Evidence for extensive but variable nutrient limitation in New Zealand lakes

Nutrient limitation causes reduced growth of organisms, which can translate into far-reaching consequences for populations, communities, and ecosystems. Phosphorus (P) limitation, in particular, is associated with reductions in organismal growth because ribosomes, upon which growth depends, require abundant phosphorus to be produced. Chromosomes are also relatively rich in P, meaning that organisms with relatively high chromosome complements (e.g. polyploids) might be especially dependent on abundant environmental P. Here we address the likelihood of nutrient limitation in multiple populations of Potamopyrgus antipodarum, a New Zealand freshwater snail featuring wide ploidy variation. We found that some form of P limitation is very likely in many, but not all, populations of this snail that we surveyed. We also detected extensive across-population variation in P and nitrogen (N) content and N and P limitation and co-limitation in the algae that P. antipodarum eat. Accordingly, we then experimentally evaluated how P and N alone and together influenced growth rate in P. antipodarum. We found that response to nutrients differed by lineage and that dietary P content was more important than dietary N content as a determinant of growth rate, a trait closely tied to fitness in P. antipodarum. The widespread likelihood of (1) P limitation and (2) variation in dietary P availability across New Zealand lakes, along with (3), evidence for lineage-level variation in sensitivity to P limitation, sets the stage for the possibility that variation in nutrient availability contributes to the distribution and maintenance of ploidy variation in P. antipodarum.     

Phytoplankton nutrient deficiency in lakes of the McMurdo dry valleys, Antarctica

1. The influence of inorganic nitrogen and phosphorus enrichment on phytoplankton photosynthesis was investigated in Lakes Bonney (east and west lobes), Hoare, Fryxell and Vanda, which lie in the ablation valleys adjacent to McMurdo Sound, Antarctica. Bioassay experiments were conducted during the austral summer on phytoplankton populations just beneath the permanent ice cover in all lakes and on populations forming deep-chlorophyll maxima in the east and west lobes of Lake Bonney. 2. Phytoplankton photosynthesis in surface and mid-depth (13 m) samples from both lobes of Lake Bonney were stimulated significantly (P < 0.01) by phosphorus enrichment (2 μM) with further stimulation by simultaneous phosphorus plus NH₄⁺ (20 μM) enrichment. Similar trends were observed in deeper waters (18 m) from the east lobe of Lake Bonney, although they were not statistically significant at P < 0.05. Photosynthesis in this lake was never enhanced by the addition of 20 μM NH₄⁺ alone. Simultaneous addition of phosphorus plus nitrogen stimulated photosynthesis significantly (P < 0.01) in both Lake Hoare and Lake Fryxell. No nutrient response occurred in Lake Vanda, where activity in nutrient-enriched samples was below unamended controls; results from Lake Vanda are suspect owing to excessively long sample storage in the field resulting from logistic constraints. 3. Ambient dissolved inorganic nitrogen (DIN) (NH4⁺+ NO₂^?+ NO₃^?): soluble reactive phosphorus (SRP) ratios partially support results from bioassay experiments indicating strong phosphorus deficiency in Lake Bonney and nitrogen deficiency in Lakes Hoare and Fryxell. DIN : SRP ratios also imply phosphorus deficiency in Lake Vanda, although not as strong as in Lake Bonney. Particulate carbon (PC): particulate nitrogen (PN) ratios all exceed published ratios for balanced phytoplankton growth, indicative of nitrogen deficiency. 4. Vertical nutrient profiles in concert with low advective flux, indicate that new (sensu Dugdale & Goering, 1967) phytoplankton production in these lakes is supported by upward diffusion of nutrients from deep nutrient pools. This contention was tested by computing upward DIN : SRP flux ratios across horizontal planes located immediately beneath each chlorophyll maximum and about 2 m beneath the ice (to examine flux to the phytoplankton immediately below the ice cover). These flux ratios further corroborated nutrient bioassay results and bulk DIN : SRP ratios indicating phosphorus deficiency in Lakes Bonney and Vanda and potential nitrogen deficiency in Lakes Hoare and Fryxell. 5. Neither biochemical reactions nor physical processes appear to be responsible for differences in nutrient deficiency among the study lakes. The differences may instead be related to conditions which existed before or during the evolution of the lakes.     

