CARBON,NITROGEN, AND PHOSPHORUS AND THE EUTROPHICATION OF FRESHWATER LAKES1

The question of nutrients responsible for eutrophication of freshwater lakes is reviewed, and recent additions to the literature on nutrient limitation are discussed. The paper by Lange is criticized on several grounds, including the facts that utilization of HCO₃^? by phytoplankton and the invasion of lake waters by atmospheric CO₂ are ignored as sources of photosynthetic carbon. The phosphorus and nitrogen concentrations used in Lange's experiments are far higher than values published by others for Lakes Erie and Ontario. Preliminary results of fertilizing a small oligotrophic lake with nitrogen and phosphorus are described. The standing crop of phytoplankton increased by 30–50 ×, while the P:N:C ratio in seston did not change from ratios found in unfertilized lakes. Other experiments done in water columns isolated with polyethylene film showed that addition of carbon did not increase the phytoplankton standing crop. Since the fertilized lake was initially lower in total CO₂ than any other recorded in the literature, it is concluded that carbon is unlikely to limit the standing crop of phytoplankton in almost any situation. Measurements of invasion of atmospheric gases to the fertilized lake by the Rn²²² technique were compared with phytoplankton production measurements, revealing that atmospheric invasion of CO₂ is sufficient to support the high phytoplankton standing crop in the epilimnion of the lake. Possible errors in interpretation of culture and bottle-bioassay experiments with respect to eutrophication are discussed.     

Variable rates of phosphate uptake by shallow marine carbonate sediments: Mechanisms and ecological significance

We determined phosphate uptake by calcareous sediments at two locations within a shallow lagoon in Bermuda that varied in trophic status, with one site being mesotrophic and the other being more eutrophic. Phosphate adsorption over a six hour period was significantly faster in sediments from the mesotrophic site. Uptake at both sites was significantly less than that reported for a similar experiment on calcareous sediments in an oligotrophic lagoon in the Bahamas. The difference in phosphorus adsorption between our sites did not appear to be related to sediment characteristics often cited as important, such as differences in surface area (as inferred from grain size distributions), total organic matter content, or iron content. However, the sediment total phosphorus contents were inversely related to phosphorus uptake at our sites in Bermuda, and at the previously studied Bahamas site.We hypothesize that phosphate uptake in these calcareous sediments is a multi-step process, as previously described for fluvial sediments or pure calcium carbonate solids, with rapid initial surface chemisorption followed by a slower incorporation into the carbonate solid-phase matrix. Accordingly, sediments already richer in solid phase phosphorus take up additional phosphate more slowly since the slower incorporation of surface-adsorbed phosphate into the carbonate matrix limits the rate of renewal of surface-reactive adsorption sites.Although carbonate sediments are a sink for phosphate, and thereby reduce the availability of phosphorus for benthic macrophytes and phytoplankton in the shallow overlying water, phosphate uptake by these sediments appears to decrease along a gradient from oligotrophic to eutrophic sites. If our result is general, it implies a positive feedback in phosphorus availability, with a proportionately greater percentage of phosphorus loading being biologically available longer as phosphorus loading increases. This pattern is supported by the significantly higher tissue phosphorus content of the seagrass,Thalassia testudinum, collected from the eutrophic inner bay site. Over time, this effect may tend to cause a shift from phosphorus to nitrogen limitation in some calcareous marine environments.     

Observations in guanotrophic environments

Summary Examples are given of initial guanotrophy in acid oligotrophic environment and of stabilized guanotrophy of long standing, both in acid oligotrophic and eutrophic environment.Characteristic of a guanotrophic environment is the accumulation of phosphate. In hard waters phosphate is accompanied by large amounts of saline nitrogen compounds. In soft waters the saline nitrogen production seems to be inhibited through low bacteriological activity. In eutrophic guanotrophic environments oxygen production and biochemical oxygen demand are both high. In oligotrophic guanotrophic environments the oxygen content as a rule does not reach saturation and biochemical oxygen demand is fairly low. The amounts of chloride and calcium do not change significantly by the addition of excrements of birds.Diatoms, blue green algae and desmids are very scarce in guanotrophic environments. In hard waters mesosaprobic forms are present in the plankton community. In soft waters no strong saprobic tendencies could be found.During the initial stage of guanotrophy in an acid oligotrophic environment, the desmids disappear together with other sensitive species as Dinobryon pediforme and Bosmina obtusirostris. Unicellular flagellates as Chlamydomonas appear in increasing numbers. Several factors in the environment respond to the changes by increasing fluctuations of the values recorded.There was evidence of transport and introduction of microorganisms by waterfowl.     

