bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment and monitoring of ecosystem health in the sea: A description of the Swedish monitoring system for coastal marine areas
Authors: Dave G.
Published: October 2002

Swedish coastal waters range in salinity from 0 psu (practical salinity units = o/oo) in the Bothnian Bay, which is part of the Baltic Sea, to 35 psu in the Skagerrak, which belongs to the North Sea and the Atlantic Ocean. Natural variations in ambient conditions include weather and climate due to latitudinal, seasonal and annual variations. Anthropogenic inputs of pollutants originate from local point sources and diffuse and distant sources. These inputs may cause local and regional as well as national and international problems. Therefore, local and regional monitoring programs are integrated into the Swedish national monitoring program, which is also co-coordinated with other national and international monitoring programs. The aim of this paper is to describe and assess the Swedish monitoring system for the marine and coastal environment and to discuss its strengths and weaknesses. The monitoring system incorporates a combination of chemical-physical and biological parameters. Measured parameters are accompanied with specific quality criteria. In most cases the criteria are based on an estimate of a ‘natural state’ and the appraisals are expressed on a scale of 1-5 (high, good, fair, poor and bad quality). Three major threats to the marine environment are eutrophication, toxic organic pollutants/metals and physical disturbance (exploitation of the coast). The parameters used to assess eutrophication are concentrations of nitrogen, phosphorus and silica, Secchi depth, concentration of chlorophyll, benthic fauna and macrovegetation. Metals and toxic organic pollutants are assessed based on their concentrations in sediment and selected organisms. The assessment of the degree of physical disturbance of coasts and seas is based on the number of buildings along the shoreline, physical disturbance along the shoreline, proportion of exploited/disturbed coastal water zones and jetty length. Other threats, which are also briefly discussed in this paper, are impact from the fishery and the potential toxic impact of contaminants, which are not being measured.
Zebrafish Danio rerio and roach Rutilus rutilus: Two species suitable for evaluating effects of endocrine disrupting chemicals?
Authors: Andersen Lene , Petersen Gitte I. , Gessbo Åsa , Örn Stefan , Holbech Henrik , Bjerregaard Poul , Norrgren Leif
Published: October 2002

Morphological studies of gonads from roach (Rutilus rutilus) in a small Swedish lake were performed. The lake is a potential recipient for drainage water from a refuse dumping area. All fishes were macroscopically identified as males, but histological examination of the gonads showed a high incidence of intersex. This high incidence might be caused by endocrine disrupting chemicals. The relationships between exposure to endocrine disrupters and intersex observations in wild fish is unknown and the effect of endocrine disrupters on zebrafish (Danio rerio) were evaluated in order to determine whether they might serve as a model laboratory species for effects of endocrine disrupting chemicals in wild fish.

Zebrafish were exposed from pre-blastula stage until sexual maturation to either standardised water (controls), 17a-methyltestosterone (1, 10 μg l-1) or 17b-estradiol (1, 10 μg l-1). Exposure to both concentrations of 17bestradiol caused a significant feminisation, while a significant increase in the proportions of males was found after exposure to 1 mg 17a-methyltestosterone l-1. Furthermore, exposure to 1 and 10 mg 17a-methyltestosterone l-1 caused development of intersex individuals. Additionally, sexually mature male zebrafish were exposed to 1 μg 17b-estradiol l-1. After 10 weeks of exposure the fish were transferred to non-contaminated water for two weeks. The control group was kept in standardised water for 12 weeks. At termination of the experiment, measurement of whole-body vitellogenin concentrations were performed. Exposure to 17b-estradiol caused a significant increase in whole body vitellogenin concentrations. After 2 weeks in water without addition of 17b-estradiol, the vitellogenin concentration was reduced by approximately 50%. Roach and zebrafish may share properties which makes these species suitable for further comparisons to evaluate effects of endocrine disrupting chemicals as well as domestic and industrial effluents containing hormone-like substances.
Burrowing mayflies (Hexagenia) as indicators of ecosystem health
Authors: Edsall Thomas A.
Published: October 2002

Three State of the Lakes Ecosystem Conferences have been held since 1996 to encourage the development of Great Lakes indicators of ecosystem health for use in reporting on progress in restoring and maintaining the chemical, physical and biological integrity of the Great Lakes ecosystem. Here we report on the development of an indicator based on burrowing mayflies, Hexagenia (Ephemeroptera: Ephemeridae), using production and biomass as the indicator metrics. Burrowing mayflies were selected because they (1) were historically abundant in unpolluted, soft-bottomed mesotrophic habitats throughout the Great Lakes, (2) are intolerant of and were extirpated by pollution in most of those habitats during the 1940s to1950s, (3) have shown the ability to recover in one of those habitats following pollution abatement, (4) are ecologically important as bioturbators of lakebed sediments and as trophic integrators that link detrital energy resources directly to fishes that feed preferentially on them, and (5) have highly visible mating flights, which carry the message directly to an informed public that the source water body is healthy. In addition, their annual production can be estimated from their mean annual biomass by the sizefrequency method. Productivity and biomass can also could be estimated with a ‘cohort-direct’ method, using the biomass of mature nymphs collected in May or early June from the cohort that is about to emerge as subimagos in late June or early July. Although both the size-frequency and cohort-direct methods provide reliable estimates of productivity and biomass, the latter method greatly reduces sample collection and processing effort and thus makes it feasible to use Hexagenia as an indicator of ecosystem health in surveys requiring the collection of large numbers of samples.
Development of multimetric indices of biotic integrity for riverine and palustrine wetland plant communities along Southern Lake Michigan
Authors: Simon Thomas P. , Stewart Paul M. , Rothrock Paul E.
Published: October 2002