Factors governing nutrient status of mountain lakes in the Tatra Mountains

1. Nutrient and chlorophyll a levels, and bacterial numbers of 84 glacial lakes in the Tatra Mountains (Slovakia and Poland, Central Europe) were determined to assess the impact of catchment vegetation and water acidity on lake trophic status. 2. Catchment vegetation was the crucial factor governing nutrient content of lakes. 3. Concentrations of organic carbon, organic nitrogen, and chlorophyll a, and bacterial numbers were tightly correlated with total phosphorus (TP) content. Their levels were the highest in forest lakes, then decreased in alpine lakes with decreasing amount of catchment vegetation and soil cover, and were the lowest in lakes situated in bare rocks. 4. The above pattern was further modified by lake water acidity. Concentrations of TP, organic carbon, and chlorophyll a were lower in alpine lakes with pH between 5 and 6 than in more or less acid alpine lakes. Zooplankton was absent in all alpine lakes with pH between 5 and 6. 5. Nitrate concentrations followed an inverse trend to TP; lowest values were in forest lakes, then increased with decreasing amount of catchment soils and vegetation. Within the lakes of the same type of catchment vegetation, nitrate concentrations were negatively correlated to TP. N‐saturation of catchment areas and lake primary production were dominant processes controlling nitrate levels in lakes and nitrate contribution to lake acidification.     

Linking nutrient limitation and water chemistry in upland lakes to catchment characteristics

Overbank sedimentation on river floodplains can result in significant reduction of the suspended sediment load transported by a river and can thus represent an important component of the catchment sediment budget. Such conveyance losses will also exert an important influence on sediment-associated contaminant fluxes and budgets. This contribution reports the results of a study of sediment-associated contaminants (i.e. total-P, Cr, Cu, Pb and Zn) fluxes in the River Swale (1346 km²) and River Aire (1002 km²) in Yorkshire, U.K., aimed at quantifying the role of overbank floodplain sedimentation in the sediment-associated contaminant budgets. The catchment of the River Aire is dominated by urban and industrial land use in its middle and lower reaches, whereas the River Swale drains a largely rural catchment, although there is a legacy of metal mining in its headwaters which impacts on heavy metal transport by the river. The results for the River Swale indicate that the conveyance losses associated with the deposition of sediment-associated contaminants on the floodplains bordering the main river can be as high as 47% of the total flux through the main channel system. Equivalent values for the River Aire range up to 26%. Contrasts between the two rivers reflect both the location of the contaminant sources within the catchments and the relative magnitude of the fine sediment deposition fluxes associated with their floodplains.     

The light : nutrient ratio in lakes: a test of hypothesized trends in bacterial nutrient limitation

The light-to-nutrient hypothesis explores how the balance between energy (as light energy) and nutrients (as total phosphorus) shapes aquatic ecosystem structure and process. The balance of energy and nutrients is thought to regulate ecosystem structure and process such that, in a "high" light-to-nutrient environment, bacteria would probably be driven towards phosphorus (P) limitation, whereas, in a "low" light-to-nutrient environment, bacteria would be driven towards carbon (C) limitation. We assessed the growth limitation of bacteria in two reservoirs of the southern U.S.A. using a mortality-corrected dilution-growth approach. We compared the frequency of P and C growth limitation with the intralake variation in the light-to-nutrient environment. As a metric of the light-to-nutrient environment, we used the ratio of the mean light in the surface mixed layer ( I _m) to the total phosphorus concentration ( TP ). In each lake, bacterial growth was more often P-limited when the I _m :  TP ratio was above the median ratio than below. We believe our data provide the first evidence supporting this aspect of the light-to-nutrient hypothesis.     

An experimental investigation of phytoplankton nutrient limitation in two contrasting low arctic lakes

We investigated whether phytoplankton communities in two lakes in SW Greenland were phosphorus or nitrogen limited. The study lakes have contrasting water chemistry (mean conductivities differ ten fold) and are located near Kangerlussuaq, SW Greenland (~67°N, 51°W). A microcosm nutrient enrichment experiment was performed in June 2003 to determine whether nitrate or phosphate addition stimulated phytoplankton growth. Samples were analysed for species composition, biomass, and alkaline phosphatase activity (APA). Initially, both lakes had extremely low total phosphorus but high total nitrogen concentrations and high APA, suggesting that the phytoplankton were phosphorus limited prior to the start of the experiment. The phytoplankton composition and biomass (mainly Ochromonas spp.) responded to phosphate but not to nitrate addition. In both lakes, chlorophyll a increased significantly when phosphate was added. Furthermore, APA was significantly lower in the two lakes when phosphate was added compared to the control and the nitrogen addition treatment. The dominance of mixotrophic phytoplankton and high DOC values suggest that these lakes may be regulated by microbial loop processes.     