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.     

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.     

Differential response of high-elevation planktonic bacterial community structure and metabolism to experimental nutrient enrichment

Nutrient enrichment of high-elevation freshwater ecosystems by atmospheric deposition is increasing worldwide, and bacteria are a key conduit for the metabolism of organic matter in these oligotrophic environments. We conducted two distinct in situ microcosm experiments in a high-elevation lake (Emerald Lake, Sierra Nevada, California, USA) to evaluate responses in bacterioplankton growth, carbon utilization, and community structure to short-term enrichment by nitrate and phosphate. The first experiment, conducted just following ice-off, employed dark dilution culture to directly assess the impact of nutrients on bacterioplankton growth and consumption of terrigenous dissolved organic matter during snowmelt. The second experiment, conducted in transparent microcosms during autumn overturn, examined how bacterioplankton in unmanipulated microbial communities responded to nutrients concomitant with increasing phytoplankton-derived organic matter. In both experiments, phosphate enrichment (but not nitrate) caused significant increases in bacterioplankton growth, changed particulate organic stoichiometry, and induced shifts in bacterial community composition, including consistent declines in the relative abundance of Actinobacteria. The dark dilution culture showed a significant increase in dissolved organic carbon removal in response to phosphate enrichment. In transparent microcosms nutrient enrichment had no effect on concentrations of chlorophyll, carbon, or the fluorescence characteristics of dissolved organic matter, suggesting that bacterioplankton responses were independent of phytoplankton responses. These results demonstrate that bacterioplankton communities in unproductive high-elevation habitats can rapidly alter their taxonomic composition and metabolism in response to short-term phosphate enrichment. Our results reinforce the key role that phosphorus plays in oligotrophic lake ecosystems, clarify the nature of bacterioplankton nutrient limitation, and emphasize that evaluation of eutrophication in these habitats should incorporate heterotrophic microbial communities and processes.     

A multidisciplinary approach to understanding the recent and historical occurrence of the freshwater plant, Littorella uniflora

1. The vulnerability of softwater, oligotrophic lakes to eutrophication has caused the disappearance of many, if not most, of the unique isoetid plant communities. We tested whether the presence or disappearance of the isoetid Littorella uniflora (L.) could be predicted from environmental parameters, soil types and land use in the catchment area, and atmospheric nitrogen deposition. 2. We found that the topographic catchment area of a lake was an irrelevant unit to study effects of soil type and land use. Instead, using a GIS‐generated buffer zone around the lakes it proved feasible to classify 472 lakes into historical (if L. uniflora had disappeared) or recent (if L. uniflora was still present) Littorella lakes, based on soil type and land use. Our analysis showed that aeolian sand deposits and heath in the buffer zone favoured the presence of L. uniflora, whereas moraine clay and agriculture were strongly linked to the disappearance of L. uniflora. 3. However, in order to understand fully the presence or disappearance of L. uniflora, environmental data were needed in addition to soil types, land use and nitrogen deposition, and the use of discriminant analysis allowed us to classify 96% of the investigated lakes correctly into recent or historical sites. Alkalinity, total phosphorus, total nitrogen, aeolian sand deposits and heath were the most important parameters explaining the presence or disappearance of L. uniflora. Our analysis also indicated that eutrophication, rather than acidification, has likely caused the disappearance of L. uniflora from 218 of the 472 lakes investigated. 4. Our findings have widespread implications for the conservation or restoration of isoetid habitats and we recommend applying a wide buffer zone around lakes, with restrictions on farming and traditional forestry activities. In addition, our buffering concept may prove a useful tool for aquatic ecologists to investigate relationships between catchment features and organisms (plants, insects and amphibians) with aquatic as well as terrestrial life forms.     