Riverine and palustrine wetland plant communities were examined in order to propose a multimetric plant index of biotic integrity. The objectives were to determine the structural and functional attributes of these wetland plant communities, calibrate reference conditions in assessing aquatic plant communities, provide methods for further development and testing of the index, and present a case study. The index is based on a rapid assessment method using the information collected from a species list and cover estimates. Sampling was done using a modified relevé

sampling approach with a modified Braun-Blanquet Cover Abundance Scale Method for estimating percent cover. More than 20 characteristics of aquatic plant communities were evaluated and 12 metrics in five categories were developed. Structural metrics focused on community composition, key indicator species such as number of Carex and Potamogeton species, and guild type. Functional metrics included sensitivity and tolerance measures; percent emergent, pioneer, and obligate wetland species; and the number of weed species as a substitute metric. Abundance was estimated based on evenness of average cover densities. Individual condition was suggested as a measure of the lowest extremes of biotic integrity. Palustrine study sites ranged across a disturbance gradient from ‘least-impacted’ to ‘poor'; riverine study sites ranged from high quality to some of the most degraded riverine sites in the Great Lakes region. Ninety-five species of aquatic vascular plants were found in 42 families. The most common families were Cyperaceae (15 species), Polygonaceae (9 species), and Juncaceae (6 species). Fourteen submergent, four floating, two woody and 75 emergent aquatic plant taxa were found. Five species were on the endangered, threatened, or rare list for the State of Indiana. Sites receiving the highest index scores included several of the a priori least-impacted sites while the lowest scores were located near-field to a large industrial landfill. The index will need to be further validated and tested but shows potential as a rapid index of biotic integrity using aquatic plant assemblages.
The status of the macroinvertebrate community in the St. Croix River, Minnesota and Wisconsin: An examination of ecological health using techniques of multivariate analysis
Authors: Boyle Terence P. , Strand Matthew
Published: October 2002

A statistical procedure that integrates physical, chemical and biological data is used to operationally define and analyze ecological health. Benthic macroinvertebrates collected from May through September from eight locations along the St. Croix River in Minnesota and Wisconsin were analyzed by canonical correspondence analyses. A sequential multivariate analysis procedure was developed that included: 1) determining which environmental variables explained the most variation in the taxonomic data, individually and collectively, 2) running canonical correspondence analyses on the taxonomic data along with environmental variables chosen from a stepwise forward selection procedure, 3) performing a cluster analysis of the taxonomic data in sampling times to determine artificial biological seasons, and 4) analyzing the seasonal data (three time intervals) separately, as in steps 1 and 2. Changes in community structure were significantly associated with changes in environmental factors (physical and chemical) that varied in time and space. The variables found to be significant were largely those expected to be associated with the variations in the structure of benthic macroinvertebrate community in an unimpacted river. A slight influence of nitrogen could be detected in agricultural areas.
Assessing atrazine pollution potential to a drinking water reservoir using remote sensing and geographic information system modeling
Authors: Atkinson S. F. , Waller W.T. , Crooks T.J.
Published: October 2002

Water quality monitoring by the City of Dallas, Texas (US) and the Institute of Applied Science, University of North Texas, has recently shown elevated atrazine concentrations in the watershed of a large drinking water reservoir in the Dallas-Fort Worth metropolitan area serving over 3,000,000 people. Atrazine is under investigation by numerous researchers as an environmental estrogen that may be involved in increasing breast cancer incidence in humans and impacting health and reproductive systems in wildlife. Since treatment technologies for atrazine removal from finished drinking water can be expensive and provide no protection to aquatic ecosystem health, watershed managers are currently seeking proactive methods to reduce the amount of atrazine entering water supply systems.