Nitrogen deposition and warming – effects on phytoplankton nutrient limitation in subarctic lakes

The aim of this study was to predict the combined effects of enhanced nitrogen (N) deposition and warming on phytoplankton development in high latitude and mountain lakes. Consequently, we assessed, in a series of enclosure experiments, how lake water nutrient stoichiometry and phytoplankton nutrient limitation varied over the growing season in 11 lakes situated along an altitudinal/climate gradient with low N‐deposition (<1 kg N ha^?1 yr^?1) in northern subarctic Sweden. Short‐term bioassay experiments with N‐ and P‐additions revealed that phytoplankton in high‐alpine lakes were more prone to P‐limitation, and with decreasing altitude became increasingly N‐ and NP‐colimited. Nutrient limitation was additionally most obvious in midsummer. There was also a strong positive correlation between phytoplankton growth and water temperature in the bioassays. Although excess nutrients were available in spring and autumn, on these occasions growth was likely constrained by low water temperatures. These results imply that enhanced N‐deposition over the Swedish mountain areas will, with the exception of high‐alpine lakes, enhance biomass and drive phytoplankton from N‐ to P‐limitation. However, if not accompanied by warming, N‐input from deposition will stimulate limited phytoplankton growth due to low water temperatures during large parts of the growing season. Direct effects of warming, allowing increased metabolic rates and an extension of the growing season, seem equally crucial to synergistically enhance phytoplankton development in these lakes.     

Phytoplankton photosynthesis parameters in central Canadian lakes

Values for two biological parameters — (i) P^B_m, the lightsaturated rate of photosynthesis per unit of chlorophyll and(ii) , the slope of the light limited part of the photosynthesisversus light curve per unit of chlorophyll — must be knownin order to be able to estimate rates of phytoplankton primaryproduction from chlorophyll data. These parameters were measuredfor periods of up to 9 years in central Canadian lakes locatedin temperate, subarctic and arctic climatic zones. Regardlessof their geographic locations, lakes where integral photosynthesiswas nutrient limited had lower values of these parameters thandid lakes where integral photosynthesis was light limited. Temperatureset an upper limit to the variability of P^B_m but was not a goodpredictor of its actual value. Year-to-year variability of photosynthesisparameters in the most intensively studied group of lakes waslarge: annual means varied by a factor of three over a 9-yearperiod. Until the sources and extent of this variability areknown, accurate production estimates can be obtained from chlorophylldata only if P^B_m and are measured in each water body and inevery year. Implications for estimating primary production fromremotely-sensed chlorophyll data are discussed.     

Phosphorus limitation in some tropical African lakes

Two of three Kenyan lakes studied between November 1979 and October 1980 have very short ³³PO₄ turnover times, indicating a high phosphorus (P) demand throughout the year. The P turnover time in Lakes Oloidien and Sonachi is as rapid as in the most P deficient temperate zone lakes. The third lake, Lake Naivasha, has a lower overall P demand and a wide seasonal range, with lowest demand between November 1979 and February 1980 when a P deficiency was unlikely. On an annual basis the Lake Naivasha status is, however, not statistically different from that recorded during the summer in Lake Memphremagog, a generally P-limited temperate zone lake. Lake Naivasha and Lake Oloidien fit well to the line of best fit for the Dillon-Rigler relationship relating total phosphorus (TP) and chlorophyll a derived in temperate zone lakes. Thus, temperate zone models predicting aspects of lake behaviour on the basis of TP may also be applicable to these two tropical lakes. Saline lake Sonachi had not only a short P turnover time but also responded dramatically to the fertilization of enclosures with P. However, it does not fit the TP-chla or the total nitrogen-chla plots from the temperate zone. This suggests that, in this saline lake at least, much of the TP is unavailable to the algae, with some of it in a particulate form that is readily extracted with boiling water. The epilimnetic N:P ratios also characterize lakes Oloidien and Sonachi lakes as highly P deficient and lake Naivasha as more moderately P limited. A single set of measurements in Winam Gulf (Lake Victoria) also showed a rapid P turnover time and thus P limitation, but as in lake Sonachi much of the TP was in a non-algal particulate form. Occasional measurements in three other hypertrophic and saline lakes suggest them to be primarily light limited on the basis of their very high photosynthetic cover. These findings support the hypothesis of a primary P limitation for those lakes not light limited, and contradicts literature suggestions that nitrogen is the primary limiting element in tropical lakes.     

