Decrease In Nutrient Availability Research Articles

Long-term response of Dreissena polymorpha larvae to physical and biological forcing in a shallow lake

Müggelsee, a shallow eutrophic lake (Berlin, Germany), has been subject to global warming and concurrent reductions of anthropogenic nutrient loading during the past decades. Here, we focus on the recent increase in abundance of Dreissena polymorpha larvae. We aimed at ascertaining whether the change in abundance of larvae was driven by changes in climate, especially by climate warming, and/or by the concurrent changes in trophic state of the lake. Both the numbers of small, newly developed larvae and their lengths have increased in recent years, suggesting that conditions for overall reproductive success have improved. The timing of the increase in abundance of larvae was matched by changes in nutrient loading and phytoplankton biomass, induced by a reduced inflow of nutrients into the lake. Besides a correlation between the first appearance of larvae each year and the timing of the requisite temperature for first spawning (12 degrees C), no relationship between changes in water temperature and abundance, length and survival rates of larvae was found. However, a sudden drop in abundance of larvae in 2003 may be primarily attributed to low dissolved oxygen conditions during an unusually long period of stratification, induced by anomalous meteorological conditions. The increase in length and survival rates of larvae was most likely due to changes in food composition, which followed the decrease in nutrient availability, and to changes in the occurrence of planktivorous fish. The results suggest that the first appearance of larvae per year and the decline in abundance of larvae in 2003 were driven by climatic influences, while the overall increase in abundance and length of D. polymorpha larvae in Müggelsee was more likely caused by changes in the trophic state of the lake rather than by climate warming.

Modelling secondary succession of neotropical mangroves: Causes and consequences of growth reduction in pioneer species

Abstract Mangrove forest structure is the result of interactions between species responses to abiotic stress factors, disturbance, dispersal and competition. The combination of abiotic conditions and disturbance history may determine the growth potential of the species, whereas dispersal, competition and external or biogenic changes in abiotic conditions may tune their succession. Even in forests with only a few species, this set of factors can create multiple species compositions. For example, pure stands of the mangrove Laguncularia are common in newly colonized areas, but they may evolve into mixed stands dominated by Rhizophora or Avicennia. We demonstrate such an evolution with a field study of mangroves established in abandoned rice fields. We use an individual-based simulation model to understand how species-dependent dispersal, growth rate and shade tolerance lead to the observed patterns in horizontal and vertical forest structure. We find that the initially dominating species will be gradually replaced in the canopy. This alteration cannot be explained exclusively by shade tolerance of the succeeding species. Rather, it is essential to assume that the height growth rate of the pioneer species slows down relative to those of the later species. A decrease in nutrient availability may be responsible for these relative changes in the growth rates of different species.

Temporal and geographic size trends in Neogene Corbulidae (Bivalvia) of tropical America: using environmental sensitivity to decipher causes of morphologic trends

Because of their abundance and ubiquity, corbulid bivalves were significant components of the marine ecosystems affected by the environmental, oceanographic, climatic, and biotic changes that occurred during the Neogene in tropical America. Tropical American corbulids show dramatic changes in size over time and space. Eastern Pacific corbulids increase in size in the Holocene, whereas in the Caribbean and western Atlantic, size decreases from maxima in the middle and upper Miocene. As a result, size differences between living eastern Pacific and Caribbean/western Atlantic corbulids are statistically significant.Previously proposed causes of faunal trends in marine invertebrates of tropical America include changes in predation intensity, changes in productivity, and climatic cooling, all of which have been linked to the emergence of the Central American Isthmus (CAI). By comparing geographic and temporal patterns at both regional and local scales, it is possible to decipher the cause of corbulid size trends. Large corbulid species tend to occur in deposits that show evidence of increased nutrient availability, either from upwelling or coastal runoff, and tend to be excluded from units deposited under more oligotrophic conditions. Regional size trends in corbulid bivalves, therefore, are best explained by a general decrease in nutrient availability and productivity in the Caribbean/western Atlantic as the CAI emerged.

A gap dynamic model of mangrove forest development along gradients of soil salinity and nutrient resources

1 A gap dynamic model ( FORMAN) was developed as a first synthesis of available data for three Caribbean mangrove species into an individual‐based model that simulates the long‐term dynamics of mangrove forest development. 2 Field observations at three sites along the Shark River estuary were compared with simulation results, assuming development following Hurricane Donna in 1960. Total basal area simulated for each site was within ±10% of that observed, although species‐specific basal area predictions were less accurate. 3 A decrease in nutrient availability from marine to mesohaline sites modelled the reduced basal area of Avicennia germinans and Laguncularia racemosa. However, at the lower nutrient site a 83% reduction in maximum sapling recruitment of both A. germinans and L. racemosa was required to fit field results. Increased basal area of A. germinans and L. racemosa limited the development of Rhizophora mangle at higher nutrient downstream sites, apparently due to competition for light resources. Both observed and simulated results indicated that R. mangle had higher frequencies in the smaller size classes at all three sites, compared to a bell‐shaped size‐class distribution of L. racemosa, particularly at the higher nutrient sites. 4 Succession was projected for the next 500 years at a site in the lower estuary. Long‐term forest dynamics were sensitive to species‐specific maximum sapling recruitment rates. In the absence of large‐scale disturbance, initial dominance by L. racemosa was predicted to be replaced eventually by A. germinans, even when maximum sapling recruitment rate of A. germinans was set at half of L. racemosa and R. mangle. 5 Response curves for each species along gradients of soil nutrient resource and salinity illustrated their relative competitive balance over time (up to 300 years). Laguncularia racemosa dominated in fertile soils with low salinity at early stages of recovery, but its abundance decreased over time while A. germinans increased. The dominance of R. mangle was limited to regions with low nutrient availability and low salinity. Avicennia germinans dominated at higher salinities, where the effect of nutrient availability was overwhelmed by the tolerance of individual species to salt stress.

