Nutrient limitation of phytoplankton in freshwater and marine environments: A review of recent evidence on the effects of enrichment

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109760/1/lno1988334part20796.pd

Seasonality of Primary productivity of phytoplankton of Lake Bosomtwe, Ghana -West Africa

The primary productivity and seasonality of phytoplankton and its seasonality in Lake Bosomtwe (Ghana), West Africa were studied from September 2005 to August 2006 using the dissolved oxygen method. The wet weight biomass (0.41±0.37 gCm-2d-1, n=25), Chlorophyll a (52.11±19.51 mg m-2, n=17), mixed layer depth (9.28±3.47 m, n=25), euphotic depth (4.43±1.76 m, n=25), ratio of mixed layer to euphotic depth (2.17±0.74, n=25), secchi disc depth (1.52±0.34 m, n=25), irradiance (1180±341.28 µE m-2s-1, n=25), extinction coefficient (0.97±0.46, n=25), and total phosphorus concentrations (1.84±0.49 µmol L-1, n=20) were measured to assess their influence on the productivity of the phytoplankton. Our assessment revealed high areal gross productivity of the phytoplankton (4.72 ± 1.56 gC m-2 d-1, n = 25) which is within the range for tropical African lakes, but concurrent high areal community respiration rates (4.34 ± 2.78 gC m-2 d-1, n = 25) contributed to a low net productivity (0.37 ± 2.32 gC m-2 d-1, n = 25) and growth rates (0.14 ± 0.33 d-1, n = 21). Variabilities in the gross productivity of the phytoplankton were high (CV =33.10 %) and driven by similarly high variabilities in the physicochemical and biological parameters. Productivity also exhibited clear seasonality associated with the mixing and stratification of the lake. The physicochemical and biological parameters (mixed layer depth, euphotic depth, secchi disc depth, irradiance, chlorophyll a, and the community respiration) all had a positive relationship with the primary production) whiles ratio of mixed layer to euphotic depth, total phosphorus, wet weigh biomass had a negative relationship with the gross productivity. Of all the measured parameters, only areal community respiration (r2 = 30.6 %) had a significant predictive value (r2 < 0.05).

The Relationship between Mixing and Stratification Regime on the Phytoplankton of Lake Bosomtwe (Ghana), West Africa

The seasonal changes in the phytoplankton community in terms of biomass composition and associated physicochemical parameters of the Lake Bosomtwe (Ghana) located in West Africa were studied between 2004 and 2006 to assess the mixing and stratification regime of the lake on the phytoplankton dynamics. From water samples obtained from a central index station, biomass composition was assessed by converting phytoplankton counts to wet weights-based approximation into cell volume values; whiles mixed layer and euphotic depths were analyzed using temperature and light profiles of the lake respectively. Total phosphorus was estimated using the Ascorbic Acid Method. Results from the dataset showed that the phytoplankton biomass was dominated by the Cyanophyceae throughout the study period despite the seasonal changes associated with the mixing and stratification regimes. There were significant inter-annual differences in the mean values of the euphotic depth and the wet weight biomass (P < 0.05). However differences in the mean values of the mixed layer depth, the ratio of the mixed layer depth:euphotic depth, and total phosphorus concentration (P > 0.05) were insignificant. High variations in the mixed layer depth (CV > 34 %) and the euphotic depth (CV > 32) drive similarly high variations in the wet weight biomass (CV > 28) as is the case for many stratifying tropical lakes. However, both were poor predictors of the phytoplankton wet weight biomass behaviour (mixed layer depth, r2 = 0.1034; euphotic depth, r

The Nile perch invasion in Lake Victoria: cause or consequence of the haplochromine decline?

We review alternative hypotheses and associated mechanisms to explain Lake Victoria’s Nile perch takeover and concurrent reduction in haplochromines through a (re)analysis of long term climate, limnological and stock observations in comparison with size-spectrum model predictions of co-existence, extinction and demographic change. The empirical observations are in agreement with the outcomes of the model containing two interacting species with life-histories matching Nile perch and a generalized haplochromine. The dynamic interactions may have depended on size related differences in early juvenile mortality: mouth-brooding haplochromines escape predation mortality in early life stages, unlike Nile perch that have miniscule planktonic eggs and larvae. In our model predation on the latter by planktivorous haplochromine fry act as a stabilizing factor for co-existence, but external mortality on the haplochromines would disrupt this balance in favor of Nile perch. To explain the observed switch, mortality on haplochromines would need to be much higher than the fishing mortality that can be realistically re-constructed from observations. Abrupt concomitant changes in algal and zooplankton composition, decreased water column transparency, and widespread hypoxia from increased eutrophication most likely caused haplochromine biomass decline. We hypothesize that the shift to Nile perch was a consequence of an externally caused, climate triggered, decrease in haplochromine biomass and associated recruitment failure rather than a direct cause of the introduction

