scispace - formally typeset
Search or ask a question
Author

Thomas L. Crisman

Bio: Thomas L. Crisman is an academic researcher from University of South Florida. The author has contributed to research in topics: Wetland & Trophic level. The author has an hindex of 28, co-authored 117 publications receiving 2936 citations. Previous affiliations of Thomas L. Crisman include University of Florida & Aristotle University of Thessaloniki.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the role of water-level fluctuations on the structure and function of shallow lakes is discussed and conclusions are presented from a workshop held at Balatonfured, Hungary in May 2002 on the Role of Water-Level Changes on the Structure and Function of Shallow Lake.
Abstract: Discussion and conclusions are presented from a workshop held at Balatonfured, Hungary in May 2002 on the role of water-level fluctuations on the structure and function of shallow lakes. Water-level regime is regarded to be an important factor for lake ecosystem functioning and affects conservation values. Biota, in particular those living in vegetated areas, respond differentially to changes in hydroperiod dynamics. Extreme water levels may cause shifts between the turbid and the clear, macrophyte-dominated state. Strong effects of anthropogenic changes in the fluctuation of water levels are shown for Mediterranean (Greece, Turkey) and north temperate (The Netherlands) regions. Additionally, effects of climate change are anticipated that might alter the functioning of shallow lakes in these regions differentially. There is a need for data on the relationships between water-level changes and ecosystem responses. A plea is made for international cooperation and information exchange and an internet site for facilitating this has been developed.

456 citations

Journal ArticleDOI
TL;DR: Community structure of ciliate populations is determined largely by lake trophy with acidic oligotrophic systems being characterized by reduced diversity and species richness compared with hypereutrophic systems.
Abstract: The abundance and biomass of ciliates are both strongly related to lake trophic status as measured by chlorophylla concentrations. Taxonomic replacements occur with increasing eutrophication such that large-bodied forms (predominantly oligotrichs) are progressively replaced by smaller-bodied ciliates (mainly scuticociliates). Highly acidic lakes display a more pronounced dominance of large-bodied forms when contrasted with less acidic lakes of comparable trophy. Community structure of ciliate populations is determined largely by lake trophy with acidic oligotrophic systems being characterized by reduced diversity and species richness compared with hypereutrophic systems. The temporal and spatial distribution of small ( 100μm) meroplanktonic ciliates enter the water column during midsummer after the development of thermal stratification and associated profundal deoxygenation. Laboratory studies indicate that large zooplankton (crustaceans) are capable of utilizing ciliates as a food source, but there is little direct evidence from field studies documenting this trophic link. Ciliates can be voracious grazers of both bacterioplankton and phytoplankton, and each species has a distinct range of preferred particle size which is a function of both mouth size and morphology. Myxotrophic ciliates may be important components in some plankton communities, particularly during periods of nutrient limitation or after their displacement from the benthos of eutrophic lakes. Evidence regarding the importance of planktonic ciliated protozoa in nutrient regeneration and as intermediaries in energy flow is discussed.

249 citations

Journal ArticleDOI
TL;DR: Analysis of planktonic ciliated protozoans in Florida lakes during 1979 found that small-bodied ciliates are reduced in oligotrophic lakes where bacterial concentrations arc limiting and are replaced by those largerbodied taxa able to ingest nannoplanktonic algae in addition to bacteria.
Abstract: The abundance, biomass, composition, and size distribution of planktonic ciliated protozoans were analyzed monthly during 1979 along a trophic gradient represented by 20 Florida lakes. Both the abundance and biomass of ciliates were positively related to trophic state. Eutrophic assemblages were codominated by members of the Scuticociliatida, Oligotrichida, and Haptorida; oligotrophic lakes were dominated principally by the Oligotrichida. In addition to a compositional shift, large-bodied ciliates (40-50 pm) were progressively replaced by small-bodied ciliates (2030 pm) as trophic state increased. The response is attributed to changes in food availability. Small-bodied (~30 pm) bactivorous taxa are reduced in oligotrophic lakes where bacterial concentrations arc limiting and are replaced by those largerbodied taxa (>30 pm) able to ingest nannoplanktonic algae in addition to bacteria.

195 citations

Journal ArticleDOI
TL;DR: The dominance within the zooplankton community shifts from macrozooplankton to microzooplANKton with increasing trophic state, and the microzooperankton can constitute between 50 and 90% of the total zoopLankton biomass in eutrophic lakes.
Abstract: Zooplankton, including ciliated protozoans, were collected from 39 Florida lakes of widely ranging trophic state. Annual mean biomass values for different zooplankton groups were regressed against ...