The most viable approach for reducing atrazine in a drinking water reservoir begins with understanding the distribution and extent of landuse in the watershed where atrazine may be applied. Understanding the spatial distribution of areas potentially contributing atrazine runoff facilitates developing an effective atrazine reduction program of the best management practices that are appropriate to a particular region. Using remotely sensed satellite imagery and geographic information system modeling, an analysis of the spatial distribution of landuse, soil erodibility, and surface slope information in a large watershed in north central Texas was conducted. An ‘atrazine pollution potential’ model was developed and applied to over 224,000 hectares draining into Lake Lewisville which provides drinking water to Dallas and surrounding communities. Model results compared well with in situ water quality measurements of atrazine, and point to areas most in need of best management practice implementation.
A methodology for identifying and classifying aquatic biodiversity investment areas: Application in the Great Lakes basin
Authors: Morrison Heather A. , Minns Charles K. , Koonce Joseph F.
Published: October 2002

A scientifically defensible methodology for identifying areas of high biodiversity in aquatic environments is presented. Areas of high biodiversity or Aquatic Biodiversity Investment Areas are identified using a technique referred to as Habitat Supply Analysis. This technique uses the microhabitat features of an ecosystem in conjunction with information on the microhabitat preferences of fish to calculate the suitability of an area to fish. The method is structured so that the suitability of habitat to lifestages of fish, species of fish, groups of fish and fish assemblages can be evaluated. The methodology recognises that to some degree all areas within an aquatic system contribute to the maintenance of biodiversity. As such, a classification scheme is proposed to evaluate the potential versus the actual contribution of an area to the maintenance of biodiversity in an ecosystem. This classification scheme is designed to help prioritise habitat restoration and preservation efforts. Prototype evaluations of the methodology for identifying and classifying Aquatic Biodiversity Investment Areas are presented.
Thraustochytrids: A neglected agent of the marine microbial food chain
Authors: Kimura Hiroyuki , Naganuma Takeshi
Published: October 2002

The base of the pelagic microbial food chain consists of bacterioplankton and mycoplankton (mostly thraustochytrids), the latter having drawn less attention. In a rather simplistic formulation, bacterioplankton is regarded as the harvester of autochthonous (marine) dissolved organic material exuded from phytoplankton, while mycoplankton is seen to be the scavenger of refractory dissolved organic material which is often allochthonous (riverine). This study presents a case study report on the abundance of thraustochytrids (mycoplankton) and bacterioplankton in the discharge area of River Shimanto, Northwestern Pacific, Japan. Thraustochytrid cells were stained with acriflavine and counted directly by epifluorescence microscopy. Thraustochytrids were found in the surface water at a density of 0.9 to 3.6 x 10 3 cells l -1 , with an overall average of 2.5 x 10 3 cells l -1 . Distribution of thraustochytrids was correlated to (or controlled by) river discharge as depicted by lowered salinity. On the other hand, abundance of bacterioplankton, 1.2 to 1.4 x 10 9 cells l -1 , showed no significant correlation with river discharge. Thraustochytrids may grow on terrestrial organic matter in the riverine input, which is often refractory to degradation, and play a role in enhancing carbon cycling in the estuarine and coastal areas.
Physical variables, carbon cycling and primary producer couplings in a shallow tropical lagoon (Barra Lagoon, Brazil)
Authors: Carmouze Jean-Pierre , Domingos Patricia
Published: October 2002

The Barra Lagoon (28°S and 43°W, 7 km², mean depth, 1m, salinities from 3 to 12 ) was investigated between October 1990 and August 1993. We report here a first synthesis of organic carbon metabolism, the phytoplankton community and their mutual interactions. Barra Lagoon exhibited a hypereutrophic state (high values of phytoplanktonic biomasses, diurnal metabolic rates, particulate and dissolved organic carbon concentrations). As with most shallow lagoons, Barra Lagoon was very sensitive to short-term meteorological changes which induced high day to day changes in organic carbon metabolism and severely dampened seasonal trends. But surprisingly, when consistent structural changes occurred, its total organic carbon metabolism was rapidly dampened by shifts from pelagic to benthic carbon metabolism and vice-versa. Seasonal auto/heterotrophic shifts of the ecosystem (generally autotrophy in summer and heterotrophy in winter) were not always verified. They were more strongly linked to growing and degeneration phases of pelagic and benthic algae. Biological activity was mainly controlled by the rate of nutrient in situ regeneration (low nutrient concentrations in water). In these conditions, small-size phytoplankton species predominated, as they are more efficient than large forms in sharing nutritive resources. Cyanophyceae were ecologically favoured by low transparency, nitrogen limitation and high nutrients regenerated in the water column, while small species of Dinophyceae and Chrysophyceae were promoted by a higher photic layer, nitrogen content and benthic nutrient regeneration. Extra input of nutrients (proceeding from fish-kill in February 1991, from decomposition of macro-algae after a temporary phase of colonization in August-September 1992, and from abundant rainfalls) induced an ephemeral growth of larger species at the expense of Cyanophyceae. Cyanophyceae lost their dominance also when temperature fell to 20°C.
The dynamics of nutrient enrichment and primary production related to recent changes in the ecosystem of the Black Sea
Authors: Yayla M. , Yilmaz A. , Morkoc E.
Published: October 2002