Atmospheric nitrogen deposition is associated with elevated phosphorus limitation of lake zooplankton

Here, we present data that for the first time suggests that the effects of atmospheric nitrogen (N) deposition on nutrient limitation extend into the food web. We used a novel and sensitive assay for an enzyme that is over‐expressed in animals growing under dietary phosphorus (P) deficiency (alkaline phosphatase activity, APA) to assess the nutritional status of major crustacean zooplankton taxa in lakes across a gradient of atmospheric N deposition in Norway. Lakes receiving high N deposition had suspended organic matter (seston) with significantly elevated carbon:P and N:P ratios, indicative of amplified phytoplankton P limitation. This P limitation appeared to be transferred up the food chain, as the cosmopolitan seston‐feeding zooplankton taxa Daphnia and Holopedium had significantly increased APA. These results indicate that N deposition can impair the efficiency of trophic interactions by accentuating stoichiometric food quality constraints in lake food webs.     

Effects of upstream lakes and nutrient limitation on periphytic biomass and nitrogen fixation in oligotrophic, subalpine streams

1. We conducted bioassays of nutrient limitation to understand how macronutrients and the position of streams relative to lakes control nitrogen (N₂) fixation and periphytic biomass in three oligotrophic Rocky Mountain catchments. We measured periphytic chlorophyll‐a (chl‐a) and nitrogen‐fixation responses to nitrogen (N) and phosphorus (P) additions using nutrient‐diffusing substrata at 19 stream study sites, located above and below lakes within the study catchments. 2. We found that periphytic chl‐a was significantly co‐limited by N and P at 13 of the 19 sites, with sole limitation by P observed at another four sites, and no nutrient response at the final two sites. On average, the addition of N, P and N + P stimulated chl‐a 35%, 114% and 700% above control values respectively. The addition of P alone stimulated nitrogen fixation by 2500% at five of the 19 sites. The addition of N, either with or without simultaneous P addition, suppressed nitrogen fixation by 73% at nine of the 19 sites. 3. Lake outlet streams were warmer and had higher dissolved organic carbon concentrations than inlet streams and those further upstream, but position relative to lakes did not affect chl‐a and nitrogen fixation in the absence of nutrient additions. Chl‐a response to nutrient additions did not change along the length of the study streams, but nitrogen fixation was suppressed more strongly by N, and stimulated more strongly by P, at lower altitude sites. The responses of chl‐a and nitrogen fixation to nutrients were not affected by location relative to lakes. Some variation in responses to nutrients could be explained by nitrate and/or total N concentration. 4. Periphytic chl‐a and nitrogen fixation were affected by nutrient supply, but responses to nutrients were independent of stream position in the landscape relative to lakes. Understanding interactions between nutrient supply, nitrogen fixation and chl‐a may help predict periphytic responses to future perturbations of oligotrophic streams, such as the deposition of atmospheric N.     

Population fluctuations and their causes in the African Fish Eagle, (Haliaeetus vocifer (Daudin)) at Lake Naivasha,Kenya

Soft water lakes possess a highly characteristic vegetation adapted to limitation of carbon. Based upon hydrology, vegetation and geographic distribution, boreal and Atlantic lake types can be distinguished. Reducing the input of nutrients or liming, or both, the stream or its catchment is generally sufficient to restore typical soft water vegetation of boreal soft water lakes. The vegetation of Atlantic soft water lakes is subject to many anthropogenic degradation processes. Therefore, spontaneous recovery in the near future is not expected and restoration is urgently required. Removal of nutrient-rich, anoxic, organic sediments is a prerequisite for restoration of these lakes. In acidified or acid-sensitive lakes, additional measures against acidification are required. Controlled supply of calcareous, nutrient-poor water is much better than direct liming. The effects of these restoration measures strongly depend on the detrimental effects of processes such as atmospheric deposition, drainage, catchment acidification, eutrophication and reduced colonisation rates.     

