Period Of Eutrophication Research Articles

The Anglesey lakes, Wales, UK—A palaeolimnological study of the eutrophication and nature conservation status

1. Palaeolimnological techniques were used to investigate recent environmental change in three shallow, coastal lakes (Coron, Dinam and Penrhyn) within biological SSSIs on Anglesey, Wales, U.K., where agriculture has influenced two sites while a third received sewage effluent. 2. The Penrhyn core was dated radiometrically and the timescale of the other two sites estimated by correlation. A range of palaeopigment, geochemical, diatom and chironomid analyses were made on the samples. 3. Results suggest that eutrophication has increased at all three sites in the last 50 years. Palaeopigment analyses indicate that Coron has had abundant blue–green algal populations, the Dinam sediments were highly organic and Penrhyn has been the most eutrophic. Trace metal profiles suggested significant sediment mixing. Although concentrations were sometimes low, diatom profiles from the sites include marked recent increases in Stephanodiscus, Cyclostephanos and Thalassiosira spp. 4. While there was a period of rapid eutrophication in Coron in the late-1960s, there are recent signs of reduced nutrient loading. Penrhyn appears the most enriched (and eutrophic from earlier time) and Dinam the least. Chironomid analyses suggest Coron has been the most enriched and two alternative explanations are put forward for the Chironomus loss in the recent sediments. Dinam has changed little, remaining mesotrophic and retaining the eutrophication-intolerant Pseudochironomus. In Penrhyn there has been a slow but progressive development of eutrophication, becoming mildly eutrophic at an early stage, with the loss of Pseudochironomus. 5. Environmental histories derived from sediment data of the three lakes have been related to specific catchment events and the significance of the relationship with lake ecosystem stability is discussed. The study shows the contribution of palaeolimnology to freshwater conservation.

Application of Geographie Information Systems (GIS) in lake monitoring with submersed macrophytes at Lake Constance. Conception and purposes

Summary In 1993 submersed vegetation of Lake Constance was mapped on base of aerial photographs. The estimation was the third of its kind since 1967 and 1978, including a period of fast eutrophication until the late seventies (caused by the use of phosphatic detergents) and a subsequent period of decreasing trophy, due to the international efforts of the riparian states in eliminating phosphate from waste water. The well known sensitivity of submersed macrophytes to changes in water quality leaded to marked changes in aquatic vegetation communities during the seventies and could help now again in success control of the redevelopement measures of the riparian states. The use of GIS enables to create geographically referenced maps of distribution areas of single species or species groups and to analyse social preferences and changes in superficial area and locations of species during the investigation period of nearly 30 years.

Significance of bacteria in carbon fluxes in the Arabian Sea

In the Arabian Sea, temporal contiguity of highly oligotrophic and eutrophic periods, along with high water temperatures, may result in unique features of bacteriaorganic matter coupling, nutrient cycling and sedimentation, which are unlike those in the classical oligotrophic and eutrophic waters. Bacteria-phytoplankton interactions are suggested to influence phytoplankton aggregation and its timing. It is also hypothesized that, within aggregates, hydrolytic ectoenzyme activity, together with condensation reactions between the hydrolysis products, produce molecular species which are not readily degraded by pelagic bacteria. Accumulation of a reservoir of such slow-to-degrade dissolved organic carbon (DOC) is proposed to be a carbon flux and energy buffer, which moderates the response of bacteria to the dramatic variations in primary production in the Arabian Sea. Use of the slow-to-degrade DOC pool during the intermonsoon could temporarily render the Arabian Sea net-heterotrophic and a source of CO2 to the atmosphere. Stored DOC is also suggested to balance the observed deficit between mesopelagic carbon demand and the sinking particulate organic carbon supply. Knowledge of the significance of bacteria in carbon storage and cycling in the Arabian Sea is needed to understand the response of the ocean’s biogeochemical state to strong physical forcing and climate change.

Elevated consumption of carbon relative to nitrogen in the surface ocean

UPTAKE of atmospheric CO2 by the ocean's 'biological pump' is driven by export of carbon from the euphotic zone to deeper waters1,2. As nitrate is a limiting nutrient in large regions of the ocean, measurements of nitrate uptake are often used to estimate the amount of carbon exported in this way3–6. This presupposes knowledge of the molar C: N ratio in the organic material exported from the upper waters, which is usually taken to be 6.6 (the Redfield ratio7,8). Recent studies have suggested, however, that the consumption ratio of C:N may deviate from this value in coastal waters9–11. Here we present time-series from both coastal waters and open-ocean sites which demonstrate that net organic carbon production greatly exceeded that predicted from nitrate consumption and the Redfield C:N ratio. We found a similar discrepancy in sections across broad regions of the North Atlantic during eutrophic periods. Our results suggest that extrapolating from nitrate consumption using the Redfield ratio leads to significant underestimates of organic carbon export from the euphotic zone.