The data collected in the southern Black Sea during the period of July 1997 to September 1998 showed that light penetrated into the upper 20-35 m, with a downward attenuation coefficient varying between 0.1 and 0.25 m -1 . The chlorophyll-a concentration for the euphotic zone ranged from <0.5 to 1.5 µg l -1 . Coherent sub-surface chlorophylla maxima formed near the base of the euphotic zone at all study points and a secondary one was observed at very low level of light (<0.1% of the surface light) in the nearshore regions. Production rates were estimated in between 62 and 785 mg C m -2 d -1 in this period. Bioassay experiments (using extra nitrate, ammonia, phosphate, silicon and iron) showed that under optimum light conditions the phytoplankton population is nitrate limited in open waters. Phosphate seems to control the growth in the nearshore regions of the southern Black Sea. Silicon concentration also influenced the phytoplankton growth since the majority of the population was determined to be diatoms.
The diversity of benthic macroinvertebrates as an indicator of water quality and ecosystem health: a case study for Brazil
Authors: Barbosa F. A. R , Callisto M. , Galdean N.
Published: October 2002

The state of Minas Gerais still has some nearly pristine aquatic ecosystems, thus representing strategic aquatic resources for Brazil. Rivers and creeks of Serra do Cipó (19° -20°S, 43° -44°W) constitute an example of natural ecosystems in preserved conditions where a broad research project was initiated in 1996 aimed at the assessment of aquatic biodiversity and water quality characterisation. This area is the natural water division between the hydrographic basins of Doce and São Francisco rivers, two of the most important watersheds of Minas Gerais. The main goal of this study was to assess the diversity of benthic macroinvertebrate communities and use them as bioindicators of water quality. A secondary goal was to classify the benthic communities into three categories: 1) non-affected communities: those preserving a pristine structure, which are significant for fragile ecosystems, 2) median-affected communities: those receiving some degree of impacts, formed by a mixture of stenotopic and euritopic populations capable of adapting to new conditions thus reflecting the ecosystem's resilience, and 3) heavily-affected communities: those with very poor diversity, generally subject to severe human impact with destructive effects, but that are still important for the functioning of these degraded ecosystems.
Toxicity and mutagenecity of urban wastewater treated with different purifying processes
Authors: Sánchez Mata José D. , Fernández Virginia , Chordi Andrés , Tejedor Carmen
Published: October 2002

The toxicity and mutagenecity of 1000-fold concentrates of 5 litre samples of wastewater from five different towns (containing 500, 600, 15000, 50000 and 190000 inhabitants) with different sewage treatment processes were determined. Two kinds of samples, including municipal wastewater entering the sewage treatment plants and the effluents discharged into the environment were analysed. After concentration through resins, overall toxicity was evaluated using the bioassay employing Photobacterium phosphoreum and samples were classified according to Vasseur et al. (1986) as 'Non-toxic', 'Slightly toxic', 'Toxic' or 'Highly toxic'. Mutagenecity was evaluated using the mutagenecity index determined by the Ames test, and samples were classified as 'Non-mutagenic', 'Slightly mutagenic', or 'Mutagenic', according to the 'two-fold' rule. The results obtained varied considerably; such that in some plants the toxicity values decreased during treatment whereas in others they remained unmodified or increased. None of the extracts analysed proved to be mutagenic. The data on toxicity and mutagenecity of the samples are apparently not correlated.
Status of the Guadiana Estuary (south Portugal) during 1996-1998: An ecohydrological approach
Authors: Chícharo M. A. , Chícharo L. M. , Galvão H. , Barbosa A. , Marques M. H. , Andrade J. P. , Esteves E. , Miguel C. , Gouveia I.
Published: October 2002

The aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary (1996-1998) before the construction of the Alqueva dam. This work was carried out to determine how environmental factors affect seasonal and tidal variations of plankton populations in the estuary. The available information on the subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated into a geographic information system-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. River flow near Mértola (ca 50 km upstream from the mouth) reached 3400 2 10 6 m 3 in winter and decreased to 42 2 10 6 m 3 in summer. With respect to nutrients, nitrogen to phosphorus ratios indicated some limitation by phosphorus, except at the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may significantly influence the retention of zooplankton in the estuary. The fish larval life cycle, especially sensitive to environmental alterations, showed high ratios of ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was concluded that an ecohydrological approach, allowing integration of different elements from the cellular to the habitat level into a geographic information system, can contribute to a better understanding of the processes that influence the aquatic biota of the estuary. The approach will be a useful assessment tool for monitoring the estuary following dam completion.
Biological structure and dynamics of littoral fish assemblages in the Eastern Finger Lakes
Authors: McKenna James E.
Published: October 2002

Fish assemblages from three of the New York Finger Lakes were examined for structure within and between lakes and over time. Species-area relationships indicated that local fish assemblages are the result of recent, lake-specific events that altered the regional species pool. Fish assemblages varied among seasons and those occupying eutrophic waters had different characteristics from those in oligotrophic waters. Bluntnose minnows (Pimephales notatus) were a persistent and important component of most assemblages, but abundance of bluegill (Lepomis macrochirus) was the most distinguishing feature. Species associations indicated that interactions among the fishes had little influence on assemblage structure. Correlations between community structure and abiotic factors were identified. Ten abiotic variables were strongly associated with the species assemblages, but could not fully explain differences between assemblages. Results indicate that the abundance and diversity of water column feeders was related to productivity of lake habitat. In general, fish populations were smaller in oligotrophic waters and water column feeders were poorly represented in those assemblages. Productivity at various trophic levels was implicated as a major factor determining lake fish assemblage structure.
Aquatic ecosystem rehabilitation: Targets, actions, responses
Authors: Zarull M. A. , Hartig J. H.
Published: October 2002