Experiments on nutrient limitation in bottles

A simple model is used to illustrate the character of production,within an incubation bottle subject to addition of a potentiallylimiting nutrient, over time periods long relative to the algaldynamics (1–10 days). Grazing by microheterotrophs significantlyaffects algal and nutrient dynamics, and production reflectsthe integration over time of grazing and nutrient-regulatedgrowth. Greater production is found with increased nutrient,but this increase continues into the region of luxuriant nutrient.Increased production per se cannot be used to determine whethera nutrient is limiting.     

Determinants of nutrient limitation in cancer

Proliferation requires that cells accumulate sufficient biomass to grow and divide. Cancer cells within tumors must acquire a variety of nutrients, and tumor growth slows or stops if necessary metabolites are not obtained in sufficient quantities. Importantly, the metabolic demands of cancer cells can be different from those of untransformed cells, and nutrient accessibility in tumors is different than in many normal tissues. Thus, cancer cell survival and proliferation may be limited by different metabolic factors than those that are necessary to maintain noncancerous cells. Understanding the variables that dictate which nutrients are critical to sustain tumor growth may identify vulnerabilities that could be used to treat cancer. This review examines the various cell-autonomous, local, and systemic factors that determine which nutrients are limiting for tumor growth.     

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.     

Climate-driven changes on phytoplankton–zooplankton coupling and nutrient availability in high mountain lakes of Southern Europe

1. The effect of climate variability on phytoplankton and zooplankton dynamics and nutrient availability was studied in two high mountain fishless lakes (La Caldera and Río Seco) of contrasting morphology, hydrology and dissolved inorganic nitrogen : soluble reactive phosphate (DIN : SRP) ratios during 1986 and after a 10‐year‐long drought in 1996 and 1997. 2. Thaw was delayed and water temperatures were lower in both lakes in 1996 than in 1986 and 1997. However, the lake‐specific DIN : SRP ratio was maintained in the 3 years studied, reflecting its local control. 3. On other hand, the presumptive limiting nutrient in each lake, P in La Caldera and N in Río Seco, showed higher concentrations in 1996 versus 1986 and 1997. Significant positive correlations between temperature and chlorophyll a were found in both lakes in 1996 but these relationships were negative or not significant in 1986 and 1997. Zooplankton biomass showed lower values in 1996 than in 1986 or 1997. 4. These findings can be explained by a decoupling of the phytoplankton–zooplankton interaction because of a constraint on zooplankton growth by low temperatures in the coldest year studied. This observation furnishes evidence that regional climatic control on the phytoplankton–zooplankton link can modulate the overall demand for nutrients.     

Phytoplankton growth in the Ohio, Cumberland and Tennessee Rivers, USA: inter-site differences in light and nutrient limitation

Seasonal patterns in resource limitation of phytoplankton growth were assessed monthly within three large rivers with differing extents of water regulation. The Ohio River is regulated by low dams that do not substantially modify discharge, while the Cumberland and Tennessee Rivers are impounded by a series of high dams to enhance water storage for downstream flood control. Laboratory dilution assays with light and nutrient manipulations indicated that light was the main factor limiting phytoplankton growth at irradiances below 7 E m^–2 d^–1. Light limited growth was frequent in the turbid, higher discharge of the Ohio River, but was rare in the heavily regulated Tennessee and Cumberland Rivers. When irradiance exceeded 7 E m^–2 d^–1, phytoplankton were either P-limited (Cumberland River), co-limited by P and N (Tennessee River), or Si limited (Ohio River). Site-specific differences in nutrient limitation were consistent with differences in ambient nutrient levels, with the Tennessee and Cumberland Rivers characterized by lower N and P concentrations, and the Ohio River by lower Si. Downstream nutrient depletion was evident in the Ohio River through comparison of an upstream and a downstream site, with nutrient limitation (Si) occurring more frequently downstream. Phytoplankton growth rates at ambient light and nutrient levels ranged from 0.1 to 1.5 d^–1 in the Ohio River and 0.2 to 0.6 d^–1 in the Tennessee and Cumberland Rivers. Growth rates were greatest at the onset of the summer base pool, as light intensities increased and nutrient levels were maximal. Our findings indicate that multiple factors regulate phytoplankton growth in regulated rivers and that spatial complexity may arise from differences in discharge and water aging.     

Regulation by nutrient limitation.

Growth with suboptimal nutrient levels elicits adaptations not observed with either starving (resting) or unstressed bacteria. The hunger response results in patterns of gene expression optimising scavenging capabilities through novel control mechanisms. In Escherichia coli, recent results indicate that outermembrane permeability (porin and glycoporin regulation) as well as transport involving the phosphotransferase system and ABC-type high affinity transporters change under glucose limitation. Many other adaptations in expression and metabolic capabilities at subsaturating growth rates are still poorly understood, even in E. coli.     