The effect of increased nitrogen load on phytoplankton in a phosphorus‐limited lake

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Climate change and Saharan dust drive recent cladoceran and primary production changes in remote alpine lakes of Sierra Nevada,Spain

Recent anthropogenic climate change and the exponential increase over the past few decades of Saharan dust deposition, containing ecologically important inputs of phosphorus (P) and calcium (Ca), are potentially affecting remote aquatic ecosystems. In this study, we examine changes in cladoceran assemblage composition and chlorophyll‐a concentrations over the past ~150 years from high‐resolution, well‐dated sediment cores retrieved from six remote high mountain lakes in the Sierra Nevada Mountains of Southern Spain, a region affected by Saharan dust deposition. In each lake, marked shifts in cladoceran assemblages and chlorophyll‐a concentrations in recent decades indicate a regional‐scale response to climate and Saharan dust deposition. Chlorophyll‐a concentrations have increased since the 1970s, consistent with a response to rising air temperatures and the intensification of atmospheric deposition of Saharan P. Similar shifts in cladoceran taxa across lakes began over a century ago, but have intensified over the past ~50 years, concurrent with trends in regional air temperature, precipitation, and increased Saharan dust deposition. An abrupt increase in the relative abundance of the benthic cladoceran Alona quadrangularis at the expense of Chydorus sphaericus, and a significant increase in Daphnia pulex gr. was a common trend in these softwater lakes. Differences in the magnitude and timing of these changes are likely due to catchment and lake‐specific differences. In contrast with other alpine lakes that are often affected by acid deposition, atmospheric Ca deposition appears to be a significant explanatory factor, among others, for the changes in the lake biota of Sierra Nevada that has not been previously considered. The effects observed in Sierra Nevada are likely occurring in other Mediterranean lake districts, especially in softwater, oligotrophic lakes. The predicted increases in global temperature and Saharan dust deposition in the future will further impact the ecological condition of these ecosystems.     

Effects of phosphorus and nitrogen enrichment on the yield of some strains of Stigeoclonium Kütz. (Chlorophyceae)

SUMMARY.

• 1 The combined effect of nitrate and phosphate concentrations on the yields of five selected strains of Stigeoclonium is demonstrated in a synthetic medium as well as in natural waters.
• 2 Increase of yield after addition of one nutrient depends on the concentration of the other. A graphic growth model based on the experiments in synthetic medium is presented, which allows prediction of yields at different combinations of nitrate and phosphorus concentrations.
• 3 In general, yields in natural waters before and after addition of nitrate and/or phosphate agree with the model. In some cases, other limiting factors appear to be involved.
• 4 The possible effects of nitrogen and phosphorus limitation on the phosphorus and nitrogen metabolism of the alga are discussed.
• 5 Neither an exponential model (Baule-Mitscherlich) nor a hyperbolic model adequately describe the interaction demonstrated between nitrogen and phosphorus limitation.

     

Phosphorus scavenging in the unicellular marine diazotroph Crocosphaera watsonii

Through the fixation of atmospheric nitrogen and photosynthesis, marine diazotrophs play a critical role in the global cycling of nitrogen and carbon. Crocosphaera watsonii is a recently described unicellular diazotroph that may significantly contribute to marine nitrogen fixation in tropical environments. One of the many factors that can constrain the growth and nitrogen fixation rates of marine diazotrophs is phosphorus bioavailability. Using genomic and physiological approaches, we examined phosphorus scavenging mechanisms in strains of C. watsonii from both the Atlantic and the Pacific. Observations from the C. watsonii WH8501 genome suggest that this organism has the capacity for high-affinity phosphate transport (e.g., homologs of pstSCAB) in low-phosphate, oligotrophic systems. The pstS gene (high-affinity phosphate binding) is present in strains isolated from both the Atlantic and the Pacific, and its expression was regulated by the exogenous phosphate supply in strain WH8501. Genomic observation also indicated a broad capacity for phosphomonoester hydrolysis (e.g., a putative alkaline phosphatase). In contrast, no clear homologs of genes for phosphonate transport and hydrolysis could be identified. Consistent with these genomic observations, C. watsonii WH8501 is able to grow on phosphomonoesters as a sole source of added phosphorus but not on the phosphonates tested to date. Taken together these data suggest that C. watsonii has a robust capacity for scavenging phosphorus in oligotrophic systems, although this capacity differs from that of other marine cyanobacterial genera, such as Synechococcus, Prochlorococcus, and Trichodesmium.     