Basin-Scale Control on the Phytoplankton Biomass in Lake Victoria, Africa

The relative bio-optical variability within Lake Victoria was analyzed through the spatio-temporal decomposition of a 1997–2004 dataset of remotely-sensed reflectance ratios in the visible spectral range. Results show a regular seasonal pattern with a phase shift (around 2 months) between the south and north parts of the lake. Interannual trends suggested a teleconnection between the lake dynamics and El-Niño phenomena. Both seasonal and interannual patterns were associated to conditions of light limitation for phytoplankton growth and basin-scale hydrodynamics on phytoplankton access to light. Phytoplankton blooms developed during the periods of lake surface warming and water column stability. The temporal shift apparent in the bio-optical seasonal cycles was related to the differential cooling of the lake surface by southeastern monsoon winds. North-south differences in the exposure to trade winds are supported by the orography of the Eastern Great Rift Valley. The result is that surface layer warming begins in the northern part of the lake while the formation of cool and dense water continues in the southern part. The resulting buoyancy field is sufficient to induce a lake-wide convective circulation and the tilting of the isotherms along the north-south axis. Once surface warming spreads over the whole lake, the phytoplankton bloom dynamics are subjected to the internal seiche derived from the relaxation of thermocline tilting. In 1997–98, El-Niño phenomenon weakened the monsoon wind flow which led to an increase in water column stability and a higher phytoplankton optical signal throughout the lake. This suggests that phytoplankton response to expected climate scenarios will be opposite to that proposed for nutrient-limited great lakes. The present analysis of remotely-sensed bio-optical properties in combination with environmental data provides a novel basin-scale framework for research and management strategies in Lake Victoria

Plankton ecology: The past two decades of progress

This is a selected account of recent developments in plankton ecology. The examples have been chosen for their degree of innovation during the past two decades and for their general ecological importance. They range from plankton autecology over interactions between populations to community ecology. The autecology of plankton is represented by the hydromechanics of plankton (the problem of life in a viscous environment) and by the nutritional ecology of phyto- and zooplankton. Population level studies are represented by competition, herbivory (grazing), and zooplankton responses to predation. Community ecology is represented by the debate about bottom- up vs. top-down control of community organization, by the PEG model of seasonal plankton succession, and by the recent discovery of the microbial food web

Potential impacts of climate and environmental change on the stored water of Lake Victoria Basin and economic implications

The changing climatic patterns and increasing human population within the Lake Victoria Basin (LVB), together with overexploitation of water for economic activities call for assessment of water management for the entire basin. This study focused on the analysis of a combination of available in situ climate data, Gravity Recovery and Climate Experiment (GRACE), Tropical Rainfall Measuring Mission (TRMM) observations, and high resolution Regional Climate simulations during recent decade(s) to assess the water storage changes within LVB that may be linked to recent climatic variability/changes and anomalies. We employed trend analysis, principal component analysis (PCA), and temporal/spatial correlations to explore the associations and covariability among LVB stored water, rainfall variability, and large-scale forcings associated with El-Niño/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Potential economic impacts of human and climate-induced changes in LVB stored water are also explored.Overall, observed in situ rainfall from lake-shore stations showed a modest increasing trend during the recent decades. The dominant patterns of rainfall data from the TRMM satellite estimates suggest that the spatial and temporal distribution of precipitation have not changed much during the period of 1998–2012 over the basin consistent with in situ observations. However, GRACE-derived water storage changes over LVB indicate an average decline of 38.2 mm/yr for 2003–2006, likely due to the extension of the Owen Fall/Nalubale dam, and an increase of 4.5 mm/yr over 2007–2013, likely due to two massive rainfalls in 2006–2007 and 2010–2011. The temporal correlations between rainfall and ENSO/IOD indices during the study period, based on TRMM and model simulations, suggest significant influence of large-scale forcing on LVB rainfall, and thus stored water. The contributions of ENSO and IOD on the amplitude of TRMM-rainfall and GRACE-derived water storage changes, for the period of 2003–2013, are estimated to be ~2.5 cm and ~1.5 cm, respectively

Novel Crystalline SiO2 Nanoparticles via Annelids Bioprocessing of Agro-Industrial Wastes

The synthesis of nanoparticles silica oxide from rice husk, sugar cane bagasse and coffee husk, by employing vermicompost with annelids (Eisenia foetida) is reported. The product (humus) is calcinated and extracted to recover the crystalline nanoparticles. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS) show that the biotransformation allows creating specific crystalline phases, since equivalent particles synthesized without biotransformation are bigger and with different crystalline structure

Biogeochemical Stoichiometry of Antarctic Dry Valley Ecosystems

Among aquatic and terrestrial landscapes of the McMurdo Dry Valleys, Antarctica, ecosystem stoichiometry ranges from values near the Redfield ratios for C:N:P to nutrient concentrations in proportions far above or below ratios necessary to support balanced microbial growth. This polar desert provides an opportunity to evaluate stoichiometric approaches to understand nutrient cycling in an ecosystem where biological diversity and activity are low, and controls over the movement and mass balances of nutrients operate over 10–10⁶ years. The simple organisms (microbial and metazoan) comprising dry valley foodwebs adhere to strict biochemical requirements in the composition of their biomass, and when activated by availability of liquid water, they influence the chemical composition of their environment according to these ratios. Nitrogen and phosphorus varied significantly in terrestrial and aquatic ecosystems occurring on landscape surfaces across a wide range of exposure ages, indicating strong influences of landscape development and geochemistry on nutrient availability. Biota control the elemental ratio of stream waters, while geochemical stoichiometry (e.g., weathering, atmospheric deposition) evidently limits the distribution of soil invertebrates. We present a conceptual model describing transformations across dry valley landscapes facilitated by exchanges of liquid water and biotic processing of dissolved nutrients. We conclude that contemporary ecosystem stoichiometry of Antarctic Dry Valley soils, glaciers, streams, and lakes results from a combination of extant biological processes superimposed on a legacy of landscape processes and previous climates