An effort to further define ecosystem health and integrity has been made through development and adoption of quantitative objectives for fourteen beneficial use impairments associated with the Great Lakes Areas of Concern. Narrative descriptions of beneficial use impairments have been used to develop ecosystem type indicators and objectives, which are then used to set goals for rehabilitative actions. This process is both a technical and a social one. Implementation of rehabilitative actions, in addition to being socially, technically and economically challenging has yielded both encouraging and surprising results. The process and the results have reinforced the need for an adaptive management approach to the rehabilitation of aquatic ecosystems.
Resilience in aquatic ecosystems—hysteresis, homeostasis, and health
Authors: Reynolds C. S.
Published: October 2002

The resilience of a system refers to its ready ability to recover structure and behavior in the face of external forcing. The term has been used in limnetic ecology for two separate phenomena. In one, it refers to the hysteretic persistence of supportive capacity in the face of a managed reduction in the resource supply, giving perplexing delays in the recovery of lakes subject to treatment to reverse the symptoms of eutrophication. In the other usage, resilience is the homeostatic damping of the effects of chaotic environmental variability on community structure, certainly within quantifiable thresholds, in all aquatic ecosystems. A simple energetic model of ecosystem function is developed in order to assimilate the two types of resilience. Although provisional terms are coined to emphasize their distinction, only structural resilience describes a general property of systems and, which, moreover, assists an understanding of their health and ascendancy. Resourcing resilience owes to the separation of the loading and the growth responses in particular kinds of water body but otherwise reveals little that is not already well known. No strong case can be made for persisting with the latter usage and certainly not without the qualification.
Seasonal dynamics in the concentrations and retention of phosphorus in shallow Danish lakes after reduced loading
Authors: Søndergaard Martin , Jensen Jens Peder , Jeppesen Erik , Møller Poul Hald
Published: October 2002

To investigate how phosphorus concentrations and retention were affected during recovery after reduced external phosphorus loading, phosphorus concentrations and loading were seasonally monitored for 11 years in 15 shallow eutrophic Danish lakes. Hydraulic loading, inlets, and lake water were sampled monthly during the winter (October–April) and bimonthly during the summer (May–September) to estimate monthly mass balances. Total phosphorus concentrations in the lakes were two to three times higher during summer than during winter; internal loading seems to be of great significance. The retention of phosphorus was negative from April until October, the most negative values generally occurring in May and July (–30% of external loading). In June, retention was less negative (−12%), probably influenced by clearwater phases which often appear in early summer. During the 11 years, the period with negative phosphorus retention decreased from five to four months and, as a median, the maximum phosphorus concentration declined from ca. 0.4 to 0.2 mg phosphorus l−l. In Lake Engelsholm, which was biomanipulated by a 66% reduction of the zooplanktivorous fish stock (mainly bream, Abramis brama), marked changes were observed in biological structure. Also affected were phosphorus concentrations and retention. Simultaneously, with an increase in Secchi depth from 0.7 to 2.0 m, summer concentrations of total phosphorus decreased to less than 50% of the pre-biomanipulation level. The period exhibiting negative phosphorus retention declined from six months before the intervention to four months afterwards. It is concluded that the recovery period after reduced phosphorus loading may last long in shallow eutrophic lakes, but that the recovery is significantly influenced by biological structure. During recovery, both the duration and net phosphorus release rates from the sediment declined progressively.
Response of phytoplankton, zooplankton, and fish to re-oligotrophication: An 11 year study of 23 Danish lakes
Authors: Jeppesen Erik , Jensen Jens Peder , Søndergaard Martin
Published: October 2002