Water pollution control by aquatic vegetation of treatment wetlands

Supplying polluted river water to nature reserves in The Netherlands often leads to eutrophication of the reserve. The eutrophication can be caused directly by the high nutrient input (external eutrophication) or indirectly by altering nutrient availability due to changes in nutrient desorption or mineralization. This paper investigates the potential of a ditch system that is tested for its potential to improve the water quality of polluted river water prior to supplying to the wet meadow reserve De Meije in The Netherlands. Concentrations of the macro-ions chloride, sulphate, calcium and bicarbonate in the polluted river water were much higher than original background values, measured in the reserve. During transport of the river water through the ditch system, no decline was observed in the concentrations of these macro-ions. The phosphorus concentration, however, decreased along the flow path and was significantly negatively correlated with the distance from the inlet point. High phosphorus removal occurred in a stretch of the ditch system where submerged and free floating species such as Fontinalis antipyretica and Lemna trisulca were dominant. The N: P ratio of F. antipyretica was especially low (N : P < 5) at sampling stations where high phosphorus concentrations were measured. The high N: P ratio indicated a luxury consumption of phosphorus. With decreasing phosphorus concentrations, the N: P ratio of F. antipyretica increased to a maximum of N: P = 25. The nutrient budget of the ditch system showed that supply of river water was the main input of phosphorus (12 kg P) whereas the main inputs of nitrogen of the ditch system were atmospheric deposition (66 kg N) and leaching from the wet meadows (44 kg N). For both nutrients, harvesting the aquatic vegetation in September was the main removal mechanism from the ditch system with 92 kg of nitrogen (80% of the annual input N) and 14 kg of phosphorus (95% of the annual P input) removed. It was concluded that the ditch system with aquatic vegetation could successfully remove nutrients from polluted river water. The concentrations of macro-ions, however, are not influenced by the ditch systems and internal eutrophication due to changes in adsorption or mineralization may still occur.     

Nutrient-limited productivity of calcareous versus fleshy macroalgae in a eutrophic,carbonate-rich tropical marine environment

The results of a study of nutrient enrichment with nitrogen (N) and phosphorus (P) on productivity and calcification of fleshy and calcareous algae are reported in this study. Plants were collected from a nearshore eutrophic site in the Florida Keys (USA) and experimentally pulsed during the night with combinations of N and P. After several days of pulsing (7–10 days), net productivity, calcification, and alkaline phosphatase activity (APA), were measured. Productivity of fleshy algae were frequently enhanced by N, P, and N+P, during both summer and winter. Phosphorus limited the productivity of Hydroclathrus clathratus during winter and Ulva spp. during summer, whereas nitrogen limited the productivity of Laurencia intricata during both seasons. During summer, Dictyota cervicornis productivity was not enhanced by any nutrient enrichment. Nitrogen limited the productivity of the three calcareous species Penicillus capitatus, Penicillus dumetosus and Halimeda opuntia during winter and that of H. opuntia during summer. Neither N nor P enrichment increased calcification of calcareous species, and P enrichment greatly inhibited calcification of P. dumetosus during winter. Nutrient enrichment enhanced the productivity of the fleshy species to a greater extent than that of calcareous algae. The seawater DIN:SRP molar ratio was low at our eutrophic study site (molar ratio average of 3:1 during winter and 9:1 during summer) compared to more oligotrophic sites in the Florida Keys, suggesting that in carbonate-rich environments, eutrophication shifts nutrient regulation of productivity from P to N. APA activities of fleshy macroalage were higher than calcareous algae, and rates of all macro algae were 2- to 7-fold higher in summer compared to winter. Productivity was also about 3-fold higher in fleshy compared to calcareous species and about 2-fold higher in summer compared to winter. These results suggest that nutrient enrichment enhances productivity of fleshy algae to a greater extent than that of calcareous algae. Thus, overgrowth of calcareous algae by more opportunistic fleshy forms could reduce carbonate accretion in tropical coastlines experiencing increased eutrophication.     

Nutrient limitation of phytoplankton in a naturally acidic lake (Lake Caviahue, Argentina)