176 citations

Journal ArticleDOI
TL;DR: The relationship between planktonic chlorophyll a and mean light availability in the mixed layer was examined for Lake Okeechobee, a shallow eutrophic lake in south-central Florida.
Abstract: The relationships between planktonic chlorophyll a and mean light availability in the mixed layer were examined for Lake Okeechobee, a shallow eutrophic lake in south-central Florida. There were significant spatial differences in the nature ofthis relationship. In the northern and central regions of the lake, concentrations of nonalgal suspended solids, tripton, were high due to muddy sediments and polymictic conditions. Light attenuation was predominantly correlated to the concentration of tripton and chlorophyll a concentrations were positively correlated to mean light availability in the mixed layer, I m . The western and southern regions of the lake had lower concentrations of tripton and light attenuation was correlated to chlorophyll a concentrations in summer and fall. Variables which estimate mean light availability in the mixed layer, such as I m , may provide insight into the role of light availability in the control of phytoplankton standing crop.

88 citations


Cited by
More filters
Journal Article
TL;DR: In this article, the authors present a document, redatto, voted and pubblicato by the Ipcc -Comitato intergovernativo sui cambiamenti climatici - illustra la sintesi delle ricerche svolte su questo tema rilevante.
Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

4,187 citations

Book ChapterDOI
01 Jan 1982
TL;DR: In this article, the authors discuss leading problems linked to energy that the world is now confronting and propose some ideas concerning possible solutions, and conclude that it is necessary to pursue actively the development of coal, natural gas, and nuclear power.
Abstract: This chapter discusses leading problems linked to energy that the world is now confronting and to propose some ideas concerning possible solutions. Oil deserves special attention among all energy sources. Since the beginning of 1981, it has merely been continuing and enhancing the downward movement in consumption and prices caused by excessive rises, especially for light crudes such as those from Africa, and the slowing down of worldwide economic growth. Densely-populated oil-producing countries need to produce to live, to pay for their food and their equipment. If the economic growth of the industrialized countries were to be 4%, even if investment in the rational use of energy were pushed to the limit and the development of nonpetroleum energy sources were also pursued actively, it would be extremely difficult to prevent a sharp rise in prices. It is evident that it is absolutely necessary to pursue actively the development of coal, natural gas, and nuclear power if a physical shortage of energy is not to block economic growth.

2,283 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined 35 long-term (5-35 years, mean: 16 years) lake re-oligotrophication studies and found that external total phosphorus loading resulted in lower in-lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes.
Abstract: SUMMARY 1. This synthesis examines 35 long-term (5–35 years, mean: 16 years) lake re-oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 l gL )1 before loading reduction), subtropical to temperate (latitude: 28–65� ), and lowland to upland (altitude: 0–481 m). Shallow northtemperate lakes were most abundant. 2. Reduction of external total phosphorus (TP) loading resulted in lower in-lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP

1,126 citations

Journal ArticleDOI
TL;DR: Model predictions indicate that global climate change will continue even if greenhouse gas emissions decrease or cease, and proactive management strategies such as removing other stressors from natural systems will be necessary to sustain freshwater fisheries.
Abstract: Despite uncertainty in all levels of analysis, recent and long-term changes in our climate point to the distinct possibility that greenhouse gas emissions have altered mean annual temperatures, precipitation and weather patterns. Modeling efforts that use doubled atmospheric CO2 scenarios predict a 1–7°C mean global temperature increase, regional changes in precipitation patterns and storm tracks, and the possibility of “surprises” or sudden irreversible regime shifts. The general effects of climate change on freshwater systems will likely be increased water temperatures, decreased dissolved oxygen levels, and the increased toxicity of pollutants. In lotic systems, altered hydrologic regimes and increased groundwater temperatures could affect the quality of fish habitat. In lentic systems, eutrophication may be exacerbated or offset, and stratification will likely become more pronounced and stronger. This could alter food webs and change habitat availability and quality. Fish physiology is inextricably linked to temperature, and fish have evolved to cope with specific hydrologic regimes and habitat niches. Therefore, their physiology and life histories will be affected by alterations induced by climate change. Fish communities may change as range shifts will likely occur on a species level, not a community level; this will add novel biotic pressures to aquatic communities. Genetic change is also possible and is the only biological option for fish that are unable to migrate or acclimate. Endemic species, species in fragmented habitats, or those in east–west oriented systems will be less able to follow changing thermal isolines over time. Artisanal, commercial, and recreational fisheries worldwide depend upon freshwater fishes. Impacted fisheries may make it difficult for developing countries to meet their food demand, and developed countries may experience economic losses. As it strengthens over time, global climate change will become a more powerful stressor for fish living in natural or artificial systems. Furthermore, human response to climate change (e.g., increased water diversion) will exacerbate its already-detrimental effects. Model predictions indicate that global climate change will continue even if greenhouse gas emissions decrease or cease. Therefore, proactive management strategies such as removing other stressors from natural systems will be necessary to sustain our freshwater fisheries.

999 citations