The first decade of oligotrophication of Lake Constance : II. The response of phytoplankton taxonomic composition.

In Lake Constance, after several decades of cutrophication, a decrease in phosphorus loading over the last decade has lead to a partial recovery from eutrophication. Here we analyse the shift in the taxonomic composition of phytoplankton during the first decade of oligotrophication in Lake Constance. During the 1980s, spring total P concentrations decreased from ca. 130 to less than 50 μ·l-1. This decrease was reflected by an approximately proportional decrease in summer phytoplankton biomass while spring phytoplankton biomass seemed unresponsive. Major taxonomic changes occured during both growth seasons. In spring, the proportion of diatoms, green algae and Chrysophyta increased while the proportion of Cryptophyta decreased. The summer trend was very different: the relative importance of diatoms decreased and Cryptophyta and Chrysophyta increased, while Chlorophyta reached their peak around 1985. These trends are also analysed at the genus level. Comparison with taxonomic trends during the eutrophication period shows the expected reversals in most cases. Comparison with other lakes shows general similarities, with the notable exception that Planktothrix rubescens has never been important in Lake Constance. The increase of diatoms during spring is attributed to their improved competitive performance with increasing Si:P ratios. Their decrease during summer is explained by the increasing silicate removal from the epilimnion by increasing spring populations.

Sedimentary record of changes in the condition of Lake Washington

Variations with depth in properties of the sediment of Lake Washington are compared with known conditions in the lake. Annual changes of deposition form pairs of cryptic layers, dominated respectively by diatoms and mineral particles, that are revealed by X‐radiography. A period of eutrophication is recorded by sediment rich in phosphorus. Two later peaks of P can be attributed to deposition of eroded material during floods. The relative importance of diatom species changed in coordination with changes in nutrition and the presence of Oscillatoria which can suppress some species of centric diatoms by antibiosis. Experiments confirm that selective feeding by oligochetes can result in nonrandom transport of different components of sediment. Sporadic, brief outbursts of rare species of diatoms give precise dating and opportunity for measuring bioturbation under fully natural conditions by repeated sampling. Precise data on vertical distribution of diatoms are given by overlapping scanning electron micrographs of dried cores.

Changes in composition of bottom fauna of a tidal-flat area during a period of eutrophication

During the last 20 yr the western half of the Dutch Wadden Sea has undergone significant eutrophication: concentrations of P and N compounds and planktonic algae have roughly doubled, as has primary production. Though oxygen levels are often low in summer, anoxic areas are small and rare due to strong tidal mixing. During the 1970 to 1990 period, macrozoobenthos was sampled annually at 15 stations at Balgzand, a 50-km2 tidal-flat area in the westernmost part of the Wadden Sea. Not only did the estimates of total numbers, biomass, and production double during these two decades, but significant changes in the composition of the benthic community were observed, too: (1) the numerical proportion of polychaetes increased at the expense of molluscs and crustaceans, (2) the overall mean weight per individual of the macrozoobenthos decreased (numbers of individuals of small-sized species increased more rapidly than those of large-sized species), and (3) though absolute numbers and biomass of all feeding types increased, the share of carnivores declined and that of deposit feeders increased; the proportion of suspension feeders showed little change. This study refers to true macrobenthos only (1-mm sieve) and further excludes two taxa (Corophium spp. andHydrobia ulvae) which occasionally exercised an undue influence on numbers. Mass mortalities caused by low oxygen concentrations were of a small-scale nature only. Total number of species fluctuated without a clear trend. As a consequence of the increasing numerical densities, trends in species numbers were slightly increasing when expressed per unit of area and slightly decreasing when estimated per 100 individuals (by rarefaction).