As a result of a low pH, the inorganic carbon of acidic lakes is present as CO₂ at air-equilibrium concentration and is substantially lower than the inorganic carbon concentration in higher-pH waters with bicarbonate. This situation is quite common in artificially acidified lakes and where inorganic carbon is considered the limiting factor in phytoplankton growth. Apart from low inorganic carbon content, Lake Caviahue in Argentina has low nitrogen and high phosphorus content. The aim of this work was to assess the importance of inorganic carbon, phosphorus, and nitrogen, relating data on lake nutrients to phytoplankton species requirements. Lake samples taken in the 2004–2006 period did not show any particular trend in the vertical distribution of the water column of ammonium, inorganic carbon, and phosphorus with reference to either seasonality or depth. A decrease of some 15% in the lake’s phosphorus concentration was observed over the same period. Although the total phytoplankton biomass in Lake Caviahue was similar throughout the period, a seasonal variation was observed. Lab bioassays were carried out with solutions of bicarbonates, ammonium, nitrates, and phosphate. We worked with three species separately, namely, two chlorophytes, Keratococcus rhaphidioides and Watanabea sp.; and one euglenophyte, Euglena mutabilis. Answers to specific nutrient requirements differed for each algal species: both chlorophytes prefer ammonium or nitrates added on their own, whereas the euglenophyte registered a higher growth rate with the joint addition of ammonium and phosphorus. Even when the limiting nutrient(s) for phytoplankton yield and rate varied between species, we observed a tendency for nitrogen limitation in Lake Caviahue.     

Ammonium and nitrate uptake by aquatic plants from poorly buffered and acidified waters

In the Netherlands, atmospheric deposition of ammonia compounds, particularly ammonium sulphate, is an important source for the acidification of oligotrophic soft waters. As a consequence, the acidified waters are generally nitrogen enriched, ammonium being the dominant N form. In this study, it is examined how this alteration in the nitrogen household affects the aquatic plant communities in acidifying waters.The uptake of ammonium and nitrate by leaves and roots of two groups of freshwater plants has been studied using glass incubation chambers. The forst group (Littorella uniflora (L.) Aschers.; Lobelia dortmanna L.; Luronium natans (L.) Raf.; Echinodorus ranunculoides (L.) Engelm.) is characteristic of nitrogen-poor soft waters, whereas the second group (Juncus bulbosus L.; Sphagnum flexuosum Dozy & Molk.;Agrostis canina L.; Drepanocladus fluitans (Hedw.) Warnst.) often occurs in dense stands in nitrogen-enriched, acid waters. Both groups have typical adaptations to the nitrogen condition of their aquatic environment. The soft-water species show a nitrate-dominated (63–73%) nitrogen utilization, with the roots as the major (83%) uptake site. Moreover, they are able to survive at very low nitrogen concentrations. The acid-tolerant species have an ammonium-dominated (85–90%) nitrogen utilization, with the leaves as the major (71–82%) uptake site. This group profits from the increased ammonium levels in acid waters. It is concluded that in the case of acidification increased ammonium concentrations additionally account for the suppression of typical soft-water communities by communities dominated by Juncus bulbosus and Sphagnum spp.     

Enhanced biodegradation of diesel fuel through the addition of particulate organic carbon and inorganic nutrients in coastal marine waters

Diesel fuel pollution in coastal waters, resulting from recreational boating and commercial shipping operations, is common and can adversely affect marine biota. The purpose of this study was to examine the effect of additions of particulate organic carbon (POC) in the form of naturally-occurring marsh grass (Spartina alterniflora), inorganic nutrients (nitrogen and phosphorus), inert particles, and dissolved organic carbon (DOC) on diesel fuel biodegradation and to attempt to formulate an effective bioremedial treatment for small diesel fuel spills in marine waters. Various combinations of treatments were added to water samples from a coastal marina to stimulate diesel fuel biodegradation. Diesel fuel was added in concentrations approximating those found in a spill and biodegradation of straight chain aliphatic constituents was estimated by measuring mineralization of ¹⁴C hexadecane added to diesel fuel. All treatments that included POC showed stimulation of biodegradation. However, the addition of inert particles (glass fiber filters and nylon screening) caused no stimulation of biodegradation. The addition of nitrogen and phosphorus alone did not result in stimulation of biodegradation, but nitrogen and Spartina (although not phosphorus and Spartina) did result in stimulation above that of Spartina alone. Maximum biodegradation rates were obtained by the addition of the Spartina POC, ammonium, and phosphate. The addition of mannitol, a labile DOC source with POC and phosphate resulted in a decrease in diesel fuel biodegradation as compared to POC and phosphate alone. The seasonal pattern of diesel fuel biodegradation showed a maximum in the summer and a minimum in the winter. Therefore, of the treatments tested, the most effective for bioremediation of diesel fuel in marine waters is the addition of POC, nitrogen, and phosphorus.