Effects of nutrient (N,P, C) enrichment,grazing and depth upon littoral periphyton of a softwater lake

Three field experiments were performed in Lake Lacawac, PA to determine the importance of potentially limiting nutrients relative to other factors (grazing, depth) in structuring shallow water algal periphyton communities. All three experiments measured periphyton growth (as chlorophyll-a, AFDM or biovolumes of the algal taxa) on artificial clay flower pot substrates which released specified nutrients to their outer surfaces.Control of standing crop by nutrient supply rate vs. grazing was examined in Expt. I. Substrates releasing excess N and P, together with one of 4 levels of C (as bicarbonate) were placed either inside or outside exclosures designed to reduce grazer densities. Chlorophyll-a rose from 1.1–25.6 µg.cm^–2, and some dominant taxa (e.g., Oedogonium, Nostoc, Anacystis) were replaced by others (e.g., Scenedesmus, Cryptomonas) as bicarbonate supply increased. Reductions in invertebrate density did not significantly affect chlorophyll-a at any of the nutrient levels.Reasons for the species shift were further evaluated in Expt. II, using a minielectrode to measure the elevation of pH within the periphyton mat through photosynthetic utilization of bicarbonate. The pH adjacent to pots diffusing N, P and large quantities of bicarbonate, and supporting high chlorophyll-a densities of 32 µg cm^–2, averaged 10.0 compared to 6.3 in the water column. Pots diffusing only N and P supported 0.7 µg chlorophyll-a cm^–2 and elevated pH to 8.2. We suspect that bicarbonate addition favored efficient bicarbonate users (e.g., Scenedesmus), while inhibiting other taxa (e.g., Oedogonium) because of the attendant high pH.Expt. III was designed to test effects of depth (0.1 m vs. 0.5 m) and N (NH₄ ⁺ vs. NO₃ ^–) upon the growth response to bicarbonate observed in Expts. I and II. Similar standing crop and species composition were noted on pots at 0.1 m vs. 0.5 m. Enrichment with NH₄ ⁺ vs. NO₃ ^– also appeared to have little effect upon the periphyton community.Shallow water periphyton communities in Lake Lacawac, when supplied with sufficient N and P, appear to show a distinctive response to increasing bicarbonate concentration and pH which is robust to moderate variation in grazer densities, distance from the water surface, and the form of N enrichment.     

Restoration of eutrophied shallow softwater lakes based upon carbon and phosphorus limitation

Plant communities from oligotrophic, poorly buffered waters are seriously threatened by both, acidification and eutrophication/alkalinization. Acidification is mainly caused by atmospheric deposition of acidifying substances while eutrophication is often the result of inlet of nutrient enriched, calcareous brook- or groundwater. The plant production in very soft waters is often limited by low levels of inorganic carbon, nitrogen and/or phosphorus. This paper deals with the possibilities for restoration of formerly oligotrophic but now eutrophied and alkalinized softwater systems. Restoration based upon nitrogen limitation is not likely to be successful as the atmospheric deposition of nitrogen in The Netherlands is very high. Phosphorus limitation can also be a problem. One can stop the input of phosphorus and remove the mud layer, but the problem remains that also the deeper mineral sandy sediments are saturated with phosphate. A possible remedy, however, is a combination of carbon- and phosphorus limitation. Many plants from eutrophic environments never occur in very soft waters, probably as a result of carbon limitation. In addition, mobilisation of phosphate is much lower in waters with very low bicarbonate levels. Restoration of a former oligotrophic softwater lake by reducing the inlet of calcareous surface water, in combination with removal of the organic sediment layer, appeared to be very successful. Many endangered plant species such asIsoetes echinospora, Luronium natans, Deschampsia setacea andEchinodorus repens developed spontaneously from the still viable seedbank.     

Could rising aquatic carbon dioxide concentrations favour the invasion of elodeids in isoetid‐dominated softwater lakes?