Growth rates of the bivalve Macoma balthica in the Wadden Sea during a period of eutrophication:relationships with concentrations of pelagic diatoms and flagellates

Probably as a consequence of eutrophication, both the length of the annual phytoplankton blooms and the mean concentrations of flagellates (dominated by Phaeocystispouchetii) have increased in the western part of the Wadden Sea during the last decades. Planktonic diatoms, on the other hand, have hardly increased, but fluctuate heavily from year to year. Among the benthic tidal-flat fauna, which has increased in total numbers and biomass during the last decades, the bivalve Macorna balthica was studied in detail. The 15 yr (1974 to 1989) patterns of its annual growth and condition were compared with abundance patterns in phytoplankton components (during the growing seasons of M. balthica). Fluctuations in M. balthica were found to parallel fluctuations of planktonic diatoms but not those of P. pouchetii. It is concluded that M. balthica responded by faster growth and higher condition to better feeding conditions in years of high diatom abundance. Diatoms rather than P. pouchetii or other flagellates will be the most important food source for M. balthica.

Atlantic Eocene planktonic foraminiferal historical biogeography and paleohydrographic indices

Analysis of a quantitative and synoptic data base of Eocene Atlantic planktonic foraminifera has illuminated many facets of foraminiferal faunal structure and composition reflective of bioprovince and useful for empirical establishment of ecologic and paleohydrographic indices. Tropical indigenes, such as the morozovellids, turborotaliids, subquadrate acarininids, and some globigerinathekids dissolve most rapidly along with juveniles of most species. Tropical faunas are high in diversity and dominance, include oxygen minimum indices such as the biserial heterohelicids only in high productivity times such as the middle Eocene, are dominated by genera with high numbers of species and species consistently typical of warm water regions until the late Eocene when faunas include a higher number of middle than lower latitude types. Truly tropical genera are replaced by subtropical, eutrophic indicators, such as the globigerinathekids, and contract to the Florida Current region prior to their extinctions at the end of the middle Eocene. Atlantic late Paleogene tropical forms first appear in the Gulf of Mexico at the end of the middle Eocene. Middle latitude faunas include high numbers of chiloguembelinids, pseudohastigerinids, small and biconvex morozovellids, round and globigerinid-form acarininids, low-spired subbotinids in the late middle Eocene, high-spired subbotinids, large and typical globigerinids in the late Eocene. These forms have intermediate dissolution susceptibilities. Middle latitude faunas are often high in diversity in midddle latitude frontal regions. Dominance is low even in warm intervals when tropical indigenes increase in number in middle latitude faunas, especially in boundary currents. Low latitude species penetrate temperate areas also during cool, eutrophic periods of vigorous circulation such as the late middle Eocene. Typical of temperate slope faunas are high abundances of high-spired subbotinids and small-sized catapsydracids. High latitude faunas are usually low in diversity except in the middle to late Eocene when frontal regions were located in the southern Labrador Sea and over Rockall Bank. Typical forms are the low-spired subbotinids until the late middle Eocene, globorotaloids, catapsydracids, tenuitellids, and in the late Eocene, the biserial heterohelicids. Indigenous species are the most solution resistant and many are mesopelagic. During warmings rare low latitude indices penetrate high latitudes; subpolar faunas have greatest affinities with middle latitude faunas at these times.

Daphnia in Lake Washington1

In 1976 Daphnia, a genus that had been inconspicuous in the zooplankton of Lake Washington, suddenly became dominant. The mean summer transparency of the lake doubled. The major change affecting the success of Daphnia evidently was a decrease in the abundance of the predatory Neomysis mercedis in the mid‐1960s. Daphnia probably did not increase at that time because of the continued persistence of significant quantities of Oscillatoria until 1975. Eight species of Daphnia have been seen in the lake, but only three have become abundant. Daphnia pulicaria has been continuously present since its appearance in May 1976, although it becomes very scarce in winter. Daphnia galeata mendotae and Daphnia thorata have had much more limited occurrence. In each year from 1976 to 1980, two species formed separate population maxima, except in fall 1979 when D. thorata, although present, failed to increase. Instead, the plankton became dominated by the rotifer Conochilus hippocrepis which had been increasing for several years. In 1980 D. thorata and D. pulicaria made maxima, but in reverse order from earlier years. Several other species of zooplankton have been less abundant since the resurgence of Daphnia than during the period of eutrophication and recovery.

Subfossil chironomids as evidence of eutrophication in Ekoln Bay, Central Sweden

Changes in the composition of chironomid remains from three 65–76 cm deep cores of profundal sediments reflect changes in the lake's trophic state during a period of approximately 150 years. A long period of moderate eutrophication and successively increasing chironomid numbers was followed by a rapid change in productivity resulting in the disappearance of characteristic oligotrophic-mesotrophic members of the chironomid fauna. Nutrient and chlorophyll concentrations during different periods of the lake's history are reconstructed from sediment data and general chemical and biological relationships in Scandinavian lakes. Prospective effects of nutrient reduction are assessed.