA synthesis from [3H]thymidine incorporation: Discrepancies among macromolecular extraction procedures

The estimation of bacterial DNA synthesis in trophic studies with [3H]thymidine requires quantitative extraction of labeled DNA. To determine the DNA contribution to total macromolecular labeling in a eutrophic ecosystem, we tested three extraction procedures currently used to estimate DNA labeling from thymidine incorporation: enzymatic fractionation, acid‐base hydrolysis, and phenol‐chloroform extraction. Because labeled macromolecular fractions are generally defined as DNA, RNA, and proteins, we used incorporation of tritiated thymidine, uridine, and leucine to preferentially label DNA, RNA, and proteins. Our data showed that each fractionation method yielded different apparent macromolecular distributions of the same radiolabeled substrates. Enzymatic digestions of the fractions obtained by acid‐base hydrolysis and phenol‐chloroform extraction showed that these two procedures are inadequate for estimating bacterial DNA labeling in our ecosystem. Finally, using the enzymatic procedure at different sites, DNA labeling appeared to represent a nearly constant proportion of the labeled macromolecules (20.1%, r = 0.952, n = 101) over a wide range of incorporation rates.

Advanced treatment of livestock wastewater using an aerobic soil column and an anaerobic contact column

Abstract Livestock wastewater is rich in nitrogen and phosphorus which induce the eutrophication of lakes and other aquatic ecosystems. In order to alleviate the detrimental impact of wastewater discharge, it is necessary to remove nitrogen and phosphorus as well as organic matter from the wastewater prior to disposal. Activated sludge process, though widely adopted for wastewater treatment, does not remove adequately nitrogen and phosphorus from livestock wastewater. In addition the equipment and maintenance of such a treatment system are expensive. It is difficult, therefore, for most of the small livestock farmers to introduce this system for livestock wastewater treatment.

Picoplankton in Six New Zealand Lakes: Abundance in Relation to Season and Trophic State

AbstractThe abundance of picoplankton (0.2‐2 μm) was measured seasonally in the surface waters of six New Zealand lakes that represent a range of trophic states. The lakes were: Wakatipu, Te Anau, Manapouri, Hayes, Mahinerangi and Ross Creek Reservoir. Among the lakes, picoplankton abundance was associated positively with temperature; picoplankton were most abundant in summer and autumn when they attained densities of 108,000‐270,000 cells/ml in the oligotrophic lakes. In these lakes, prokaryotic picoplankton was generally an order of magnitude more abundant than eukaryotic picoplankton. Consistent with the hypothesis that picoplankton are more important in oligotrophic than eutrophic ecosystems, there was a weak negative correlation between the density of prokaryotic picoplankton in the lakes and the level of chlorophyll a. The presence of large numbers of chroococcoid cyanobacteria in the guts of Ceriodaphnia dubia and Bosmina meridionalis implies that prokaryotic picoplankton are collected, but not digested, by these species.

Transfers between a eutrophic ecosystem, the river Rh�ne, and an oligotrophic ecosystem, the north-western Mediterranean Sea

Transfer processes from a eutrophic ecosystem, the river Rhone, to an oligotrophic environment, the north-west Mediterranean Sea, were studied during the winter period, when inputs of dissolved and particulate matter are at their highest.