The response of the biological community to total phosphorus loading reductions was studied by sampling fortnightly during the summer for 11 years in 18 lakes with significant in-lake total phosphorus reductions, as well as in five reference lakes. Fish manipulation was conducted in four of the total phosphorus-reduced lakes during the study period. For the majority of lakes, a fast response to total phosphorus reduction (but not necessarily to TP loading reduction due to internal loading) was found for phytoplankton (as measured by chlorophyll a) and fish, while less pronounced changes were observed for the zooplankton. In contrast to zooplankton biomass, phytoplankton, and fish biomass generally declined, leading to an overall higher ratio of zooplankton to phytoplankton, which suggests enhanced grazing pressure on algae. A response at the community level also was found. Generally, the share of non-heterocystous cyanobacteria declined substantially, while the contribution of heterocystous cyanobacteria in particular, and in some lakes also dinophytes, cryptophytes and chlorophytes, increased. The biomass of planktivorous fish declined and the share of potential piscivores increased. Accordingly, in some, but not all, lakes the share of Daphnia spp. among cladocerans and the body weight of Daphnia spp. and cladocerans increased, suggesting a reduced predation pressure on zooplankton. The biological response to TP loading reduction was not restricted to low-total phosphorus lakes, but was also found in lakes in the total phosphorus range 0.2–0.4 mg P l−1. However, only minor changes to a total phosphorus reduction from 1.2 to 0.4 mg P l−1 were recorded in the most hypertrophic lake. In the biomanipulated lakes, an overall stronger response was found, now also including zooplankton. In general, no changes were found in the reference lakes, suggesting that the changes in the total phosphorus-reduced lakes were not attributable to variations in climate during the study period. We use the results for discussion of various recently proposed hypotheses of lake response to re-oligotrophication.
Alteration of phytoplankton structure in Lake Lucerne due to trophic conditions
Authors: Bürgi H. R. , Stadelmann P.
Published: October 2002

During the last 45 years, Lake Lucerne (Switzerland) was characterized by four major periods of varying trophic state: 1) the oligotrophic period (1955 to 1969): total phosphorus concentrations below 20 mg m−3, nitrate-nitrogen 300 to 400 mg m−3; 2) a period of accelerated eutrophication (1970 to 1977): total phosphorus concentration 20 to 30 mg m−3, nitrate-nitrogen 400 to 500 mg m−3; 3) a moderate mesotrophic period (1978 to 1988): total phosphorus concentration 20 to 25 mg m−3, nitrate-nitrogen 500 to 600 mg m−3; and 4) a period of growth limiting phosphorus concentration (1989–2001): total phosphorus concentration 5 to 10 mg m−3, nitrate-nitrogen 600 to 700 mg m−3.

The biomass, evenness, species richness and biodiversity of the plankton community was analyzed over 40 years. Annual means of biomass were not closely correlated with nutrient loading. Biodiversity, evenness and monthly changes in biomass proved to be better indicators of environmental changes. Clear water periods due to zooplankton overgrazing were observed during the mesotrophic period. The growth of phytoplankton appeared to be limited by phosphorus. Blooms of nitrogen gas-fixing (N2) cyanobacteria occurred only during the 1971 to 1983 period.
Biodiversity of periphyton (diatoms) and echinoderms around a refinery effluent, and possible associations with stability
Authors: Izsak C. , Price A. R. G. , Hardy J. T. , Basson P. W.
Published: October 2002

We examine biodiversity in Tarut Bay, Saudi Arabia, around the effluent of a refinery that has operated since 1945. The spatial study involved quarterly assessment of diatom biodiversity in 1976/77 at 24 sites. Taxonomic distinctness decreased significantly towards the refinery outfall, in contrast to the pattern for number of species, Simpson's index and Margalef's species richness index. Ammonia-nitrogen concentrations and primary productivity (mg chlorophyll-a cm−1 d−1) also increased significantly towards the effluent, probably due to nearby sewage/nutrient enrichment.

The spatio-temporal assessment involved comparison of echinoderm biodiversity at eight sites in 1945 through 1947 and 1977. No significant temporal differences were observed in number of species, taxonomic distinctness or beta-diversity, nor was significant correlation detected between biodiversity and proximity to the refinery outfall. The absence of obvious impact is confirmed by statistical comparison of taxonomic distinctness for echinoderms in Tarut Bay with values for the whole Gulf.

Periphyton in Tarut Bay may be perturbed towards the refinery outfall, ‘positively‘ when measured by Simpson's and other ‘absolute’ biodiversity measures, but ‘negatively’ according to taxonomic distinctness, a measure of ‘average’ properties. Hence, diatom persistence stability appears moderate to low. In contrast, the echinoderm fauna may exhibit high stability, explained by either high persistence (withstanding perturbation), or high resilience (perturbation experienced, but system reverted or acclimated to ‘normal’ Gulf state) over a time scale of 30 y.
Pollution and recovery of Lake Orta (Italy): Resilience at work?
Authors: Baudo Renato
Published: October 2002

This paper attempts to fit the history of pollution and recovery of Lake Orta, Italy, to the ecological theory of resilience, or the ability to restore structure following perturbation. The evolution of this lake can be represented by a model of a folded surface. In the case of Lake Orta, a disturbance, represented by the onset of pollution in 1926, determined the transition to conditions of an extreme environment. If an opposite change is imposed on the environment (in this case, the liming of the whole lake), the model predicts that the ecosystem will not simply revert to the pathway that it has followed up to this point, but will evolve in a different way (hysteresis). Ultimately, the system could arrive either at similar (but never completely identical) conditions to those existing prior to the disturbance, or at some completely different state.