Phytoplankton primary production in several karst lakes in central Russia

The phytoplankton primary production was studied in different types of six soft-water, weakly-mineralized karst lakes: Kschara, Sankhar, Yukhor, Poridovo, Svetlen’koye, and Bol’shiye Garavy (Vladimir oblast). The following aspects were studied: seasonal dynamics, vertical distribution of the photosynthetic intensity, relative algal photosynthetic activity, the relationships between production processes and water transparency, BOD₅, and the concentrations of total forms of nitrogen and phosphorus. It was revealed that the maximal photosynthesis rate depends more on the total nitrogen than on the total phosphorus. A close correlation was found between the maximal photosynthesis rate and BOD₅.     

Unstable dynamics and population limitation in mountain hares

The regular large-scale population fluctuations that characterize many species of northern vertebrates have fascinated ecologists since the time of Charles Elton. There is still, however, no clear consensus on what drives these fluctuations. Throughout their circumpolar distribution, mountain hares Lepus timidus show regular and at times dramatic changes in density. There are distinct differences in the nature, amplitude and periodicity of these fluctuations between regions and the reasons for these population fluctuations and the geographic differences remain largely unknown. In this review we synthesize knowledge on the factors that limit or regulate mountain hare populations across their range in an attempt to identify the drivers of unstable dynamics. Current knowledge of mountain hare population dynamics indicates that trophic interactions--either predator-prey or host-parasite--appear to be the major factor limiting populations and these interactions may contribute to the observed unstable dynamics. There is correlative and experimental evidence that some mountain hare populations in Fennoscandia are limited by predation and that predation may link hare and grouse cycles to microtine cycles. Predation is unlikely to be important in mountain hare populations in Scotland as most hares occur on sporting estates where predators are controlled, but this hypothesis remains to be experimentally tested. There is, however, emerging experimental evidence that some Scottish mountain hare populations are limited by parasites and that host-parasite interactions contribute to unstable dynamics. By contrast, there is little evidence from Fennoscandia that parasitism is of any importance to mountain hare population dynamics, although disease may cause periodic declines. Although severe weather and food limitation may interact to cause periodic high winter mortality there is little evidence that food availability limits mountain hare populations. There is a paucity of information concerning the factors limiting or regulating mountain hare populations in the Alps of Central Europe or in the tundra and taiga belts of Russia. Future research on mountain hare population dynamics should focus on the interactions between predation, parasitism and nutrition with stochastic factors such as climate and anthropogenic management including harvesting.     

Desmids in mountain lakes of the subpolar Urals

The species composition of desmids was studied in eight mountain lakes of the Kozhim and Malyi Patok River basins in the “Yugyd Va” National Park (subpolar Urals, Russia). A total of 98 desmid taxa representing 13 genera belonging to 4 families were identified. Geographical and ecological analyses showed that the desmid flora is typical, with a predominance of cosmopolitan species, planktic-benthic forms, acidophilic and pH indifferent species, and halophobic to salinity indifferent species. The investigated lakes can be classified as pristine and in good ecological condition on the basis of their hydrochemical and algal biodiversity characteristics. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Water chemistry of high elevation Colorado wilderness lakes

High elevation alpine and subalpine Rocky Mountain lakes in Colorado and southeastern Wyoming were examined to determine regional variability in water chemistry and their sensitivity to atmospheric deposition. Acid neutralizing capacity, pH, conductivity and concentrations of major anions and cations were compared. Regional differences in water chemistry are evident. The south-eastern most lakes have significantly higher pH, conductivity, ANC, and sums of acid and base concentrations than lakes in the other regions of the state. In contrast the north-western most lakes are significantly more dilute than those from other regions. Despite these two regional differences, most regions are similar in having a wide range of variability in potential sensitivity of their lakes to acidification and nitrogen export. Many wilderness areas in western and eastern regions contains lakes that are extremely sensitive and other lakes not susceptible to deposition. Overall, 70% of the Colorado lakes are sensitive to acidification and 15% are extremely sensitive to acidification. All of the regions had lakes that are classified as susceptible or sensitive to acidification, with 12 of the 17 areas having all of their sampled lakes susceptible or sensitive. Generally NO concentration in surface waters decreased from mid-season to late season; yet a large number of the lakes export NO late in the season, suggesting nitrogen saturation. The results confirm the sensitivity of high elevation wilderness aquatic ecosystems in all regions of Colorado to acidification and nitrogen deposition.