1. During the past century, isoetid vegetation types in softwater lakes have often been invaded by faster‐growing elodeids. In these C‐limited systems, this may be related to rising aquatic CO₂ levels. 2. In a laboratory experiment we tested the growth response of two elodeid species, Myriophyllum alterniflorum and Callitriche hamulata, at four different CO₂ levels, ranging from 20 to 230 μmol L⁻¹. In addition, we tested the effect of the nutrient status of the sediment on the growth of C. hamulata at the different CO₂ levels. 3. Shoot and root growth increased with rising CO₂ availability. Irrespective of sediment type, growth was minimal to negative at the lowest CO₂ treatment level, while becoming positive at CO₂ levels around 40–50 μmol L⁻¹. Substantial growth was only obtained when the macrophytes were growing on mesotrophic sediments. The plants reached close to maximal growth at CO₂ levels of c. 100 μmol L⁻¹. 4. Within this experiment, the growth of C. hamulata at CO₂ levels above 90 μmol L⁻¹ may have been limited by N and P availability in both sediment types. The growth rate of M. alterniflorum did not seem to be limited by N and P availability, most likely due to its much higher relative root production. 5. The experimental results show that neither M. alterniflorum nor C. hamulata is able to invade isoetid‐dominated softwater lakes at very low aquatic CO₂ concentrations. However, if the sediments contain enough nutrients, a rise in aquatic CO₂ could allow the invasion of elodeid species leading to the subsequent disappearance of slow‐growing isoetids.     

Degraded Softwater Lakes: Possibilities for Restoration

In the Netherlands, the characteristic flora of shallow softwater lakes has declined rapidly as a consequence of eutrophication, alkalization and acidification. The sediment of most lakes has become nutrient rich and anaerobic. We expected that, if a vital seed bank was still present, restoration of the original water quality and sediment conditions would lead to the return of softwater macrophytes. The restoration of 15 degraded, shallow, softwater lakes in the Netherlands was monitored from 1983 to 1998. In eutrophied as well as in acidified lakes, removal of accumulated organic matter from the sediment and shores was followed by rapid recolonization of softwater macrophytes present in the seedbank. After isolation from alkaline water and subsequent mud removal, this recovery was also observed in alkalized lakes. Further development of softwater vegetation correlated strongly with the water quality. When renewed eutrophication was successfully prevented, softwater macrophytes could expand. However, in acidified lakes, Juncus bulbosus and Sphagnum species became dominant after restoration. Liming of an acidified lake was followed by re‐acidification within 3 years. Recolonization by softwater macrophytes was inhibited by high turbidity of the water column and spreading of large helophytes on the shore. As an alternative, controlled inlet of alkaline, nutrient‐poor groundwater was studied in a few lakes. The pH of those lakes increased, the carbon and nitrogen availability decreased and softwater macrophytes returned. Successful restoration has contributed considerably to maintaining biodiversity in softwater lakes in the Netherlands.     

Nutrient concentrations in a Littorella uniflora community at higher CO2 concentrations and reduced light intensities

1. Oligotrophic softwater lakes represent a special type of aquatic ecosystem with unique plant communities where generalisations from other aquatic plant communities to rising CO₂ in the water column may not apply. 2. In the present study, we set up large in situ mesocosms and supporting laboratory experiments with isoetid vegetation (Littorella uniflora) where water column CO₂ and light could be manipulated in order to test whether (i) light and CO₂ availability affect nutrient concentrations in isoetid vegetation, and (ii) if changes in light and CO₂ climate affect fluxes of inorganic nitrogen (N) and phosphorus (P) from sediment to water column, which potentially could result in increased growth of epiphytic algae. 3. The results showed that the standing stocks of phosphorus and nitrogen in the L. uniflora vegetation were significantly influenced by CO₂ concentration and light intensity. Both standing stocks of P and N were significantly higher in the mesocosm treatments with high CO₂ concentration than in those at low CO₂ concentration. Similarly, standing stocks of P and N enhanced with increasing light intensity. 4. Measurements of nutrient fluxes both in the field and the laboratory did not show any significant release of nutrients to the water column from plants or sediments at any of the light or CO₂ treatments. However, mats of epiphytic algae developed from the beginning of June to late September and caused a light reduction for the isoetid vegetation. 5. Increasing CO₂ concentrations in the water column may over time potentially result in a change in soft water plant communities.     

HYDROGEN ION BUFFERING OF CULTURE MEDIA FOR ALGAE FROM MODERATELY ACIDIC,OLIGOTROPHIC WATERS 1

Five hydrogen ion buffers were compared for their usefulness in regulating pH in a model oligotrophic, moderately acidic (pH 6.0) algal growth medium. These were 3,3-dimethylglutaric acid (DMGA), tricarbaliylic acid (TCA), trans-aconitic acid (tAA), N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES) and 2-(N-morpholino) ethanesulfonic acid (MES). All buffers (2.5 mM) except HEPES limited the reduction of pH in a NH₄⁺-based medium during growth of Chrysochromulina breviturrita Nich. to less than 0.12 units, compared with more than 2 units in an unbuffered medium. Long term growth of C. breviturrita in these media was significantly inhibited (P < 0.05) by TCA and tAA. MES was able to control pH with the minimum amount of NaOH (1.0 mM) added to the medium to adjust to pH 6.0. Four of five bacterial isolates were capable of utilizing tAA as a sole organic-C source, and no isolate could metabolize HEPES or MES. No significant differences (P > 0.05) were found in the maximum growth rates of six algal species (from five classes) in a medium with or without MES buffer, although significantly greater cell yields of Ochromonas danica Prings. were obtained in the buffered medium. MES (pK₄=6.15) was considered to be the most useful buffer in the pH range 5.0–6.5, due to its biological inertness, buffering capacity, the minimal requirement for excess base to adjust pH and its minimal metal complexing ability.     