The variations of phytoplankton, zooplankton, benthos, and fish in Lake Orta have been summarized by applying a stochastic exponential population growth model. This model succeeds in showing how resilience and resistance combine together, offering a fairly good description of both the pollution and the recovery of the lake. It can be concluded that at least nothing contradicts the hypothesis that past changes can be explained by the ecological theory of resilience and resistance.
Is Lake Erie a resilient ecosystem?
Authors: Munawar M. , Munawar I. F. , Dermott R. , Niblock H. , Carou S.
Published: October 2002

Lake Erie has a long history of natural and cultural perturbations ranging from glacial origins, arrival of Europeans, exploration-early colonization, degradation, exotic invasion, and phosphorus reduction to its recent recovery. Is Lake Erie a resilient ecosystem responding to phosphorus abatement and exotic invasion? It is believed that Erie was an oligotrophic system when glaciers receded followed by a long period of mesotrophic conditions. It has been classified from mesotrophic to eutrophic ecosystem during the past three decades. In the 1970s the Great Lakes Water Quality Agreement was signed between Canada and the United States and steps were taken to reduce the phosphorus loading to the Great Lakes including Lake Erie. Total phosphorus and chlorophyll a levels in the eutrophic west have dropped from 41 µg L −1 and 13.8 µg L −1 in the 1970s to <20 µg L −1 and 5.6 µg L −1 in the 1990s. Similarly a significant decrease in phytoplankton biomass was recorded from 1970 to 1992 in the western basin. During the same period Diatomeae decreased markedly from 55% to 10% whereas Chlorophyta increased from 8% to 55%. Similar trends were evident in the other biota. Primary production rates in the 1990s were dominated by small sized organisms (picoplankton and nanoplankton) similar to Lake Superior—a pristine oligotrophic ecosystem. Based on several criteria such as reduction of biomass and primary production, high species diversity, decrease of eutrophic and increase of mesotrophic-oligotrophic species and prevalence of picoplankton-nanoplankton, Lake Erie appears to be a rapidly changing and resilient ecosystem altering from eutrophic to meso-oligotrophic conditions. These observations are also supported by the response of other biota such as zooplankton and benthos. For example during 1993 the non-zebra mussel benthic biomass in the western basin had returned to a similar composition observed earlier in 1952 including the recovery of the mayfly. On the other hand eastern basin benthos has not shown the same extent of recovery as the west. Fish community trends are very complex, but the return of the walleye and whitefish in the western and eastern basins respectively are encouraging signs of recovery. The changes observed at various trophic levels are indicative of a meso-oligotrophic environment.
Governance of transboundary pollution in the Danube River
Authors: McGlade Jacqueline M.
Published: October 2002

Two major issues now influence the effective governance of transboundary pollution in major watercourses such as the River Danube: One is institutional responsiveness in light of changes in global politics and the other relates to the dynamics of the river ecosystem itself. As a result of shifts in economic and political activities arising from globalization a new geography is taking shape in which many nation-states have become 'hollowed-out' and unable to deal properly with environmental issues across varying geographic scales. Without strong institutional frameworks and clear leadership, pathological syndromes can flourish, leading to further significant environmental problems and disparities in ecosystem health.

Similarly, ecosystems do not exist in a steady state; they constantly react to both external and internal changes in ways that cause sudden, and sometimes dramatic, shifts in their make-up. Changes can occur because of subtle long-term alterations as well as catastrophic events. However, if an ecosystem has a high degree of resilience it may recover from a catastrophic event without any intervention. It is very important to understand whether or not particular ecosystems are or are not likely to recover, so that appropriate contingency planning, especially for transboundary aquatic ecosystems, can be undertaken. However, embedding resilience within current management regimes requires a shift in thinking from operating on an ad hoc basis where ecosystems are treated as static entities to one based on the generic principles of dynamical systems.

This paper explores the ramifications of various ecological, legal and social processes on transboundary aquatic system management of the River Danube in central and eastern Europe.
Lake Peipsi: Changes in nutrient elements and plankton communities in the last decade
Authors: Kangur Külli , Milius Anu , Möls Tõnu , Laugaste Reet , Haberman Juta
Published: October 2002

In the 1990s, as a consequence of a decline in agricultural production in the watershed and a decrease in the amount of waste water discharged into rivers, the nutrient load carried from the catchment area into large, shallow, eutrophic Lake Peipsi (area 3,555 km2) decreased. The aim of the present study was to analyze the in-lake response of key physical and chemical variables and the biota to large-scale changes in the nutrient load. Yearly changes in water transparency, nutrient elements of surface water, chlorophyll a content, as well as in phyto- and zooplankton biomass were studied during the growth season of 1992–2000. A clear decline in total nitrogen, ammonium ion, and orthophosphate ions was revealed in the northern part of the lake over the studied years. Beginning from 1996–1997, a decreasing tendency was revealed for the nitrate ion and total phosphorus. A significant decline of the total nitrogen:total phosphorus ratio was also observed from 1992–2000. However, the biomass of phytoplankton (particularly cyanobacteria) and chlorophyll a concentration did not follow the dynamics of nutrients, but displayed an increasing trend. Concentrations of nutrients in the lake during the last decade were not so low as to limit phytoplankton growth directly. In Lake Peipsi, strong and long-lasting algal blooms were observed in recent years, despite a definite decline in the nutrient content of surface water. Weather conditions appear to be very important factors in causing algal blooms in Lake Peipsi.
Long-term trends in the fish communities of Lakes Peipsi and Võrtsjärv (Estonia)
Authors: Kangur Andu , Kangur Peeter , Pihu Ervin
Published: October 2002