Modeling nutrient and plankton processes in the California coastal transition zone: 3. Lagrangian drifters

Two types of numerical Lagrangian drifter experiments were conducted, using a set of increasingly complex and sophisticated models, to investigate the processes associated with the plankton distributions in the California coastal transition zone (CTZ). The first experiment used a one‐dimensional (1‐D; vertical) time‐dependent physical‐bio‐optical model, which contained a nine‐component food web. Vertical velocities, along the track of simulated Lagrangian drifters, derived from a three‐dimensional (3‐D), primitive equation circulation model developed to simulate the flow observed within the CTZ, were used to parameterize the upwelling and downwelling processes. The second experiment used 880 simulated Lagrangian drifters from a 3‐D primitive equation circulation model which was coupled to the same food web and bio‐optical model used in the first experiment. Parameterization of the biological processes in both experiments were based upon data obtained during the CTZ field experiments. Comparison of simulations with data provided insight into the role of the biological and physical processes in determining the development of the subsurface chlorophyll maximum and other related features. In both studies, the vertical velocities experienced by a simulated Lagrangian drifter as it was advected offshore while entrained within a filament played a major role in determining the depth to which the euphotic zone and the chlorophyll maximum developed. Also, as the drifters moved offshore, the food web changed from a coastal, neritic food web to an offshore, oligotrophic food web due to the decrease in nutrient availability. The temporal development of the food web constituents following the simulated drifters was dependent upon the environment to which the drifter was exposed. For example, the amount of time upwelled or downwelled and the initial location in the CTZ region greatly affected the development of the food web.

On the synergistic effects of enzymes in food with enzymes in the human body. A literature survey and analytical report

Recently, a theory has been postulated that suggests that vital enzymes in ingested food interact synergistically with enzymes within the human body and more specifically with enzymes in the digestive tract. Alterations in food enzymes induced by bulk processing including heating and irradiation and also the addition of chemical additives have been proposed to create a decrease in metabolic availability of nutrients, with the long-term consequence being disease. This review of the medical literature provides evidence that enzymes in food do in fact survive during digestion and can indeed, add significantly to the nutritive value of ingested foodstuffs. Examples of enzyme synergy in human nutrition are provided in whole grains, milk and dairy products, beans and seeds, and meat products. A bibliography on this interesting finding is included as well as concluding remarks on enzyme synergy and its putative interaction with cell metabolism. Finally, the interaction of enzyme synergy with disease is discussed.

Repression of nitrification in soils under a climax grassland vegetation

Two hypotheses on repression of nitrification in climax vegetations (i.e. nitrogen immobilization and allelopathy) were investigated. In this study the potential nitrification activities and numbers of ammonium-oxidizing bacteria were established in a nature reserve with a series of natural grasslands with vegetational different stages of succession of plants species. The pastures had not been fertilized for 3, 7, 20 and 46 years, respectively, and the gradual decrease in availability of nutrients had led to pastures dominated by different grass species. In each field soil parameters, potential nitrification activities (PNA) and numbers of ammonium-oxidizing bacteria were determined in the root zone of Holcus lanatus as well as in that of a grass species characteristic of the stage of succession. In the rhizosphere of H. lanatus decreasing PNA and numbers of ammonium-oxidizing bacteria were observed as the period of non fertilization increased. Within each field no significant differences in PNA were observed between the root zones of H. lanatus and those of the dominant grass species. From these results it is concluded that, in these fields, decreasing nitrification was related only to decreasing ammonium availability and not to species composition. No indications were obtained that allelochemicals were involved in the flow nitrification potentials of late stages of succession. The optimum pH of the ammonium-oxidizing community, measured as PNA, decreased as the period of non fertilization increased. It is suggested that impoverishment of the grassland soil with respect to nitrogen availability selects against ammonium-oxidizing bacteria with a relatively high pH optimum.

Repression of nitrification in soils under a climax grassland vegetation

Two hypotheses on repression of nitrification in climax vegetations (i.e. nitrogen immobilization and allelopathy) were investigated. In this study the potential nitrification activities and numbers of ammonium-oxidizing bacteria were established in a nature reserve with a series of natural grasslands with vegetational different stages of succession of plants species. The pastures had not been fertilized for 3, 7, 20 and 46 years, respectively, and the gradual decrease in availability of nutrients had led to pastures dominated by different grass species. In each field soil parameters, potential nitrification activities (PNA) and numbers of ammonium-oxidizing bacteria were determined in the root zone of Holcus lanatus as well as in that of a grass species characteristic of the stage of succession. In the rhizosphere of H. lanatus decreasing PNA and numbers of ammonium-oxidizing bacteria were observed as the period of non fertilization increased. Within each field no significant differences in PNA were observed between the root zones of H. lanatus and those of the dominant grass species. From these results it is concluded that, in these fields, decreasing nitrification was related only to decreasing ammonium availability and not to species composition. No indications were obtained that allelochemicals were involved in the flow nitrification potentials of late stages of succession. The optimum pH of the ammonium-oxidizing community, measured as PNA, decreased as the period of non fertilization increased. It is suggested that impoverishment of the grassland soil with respect to nitrogen availability selects against ammonium-oxidizing bacteria with a relatively high pH optimum.