Water‐level fluctuations affect sediment properties,carbon flux and growth of the isoetid Littorella uniflora in oligotrophic lakes

相似文献   

Competition between isoetids and invading elodeids at different concentrations of aquatic carbon dioxide

1. The growth of submerged macrophytes in softwater lakes is often assumed to be carbon limited. Isoetid species are well adapted to grow at low carbon availability and therefore commonly dominate the submerged macrophyte vegetation in softwater lakes. In many such lakes, however, large‐scale invasions of fast‐growing elodeid species, replacing the isoetid vegetation, have been observed. 2. In a laboratory experiment, we tested how rising aquatic carbon availability, in interaction with different densities of the isoetid Littorella uniflora, affected the growth (and thereby the potential invasion success) of the elodeid Myriophyllum alterniflorum. For this purpose, the growth of M. alterniflorum was determined at a combination of three concentrations of dissolved CO₂ (15, 90, 200 μmol L^?1) and three densities of L. uniflora (0, 553, 1775 plants m^?2). 3. At an ambient CO₂ of 15 μmol L^?1, M. alterniflorum could not sustain itself, whereas at raised CO₂ concentrations, growth became positive and increased with higher CO₂ availability. 4. The presence of L. uniflora, independent of its density, reduced the growth of M. alterniflorum by 50%. Whether this is related to nutrient availability or other factors is not clear. 5. Despite the growth reduction of M. alterniflorum by L. uniflora, at CO₂ ≥90 μmol L^?1, L. uniflora was still overgrown by M. alterniflorum. This may imply that, in field situations, M. alterniflorum can invade softwater systems with relatively high CO₂ availability, even in the presence of dense stands of L. uniflora.     

Effects of nitrogen,phosphorus and carbon enrichment on planktonic and periphytic algae in a softwater,oligotrophic lake in Florida,USA

The objective of this study was to investigate nutrient limitation of algal abundance in Anderson-Cue Lake, a softwater clear oligotrophic lake in north-central Florida. Nutrient diffusing clay pots and cylindrical enclosures were used in the field to test effects of different combinations of nitrogen, phosphorus, silica, and carbon on algal standing crop and composition of periphytic and planktonic algae, respectively. Effects of nutrient enrichment on periphytic algae were examined in two studies conducted 31 May – 8 July and 10 June – 15 July 1991. Nutrient effects on planktonic algae were examined in one study from 13 June – 1 July 1991. Planktonic and periphytic algal biovolume was significantly higher (p<0.05) when nitrogen and carbon were added in combination than with treatments without nitrogen, carbon, or nitrogen and carbon. Treatments with nitrogen and carbon combined resulted in lower algal diversity and dominance by coccoid green algae andScenedesmus. Results indicate that carbon and nitrogen can be limiting factors to algal growth in Anderson-Cue Lake and possibly other lakes of similar water quality.     

Calcium content of crustacean zooplankton and its potential role in species distribution

SUMMARY 1. The occurrence and species composition of crustacean zooplankton in Norwegian lakes was related to ambient Ca concentrations, pH, total phosphorus and chlorophyll a , and to the presence/absence of other zooplankters and a planktivorous fish (roach: Rutilus rutilus ).
2. Ambient Ca concentrations appeared to influence the distribution of Daphnia species: Daphnia longispina often occurred in Ca-rich lakes with low fish-predation pressure while the smaller Daphnia cristata often occurred in opposite conditions.
3. Body Ca contents were measured in zooplankters from a wide range of localities, to examine Ca requirements and thus the potential for Ca-limitation of common species.
4. All Daphnia species had relatively high specific Ca contents [ranging from 0.8 to 4.4% Ca dry weight (DW)⁻¹] compared with other cladocerans and also copepods (ranging from 0.1 to 0.4% Ca DW⁻¹). Within the Daphnia genus, the specific Ca content increased with increasing body size of the species, and thus the large-bodied species had especially high Ca demands.
5. Because of their high Ca demands, species of Daphnia could be competitively disadvantaged in softwater lakes relative to less Ca-demanding species.