This study was undertaken to determine the direction and extent of time related changes in the fish communities of the large shallow eutrophic lakes Peipsi and Võrtsjärv. The official statistics of commercial fisheries for the periods 1931–1940 and 1950–1999 were used for trend analysis. In the ichthyocoenosis of both lakes, several drastic and economically important changes have occurred during recent decades. Some trends in the population dynamics of fish (e.g., sharp decline of the stock of vendace Coregonus albula (L.) in Lake Peipsi) are probably irreversible owing to the eutrophication of the lake. A sharp decrease in the stock of smelt Osmerus eperlanus (L.), caused by nighttime water anoxia in the summer of several years, was followed by a quick recovery. Periodic changes in the population of pike Esox lucius L., are related to water level fluctuations. The population dynamics of several fishes, particularly pikeperch Stizostedion lucioperca (L.), are, to a large extent, controlled by fishery policy, although climatic factors are also of importance. The state of the stock of eel Anguilla anguilla (L.), depends entirely on introduction of young eels.
GLOW II conference, Ireland, 2000: Sustainability, research, monitoring, and management
Authors: Coulter G. , Irvine K.
Published: October 2002

The final session of GLOW II on July 21, 2000 was a discussion of general key issues for sustainability of the Great Lakes among an audience with tremendous collective and relevant experience. The session presented four questions for discussion. A thematic question at GLOW II was whether or not the sustainability of Great Lakes is a scientifically sound and practical concept. The discussion was lively and its reporting has necessitated editing, for which the responsibility lies completely with the editors and bears no reflection on strength of opinions.
Key elements of fisheries management on Lake Victoria
Authors: van der Knaap M. , Ntiba M. J. , Cowx I. G.
Published: October 2002

The fisheries of Lake Victoria have always been dynamic and the relevant authorities have continually tried to manage them. During the second half of the last century, numerous changes took place and fisheries managers had to cope with influences other than exploitation, including species introductions, invasive weeds, lake level rise, changes in water quality, and illegal fishing practices. These have influenced the way the fisheries have been managed.

In the 1920s, measures existed to manage the fisheries of Lake Victoria. In those days, a minimum net mesh size of one inch was in place, as well as certain restrictions for trawling and other fishing methods. Over the years, certain fishing gears and methods have been banned; some bans were lifted and then reimposed; minimum mesh sizes have shifted as a result of changing species compositions and changing needs to protect components of the stock. More recently, the fishery has been subjected to a series of bans on export to the European Union because of outbreaks of cholera and fish poisoning practices.

This article presents an overview of fisheries management on Lake Victoria, the successes and failures, impacts of fish exploitation and invasive weeds on species diversity, results of a major research project on the lake to assess the status of the fisheries, and the way forward.
Comparison of thermal stratification, light attenuation, and chlorophyll-a dynamics between the ends of Lake Tanganyika
Authors: Langenberg V. T. , Mwape L. M. , Tshibangu K. , Tumba J.-M. , Koelmans A. A. , Roijackers R. , Salonen K. , Sarvala J. , Mölsä H.
Published: October 2002

Thermal structure, light attenuation, and chlorophyll-a dynamics within the upper 100 m at the northern and southern ends of Lake Tanganyika were measured from August 1995–July 1996. Pronounced variability of thermal structure in time, depth and region were observed. During the dry windy season (June–September), the water column in the south was largely isothermal down to 100 m, while in the north stratification was detectable. Subsequently, in October, cessation of winds coincided with a reestablishment and strengthening of thermal stratification in the south, and a distinct rise of a weakened thermocline in the north was accompanied by an increase in epilimnetic concentrations of dissolved solids.

The depth of photic zone was highly variable with the average position of 1% of incident photosynthetically active radiance found between 20 and 70 m, sometimes showing vertical shifts of 25 m a week. Weekly observations showed that concentrations of chlorophyll-a were rather similar at both ends of the lake. At both stations, periods of unstable or absent thermal stratification were accompanied by increased concentrations of chlorophyll-a, although in the north chlorophyll-a also peaked during periods of deep thermal stratification and low rates of mixing. Concentrations of chlorophyll-a did not show significant relationship with the available amount of underwater available photosynthetically active radiance (Im from 11–173 μEm−2 s−).

We suggest that in Lake Tanganyika chlorophyll-a maxima can occur whenever growth rates exceed spatial mixing rates, that is, if mixing is less than a critical turbulence. Our observations underscore the consequences of hydrodynamic processes on biological productivity either by securing internal nutrients or by controlling the timing and magnitude of phytoplankton biomass production.